TNFSF13B, also named as BAFF, BLYS, TALL1, TNFSF20, ZTNF4 and CD257, is a cytokine that binds to TNFRSF13B/TACI and TNFRSF17/BCMA. TNFSF13B is localized in chromosome region 13q32-q34 and is implicated in the regulation of immune response to infections, autoimmune disease, and inflammation. This cytokine is expressed in B cell lineage cells, and acts as a potent B cell activator. It has been also shown to play an important role in the proliferation and differentiation of B cells. At the placental level, it is believed that TNFSF13B has an antiapoptotic effect. TNFSF13B is overexpressed in several autoimmune patients although the mechanism behind this feature is unclear.