Human B cell stimulatory factor 2 (originally designated BSF2) was initially characterized and isolated as a T cell‐derived factor that caused the terminal maturation of activated B cells to immunoglobulin producing cells. Molecular cloning of the cDNA has revealed that BSF2 is identical with 26 kD protein, interferon β2, plasmacytoma growth factor and hepatocyte stimulating factor and the designation “IL‐6” has been proposed for this molecule. It is now known that BSF2/IL‐6 has a wide variety of biological functions and that (...) abnormal regulation of BSF2/IL‐6 expression may be related to the pathogenesis of certain autoimmune diseases such as rheumatoid arthritis and multiple myeloma. (shrink)