Description
Introduction: Immunoglobulin A (IgA) is an antibody which plays a critical role in mucosal immunity. More IgA is produced in mucosal linings than all other types of antibody combined; between 3 and 5g is secreted into the intestinal lumen each day. The high prevalence of IgA in mucosal areas is a result of a cooperation between plasma cells that produce polymeric IgA (pIgA), and mucosal epithelial cells that express an immunoglobulin receptor called the polymeric Ig receptor (pIgR). pIgA is released from the nearby activated plasma cells and binds to pIgR. This results in transportation of IgA across mucosal epithelial cells and its cleavage from pIgR for release into external secretions. In the blood, IgA interacts with an Fc receptor called FcalphaRI (or CD89), which is expressed on immune effector cells, to initiate inflammatory reactions. Ligation of FcalphaRI by IgA containing immune complexes causes antibody-dependent cell-mediated cytotoxicity (ADCC), degranulation of eosinophils and basophils, phagocytosis by monocytes, macrophages, neutrophils and eosinophils, and triggering of respiratory burst activity by polymorphonuclear leukocytes.
Principle of the Assay: The microtiter plate provided in this kit has been pre-coated with an antibody specific to IgA. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated antibody preparation specific for IgA 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 IgA, 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 IgA in the samples is then determined by comparing the O.D. of the samples to the standard curve