Property and physiological role of biliary secretory IgA in rats

Secretory IgA (sIgA) and monomeric IgA (mIgA) were purified from normal rat bile, and their role in the gastrointestinal tract was investigated. Biliary sIgA has a molecular weight of approximately 400,000 daltons and a sedimentation constant of 11.7S. Thus, sIgA obtained from rat bile had physicochemical properties similar to those reported for sIgA in other secretions, and probably consists of L-chains, alpha-chains and secretory component. After in vitro incubation with trypsin or intestinal fluid, sIgA remained intact, whereas mIgA was hydrolyzed. Rats challenged repeatedly with dinitrophenylated bovine serum albumin (DNP-BSA) had specific IgA antibody against DNP in the bile and feces as measured by a radioimmunoassay using [3H]-DNP-lysine. Our results demonstrate a possibility that biliary sIgA, not mIgA, has an important role which inhibits the absorption of foreign antigen from intestine.