BAFF/CD257 is a type II transmembrane protein, and a member of the tumor necrosis factor ligand superfamily. It is proteolytically cleaved to form a soluble protein. BAFF, like other TNF ligand family members, forms homo-trimers. The predicted molecular weight of a BAFF monomer is approximately 31kDa. It is expressed on peripheral blood B and T lymphocytes, monocytes, macrophages, and dendritic cells and is upregulated by IFN- BAFF prevents apoptosis and promotes B cell survival by binding the BAFF-specific receptor (BAFFR/BR3).