Description
A new family of cytokines, Interleukin-17, has recently been defined that reveals a distinct ligand-receptor signaling system. There is high evidence for its importance in the regulation of immune responses. IL-17A was first characterised and six IL-17 family members (IL-17A-F) have subsequently been described. IL-17A, a homodimeric cytokine of about 32 kDa, is largely produced by activated memory T lymphocytes, but stimulates innate immunity and host defense. IL-17A and IL-17F both mobilize neutrophils partly through granulopoeisis and CXC chemokine induction, as well as increased survival locally. IL-17A and IL-17F production by T lymphocytes is regulated by IL-23 independent of T cell receptor activation. The T help 1 (Th1) and Th2 cell classification has until recently provided the framework for understanding CD4(+) T cell biology and the interplay between innate and adaptive immunity. Recent studies have defined a previously unknown arm of the CD4(+) T cell effector response, the Th17 lineage. This subset of T cells produces interleukin 17, which is highly proinflammatory and induces severe autoimmunity. Whereas IL-23 serves to expand previously differentiated T(H)-17 cell populations, IL-6 and transforming growth factor-beta (TGF-beta) induce the differentiation of T(H)-17 cells from naive precursors. Increasing evidence shows that IL-17 family members play an active role in inflammatory diseases, autoimmune diseases, and cancer. The IL-17 signaling system is operative in disparate tissues such as articular cartilage, bone, meniscus, brain, hematopoietic tissue, kidney, lung, skin and intestine. Thus, the evolving IL-17 family of ligands and receptors may play an important role in the homeostasis of tissues in health and disease beyond the immune system. Increased levels of IL-17 have been associated with several conditions, including airway inflammation, rheumatoid arthritis, intraperitoneal abscesses and adhesions, inflammatory bowel disease,allograft rejection, psoriasis, cancer and multiple sclerosis