BAFF is a master regulator of peripheral B cell survival and, together with IL-6, promotes Ig class-switching and plasma cell differentiation. BAFF co-stimulates activated T cells. Increased levels of soluble BAFF have been detected in the serum of patients with various autoimmune diseases, such as Sjogren’s syndrome, rheumatoid arthritis, multiple sclerosis and systemic lupus erythematosus (SLE). Furthermore, BAFF is found in inflammatory sites in which there is lymphoid neogenesis. BAFF levels are elevated in patients with multiple myeloma and B cell chronic lymphoid leukemia (B-CCL).