QUANTITATIVE IMMUNOSORBE NT ASSAY FOR SlgA:

Studies of the secretory immune system have been hampered by the lack of an assay to specifically measure SIgA in secretions which also contain serum IgA and free secretory componet (FSC). We have developed an assay for SIgA utilizing commercially available acrylamide beads coated with antibodies against human alpha chains (lmmuno-Fluor,Bio-Rad Labs). After incubation with IgA containing solutions, SIgA bound to the beads was labeled with a fluorescein conjugated antibody against secretory component. The fluorescence measured was directly proportional to the added purified SIgA, and was linear over a 10-fold range of concentrations with a sensitivity of approximately 50 ng. The effect of serum IgA was studied using mixtures containing varying proportions of SIgA and serum IgA. Quantitation of SIgA was not affected by serum IgA when these mixtures were assayed in the presence of excess antibody coated beads. Knowing the SIgA concentration, serum IgA levels in a sample could be calculated from the fluorescence developed with an anti-alpha fluorescein conjugate. An immunosorbent assay utilizing antibodies of two different specificities for binding and detection thus allows the specific quontitation of complex proteins (SIgA) In the presence of their subunits (FSC and IgA). This assay for SIgA will allow further investigation of the role of secretory immunity in both health and disease states.