Ultimately, a recently discovered cytokine belonging to the TNF family, B-cell activating factor (BAFF), would seem to play an essential role in the maturation, proliferation, and clonal expansion of B lymphocytes; the detection of high serum levels of BAFF in patients with LES, AR, SS, and chronic HCV infection strongly suggests the correlation between BAFF and HCV cryoglobulinemia. The gene discussed is TNFSF13B; the disease is synovial sarcoma.