CD72 (Cluster of Differentiation 72), also known in murine biology as Lyb-2, is a protein active in the immune system of animals. It 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. It is a ligand for CD5.