AN ENZYME-IMMUNOASSAY FOR THE DETERMINATION OF ANTI-IGA ANTIBODIES USING POLYCLONAL HUMAN-IGA

An enzyme immunoassay (EIA) for screening and quantitation of serum an ti-IgA antibodies of IgG class is described. This method is based on t he use of purified polyclonal human serum IgA as the coating antigen a nd a commercial alkaline phosphatase-conjugated anti-human IgG as the detecting antibody. Nonspecific reactions were minimized by blocking v acant protein binding sites with bovine serum albumin and by using ind ividual sample blanks. The IgA specificity of a positive antibody find ing was confirmed by testing inhibition: pooled normal human serum inh ibited the binding of specific antibodies by over 80%. The same degree of inhibition could also be demonstrated by a commercial myeloma TgA preparation and by the IgA used for coating but not by IgA-deficient s erum (<0.05 mg/l). On the basis of the mean anti-IgA antibody titre in EIA, a value of 12000 arbitrary units of anti-IgA per litre (AU/1) wa s assigned to a patient serum used as standard in the assay. Anti-IgA results obtained by EIA and haemagglutination correlated well, which m akes it possible to compare earlier KA results with those obtained now by EIA. The measuring range of the assay was 0.6-27 AU/1 and the lowe st quantifiable concentration 7 AU/1. The dilution requirement for ser um was 1/16. The interassay coefficients of variation for control sera with antibody levels from 35 AU/1 to 3770 AU/1 varied from 9 to 12%.