BAFF Receptor (BAFFR), 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. BAFFR is a type III transmembrane protein that binds with high specificity to BAFF (TNFSF13B). BAFFR/BAFF signaling plays a critical role in B cell survival and maturation. Recombinant human BAFFR is a 76 amino acid polypeptide (7.7 kDa) corresponding to the extracellular portion of the full BAFFR protein.