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Summary Platelets are primarily involved in thrombosis and haemostasis, and they have recently been shown to have a role in innate immunity and in inflammation. We have determined the markers of innate immunity that are expressed by platelets, specifically the Toll-like receptors (TLR), originating from mixes of platelet concentrates (MPC, n = 5) between day zero and day five after blood collection. The surface membrane and intracellular expression of TLR were measured, both after and without permeabilization, using flow cytometry. We observed weak expression of TLR2, TLR4 and TLR9 on the surface of CD41 + platelets. The expression levels of TLR4 were high (59 ± 2.2%). Moreover, there was a significant expression of TLR2 (47.5 ± 4.8%), TLR4 (78.8 ± 1.3%) and TLR9 (34.2 ± 7.5%) in the cytoplasm of CD41 + platelets. The expression of the three receptors did not change significantly during the course of the 5 day observation period. The percentage of TLR expression is significantly modulated between activated versus non-activated platelets, both after and without permeabilization ( P < 0.01). Study of the expression of TLR could increase our knowledge of the level of platelet participation during an immune reaction and inflammation. In the same way as the platelet ligand/receptor pair CD40L/CD40 is, the TLR are expressed by platelets, and could serve as a link between innate and adaptive immunity.

Our data provide evidence that stored PLTs contain molecules with known immunomodulatory competence and secrete them differentially over time during storage for transfusion purposes.

Corneal endothelial cells (CECs) are terminally differentiated cells, specialized in regulating corneal hydration and transparency. They are highly polarized flat cells that separate the cornea from the aqueous humor. Their apical surface, in contact with aqueous humor is hexagonal, whereas their basal surface is irregular. We characterized the structure of human CECs in 3D using confocal microscopy of immunostained whole corneas in which cells and their interrelationships remain intact. Hexagonality of the apical surface was maintained by the interaction between tight junctions and a submembraneous network of actomyosin, braced like a drum. Lateral membranes, which support enzymatic pumps, presented complex expansions resembling interdigitated foot processes at the basal surface. Using computer-aided design and drafting software, we obtained a first simplified 3D model of CECs. By comparing their expression with those in epithelial, stromal and trabecular corneal cells, we selected 9 structural or functional proteins for which 3D patterns were specific to CECs. This first 3D map aids our understanding of the morphologic and functional specificity of CECs and could be used as a reference for characterizing future cell therapy products destined to treat endothelial dysfunctions.

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