CD72 is a 39-43 kD type II membrane glycoprotein. It is a disulfide-linked homodimer belonging to C-type lectin family. CD72 is a pan-B cell marker expressed on B cells throughout B cell differentiation with the exception of plasma cells. It is also expressed on follicular dendritic cells, splenic red pulp macrophages (but not on peripheral blood monocytes), and liver Kupffer cells. CD72, a negative coreceptor of B cells, contains immunoreceptor tyrosine-based inhibitory motifs in the cytoplasmic domain which has been shown to recruit the tyrosine phosphatase SHP-1. Ligation of CD72 with its ligand regulates CD72 tyrosine dephosphorylation and SHP-1 dissociation to promote B cell activation and proliferation. CD100 and CD5 have been shown to be CD72 ligands. The CD100-CD72 interaction plays a role in maintenance of B cell homeostasis.