IgA antibodies in the bile of rats. II. Evidence for immunological memory in secretory immunity.

The Peyer's patches of Wistar rats were injected with suspensions of either sheep red blood cells (SRBC) or killed Brucella abortus organisms in doses that were insufficient to induce the appearance of biliary antibodies. The rats were challenged after periods ranging from 1 week to 1 year with the same dose of antigen given by the same route, and their bile was monitored for the appearance of specific antibodies. The test animals produced biliary antibodies to a much higher titre, and usually more rapidly, than control rats which had received the total dose of antigen as a single injection. As in primary responses, the biliary antibodies produced by challenging the primed rats were predominantly from the IgA class. The ability to mount substantial biliary responses to suboptimal doses of antigen could be transferred from primed donor rats to unimmunized recipients by thoracic duct lymphocytes, but not humoral factors, collected between 3 weeks and 5 months after priming. Gamma-irradiation of the lymphocytes abolished this effect. These results suggest strongly that immunological memory exists in the IgA system and that it is mediated by circulating lymphocytes.