Generation of gamma interferon responses in murine Peyer's patches following oral immunization.

To date, oral immunizations have been shown to generate only Th2 responses in murine Peyer's patches (PP), raising the possibility that T cells present in PP may be capable of mounting only Th2 responses or that the microenvironment of PP does not favor the generation of Th1 cells. However, it is also possible that antigens that can generate Th1 responses have not yet been used for oral immunizations. This study shows that T cells in PP of mice immunized orally with live Salmonella typhimurium secrete large amounts of gamma interferon (IFN-gamma) when they are stimulated with bacterial sonicate in vitro. Moreover, oral challenge of mice with live bacteria 4 months after immunization elicits a secondary IFN-gamma response in PP and mesenteric lymph nodes. Parenteral immunization does not generate an IFN-gamma T-cell response in PP, and parenteral challenge of orally immunized mice does not elicit a secondary response in PP. However, oral challenge of intraperitoneally immunized mice elicits a secondary IFN-gamma response in PP and mesenteric lymph nodes, and intraperitoneal challenge of orally immunized mice elicits a secondary response in the spleen. The data suggest that memory T cells recirculate between mucosal and nonmucosal compartments and that they may be recruited to the site of antigenic challenge.