Search

SummarySystemic lupus erythematosus (SLE) is an autoimmune condition developing thrombocytopenia in about 10-15% of cases, however, mechanisms leading to low platelet count were not deeply investigated in this illness. Here we studied possible causes of thrombocytopenia, including different mechanisms of platelet clearance and impairment in platelet production. Twenty-five SLE patients with and without thrombocytopenia were included. Platelet apoptosis, assessed by measurement of loss of mitochondrial membrane potential, active caspase 3 and phosphatidylserine exposure, was found to increase in thrombocytopenic patients. Plasma from 67% SLE patients (thrombocytopenic and non-thrombocytopenic) induced loss of sialic acid (Ricinus communis agglutinin I and/or Peanut agglutinin binding) from normal platelet glycoproteins. Concerning platelet production, SLE plasma increased megakaryopoiesis (evaluated using normal human cord blood CD34+ hematopoietic progenitors), but inhibited thrombopoiesis (proplatelet count). Anti-platelet autoantibody depletion from SLE plasma reverted this inhibition. Overall, abnormalities were more frequently observed in thrombocytopenic than non-thrombocytopenic SLE patients and in those with active disease (SLEDAI≥5). In conclusion, platelet clearance due to apoptosis and desialylation, and impaired platelet production mainly due to inhibition of thrombopoiesis, could be relevant mechanisms leading to thrombocytopenia in SLE. These findings could provide a rational basis for the choice of proper therapies to correct platelet counts in these patients.[Figure: see text].

New findings What is the central question of this study? In a model of salt-sensitive hypertension in ovariectomized (oVx) adult Wistar rats, we evaluated the expression of proteins related to sodium transport in peripheral blood mononuclear cells (PBMC), and we compared the response of proteins to high sodium intake and changes in blood pressure in intact female rats. What is the main finding and its importance? Sodium transport proteins in PBMC react to high sodium and blood pressure markedly differently in oVx versus intact female rats. Protein expressions indicate sodium and pressure sensitivity. Renal immune cells increase in oVx under high salt. Abstract Hypertension is a worldwide public health problem. High sodium consumption is associated with hypertension, and hypertensive mechanisms involve immunity cells. Peripheral blood mononuclear cells (PBMC) are endowed with proteins related to sodium transport. We studied their abundance in PBMC from intact (IF) or ovariectomized (oVx) adult Wistar rats under normal (NS) or high salt (HS) intake. Ovariectomy was performed at 60 days of life. At 145 days, one group of IF and oVx rats received NS or HS intake for 5 days. Another group of IF HS and oVx HS rats received hydralazine (HDZ) to reduce blood pressure (BP). Sodium balance and BP were recorded. Expression of Na+ , K+ -ATPase (NKA), Na/K/2Cl 1 (NKCC1), serum/glucocorticoid-regulated kinase 1 (SGK1), Dopamine D1 like receptor (D1DR), CD4+ and CD8+ were determined in PBMC, and CD45+ leukocytes in renal tissue. IF HS rats showed increased natriuresis and normal BP. NKA and CD4+ expression diminished in IF HS. Instead, oVx HS rats had sodium retention and high BP and increased the expression of NKA, NKCC1, D1DR, CD4+ and CD8+ in PBMC. Renal CD45+ leukocytes increased in oVx HS. HDZ decreased BP in all rats. Upon HDZ treatment, NKA did not change, NKCC1 decreased in oVx HS rats, while SGK1 increased in both IF HS and oVx HS rats. Hormonal background determines BP response and the expression of proteins related to sodium transport in PBMC and renal immune cells at HS intake. The analysis of NKA, NKCC1, and SGK1 expression in PBMC differentiated salt-sensitivity from BP variations. This article is protected by copyright. All rights reserved.

Primary immune thrombocytopenia (ITP) is an autoimmune disorder characterized by the decrease in peripheral blood platelet count below 100 x 109/L, and an increased bleeding risk when thrombocytopenia drops below 30 x 109/L. The mechanisms leading to ITP in adults, although not completely elucidated, involves an imbalance between effector and regulatory cells that results in a breakdown of the immune tolerance. Autoantibodies are considered the main responsible for thrombocytopenia, although direct T-cell cytotoxic effect and lysis by Complement attachment and activation could also contribute to platelet elimination from circulation. In addition to increased peripheral clearance, abnormalities in platelet production also favors platelet count reduction. This review is intended to describe some specific knowledge about peripheral and bone marrow mechanisms leading to thrombocytopenia in adult ITP. Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Familial platelet disorder with predisposition to acute myelogenous leukemia (FPD/AML) is an autosomal dominant condition characterized by abnormal platelet number and function and 30-60% risk of hematologic malignancies, including myelodysplastic syndrome, acute myelogenous leukemia and T-cell lymphoblastic leukemia.1 It is caused by heterozygous germline muta- tions in the gene encoding the transcription factor RUNX1, which is essential in the emergence of definitive hematopoiesis and plays a key role in the lymphoid and megakaryocyte lineages.1,2 RUNX1 mutations predispose to leukemia by inducing genomic instability which favors the acquisition of secondary somatic mutations.3 Thrombocytopenia is mild to moderate with normal- sized platelets and most patients display a platelet func- tion defect with impaired platelet aggregation and dense- granule deficiency.1 However, the platelet phenotype is heterogeneous4 and even normal platelet count and func- tion have been reported in rare carriers of RUNX1 muta- tions,5 highlighting that the diagnosis may be overlooked. Dysregulated expression of RUNX1-targets in platelets, including downregulation of the α2 subunit (GPIa) of col- lagen receptor α2b16 or persistent myosin 10 (MYH10) expression,7 have been proposed as screening tools to guide diagnosis, although it is at present unknown whether all FPD/AML patients harbor these defects. Therefore, molecular screening is still required to ade- quately identify RUNX1 mutation carriers.We report the finding of genetic mosaicism in a patient belonging to a well-characterized FPD/AML pedigree and describe the relationship between molecular and clinical features over a 12-year follow-up. Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marin Oyarzún, Cecilia Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: de Luca, Geraldine. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marzac, Christophe. Inserm; Francia Fil: Auger, Nathalie. Inserm; Francia Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Raslova, Hana. Inserm; Francia Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Essential thrombocythemia (ET) is comprised among chronic myeloproliferative neoplasms (MPN) and is caused by driver mutations in JAK2, CALR and MPL, which lead to megakaryocyte proliferation and prominent thrombocytosis. Thrombosis remains the main cause of morbidity in ET and is driven by the interplay between blood cells, the endothelium, the clotting cascade and host-derived inflammatory mediators. Platelet activation plays a key role in the thrombotic predisposition, although the underlying mechanisms remain poorly defined. In addition to their role in hemostasis, platelets participate in innate immunity and inflammation owing to the expression of toll-like receptors (TLR), which recognize inflammatory signals, triggering platelet functional responses. Considering the impact of inflammation on ET procoagulant state, we assessed the contribution of TLR2 and TLR4 to platelet hemostatic and inflammatory properties in ET patients, by using Pam3CSK4 and lipopolysaccharide (LPS) as specific TLR2 and TLR4 ligands, respectively. TLR2 ligation induced increased surface translocation of α-granule-derived P-selectin and CD40L, which mediate platelet interaction with leukocytes and endothelial cells, respectively, and higher levels of dense granule-derived CD63 in patients, whereas PAC-1 binding was not increased and LPS had no effect on these platelet responses. Platelet-neutrophil aggregate formation was elevated in ET at baseline and after stimulation of both TLR2 and TLR4. In addition, ET patients displayed higher TLR2- and TLR4-triggered platelet secretion of the chemokine RANTES (CCL5), whereas von Willebrand factor release was not enhanced, revealing a differential releasate pattern for α-granule-stored inflammatory molecules. TLR-mediated hyperresponsiveness contrasted with impaired or preserved responses to classic platelet hemostatic agonists, such as TRAP-6 and thrombin. TLR2 and TLR4 expression on the platelet surface was normal, whereas phosphorylation of downstream effector ERK1/2 was higher in patients at baseline and after incubation with Pam3CSK4, which may partly explain the enhanced TLR2 response. In conclusion, exacerbated response to TLR stimulation may promote platelet activation in ET, boosting platelet/leukocyte/endothelial interactions and secretion of inflammatory mediators, overall reinforcing the thromboinflammatory state. These findings highlight the role of platelets as inflammatory sentinels in MPN prothrombotic scenario and provide additional evidence for the close intertwining between thrombosis and inflammation in this setting. Fil: Marin Oyarzún, Cecilia Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: de Luca, Geraldine. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Baroni Pietto, Maria Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Moiraghi, Beatriz. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; Argentina Fil: Castro Ríos, Miguel A.. Consultorios Hematológicos; Argentina Fil: Vicente, Angeles. Hospital Alemán; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Schattner, Mirta Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Immune thrombocytopenia (ITP) is characterized by itsheterogeneity among patients with regard to both clinicalfeatures and response to treatment. Although there isstill much to investigate, this heterogeneity could be thereflection of multiple mechanisms contributing to thrombocytopenia,affecting individual patients in variable proportions.These mechanisms include increased platelet clearanceby autoantibodies targeting main platelet glycoproteins(GPs) (IIbIIIa, IbIX and IaIIa) and impaired megakaryopoiesis(McMillan et al, 2004). Recently, we reported thatITP plasma samples inhibit proplatelet (PP) formation bynormal megakaryocytes (MKs) (Lev et al, 2014), demonstratingthat thrombopoiesis, the key step of platelet production,is altered, a finding further confirmed by others(Iraqi et al, 2015). In agreement with these experimentaldata, studies on platelet kinetics show inadequate plateletproduction according to the degree of thrombocytopenia(Ballem et al, 1987). Fil: Grodzielski, Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Di Buduo, Christian A.. Universidad de Pavía; Italia. Fundacion San Matteo; Italia Fil: Goette, Nora Paula. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Soprano, Paolo M.. Universidad de Pavía; Italia. Fundacion San Matteo; Italia Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Balduini, Alessandra. Universidad de Pavía; Italia. Fundacion San Matteo; Italia. Tufts Univwersity Medford; Estados Unidos Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Mechanisms leading to low platelet count in immune thrombocytopenia (ITP) involves both decreased production and increased destruction of platelet. However, the contribution of these pathologic mechanisms to clinical outcome of individual patients is uncertain. Here we evaluated diferent pathogenic mechanisms including in vitro megakaryopoiesis, platelet/megakaryocyte (MK) desialylation and MK apoptosis, and compared these efects with thrombopoyesis and platelet apoptosis in the same cohort of ITP patients. Normal umbilical cord blood-CD34+ cells, mature MK derived cells or platelets were incubated with plasma from ITP patients. Despite inhibition of thrombopoiesis previously observed, megakaryopoiesis was normal or even increased. Plasma from ITP patients afected the sialylation pattern of control platelets and this efect occurred concomitantly with apoptosis in 35% ITP samples. However, none of these abnormalities were observed in control MKs incubated with ITP plasma. Addition of mononuclear cells as immune efectors did not lead to phosphatidylserine exposure in MK, ruling out an antibody-mediated cytotoxic efect. These results suggest that both desialylation and apoptosis may be relevant mechanisms leading to platelet destruction although, they do not interfere with MK function. Analysis of these thrombocytopenic factors in individual patients showed no specifc distribution pattern. However, the presence of circulating antiplatelet autoantibodies was associated with higher incidence of abnormalities. In conclusion, the causes of thrombocytopenia are multifactorial and may occur together, providing a rational basis for the use of combination therapies targeting concomitant ITP mechanisms in patients with refractory disease. Fil: Grodzielski, Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Baroni Pietto, Maria Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Mendez Huergo, Santiago Patricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina Fil: Pierdominici, Marta S.. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; Argentina Fil: Montero, Verónica S.. Centro de Educaciones Médicas e Investigación Clínica "Norberto Quirno"; Argentina Fil: Rabinovich, Gabriel Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

The SDF-1-CXCR4 axis plays an essential role in the regulation of platelet production, by directing megakaryocyte (MK) migration toward the vascular niche, thus allowing terminal maturation and proplatelet formation, and also regulates platelet function in an autocrine manner. Inherited thrombocytopenias (IT) comprise a spectrum of diverse clinical conditions caused by mutations in genes involved in platelet production and function. We assessed CXCR4 expression and SDF-1 levels in a panel of well-characterized forms of IT. Decreased surface CXCR4 levels were found in 8 of 27 (29.6%) IT patients by flow cytometry, including 4 of 6 patients with ANKRD26-RT, 3 of 3 patients with GPS and 1 of 6 patients with FPD/AML. Low CXCR4 levels were associated with impaired SDF-1-triggered platelet aggregation, indicating that this decrease is functionally relevant, whereas a normal platelet response was shown in patients harbouring preserved membrane CXCR4. Reduced CXCR4 was not due to decreased gene expression, as platelet RNA levels were normal or increased, suggesting a post-transcriptional defect. Increased ligand-induced receptor internalization was ruled out, as circulating SDF-1 levels were similar to controls. MK CXCR4 expression was normal, indicating that the defect in CXCR4 arises after the step of platelet biogenesis. In conclusion, the finding of defective CXCR4 expression specifically associated with certain IT disorders highlights the fact that abnormalities in several megakaryocytic regulators underlie IT pathogenesis and further reveal the heterogeneous nature of these conditions. Fil: Salim, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marin Oyarzún, Cecilia Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Mechanisms leading to decreased platelet count in immune thrombocytopenia (ITP) are heterogeneous. This study describes increased platelet apoptosis involving loss of mitochondrial membrane potential (ΔΨm), caspase 3 activation (aCasp3) and phosphatidylserine (PS) externalization in a cohort of adult ITP patients. Apoptosis was not related to platelet activation, as PAC-1 binding, P-selectin exposure and GPIb-IX internalization were not increased. Besides, ITP platelets were more sensitive to apoptotic stimulus in terms of aCasp3. Incubation of normal platelets with ITP plasma induced loss of ΔΨm, while PS exposure and aCasp3 remained unaltered. The increase in PS exposure observed in ITP platelets could be reproduced in normal platelets incubated with ITP plasma by adding normal CD3+ lymphocytes to the system as effector cells. Addition of leupeptin -a cathepsin B inhibitor- to this system protected platelets from apoptosis. Increased PS exposure was also observed when normal platelets and CD3+ lymphocytes were incubated with purified IgG from ITP patients and was absent when ITP plasma was depleted of auto-antibodies, pointing to the latter as responsible for platelet damage. Apoptosis was present in platelets from all patients carrying anti-GPIIb-IIIa and anti-GPIb auto-antibodies but was absent in the patient with anti-GPIa-IIa auto-antibodies. Platelet damage inversely correlated with platelet count and decreased during treatment with a thrombopoietin receptor agonist. These results point to a key role for auto-antibodies in platelet apoptosis and suggest that antibody-dependent cell cytotoxicity is the mechanism underlying this phenomenon. Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Grodzielski, Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Contrufo, Geraldine. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Pierdominici, Marta S.. Departamento de Hematología, Hospital Ramos Mejía, Buenos Aires, Argentina; Argentina Fil: Espasandin, Yesica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Riveros, Dardo Alberto. Centro de Educación Médica e Investigaciones Clínicas “Norberto Quirno”; Argentina Fil: García, Alejandro Jorge. Centro de Educación Médica e Investigaciones Clínicas “Norberto Quirno”; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Inherited thrombocytopenias (ITs) are heterogeneous genetic disorders that frequently represent a diagnostic challenge. The requirement of highly specialized tests for diagnosis represents a particular problem in resourcelimited settings. To overcome this difficulty, we applied a diagnostic algorithm and developed a collaboration program with a specialized international center in order to increase the diagnostic yield in a cohort of patients in Argentina. Methods: Based on the algorithm, initial evaluation included collection of clinical data, platelet size, blood smear examination and platelet aggregation tests. Confirmatory tests were performed according to diagnostic suspicion, which included platelet glycoprotein expression, immunofluorescence for myosin- 9 in granulocytes and platelet thrombospondin-1 and molecular screening of candidate genes. Results: Thirty-one patients from 14 pedigrees were included; their median age was 32 (4?72) years and platelet count 72 (4?147) · 109 L)1. Autosomal dominant inheritance was found in nine (64%) pedigrees; 10 (71%) had large platelets and nine (29%) patients presented with syndromic forms. A definitive diagnosis was made in 10 of 14 pedigrees and comprised MYH9-related disease in four, while classic and monoallelic Bernard?Soulier syndrome, gray platelet syndrome, X-linked thrombocytopenia, thrombocytopenia 2 (ANKRD26 mutation) and familial platelet disorder with predisposition to acute myelogenous leukemia were diagnosed in one pedigree each. Conclusions: Adoption of an established diagnostic algorithm and collaboration with an expert referral center proved useful for diagnosis of IT patients in the setting of a developing country. This initiative may serve as a model to develop international networks with the goal of improving diagnosis and care of patients with these rare diseases. Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Pecci, Alessandro. Universita Degli Studi Di Pavia; Italia Fil: de Rocco, Daniela. Institute for Maternal and Child Health – IRCCS "Burlo Garofolo"; Italia Fil: Gnan, Chiara. Institute for Maternal and Child Health – IRCCS "Burlo Garofolo"; Italia Fil: Espasandin, Yesica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Negro, F.. Instituto Médico Sagrado Corazón; Argentina Fil: Noris, Patrizia. Universita Degli Studi Di Pavia; Italia Fil: Savoia, Anna. Institute for Maternal and Child Health – IRCCS "Burlo Garofolo"; Italia. Università degli Studi di Trieste; Italia Fil: Balduini, C. L.. Universita Degli Studi Di Pavia; Italia Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

TGF-beta1 plays a main role in tissue repair by regulating extracellular matrix production and tissue granulation. Platelets are one of the main sources of this cytokine in the circulation. The aim of this study was to evaluate the presence of the TGF-beta receptors on platelets, the effect of TGF-beta1 on platelet aggregation and the underlying intracellular mechanisms. TGF-beta receptors on platelets were studied by flow cytometry and their mRNA by PCR. Platelet aggregation was assessed by turbidimetric methods and intracellular pathways by Western blot. TGF-beta receptor type II and mRNA codifying for TbetaRI and TbetaRII were found in platelets. We demonstrated that TGF-beta1 did not trigger platelet aggregation by itself but had a modulating effect on ADP-induced platelet aggregation. Either inhibition or increase in platelet aggregation, depending on the exposure time to TGF-beta1 and the ADP concentration used, were shown. We found that platelets possess Smad2 protein and that its phosphorylation state is increased after exposure to TGF-beta1. Besides, TGF-beta1 modified the pattern of ADP-induced tyrosine phosphorylation. Increased phosphorylation levels of 64-, 80- and 125-kDa proteins during short time incubation with TGF-beta1 and increased phosphorylation of 64- and 125-kDa proteins after longer incubation were observed. The modulating effect of TGF-beta1 on platelet aggregation could play a role during pathological states in which circulating TGF-beta1 levels are increased and intravascular platelet activation is present, such as myeloproliferative disorders. In vascular injury, in which platelet activation followed by granule release generates high local ADP concentrations, it could function as a physiological mechanism of platelet activation control.

Anagrelide represents a treatment option for essential thrombocythemia, although its place in therapy remains controversial.To assess the impact of mutational status in response rates and development of adverse events during long-term use of anagrelide.We retrospectively evaluated 67 patients with essential thrombocythemia treated with anagrelide during 68 (4-176) months.Mutational frequencies were 46.3%, 28.3%, and 1.5% for JAK2V617F, CALR and MPL mutations. Anagrelide yielded a high rate of hematologic responses, which were complete in 49.25% and partial in 46.25%, without differences among molecular subsets. The rate of thrombosis during treatment was one per 100 patient-years, without excess bleeding. Anemia was the major adverse event, 30.3% at 5-yr follow-up, being more frequent in CALR(+) (P0.05). Myelofibrotic transformation developed in 14.9% (12.9%, 21%, and 12.5% in JAK2V617F(+), CALR(+), and triple-negative patients, respectively, P = NS) and those treated60 months were at higher risk, OR (95% CI) 9.32 (1.1-78.5), P0.01, indicating the need for bone marrow monitoring during prolonged treatment.Although CALR(+) patients were at higher risk of developing anemia, anagrelide proved effective among all molecular subsets, indicating that mutational status does not seem to represent a major determinant of choice of cytoreductive treatment among essential thrombocythemia therapies.

Background and Objectives: Anagrelide represents a treatment option for essential thrombocythemia patients. It lowers platelet counts through inhibition of megakaryocyte maturation and polyploidization, although the basis for this effect remains unclear. Based on its rapid onset of action, we assessed whether, besides blocking megakaryopoiesis, anagrelide represses proplatelet formation (PPF) and aimed to clarify the underlying mechanisms. Methods and Results: Exposure of cord blood-derived megakaryocytes to anagrelide during late stages of culture led to a dose- and time-dependent inhibition of PPF and reduced proplatelet complexity, which were independent of the anagrelide-induced effect on megakaryocyte maturation. Whereas anagrelide was shown to phosphorylate cAMP-substrate VASP, two pharmacologic inhibitors of the cAMP pathway were completely unable to revert anagrelide-induced repression in megakaryopoiesis and PPF, suggesting these effects are unrelated to its ability to inhibit phosphodiesterase (PDE) 3. The reduction in thrombopoiesis was not the result of down-regulation of transcription factors which coordinate PPF, while the myosin pathway was identified as a candidate target, as anagrelide was shown to phosphorylate the myosin light chain and the PPF phenotype was partially rescued after inhibition of myosin activity with blebbistatin. Conclusions: The platelet-lowering effect of anagrelide results from impaired megakaryocyte maturation and reduced PPF, both of which are deregulated in essential thrombocythemia. These effects seem unrelated to PDE3 inhibition, which is responsible for anagrelide′s cardiovascular side-effects and antiplatelet activity. Further work in this field may lead to the potential development of drugs to treat thrombocytosis in myeloproliferative disorders with an improved pharmacologic profile. Fil: Espasandin, Yesica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Grodzielski, Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Background: Familial platelet disorder with a predisposition to acute myelogenous leukemia (FPD/AML) is an inherited platelet disorder caused by a germline RUNX1 mutation and characterized by thrombocytopenia, a platelet function defect, and leukemia predisposition. The mechanisms underlying FPD/AML platelet dysfunction remain incompletely clarified. We aimed to determine the contribution of platelet structural abnormalities and defective activation pathways to the platelet phenotype. In addition, by using a candidate gene approach, we sought to identify potential RUNX1-regulated genes involved in these defects. Methods: Lumiaggregometry, α-granule and dense granule content and release, platelet ultrastructure, αIIbβ3 integrin activation and outside-in signaling were assessed in members of one FPD/AML pedigree. Expression levels of candidate genes were measured and luciferase reporter assays and chromatin immunoprecipitation were performed to study NF-E2 regulation by RUNX1. Results: A severe decrease in platelet aggregation, defective αIIbβ3 integrin activation and combined αδ storage pool deficiency were found. However, whereas the number of dense granules was markedly reduced, α-granule content was heterogeneous. A trend towards decreased platelet spreading was found, and β3 integrin phosphorylation was impaired, reflecting altered outside-in signaling. A decrease in the level of transcription factor p45 NF-E2 was shown in platelet RNA and lysates, and other deregulated genes included RAB27B and MYL9. RUNX1 was shown to bind to the NF-E2 promoter in primary megakaryocytes, and wild-type RUNX1, but not FPD/AML mutants, was able to activate NF-E2 expression. Conclusions: The FPD/AML platelet function defect represents a complex trait, and RUNX1 orchestrates platelet function by regulating diverse aspects of this process. This study highlights the RUNX1 target NF-E2 as part of the molecular network by which RUNX1 regulates platelet biogenesis and function. Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Bluteau, D.. Universite Paris Sud; Francia. Inserm; Francia Fil: Espasandin, Yesica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marin Oyarzun, C. P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Korin, L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Laguens, R. P.. Universidad Favaloro; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Raslova, H.. Universite Paris Sud; Francia. Inserm; Francia Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

The aim of this study was to evaluate cell maturation and the platelet production capacity of the megakaryoblastic DAMI cell line, to characterize platelet-like particles produced and to investigate the mechanisms involved in their production. DAMI cell maturation was induced by phorbol myristate acetate (PMA) and thrombopoietin (TPO). Expression levels of GATA-1, Fli-1 and NF-E2 were evaluated using real-time PCR and western blot. Platelet-like particles were characterized by the presence of GPIb and GPIIb by flow cytometry, while the soluble fragment of GPIb, glycocalicin, was detected by enzyme immunoassay. Dense and alpha granules were evaluated by mepacrine staining and thrombospondin-1 detection, respectively, and by electron microscopy. Functional capacity of platelet-like particles was studied by measuring P-selectin membrane after thrombin stimulation by flow cytometry and actin polymerization using phalloidin-FITC by immunofluorescence. We found that stimulation of DAMI cells with high concentration of PMA and TPO induced the expression of transcription factors GATA-1 and Fli-1 followed by an increase in the isoform a of NF-E2. Mature DAMI cells give rise to extensions resembling proplatelets and later, produce platelet-like particles expressing GPIIb and GPIb on their surface and containing dense and alpha granules, which were confirmed by electron microscopy. Platelet functionality was demonstrated by the increase in P-selectin membrane expression after thrombin stimulation and by their ability to spread on fibrinogen matrices. DAMI cell line induced to differentiate into mature megakaryocytes is able to produce functional platelets providing a suitable model to study the mechanisms involved in platelet generation. Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Glembotsky, Ana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Laguens, Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Favaloro; Argentina Fil: Cabeza Meckert, Patricia. Universidad Favaloro; Argentina Fil: Salim, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Pozner, Roberto Gabriel. Academia Nacional de Medicina de Buenos Aires. Instituto de Investigaciones Hematológicas "Mariano R. Castex"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Objective: In a previous study, we found increased plasma soluble receptor for interleukin-6 (sIL-6R) levels in patients with essential thrombocythemia (ET) that could promote megakaryopoiesis through IL-6 binding and further interaction with the signal transducer gp130. Here we have searched for the cell source of sIL-6R within mononuclear cells in these patients and the underlying abnormalities involved in its overproduction. Materials and Methods: Thirty patients with the diagnosis of ET were studied. sIL-6R levels were measured by enzyme-linked immunosorbent assay technique in the supernatants of peripheral monocyte and lymphocyte cultures. Expression of membrane-anchored IL-6R was determined by flow cytometry. In order to study the mechanism of sIL-6R production, tumor necrosis factor−α protease inhibitor was added to specifically block IL-6R shedding. Gene expression of sIL-6R levels were evaluated by reverse transcription polymerase chain reaction. Results: Monocytes were the main source of sIL-6R. Besides, in ET patients, monocyte sIL-6R release was higher than that of controls (p = 0.0014). Lymphocytes enhanced monocyte sIL-6R production by cell-mediated contact in normal controls, but this cooperation could not be seen in patients. Membrane expression of IL-6R was increased after monocyte adhesion in ET. sIL-6R synthesis was upregulated in most patients, while messenger RNA was normal. Conclusions: Our results indicate that ET monocytes are responsible for sIL-6R overproduction within mononuclear cells through synthesis upregulation. In addition, the lack of cooperation of lymphocytes in monocyte sIL-6R production in ET could be due to a monocyte abnormality. The agonistic effect of sIL-6R on IL-6 action could contribute to the exacerbated megakaryocytic growth in ET. Fil: Goette, Nora Paula. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Lev, Paola Roxana. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Heller, Paula Graciela. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Glembotsky, Ana Claudia. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Chazarreta, Carlos Daniel. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Salim, Juan Pablo. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Molinas, Felisa Concepcion. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina Fil: Marta, Rosana Fernanda. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; Argentina

The development of bone marrow fibrosis and thrombosis are main causes of morbidity in essential thrombocythemia (ET). Monocyte activation has been associated to the production of fibrosis-related cytokines and pro-thrombotic factors. The aim of this study was to identify new markers of monocyte activation in Phi-negative myeloproliferative neoplasms and to search for their relationship with clinical features. Forty-five patients comprising 30 ET, eight myelofibrosis and seven polycythemia vera were included. We evaluated the alpha subunit of IL-2 receptor (CD25) on monocytes, basal and LPS-induced IL-1beta release from mononuclear cells, and monocyte TGF-beta mRNA content. Patients who had thrombotic events displayed higher monocyte CD25 levels (6.2%) than those without symptoms (1.3%) and controls (2.6%), p=0.0006. JAK2V617F-positive patients had higher monocyte CD25 expression levels (4.7%), than JAK2V617F-negative (2.6%), p=0.0213. Patients with myeloproliferative neoplasms had similar monocyte CD25 expression than controls, both, in basal conditions and after cell adhesion. IL-1beta release and TGF-beta mRNA levels were normal. In conclusion, increased monocyte CD25 expression is associated with history of thrombosis and is also up-regulated in patients harboring JAK2V617F mutation. The finding of increased CD25 levels together with normal IL-1beta and TGF-beta production reveals a selective monocyte activation profile in myeloproliferative neoplasms.

This study investigated the involvement of chemokines including stromal derived factor 1 (SDF-1), interleukin 8 (IL-8), growth-related oncogene alpha (GRO-a) and their receptors, CXCR4, CXCR2 and CXCR1 in essential thrombocythemia (ET), a chronic myeloproliferative disease characterized by megakaryocytic hyperplasia and high platelet count. Fifty-three ET patients were studied. Plasma levels of SDF-1, IL-8 and GRO-a, evaluated by enzymelinked immunosorbent assay, and flow cytometric analysis of CXCR1 and CXCR2 on the platelet membrane, were found to be normal in ET patients. CXCR4 expression on platelet surface aswell as platelet CXCR4mRNAdetected by real-time reverse transcription polymerase chain reaction, were decreased. Platelet CXCR4 internalization rate was normal while SDF-1-induced platelet aggregation was delayed, decreased or absent. Immunohistochemical staining revealed that megakaryocytes were also affected. CXCR4 decrease was not observed either in peripheral white blood cells or in circulating CD34+ precursors. These results show that CXCR4 is decreased in the megakaryocytic lineage in ET, mainly due to a reduced CXCR4 production, and an abnormal platelet response to SDF-1. This report is the first to describe platelet and megakaryocytic CXCR4 deficiency in a human disease and the presence of this abnormality in a megakaryocytic-related illness highlights the important role of SDF-1/CXCR4 axis in platelet development. Fil: Salim, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Goette, Nora Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Lev, Paola Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Chazarreta, Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Heller, Paula Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Alvarez, Clarisa Ester. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Molinas, Felisa Concepción. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Marta, Rosana Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

Objective: JAK2V617F mutation rate in granulocytes from essential thrombocythemia (ET) patients ranges from 12% to 57%. Our aim was to evaluate the frequency of this mutation in the megakaryocyte/platelet lineage, and to analyze its clinical associations in ET. In addition, we determined whether this mutation leads to constitutive phosphorylation of STAT5 in platelets. Materials and Methods: Consecutive patients with ET were included and clinical features were retrospectively reviewed. Mutation detection was performed by allele specific RT-PCR (AS-RT-PCR) and Restriction fragment length polymorphism (RFLP) analysis of platelet RNA. Constitutive phosphorylation of STAT5 in platelets was studied by Western blot. Results: Fifty patients were included, 24 (48%) were JAK2V617F-positive by both AS-RT-PCR and RFLP. Patients with the mutation were older, had significantly higher hemoglobin levels, and lower platelet counts. Besides, higher frequency of thrombotic events was found in JAK2V617F-positive patients younger than 60, 53% vs. 4%, P = 0.0008. In addition, constitutive STAT5 phosphorylation was not detected in platelets from 12 patients. Conclusions: The frequency of the JAK2V617F mutation in platelets was similar to that reported in granulocytes in the literature, suggesting this mutation does not occur as an isolated event in the megakaryocyte lineage. If confirmed in a larger study, the observed higher frequency of thrombosis in patients younger than 60 might be a useful predictive marker for thrombosis in this subset of patients. Even though this mutation has been predicted to constitutively activate the JAK2 kinase, spontaneous phosphorylation of STAT5 does not seem to be a frequent finding in platelets from ET patients.

Interleukin 6 is a multifunctional cytokine that exerts its biological activity through binding to an 80 Kd specific receptor (IL-6Ralpha) and a 130 Kd signal-transducing unit (gp130). A 55 Kd soluble IL-6R (IL-6sR) has also been described which, after binding to IL-6 is also able to activate gp130. The presence of IL-6Ralpha was described in some megakaryoblastic cell lines but is still controversial in normal megakaryocytes. In this study we demonstrate the presence of intraplatelet IL-6sR by Western blot through the appearance of a 55 Kd protein and the finding of detectable amounts of IL-6sR in the platelet content by ELISA technique. Besides, we showed IL-6sR release during platelet activation induced by thrombin and a complex of ADP and epinephrine. IL-6Ralpha on platelet membrane could not be found neither by Western blot nor by flow cytometry. The IL-6sR released during platelet activation and complexed to IL-6 could act on cell types such as endothelial cells that do not possess IL-6Ralpha through binding to gp130.Besides, since we could not find IL-6R on platelet membrane, the potentiating effect of IL-6 on platelet function could be explained through binding of IL-6sR/IL-6 complex to platelet membrane gp130.

Similarly to nucleated cells, platelet life span is also controlled by an intrinsic apoptotic program that triggers collapse of the mitochondrial inner membrane potential, activation of caspases-3, -8 and -9, phosphatidylserine (PS) externalization and microparticle shedding. The aim of the present study was to investigate platelet apoptosis in adult patients with immune thrombocytopenia (ITP) under different treatment conditions and to search for its relationship with the type of auto-antibody and the platelet-activation status. Twenty-four patients with chronic ITP, age 42 (21-80) years (median and range) diagnosed according to current criteria (Rodeghiero et al, 2009) were included after written informed consent in accordance with the Declaration of Helsinki. The study was approved by the Ethics Committee from Instituto de Investigaciones Medicas Alfredo Lanari. Platelet count was 38x109/L (6-85). Platelet apoptosis was evaluated by phosphatidylserine (PS) exposure on the platelet surface using FITC-conjugated Anexin-V, mitochondrial electrochemical potential changes (ΔΨm) using the cell penetrating lipophilic cationic fluorochrome JC-1, and activated caspase-3 (a-casp3) measured by the cell-penetrating carboxyfluorescein-labelled fluoromethyl ketone tetrapeptide (FAM-DEVD-FMK). These parameters were studied in resting platelets and after stimulation with calcium ionophore (A23187). Platelet activation was evaluated by FITC-PAC-1 binding to activated GPIIb-IIIa and GPIb-IX internalization using PE-CD42b, in resting conditions and after stimulation either with ADP or TRAP. Apoptosis and activation parameters were evaluated by flow cytometry. In resting conditions, platelets from ITP patients showed increased PS expression and a- casp3 and abnormal ΔΨm (table 1). TablePSΔΨma-casp3Patients19.6 (1.9-82.0)31.2 (5.8-92.4)11.3 (1.8-40.9)Controls4.7 (1.9-10.8)10.3 (2.2-27.5)4.3 (1.9-8.2)p (Mann-Whitney)0.002 After stimulation with A23187, ITP platelets had similar levels of PS expression (p=0.305, n=20) and ΔmΨ (p=0.383, n=25) compared to normal controls. However, an increased sensitivity to the apoptotic stimulus was evidenced by elevated levels of a-casp3 at low and high A23187 concentrations (1-3 mM, p=0.097; 6-10 mM, p=0.002). Platelet apoptosis was not related to platelet activation, as PAC-1 binding was not increased in ITP platelets (basal p=0.847, ADP-induced p=0.059, TRAP-induced p=0.103, n=16). Besides, internalization of GPIb-IX after ADP and TRAP stimulation was also normal (p=NS, n=9 for both agonists). Platelets from ITP patients bearing two of the most frequently found auto-antibodies (5 with anti-GPIIb-IIIa and 1 with anti-GPIb-IX) had similar levels of PS expression and ΔmΨ at resting conditions than those who were negative for these auto-antibodies (n=14) (p=0.265 and 0.148, respectively). There were no differences in apoptosis markers either in resting platelets or after stimulation when comparing untreated patients (n=9) vs patients under any kind of treatment (n=15) (resting conditions, PS p=0.737; ΔmΨ p=0.270; stimulated, PS p=0.966; ΔmΨ p=0.987), although platelet count was similar in both groups. Normal platelets incubated during 1 hour with plasma from ITP had higher a-casp3 than those incubated with normal plasma (n=12 and 9, respectively, p=0.027), suggesting a plasmatic component could be responsible for the apoptotic stimulus. In conclusion, increased platelet apoptosis in ITP patients could be induced by a plasmatic factor, contributing to thrombocytopenia in this entity. Disclosures Riveros: Roche: Speakers Bureau.

Abstract 1163 Inherited thrombocytopenias are rare genetic disorders which frequently represent a diagnostic challenge, even after extensive diagnostic work-up. This is due to the requirement of specialized laboratory tests and to the fact that the underlying disease-causing mutation remains in many cases still unknown. Increasing knowledge regarding the molecular etiology of inherited thrombocytopenias contributes both to patient diagnosis, prognosis and genetic counseling and may lead to the identification of novel regulators of platelet production. Recently, mutations in the ANKRD26 gene have been described, which underlie inherited thrombocytopenias with normal platelet size. We applied a previously proposed algorithm (Haematologica 2003; 88: 582–592) and developed a twining program in collaboration with a specialized center to improve the diagnostic yield in a cohort of patients in Argentina. Based on this algorithm, patients were classified according both to the presence or absence of clinical or laboratory features other than thrombocytopenia and to platelet size. Simple laboratory tests, such as platelet function studies, peripheral blood smear and flow cytometry were performed in all cases, while confirmatory tests were performed according to initial diagnostic suspicion, and included analysis of non-muscle myosin heavy chain IIA distribution in neutrophils by immunofluorescence and mutational screening of candidate genes, such as MYH9, RUNX1, MPL, WASP, GPIBA and ANKRD26. Studies unavailable at the local institution were performed in a specialized center in the setting of the twining program. Thirty-five patients, belonging to 14 pedigrees, were included, age 32 (4–72) years old, 20 were female. Platelet count was 83 (5–170)×109/L, 49% were classified as macrothrombocytopenia, 46% had normal platelet size while 6% harboured small platelets. In the latter, a diagnosis of X-linked thrombocytopenia secondary to WASP mutation was made. Four pedigrees with macrothrombocytopenia had MYH9-related disease, one had Bernard-Soulier syndrome, while in four other, no molecular diagnosis was reached. Among pedigrees with normal platelet size, one had FPD/LMA due to RUNX1 mutation, whereas the c.-127A>G mutation in 5'UTR region of the ANKRD26 gene was detected in another family. In addition, a working diagnosis of familial ITP was made in a three-generation pedigree who had autosomal dominant thrombocytopenia and normal platelet size, based on the finding of shortened platelet life-span and complete response to splenectomy. Overall, a molecular diagnosis was established in 9 of 14 (64%) pedigrees, and MYH9-RD comprised the most frequent single disorder. Application of this diagnostic algorithm proved feasible in a resource-limited setting, as data provided by careful medical history and simple laboratory tests allowed to identify patients in whom further, specialized studies were justified. Collaboration of a specialized center was essential for molecular diagnosis and proved invaluable to build local capacities. Disclosures: No relevant conflicts of interest to declare.

Interleukin 6 (IL-6) plays a stimulatory role in megakaryocytic development acting through a specific receptor (IL-6Ra) and a signal transducing unit, gp130. A soluble IL-6R (IL-6sR) has also been described which retains the ability to bind IL-6 and associate to gp130 acting agonistically on cells that do not express IL-6R. We have previously described increased IL-6sR in essential thrombocythemia (ET), an illness characterized by megakaryocytic hyperplasia and high platelet count. The aim of this study was to evaluate the participation of IL-6sR in CD34+ cell survival and in platelet signaling in physiologic conditions and in ET. Therefore we studied: The ability of IL-6/IL-6sR to protect CD34+ cells from death by evaluating propidium iodine (PI) uptake, anexin-V binding and caspase 3 activation. We worked with normal CD34+ cells obtained from umbilical blood cord and with peripheral blood CD34+ cells from ET patients. Cells were purified by immunomagnetic means and cultured for 16 hours in the presence of culture media (IMDM), 100 ng/ml IL-6, 100 ng/ml thrombopoietin (Tpo) or 100 ng/ml IL-6 + 200 ng/ml IL-6sR (IL-6/IL-6sR). After that, PI uptake, anexin-V binding and activated caspase 3 were evaluated by flow cytometry using standard techniques. Besides, we have measured IL-6Ra on CD34+ cell surface by flow cytometry. JAK-2 and STAT-3 phosphorylation in normal and ET platelets. After stimulation with 100 ng/ml IL-6 plus 200 ng/ml IL-6sR or 100 ng/ml IL-6 alone, washed platelets were evaluated by western-blot with antibodies against phosphorylated and unphosphorylated proteins. Normal cells treated with Tpo and IL-6/IL-6sR displayed lower PI uptake than those cultured in IMDM or IL-6, while 3 patients did not show this pattern. Mean values are shown in table 1. Anexin-V binding did not differ among these four conditions. Next, we evaluated activated caspase 3 in CD34+ cells treated with either IL-6 or IL-6/IL-6sR. Mean flourescence intensity (Gm) from cells cultured in the presence of IL-6sR/IL-6 was lower than that of cells cultured in IL-6, in controls (p=0.002, Wilcoxon signed runk sum test) as well as ET patients (p=0.002). Median values are shown in table 2. A trend to increased apoptosis was found in controls compared to ET samples (p=0.051 for IL-6/IL-6sR; p=0.074 for IL-6). Normal CD34+ cells from five blood cord samples showed 0.12% (0–2.5) of positivity for IL-6Ra, while CD34+ cells from ET patients had 4.0% (0.73–24) (n=8, p=0.023, Wilcoxon rank sum test). We found an increased STAT-3 phosphorylation status in ET platelets (n=3) compared to normal controls (n=2) when platelets were stimulated with IL-6/IL-6sR, while JAK2 was found equally phosphorylated in these conditions. On the contrary, the same samples challenged with 100 ng/ml Tpo displayed similar intensity in STAT-3 phosphorylation. We conclude that IL-6/IL-6sR can protect normal and ET CD34+ cells from apoptosis more efficiently than IL-6. Besides, CD34+ cells from ET seem to be more resistant to apoptosis than their normal counterpart when cultured in the presence either of IL-6 or IL-6/IL-6sR. This effect could be due to an increased IL-6Ra expression on cell surface. Table 1 % of PI uptake IMDM IL-6 Tpo IL-6/IL-6sR (1) differed significantly from (2) p

Chemokines are soluble mediators implicated in a wide range of physiologic and pathologic processes including megakaryocytic development and platelet production. Previously, we found decreased levels of CXCR4, the only known receptor for the chemokine SDF-1, on platelet membrane from essential thrombocythemia (ET) patients, a chronic myeloproliferative disease characterized by megakaryocytic hyperplasia and high platelet count. In the present work we sought to evaluate the expression levels of platelet CXCR4 mRNA, the functional consequences of CXCR4 decrease in ET platelets as well as whether the receptor reduction was also extended to other lineages. We studied the expression levels of CXCR4 mRNA in platelets from ET patients by semi-quantitative RT-PCR. For semi-quantification, co-amplification of a GAPDH internal control sequence was performed. Functional studies consisted in turbidimetric evaluation of platelet aggregation induced by SDF-1 and/or ADP. In order to evaluate CXCR4 expression on leukocyte membrane, white cell subpopulations were individualized by the addition of specific MoAbs directed against CD45 labeled with PerCP and CD3 and CD14 labeled with FITC. Data were expressed as relative fluorescence intensity (RFI, ratio between the mean fluorescence intensity of CXCR4 antibody and the corresponding isotype control). The ratio between CXCR4 mRNA and the housekeeping gene GADPH in platelets from patients, 0.16 (0.1–0.24) was significantly decreased compared to controls, 0.35 (0.18–0.86), n=11, p=0.0002 (Wilcoxon signed rank sum test). Functional studies in response to SDF-1 showed a biphasic, dose-dependent full platelet aggregation in PRP in normal controls. On the contrary, abnormalities in SDF-1 response were observed in all 8 patients evaluated. Our results showed that platelet response to SDF-1 in ET patients closely paralleled that of ADP. Three patients did not respond either to SDF-1 or to ADP. From the remaining five patients, three had a delay in the second wave of aggregation induced by SDF-1 and the other two displayed only a primary wave of aggregation. These patients had a normal response to ADP when standard concentrations were used (2 mmol/L), but displayed a decreased response compared to normal controls when challenged with suboptimal doses of this agonist (0.8 to 1.2 mmol/L). CXCR4 RFI in granulocytes from patients was found elevated, 11.1 (2.22–22.74) compared to normal controls, 7.54 (1.73–9.52), p=0.036 (n=7). Similar results were found in CD3-positive lymphocytes, 40.0 (6.78–67.91) from patients and 17.23 (5.22–29.97) from normal controls, p=0.036 (Mann-Whitney Wilcoxon Rank Sum Test). On the contrary, CXCR4 on monocyte membrane was normally expressed, RFI from patients, 49.81 (1.17–118.28), and normal controls, 74.23 (3.0–80.49), p=0.8. These results indicate that the decrease in CXCR4 membrane expression on ET platelets is related to a reduced CXCR4 mRNA, and also to the abnormal platelet response to SDF-1. Besides, flow cytometric studies on leukocyte subpopulations demonstrated that CXCR4 decrease is restricted to the megakaryocytic lineage. Deregulation of SDF-1/CXCR4 axis in ET patients could be implicated in the megakaryocytic alterations seen in this illness and its presence in a megakaryocyte-related disease highlights the important role of SDF-1/CXCR4 axis in platelet development.

The JAK2V617F mutation has been recently reported in patients with polycythemia vera (PV) and a proportion of patients with ET and myelofibrosis with myeloid metaplasia. This acquired point mutation constitutively activates JAK2 tyrosine kinase and is believed to underlie growth factor hypersensitivity displayed by hematopoietic progenitors in these disorders. Identification of this genetic abnormality may be useful for diagnostic purposes although its prognostic implication remains to be determined. The prevalence of this mutation in granulocytes from ET patients ranges from 23 to 57% depending on the detection technique used. ET is characterized by predominant involvement of the megakaryocytic lineage and increased platelet production. In order to evaluate whether the frequency of the V617FJAK2 mutation in platelets from ET patients differs from that previously reported in granulocytes, we amplified a fragment of JAK2 cDNA from leukocyte-depleted platelets by RT-PCR followed by digestion with BsaXI restriction endonuclease (PCR-RFLP). The JAK2V617F mutation abolishes a BsaXI restriction site present in the wild-type sequence and generates a different band pattern. In addition, allele-specific RT-PCR (ASPCR) was performed with a primer pair common to both wild-type and mutant alleles and a third primer complementary to the mutant allele. Forty four patients with ET diagnosed according to the PVSG criteria were included, median age 39 years old (14–81), 10 were men; 21 were studied before treatment, 10 during treatment with anagrelide or hydroxyurea and 13 both before and during treatment. Twenty-two (50%) patients were found to harbour the JAK2V617F mutation by both PCR-RFLP and ASPCR, 3 were homozygous. No change in genotype was found in repeated samples from patients studied both before and during treatment. Hemoblobin levels and the frequency of thrombosis were significantly higher in patients with the mutation respect to those without (141 ±14 g/L vs. 129 ± 11 g/L, p=0.009, and 41% vs. 4.5%, p=0.004, respectively). In addition, patients carrying the mutation were significantly older (51 vs. 33 years old, p=0.002) and had lower platelet counts at diagnosis (1.070 x 109/L vs. 1.500 x 109/L, p=0.02). Interestingly, 2 patients harbouring the mutation developed PV on follow-up. In conclusion, the prevalence of the JAK2V617F mutation in platelets from ET patients did not differ from that previously reported in granulocytes. The increase in the frequency of thrombosis found in patients carrying the mutation should be confirmed in a larger study. Besides, the finding of higher hemoglobin levels in this group of patients is of interest since JAK2V617F-positive ET patients have been reported to display PV markers such as endogenous erythroid colony growth and PRV-1 overexpression, suggesting they may have larger involvement of the erythroid lineage. Further studies will help clarify whether the risk of developing PV is higher in this subset of patients.

Introduccion: Patients with essential thrombocythemia (ET) may have abnormalities of platelet function (PF), the most frecuently are reduced response to epinephrine and ADP-induced aggregation and spontaneous aggregation. Anagrelide (A) has a phosphodiesterase inhibitor activity and may inhibit PF. Therefore, we evaluated the follow-up of clinical manifestations (CM) and the PF in a group of 42 ET patients before treatment and on hematological remission. Materials and methods: 42 ET patients (33/9, F/M) who meet de PVSG criteria, were studied before treatment with A and on hematological remission. The CM were grouped into thrombosis (T), hemorrhages (H), microcirculation disturbances (MD) and combined (C), that included H plus MD or H plus T. Platelet function tests were perfomed with different agonists such as epinephrine, ADP, ristocetine, arachidonic acid and bovine vWF. Results: are shown in Table I. Abbreviations: T≠ (4 TIAs, 1 stroke, 1 AMI), H* (1 upper gastrointestinal bleeding, 4 minor hemorrhages) C± (1 mesenteric, portal and splenic vein thrombosis plus minor hemorrhage, 4 minor hemorrhages plus MCD), Tψ (1 TIA, 1 stroke), H§ (1 lower gastrointestinal bleeding) C† (1 AIT plus minor hemorrhage). During hematological remission spontaneous platelet aggregation disappeared in all patients except one. Abnormal epinephrine response desappeared in 16 patients, was not corrected in 10 and this abnormality appeared in 2 whose response were previously normal. Abnormal ADP response disappeared in 4 cases during treatment and this abnormality was found in 5 previously normal cases. No correlation was found between spontaneous platelet aggregation and clinical manifestations p= NS. No correlation was found between both epinephrine and ADP response and hemorrhages. No significant abnormalities were found in the response to arachidonic acid, ristocetin, and bovine vWF before or during treatment with anagrelide. Conclusions: In this group of ET patients platelet function was not affected by the phosphodiesterase inhibibitor activity of anagrelide. Similarly bleeding manifestations were not worsen during this therapy. As previously shown spontaneous platelet aggregation desappeared in all but one patient. We have not yet an explanation for the increased microvascular disturbances during treatment. | | Pre treatment | On treatment | |:--------------------------------------:| ------------- | ------------ | | Clinical Manifestations (42 patients ) | | | | Asymptomatic | 16 | 18 | | Thrombosis | 6≠ | 2ψ | | Hemorrhages | 5* | 4§ | | Microvascular disturbances | 10 | 17 | | Combined | 5± | 1† | | Platelet function | | | | Spontaneous aggregation | 17/42 | 1/41 | | Abnormal epinephrine response | 26/41 | 12/42 | | Abnormal ADP response | 17/41 | 9/41 | Table I

Essential thrombocythemia (ET), polycythemia vera and mielofibrosis with mieloid metaplasia (MMM) are myeloproliferative diseases that differ in their potential for developing bone marrow fibrosis. In addition to the role of megakaryocytes, the participation of monocytes in collagen deposits and fibroblast proliferation in the pathophysiology of MMM has already been described. We studied here monocyte activation in ET patients by measuring IL-2 receptor expression (CD25) in ex vivo monocytes and after its adhesion to polyestirene. Besides, we evaluated IL-1-b released by mononuclear cells after 24 hs culture. We evaluated 14 untreated ET patients. Blood samples were obtained under sterility conditions and mononuclear cells were separated by Ficoll-Hypaque gradient. CD25 positivity was evaluated by flow cytometry identifying monocytes as the CD14 + population before and after 18 hs cell culture in IMDM and 2% albumin. IL-1b was measured by ELISA technique in the supernatant of cells cultured in IMDM supplemented with 10% FCS during 18 hs. There were no statistical differences in CD25 expression in ET patients (n=8) neither before (3.1%, 1–11.4%) (median and range) nor after (15.2%, 4.7–39.3%) cell culture of CD14 population compared to normal controls (n=12, 2.0%, 0.2–10.3% and 20.3%, 1.4–34.3%, respectively). Levels of IL-1b were found decreased in patients with ET (n=10), 481 pg/ml, 53–1290 pg/ml, compared to normal controls (n=11), 779 pg/ml, 68.7–2166 pg/ml, although not reaching statistical difference (p=0.057). In conclusion, we did not find monocyte activation in ET patients as demonstrated by CD25 expression and IL-1b release. These results suggest that there is not a constitutive or induced activation of monocytes in ET but a trend towards a decreased capacity of activation. We believe this different monocyte behaviour from ET patients compared to that described in MMM patients could account for the dissimilar natural course of these diseases.

Recently we described increased IL-6 soluble receptor (IL-6sR) levels in plasma of essential thrombocythemia (ET) patients as well as elevated IL-6sR release by cultured mononuclear cells. IL-6sR can be generated by two different mechanisms: alternative splicing and proteolytic cleavage. Here we evaluated the participation of metalloproteases responsible for the proteolytic cleavage in the increase of IL-6sR levels produced by cultured cells. We studied expression changes in anchored IL-6 receptor (IL-6R) in CD3 lymphocytes as well as monocytes before and after cell culture. We also assessed the IL-6sR levels in the supernatant of cell culture in the presence and absence of a metalloprotease inhibitor, TAPI, that prevents most of the IL-6sR shedding from the anchored receptor. Seventeen patients with ET were studied, 14 without treatment and 3 under anagrelide treatment. Blood samples were obtained under sterility conditions and mononuclear cells were separated by Ficoll-Hypaque gradient. Afterwards, cells were cultured during 24 hs in IMDM supplemented with 10% FCS in the presence and absence of 150 mMol/L TAPI and IL-6sR released to culture media was measured by ELISA technique. Anchored IL-6R was evaluated before and after cell culture by flow cytometry using anti-CD126-PE. Monocyte and lymphocyte populations were selected using anti-CD14 and anti-CD3 respectively. IL-6sR levels in supernatant of mononuclear cells from 10 untreated ET patients were found increased, 122.5pg/ml (74–248 pg/ml) (median and range), compared to 9 normal controls, 83 pg/ml (22–130 pg/ml), p=0.011. In the presence of TAPI, patients and normal controls showed similar results, 54.95 pg/ml (18–137 pg/ml) and 48 pg/ml (18–96 pg/ml), respectively, p=NS. The difference between the amount of IL-6sR released in the absence and the presence of TAPI (D) would correspond to IL-6sR generated by proteolytic cleavage. This D was statistically higher in ET patients (61 pg/ml, 18–111 pg/ml) than in normal controls (28 pg/ml, 2–87 pg/ml), p=0.034. Expression of IL-6R on monocyte and lymphocytes from 5 untreated and 3 anagrelide treated ET patients before and after cell culture was similar to that of normal controls as shown by flow cytometry analysis. In conclusion, we found that proteolytic cleavage of IL-6R is increased in cultured mononuclear cells from patients with ET although the steady-state of IL-6R on monocytes and lymphocytes membrane is not altered.