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The clearance of senescent and altered red blood cells (RBCs) in the red pulp of the human spleen involves sequential processes of prefiltration, filtration, and postfiltration. While prior work has elucidated the mechanisms underlying the first two processes, biomechanical processes driving the postfiltration phagocytosis of RBCs retained at interendothelial slits (IES) are still poorly understood. We present here a unique computational model of macrophages to study the role of cell biomechanics in modulating the kinetics of phagocytosis of aged and diseased RBCs retained in the spleen. After validating the macrophage model using in vitro phagocytosis experiments, we employ it to probe the mechanisms underlying the kinetics of phagocytosis of mechanically altered RBCs, such as heated RBCs and abnormal RBCs in hereditary spherocytosis (HS) and sickle cell disease (SCD). Our simulations show pronounced deformation of the flexible and healthy RBCs in contrast to minimal shape changes in altered RBCs. Simulations also show that less deformable RBCs are engulfed faster and at lower adhesive strength than flexible RBCs, consistent with our experimental measurements. This efficient sensing and engulfment by macrophages of stiff RBCs retained at IES are expected to temper splenic congestion, a common pathogenic process in malaria, HS, and SCD. Altogether, our combined computational and in vitro experimental studies suggest that mechanical alterations of retained RBCs may suffice to enhance their phagocytosis, thereby adapting the kinetics of their elimination to the kinetics of their mechanical retention, an equilibrium essential for adequately cleaning the splenic filter to preserve its function., Competing Interests: Competing interests statement:The authors declare no competing interest.

The spleen constantly clears altered red blood cells (RBCs) from the circulation, tuning the balance between RBC formation (erythropoiesis) and removal. The retention and elimination of RBCs occur predominantly in the open circulation of the spleen, where RBCs must cross submicron-wide inter-endothelial slits (IES). Several experimental and computational studies have illustrated the role of IES in filtrating the biomechanically and morphologically altered RBCs based on a rigid wall assumption. However, these studies also reported that when the size of IES is close to the lower end of clinically observed sizes (less than 0.5 μm), an unphysiologically large pressure difference across the IES is required to drive the passage of normal RBCs, sparking debates on the feasibility of the rigid wall assumption. In this work, We propose two deformable IES models, namely the passive model and the active model, aiming to explore the impact of the deformability of IES on the filtration function of the spleen. In the passive model, we implement the worm-like string model to depict the IES's deformation as it interacts with blood plasma and allows RBC to traverse. In contrast, the active model involved regulating the IES deformation based on the local pressure surrounding the slit. To demonstrate the validity of the deformable model, we simulate the filtration of RBCs with varied size and stiffness by IES under three scenarios: (1) a single RBC traversing a single slit; (2) a suspension of RBCs traversing an array of slits, mimicking in vitro spleen-on-a-chip experiments; (3) RBC suspension passing through the 3D spleen filtration unit known as'the splenon'. Our simulation results of RBC passing through a single slit show that the deformable IES model offers more accurate predictions of the critical cell surface area to volume ratio that dictate the removal of aged RBCs from circulation compared to prior rigid-wall models. Our biophysical models of the spleen-on-a-chip indicate a hierarchy of filtration function stringency: rigid model > passive model > active model, providing a possible explanation of the filtration function of IES. We also illustrate that the biophysical model of 'the splenon' enables us to replicate the ex vivo experiments involving spleen filtration of malaria-infected RBCs. Taken together, our simulation findings indicate that the deformable IES model could serve as a mesoscopic representation of spleen filtration function closer to physiological reality, addressing questions beyond the scope of current experimental and computational models and enhancing our understanding of the fundamental flow dynamics and mechanical clearance processes within in the human spleen., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Although refrigerated storage slows the metabolism of volunteer donor RBCs, cellular aging still occurs throughout this in vitro process, which is essential in transfusion medicine. Storage-induced microerythrocytes (SMEs) are morphologically-altered senescent RBCs that accumulate during storage and which are cleared from circulation following transfusion. However, the molecular and cellular alterations that trigger clearance of this RBC subset remain to be identified. Using a staining protocol that sorts long-stored SMEs (i.e., CFSE high ) and morphologically-normal RBCs (CFSE low ), these in vitro aged cells were characterized. Metabolomics analysis identified depletion of energy, lipid-repair, and antioxidant metabolites in CFSE high RBCs. By redox proteomics, irreversible protein oxidation primarily affected CFSE high RBCs. By proteomics, 96 proteins, mostly in the proteostasis family, had relocated to CFSE high RBC membranes. CFSE high RBCs exhibited decreased proteasome activity and deformability; increased phosphatidylserine exposure, osmotic fragility, and endothelial cell adherence; and were cleared from the circulation during human spleen ex vivo perfusion. Conversely, molecular, cellular, and circulatory properties of long-stored CFSE low RBCs resembled those of short-stored RBCs. CFSE high RBCs are morphologically and metabolically altered, have irreversibly oxidized and membrane-relocated proteins, and exhibit decreased proteasome activity. In vitro aging during storage selectively alters metabolism and proteostasis in SMEs, targeting these senescent cells for clearance.

Splenomegaly frequently occurs in patients with Plasmodium falciparum (Pf) or P. vivax (Pv) malarial anemia, but mechanisms underlying this co-occurrence are unclear. In malaria-endemic Papua, Indonesia, we prospectively analyzed red blood cell (RBC) concentrations in the spleen and spleen-mimetic retention in 37 subjects splenectomized for trauma or hyperreactive splenomegaly, most of whom were infected with Plasmodium. Splenomegaly (median 357 g [range: 80-1918 g]) was correlated positively with the proportion of red-pulp on histological sections (median 88.1% [range: 74%-99.4%]; r = .59, p = .0003) and correlated negatively with the proportion of white-pulp (median 8.3% [range: 0.4%-22.9%]; r = -.50, p = .002). The number of RBC per microscopic field (>95% uninfected) was correlated positively with spleen weight in both Pf-infected (r = .73; p = .017) and Pv-infected spleens (r = .94; p = .006). The median estimated proportion of total-body RBCs retained in Pf-infected spleens was 8.2% (range: 1.0%-33.6%), significantly higher than in Pv-infected (2.6% [range: 0.6%-23.8%]; p = .015) and PCR-negative subjects (2.5% [range: 1.0%-3.3%]; p = .006). Retained RBCs accounted for over half of circulating RBC loss seen in Pf infections. The proportion of total-body RBC retained in Pf- and Pv-infected spleens correlated negatively with hemoglobin concentrations (r = -.56, p = .0003), hematocrit (r = -.58, p = .0002), and circulating RBC counts (r = -.56, p = .0003). Splenic CD71-positive reticulocyte concentrations correlated with spleen weight in Pf (r = 1.0; p = .003). Retention rates of peripheral and splenic RBCs were correlated negatively with circulating RBC counts (r = -.69, p = .07 and r = -.83, p = .008, respectively). In conclusion, retention of mostly uninfected RBC in the spleen, leading to marked congestion of the red-pulp, was associated with splenomegaly and is the major mechanism of anemia in subjects infected with Plasmodium, particularly Pf., (© 2023 The Authors. American Journal of Hematology published by Wiley Periodicals LLC.)

Being the largest lymphatic organ in the body, the spleen also constantly controls the quality of red blood cells (RBCs) in circulation through its two major filtration components, namely interendothelial slits (IES) and red pulp macrophages. In contrast to the extensive studies in understanding the filtration function of IES, fewer works investigate how the splenic macrophages retain the aged and diseased RBCs, i.e., RBCs in sickle cell disease (SCD). Herein, we perform a computational study informed by companion experiments to quantify the dynamics of RBCs captured and retained by the macrophages. We first calibrate the parameters in the computational model based on microfluidic experimental measurements for sickle RBCs under normoxia and hypoxia, as those parameters are not available in the literature. Next, we quantify the impact of key factors expected to dictate the RBC retention by the macrophages in the spleen, namely, blood flow conditions, RBC aggregation, hematocrit, RBC morphology, and oxygen levels. Our simulation results show that hypoxic conditions could enhance the adhesion between the sickle RBCs and macrophages. This, in turn, increases the retention of RBCs by as much as four-fold, which could be a possible cause of RBC congestion in the spleen of patients with SCD. Our study on the impact of RBC aggregation illustrates a 'clustering effect', where multiple RBCs in one aggregate can make contact and adhere to the macrophages, leading to a higher retention rate than that resulting from RBC-macrophage pair interactions. Our simulations of sickle RBCs flowing past macrophages for a range of blood flow velocities indicate that the increased blood velocity could quickly attenuate the function of the red pulp macrophages on detaining aged or diseased RBCs, thereby providing a possible rationale for the slow blood flow in the open circulation of the spleen. Furthermore, we quantify the impact of RBC morphology on their tendency to be retained by the macrophages. We find that the sickle and granular-shaped RBCs are more likely to be filtered by macrophages in the spleen. This finding is consistent with the observation of low percentages of these two forms of sickle RBCs in the blood smear of SCD patients. Taken together, our experimental and simulation results aid in our quantitative understanding of the function of splenic macrophages in retaining the diseased RBCs and provide an opportunity to combine such knowledge with the current knowledge of the interaction between IES and traversing RBCs to apprehend the complete filtration function of the spleen in SCD., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Li et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Red blood cells (RBC) transfusion is used to alleviate symptoms and prevent complications in anemic patients by restoring oxygen delivery to tissues. RBC transfusion efficacy, that can be measured by a rise in hemoglobin (Hb) concentration, is influenced by donor-, product-, and recipient-related characteristics. In some studies, severe pre-transfusion anemia is associated with a greater than expected Hb increment following transfusion but the biological mechanism underpinning this relationship remains poorly understood. We conducted a prospective study in critically ill patients and quantified Hb increment following one RBC transfusion. In a murine model, we investigated the possibility that, in conjunction with the host erythropoietic response, the persistence of transfused donor RBC is improved to maintain a highest RBC biomass. We confirmed a correlation between a greater Hb increment and a deeper pre-transfusion anemia in a cohort of 17 patients. In the mouse model, Hb increment and post-transfusion recovery were increased in anemic recipients. Post-transfusion RBC recovery was improved in hypoxic mice or those receiving an erythropoiesis-stimulating agent and decreased in those treated with erythropoietin (EPO)-neutralizing antibodies, suggesting that EPO signaling is necessary to observe this effect. Irradiated recipients also showed decreased post-transfusion RBC recovery. The EPO-induced post-transfusion RBC recovery improvement was abrogated in irradiated or in macrophage-depleted recipients, but maintained in splenectomized recipients, suggesting a mechanism requiring erythroid progenitors and macrophages, but which is not spleen-specific. Our study highlights a physiological role of EPO in downregulating post-transfusion RBC clearance, contributing to maintain a vital RBC biomass to rapidly cope with hypoxemia., (© 2023 The Authors. American Journal of Hematology published by Wiley Periodicals LLC.)

The spleen clears altered red blood cells (RBCs) from circulation, contributing to the balance between RBC formation (erythropoiesis) and removal. The splenic RBC retention and elimination occur predominantly in open circulation where RBCs flow through macrophages and inter-endothelial slits (IESs). The mechanisms underlying and interconnecting these processes significantly impact clinical outcomes. In sickle cell disease (SCD), blockage of intrasplenic sickled RBCs is observed in infants splenectomized due to acute splenic sequestration crisis (ASSC). This life-threatening RBC pooling and organ swelling event is plausibly triggered or enhanced by intra-tissular hypoxia. We present an oxygen-mediated spleen-on-a-chip platform for in vitro investigations of the homeostatic balance in the spleen. To demonstrate and validate the benefits of this general microfluidic platform, we focus on SCD and study the effects of hypoxia on splenic RBC retention and elimination. We observe that RBC retention by IESs and RBC-macrophage adhesion are faster in blood samples from SCD patients than those from healthy subjects. This difference is markedly exacerbated under hypoxia. Moreover, the sickled RBCs under hypoxia show distinctly different phagocytosis processes from those non-sickled RBCs under hypoxia or normoxia. We find that reoxygenation significantly alleviates RBC retention at IESs, and leads to rapid unsickling and fragmentation of the ingested sickled RBCs inside macrophages. These results provide unique mechanistic insights into how the spleen maintains its homeostatic balance between splenic RBC retention and elimination, and shed light on how disruptions in this balance could lead to anemia, splenomegaly, and ASSC in SCD and possible clinical manifestations in other hematologic diseases.

Refrigerated storage of red cell concentrates before transfusion is associated with progressive alterations of red blood cells (RBC). Small RBC (type III echinocytes, sphero-echinocytes, and spherocytes) defined as storage-induced micro-erythrocytes (SME) appear during pretransfusion storage. SME accumulate with variable intensity from donor to donor, are cleared rapidly after transfusion, and their proportion correlates with transfusion recovery. They can be rapidly and objectively quantified using imaging flow cytometry (IFC). Quantifying SME using flow cytometry would further facilitate a physiologically relevant quality control of red cell concentrates. RBC stored in blood bank conditions were stained with a carboxyfluorescein succinimidyl ester (CFSE) dye and incubated at 37°C. CFSE intensity was assessed by flow cytometry and RBC morphology evaluated by IFC. We observed the accumulation of a CFSE high RBC subpopulation by flow cytometry that accounted for 3.3 and 47.2% at day 3 and 42 of storage, respectively. IFC brightfield images showed that this CFSE high subpopulation mostly contains SME while the CFSE low subpopulation mostly contains type I and II echinocytes and discocytes. Similar numbers of SME were quantified by IFC (based on projected surface area) and by flow cytometry (based on CFSE intensity). IFC and scanning electron microscopy showed that ≥95% pure subpopulations of CFSE high and CFSE low RBC were obtained by flow cytometry-based sorting. SME can now be quantified using a common fluorescent dye and a standard flow cytometer. The staining protocol enables specific sorting of SME, a useful tool to further characterize this RBC subpopulation targeted for premature clearance after transfusion., Competing Interests: PA is funded in part by New Health Science. MM, SP, MD, CR, PB, and PA declare that the European patent application EP21306765 was filed on December 12th, 2021. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Marin, Peltier, Hadjou, Georgeault, Dussiot, Roussel, Hermine, Roingeard, Buffet and Amireault.)

Background: A very large biomass of intact asexual-stage malaria parasites accumulates in the spleen of asymptomatic human individuals infected with Plasmodium vivax. The mechanisms underlying this intense tropism are not clear. We hypothesised that immature reticulocytes, in which P. vivax develops, may display high densities in the spleen, thereby providing a niche for parasite survival., Methods and Findings: We examined spleen tissue in 22 mostly untreated individuals naturally exposed to P. vivax and Plasmodium falciparum undergoing splenectomy for any clinical indication in malaria-endemic Papua, Indonesia (2015 to 2017). Infection, parasite and immature reticulocyte density, and splenic distribution were analysed by optical microscopy, flow cytometry, and molecular assays. Nine non-endemic control spleens from individuals undergoing spleno-pancreatectomy in France (2017 to 2020) were also examined for reticulocyte densities. There were no exclusion criteria or sample size considerations in both patient cohorts for this demanding approach. In Indonesia, 95.5% (21/22) of splenectomy patients had asymptomatic splenic Plasmodium infection (7 P. vivax, 13 P. falciparum, and 1 mixed infection). Significant splenic accumulation of immature CD71 intermediate- and high-expressing reticulocytes was seen, with concentrations 11 times greater than in peripheral blood. Accordingly, in France, reticulocyte concentrations in the splenic effluent were higher than in peripheral blood. Greater rigidity of reticulocytes in splenic than in peripheral blood, and their higher densities in splenic cords both suggest a mechanical retention process. Asexual-stage P. vivax-infected erythrocytes of all developmental stages accumulated in the spleen, with non-phagocytosed parasite densities 3,590 times (IQR: 2,600 to 4,130) higher than in circulating blood, and median total splenic parasite loads 81 (IQR: 14 to 205) times greater, accounting for 98.7% (IQR: 95.1% to 98.9%) of the estimated total-body P. vivax biomass. More reticulocytes were in contact with sinus lumen endothelial cells in P. vivax- than in P. falciparum-infected spleens. Histological analyses revealed 96% of P. vivax rings/trophozoites and 46% of schizonts colocalised with 92% of immature reticulocytes in the cords and sinus lumens of the red pulp. Larger splenic cohort studies and similar investigations in untreated symptomatic malaria are warranted., Conclusions: Immature CD71+ reticulocytes and splenic P. vivax-infected erythrocytes of all asexual stages accumulate in the same splenic compartments, suggesting the existence of a cryptic endosplenic lifecycle in chronic P. vivax infection. Findings provide insight into P. vivax-specific adaptions that have evolved to maximise survival and replication in the spleen., Competing Interests: The authors have declared that no competing interests exist.

Permanent availability of red blood cells (RBCs) for transfusion depends on refrigerated storage, during which morphologically altered RBCs accumulate. Among these, a subpopulation of small RBCs, comprising type III echinocytes, spheroechinocytes, and spherocytes and defined as storage-induced microerythrocytes (SMEs), could be rapidly cleared from circulation posttransfusion. We quantified the proportion of SMEs in RBC concentrates from healthy human volunteers and assessed correlation with transfusion recovery, investigated the fate of SMEs upon perfusion through human spleen ex vivo, and explored where and how SMEs are cleared in a mouse model of blood storage and transfusion. In healthy human volunteers, high proportion of SMEs in long-stored RBC concentrates correlated with poor transfusion recovery. When perfused through human spleen, 15% and 61% of long-stored RBCs and SMEs were cleared in 70 minutes, respectively. High initial proportion of SMEs also correlated with high retention of RBCs by perfused human spleen. In the mouse model, SMEs accumulated during storage. Transfusion of long-stored RBCs resulted in reduced posttransfusion recovery, mostly due to SME clearance. After transfusion in mice, long-stored RBCs accumulated predominantly in spleen and were ingested mainly by splenic and hepatic macrophages. In macrophage-depleted mice, splenic accumulation and SME clearance were delayed, and transfusion recovery was improved. In healthy hosts, SMEs were cleared predominantly by macrophages in spleen and liver. When this well-demarcated subpopulation of altered RBCs was abundant in RBC concentrates, transfusion recovery was diminished. SME quantification has the potential to improve blood product quality assessment. This trial was registered at www.clinicaltrials.gov as #NCT02889133., (© 2021 by The American Society of Hematology.)

Background: Red blood cells (RBC) change upon hypothermic conservation, and storage for 6 weeks is associated with the short-term clearance of 15% to 20% of transfused RBCs. Metabolic rejuvenation applied to RBCs before transfusion replenishes energetic sources and reverses most storage-related alterations, but how it impacts RBC circulatory functions has not been fully elucidated., Study Design and Methods: Six RBC units stored under blood bank conditions were analyzed weekly for 6 weeks and rejuvenated on Day 42 with an adenine-inosine-rich solution. Impact of storage and rejuvenation on adenosine triphosphate (ATP) levels, morphology, accumulation of storage-induced microerythrocytes (SMEs), elongation under an osmotic gradient (by LORRCA), hemolysis, and phosphatidylserine (PS) exposure was evaluated. The impact of rejuvenation on filterability and adhesive properties of stored RBCs was also assessed., Results: Rejuvenation of RBCs restored intracellular ATP to almost normal levels and decreased the PS exposure from 2.78% to 0.41%. Upon rejuvenation, the proportion of SME dropped from 28.2% to 9.5%, while the proportion of normal-shaped RBCs (discocytes and echinocytes 1) increased from 47.7% to 67.1%. In LORCCA experiments, rejuvenation did not modify the capacity of RBCs to elongate and induced a reduction in cell volume. In functional tests, rejuvenation increased RBC filterability in a biomimetic splenic filter (+16%) and prevented their adhesion to endothelial cells (-87%)., Conclusion: Rejuvenation reduces the proportion of morphologically altered and adhesive RBCs that accumulate during storage. Along with the improvement in their filterability, these data show that rejuvenation improves RBC properties related to their capacity to persist in circulation after transfusion., (© 2020 AABB.)

The current paradigm in the pathogenesis of several hemolytic red blood cell disorders is that reduced cellular deformability is a key determinant of splenic sequestration of affected red cells. Three distinct features regulate cellular deformability: membrane deformability, surface area-to-volume ratio (cell sphericity), and cytoplasmic viscosity. By perfusing normal human spleens ex vivo, we had previously showed that red cells with increased sphericity are rapidly sequestered by the spleen. Here, we assessed the retention kinetics of red cells with decreased membrane deformability but without marked shape changes. A controlled decrease in membrane deformability (increased membrane rigidity) was induced by treating normal red cells with increasing concentrations of diamide. Following perfusion, diamide-treated red blood cells (RBCs) were rapidly retained in the spleen with a mean clearance half-time of 5.9 minutes (range, 4.0-13.0). Splenic clearance correlated positively with increased membrane rigidity ( r = 0.93; P < .0001). To determine to what extent this increased retention was related to mechanical blockade in the spleen, diamide-treated red cells were filtered through microsphere layers that mimic the mechanical sensing of red cells by the spleen. Diamide-treated red cells were retained in the microsphilters (median, 7.5%; range, 0%-38.6%), although to a lesser extent compared with the spleen (median, 44.1%; range, 7.3%-64.0%; P < .0001). Taken together, these results have implications for understanding the sensitivity of the human spleen to sequester red cells with altered cellular deformability due to various cellular alterations and for explaining clinical heterogeneity of RBC membrane disorders., (© 2018 by The American Society of Hematology.)

In red blood cell (RBC) diseases, the spleen contributes to anemia by clearing the damaged RBCs, but its unique ability to mechanically challenge RBCs also poses the risk of inducing other pathogenic effects. We have analyzed RBCs in hereditary spherocytosis (HS) and hereditary elliptocytosis (HE), two typical examples of blood disorders that result in membrane protein defects in RBCs. We use a two-component protein-scale RBC model to simulate the traversal of the interendothelial slit (IES) in the human spleen, a stringent biomechanical challenge on healthy and diseased RBCs that cannot be directly observed in vivo. In HS, our results confirm that the RBC loses surface due to weakened cohesion between the lipid bilayer and the cytoskeleton and reveal that surface loss may result from vesiculation of the RBC as it crosses IES. In HE, traversing IES induces sustained elongation of the RBC with impaired elasticity and fragmentation in severe disease. Our simulations thus suggest that in inherited RBC disorders, the spleen not only filters out pathological RBCs but also directly contributes to RBC alterations. These results provide a mechanistic rationale for different clinical outcomes documented following splenectomy in HS patients with spectrin-deficient and ankyrin-deficient RBCs and offer insights into the pathogenic role of human spleen in RBC diseases., Competing Interests: The authors declare no conflict of interest., (Copyright © 2018 the Author(s). Published by PNAS.)

Red blood cells (RBC) ability to circulate is closely related to their surface area-to-volume ratio. A decrease in this ratio induces a decrease in RBC deformability that can lead to their retention and elimination in the spleen. We recently showed that a subpopulation of "small RBC" with reduced projected surface area accumulated upon storage in blood bank concentrates, but data on the volume of these altered RBC are lacking. So far, single cell measurement of RBC volume has remained a challenging task achieved by a few sophisticated methods some being subject to potential artifacts. We aimed to develop a reproducible and ergonomic method to assess simultaneously RBC volume and morphology at the single cell level. We adapted the fluorescence exclusion measurement of volume in nucleated cells to the measurement of RBC volume. This method requires no pre-treatment of the cell and can be performed in physiological or experimental buffer. In addition to RBC volume assessment, brightfield images enabling a precise definition of the morphology and the measurement of projected surface area can be generated simultaneously. We first verified that fluorescence exclusion is precise, reproducible and can quantify volume modifications following morphological changes induced by heating or incubation in non-physiological medium. We then used the method to characterize RBC stored for 42 days in SAG-M in blood bank conditions. Simultaneous determination of the volume, projected surface area and morphology allowed to evaluate the surface area-to-volume ratio of individual RBC upon storage. We observed a similar surface area-to-volume ratio in discocytes (D) and echinocytes I (EI), which decreased in EII (7%) and EIII (24%), sphero-echinocytes (SE; 41%) and spherocytes (S; 47%). If RBC dimensions determine indeed the ability of RBC to cross the spleen, these modifications are expected to induce the rapid splenic entrapment of the most morphologically altered RBC (EIII, SE, and S) and further support the hypothesis of a rapid clearance of the "small RBC" subpopulation by the spleen following transfusion.

The proportion of transfused red blood cells (RBCs) that remain in circulation is an important surrogate marker of transfusion efficacy and contributes to predict the potential benefit of a transfusion process. Over the last 50 years, most of the transfusion recovery data were generated by chromium-51 ( 51 Cr)-labeling studies and were predominantly performed to validate new storage systems and new processes to prepare RBC concentrates. As a consequence, our understanding of transfusion efficacy is strongly dependent on the strengths and weaknesses of 51 Cr labeling in particular. Other methods such as antigen mismatch or biotin-based labeling can bring relevant information, for example, on the long-term survival of transfused RBC. These radioactivity-free methods can be used in patients including from vulnerable groups. We provide an overview of the methods used to measure transfusion recovery in humans, compare their strengths and weaknesses, and discuss their potential limitations. Also, based on our understanding of the spleen-specific filtration of damaged RBC and historical transfusion recovery data, we propose that RBC deformability and morphology are storage lesion markers that could become useful predictors of transfusion recovery. Transfusion recovery can and should be accurately explored by more than one method. Technical optimization and clarification of concepts is still needed in this important field of transfusion and physiology.

Artesunate, the recommended drug for severe malaria, rapidly clears the malaria parasite from infected patients but frequently induces anemia-called post-artesunate delayed hemolysis (PADH)-for which a simple predictive test is urgently needed. The underlying event in PADH is the expulsion of artesunate-exposed parasites from their host erythrocytes by pitting. We show that the histidine-rich protein 2 (HRP2) of the malaria parasite Plasmodium falciparum persists in the circulation of artesunate-treated malaria patients in Bangladesh and in French travelers who became infected with malaria in Africa. HRP2 persisted in whole blood (not plasma) of artesunate-treated patients with malaria at higher levels compared to quinine-treated patients. Using an optimized membrane permeabilization method, HRP2 was observed by immunofluorescence, Western blotting, and electron microscopy to persist in once-infected red blood cells from artesunate-treated malaria patients. HRP2 was deposited at the membrane of once-infected red blood cells in a pattern similar to that for ring erythrocyte surface antigen (RESA), a parasite invasion marker. On the basis of these observations, we developed a semiquantitative titration method using a widely available HRP2-based rapid diagnostic dipstick test. Positivity on this test using a 1:500 dilution of whole blood from artesunate-treated patients with malaria collected shortly after parasite clearance predicted subsequent PADH with 89% sensitivity and 73% specificity. These results suggest that adapting an existing HRP2-based rapid diagnostic dipstick test may enable prediction of PADH several days before it occurs in artesunate-treated patients with malaria., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Background: Storage lesion may explain the rapid clearance of up to 25% of transfused red blood cells (RBCs) in recipients. Several alterations affect stored RBC but a quantitative, whole cell-based predictor of transfusion yield is lacking. Because RBCs with reduced surface area are retained by the spleen, we quantified changes in RBC dimensions during storage., Study Design and Methods: Using imaging flow cytometry we observed the dimension and morphology of RBCs upon storage, along with that of conventional biochemical and mechanical markers of storage lesion. We then validated these findings using differential interference contrast (DIC) microscopy and quantified the accumulation of microparticles (MPs)., Results: Mean projected surface area of the whole RBC population decreased from 72.4 to 68.4 µm 2 , a change resulting from the appearance of a well-demarcated subpopulation of RBCs with reduced mean projected surface (58 µm 2 , 15.2%-19.9% reduction). These "small RBCs" accounted for 4.9 and 23.6% of all RBCs on Days 3 and 42 of storage, respectively. DIC microscopy confirmed that small RBCs had shifted upon storage from discocytes to echinocytes III, spheroechinocytes, and spherocytes. Glycophorin A-positive MPs and small RBCs appeared after similar kinetics., Conclusion: The reduction in surface area of small RBCs is expected to induce their retention by the spleen. We propose that small RBCs generated by MP-induced membrane loss are preferentially cleared from the circulation shortly after transfusion of long-stored blood. Their operator-independent quantification using imaging flow cytometry may provide a marker of storage lesion potentially predictive of transfusion yield., (© 2017 AABB.)

Background: Artesunate (AS) is the WHO first-line treatment of severe malaria in endemic countries, in adults and children. However, despite solid evidence that AS is safe and more effective than quinine in endemic areas, its deployment in non-endemic areas has been slow, due in part to the absence of a full good manufacturing practice (GMP) qualification (although prequalification has been granted in 2010). Prospective comparative trials were not conducted in travellers, but several retrospective studies and case reports are providing insights into the efficacy and safety of AS in imported severe malaria., Methods: We performed a systematic review on AS use in non-endemic areas for the treatment of imported severe malaria, using the Prisma method for bibliographic reports. Post-AS delayed haemolysis (PADH) was defined by delayed haemolytic episodes occurring 7-30 days after treatment initiation. We summarized prescription guidelines and generated answers to frequently asked questions regarding the use of AS in travellers with severe malaria., Results: We analysed 12 retrospectives and 1 prospective study as well as 7 case reports of AS treatment in 624 travellers. Of 574 patients with reported outcome, 23 died (4%). No death was attributed to AS toxicity. Non-haematological side effects were uncommon and mainly included mild hepatitis, neurological, renal, cutaneous and cardiac manifestations. PADH occurred in 15% of the treated patients. No death or sequelae were reported. Overall blood transfusion was administered in 50% of travellers with PADH., Conclusion: AS is highly efficacious in travellers with severe malaria. The frequency of PADH supports the need of weekly follow-up of haematological parameters during 1 month. Full GMP qualification for the drug and rapid approval by drug agencies is warranted, backed by clear recommendations for optimal use., (© International Society of Travel Medicine, 2017. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com)

Background: Sickle-cell trait (HbAS) reduces falciparum malaria risk and suppresses parasitaemia. Although several candidate mechanisms have been proposed, their epidemiological, clinical and experimental correlates have not been adequately explained. To explore the basis for generally lower parasitaemias and delayed malaria episodes in children with HbAS, it is hypothesized here that their spleen-dependent removal of ring-infected red blood cells (RBCs) is more efficient than in children with normal haemoglobin A (HbAA)., Methods: The mechanical splenic retention of Plasmodium falciparum-infected RBCs from subjects with HbAS or HbAA was investigated using two physiologically relevant methods: microsphiltration and ex vivo spleen perfusion. P. falciparum-infected RBCs obtained from in vitro cultures and from patients were used in either normoxic or hypoxic conditions. The effect of sickling in ring-infected HbAS RBCs was also investigated., Results: When a laboratory-adapted parasite strain was analysed, ring-infected HbAA RBCs were retained in microsphilters at similar or greater levels than ring-infected HbAS RBCs, under normoxic (retention rate 62.5 vs 43.8 %, P < 0.01) and hypoxic (54.0 vs 38.0 %, P = 0.11) conditions. When parasitized RBCs from Malian children were analysed, retention of ring-infected HbAA and HbAS RBCs was similar when tested either directly ex vivo (32.1 vs 28.7 %, P = 0.52) or after one re-invasion in vitro (55.9 vs 43.7 %, P = 0.30). In hypoxia, sickling of uninfected and ring-infected HbAS RBCs (8.6 vs 5.7 %, P = 0.51), and retention of ring-infected HbAA and HbAS RBCs in microsphilters (72.5 vs 68.8 %, P = 0.38) and spleens (41.2 vs 30.4 %, P = 0.11), also did not differ. Retention of HbAS and HbAA RBCs infected with mature P. falciparum stages was greater than 95 %., Conclusions: Sickle-cell trait is not associated with higher retention or sickling of ring-infected RBCs in experimental systems reflecting the mechanical sensing of RBCs by the human spleen. As observed with HbAA RBCs, HbAS RBCs infected with mature parasites are completely retained. Because the cytoadherence of HbAS RBCs infected with mature parasites is impaired, the very efficient splenic retention of such non-adherent infected RBCs is expected to result in a slower rise of P. falciparum parasitaemia in sickle-cell trait carriers.

Red blood cells (RBCs) can be cleared from circulation when alterations in their size, shape, and deformability are detected. This function is modulated by the spleen-specific structure of the interendothelial slit (IES). Here, we present a unique physiological framework for development of prognostic markers in RBC diseases by quantifying biophysical limits for RBCs to pass through the IES, using computational simulations based on dissipative particle dynamics. The results show that the spleen selects RBCs for continued circulation based on their geometry, consistent with prior in vivo observations. A companion analysis provides critical bounds relating surface area and volume for healthy RBCs beyond which the RBCs fail the "physical fitness test" to pass through the IES, supporting independent experiments. Our results suggest that the spleen plays an important role in determining distributions of size and shape of healthy RBCs. Because mechanical retention of infected RBC impacts malaria pathogenesis, we studied key biophysical parameters for RBCs infected with Plasmodium falciparum as they cross the IES. In agreement with experimental results, surface area loss of an infected RBC is found to be a more important determinant of splenic retention than its membrane stiffness. The simulations provide insights into the effects of pressure gradient across the IES on RBC retention. By providing quantitative biophysical limits for RBCs to pass through the IES, the narrowest circulatory bottleneck in the spleen, our results offer a broad approach for developing quantitative markers for diseases such as hereditary spherocytosis, thalassemia, and malaria.

During their lifespan, circulating RBC are frequently checked for their deformability. This mechanical quality control operates essentially in the human spleen. RBC unable to squeeze though narrow splenic slits are retained and cleared from the blood circulation. Under physiological conditions this prevents microvessels from being clogged by senescent, rigid RBC. Retention of poorly deformable RBC is an important determinant of pathogenesis in malaria and may also impact the clinical benefit of transfusion. Modulating the splenic retention of RBC has already been proposed to support therapeutic approaches in these research fields. To this aim, the development of microplates for high throughput filtration of RBC through microsphere layers (microplate-based microsphiltration) has been undertaken. This review focuses on potential therapeutic applications provided by this technology in malaria chemotherapy and transfusion., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Plasmodium falciparum is transmitted from humans to Anopheles mosquito vectors via the sexual erythrocytic forms termed gametocytes. Erythrocyte filtration through microsphere layers (microsphiltration) had shown that circulating gametocytes are deformable. Compounds reducing gametocyte deformability would induce their splenic clearance, thus removing them from the blood circulation and blocking malaria transmission. The hand-made, single-sample prototype for microsphiltration was miniaturized to a 96-well microtiter plate format, and gametocyte retention in the microsphere filters was quantified by high-content imaging. The stiffening activity of 40 pharmacological compounds was assessed in microtiter plates, using a small molecule (calyculin) as a positive control. The stiffening activity of calyculin was assessed in spleen-mimetic microfluidic chips and in macrophage-depleted mice. Marked mechanical retention (80% to 90%) of mature gametocytes was obtained in microplates following exposure to calyculin at concentrations with no effect on parasite viability. Of the 40 compounds tested, including 20 antimalarials, only 5 endoperoxides significantly increased gametocyte retention (1.5- to 2.5-fold; 24 h of exposure at 1 μM). Mature gametocytes exposed to calyculin accumulated in microfluidic chips and were cleared from the circulation of macrophage-depleted mice as rapidly as heat-stiffened erythrocytes, thus confirming results obtained using the microsphiltration assay. An automated miniaturized approach to select compounds for their gametocyte-stiffening effect has been established. Stiffening induces gametocyte clearance both in vitro and in vivo. Based on physiologically validated tools, this screening cascade can identify novel compounds and uncover new targets to block malaria transmission. Innovative applications in hematology are also envisioned., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Background: In Plasmodium falciparum-infected patients treated with artemisinins, parasitemia declines through so-called pitting, an innate splenic process that transforms infected red blood cells (iRBCs) into once-infected RBCs (O-iRBCs)., Methods: We measured pitting in 83 French travelers and 42 Malian children treated for malaria with artesunate., Results: In travelers, O-iRBCs peaked at 107.7% initial parasitemia. In Malian children aged 1.5-4 years, O-iRBCs peaked at higher concentrations than in children aged 9-13 years (91.60% vs 31.95%; P = .0097). The parasite clearance time in older children was shorter than in younger children (P = .0001), and the decline in parasitemia in children aged 1.5-4 years often started 6 hours after treatment initiation, a lag phase generally absent in infants and older children. A 6-hour lag phase in artificial pitting of artesunate-exposed iRBCs was also observed in vitro. The proportion of iRBCs recognized by autologous immunoglobulin G (IgG) correlated with the parasite clearance time (r = -0.501; P = .0006) and peak O-iRBC concentration (r = -0.420; P = .0033)., Conclusions: Antimalarial immunity correlates with fast artemisinin-induced parasite clearance and low pitting rates. In nonimmune populations, artemisinin-induced P. falciparum clearance is related to pitting and starts after a 6-hour lag phase. In immune populations, passively and naturally acquired immune mechanisms operating faster than pitting may exist. This mechanism may mitigate the emergence of artemisinin-resistant P. falciparum in Africa., (© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

The mechanisms underlying reduced red blood cell (RBC) deformability during Plasmodium falciparum (Pf) malaria remain poorly understood. Here, we explore the possible involvement of the L-arginine and nitric oxide (NO) pathway on RBC deformability in Pf-infected patients and parasite cultures. RBC deformability was reduced during the acute attack (day0) and returned to normal values upon convalescence (day28). Day0 values correlated with plasma L-arginine levels (r = 0.69; p = 0.01) and weakly with parasitemia (r = -0.38; p = 0.006). In vitro, day0 patient's plasma incubated with ring-stage cultures at 41°C reduced RBC deformability, and this effect correlated strongly with plasma L-arginine levels (r = 0.89; p < 0.0001). Moreover, addition of exogenous L-arginine to the cultures increased deformability of both Pf-free and trophozoite-harboring RBCs. NO synthase activity, evidenced in Pf-infected RBCs, induced L-arginine-dependent NO production. These data show that hypoargininemia during P. falciparum malaria may altogether impair NO production and reduce RBC deformability, particularly at febrile temperature.

Background: Cutaneous leishmaniasis (CL) is a disfiguring but not life-threatening disease. Because antileishmanial drugs are potentially toxic, the World Health Organization (WHO) recommends simple wound care or local therapy as first-line treatment, followed or replaced by systemic therapy if local therapy fails or cannot be performed., Methods: To determine the feasibility and impact of the recommended approach, we analyzed the results of a centralized referral treatment program in 135 patients with parasitologically proven CL., Results: Infections involved 10 Leishmania species and were contracted in 29 different countries. Eighty-four of 135 patients (62%) were initially treated without systemic therapy. Of 109 patients with evaluable charts, 23 of 25 (92%) treated with simple wound care and 37 of 47 (79%) treated with local antileishmanial therapy were cured by days 42-60. In 37 patients with large or complex lesions, or preexisting morbidities, or who had not been cured with local therapy, the cure rate with systemic antileishmanial agents was 60%. Systemic adverse events were observed in 15 patients, all receiving systemic therapy., Conclusions: In this population of CL patients displaying variable degrees of complexity and severity, almost two-thirds of patients could be initially managed without systemic therapy. Of these, 60 were cured before day 60. The WHO-recommended stepwise approach favoring initial local therapy therefore resulted in at least 44% of all patients being cured without exposure to the risk of systemic adverse events. Efforts are needed to further simplify local therapy of CL and to improve the management of patients with complex lesions and/or preexisting comorbidities.

Ex vivo perfusion of human spleens revealed innate retention of numerous cultured Plasmodium falciparum ring-infected red blood cells (ring-iRBCs). Ring-iRBC retention was confirmed by a microsphiltration device, a microbead-based technology that mimics the mechanical filtering function of the human spleen. However, the cellular alterations underpinning this retention remain unclear. Here, we use ImageStream technology to analyze infected RBCs' morphology and cell dimensions before and after fractionation with microsphiltration. Compared to fresh normal RBCs, the mean cell membrane surface area loss of trophozoite-iRBCs, ring-iRBCs and uninfected co-cultured RBCs (uRBCs) was 14.2% (range: 8.3-21.9%), 9.6% (7.3-12.2%) and 3.7% (0-8.4), respectively. Microsphilters retained 100%, ∼50% and 4% of trophozoite-iRBCs, ring-iRBCs and uRBCs, respectively. Retained ring-iRBCs display reduced surface area values (estimated mean, range: 17%, 15-18%), similar to the previously shown threshold of surface-deficient RBCs retention in the human spleen (surface area loss: >18%). By contrast, ring-iRBCs that successfully traversed microsphilters had minimal surface area loss and normal sphericity, suggesting that these parameters are determinants of their retention. To confirm this hypothesis, fresh normal RBCs were exposed to lysophosphatidylcholine to induce a controlled loss of surface area. This resulted in a dose-dependent retention in microsphilters, with complete retention occurring for RBCs displaying >14% surface area loss. Taken together, these data demonstrate that surface area loss and resultant increased sphericity drive ring-iRBC retention in microsphilters, and contribute to splenic entrapment of a subpopulation of ring-iRBCs. These findings trigger more interest in malaria research fields, including modeling of infection kinetics, estimation of parasite load, and analysis of risk factors for severe clinical forms. The determination of the threshold of splenic retention of ring-iRBCs has significant implications for diagnosis (spleen functionality) and drug treatment (screening of adjuvant therapy targeting ring-iRBCs).

Splenic sequestration of RBCs with reduced surface area and cellular deformability has long been recognized as contributing to pathogenesis of several RBC disorders, including hereditary spherocytosis. However, the quantitative relationship between the extent of surface area loss and splenic entrapment remains to be defined. To address this issue, in the present study, we perfused ex vivo normal human spleens with RBCs displaying various degrees of surface area loss and monitored the kinetics of their splenic retention. Treatment with increasing concentrations of lysophosphatidylcholine resulted in a dose-dependent reduction of RBC surface area at constant volume, increased osmotic fragility, and decreased deformability. The degree of splenic retention of treated RBCs increased with increasing surface area loss. RBCs with a > 18% average surface area loss (> 27% reduced surface area-to-volume ratio) were rapidly and completely entrapped in the spleen. Surface-deficient RBCs appeared to undergo volume loss after repeated passages through the spleen and escape from splenic retention. The results of the present study for the first time define the critical extent of surface area loss leading to splenic entrapment and identify an adaptive volume regulation mechanism that allows spherocytic RBCs to prolong their life span in circulation. These results have significant implications for understanding the clinical heterogeneity of RBC membrane disorders.

Plasmodium vivax threatens nearly half the world's population and is a significant impediment to achievement of the millennium development goals. It is an important, but incompletely understood, cause of anaemia. This review synthesizes current evidence on the epidemiology, pathogenesis, treatment and consequences of vivax-associated anaemia. Young children are at high risk of clinically significant and potentially severe vivax-associated anaemia, particularly in countries where transmission is intense and relapses are frequent. Despite reaching lower densities than Plasmodium falciparum, Plasmodium vivax causes similar absolute reduction in red blood cell mass because it results in proportionately greater removal of uninfected red blood cells. Severe vivax anaemia is associated with substantial indirect mortality and morbidity through impaired resilience to co-morbidities, obstetric complications and requirement for blood transfusion. Anaemia can be averted by early and effective anti-malarial treatment.

Retention of poorly deformable red blood cells (RBCs) by the human spleen has been recognized as a critical determinant of pathogenesis in hereditary spherocytosis, malaria, and other RBC disorders. Using an ex vivo perfusion system, we had previously shown that retention of Plasmodium falciparum-infected RBCs (Pf-RBCs) occur in the splenic red pulp, upstream from the sinus wall. To experimentally replicate the mechanical sensing of RBCs by the splenic microcirculation, we designed a sorting device where a mixture of 5- to 25-μm-diameter microbeads mimics the geometry of narrow and short interendothelial splenic slits. Heated RBCs, Pf-RBCs, and RBCs from patients with hereditary spherocytosis were retained in the microbead layer, without hemolysis. The retention rates of Pf-RBCs were similar in microbeads and in isolated perfused human spleens. These in vitro results directly confirm the importance of the mechanical sensing of RBCs by the human spleen. In addition, rigid and deformable RBC subpopulations could be separated and characterized at the molecular level, and the device was used to deplete a stored RBC population from its subpopulation of rigid RBCs. This experimental approach may contribute to a better understanding of the role of the spleen in the pathogenesis of inherited and acquired RBC disorders.

Because it relies on potentially toxic, difficult-to-handle, or expensive compounds the therapy of leishmaniasis is still a complex issue in 2010, especially for visceral leishmaniasis in immuno-suppressed subjects, or in patients with cutaneous and mucosal involvement. This induces a wide diversity of observed therapeutic practices, some being sub-optimal. The Société de Pathologie Exotique organised a meeting dedicated to the therapy of leishmaniasis in France that led to the first consensus on therapeutic guidelines. Liposomal amphotericin B is the first-line option for visceral leishmaniasis both in immunocompetent, and immunosuppressed patients (cumulated doses of 20 mg/kg and 30-40 mg/kg, respectively). Secondary prophylaxis with either liposomal amphotericin B, pentamidine or meglumine antimoniate is proposed to patients with heavy immunosuppression until immunity has been restored for at least 6 months. While the efficacy of new topical formulations of paromomycin is being tested, patients with Old World cutaneous leishmaniasis may be left untreated, or be administered a combination of superficial cryotherapy plus intralesional antimony, or even--in complex situations--receive systemic therapy. The efficacy of a short course of pentamidine (L. guyanensis/L. panamensis) and a 20-day schedule of meglumine antimoniate (L. braziliensis) is solidly established. However, in well-defined situations, local therapy of New World cutaneous leishmaniasis is now considered acceptable., (Copyright © 2010 Elsevier Masson SAS. All rights reserved.)

Clinical manifestations of Plasmodium falciparum infection are induced by the asexual stages of the parasite that develop inside red blood cells (RBCs). Because splenic microcirculatory beds filter out altered RBCs, the spleen can innately clear subpopulations of infected or uninfected RBC modified during falciparum malaria. The spleen appears more protective against severe manifestations of malaria in naïve than in immune subjects. The spleen-specific pitting function accounts for a large fraction of parasite clearance in artemisinin-treated patients. RBC loss contributes to malarial anemia, a clinical form associated with subacute progression, frequent splenomegaly, and relatively low parasitemia. Stringent splenic clearance of ring-infected RBCs and uninfected, but parasite-altered, RBCs, may altogether exacerbate anemia and reduce the risks of severe complications associated with high parasite loads, such as cerebral malaria. The age of the patient directly influences the risk of severe manifestations. We hypothesize that coevolution resulting in increased splenic clearance of P. falciparum-altered RBCs in children favors the survival of the host and, ultimately, sustained parasite transmission. This analysis of the RBC-spleen dynamic interactions during P falciparum infection reflects both data and hypotheses, and provides a framework on which a more complete immunologic understanding of malaria pathogenesis may be elaborated.

Topical therapy is an attractive approach for the treatment of Leishmania major cutaneous leishmaniasis (CL). WR279396, an expanded-spectrum aminoglycoside ointment, is now in phase 3 trials. Because the application of a cream is easier than the injection of pentavalent antimony, many patients with CL will likely be treated with WR279396 soon after the onset of a lesion. However, this new therapeutic approach may impair the acquisition of immunity. We evaluated the impact of early topical therapy on acquired immunity in an optimized mouse model of L. major-induced CL. The efficacy of the WR279396 ointment in this model has been established previously. Acquired immunity was defined as the absence of lesions upon reinoculation of the same parasite isolate at a different skin site. Bioluminescence-based follow-up of luciferase-expressing L. major loads was also performed. In this model, the control of L. major loads at the initial inoculation site and the acquisition of immunity are simultaneous (day 22 postinoculation). The clinical and parasitological efficacies of WR279396 applied as early as day 11 postinoculation, i.e., during the L. major multiplication phase, did not impair the acquisition of immunity to a second L. major challenge. This is reassuring from the perspective of the wide deployment of WR279396-based therapy in foci where L. major is endemic.

AA-amyloidosis in the setting of chronic visceral leishmaniasis (VL) has been reported in animal models but documentation in humans is unavailable. Here, we report on a Portuguese man who in 1996 was diagnosed with both human immunodeficiency virus (HIV)-infection and VL. Antiretroviral treatment led to sustained suppression of HIV viremia but CD4+ lymphocytes rose from 8 to only 160 cells/mL. Several courses of antimony treatment did not prevent VL relapses. Renal failure developed in 2006 and renal biopsy revealed AA-amyloidosis. The patient had cryoglobulinemia and serum immune complexes containing antibodies directed against seven leishmanial antigens. Antimony plus amphotericin B, followed by oral miltefosine resulted in a sustained VL treatment response with elimination of circulating Leishmania infantum DNA and CD4+ recovery. The concomitant reduction of serum AA levels and disappearance of circulating leishmanial immune complexes suggests that prolonged VL may lead to AA-amyloidosis in immunocompromised humans.

We report a case of drug hypersensitivity syndrome (drug reaction with eosinophilia and systemic symptoms [DRESS]) induced by parenteral meglumine antimoniate (Glucantime) in a 40-year-old man who traveled to Bolivia and was treated for mucocutaneous leishmaniasis. Two weeks after starting therapy, the patient had fever, joint pain, a cutaneous eruption, and hypereosinophilia (1,358 cells/mm(3)). These symptoms resolved after drug withdrawal but reappeared upon reintroduction of the drug. Pentavalent antimonials should be definitively withdrawn in patients with hypereosinophilia > 1,000 cells/mm(3) accompanied by systemic manifestations consistent with DRESS.

Purpose of Review: Splenomegaly is frequent in acute or chronic forms of Plasmodium falciparum malaria, and splenectomy is associated with more frequent fever and parasitaemia. A novel role for the spleen in malaria is indicated by recent epidemiological and experimental data, bringing about a novel paradigm on severe malaria pathogenesis., Recent Findings: In Sudanese children, severe malarial anaemia was associated with larger spleen, longer fever duration, and lower parasitaemia than cerebral malaria. These findings are consistent with evolution toward severe malarial anaemia being linked to the presence of a spleen-dependent mechanism that is absent or inefficient in cerebral malaria. An isolated-perfused human spleen model revealed unexpected retention of numerous erythrocytes harbouring young parasite stages (rings), probably through an innate mechanical process., Summary: A new paradigm is discussed, whereby the extent of erythrocyte retention in the spleen conditions not only haemoglobin concentration and spleen size but also the rate of parasite load increase. The prediction is that, in nonimmune children, stringent splenic retention of rings and uninfected erythrocytes reduces the risk of cerebral malaria (a complication associated with high parasite loads) but increases the risk of severe malarial anaemia. This hypothesis casts new light on epidemiological, genetic, and experimental studies in malaria pathogenesis.

Background: Cutaneous leishmaniasis (cl) is a disfiguring disease that confronts clinicians with a quandary: leave patients untreated or engage in a complex or toxic treatment. Topical treatment of CL offers a practical and safe option. Accordingly, the treatment of CL with WR279,396, a formulation of paromomycin and gentamicin in a hydrophilic base, was investigated in a phase 2 clinical study in Tunisia and France., Methods: A phase 2, randomized, double blind, vehicle-controlled study was conducted to assess the safety and efficacy of topical WR279,396 when applied twice a day for 20 days as treatment for parasitologically confirmed CL. The study protocol established the primary efficacy end point as complete clinical response (CCR) defined as 50% or greater reduction in the ulceration size of an index lesion by day 50 (D50) followed by complete re-epithelialization by D100, and no relapse through D180., Results: Ninety-two subjects were randomized. Leishmania major was identified in 66 of 68 isolates typed (97%). In the intent-to-treat population, 47 of 50 WR279,396 treated participants (94%) met the definition of CCR, compared with 30 of 42 vehicle-placebo participants (71%) [p = 0.0045]. Erythema occurred in 30% and 24% of participants receiving WR279,396 and placebo, respectively [p = 0.64]. There was no clinical or laboratory evidence of systemic toxicity., Conclusion: Application of WR279,396 for 20 days was found to be safe and effective in treating L. major CL, and offers great potential as a new, simple, easily applicable, and inexpensive topical therapy for this neglected disease., Trial Registration: ClinicalTrials.gov NCT00703924.

Intermittent preventive treatment is the prescheduled administration of antimalarial drugs to at-risk patients in endemic areas. This approach, which is recommended for pregnant women, is being evaluated in children. Sulfadoxine-pyrimethamine plus amodiaquine recently proved to be more protective than artemisinin-containing regimens. Therefore, the use of artemisinin derivatives could potentially be restricted to symptomatic patients. Determinants of three pending issues: safety, efficacy throughout childhood, and effectiveness--the latter depending on the implementation of sustainable delivery mechanisms--are analyzed in this comment.

The current paradigm in Plasmodium falciparum malaria pathogenesis states that young, ring-infected erythrocytes (rings) circulate in peripheral blood and that mature stages are sequestered in the vasculature, avoiding clearance by the spleen. Through ex vivo perfusion of human spleens, we examined the interaction of this unique blood-filtering organ with P falciparum-infected erythrocytes. As predicted, mature stages were retained. However, more than 50% of rings were also retained and accumulated upstream from endothelial sinus wall slits of the open, slow red pulp microcirculation. Ten percent of rings were retained at each spleen passage, a rate matching the proportion of blood flowing through the slow circulatory compartment established in parallel using spleen contrast-enhanced ultrasonography in healthy volunteers. Rings displayed a mildly but significantly reduced elongation index, consistent with a retention process, due to their altered mechanical properties. This raises the new paradigm of a heterogeneous ring population, the less deformable subset being retained in the spleen, thereby reducing the parasite biomass that will sequester in vital organs, influencing the risk of severe complications, such as cerebral malaria or severe anemia. Cryptic ring retention uncovers a new role for the spleen in the control of parasite density, opening novel intervention opportunities.

Background: A meeting was organized by Drugs for Neglected Diseases initiative (DNDi) and the Institute Pasteur (IP), Paris, to review the treatment for all forms of cutaneous leishmaniasis (CL) and to propose a strategy for the development of new efficacious and affordable treatments., Method: The global burden of CL was discussed with respect to financial impact; relation to poverty; the stigma of CL lesions and scars (particularly in young women); lack of effective, affordable, easily implemented tools and political will and resources to implement available control tools; and lack of input from pharmaceutical and biotechnology companies to develop new drugs and vaccines., Results: According to the experts from different endemic countries present, the financial and social burdens of CL are high, but we have limited quantitative data. The analysis of published trials indicates that the quality of most trials is poor and requires both improvement and standardization. The available drugs are inadequate. Criteria by which different CL types could be prioritized as target disease were set. These criteria included: severity of the disease; lack of response to available drugs; overall incidence and prevalence of the disease; sequelae of the disease, (including recidivans and mucosal leishmaniasis); the impact of treatment of individuals on control of transmission and lack of other major parties involved in drug development. Based on these, the anthroponotic CL and its sequel "recidivans" caused by L. tropica and CL caused by L. braziliensis and its sequel, mucosal leishmaniasis were considered to be the target diseases. The mechanism for controlling Leishmania infection to reach a stable self healing process is a balanced immune response. Immune stimulation during chemotherapy can enhance cure. There is no adequately effective vaccine, but some encouraging results have been obtained with whole killed Leishmania parasites or imiquimod (an immuno-modulator) plus antimonials. Further studies are needed. One safety/immunogenicity clinical trial is currently ongoing with a Second Generation Vaccine (SGV)., Conclusions and Recommendations: There is an urgent need for new treatments for all CL types. CL should be considered as a neglected disease and organizations, such as DNDi, should include it in their list of target diseases. It was agreed that immuno-chemotherapy (with "therapeutic" vaccines or immunomodulators) has a strong potential to make an impact as a new therapy of CL with the view of shortening/reducing duration and dose of drug treatment and preventing resistance. There is also a need for safe, affordable and efficacious new chemotherapeutics. The quality of clinical trials needs to be enhanced and standardized. Short and long-term objectives and activities were defined as a part of meeting recommendations.

The efficacy of fluconazole was evaluated in 35 travelers with parasitologically proven imported Old World cutaneous leishmaniasis (CL). Leishmania major (mainly MON-25) was identified in 15 patients and strongly suspected given the transmission area in 12 of these patients. Daily oral fluconazole (200 mg/day for adults and 2.5 mg/kg/day for children) was prescribed for six weeks. Outcome definition was based on re-epithelialization rate at day 50. Of the 27 L. major-infected patients, 12 (44.4%) were cured. This cure rate is similar to the placebo cure rate from trials in L. major CL in which, as in the present report, the definition of outcome relied exclusively on re-epithelialization. These data question the assumption that oral fluconazole is consistently effective for treatment of CL caused by L. major.

A patient with an ulcerated cutaneous leishmaniasis of the pinna had suppurative otochondritis after a first unsuccessful course of treatment with meglumine antimoniate. Although the Leishmania ulceration healed after a second course of meglumine antimoniate, and despite three oral dicloxacillin or pristinamycin courses, the otochondritis extended and an abscess developed. Pus from the abscess revealed a pure culture of Pseudomonas aeruginosa. Five days of oral ciprofloxacin plus rifampin led to a marked improvement. The P. aeruginosa isolate was sensitive to ciprofloxacin but fully resistant to rifampin. Healing with minimal mutilation was obtained at the end of a six-week course of multiple antibiotic therapy. Pseudomonas aeruginosa otochondritis was a co-factor of cartilage mutilation in this patient. Thus, infection with P. aeruginosa should be promptly treated when present in tender cutaneous or mucosal leishmaniasis lesions near cartilaginous areas.

The spleen plays a central role in the pathophysiology of several potentially severe diseases such as inherited red cell membrane disorders, hemolytic anemias, and malaria. Research on these diseases is hampered by ethical constraints that limit human spleen tissue explorations. We identified a surgical situation--left splenopancreatectomy for benign pancreas tumors--allowing spleen retrieval at no risk for patients. Ex vivo perfusion of retrieved intact spleens for 4 to 6 hours maintained a preserved parenchymal structure, vascular flow, and metabolic activity. Function preservation was assessed by testing the ability of isolated-perfused spleens to retain Plasmodium falciparum-infected erythrocytes preexposed to the antimalarial drug artesunate (Art-iRBCs). More than 95% of Art-iRBCs were cleared from the perfusate in 2 hours. At each transit through isolated-perfused spleens, parasite remnants were removed from 0.2% to 0.23% of Art-iRBCs, a proportion consistent with the 0.02% to 1% pitting rate previously established in artesunate-treated patients. Histologic analysis showed that more than 90% of Art-iRBCs were retained and processed in the red pulp, providing the first direct evidence of a zone-dependent parasite clearance by the human spleen. Human-specific physiologic or pathophysiologic mechanisms involving clearing or processing functions of the spleen can now be experimentally explored in a human tissue context.

Today no drug likely to be efficient on the majority of human-infecting species, well tolerated, and easy to administer is available for the treatment of human cutaneous leishmaniasis. But recent progress has been made. Efficient against visceral leishmaniasis, orally administered miltefosine may supplant pentavalent antimonials for the treatment of cutaneous leishmaniasis acquired in the New World. Right now, the reference treatment is still parenteral pentavalent antimonials 20 mg Sbv/kg/d for a duration that may probably be reduced from 20 to 10 days. The benefit/risk ratio of pentamidine still compares well with that of pentavalent antimonials for the treatment of lesions due to species belonging to the L. panamensis/L. guyanensis/L. shawi group. Pentamidine, which is easier to handle than antimonials, remains the reference treatment for cases from areas where these species predominate. Oral fluconazole is an improvement, readily available for cases from L. major foci. If its efficacy is confirmed in other foci and against other species, mechanisms will have to be implemented to make this therapeutic improvement affordable to poor patients in endemic countries. The development of an efficient and well tolerated topical treatment is still warranted. A new formulation of aminosidine is currently under evaluation. One can hope that the treatment of cutaneous leishmaniasis will soon become simpler, both for patients and doctors. For the benefits of this simplification to be rapidly affordable to all patients, the pharmaceutical and clinical research outlay must be maintained.