B Cell Activating Factor Receptor (BAFF-R), also named tumor necrosis factor receptor superfamily member 13C, is a member of the TNFR superfamily. It is highly expressed in spleen, lymph node, and resting B cells and to some extent in activated B cells, resting CD4+ cells and peripheral blood leukocytes. BAFF receptor is a type III transmembrane protein containing a single extracellular phenylalanine-rich domain and binds with high specificity to BAFF (TNFSF13B). It enhances B-cell survival in vitro and is a regulator of the peripheral B-cell population. BAFF receptor/BAFF signaling plays a critical role in B cell survival and maturation.