IgA antibodies in the bile of rats. V. Primacy of the GALT as a source of IgA.

In each of a series of rats the common bile duct and the thoracic duct (cisterna chyli) were cannulated so that both bile and thoracic duct lymph could be collected quantitatively for several hours. The concentrations of IgA in samples of lymph and bile were measured by radioimmunoassay so that the output of IgA per unit time could be calculated. Although the output of IgA in the lymph did not decline significantly, the output in the bile fell so that by 2 hr it had been reduced to less than 20% of the peak value. Similar experiments in rats which had been immunized actively by injecting antigens into the GALT showed a corresponding rapid decline in titres of specific biliary antibodies after fistulation of the thoracic duct. The low levels of IgA in the bile of rats that had been drained of thoracic duct lymph were restored quickly to normal values by the intravenous infusion of a volume of thoracic duct lymph equal to that which had been lost; this restoration was transient, and the concentration of IgA in the bile soon declined again after the infusion ceased.