B cell-activating factor receptor (BAFF-R) is a 19 kD type III membrane protein. It belongs to TNFR superfamily, also known as TNFRSF member 13C (TNFRSF13C), BAFF receptor 3 (BR3), or CD268. BAFF-R is expressed on mature B cells, B cell lymphoma, and T cell subset. BAFF-R is the major receptor for BAFF/BLys (or TALL-1, THANK) which binds to TACI and BCMA as well. The interaction of BAFF with BAFF-R promotes NF-kappa B activation and plays predominant roles in B-cell maturation and survival as well as costimulates T cell activation and proliferation. TRAF3 is a BAFF-R intracellularly associated protein, which negatively regulates BAFF-R-mediated NF-kappa B activation.