The initial suppression of bacterial growth in a salmonella infection is mediated by a localized rather than a systemic response.

Mice were infected intravenously with two antibiotic resistance tagged variants of the same S. typhimurium strain given in close succession, or simultaneously with strains of different virulence. The first manifestation of acquired resistance--suppression of exponential bacterial growth in liver and spleen--occurred independently for the different strains in the same individuals, implying that it is due to localized rather than systemic events. This early suppression of bacterial growth was ablated by whole body X-irradiation (800R), whereas the immediately preceding phase of exponential growth (Ity controlled innate resistance) was not affected. Transfer of spleen cell suspensions from infected mice into syngeneic recipients conferred protection by suppressing the growth of an intravenous challenge. Pre-treatment of the suspensions to deplete them of macrophages abolished their protective capacity, while depletion of T-cells did not. Mice deficient in T-cells by adult thymectomy and anti-T-cell monoclonal antibody treatment were able to suppress the growth of an intravenous challenge. Taken collectively, the present data show that the very early phase of acquired resistance to salmonellae, essential for survival, is not the result of systemically developing resistance but a localized event at the site of infection.