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Sepsis is an evolutive pathology that affects the prognosis and is characterized by an inappropriate or dysregulated inflammatory and immune response to a bacterial infection. The alteration of coagulation processes and the occurrence of thrombocytopenia are also frequently observed during the course of sepsis. Thus, platelets, which are both major coagulation cells and active players of the inflammatory response, play a dual role in the pathophysiology of sepsis. Many studies show that antiplatelet molecules improve survival in experimental sepsis models but is also beneficial for sepsis patient outcome. Therefore, a therapeutic strategy targeting platelets could be considered in sepsis in order to reduce coagulation disorders as well as the platelet-related exacerbation of the inflammatory loop. The aim of this review is to look over the knowledge about the relationships between platelets, bacteria and inflammation, about the contribution of platelets to the dysfunction of coagulation during sepsis, but also about the use of antiplatelet molecules in clinical trials. [ABSTRACT FROM AUTHOR]

Background: Red blood cells (RBCs) contain large amounts of iron, and periodic therapeutic phlebotomy is thus the main treatment for hereditary hemochromatosis (HH). However, the donation of therapeutic phlebotomy products from asymptomatic patients for transfusion purposes remains controversial. In this study, we compared the quality of RBCs obtained from HH patients with those of non-HH RBCs, within the allowed 42-day storage period.Study Design and Methods: RBCs were obtained from HH patient donors and random regular blood donors by whole blood collection. RBCs were stored for up to 42 days, according to national regulations and standard blood bank conditions in France. The following variables were assessed: hematologic and biochemical results, RBC membrane and soluble inflammatory markers, and the proinflammatory potential of HH RBC supernatant toward endothelial cells in an in vitro model.Results: There were no major differences between the two groups in terms of biophysical, biochemical, or soluble immunomodulatory factors. However, we observed small but significant differences in changes in RBC membrane proteins during storage, including increased phosphatidylserine expression and decreased hemolysis in HH compared with normal RBCs. However, there were no differences in terms of bioactivity of soluble immunomodulatory factors in the RBC supernatant during storage between HH and control donors, as determined by their effects on endothelial cells in vitro.Conclusions: These in vitro studies suggest that RBCs from HH patients appear, while exhibiting subtle differences, to be suitable for transfusion purposes according to currently accepted criteria. [ABSTRACT FROM AUTHOR]

Microparticles are small membrane-bound vesicles found in body fluids including peripheral blood. Microparticles are an intrinsic part of blood labile products delivered to transfused patients and have active roles in inflammation. They are delimited by a lipid bilayer composed mainly of phospholipids, cholesterol, membrane-associated proteins, intracellular components such as metabolic enzymes, proteins-involved in adhesion and fusion, cytoskeletal-associated proteins, surface glycoproteins and/or chemokines. Microparticles can trigger a pro-inflammatory message to neighbouring or target cells. Microparticles originating from platelets, leukocytes, erythrocytes, and endothelial cells are associated with a variety of pathophysiological conditions. This review summarises the role of Microparticles in modulating inflammation. [ABSTRACT FROM AUTHOR]

Platelets are non-nucleated cells that play central roles in the processes of hemostasis, innate immunity, and inflammation; however, several reports show that these distinct functions are more closely linked than initially thought. Platelets express numerous receptors and contain hundreds of secretory products. These receptors and secretory products are instrumental to the platelet functional responses.The capacity of platelets to secrete copious amounts of cytokines, chemokines, and related molecules appears intimately related to the role of the platelet in inflammation. Platelets exhibit non-self-infectious danger detection molecules on their surfaces, including those belonging to the "toll-like receptor" family, as well as pathogen sensors of other natures (Ig- or complement receptors, etc.). These receptors permit platelets to both bind infectious agents and deliver differential signals leading to the secretion of cytokines/chemokines, under the control of specific intracellular regulatory pathways. In contrast, dysfunctional receptors or dysregulation of the intracellular pathway may increase the susceptibility to pathological inflammation. Physiological vs. pathological inflammation is tightly controlled by the sensors of danger expressed in resting, as well as in activated, platelets. These sensors, referred to as pathogen recognition receptors, primarily sense danger signals termed pathogen associated molecular patterns. As platelets are found in inflamed tissues and are involved in auto-immune disorders, it is possible that they can also be stimulated by internal pathogens. In such cases, platelets can also sense danger signals using damage associated molecular patterns (DAMPs). Some of the most significant DAMP family members are the alarmins, to which the Siglec family of molecules belongs. This review examines the role of platelets in anti-infection immunity via their TLRs and Siglec receptors. [ABSTRACT FROM AUTHOR]

Platelets can be considered sentinels of vascular system due to their high number in the circulation and to the range of functional immunoreceptors they express. Platelets express a wide range of potential bacterial receptors, including complement receptors, FcgRII, Toll-like receptors but also integrins conventionally described in the hemostatic response, such as GPIIb-IIIa or GPIb. Bacteria bind these receptors either directly, or indirectly via fibrinogen, fibronectin, the first complement C1q, the von Willebrand Factor, etc. The fate of platelet-bound bacteria is questioned. Several studies reported the ability of activated platelets to internalize bacteria such as Staphylococcus aureus or Porphyromonas gingivalis, though there is no clue on what happens thereafter. Are they sheltered from the immune system in the cytoplasm of platelets or are they lysed? Indeed, while the presence of phagolysosome has not been demonstrated in platelets, they contain antimicrobial peptides that were shown to be efficient on S. aureus. Besides, the fact that bacteria can bind to platelets via receptors involved in hemostasis suggests that they may induce aggregation; this has indeed been described for Streptococcus sanguinis, S. epidermidis, or C. pneumoniae. On the other hand, platelets are able to display an inflammatory response to an infectious triggering. We, and others, have shown that platelet release soluble immunomodulatory factors upon stimulation by bacterial components. Moreover, interactions between bacteria and platelets are not limited to only these two partners. Indeed, platelets are also essential for the formation of neutrophil extracellular traps by neutrophils, resulting in bacterial clearance by trapping bacteria and concentrating antibacterial factors but in enhancing thrombosis. In conclusion, the platelet-bacteria interplay is a complex game; its fine analysis is complicated by the fact that the inflammatory component adds to the aggregation response. [ABSTRACT FROM AUTHOR]

A subset of coxsackieviruses B (CV-B) is able to initiate intestinal infection via the attachment to two cell surface proteins, decayaccelerating factor (DAF) and coxsackie adenovirus receptor (CAR). The aim of the present study was to investigate the expression pattern of these receptors in the polarized CaCo-2 cell line using flow cytometry. The expression of CAR-specific mRNA and proteins was analyzed by reverse transcriptase polymerase chain reaction and western blotting, respectively. Flow cytometry analysis was used to study the surface expression patterns of CAR and DAF. CAR and DAF were well detected at the surface of CaCo-2 cells by flow cytometry. Despite the fact that CAR was susceptible to the action of trypsin, a few amounts of the latter enzyme and a precise dilution did not impair its correct detection by flow cytometry. This technique was used to demonstrate that the density of cells did not influence the expression of CAR at the cell surface. CaCo-2 cells express high levels of CAR and DAF at their surface. Flow cytometry, if used adequately, represents a helpful tool for the study of the interactions between these cells and various viral targets. [ABSTRACT FROM AUTHOR]

B-cell expression of certain Toll-like receptors (TLRs) is important in linking innate and adaptive immune responses in normal and pathological conditions. The expression of TLR9 plays a role in the recognition of conserved pathogen motifs in a manner that is dependent on B-cell localization, deduced from B-cell phenotype. The nature of TLR9 function is unclear. A first step in unravelling the function of this pattern recognition receptor is to discover the precise nature of the cell types that express TLR9. This study used three-colour flow cytometry to characterize the B lymphocytes from human peripheral blood mononuclear cells (PBMCs) that express TLR9 on the surface. We sorted TLR9-positive B and non-B cells from the PBMC population and detected TLR9 expression on naïve and memory B cells. Moreover, we identified two discrete subpopulations of B cells: CD19+ CD27− CD23+ cells and CD19+ CD27high CD80+ cells. These subpopulations expressed high levels of membrane TLR9 and exhibited a strong in vitro response to binding a relevant CpG motif by secreting high levels of interleukin-6 (compared to controls). Our finding that this pattern recognition receptor is expressed on a variety of cell subsets adds to the current understanding of the functional complexity of B-cell membrane TLR9. [ABSTRACT FROM AUTHOR]

Mitochondrial DNA (mtDNA) is a highly potent inflammatory trigger and is reportedly found outside the cells in blood in various pathologies. Platelets are abundant in blood where they promote hemostasis. Although lacking a nucleus, platelets contain functional mitochondria. On activation, platelets produce extracellular vesicles known as microparticles. We hypothesized that activated platelets could also release their mitochondria. We show that activated platelets release respiratory-competent mitochondria, both within membrane-encapsulated microparticles and as free organelles. Extracellular mitochondria are found in platelet concentrates used for transfusion and are present at higher levels in those that induced acute reactions (febrile nonhemolytic reactions, skin manifestations, and cardiovascular events) in transfused patients. We establish that the mitochondrion is an endogenous substrate of secreted phospholipase A2 IIA (sPLA2-IIA), a phospholipase otherwise specific for bacteria, likely reflecting the ancestral proteobacteria origin of mitochondria. The hydrolysis of the mitochondrial membrane by sPLA2-IIA yields inflammatory mediators (ie, lysophospholipids, fatty acids, and mtDNA) that promote leukocyte activation. Two-photon microscopy in live transfused animals revealed that extracellular mitochondria interact with neutrophils in vivo, triggering neutrophil adhesion to the endothelial wall. Our findings identify extracellular mitochondria, produced by platelets, at the midpoint of a potent mechanism leading to inflammatory responses. [ABSTRACT FROM AUTHOR]

Background: Structural and biochemical changes in stored platelets are influenced by collection and processing methods. Lesions may appear during platelet concentrate storage, some of which may be involved in adverse transfusion reactions. The preparation and storage of platelet concentrates (PC) may modify and even damage the lipid mediator content. The aim of this study was to investigate the lipidomic profile identified in the supernatants of PCs according to processing and storage conditions, both after leukocyte filtration and contained in platelet additive solution (PAS), comparing single donor apheresis (SDA) products with pooled buffy coat (BC) products., Materials and Methods: We investigated the accumulation of various lipid mediators including lysophospholipids (LP) and eicosanoids in SDA and BC products stored for 0-5 days. All products were processed following French Blood Establishment (EFS) procedures in accordance with EDQM/GTS European Standards. Both SDA and BC were leukocyte reduced and conserved in 35% autologous donor plasma and 65% platelet additive solution. Lipidomic analysis was performed on PC supernatants using LS/MS spectrometry., Results: Our data demonstrate that lysophosphatidylcholine (LPC) levels were higher in BCs compared to SDAs, with no difference in lysophosphatidic acid (LPA) expression between the two preparation methods. Results for other eicosanoids showed greater similarity; indeed, no clear pattern emerged from analysis of eicosanoids in terms of storage time and process. In general, we observed longitudinal lipid mediator modulation for both SDAs and BCs, particularly at later time points., Discussion: The expression of LPC and some eicosanoids in BCs could be used as novel biomarkers of PC quality. Future studies are needed to explore their impact on adverse transfusion reactions.

Background: Platelet transfusions can be associated with adverse reactions, such as febrile non-haemolytic transfusion reaction (FNHTR). It has been suggested that damage-associated molecular patterns (DAMP) and complement play a role in FNHTR. This study investigated the nature of DAMPs and complement activation products contained in platelet concentrates during storage, with a specific focus on different platelet storage solutions., Materials and Methods: Buffy coats (BC) from healthy donors were pooled (15 BC per pool) and divided into three groups of the same volume. After addition of different storage solutions (plasma, platelet additive solutions [PAS]-C or PAS-E; n=6 for each group), BC pools were processed to platelet concentrates (PC). Leukoreduced PCs were stored on a shaking bed at 20-24°C and sampled on days 1, 2, 6 and 8 after collection for selected quality parameters: platelet activation, DAMPs (High Mobility Group Box 1 [HMGB1], nucleosomes), and complement activation products., Results: During storage, equal levels of free nucleosomes and increasing concentrations of HMGB1 were present in all groups. Complement activation was observed in all PC. However, by day 8, the use of PAS had reduced C3b/c levels by approximately 90% and C4b/c levels by approximately 65%., Discussion: Nucleosomes and HMGB1 were present in PCs prepared in plasma and PAS. Complement was activated during storage of platelets in plasma and in PAS. The use of PAS is associated with a lower amount of complement activation products due to the dilution of plasma by PAS . Therefore, PC in PAS have less complement activation products than platelets stored in plasma. These proinflammatory mediators in PC might induce FNHTR.

Platelet components (PCs) are occasionally associated with adverse transfusion reactions (ATRs). ATRs can occur regardless of the type of PC being transfused, whether it is a single-donor apheresis PC (SDA-PC) or a pooled PC (PPCs). The purpose of this study was to investigate the proteins and dysregulated pathways in both of the main types of PCs. The proteomic profiles of platelet pellets from SDA-PCs and PPCs involved in ATRs were analysed using the label-free LC-MS/MS method. Differentially expressed proteins with fold changes >|1.5| in clinical cases versus controls were characterised using bioinformatic tools (RStudio, GeneCodis3, and Ingenuity Pathways Analysis (IPA). The proteins were confirmed by western blotting. The common primary proteins found to be dysregulated in both types of PCs were the mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), multimerin-1 (MMRN1), and calumenin (CALU), which are associated with the important enrichment of platelet activation, platelet degranulation, and mitochondrial activity. Furthermore, this analysis revealed the involvement of commonly dysregulated canonical pathways, particularly mitochondrial dysfunction, platelet activation, and acute phase response. This proteomic analysis provided an interesting contribution to our understanding of the meticulous physiopathology of PCs associated with ATR. A larger investigation would assist in delineating the most relevant proteins to target within preventive transfusion safety strategies. BIOLOGICAL SIGNIFICANCE: Within platelet transfusion strategies, the two primary types of PCs predominantly processed in Europe, include (i) single donor apheresis PCs (SDA-PCs) from one donor and (ii) pooled PCs (PPCs). The current study used PCs from five buffy coats derived from five whole blood donations that were identical in ABO, RH1 and KEL1 groups. Both PC types were shown to be associated with the onset of an ATR in the transfused patient. Several common platelet proteins were found to be dysregulated in bags associated with ATR occurrences regardless of the type of PCs transfused and of their process. The dysregulated proteins included mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), which is involved in a fatty acid oxidation disorder; calumenin (CALU); and multimerin-1 (MMRN1), which is chiefly involved in platelet activation and degranulation. Dysregulated platelet protein pathways for ATRs that occurred with SDA-PCs and PPCs could support the dysregulated functions found in association with those three proteins. Those common platelet proteins may become candidates to define biomarkers associated with the onset of an ATR from PC transfusions, including monitoring during the quality steps of PC manufacturing, provided that the results are confirmed in larger cohorts. This study enriches our knowledge of platelet proteomics in PCs under pathological conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflicts of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Platelet transfusions can cause adverse reactions in their recipients, including transfusion-related acute lung injury (TRALI). The pathophysiology of TRALI depends on a number of signaling pathways and the inflammatory role played by blood platelets remains controversial. Platelets are important in inflammation, particularly via the immunomodulator complex CD40/CD40L. We studied the specific function of the CD40/CD40L interaction in regulating an experimental TRALI Two-hit model. A mouse model of immune TRALI was triggered by injection of LPS and an anti-MHC I antibody, and the effect of injection of a neutralizing anti-CD40L antibody before induction of TRALI investigated. The characteristics of TRALI were decreased body temperature, pulmonary lesions, and immune cell infiltration into the alveolar space. Pulmonary infiltration was evaluated by blood counts of specific immune cells and their detection in lung sections. Inhibition of the CD40/CD40L immunomodulator interaction significantly reduced communication between immune and/or endothelial cells and the development of pulmonary edema. Hence, our results indicate that targeting of the CD40/CD40L interaction could be an important method to prevent TRALI. While considering that our work concerned a mouse model, we postulate that improvement of the conditions under which platelet concentrates are prepared/stored would assist in alleviating the risk of TRALI.

Platelets found within platelet components (PCs) intended for transfusion release inflammatory molecules. Despite the implementation of leukoreduction, some of these PCs are occasionally associated with adverse transfusion reactions (ATRs). The aim of this study was to decipher the platelet proteome in two types of PCs, buffy-coat-derived pooled PCs (PPCs) and single-donor apheresis PCs (SDA-PCs), associated with ATRs. A label-free LC-MS/MS method was used for the proteomic analysis of washed platelet pellets from 3 PPCs and 3 SDA-PCs associated with ATRs, compared to matched controls. Bioinformatics tools allowed us to characterise the differentially expressed (DE) proteins between cases (ATR-PCs) and controls (no.ATR-PCs). From the PPCs and SDA-PCs, 473 and 146 proteins were DE, respectively. The functional interpretation of these proteins revealed enrichment in platelet activation and degranulation as the most important biological process. The most dysregulated pathways were integrin signaling for PPCs and acute phase response signaling for SDA-PCs. Interestingly, inflammatory disorders were found to be enriched in both PC types. Profound proteome changes were found in the platelets of PCs that led to clinical ATRs in patients. This study presents the first exploration of the platelet proteomic signature associated with ATRs and could provide clues to improving transfusion medicine. BIOLOGICAL SIGNIFICANCE: Adverse transfusion reactions (ATRs) can still occur after transfusion of platelet components (PC). This is the first report on the proteomic analysis of PCs associated with ATR. In this study, the contents of PC bags implicated in ATRs were examined. The aims of this study were to characterise molecules that could be central to the inflammation of ATRs and to highlight dysregulated mechanisms to explain the onset of ATRs. Two types of PCs were used: 3 PPCs (each from 5 donors) and 3 SDA-PCs (each from one donor). We have shown that the two types of PCs, from bags undergoing different processing (i.e., sampling, preparation), involve two types of dysregulated - pathophysiological mechanisms associated with the onset of ATRs. The most dysregulated signaling pathways were cytoskeleton and integrin regulation for PPCs, acute phase response signaling and remodelling of adherens junctions for SDA-PCs. Inflammation, platelet activation and degranulation processes were present in both PC types but were more important for PPCs. This proteomics analysis provides a better understanding of the pathophysiological mechanisms involved in ATRs and may lead to novel steps to ensure safe PC transfusion., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Platelet transfusions may be associated with certain adverse effects in recipients, potentially caused by the presence of biological response modifiers contained in the platelet concentrates. The aim of this study is to identify the parameters that reflect platelet activation during both the preparation process and the storage of platelet concentrates. A total of 3,949apheresis platelet concentrate samples were studied with regard to parameters related to the donor as well as to the preparation process and their storage. Key glycoproteins characteristic of platelet activation, i.e. soluble CD40L and CD62P, were quantified in platelet concentrate supernatants on completion of their processing and during storage, using Luminex technology. We observed an increase in soluble factors over time. However, the different parameters studied in connection either with the donors or with the donations, such as (i) donor gender, (ii) donor blood group, (iii) time of collection and (iv) type of apheresis separator, do not seem to have any effect on platelet activation or the release of soluble CD40L and CD62P., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Red blood cell (RBC) transfusion is a life-saving treatment for several pathologies. RBCs for transfusion are stored refrigerated in a preservative solution, which extends their shelf-life for up to 42 days. During storage, the RBCs endure abundant physicochemical changes, named RBC storage lesions, which affect the overall quality standard, the functional integrity and in vivo survival of the transfused RBCs. Some of the changes occurring in the early stages of the storage period (for approximately two weeks) are reversible but become irreversible later on as the storage is extended. In this review, we aim to decipher the duration of RBC storage and inflammatory marker generation. This phenomenon is included as one of the causes of transfusion-related immunomodulation (TRIM), an emerging concept developed to potentially elucidate numerous clinical observations that suggest that RBC transfusion is associated with increased inflammatory events or effects with clinical consequence.

Mitochondrial DNA (mtDNA) is a highly potent inflammatory trigger and is reportedly found outside the cells in blood in various pathologies. Platelets are abundant in blood where they promote hemostasis. Although lacking a nucleus, platelets contain functional mitochondria. On activation, platelets produce extracellular vesicles known as microparticles. We hypothesized that activated platelets could also release their mitochondria. We show that activated platelets release respiratory-competent mitochondria, both within membrane-encapsulated microparticles and as free organelles. Extracellular mitochondria are found in platelet concentrates used for transfusion and are present at higher levels in those that induced acute reactions (febrile nonhemolytic reactions, skin manifestations, and cardiovascular events) in transfused patients. We establish that the mitochondrion is an endogenous substrate of secreted phospholipase A2 IIA (sPLA2-IIA), a phospholipase otherwise specific for bacteria, likely reflecting the ancestral proteobacteria origin of mitochondria. The hydrolysis of the mitochondrial membrane by sPLA2-IIA yields inflammatory mediators (ie, lysophospholipids, fatty acids, and mtDNA) that promote leukocyte activation. Two-photon microscopy in live transfused animals revealed that extracellular mitochondria interact with neutrophils in vivo, triggering neutrophil adhesion to the endothelial wall. Our findings identify extracellular mitochondria, produced by platelets, at the midpoint of a potent mechanism leading to inflammatory responses., (© 2014 by The American Society of Hematology.)

Background: Cytokines have essential roles on intercellular communications and are effective in using a variety of intracellular pathways. Among this multitude of signalling pathways, the NF-kappaB (nuclear factor kappaB) and STAT (signal transducer and activator of transcription) families are among the most frequently investigated because of their importance. Indeed, they have important role in innate and adaptive immunity. Current techniques to study NF-kappaB and STAT rely on specific ELISAs, Western Blots and--most recently described--flow cytometry; so far, investigation of such signalling pathways are most commonly performed on homogeneous cells after purification., Results: The present investigation aimed at developing a flow cytometry technique to study transcription factors in various cellular types such as mixtures of B-cells, T-lymphocytes and monocytes/macrophages stimulated in steady state conditions (in other words, as peripheral blood mononuclear cells). To achieve this goal, a two step procedure was carried out; the first one consisted of stimulating PBMCs with IL1beta, sCD40L and/or IL10 in such a manner that optimal stimulus was found for each cell subset (and subsequent signal transduction, therefore screened by specific ELISA); the second step consisted of assessing confirmation and fine delineation of technical conditions by specific Western-Blotting for either NF-kappaB or STAT products. We then went on to sensitize the detection technique for mixed cells using 4 color flow cytometry., Conclusion: In response to IL1beta, or IL10, the levels of phosphorylated NF-kappaB and STAT3--respectively--increased significantly for all the studied cell types. In contrast, B-cells and monocytes/macrophages--but, interestingly, not T-lymphocytes (in the context of PBMCs)--responded significantly to sCD40L by increasing phosphorylated NF-kappaB.