B cell Activating Factor (BAFF) is a type II member of the Tumor Necrosis Factor (TNF) superfamily. BAFF is expressed as a transmembrane protein on T cells, macrophages, and dendritic cells. The transmembrane domain of BAFF can also be cleaved to produce a soluble protein fragment. BAFF binds to the TNF receptors known as B cell maturation antigen (BCMA), transmembrane activator and CAml interactor (TACI), and BAFF receptor (BAFFR). BAFF is important for the survival and maturation of peripheral B cells. Human BAFF shows activity on mouse splenocytes.