B-cell differentiation antigen CD72 is also known as Lyb-2. CD72 contains one C-type lectin domain. CD72 is a protein active in the immune system of animals. CD72 consists of two identical halves, each of about 39-43 kD, and is a C-type lectin. Its primarily locus of expression is B-cells, where it appears to mediate aspects of B-cell - T-cell interaction. CD72 plays a role in B-cell proliferation and differentiation. CD72 is a ligand for CD5.