Biological effects of interleukin-6: Clinical applications in autoimmune diseases and cancers.

Interleukin-6 (IL-6) is a pro-inflammatory cytokine involved in the pathogenesis of various autoimmune and chronic inflammatory diseases. Binding of IL-6 to its receptor (IL-6R) initiates both classical- and trans-signaling pathways. A number of autoimmune diseases are characterized by overproduction of IL-6. Tocilizumab, a humanized monoclonal antibody against IL-6R, blocks IL-6-mediated signaling and has been approved for the treatment of rheumatoid arthritis and Castleman's disease. IL-6 levels are also upregulated in various tumors, and the levels of circulating IL-6 are associated with prognosis in cancer patients. The major issues covered in this commentary include (1) how IL-6-mediated biological effects may lead to the pathogenesis of autoimmune diseases and cancers, (2) the rationale of developing anti-IL-6 strategies for therapeutic purposes, (3) recent advances in anti-IL-6 therapeutics (clinical benefits and adverse events), (4) current knowledge about clinical trials evaluating newly emerging anti-IL-6 treatments, (5) strategies to improve anti-IL-6 therapeutics from both basic and clinical aspects. This commentary provides a useful overview of the role of IL-6 in both autoimmune diseases and cancers from the laboratory as well as clinical perspectives.