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Venous thromboembolism (VTE) is the third leading cardiovascular cause of death and is conventionally treated with anticoagulants that directly antagonize coagulation. However, recent data have demonstrated that also platelets play a crucial role in VTE pathophysiology. In the current review, we outline how platelets are involved during all stages of experimental venous thrombosis. Platelets mediate initiation of the disease by attaching to the vessel wall upon which they mediate leukocyte recruitment. This process is referred to as immunothrombosis, and within this novel concept inflammatory cells such as leukocytes and platelets directly drive the progression of VTE. In addition to their involvement in immunothrombosis, activated platelets can directly drive venous thrombosis by supporting coagulation and secreting procoagulant factors. Furthermore, fibrinolysis and vessel resolution are (partly) mediated by platelets. Finally, we summarize how conventional antiplatelet therapy can prevent experimental venous thrombosis and impacts (recurrent) VTE in humans.

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.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.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.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.

In addition to their hemostatic role, platelets play a significant role in immunity. Once activated, platelets release extracellular vesicles (EVs) formed by the budding of their cytoplasmic membranes. Because of their heterogeneity, platelet EVs (PEVs) are thought to perform diverse functions. It is unknown, however, whether the proteasome is transferred from platelets to PEVs or whether its function is retained. We hypothesized that functional protein processing and antigen presentation machinery are transferred to PEVs by activated platelets. Using molecular and functional assays, we found that the active 20S proteasome was enriched in PEVs, along with major histocompatibility complex class I (MHC-I) and lymphocyte costimulatory molecules (CD40L and OX40L). Proteasome-containing PEVs were identified in healthy donor blood, but did not increase in platelet concentrates that caused adverse transfusion reactions. They were augmented, however, after immune complex injections in mice. The complete biodistribution of murine PEVs after injection into mice revealed that they principally reached lymphoid organs, such as spleen and lymph nodes, in addition to the bone marrow, and to a lesser extent, liver and lungs. The PEV proteasome processed exogenous ovalbumin (OVA) and loaded its antigenic peptide onto MHC-I molecules, which promoted OVA-specific CD8+ T-lymphocyte proliferation. These results suggest that PEVs contribute to adaptive immunity through cross-presentation of antigens and have privileged access to immune cells through the lymphatic system, a tissue location that is inaccessible to platelets.

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.

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

Background The SARS-CoV-2 virus is the causing agent of the Coronavirus disease 2019 (COVID-19) characterized by a huge pro-inflammatory response and coagulation disorders that may lead to for its severe forms, in organ failure or even death. As major players of thrombo-inflammation, platelets release large amounts of immunomodulatory molecules and regulate leukocyte and endothelial activity, which are both altered in COVID-19. Altogether, this makes platelets a very likely actor of the thrombo-inflammatory complications of COVID-19. Thus, we propose to identify a platelet inflammatory signature of severe COVID-19 specifically modulated throughout the course of the disease. Methods Luminex technology and enzyme-linked immunosorbent assay were used to assess plasma levels of platelet inflammatory markers in patients with severe acute respiratory syndrome coronavirus 2 infection on admission and for 14 days afterwards. Results In accordance with the observations of other teams, we evidence that the plasma levels of the platelet soluble (s)CD40L is significantly elevated in the early stages of the disease. Interestingly we observe that the plasma level of sCD40L decreases overtime while that of sCD62P increases significantly. Conclusions Our data suggest that there is a platelet signature of inflammatory response to SARS-COv-2 infection which varies overtime and could serve as monitoring biomarkers of patient inflammatory state. Clinical trial registration number: 2020-A01100-39; title: Human Ab Response & immunoMONItoring of COVID-19 Patients, registration date: 05/25/2020; URL of the registry: https://clinicaltrials.gov/ct2/history/NCT04373200?V_5=View.

BACKGROUND Whereas platelet transfusion is a common medical procedure, inflammation still occurs in a fraction of transfused individuals despite the absence of any apparent infectious agents. Platelets can shed membrane vesicles, called extracellular vesicles (EVs), some of which contain mitochondria (mito+EV). With its content of damage-associated molecular pattern (DAMP), the mitochondrion can stimulate the innate immune system. Mitochondrial DNA (mtDNA) is a recognized DAMP detected in the extracellular milieu in numerous inflammatory conditions and in platelet concentrates. We hypothesized that platelet-derived mitochondria encapsulated in EVs may represent a reservoir of mtDNA. STUDY DESIGN AND METHODS Herein, we explored the implication of mito+EVs in the occurrence of mtDNA quantified in platelet concentrate supernatants that induced or did not induce transfusion adverse reactions. RESULTS We observed that EVs were abundant in platelet concentrates, and platelet-derived mito+EVs were more abundant in platelet concentrates that induced adverse reactions. A significant correlation (rs = 0.73; p

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.

Circulating autoantibodies (auto-Abs) neutralizing high concentrations (10 ng/mL, in plasma diluted 1 to 10) of IFN-α and/or -ω are found in about 10% of patients with critical COVID-19 pneumonia, but not in subjects with asymptomatic infections. We detect auto-Abs neutralizing 100-fold lower, more physiological, concentrations of IFN-α and/or -ω (100 pg/mL, in 1/10 dilutions of plasma) in 13.6% of 3,595 patients with critical COVID-19, including 21% of 374 patients80 years, and 6.5% of 522 patients with severe COVID-19. These antibodies are also detected in 18% of the 1,124 deceased patients (aged 20 days-99 years; mean: 70 years). Moreover, another 1.3% of patients with critical COVID-19 and 0.9% of the deceased patients have auto-Abs neutralizing high concentrations of IFN-β. We also show, in a sample of 34,159 uninfected subjects from the general population, that auto-Abs neutralizing high concentrations of IFN-α and/or -ω are present in 0.18% of individuals between 18 and 69 years, 1.1% between 70 and 79 years, and 3.4%80 years. Moreover, the proportion of subjects carrying auto-Abs neutralizing lower concentrations is greater in a subsample of 10,778 uninfected individuals: 1% of individuals70 years, 2.3% between 70 and 80 years, and 6.3%80 years. By contrast, auto-Abs neutralizing IFN-β do not become more frequent with age. Auto-Abs neutralizing type I IFNs predate SARS-CoV-2 infection and sharply increase in prevalence after the age of 70 years. They account for about 20% of both critical COVID-19 cases in the over-80s, and total fatal COVID-19 cases.

Platelets are hematopoietic cells whose main function has for a long time been considered to be the maintenance of vascular integrity. They have an essential role in the hemostatic response, but they also have functional capabilities that go far beyond it. This review will provide an overview of platelet functions. Indeed, stress signals may induce platelet apoptosis through proapoptotis or hemostasis receptors, necrosis, and even autophagy. Platelets also interact with immune cells and modulate immune responses in terms of activation, maturation, recruitment and cytokine secretion. This review will also show that platelets, thanks to their wide range of innate immune receptors, and in particular toll-like receptors, and can be considered sentinels actively participating in the immuno-surveillance of the body. We will discuss the diversity of platelet responses following the engagement of these receptors as well as the signaling pathways involved. Finally, we will show that while platelets contribute significantly, via their TLRs, to immune response and inflammation, these receptors also participate in the pathophysiological processes associated with various pathogens and diseases, including cancer and atherosclerosis.

Aside from their canonical role in hemostasis, it is increasingly recognized that platelets have inflammatory functions and can regulate both adaptive and innate immune responses. The main topic this review aims to cover is the proinflammatory effects and side effects of platelet transfusion. Platelets prepared for transfusion are subject to stress injury upon collection, preparation, and storage. With these types of stress, they undergo morphologic, metabolic, and functional modulations which are likely to induce platelet activation and the release of biological response modifiers (BRMs). As a consequence, platelet concentrates (PCs) accumulate BRMs during processing and storage, and these BRMs are ultimately transfused alongside platelets. It has been shown that BRMs present in PCs can induce immune responses and posttransfusion reactions in the transfusion recipient. Several recent reports within the transfusion literature have investigated the concept of platelets as immune cells. Nevertheless, current and future investigations will face the challenge of encompassing the immunological role of platelets in the scope of transfusion.

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.

Sepsis is associated with thrombocytopenia and microvascular thrombosis. Studies have described platelets implication in this pathology but their kinetics of activation and behavior remain poorly known. We show in a mouse model of peritonitis, the appearance of platelet-rich thrombi in organ microvessels and organ damage. Complementary methods are necessary to characterize platelet activation during sepsis as circulating soluble markers and platelet-monocyte aggregates revealed early platelet activation, while surface activation markers were detected at later stage. A microfluidic based ex-vivo thrombosis assay demonstrated that platelets from septic mice have a prothrombotic behavior at shear rate encountered in microvessels. Interestingly, we found that even though phosphoinositide-3-kinase β−deficient platelet mice formed less thrombi in liver microcirculation, peritoneal sepsis activates a platelet alternative pathway to compensate the otherwise mandatory role of this lipid-kinase to form stable thrombi at high shear rate. Platelets are rapidly activated during sepsis. Thrombocytopenia can be attributed in part to platelet-rich thrombi formation in capillaries and platelet-leukocytes interactions. Platelets from septic mice have a prothrombotic phenotype at a shear rate encountered in arterioles. Further studies are necessary to unravel molecular mechanisms leading to this prothrombotic state of platelets in order to guide the development of future treatments of polymicrobial sepsis.

Even though used systematically with leukocyte reduction, platelet transfusions still cause adverse reactions in recipients. They include Transfusion-Related Acute Lung Injury (TRALI), respiratory distress that occurs within six hours of the transfusion. The pathophysiology of this transfusion complication brings complex cellular communication into play. The role, particularly inflammatory, played by blood platelets in TRALI pathophysiology has been demonstrated, but is still under debate. Blood platelets play a role in inflammation, particularly via the CD40/CD40L (sCD40L) immunomodulator complex. In this study, we examine in particular the specific involvement of the CD40/CD40L (sCD40L) complex in the inflammatory pathogenesis of TRALI. This molecular complex could be a major target in a TRALI prevention strategy. Improving the conditions in which the platelet concentrates (PC) are prepared and stored would contribute to controlling partly the risks of non-immune TRALI.

Cette etude vise a dechiffrer le proteome plaquettaire dans les concentres plaquettaires (CP) en pool (MCP) provenant de 5 donneurs et les CP d’apherese a donneur unique (CPA), associes a des effets indesirables receveur (EIR). En effet, certaines poches de concentres plaquettaires (CP) transfuses provoquent encore des EIR. Les culots plaquettaires provenant de 3 MCP et 3 CPA associees a des EIR vs leurs temoins apparies ont ete analyses par le systeme LC couple a un spectrometre de masse benchtop Orbitrap quadripole Electrospray Q-Exactive. Les proteines ont ete identifiees par SEQUEST via Proteome Discoverer 1.4. Les donnees brutes de LC-MS/MS ont ete importees dans Progenesis QI 2.0 pour quantification des peptides et comparaison statistique. Nous avons identifie 1723 et 4116 proteines, parmi lesquelles 473 et 146 etaient differentiellement exprimees (DE) dans les MCP et CPA respectivement, entre les cas (EIR-CP) et les temoins (no.EIR-CP). L’interpretation fonctionnelle a revele un enrichissement important de l’activation et de la degranulation plaquettaires, constituant les processus biologiques les plus significativement associes aux EIR. Les voies de signalisation etaient celles des integrines pour les MCP et celle du syndrome d’inflammation aigue pour les CPA. Les troubles inflammatoires se sont reveles enrichis dans les deux types de CP. Des modifications profondes du proteome ont ete identifiees dans les plaquettes des CP qui ont conduit a des EIR chez les patients. Cette etude presente la premiere exploration de la signature proteomique plaquettaire associee aux EIR et pourrait ainsi fournir des indices pour ameliorer la medecine transfusionnelle ( Fig. 1 , Fig. 2 , Fig. 3 , Fig. 4 ).

Background Platelets (PLTs) are prone to activation and the release of biologic response modifiers (BRMs) under storage conditions. The transfusion inflammatory reaction in the vascular compartment involves endothelial cell activation due to cell-cell interactions and BRMs infused with the blood products. Endocan/ESM-1 is a proteoglycan secreted by endothelial cells under the control of proinflammatory cytokines. We aimed to measure endocan activity in supernatants of PLT components (PCs), implicated in serious adverse reactions (SARs) or not (no.AR), sampled at different stages during storage. Study design and methods PLT function, by quantification of soluble CD62P, and their ability to produce endocan were assessed. Functional testing of PC supernatants was performed on EA.hy926 endothelial cells in vitro by exposing them to PC supernatants from each group (no.AR or SARs); EA.hy926 activation was evaluated by their production of interleukin (IL)-6 and endocan. Results PLT endocan secretion was not induced in response to PLT surface molecule agonists, and no significant correlation was observed between sCD62P and endocan concentration after PLT activation. However, we observed a significant increase in the secretion of IL-6 and endocan after EA.hy926 activation by all PC supernatants. IL-6 and endocan secretion were significantly higher for cells stimulated with SAR than those stimulated with no.AR PC supernatants, as well as cell apoptosis. Conclusion The correlation between the secretion of endocan and that of IL-6 by endothelial cells suggests that endocan can be used as a predictive marker of inflammation for the quality assessment of transfusion grade PLTs.

Le sepsis est une entite evolutive, caracterisee par une condition clinique menacant le pronostic vital, en lien a une reponse inappropriee ou deregulee a une infection bacterienne de l’hote infecte. On observe frequemment une deregulation de la coagulation ainsi qu’une thrombopenie. Les plaquettes, cellules cles de l’hemostase, exercant en parallele un role pro-inflammatoire, interviennent de facon exacerbee a ce double titre. De nombreuses etudes utilisant des agents antiplaquettaires montrent un effet benefique sur la mortalite dans des modeles experimentaux de sepsis, mais egalement chez les patients en etat septique grave. Une strategie therapeutique, ciblant les plaquettes, pourrait ainsi etre envisagee dans le sepsis afin de controler tant la coagulation que la boucle inflammatoire. Cette revue a pour objectif de faire un point d’actualite sur la relation plaquettes/bacteries/inflammation, d’une part, et plaquettes/coagulation/sepsis, d’autre part, et d’aborder l’utilisation de molecules antiplaquettaires dans les essais cliniques.

An adverse reaction is an undesirable response in a patient associated with the administration blood component (BC) (1). The scientific community consents that platelets play a role in inflammatory responses (2). However, when transfusion is linked with SARs, most can be linked to an inflammatory state that is either apparent (allergy, FNHTR) or attributed by present understanding (alloimmunization) to such a state. The involvement of platelet concentrates (PC) in SARs could be related, at least in part, to the inflammatory functions of platelets acquired during storage lesions. We have previously shown an association between the levels of sCD40L, sCD62P, IL27, IL-13, sOX40L, and mitochondrial DNA in PCs and the risk for SARs (3).

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.

Background Transfusion-related acute lung injury (TRALI) is a severe pulmonary reaction due to blood transfusions. The pathophysiology of this complication is still not widely elucidated by the scientific community, especially regarding the direct role of blood platelets within the cellular mechanism responsible for the development of TRALI. Study design and methods In this study, a mouse model was used to induce the development of antibody-mediated acute lung injury through injections of lipopolysaccharide and an anti-major histocompatibility complex Class I antibody. BALB/c mice were pretreated with an anti-GPIbα antibody, which induces platelet depletion, or ML354, a protease receptor 4 pathway inhibitor, 30 minutes before TRALI induction. Results Depletion of platelets before TRALI induction appeared to reduce the severity of TRALI without completely inhibiting its development. Also, inhibition of platelet activation by ML354 did not prevent the onset of TRALI. Finally, the stimuli used for TRALI induction also triggered specific platelet activation upon ex vivo stimulation. Conclusions This study suggests that blood platelets are not critically required for TRALI induction, although they are to some extent involved in its pathophysiology.

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.