The founding member of the IL17 family of cytokines, IL17A plays an important role in antimicrobial and chronic inflammation. All the six IL17 cytokines (IL17A-F) share a cystine knot fold and are secreted as homodimers. Mature human IL17A shares 60% amino acid sequence identity with rat and mouse IL17A. IL17 cytokines bind to two receptors; IL17RA and IL17RC that together form a heterodimer. The receptor heterodimer is preferred by IL17 ligands, and thus, either IL17RA or IL17RC knockouts completely abolish IL17 signalling. Recombinant human IL17A is a non-glycosylated, 32 kDa disulfide-linked homodimer.