IL-17F (Interleukin 17F, CTLA-8)) is a cytokine belonging to the IL-17 family that is produced by inflammatory cells such as activated T cells, mast cells, and basophils. IL-17F is involved in allergic airway inflammation, and can induce several cytokines, chemokines, and adhesion molecules in bronchial epithelial cells, vein endothelial cells, fibroblasts, and eosinophils. IL-17F may be secreted as a homodimer, or a heterodimer with IL17A. It acts by binding to the type I receptor, IL-17R, aiding recruitment of monocytes and neutrophils at the site of inflammation by increasing chemokine production. IL-17F also stimulates induction of other pro-inflammatory cytokines TNF alpha, IL-1 beta, IL-6, and IL-8, and reports strongly suggest the involvement of IL-17 in several chronic inflammatory diseases such as rheumatoid arthritis, psoriasis and multiple sclerosis. TGF-beta (differentiation) and IL-23 (expansion) are required for induction and maintenance of Th17 (IL-17 producing) cells, which in turn induce the other pro-inflammatory cytokines. IL-17F is produced, and exists, as a homo-dimer, with homology to a herpes virus early protein, is one of the six members (IL-17A-F) of this cytokine family, and is well characterized and highly expressed by activated effector memory T cells. IL-17F has been found to inhibit the angiogenesis of endothelial cells and induce endothelial cells to produce IL2, TGFB1/TGFB, and monocyte chemoattractant protein-1.