Cellular immunity in enteric disease

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Abstract
The dynamics of the infection process in normal C57BL mice following intragastric inoculation with sublethal doses of Salmonella enteritidis were followed over the first 3 days of the infection. More than 90% of the inoculum was eliminated during the first 6 hours of the infection but by this time, small numbers of Salmonellae had appeared in the ileal Peyer’s patches. No evidence was observed of infection in the Peyer’s patches of the duodenum or the colon. The infection quickly spread to the draining mesenteric lymph node, the liver, and the spleen. Mice vaccinated with sublethal doses of living S. enteritidis Se 795, given either intravenously or intragastrically were fully protected against a subsequent challenge with S. enteritidis SMR. On the other hand, living S. pullorum vaccines failed to protect the host, regardless of the route of vaccination or challenge. Heat-killed S. enteritidis vaccine showed minimal protective ability when given orally but far higher levelsof resistance were achieved when the vaccine was suspended in Freund’s complete adjuvant and injected subcutaneously. Suspension in incomplete adjuvant was not as effective, despite the enhanced humoral responses seen in the mice. Heat-killed S. enteritidis and S. pullorum, when given as 2 doses of 200 µg of cells in Freund’s complete adjuvant, were protective against an oral challenge with virulent S. enteritidis. Immune responses to decreasing doses of the two organisms indicated that quantitative differences existed in the amount of sensitizing antigens in the two strains. The significance of these findings is discussed in relation to the mechanism of acquired resistance to enteric disease.