“…In contrast, orally inoculated mice had only a short persistence of vaccine organisms, which might be not sufficient to stimulate antibody responses in the lungs, and this likely accounted partially for the poor antibody responses against the heterologous antigen in this local tissue. The stronger persistence of vaccine organisms in the Peyer's patches may result from the environment, which is less hostile than that in either the lungs or the spleen of mice based on tissue specificity (13). Simultaneously, large numbers of organisms were isolated from the lungs, spleen, and Peyer's patches of mice following s.c. inoculation, suggesting that the s.c. inoculum may establish a reservoir in the lymph nodes, where Salmonella readily spreads throughout the body via the lymph stream and becomes systemic (5,35), finally reaching the lungs and other tissues for the generation of systemic and local immune responses.…”