Interleukin 6 (IL-6) is a multifunctional protein that plays important roles in host defense, acute phase reactions, immune responses, and hematopoiesis. Synonyms for IL-6 include: B cell stimulatory factor-2 (BSF-2), hybridoma/plasmacytoma growth factor, hepatocyte stimulating factor, cytotoxic T cell differentiation factor and macrophage-granulocyte inducing factor 2A (MGI-2A). IL-6 is expressed by a variety of normal and transformed cells including T cells, B cells, monocytes/macrophages, fibroblasts, hepatocytes, keratinocytes, astrocytes, vascular endothelial cells, mesangial cells, osteoblasts, carcinomas, sarcomas, myelomas, glioblastomas, and melanomas. The production of IL-6 is up-regulated by numerous signals including mitogenic or antigenic stimulation, lipopolysaccharide, calcium ionophore, IL-1, IL-2, IFN, TNF, PDGF, and viruses. IL-4 and IL-13 inhibit IL-6 expression in monocytes. Natural human and murine IL-6 are glycoproteins containing N-and/or O-linked carbohydrates (