VALIDATION OF IGA1 AND IGA2 MEASUREMENTS BY A SOLID-PHASE IMMUNORADIOMETRIC ASSAY IN SERUM AND SECRETIONS

We describe specific, sensitive and reproducible immunoradiometric ass ays to measure total IgA and IgA subclass levels in biological fluids, which take into account the problem that polymeric forms are differen tly recognized in immunoassays. Sera from subjects totally deficient i n one ofthe IgA subclasses allowed us to ensure the specificity of the subclass assays and to define the proportions of IgA1 (84%) and IgA2 (16%) in the normal pooled serum (from 30 blood donors) used as standa rd. With purified milk 11-S secretory IgA1 and 11-S secretory IgA2, we determined a correction factor for the corresponding polymeric forms using, respectively, monomeric IgA1 and monomeric IgA2 from pooled ser um as standards. With the monoclonal antibodies used, purified 11-S se cretory IgA1 was similarly recognized by both the total IgA assay and the IgA1 assay; both total IgA and IgA1 concentrations were underestim ated compared with monomeric IgA or monomeric IgA1. In contrast, 11-S secretory IgA2 was better recognized by the IgA2 assay than by the tot al IgA assay and the values were thus overestimates. Considering this problem of recognition, we fractionated saliva and lung secretions by sucrose density gradient ultracentrifugation before measuring their Ig A1 and IgA2 levels.