Interleukin-17A(IL-17A) , also known as CTLA-8, is a 15-20 kDa glycosylated cytokine that plays an important role in anti-microbial and chronic inflammation. The six IL-17 cytokines (IL-17A-F) are encoded by separate genes but adopt a conserved cystine knot fold [1, 2]. Mature mouse IL-17A shares 61% and 89% amino acid sequence identity with human and rat IL-17A, respectively [3, 4]. IL-17A is secreted by Th17 cells, gamma /δ T cells, iNKT cells, NK cells, LTi cells, neutrophils, and intestinal Paneth cells [2]. It forms disulfide-linked homodimers as well as disulfide-linked heterodimers with IL-17F[5, 6]. IL-17A exerts its effects through the transmembrane IL-17RA in complex with IL-17RC or IL-17RD [7, 8]. Both IL-17RA and IL-17RC are required for responsiveness to heterodimeric IL-17A/F [7]. IL-17A promotes protective mucosal and epidermal inflammation in response to microbial infection [9-12]. IL-17A/F likewise induces neutrophil migration, but IL-17F does not [11]. IL-17A additionally enhances the production of inflammatory mediators by rheumatoid synovial fibroblasts and contributes to TNF-alpha induced shock [13, 14]. In contrast, it can protect against the progression of colitis by limiting chronic inflammation [12]. IL-17A encourages the formation of autoreactive germinal centers and exacerbates the onset and progression of experimental models of autoimmunity [15,16]. IL-17A has been shown to exert either tumorigenic or anti-tumor effects [17, 18].
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