CD99 and CD99-L2

CD99 (also called PILR-L) and its family member, CD99 antigen-like 2 (CD99-L2) are type I transmembrane glycoproteins. CD99 and CD99-L2 share three conserved acidic motifs, show nearly ubiquitous expression and are thought to originate from the same ancestral gene. Both are expression on vascular endothelial cells and leukocytes and are reported to mediate leukocyte extravasation to inflamed tissue in vivo. CD99 is a receptor for PILR-alpha and -beta, which are found on selected leukocytes.