Biological and clinical aspects of interleukin 6

Interleukin (IL) 6 is a pleiotropic cytokine previously known as hybridoma/plasmacytoma growth factor, interferon β2 (IFN-β2), B cell stimulatory factor and hepatocyte stimulating factor. It regulates immune response, acute phase reactions and haematopoiesis, and may play a central role in the host defense mechanism. Along with tumour necrosis factor and IL- 1, IL-6 belongs to the endogenous mediators of the complex reaction of the host to injury or infection, referred to as the acute-phase response. IL-6 is produced by a variety of cells and acts on a wide range of tissues, exerting growth-inducing, growth-inhibitory and differentiation-inducing effects, depending on the nature of the target cells. The physiological effects exerted by IL-6 include induction of fever, immunoglobulin synthesis in activated B cells, activation of resting T cells and natural killer cells as well as stimulation of megakaryocytopoiesis and induction of acute-phase protein synthesis by the liver. Elevated IL-6 levels have been found in diseases like rheumatoid arthritis, multiple myeloma, Castleman's disease, mesangium proliferative glomerulonephritis and systemic lupus erythematosus. The abnormal expression and dysregulation of IL-6 in certain disorders may be a typical feature of this cytokine which may be directly related to pathogenesis.