Platelet-endothelial interactions in inflamed mesenteric venules

The selectins are membrane glycoproteins promoting adhesive events between leukocytes, platelets, and endothelial cells. We have previously demonstrated that platelets roll on P-selectin expressed on stimulated endothelium. In this study, we wished to examine the function of both the platelet and endothelial selectins, P- and E-selectins, in mediating platelet-endothelial interactions during inflammation. We demonstrate, using intravital microscopic examination of venules inflamed with tumor necrosis factor-alpha (TNF-alpha), that resting platelets interact with both P- and E-selectins and that the leukocyte alpha(1,3)fucosyltransferases FucT IV and FucT VII do not provide platelets with selectin ligand activity. We also show that after thrombin activation of wild-type (+/+) platelets, platelet P-selectin can mediate interactions on a TNF-alpha-inducible endothelial ligand. To evaluate the potential role of platelet P-selectin in the recruitment of leukocytes to inflammatory sites, we reconstituted the bone marrow of mice deficient in both P- and E-selectins (P/E-/-) with wild-type (+/+) or P-selectin-deficient (P-/-) bone marrow containing megakaryocytic precursors. Providing +/+ platelets to P/E-/- mice by bone marrow transplantation did not rescue the immunodeficient phenotype, suggesting that platelet P-selectin does not have an active function in the recruitment of leukocytes into inflammatory sites. To participate in inflammatory or hemostatic responses, platelets may use the endothelial selectins.