Interleukin-17C promotes Th17 cell responses and autoimmune disease via interleukin-17 receptor E

Abstract

Although several interleukin-17 (IL-17) family members and their receptors have been recently appreciated as important regulators in inflammatory diseases, the function of other IL-17 cytokines and IL-17 receptor-like molecules is unclear. Here we show that an IL-17 cytokine family member, IL-17C, was induced in a Th17 cell-dependent autoimmune disease and was required for its pathogenesis. IL-17C bound to IL-17RE, a member of IL-17 receptor family whose full-length isoform was selectively expressed in Th17 cells and signaled via an IL-17RA-RE receptor complex and the downstream adaptor Act1. IL-17C-IL-17RE induced the expression of a nuclear IkappaB family member, IκBζ, in Th17 cells to potentiate the Th17 cell response. Thus, our work has identified a cytokine-receptor pair with important function in regulating proinflammatory responses. This pathway may be targeted to treat autoimmune diseases.

Figure 1. IL-17C Is Necessary for Full Development of EAE

(A) EAE was induced in WT and Il17c^−/− animals. Bottom graph y axis indicates ratios of animals developing EAE. Data are representative of four independent experiments.*p < 0.05 (Student’s t test). (B) Total infiltrating CNS cell counts and percentages of infiltrating CD4⁺, CD11b⁺, IL-17A⁺, and IFN-γ⁺ cells. (C) Representative CNS intracellular cytokine staining of WT and Il17c^−/− mice after 5 hr PMA plus ionomycin restimulation. (D) mRNA was analyzed in the CNS tissues of three individual mice per group on day 14 after EAE initiation by real-time RT-PCR. Gene expression data were normalized to actin (Actb). (E) Splenic intracellular cytokine staining. Splenocytes derived from each group were restimulated with or without MOG35-55 peptide and intracellular cytokine staining was conducted and analyzed in CD4⁺ gate. See also Figure S1.

Figure 2. IL-17C Binds to IL-17RE In Vitro

(A) Binding of IL-17C-Ig to IL-17RE. 293T cells were transfected with empty or IL-17RE expression vector (pcDNA3) and subsequently stained with IL-17C-hIg, followed by anti-hIg APC. (B) IL-17C-hIg binds to IL-17RE but not to other IL-17R family. 293T cells were transfected with empty or IL-17R family expression vector (pcDNA3). Staining with IL-17C-hIg was performed same as (A). See also Figure S2.

Figure 3. IL-17RE Is Highly Expressed in Th17 Cells

(A) Real-time RT-PCR of Il17re mRNA expression in sorted naive, nTreg, and activated CD4⁺ T cells differentiated under Th1, Th2, Th17, and iTreg cell conditions. Fold induction was calculated with naive cells as control and normalizing to β-actin (Actb) expression. The data are expressed as the mean ± SD of triplicate samples. (B) Real-time RT-PCR analysis of Il17re expression in CD4⁺ T cells from WT, Stat3^−/−, Rorc^−/−, and Rora^sg/sg mice. Naive CD4⁺ T cells from each strain were differentiated under Th17 cell conditions for 4 days. (C) Real-time RT-PCR analysis of Il17re mRNA expression in T cells activated with the indicated cytokines for 4 days. (D) RT-PCR analysis of Il17re in T cells activated with the indicated cytokines. The PCR products are amplified with forward primer before the transmembrane domain and reverse primer at the end of the coding sequence. Data shown are representative of at least three independent experiments. See also Figure S3.

Figure 4. IL-17C-IL-17RE Regulates Th17 Cell Differentiation

(A) Intracellular cytokine staining of IL-17A and IFN-γ. After naive CD4⁺ T cells were retrovirally transduced with control viral vector or IL-17RE, different IL-17 family cytokines were added during Th17 cell differentiation. The cells were restimulated with PMA and ionomycin for cytokine staining. (B) Statistical analysis of IL-17A-positive cells. (C) IL-17C induced IL-17A expression in Th17 cells over-expressing IL-17RE but not other IL-17R family members. CD4⁺ T cells were retrovirally transduced with each IL-17R-IRES-GFP and were cultured with IL-17C in Th17 cell polarizing condition. Cells were restimulated with PMA and ionomycin and GFP-positive cells were gated to show expression of IL-17A and IFN-γ. (D) Intracellular cytokine staining of WT and Il17ra^−/− T cells retrovirally transduced with IL-17RE and cultured with IL-17C for 2 days, followed by 5 hr of PMA and ionomycin. Data shown are gated GFP⁺ cells. Data shown are representative of at least three experiments. (E) Coimmunoprecipitation of IL-17RA with HA-tagged IL-17RE. 293T cells were transfected with IL-17RA or HA-tagged IL-17RE or both and immunoprecipitated with anti-HA. (F) Intracellular cytokine staining of WT and Act1^−/− T cells retrovirally transduced with IL-17RE or control viral vector (RV-GFP) and followed by 5 hr of PMA and ionomycin. Data shown are gated GFP⁺ cells. Data shown are representative of at least three experiments. See also Figure S4.

Figure 5. IL-17C-IL-17RE Regulates IκBζ Expression

(A) ELISA of cytokine production in CD4⁺ T cells retrovirally transduced with IL-17RE or control viral vector and treated with IL-17C for 2 days in Th17 cell condition. Sorted GFP⁺ cells were activated with anti-CD3 for 24 hr. (B) Real-time RT-PCR analysis of cytokine and transcription factor expression in CD4⁺ T cells retrovirally transduced and cultured either in neutral or Th17 cell conditions. The cells were activated with anti-CD3 for 4 hr for cytokine mRNA detection. (C) Real-time RT-PCR analysis of Nfkbiz prepared as above. *p < 0.05 (Student’s t test). (D) Real-time RT-PCR analysis of cytokine and transcription factor in CD4⁺ T cells retrovirally transduced with hCD2- IκBζ or control viral vector (PMIG- hCD2). Sorted hCD2⁺ cells were activated with anti-CD3 for 4 hr. (E) Intracellular IL-17A and IFN-γ staining in CD4⁺ T cells retrovirally transduced with IκBζ or control viral vector and cultured in Th17 cell condition. Data shown are representative of at least three independent experiments. See also Figure S5.

Figure 6. CD4-IL-17RE Transgenic Mice Develop Exacerbated EAE Symptoms and Enhanced IκBζ Expression in CNS

(A) Real-time RT-PCR analysis of Il17re mRNA expression in naive T cells isolated from WT or different lines of transgenic mice. (B) Frequency of IL-17A- and IFN-γ-producing cells in naive T cells isolated from WT or CD4-IL-17RE (TG) mice and activated with anti-CD3, anti-CD28, TGF-β, and IL-6 in the presence or absence of IL-17C for 4 days, followed by 5 hr of PMA and ionomycin stimulation in the presence of protein transport inhibitor (BD GolgiStop). (C) EAE was induced in WT and TG animals. Data represent the mean ± SD of n = 11 (WT) and n = 12 (TG) from three independent experiments. (D) Total number of mononuclear cells recovered from CNS. (E) Real-time RT-PCR analysis of Nfkbiz mRNA expression. Data represent the mean ± SD from two independent experiments. *p < 0.05 (Student’s t test). (F) ELISA of cytokine production from splenocytes expanded with MOG_35-55 peptide for 3 days. All comparisons presented were statistically significant (p < 0.05).

Figure 7. IL-17C-IL-17RE Enhanced Polarized Th17 Cell Response

(A) Representative flow cytometry plot of Th17 cells from IL-17F^RFP mice polarized with TGF-β and IL-6 at day 5. (B) ELISA of IL-17A production in polarized Th17 cells with or without IL-17C in the presence of increasing concentration of αCD3. (C) ELISA of cytokine production in polarized Th17 cells cultured with irradiated splenocytes in the presence of increasing concentration of IL-17C. (D) Real-time RT-PCR analysis of Il17c in CNS and spleen from normal and EAE mice. All comparisons presented were statistically significant (***p < 0.001, **p < 0.01, *p < 0.05).