BAFF (for B cell Activating Factor) is a novel member in the TNF family. BAFF/BLyS was characterized as a B cell stimulator since it induced B cell proliferation and immunoglobulin secretion. Two receptors for BAFF were recently identified and designated TACI and BCMA. BAFF and its receptors are involved in the development of systemic lupus erythaematosus and other B cell associated autoimmune diseases. Like TNF-α and TRAIL, THANK was shown to activate NF-kB and c-Jun N-terminal kinase (JNK) and to induce apoptosis.