Microparticles (Ectosomes) Shed by Stored Human Platelets Downregulate Macrophages and Modify the Development of Dendritic Cells

Abstract

Microparticles (MP) shed by platelets (PLT) during storage have procoagulant activities, but little is known about their properties to modify inflammation or immunity. In this study, we studied the capacity of MP present in PLT concentrates to alter the function of macrophages and dendritic cells (DC). The size of the purified MP was between 100 and 1000 nm, and they expressed phosphatidylserine; surface proteins of PLT (CD61, CD36, CD47), including complement inhibitors (CD55, CD59), but not CD63; and proteins acquired from plasma (C1q, C3 fragments, factor H). These characteristics suggest that the MP shed by PLT are formed by budding from the cell surface, corresponding to ectosomes. The purified PLT ectosomes (PLT-Ect) reduced the release of TNF-α and IL-10 by macrophages activated with LPS or zymosan A. In addition, PLT-Ect induced the immediate release of TGF-β from macrophages, a release that was not modified by LPS or zymosan A. Macrophages had a reduced TNF-α release even 24 h after their exposure to PLT-Ect, suggesting that PLT-Ect induced a modification of the differentiation of macrophages. Similarly, the conventional 6-d differentiation of monocytes to immature DC by IL-4 and GM-CSF was modified by the presence of PLT-Ect during the first 2 d. Immature DC expressed less HLA-DP DQ DR and CD80 and lost part of their phagocytic activity, and their LPS-induced maturation was downmodulated when exposed to PLT-Ect. These data indicate that PLT-Ect shed by stored PLT have intrinsic properties that modify macrophage and DC differentiation toward less reactive states.

Platelets regulate leucocyte responses to Toll‐like receptor stimulation

“…It has previously been shown that, in platelet–PBMC coculture, activated platelets slightly but nonsignificantly reduced monocyte HLA‐DR expression in response to LPS 19. Similarly, platelet microparticles can reduce HLA‐DP, DQ and DR expression on monocyte‐derived dendritic cells, with the authors suggesting that monocytes that come into contact with platelet microparticles may be less likely to develop into fully pro‐inflammatory dendritic cells 15. In our study, it is unclear why an effect of platelets was observed with low‐dose LPS, but not observed under any other condition tested.…”

“…Platelets have been shown to dampen leucocyte activation and pro‐inflammatory cytokine production in both mouse models of sepsis14 and in vitro cell models of infection,15, 16 and this platelet effect is associated with host defence and survival in sepsis 17, 18. The regulatory effect of platelets has largely been characterised in peripheral blood mononuclear cells (PBMCs) in vitro exposed to lipopolysaccharide (LPS; a TLR4 agonist), or in mouse models of sepsis 14, 17, 19, 20.…”

Changing world of neutrophils

“…Most of the data on PMN-derived EVs (called in these studies ectosomes) come from the laboratory of Dr. Schifferli [26,[34][35][36]39,40,45,[93][94][95][96]. They characterized the size and surface properties of EVs released upon fMLP-stimulation and came to the conclusion that both the in vitro and the in vivo generated EVs are right-side out [39,45].…”

“…However, the specificity of PMN-derived EVs in this process remains to be determined, as EVs produced by stored erythrocytes [94] and platelets [93] have also been reported to down-regulate macrophages and dendritic cells.…”

Thalassemic erythrocytes release microparticles loaded with hemichromes by redox activation of p72Syk kinase

“…11 The composition and pathogenic roles of MP have been extensively studied in various diseases, such as ischemia, diabetes and atherosclerosis, revealing complex pathogenic roles in modulating nitric oxide and prostacyclin production, stimulating cytokine release, inducing tissue factor expression, as well as monocyte chemotaxis and adherence to the endothelium. [12][13][14][15][16][17][18] Recent studies on the mechanisms of redox regulation of RBC membrane stability 19,20 indicate that oxidative stress induces a phosphorylative response that specifically involves two tyrosine residues located in the cytoplasmic domain of band 3. 20 Band 3 is the most abundant RBC membrane protein, and represents one of the major components of the junctional complexes that connect the lipid bilayer to the cytoskeleton.…”