Description
Introduction: 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. In addition to IL-17A, members of the IL-17 family include IL-17B, IL-17C, IL-17D, IL-17E (also called IL-25), and IL-17F. All members of the IL-17 family have a similar protein structure, with four highly conserved cysteine residues critical to their 3-dimensional shape yet they have no sequence similarity to any other known cytokines. Numerous immune regulatory functions have been reported for the IL-17 family of cytokines, presumably due to their induction of many immune signaling molecules. Most notably, IL-17 is involved in inducing and mediating proinflammatory responses. IL-17 is commonly associated with allergic responses. IL-17 induces the production of many other cytokines (such as IL-6, G-CSF, GM-CSF, IL-1beta, TGF-beta, TNF-alpha), chemokines (including IL-8, GRO-alpha and MCP-1) and prostaglandins (e.g. PGE2) from many cell types (fibroblasts, endothelial cells, epithelial cells, keratinocytes and macrophages). The release of cytokines causes many functions, such as airway remodeling, a characteristic of IL-17 responses. The increased expression of chemokines attracts other cells including neutrophils but not eosinophils. IL-17 function is also essential to a subset of CD4+ T-Cells called T helper 17 (Th17) cells. As a result of these roles, the IL-17 family has been linked to many immune/autoimmune related diseases including rheumatoid arthritis, asthma, lupus, allograft rejection and anti-tumour immunity. 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.
Principle of the Assay: The microtiter plate provided in this kit has been pre-coated with an antibody specific to IL-17. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated antibody preparation specific for IL-17 and Avidin conjugated to Horseradish Peroxidase (HRP) is added to each microplate well and incubated. Then a TMB (3,3',5,5' tetramethyl-benzidine) substrate solution is added to each well. Only those wells that contain IL-17, biotin-conjugated antibody and enzyme-conjugated Avidin will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450 nm +/- 2 nm. The concentration of IL-17 in the samples is then determined by comparing the O.D. of the samples to the standard curve