CD99 antigen-like protein 2, also known as MIC2-like protein 1, CD99L2 and MIC2L1, is a single-pass type I membrane protein which belongs to theCD99 family. CD99L2 is expressed in brain, heart, lung, liver, spleen, kidney, stomach, small intestine, skeletal muscle, ovary, thymus, testis and uterus. Lower expression of CD99L2 is seen in thymus. It is also expressed in E18 uterus and placenta. CD99 and CD99L2 were required for leukocyte extravasation in the cremaster after stimulation with tumor necrosis factor-alpha, where the need for PECAM-1 is known to be bypassed. CD99 and CD99L2 act independently of PECAM-1 in leukocyte extravasation and cooperate in an independent way to help neutrophils overcome the endothelial basement membrane. CD99L2 may function as a homophilic adhesion molecule. It functions in leukocyte-endothelial cell interactions during leukocyte extravasation, and in particular, at the diapedesis step. CD99L2 does not seem to be involved in docking of leukocytes to the vessel wall or in lymphocyte diapedesis.