Description
Introduction: Interleukin 13 (IL-13) is a cytokine secreted by many cell types, but especially T helper type 2 (Th2) cells, that is an important mediator of allergic inflammation and disease. In addition to effects on immune cells that are similar to those of the closely related cytokine IL-4, IL-13 is more importantly implicated as a central mediator of the physiologic changes induced by allergic inflammation in many tissues. IL-13 induces its effects through a multi-subunit receptor that includes the alpha chain of the IL-4 receptor (IL-4Ralpha), which is also a component of the IL-4 receptor, and at least one of two known IL-13-specific binding chains. Most of the biological effects of IL-13 are linked to a single transcription factor, signal transducer and activator of transcription 6 (STAT6). The functions of IL-13 overlap considerably with those of IL-4, especially with regard to changes induced on hematopoietic cells, but these effects are probably less important given the more potent role of IL-4. Thus, although IL-13 can induce immunoglobulin E (IgE) secretion from activated human B cells, deletion of IL-13 from mice does not markedly affect either Th2 cell development or antigen-specific IgE responses induced by potent allergens. In comparison, deletion of IL-4 abrogates these responses. Thus, rather than a lymphoid cytokine, IL-13 acts more prominently as a molecular bridge linking allergic inflammatory cells to the non-immune cells in contact with them, thereby altering physiological function. Although IL-13 is associated primarily with the induction of airway disease, it also has anti-inflammatory properties. Airway matrix metalloproteinases (MMPs), which are protein-degrading enzymes, are required to induce egression of effete parenchymal inflammatory cells into the airway lumen where they are then cleared. Among other factors, IL-13 induces these MMPs as part of a mechanism that protects against excessive allergic inflammation that predisposes to asphyxiation.
Principle of the Assay: The microtiter plate provided in this kit has been pre-coated with an antibody specific to IL-13. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated polyclonal antibody preparation specific for IL-13 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-13, 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-13 in the samples is then determined by comparing the O.D. of the samples to the standard curve