B cell maturation antigen (BCMA) is a member of the TNF receptor superfamily. It has been designated TNFRSF17. Mouse BCMA is a 185 amino acid (aa) protein consisting of a 49 aa extracellular domain, a 23 aa transmembrane domain, and a 113 aa intracellular domain. BCMA is a type III membrane protein containing one extracellular cysteine rich domain. Within the TNFRSF, it shares the highest homology with TACI. BCMA and TACI have both been shown to bind to APRIL and BAFF, members of the TNF ligand superfamily. BCMA expression has been found in immune organs and mature B cell lines. Although some expression has been observed at the cell surface, BCMA appears to be localized to the Golgi compartment. The binding of BCMA to APRIL or BAFF has been shown to stimulate IgM production in peripheral blood B cells and increase the survival of cultured B cells. This data suggests that BCMA may play an important role in B cell development,function and regulation.