A solid phase, direct competition, radioimmunoassay for quantitation of secretory IgA in human serum

A solid phase radioimmunoassay is described for measurement of secretory IgA (sIgA) in human serum. The assay is based on direct competition between sIgA in serum and purified labelled milk sIgA for anti-secretory-component antibodies coated on disposable plastic cups. The assay is relatively rapid, reproducible and of adequate sensitivity. A wide range of sIgA concentrations (5--120 microgram/ml) can be tested with the same dilution of human serum. The arithmetic mean +/- S.D. of the serum sIgA levels of 120 random blood donors (both sexes) was 10.9 +/- 4.6 microgram/ml. Compared to previously published methods and results of quantitation of sIgA in human sera, the present assay is an improvement which should yield interesting data in human hepatic physiopathology.