P-Selectin binding to an endothelial L-selectin ligand: A common pathway of activated platelet and leukocyte recruitment

The ability of blood-borne cells to Interact with endothellum through selectin binding to a vascular llgand Is a phenomenon that has been solely ascribed to L-setecttn bearing leukocytes. Here we report in vivo evidence that P-selectin expressed on circulating activated platelets can mediate binding to peripheral node addressln (PNAd) glycoprotelns on high endothelial venules (HEV) in murine peripheral lymph nodes. Using intravital microscopy, interacting platelets were observed to tether and roll in a manner reminiscent of L-selecHn-dependent lymphocyte Interactions. Incubation of platelets with anti-P-sstecBn mAb or mice with anti-peripheral node addressln (PNAd) mAb significantly reduced attachment. P-selectindependent interactions with HEV llgands was confirmed by the ability of both activated platelets and P-setecon transfected lymphold cells to Interact with purified human tonsil PNAd and one of Its major constituents, CD34. In In vitro flow assays, rolling was abolished by P-selecHn mAb and by treatment of PNAd or CD34 substrate with neuraminidase, Oglycoprolease, and antl-PNAd mAb, as previously observed for LseiectJn-dependent interactions. Most Importantly, a smaN number of rolling platelets dramatically enhanced tethering of lymphocytes to PNAd even In the absence of functional L-selecVn in vitro. These results suggest that Pand L-selectin can share common endothelial ligand(s) and that platelet binding to HEV may enhance the tethering of lymphocytes through high density expression of platelet P-selectln.