Rapid active transport of immunoglobulin A from blood to bile

Immunoglobulins were isolated from the serum or ascitic fluid of Lou/Wsl rats bearing plasmacytomas and labeled with 125I. When labeled IgA was injected i.v. it disappeared from the blood serum much more rapidly than IgG2 so that after 3 h less than 10% remained. This rapid disappearance of the injected IgA was not seen in rats with ligated bile ducts. In rats with cannulated bile ducts, the labeled IgA appeared rapidly in the bile so that 25% of the injected dose was recovered in 3 h; at the peak of this biliary excretion the specific radioactivity of the bile (cpm/milligram protein) was about 200 times greater than that of the blood serum. Thus much of the IgA which finds its way into the blood is rapidly and actively transported across the liver so that it enters the gut lumen via the biliary tract.