CD72 is an Mr 45,000 transmembrane type II glycoprotein that shares sequence homology with asialoglycoprotein receptors. It is expressed as a disulfide-linked homodimer on the surface of the B cells.
The extracellular portion contains a carboxyl-terminal polymorphic region, an intermediate calcium-dependent C-type lectin domain, and a membrane proximal α-helical coiled-coil region. The cytoplasmic domain contains two potential ITIMs.
CD72 is considered to be a pan-B-cell marker from pre-B to mature B cells. However, its expression is lost on terminally differentiated plasma cells.
CD72-/- mice showed that:
The semaphorin CD100 is a ligand of CD72. This ligand, expressed on T cells and activated B cells, turns off the negative regulation of CD72.
In the mouse, four allelic forms of CD72 are correlated with amino acid polymorphisms in the extracellular domain and alternative splicing. In contrast to CD72a and CD72c, the CD72b allele is expressed on a fraction of peripheral T cells.