IL-6 (interleukin 6) is a pleiotropic cytokine that plays an important role in host defense by regulating immune and inflammatory responses. Produced by T cells, monocytes, fibroblasts, endothelial cells and keratinocytes, IL-6 has diverse biological functions. It stimulates B-cell differentiation and antibody production, synergizes with IL-3 in megakaryocyte development and platelet production, induces expression of hepatic acute-phase proteins, and regulates bone metabolism. IL-6 is associated with various autoimmune and inflammatory diseases. High levels of IL-6 are present in the synovial fluid from rheumatoid arthritis patients. It is also linked with chronic inflammatory proliferative disease and B cell malignancy, Castleman′s disease, and plasmacytoma/multiple myeloma.
