FIG. 7.

Neonatal mice deficient in CD4⁺ cells (CD4^−/−) and IFN-γ (IFN-γ^−/−) are more susceptible to orogastric infection, while the absence of B cells only modestly increases their susceptibility to Y. enterocolitica. (A and B) Wild-type C57BL/6 and μMT neonates and adults were infected orogastrically with 1 × 10⁷ CFU of Y. enterocolitica. The percent survival from three experiments for each age group is depicted with a connecting line (n = 2 to 6 neonates and n = 3 to 6 adults of each strain per experiment). Differences between groups were analyzed by an unpaired t test. n.s., not significant. (B) The data in panel A were used to generate survival curves for neonates (10 wild-type and 13 μMT mice) and adults (11 wild type and 18 μMT mice). Survival curves were analyzed by the Mantel-Haenszel log rank test. n.s., not significant. (C) Wild-type C57BL/6 and CD4^−/− neonatal and adult mice were infected orogastrically with 1 × 10⁷ CFU of Y. enterocolitica (left) or 1 × 10⁸ CFU of Y. enterocolitica (right). The percent survival from three experiments is connected with a line. Differences between groups were analyzed by an unpaired t test. *, P = 0.04. (D) The data shown in panel C were pooled for neonates (17 wild-type and 14 CD4^−/− mice) and adults (15 wild-type and 20 CD4^−/− mice) and analyzed by the Mantel-Haenszel log rank test. n.s., not significant; **, P = 0.0052. (E) Neonatal and adult C57BL/6 (wild type)and IFN-γ^−/− mice were infected orogastrically with 1.4 × 10⁷ CFU of Y. enterocolitica. Survival was recorded from two experiments with 7 wild-type and 16 IFN-γ^−/− neonates and 11 wild-type and 13 IFN-γ^−/− mice adults. (F) Adult mice were also infected with 3 × 10⁸ CFU of Y. enterocolitica, and survival curves were generated from 10 wild-type and 13 IFN-γ^−/− mice. Data were analyzed by the Mantel-Haenszel log rank test. n.s., not significant; **, P = 0.0014; ***, P = 0.0005.