CD99 Antigen-Like Protein 2 (CD99L2) belongs to the CD99 family. CD99L2 is a single-pass type I membrane protein and expressed in many tissues, with low expression in thymus. CD99L2 plays a role in a late step of leukocyte extravasation helping cells to overcome the endothelial basement membrane. CD99L2 and CD99 are involved in trans-endothelial migration of neutrophils in vitro and in the recruitment of neutrophils into inflamed peritoneum. A similar protein in mouse functions as an adhesion molecule during leukocyte extravasation. Alternate splicing results in multiple transcript variants.