Group 3 innate lymphoid cells inhibit T-cell-mediated intestinal inflammation through aryl hydrocarbon receptor signaling and regulation of microflora

Abstract

Aryl hydrocarbon receptor (Ahr) is crucial for the maintenance and function of group 3 innate lymphoid cells (ILCs), which are important in gut immunity. Because Ahr promotes T helper 17 (Th17) cell differentiation in vitro, it is reasonable to expect that Ahr would enhance Th17 cells in vivo. Instead, we show that Ahr deficiency caused increased intestinal Th17 cells, raising the possibility that group 3 ILCs could negatively regulate Th17 cells. Reduced innate interleukin-22 (IL-22) in Ahr-deficient mice allowed expansion of commensal segmented filamentous bacteria (SFB), known to promote Th17 cells. Compared to Rorc(+/+)Ahr(-/-) mice, Rorc(gfp/+)Ahr(-/-) mice had further reduced group 3 ILCs and were prone to spontaneous colitis with increased SFB and Th17 cells. Innate expression of Ahr played a protective role in T-cell-mediated experimental colitis by suppressing pathogenic Th17 cells. Our data reveal an intricate balance between ILCs and Th17 cells regulated by Ahr and commensal flora.

Figure 1. Th17 Cells Were Enhanced in the Small Intestine of Ahr-Deficient Mice

(A–C) Small-intestinal (“SI”) and large-intestinal (“LI”) LPLs were isolated from Ahr^−/− and littermate Ahr^+/+ mice. Cells were stimulated with PMA and ionomycin for 4 hr. Expression of IFN-γ, IL-17, and IL-22 in CD4⁺TCRβ⁺ cells was analyzed by flow cytometry, as shown in (A). Percentages of the indicated cell populations gated on CD4⁺TCRβ⁺ cells are shown in (B) and (C). (D) Peripheral-blood mononuclear cells from Ahr^−/− mice and Ahr^Ctrl (Ahr^+/+ or Ahr^+/−) littermate mice of the indicated ages were stimulated with PMA and ionomycin for 4 hr. Percentages of IL-17⁺ cells gated on CD4⁺TCRβ⁺ cells were analyzed by intracellular staining followed by flow cytometry. Data are representative of two independent experiments. Horizontal lines show the mean. Error bars represent the SEM. Statistical analyses were performed using Mann-Whitney paired U test. See also Figure S1.

Figure 2. Increased Th17 Cells in the Small Intestine of Ahr-Deficient Mice Was Dependent on RORγt

(A and B) Small-intestinal (“SI”) and large-intestinal (“LI”) LPLs were isolated from Ahr^−/− and littermate Ahr^+/+ mice. RORγt expression inCD4⁺TCRβ⁺ cells was analyzed by flow cytometry, as shown in (A). Percentages of RORγt⁺ cells gated on CD4⁺TCRβ⁺ cells are shown in (B). Data are representative of two independent experiments. Horizontal lines show the mean. Error bars represent the SEM. (C) Small-intestinal LPLs were isolated from Ahr^−/− (n = 3) or Rorc^gfp/gfpAhr^−/− (n = 6) littermate mice. Cells were stimulated with PMA and ionomycin for 4 hr. Expression of IL-17 and IL-22 in CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. Percentages of IL-17 and IL-22 gated on CD4⁺ TCRβ⁺ cells are shown. Data are representative of three independent experiments. Horizontal lines show the mean. Error bars represent the SEM.

Figure 3. Inhibitory Effect of IL-22 on SFB and Th17 Cells

(A) Ahr^−/− mice were treated with or without an antibiotic cocktail in drinking water for 10 days. Small-intestinal LPLs (“SI”) and splenocytes (“SP”) were isolated and stimulated with PMA and ionomycin for 4 hr. Expression of IL-17, IFN-γ, and IL-22 gated on CD4⁺TCRβ⁺ cells were analyzed by flow cytometry. Data are representative of two independent experiments. (B) Bacterial DNA from fecal pellets was extracted from cohoused Ahr^−/− (n = 4) or Ahr^+/+ (n = 4) littermate mice. The amount of the indicated bacteria species relative to universal bacteria was analyzed by real-time PCR with primers specific to 16S rRNA genes. Error bars represent the SEM. Data are representative of two independent experiments. (C) At day 0, Ahr^Ctrl (Ahr^+/+ or Ahr^+/−) mice (n = 3) were treated with PBS. Ahr^−/− mice were treated with PBS (n = 4) or IL-22-Ig (n = 4). Bacterial DNA was extracted from fecal pellets, and the amount of SFB relative to universal bacteria was analyzed at the indicated time points by real-time PCR using primers specific to 16S rRNA genes. Statistical analyses were performed with the Mann-Whitney U test. Horizontal lines show the mean. Error bars represent the SEM. (D) Small-intestinal LPLs were isolated on day 10 after IL-22-Ig injection and stimulated with PMA and ionomycin. Expression of IL-17 and IL-22 gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. (E–G) Wild-type mice were intraperitoneally injected with control IgG (n = 8) or IL-22-specific neutralizing antibody (n = 7) every 4 days. Bacterial DNA was extracted from fecal pellets (E) or contents of the small intestine (F) of the mice 10 days after treatment. The amount of SFB relative to universal bacteria was analyzed by real-time PCR using primers specific to 16S rRNA genes. Horizontal lines show the mean. Error bars represent the SEM. Small and large intestinal LPLs were isolated and stimulated with PMA and ionomycin (G). Expression of IL-17 and IL-22 gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. Data are representative of two independent experiments. See also Figure S2.

Figure 4. ILCs Inhibit SFB and Th17 Cells in the Gut

(A) Rag1^−/− mice were injected with control IgG (n = 4) or anti-Thy1.2 antibody (n = 3) every 3 days. Fecal DNA was extracted at day 7, and the amount of SFB relative to universal bacteria was analyzed by real-time PCR using primers specific to 16S rRNA genes. Horizontal lines show the mean. Error bars represent the SEM. (B and C) A total of 4 × 10⁵ CD4⁺CD25⁻CD45RB^hiThy1.1⁺ splenocytes were sorted by flow cytometry and transferred to Rag1^−/− mice. Mice were injected with control IgG or Thy1.2-specific neutralizing antibody on the same day of the transfer and then every 3 days after the transfer. Mice were sacrificed at day 10 after the adoptive T cell transfer. Small-intestinal LPLs were isolated and stimulated with PMA and ionomycin for 4 hr. Expression of IL-17 and IFN-γ gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry, as shown in (B). Percentages of IL-17⁺, IFN-γ⁺, and IL-22⁺ cells gated on CD4⁺TCRβ⁺ cells are shown in (C). Horizontal lines show the mean. Error bars represent the SEM. Data are representative of two independent experiments. See also Figure S3.

Figure 5. Rorc ^gfp/+Ahr^−/− Mice Developed Spontaneous Colitis

(A) Expression of RORγt in CD3⁻ cells was analyzed by flow cytometry. Numbers in red squares show the mean fluorescence intensity of RORγt. Data are representative of two independent experiments. “SSC” stands for side scatter. (B) Cells were incubated with brefeldin A for 2 hr. The expression of IL-22 gated on CD3⁻ cells was analyzed by flow cytometry. Data are representative of two independent experiments. (C) Paraffin-embedded colon sections were stained with hematoxylin and eosin (H&E). Magnification is 20×. (D) Large-intestinal LPLs were isolated and stimulated with PMA and ionomycin for 4 hr. Expression of IL-17 and IFN-γ gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. (E) Expression of CD11b and Gr-1 gated on live cells was analyzed by flow cytometry. (F) Percentages of CD11b⁺Gr-1⁺ neutrophils in live cells from the mice of the indicated genotypes are shown. Horizontal lines showthe mean. Error bars represent the SEM. Data are representative of three independent experiments. 28-day-old mice of the indicated genotypes (A and B) or 16-week-old Rorc^gfp/+Ahr^−/− and littermate Rorc^gfp/+Ahr^+/+ mice (C–F) were sacrificed. Large-intestinal LPLs were isolated from mice of the indicated genotypes in (D)–(F). See also Figure S4.

Figure 6. Exacerbated CD45RB^hi T-Cell-Induced Colitis in Rag1^−/−Ahr^−/− Mice

A total of 4 × 10⁵ CD4⁺CD25⁻CD45RB^hi splenocytes were sorted by flow cytometry and transferred to Rag1^−/−Ahr^−/− (n = 5) or Rag1^−/−Ahr^+/+ (n = 5) littermate mice. Mice in (C)–(F) were sacrificed at the end of the experiment. (A) Body weight was monitored at the indicated time points. Results are shown as mean percentage of body-weight change ± SEM. (B) Linear regression analysis of the body-weight change. Data are representative of four independent experiments. Horizontal lines show the mean. Error bars represent the SEM. (C) Representative colon histology of mice with the indicated genotypes is shown (H&E staining with original 10× magnification). (D) Colonic histology scores are shown. Horizontal lines show the mean. Error bars represent the SEM. (E and F) A total of 4 × 10⁵ CD4⁺CD25⁻ CD45RB^hi splenocytes were sorted by flow cytometry and transferred to Rag1^−/−Ahr^−/− mice. Mice were gavaged with 200 μl/day of broad-spectrum antibiotics (“abx”) (1 g/l ampicillin, 1 g/l neomycin, 1 g/l metronidazole, 0.5 g/l vancomycin, and 1 g/l gentamycin) or water. Representative colon histology of mice with the indicated groups (H&E staining with original 10× magnification) is shown in (E). Histology scores are shown in (F). Horizontal lines show the mean, error bars represent the SEM, and data are representative of two independent experiments. See also Figure S5.

Figure 7. Enhanced Proinflammatory Cytokine Production by T Cells without Innate Expression of Ahr

A total of 4 × 10⁵ CD4⁺CD25⁻ CD45RB^hi splenocytes were sorted by flow cytometry and transferred to Rag1^−/−Ahr^−/− (n = 5) or Rag1^−/−Ahr^+/+ (n = 5) littermate mice. (A) Large-intestinal LPLs were isolated and stimulated with PMA and ionomycin for 4 hr. Expression of IL-17 and IFN-γ gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. (B) Percentages of the indicated cell populations gated on CD4⁺TCRβ⁺ cells are shown. Horizontal lines show the mean. Error bars represent the SEM. Data are representative of two independent experiments. (C) Small-intestinal (SI) or large-intestinal (LI) LPLs were isolated and stimulated with PMA and ionomycin for 4 hr. Expression of GM-CSF gated on CD4⁺TCRβ⁺ cells was analyzed by flow cytometry. “SSC” stands for side scatter. (D) Percentages of GM-CSF gated on CD4⁺TCRβ⁺ cells are shown. Horizontal lines show the mean. Error bars represent the SEM. Data are representative of three independent experiments.