IL-6 biology: implications for clinical targeting in rheumatic disease

IL-6 has been linked to numerous inflammatory conditions (such as rheumatoid arthritis), and many IL-6-directed therapies are currently in development. The authors outline the basic biology of IL-6 and IL-6 signalling pathways before discussing the clinical implications of targeting IL-6 in the context of rheumatic diseases. Current and future indications for the use of IL-6-targeted therapies and safety of these agents are discussed. IL-6 has been linked to numerous diseases associated with inflammation, including rheumatoid arthritis, inflammatory bowel disease, vasculitis and several types of cancer. Moreover, IL-6 is important in the induction of hepatic acute-phase proteins for the trafficking of acute and chronic inflammatory cells, the differentiation of adaptive T-cell responses, and tissue regeneration and homeostatic regulation. Studies have investigated IL-6 biology using cell-bound IL-6 receptors expressed predominantly on hepatocytes and certain haematopoietic cells versus activation mediated by IL-6 and soluble IL-6 receptors via a second protein, gp130, which is expressed throughout the body. Advances in this research elucidating the differential effects of IL-6 activation provide important insights into the role of IL-6 in health and disease, as well as its potential as a therapeutic target. Knowledge of the basic biology of IL-6 and its signalling pathways can better inform both the research agenda for IL-6-based targeted therapies as well as the clinical use of strategies affecting IL-6-mediated inflammation. This Review covers novel, emerging aspects of the biology of IL-6, which might lead to more specific blockade of IL-6 signalling without compromising the protective function of this cytokine in the body's defence against infections.