IL17A (Interleukin 17A), also referred to IL17 or CTLA8 (Cytotoxic T-lymphocyte-associated serine esterase 8), is a 17.5 kDa glycoprotein encoded in humans by the IL17A gene that is located at the chromosome 6p12.2. It is composed of 155 amino acids and belongs to the IL17 protein family (IL17A- IL17F), of which each monomer contains four highly conserved cysteine residues. IL17A is a proinflammatory cytokine released by CD4+ T cells (Th17 cells), CD8+ T cells (Tc17 cells), invariant natural killer T cells (iNKT cells), γδ T cells and innate lymphoid cells (ILCs). This cytokine functions in the regulation of activities of NF-kappaB and mitogen-activated protein kinases. Its high levels are associated with several chronic inflammatory diseases such as psoriasis, rheumatoid arthritis, and multiple sclerosis. IL17F (Interleukin 17F), also known as fInterleukin-17F (IL-17F), cytokine ML-1, ML-1, ML1 or CANDF6, is a cytokine of 18 kDa that consists of 163 amino acids. It is encoded by the chromosome 6p12.2 and belongs to the IL-17 cytokine family composed of six members. IL17F shares greatest sequence similarity with a widely known inflammatory cytokine, IL17. Both of them are expressed on the CD4+ and γδ T cells and IL-17F is found to be released as homodimers or heterodimers with IL-17. The study shows that it is implicated in the stimulation of producing several cytokines, including IL6, IL8 and CSF2/GM_CSF, as well as regulating the cartilage matrix turnover. Also, IL17F inhibits the angiogenesis of endothelial cells and induces endothelial cells to generate IL2, TGFB1/TGFB, and MCP-1. This cytokine involves in the exacerbation of antigen-induced pulmonary allergic inflammation.