Members in the TNF superfamily regulate immune responses and induce apoptosis. Two novel members in the TNF family were recently identified and designated BAFF/BLyS/TALL-1/THANK/zTNF4 and April/TALL-2, respectively. BAFF was characterized as a B cell activator since it induced B cell proliferation and immunoglobulin secretion. April regulates immunological and non-immunological cell growth. Three receptors, BCMA, TACI, and BAFF-R, for BAFF and April were recently identified. TACI, like BCMA, binds BAFF and April. TACI and its ligands regulate humoral immune responses, activate NF-kappaB and c-jun N-terminal kinase, and are involved in B cell associated autoimmune diseases.