CD63 positions CD62P for rolling

Doyle and colleagues identify the tetraspanin CD63 as an essential co-factor for endothelial P-selectin function.¹ In the absence of CD63 (by knockout in mice or knockdown in cultured endothelial cells), P-selectin (also known as CD62P) cannot mediate leukocyte tethering and rolling. This surprising finding suggests that Pselectin must be positioned in organized membrane microdomains to function.