Human antibodies to immunoglobulin A (IgA). A radioimmunological method for differentiation between anti-IgA antibodies and IgA in the serum of IgA deficient individuals.

In the sera of 12 out of 27 individuals with IgA deficiency (serum level below 0.02 mg IgA/ml) class-specific anti-IgA antibodies were demonstrated by haemagglutination. These sera showed false-positive results in a solid-phase inhibition radioimmunoassay (RIST) (apparent IgA concentration between 0.6 and 13.7 microgram IgA/ml) indicating that the RIST is not an appropriate test for the analysis of serum of IgA deficient individuals. A modification of the RIST is proposed (titration RIA) that permits differentiation between low levels of IgA and class-specific anti-IgA antibodies. With this test IgA deficient individuals could be classified as those with low but detectable levels of IgA and those with class-specific anti-IgA antibodies. A computer procedure was developed to calculate both the amount and the avidity (K) of the anti-IgA antibodies and to simulate the assay system. The K value calculated from experimental points proved to be an overestimation of the K value which fitted most adequately in the simulation. The comparison of the results with clinical findings indicated a possible correlation between the amount and the avidity of the anti-IgA antibodies and the appearance of anaphylactic reactions after transfusion of IgA.