IgA antibodies in the bile of rats. I. Some characteristics of the primary response.

About a week after suspensions of sheep red blood cells (SRBC) or killed Brucella abortus organisms were injected into the Peyer's patches of Wistar rats specific agglutinins of the IgA class appeared in the bile of titres which equalled or exceeded those of the IgG and IgM agglutinins in the blood serum. The injection of these antigens by conventional routes was relatively ineffective in inducing biliary antibodies. The relationship between the dose of B. abortus injected into the Peyer's patches and ensuing humoral response in the bile was investigated; a single dose of 5x10(5) organisms caused no detectable biliary response, while a dose of 10(9) organisms caused a substantial response in which specific antibodies persisted in the bile for several months, even though immunogenic material could not be recovered from the injection sites (the Peyer's patches) after a few weeks. A haemolytic plaque assay showed that many antibody-forming cells occurred in the mesenteric nodes and that up to half of them were synthesizing IgA. Few antibody-forming cells were found in Peyer's patches, and although some IgA-forming cells were found in the spleen they were less numerous, both in absolute terms and relative to cells producing other isotypes, than in the mesenteric nodes. The active production of biliary antibody was transferred to unimmunized recipients by thoracic duct lymph cells collected a few days after immunization of the donors when their lymph contained an increased percentage of immunoblasts. Athymic (nude) rats produced normal amounts of specific, biliary, IgA antibodies after immunization in the Peyer's patches with B. abortus but made no detectable response to similar injections of SRBC.