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 daltons, and is a C-type lectin. It's 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.

ITIMs are sites for alternative phosphorylation, typically by a Src kinase, and dephosphorylation, either by the tyrosine phosphatase SHP1 or the inositol phosphatase SHIP, transducing signals to distinct pathways. B cells from CD72-deficient mice are hyperresponsive to lipopolysaccharide stimulation and B cell receptor aggregation.