Background
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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. Mature rat IL-17 is 61% and 60% aa identical to mouse and rat IL-17, respectively. It also shows limited aa sequence identity to other rat IL-17 family members. In particular, it shows 34%, 38%, 34% and 26%aa sequence identity to IL-17B, C, D, and E, respectively, and 49% aa sequence identity to IL-17F with which it is most homologous. While rodent and rat mature sequences show modest aa sequence identity, rat IL-17 is active on both mouse and rat cells. The cells principally known to produce IL-17 are the memory CD4+ T cells. In addition, CD8+ T cells as well as TCR+ CD4-CD8- T cells, neutrophils (PMNs) and eosinophils have also been reported to express mRNA transcripts for IL-17.
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