BAFF Receptor (BAFF-R), a member of the TNFR superfamily, 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-R is a type III transmembrane protein that binds with high specificity to BAFF (TNFSF13B). BAFF-R/BAFF signaling plays a critical role in B cell survival and maturation.