Transmembrane Activator and CAML Interactor (TACI) is a tumor necrosis factor receptor superfamily (TNFSF) member. It is a type III transmembrane protein sharing a high degree of homology with B cell maturation antigen (BCMA) among TNFSF members. It binds to the ligands BAFF (BLyS) and APRIL. CD267 appears to be particularly important for the regulation of B cell survival and maturation in the spleen. It is a major mediator of BAFF-dependent costimulatory responses in peripheral B cells. Signaling through TACI may serve to down-regulate B cell activity as well. The actual role for TACI in the mouse has still not been fully determined.