Lymphocyte antigen 9, also known as LY9, has also recently been designated CD229 . LY9 has been shown to interact with SH2D1A.By sequence analysis of cDNA clones, Sandrin et al. (1992) demonstrated that the mouse lymphocyte surface antigen Ly9 is a novel member of a subgroup of the immunoglobulin superfamily, together with the antigens CD2, BCM1 (CD48), and LFA3 (CD58).
Kingsmore et al. (1995) noted that, though the function of Ly9 was unknown, other subgroup members are involved in adhesion reactions between T lymphocytes and accessory cells. CD2, CD48, and CD58 are also distinguished by homophilic interactions with one another; thus, human CD48 and CD58 are both ligands for CD2.