The function of CD72 (CD72 molecule, Ensembl gene identifier ENSG00000137101) is as follows. Co-receptor of B cell receptor (BCR) that plays both positive and negative roles on B-cell functions. Recognizes the Sm/ribonucleoprotein (RNP) self-antigen ligand, and coligation of CD72 and BCR inhibits BCR signaling. Mechanistically, ligand binding leads to the recruitment of PTPN6/SHP-1 to the BCR complex which is inhibitory to BCR signaling. Also acts as a ligand for CD5 and thereby plays a critical role in maintaining regulatory T and B-cell homeostasis. .