BCMA (B cell maturation) is a nonglycosylated integral membrane type I protein that is preferentially expressed in mature B lymphocytes.The N-terminal part of both mouse and human proteins contains a conserved six-cysteine motif. BLyS binds to three receptors of the TNF receptor family (B cell maturation antigen BCMA, TACI, and BAFF-R), all of which are expressed by mature B cells.