Interleukin 17 (IL-17; also known as IL-17A) is a 30 - 35 kDa variably glycosylated homodimeric protein that belongs to a unique family of cysteine-knot related proteins. Its sequence was originally isolated from an activated rodent hybridoma and termed CTLA-8 . It is synthesized as a 155 amino acid (aa) precursor that contains a 23 aa signal sequence and a 15 kDa, 132 aa mature segment. Although there are two intrachain disulfide bonds that create a ring reminiscent of those found in cysteine-knot proteins, the actual closed knot structure does not appear to form.

IL-17 has one potential N-linked glycosylation site.IL-17, a T cell-derived proinf lammatory cytokine, is produced by TCRα/β+CD4-CD8- thymocytes, as well as by activated CD4+ and CD4+CD45RO+ memory T cells.