Quantitation of exocrine IgA in human serum in health and disease.

Exocrine IgA in serum was estimated by a sensitive haemagglutination-inhibition technique using a specific anti-secretory piece antiserum and colostral IgA coated cells. The mean level in healthy individuals was 5·2 μg/ml. Decreased levels are found in cord sera and the sera of IgA deficient individuals. Normal levels were found in the sera of patients with renal disease and slightly elevated levels in the sera of a group of patients with neoplastic disease. Elevated levels were found in the sera of lactating women, patients with acute chest infection, and patients with sero-positive rheumatoid arthritis.