Elimination of intestinally absorbed antigen into the bile by IgA

Polymeric serum IgA has been shown to transport antigens in the form of IgA immune complexes from the circulation into the bile. To test the hypothesis that this mechanism could aid in the clearance of intestinally absorbed antigens, mice were gastrically intubated with trinitrophenylated human serum albumin (TNP-HSA). After 3 hr, two groups were injected i.v. with either MOPC 315 (IgA, anti-TNP) or control ascitic fluid. One hour later, blood and bile samples were taken. Small amounts of antigen (0.0008% of the intubated dose) were detected in the serum of control animals by solid phase radioimmunoassay. In animals receiving anti-TNP IgA, serum levels were decreased significantly and intact antigen appeared in the bile, whereas no antigen was detectable in the bile of control mice. These results suggest that IgA-mediated hepatobiliary transport can function as one of the mechanisms for the elimination of intestinally absorbed antigens.