Microbial colonization drives expansion of IL-1 receptor 1-expressing and IL-17-producing gamma/delta T cells

Abstract

IL-17 cytokine production by the Th17 T cell subset is regulated by intestinal commmensals. We show that microbial colonization also regulates innate IL-17 production. A population of CD62L(-) gamma/delta T cells, in particular a lineage expressing the IL-1 receptor 1 (IL-1R1), can be quickly activated by microbes to produce IL-17. Antibiotic treatment and monocolonization of mice suggest that specific commensals-but not metronidazole-sensitive anaerobes like Bacteroides species-are required for maintaining IL-1R1(+) gamma/delta T cells. Signaling through the guanine nucleotide exchange factor VAV1, but not through Toll-like receptors or antigen presentation pathways, is essential for inducing IL-1R1(+) gamma/delta T cells. Furthermore, IL-1R1(+) gamma/delta T cells are a potential source of IL-17 that can be activated by IL-23 and IL-1 in both infectious and noninfectious settings in vitro and in vivo. Thus, commensals orchestrate the expansion of phenotypically distinct gammadelta T cells, and innate immunity is a three-way interaction between host, pathogens, and microbiota.

Figure 1. Microbial colonization is a key driving force in the expansion of CD62L⁻ and IL-1R1⁺ γ/δ T cells

Cells from the peritoneum (A and B), lung, and small-intestinal lamina propria (iLP) (D and E) of individual SPF mice (Swiss Webster), GF mice, GFC1 mice (GF mice reconstituted with complex flora for 7 weeks, and GFC2 mice (GF mice reconstituted with complex flora for 12 weeks) were analyzed by FACS after staining with mAbs to CD3ε, γ/δ TCR, and CD62L (or IL-1R1) as well as isotype controls. (C and F) Cells from the peritoneum and iLP of individual mice, as indicated, were cultured with medium only or with medium containing rIL-1β and rIL-23 (1 ng/mL) for 7 h. Percentages of CD62L⁻ (or IL-1R1⁺ or IL-17⁺) γ/δ T cells are shown as mean ± SEM values. Each data point represents an individual mouse, and all collected data pooled from at least five independent experiments are shown. ○ (open dots) refer to data from SPF and GF mice at 7 weeks age; ● (closed dots) refer to data from SPF and GF mice at ~12 weeks age.

Figure 2. Effects of different antibiotic treatments on IL-1R1⁺ γ/δ T cell population

From birth onward, Swiss Webster mice received water containing no drugs (CTRL, SPF mice), metronidazole (METRO), neomycin sulfate (NEO), or vancomycin hydrochloride (VANCO), as described in Experimental Procedures. (A) Gram's staining of cecal contents from SPF mice and antibiotic-treated mice; (B) Cells from the peritoneum and small-intestinal lamina propria (iLP) of individual mice were analyzed by FACS after staining with mAbs to CD3ε, γ/δ TCR, and IL-1R1. (C) Cells from the peritoneum and iLP from individual mice were cultured with medium only or with rIL-1β and rIL-23 (1 ng/mL) for 7 h. Percentages of IL-1R1- and IL-17-expressing γ/δ T cells are shown as mean ± SEM values. Each data point represents an individual 6 weeks old mouse living in the same housing, and all collected data pooled from at least six independent experiments are shown.

Figure 3. Role of signalings through adaptive and innate pathways in IL-1R1⁺ γ/δ T cell expansion

IL-1R1 expression was measured by FACS on γ/δ T cells from the peritoneumof C57BL/6 (B6) and MyD88^−/− mice, B6129SF1/J and B6;129S1-Tlr3^tm1Flv/J (B6;129S1-Tlr3^−/−) mice (A); B6, MHCI^−/−, and MHCII^−/− mice (B); B6 and CD1^−/− mice (C); and B6 and VAV1^−/− mice (D). For VAV1^−/− mice and their controls, IL-1R1 expression on γ/δ T cells from cells from the lung and small-intestinal lamina propria (iLP) (D) was also analyzed. (E) Cells from the peritoneum and iLP from VAV1^−/− mice and their controls were cultured with medium only or with rIL-1β and rIL-23 (1 ng/mL) for 7 h. Each data point represents an individual mouse. Genetically deficient mice of each strain and their respective age-matched controls were housed in the same conditions before use.

Figure 4. IL-1 acts synergistically with IL-23 to promote IL-1R1-associated IL-17 production by CD44⁺CD62L⁻CD27⁻ γ/δ T cells in a p38-, PKC-, NF-kB-, and PI3K-dependent manner

(A and B) CD90.2⁺ cells (~1.5 × 10⁵/mL) from the peritoneum, lungs, and spleen of 6–8 WT mice (C57BL/6J) were cultured for 7 h with medium only or with medium containing rIL-1β alone (1 ng/mL), rIL-23 alone (1 ng/mL), or both rIL-1β and rIL-23 (1 ng/mL). (A) FACS plots gated on CD90.2⁺ cells are representative of four independent experiments, and the numbers in parentheses indicate the percentages of IL-17-producing γ/δ T cells. (B) Data from four experiments are combined as mean ± SEM values. ^*p > 0.1 and ^**p < 0.03 relative to medium alone. (C) A representative FACS plot demonstrating IL-1R1 expression on γ/δ T cells from 4 individual WT (C57BL/6J) or IL-1R1^−/− mice is shown. Numbers in quadrants refer to percentages of CD3ε⁺ cells. Numbers in parentheses indicate percentages of IL-1R1⁺ γ/δ T cells. (D) A representative FACS plot gated on TCRγ/δ⁺ from 4 individual mice indicates that IL-1R1-expressing γ/δ T cells are CD62L⁻. (E) Sorted IL-1R1⁺ and IL-1R1⁻ γ/δ T cells from the peritoneum (~1.5 × 10⁴/mL) or lungs (~5 × 10⁴/mL) of 6 WT mice were stimulated with rIL-1β and rIL-23 (1 ng/mL) for 24 h. The supernatants were analyzed for IL-17 concentrations by ELISA. (F) T cells from the peritoneum and lungs of 4–6 WT mice were cultured for 7 h with or without rIL-1β and rIL-23 (1 ng/mL). The FACS plots gated on TCRγ/δ⁺ represent one of three experiments. (G) γ/δ T cells were sorted from the peritoneum (~5 × 10⁴/mL) and lungs (~1 × 10⁵/mL) of 8–12 WT mice and were stimulated with rIL-1β and rIL-23 (1 ng/mL) in the absence (control) or presence (30-min pretreatment) of SB203580 (p38 inhibitor at 5 µM), rottlerin (PKC inhibitor at 10 µM), BAY 11-7082 (NF-κB inhibitor at 8 µM), or LY294002 (PI3K inhibitor at 40 µM). After 24 h, supernatants were collected for analysis of IL-17 concentrations by ELISA. ⁺p < 0.047 and ⁺⁺p < 0.011 relative to control. Results are mean ± SEM values from two independent experiments with similar results.

Figure 5. IL-1 signaling is required for optimal IL-17 production by γ/δ T cells in response to microbial products and microbes

(A and B) PECs (6×10⁶/mL) from WT mice were pretreated with Armenian hamster IgG or mAbs (10 µg/mL) to IL-1R1 for 30 min and subsequently stimulated with E. coli LPS (1 µg/mL) for 7 h. FACS plots (A) are gated on CD3ε⁺ cells. Numbers in parentheses, indicating percentages of IL-17-producing γ/δ T cells, are summarized as mean ± SEM values (B) from three independent experiments. (C) CFSE-labeled PECs from WT (or IL-1R1^−/−) mice were mixed (1:1) with unlabeled IL-1R1^−/− (or WT) PECs. The resulting PECs (4×10⁶/mL/tube) were incubated for 7 h with and without LPS (1 µg/mL). The FACS plots are gated on TCRγ/δ⁺ and represent one of three experiments. (D and E) Brefeldin A was injected intraperitoneally into WT mice (8–10 per group) and IL-1R1^−/− mice (5 or 6 per group) 2 h after ip infections with E. coli (ATCC 26, 1 × 10⁸ CFU/ mouse), B. fragilis NCTC 9343 (6 × 10⁸ CFU/mouse), or group B Streptococcus serotype Ia 515 (GBS, 1 × 10⁸ CFU/ mouse). After 5 h, PECs were tested for intracellular IL-17. FACS plots (D) are gated on CD3ε⁺ cells. Numbers in parentheses indicate percentages of IL-17-producing γ/δ T cells. All collected data pooled from individual mice are summarized as mean ± SEM values (E). (F) WT mice (6 per group) and IL-1R1^−/− mice (5 per group) were infected ip with E. coli (1 × 10⁸ CFU/mouse), B. fragilis NCTC 9343 (6 × 10⁸ CFU/ mouse), or GBS serotype Ia 515 (2 × 10⁷ CFU/mouse). After 24 h, IL-17 in peritoneal fluid was measured by ELISA. Data are representative of three independent experiments.

Figure 6. A proposed model for how the commensal microbiota facilitates IL-17-mediated protective immune responses of γ/δ T cells to pathogenic bacteria

Commensal bacteria and VAV1 signaling drive expansion of γ/δ T cells bearing IL-1R1 (a). In the setting of infection with potentially pathogenic microbes, macrophages and dendritic cells are stimulated to produce IL-1 and IL-23 (b), thus activating IL-1R1-bearing γ/δ T cells to produce IL-17 (c). IL-17 mediates a protective immune response to the pathogenic bacteria by recruiting neutrophils from blood vessels (d) to the site of infection (e).