Reassessment of levels of secretory IgA in pathological sera using a quantitative radioimmunoassay.

Serum levels of sIgA were quantitated by a new radioimmunoassay in patients with a variety of diseases, lactating women and clinically healthy blood donors. Significantly elevated levels compared to controls were found in lactating women, patients with Crohn's disease and patients with cirrhosis, but not in patients with rheumatoid arthritis, IgA myeloma or neoplastic disease. Patients with inflammatory disease and serum IgA levels at least two-fold greater than the normal mean and patients with a variety of other diseases did not show elevated levels of sIgA. In the two latter groups, patients with hepatic disease were excluded. High levels of sIgA were found in four patients with liver metastases from extrahepatic neoplasms. The results indicate that the liver is important for the maintenance of normal serum levels of sIgA.