(A) Colon from B6 mice left uninfected or infected with C. rodentium for 2 weeks was immunostained with anti-GM-CSF antibody. Infected mice manifest marked colonic crypt hyperplasia. Original magnification, x 100. (B) GM-CSF in colon tissue was determined by ELISA at the indicated times after infection. Data are mean ± SEM (n = 5 mice at each time point). ND = none detected. *; p < 0.05 vs. uninfected control. (C). Top row. Colon from B6 mice infected with C. rodentium for 2 weeks was immunostained for GM-CSF (left panel, red) and CD11c (middle panel, green). Right panel is a merged image of the left and middle panels and also includes nuclear staining. Bottom row. Colon was stained for GM-CSF (left panel, red) and F4/80 (middle panel, green). Right panel is a merged image including nuclear staining. Merged images were created using Adobe Photoshop software. Arrows indicate GM-CSF producing cells. Original magnification, x 400.

(A) CD11c⁺ cells in the colon of B6 and GM-CSF^-/- mice infected for 2 weeks with C. rodentium or left uninfected. CD11c⁺ cells are shown in red and phalloidin staining of F-actin is in green. Arrows indicate CD11c⁺ cells underlying surface epithelial cells. Original magnification, x 200. Similar results were obtained from 3 week-infected mice. (B) Flow cytometric analysis of cells isolated from the colon lamina propria of B6 and GM-CSF^-/- mice 2 weeks after infection or left uninfected. Cells were stained with PE-conjugated CD11c and FITC-conjugated I-A^b. Results of a representative experiment are shown. Similar results were obtained in 3 repeated experiments. (C) Flow cytometric analysis of CD11c⁺ DCs isolated from the colon of B6 and GM-CSF^-/- mice infected for 2 weeks. DCs were stained with PE-conjugated CD103 and FITC-conjugated CD11b. Results of a representative experiment are shown. Similar results were obtained in 2 repeated experiments. (D) DCs were isolated from 2 week infected colon as in (C) and surface marker expression of the activation markers CD40, CD80, CD86 and the expression of the chemokine receptors CCR6 and CCR7 on DCs was assessed by flow cytometry. (E) Spleen and MLN cells from B6 and GM-CSF^-/- mice obtained 2 weeks after infection were characterized as in (B). (F,G) C. rodentium-infected colon from B6 and GM-CSF^-/- mice was stained 2 weeks after infection for F4/80 (red, F) and Gr-1 (red, G). F-actin was stained with Alexa-Fluoro 488 phalloidin (green). Original magnification, x 200.

(A) H&E staining of the colon from 2 week-infected B6 and B6 DTR-BM chimera mice treated with DT. Original magnification, x 100. Scale bar is 200 μm. (B) MPO in colon tissue from 2 week infected mice treated with DT was quantified by ELISA. Data are mean ± SEM (n = 10). (C) Fecal CFU of C. rodentium were determined at 1 and 2 weeks after oral gavage of 5 × 10⁸ C. rodentium to B6 and B6 DTR-BM chimera mice treated with DT. Data are mean ± SEM (n = 9 mice per group). (D) C. rodentium CFU in the spleens of DT treated mice were determined 2 weeks after infection. Data are shown from individual mice. Bar represents the geometric mean (n = 9). Dotted line indicates the detection limit of the CFU assay. (E) Serum anti-C. rodentium IgG at the indicated times after infection with C. rodentium in B6 and B6 DTR-BM chimera mice treated with DT was determined by ELISA. Data are mean ± SEM (n = 5-10 mice for each group at each time point). * p < 0.05 relative to B6 mice.

(A) mRNA transcripts for the three DC chemoattractant chemokines, CCL22, CCL8 and CCL20, were assayed by real time RT-PCR in the colon of B6 and GM-CSF^-/- mice left uninfected or infected with C. rodentium (n = 4-5 mice per group at each time point). (B) CCL22 protein was assayed in colon extracts from B6 and GM-CSF^-/- mice. Data are mean ± SEM (n = 5 mice per group at each time point). For (A, B) * p < 0.05 relative to B6 mice at the indicated time points. (C) Colon sections from B6 mice left uninfected and B6 and GM-CSF^-/- mice infected for 3 weeks with C. rodentium were stained for CCL22 (red). Original magnification, x 200. (D) Colon sections from B6 mice infected for 3 weeks were stained for CCL22 (red) and β-catenin (green) as an epithelial cell marker. Nuclei were stained with Hoechst 33258 (blue). Specificity controls using control antibody or anti-CCL22 absorbed with CCL22 peptide showed no immunostaining (see Fig. S3). (E) Colon sections from B6 mice infected for 3 weeks were stained for CCL22 (red) and CD11c (green). Original magnification, x 400. (F) WT B6 mice were infected with C. rodentium for 2 weeks. On days 9, 11 and 13 after infection mice were injected i.p. with 20 μg IgG goat anti-CCL22 or control goat IgG.. Colon sections from anti-CCL22 and control goat IgG treated mice were stained for CD11c (red) and F-actin (green). Original magnification, x 200. (G) Cells isolated from colon lamina propria, spleen, and MLN of anti-CCL22 and control goat IgG treated mice were characterized by flow cytometry. Similar results were obtained in 2 independent experiments.

(A) One week after C. rodentium infection, colon sections from B6 and GM-CSF^-/- mice were co-stained for C. rodentium (red) and F-actin (green). Co-localization of C. rodentium and F-actin is shown in yellow. Original magnification, x 100. (B) Fecal counts (CFU) of C. rodentium were determined at the indicated times after oral gavage of 5 × 10⁸ C. rodentium to B6 and GM-CSF^-/- mice. Data are mean ± SEM of 3 independent experiments (n = 10-17 mice for each data point). Dotted line indicates detection limit of the CFU assay. (C) C. rodentium in spleen and MLN of B6 and GM-CSF^-/- mice were determined 2 weeks after infection. Data are shown as CFU from individual mice and bars represent the geometric means (n = 15-16). Dotted line indicates the detection limit of the CFU assay. (D) IgG and IgM serum antibodies to C. rodentium in B6 and GM-CSF^-/- mice were assayed by ELISA at the indicated times after infection. Data are mean ± SEM of optical density (n = 10-15 mice time point). (E) B6 and GM-CSF^-/- mice were left uninfected or infected with C. rodentium for up to 4 weeks. Sections of colon obtained at the indicated times were stained with H&E. Original magnification, x 100. Scale bar is 200 μm. (F) Colonic crypt depth in C. rodentium infected B6 and GM-CSF^-/- mice was assessed at the indicated times after infection. Data are mean ± SEM (n = 5-10 mice per group at each time point). (G) MPO in colon tissue was assayed by ELISA. Data are mean ± SEM (n = 5-10 mice per group at each time point). (H) TNFα, KC and MIP-2α mRNA transcripts in colon tissue of B6 and GM-CSF^-/- mice were assayed by real time RT-PCR (n = 4-5 mice per group at each time point). * p < 0.05 relative to B6 mice at indicated time points.

(A) GM-CSF^-/- mice infected with 5 × 10⁸ C. rodentium were injected with PBS or GM-CSF (5 μg/mouse) i.p. daily for 2 weeks, after which lamina propria cells from the colon were isolated and analyzed by flow cytometry as in Fig. 2B. Similar results were obtained in 2 repeated experiments. (B) IgG antibodies to C. rodentium from PBS or GM-CSF-treated C. rodentium-infected GM-CSF^-/- mice were assayed by ELISA. Data are mean ± SEM (n = 12 mice per group). (C) C. rodentium in the spleen and MLN of PBS or GM-CSF treated GM-CSF^-/- mice were determined by CFU assay 2 weeks after infection as in Fig. 2. Data are shown as CFU from individual mice (n =11) and the bar indicates the geometric mean. Dotted line indicates the detection limit of the CFU assay. * p < 0.05 relative to PBS-treated mice at the indicated time points.

(A) BrdU staining (red) in colon sections of C. rodentium-infected (2 weeks) B6 and GM-CSF^-/- mice. Nuclei were stained with Hoechst 33258 (blue). Original magnification, x 200. (B) TUNEL staining (green, examples of apoptotic cells shown by arrows) of colon sections from 2 week-infected B6 and GM-CSF^-/- mice. F-actin (red) was stained with Alexa-Fluoro 568-conjugated phalloidin. Original magnification, x 200. (C) Colon sections from 2 week-infected GM-CSF^-/- mice. TUNEL staining (green), F-actin staining (red), nuclear staining (blue, Hoechst 33258 dye) and merged image. Arrows indicate TUNEL-positive cells in the lamina propria and arrowheads indicate TUNEL-positive epithelial cells, respectively. Original magnification, x 200 (D) Colon sections from 2 week-infected GM-CSF^-/- mice. TUNEL staining (green) and CD11c staining (red). Merged image and magnified image of the inset (right panel) are also shown. Arrows indicate TUNEL and CD11c double positive cells. Original magnification x 200. (E) TUNEL staining of CD11c⁺ DCs isolated from the colon of 2 week-infected B6 and GM-CSF^-/- mice. The percentage of TUNEL-positive cells in 3 different 400 x visual fields of each cytospin slide was calculated and is shown as mean ± SD. Results of a representative experiment are shown. Similar results were obtained in 2 repeated experiments. *p<0.05 relative to B6 mice.