(A) Representative IF images of IDO1, Chlamydia MOMP, and nuclei costaining on PC sections from age-matched (11–12 weeks) CONV Tnf^ΔARE/+ mice treated with doxycycline or vehicle. N = 4 mice per condition. Scale bars: 100 μm. (B) Representative IF images as in A of PC sections from age-matched (16–20 weeks) SPF-B Tnf^ΔARE/+ mice that are sham or CM001-GFP inoculated. N = 5 mice per condition. Scale bars: 200 μm. (C) Experimental paradigm for secretory cell ablation in Tnf^ΔARE/+ mice. (D) Representative H&E-stained PC sections, with insets, from age-matched (20–27 weeks) Tnf^ΔARE/+ mice with (N = 3) or without (N = 5) secretory cell ablation. Scale bars: 200 μm. (E) Representative IF images as in A of PC sections from age-matched Tnf^ΔARE/+ mice in D with or without secretory cell ablation. Scale bars: 100 μm. (F) Colitis scores from histopathological scoring of colons from D. (G) Colitis subscores that contribute to overall colitis score in F. (H) Ratio of kynurenine to tryptophan, measured by liquid chromatography–mass spectrometry, in PC tissue from age-matched mice. N = 4 per condition. (I) Experimental paradigm for administration of tryptophan-deficient diet to Tnf^ΔARE/+ mice from the CONV facility. (J) Representative H&E-stained PC sections from age-matched (11–12 weeks) CONV Tnf^ΔARE/+ mice fed a control diet (N = 7) or a tryptophan-deficient diet (N = 5). Scale bars: 200 μm. (K and L) Histopathological scoring analysis as in F and G of colons from J. (M) Representative IF images as in A of PC sections from age-matched Tnf^ΔARE/+ mice in J fed a control or tryptophan-deficient diet. Scale bars: 100 μm. Data are shown as the mean ± SEM in quantifications. Statistical significance was determined using an unpaired 2-tailed t test (F and K), multiple unpaired 2-tailed t tests with FDR of 1% (G and L), or an ordinary 1-way ANOVA with Šidák’s multiple-comparison test (H). *P < 0.05, **P < 0.01, ****P < 0.0001. See also Supplemental Figures 7 and 8.