Description
Introduction: Interleukin-21 is a protein that in humans is encoded by the IL21 gene. Interleukin 21 is a cytokine that has potent regulatory effects on cells of the immune system, including natural killer (NK) cells and cytotoxic T cells that can destroy virally infected or cancerous cells. This cytokine induces cell division/proliferation in its target cells. IL-21 is expressed in activated human CD4+ T cells but not in most other tissues. In addition, IL-21 expression is up-regulated in Th2 and Th17 subsets of T helper cells, as well as T follicular cells. Furthermore IL-21 is expressed in NK T cells regulating the function of these cells. Interleukin-21 is also produced by Hodgkin's lymphoma (HL) cancer cells (which is surprising because IL-21 was thought to be produced only in T cells). This observation may explain a great deal of the behavior of classical Hodgkin's lymphoma including clusters of other immune cells gathered around HL cells in cultures. Targeting IL-21 may be a potential treatment or possibly a test for HL. It has been shown that IL-21R knock-out mice express higher levels of IgE and lower levels of IgG1 than normal mice after antigen exposure. IgE levels decreased after mice were injected with IL-21. This has implications for the role of IL-21 in controlling allergic responses because of the role of IgE in hypersensitivity type 1 responses. IL-21 has been tried as therapy for alleviating allergic responses. It was shown to be successful in decreasing pro-inflammatory cytokines produced by T cells in addition to decreasing IgE levels in a mouse model for rhinitis (nasal passage inflammation). A study using mice with peanut allergies showed that systemic treatment of IL-21 was an effective means of mitigating the allergic response. This has strong implications for the pharmacological development of IL-21 for controlling both localized and systemic allergies. IL-21 was approved for Phase 1 clinical trials in metastatic melanoma (MM) and renal cell carcinoma (RCC) patients. It was shown to be safe for administration with flu-like symptoms as side effects. Dose-limiting toxicities included low lymphocyte, neutrophil, and thrombocyte count as well as hepatotoxicity. According to the Response Evaluation Criteria in Solid Tumors (RECIST) response scale, 2 out of 47 MM patients and 4 out of 19 RCC patients showed complete and partial responses, respectively. In addition, there was an increase of perforin, granzyme B, IFN-gamma, and CXCR3 mRNA in peripheral NK cells and CD8+ T cells. This suggested that IL-21 enhances the CD8+ effector functions thus leading to anti-tumor response. IL-21 proceeded to Phase 2 clinical trials where it was administered alone or coupled with drugs as sorafinib and rituximab.
Principle of the Assay: The microtiter plate provided in this kit has been pre-coated with an antibody specific to IL-21. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated polyclonal antibody preparation specific for IL-21. 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-21, 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-21. in the samples is then determined by comparing the O.D. of the samples to the standard curve