Plays a role in a late step of leukocyte extravasation helping cells to overcome the endothelial basement membrane. Acts at the same site as, but independently of, PECAM1 (By similarity). Homophilic adhesion molecule, but these interactions may not be required for cell aggregation (By similarity). . This is the function of CD99L2 (CD99 molecule like 2, Ensembl gene identifier ENSG00000102181).