Citrobacter rodentium Infection in Mice Elicits a Mucosal Th1 Cytokine Response and Lesions Similar to Those in Murine Inflammatory Bowel Disease

Bacteria were visualized on the epithelial surface (a) and in the mucosa and submucosa (b) of C. rodentium-infected Swiss NIH mice. The clear area between the muscularis mucosa and the external muscle layer is the submucosa, which becomes edematous duringCitrobacter infection. The arrows indicate bacteria. Immunoperoxidase immunohistochemistry was performed with anti-intimin antibody. Magnification, ×400.

Mean cell counts for peroxidase-containing cells in the mucosa and submucosa (A) and for CD3⁺ (B), CD4⁺(C), and CD8⁺ (D) cells infiltrating the lamina propria of Swiss NIH mice were determined on days 2, 6, and 12 postinfection. In addition to the massive increase in numbers of CD3⁺ and CD4⁺ cells in the mucosa of C. rodentium-infected mice, there was also a slight increase in numbers of these cells in control mice. This probably reflected the increase which is seen in normal mice around this time (21). Closed bars represent mice infected with an intimin mutant strain; open bars represent mice infected with wild-type C. rodentium. Error bars indicate standard errors. Each group contained five mice. ∗, P < 0.05).

Immunoperoxidase immunohistochemistry of colon tissue of infected Swiss NIH mice. (a and b) CD4⁺ cells in mice infected with an intimin mutant strain (a) or wild-type C. rodentium (b). In colon tissues of control mice, only a few CD4⁺ cells are visible in the lamina propria (arrows). InCitrobacter-infected mice, there is a massive accumulation of CD4⁺ cells at the crypt bases and in the lamina propria (arrows). (c and d) MHC class II-positive cells in the lamina propria of intimin-mutant-infected mice (c) and wild-type-C. rodentium-infected mice (d). In control mice, MHC class II-positive cells can be seen in the lamina propria, and the surface epithelium is also positive (arrows). InCitrobacter-infected mice, every surface and crypt epithelial cell is strongly class II positive, as are all cells in the lamina propria. Serial sections stained with control antibodies showed only a few cells expressing endogenous peroxidase in the mucosa, although these cells were more abundant in the submucosa (see Fig. 3A). Original magnification, ×100.

Quantitation of intraepithelial cells. Counts are expressed as the number of positive intraepithelial lymphocytes per 100 epithelial cells. Each group contained five Swiss NIH mice. Closed bars represent mice infected with the intimin mutant strain; open bars represent mice infected with wild-type C. rodentium. Values are means ± standard errors. (A) CD3⁺ cells; (B) CD4⁺ cells; (C) CD8⁺ cells. ∗, P < 0.05.

Cytokine and KGF mRNA transcripts in distal colonic tissue as measured by RT-PCR on days 6 and 12 postinfection. Closed bars represent mice infected with the intimin mutant strain; open bars represent mice infected with wild-type C. rodentium. Each group contained five Swiss NIH mice. Values are means ± standard errors. (A) IL-1; (B) TNF-α; (C) IL-12; (D) IFN-γ; (E) IL-4; (F) KGF. ∗, P < 0.05.