The 8F10 antibody reacts with mouse CD267 (transmembrane activator and CAML interactor, or TACI), an ~30 kDa type III transmembrane protein of the TNF receptor superfamily that is expressed primarily on the surface of maturing subsets of splenic B cells, including transition type 2 (T2) and marginal zone (MZ) B cells, as well as on plasma cells and plasmablasts. Expression of CD267 is upregulated on B cells exposed to LPS both in vitro and in vivo. CD267 plays important roles in humoral immunity by regulating B cell survival, proliferation, and maturation through its interaction with the ligands APRIL and BAFF. Ligand binding stimulates activation of several transcription factors, including NF-kappa-B, and has been shown to induce either proliferation or apoptosis, suggesting a dual role in the regulation of B cells. CD267 also appears to have an essential function in immunoglobulin isotype switching and B cell differentiation in response to thymus-independent antigens.