The formation and clearance of circulating IgA immune complexes from blood to bile was investigated in this study. The i.v. injection of either MOPC-315, an IgA M-component with antidinitrophenyl (DNP) specificity, or TEPC-15, an IgA M-component of a different specificity, was followed by i.v. injection of '2511-DNPlo-bovine serum albumin (BSA) as the antigen. The formation and clearance of IgA immune complexes in the circulation of MOPC-315-treated, but not TEPC-15treated animals was de9monstrated by immunoprecipitation with polyacrylamide beads coated with rabbit anti-mouse IgA. IgA-'251-DNPlo-BSA complexes were identified in the bile from MOPC-315-treated, but not TEPC-15-treated animals utilizing this same immunoprecipitation technique. These observations suggest that the liver or bile ducts transport JgA immune complexes from blood into bile. The clearance of '251-DNPlo-BSA from the circulation was documented by coprecipitation with rabbit anti-BSA and BSA. The clearance of this circulating antigen was slower in the MOPC-315-treated than in the TEPC-15-treated animals suggesting that under the conditions of the present experiment, circulating antigen is cleared more slowly after IgA immune complex formation.
Proteins and polypeptide fragments are absorbed in small quantities from the gastrointestinal tract of normal animals including man (1, 2). Although insignificant nutritionally, these molecules may have important immunologic consequences (3). Increased levels of circulating enteric antigens are found in mucosal inflammation (4), atopy (51, infectious enteritis (6), and selective IgA deficiency (7). These increased levels of antigen may be responsible for stimulating systemic antibody formation in these conditions.
The liver has been documented to remove soluble proteins, aggregated proteins, and antigen-antibody complexes from the circulation (8-10). Stokes et al. (11) recently found that the rate of clearance of circulating antigen increased after infusion of an IgA antibody directed against the antigen. The identification in the rat ~