Platelet agonist F11 receptor is a member of the immunoglobulin superfamily and identical with junctional adhesion molecule (JAM): Regulation of expression in human endothelial cells and macrophages

The stimulatory mAb F11 binds two platelet membrane proteins of 32 and 35 k Da and causes activation of platelets when crosslinked with the Fc gamma RI I receptor. We used bioinformatics to identify expressed sequence tags from libraries of cytokine-stimulated human endothelial cell (EC) cDNAs, The pr otein sequence deduced from full-length F11 cDNA was identical to partial s equences of peptides derived from affinity-purified platelet F11 antigen. F 11 mRNA is expressed in human EC, macrophages, and a variety of non-hematop oietic vascular tissues. Expression of F11 mRNA is modulated by cytokines i n EC and is up-regulated by oxidized low-density lipoprotein in human macro phages, The F11 receptor contains two immunoglobulin-like domains in its 23 6-amino-acid-long extracellular region, and has identity to the recently de scribed junctional adhesion molecule. The data indicate that the F11 antige n is a novel receptor or cell adhesion molecule belonging to the immunoglob ulin superfamily.