(A and B) Susceptibility to infection with 1 × 10⁹ CFU of C. rodentium in FcRn^–/– BALB/c mice. (A) Body weight changes in FcRn^–/– and FcRn^+/– mice with C. rodentium infection. (B) CFU of C. rodentium in feces of FcRn^–/– and FcRn^+/– mice 21 days after infection. Mean ± SD are shown for each group (n = 6). (C–E) Susceptibility to infection with C. rodentium in FcRn^–/– C57BL/6 mice. Survival rate (C) and body weight changes (D) in FcRn^–/– and FcRn^+/– mice with C. rodentium infection. (E) CFU of C. rodentium in feces of FcRn^–/– and FcRn^–/+ mice 21 days after infection. Mean ± SD are shown for each group (n = 8). (F) Immunohistochemical analysis of the colon to detect intimin in mice with C. rodentium infection. Colonic tissues were collected at day 7 from selected mice on a C57BL/6 background. Sections were stained for intimin using a polyclonal rabbit anti–C. rodentium intimin antibody (red) and nuclei (blue) and were examined by confocal microscopy. Magnification, ×400. Macroscopic findings (G) and the length of colon (H) in FcRn^–/– and FcRn^+/– C57BL/6 mice, uninfected or infected with C. rodentium, at 21 days after infection. (I) Histological findings of colon in FcRn^–/– and littermate FcRn^+/– C57BL/6 mice with or without C. rodentium infection (21 days after infection). Magnification, ×100. (J) Histological score of colonic tissue in the mice with or without C. rodentium infection at day 21. *P < 0.05.