IL-4/IL-13 Heteroreceptor Influences Th17 Cell Conversion and Sensitivity to Regulatory T Cell Suppression To Restrain Experimental Allergic Encephalomyelitis

Abstract

IL-4 and IL-13 have been defined as anti-inflammatory cytokines that can counter myelin-reactive T cells and modulate experimental allergic encephalomyelitis. However, it is not known whether endogenous IL-4 and IL-13 contribute to the maintenance of peripheral tolerance and whether their function is coordinated with T regulatory cells (Tregs). In this study, we used mice in which the common cytokine receptor for IL-4 and IL-13, namely the IL-4Rα/IL-13Rα1 (13R) heteroreceptor (HR), is compromised and determined whether the lack of signaling by endogenous IL-4 and IL-13 through the HR influences the function of effector Th1 and Th17 cells in a Treg-dependent fashion. The findings indicate that mice-deficient for the HR (13R^-/-) are more susceptible to experimental allergic encephalomyelitis than mice sufficient for the HR (13R^+/+) and develop early onset and more severe disease. Moreover, Th17 cells from 13R^-/- mice had reduced ability to convert to Th1 cells and displayed reduced sensitivity to suppression by Tregs relative to Th17 effectors from 13R^+/+ mice. These observations suggest that IL-4 and IL-13 likely operate through the HR and influence Th17 cells to convert to Th1 cells and to acquire increased sensitivity to suppression, leading to control of immune-mediated CNS inflammation. These previously unrecognized findings shed light on the intricacies underlying the contribution of cytokines to peripheral tolerance and control of autoimmunity.

Figure 1

13R^-/- mice develop early onset and more severe EAE. 13R^+/+ and 13R^-/- C57BL/6 mice (6-8 per group) were induced for EAE with 300μg MOGp and monitored daily for clinical signs of paralysis. (A, B) Mean clinical score of disease severity ± SD and percentage of mice that remained disease free for the initial 10 day-phase of disease onset. (C) Shows the mean clinical score of disease severity ± SD for the entire 30 day-monitoing phase. (D-F) Show mean clinical score of disease severity ± SD for 13R^+/+ and 13R^-/- mice (6 mice per group) induced for EAE with 100 (D), 60, (E) or 20 (F) μg of MOGp. *p<0.05, **p<0.01 as determined by Mann-Whitneys U test. (G-I) Draining lymph nodes were harvested at day 10 post-disease induction from mice induced for EAE with 100μg MOGp and the cells were stimulated with PMA and ionomycin (G, H,) or graded concentrations of MOGp (I) and IFNγ and IL-17 responses were measured. (G) Shows the percentages while (H) illustrates the absolute numbers of cytokine secreting CD4⁺MOG^tet+ T cells. (I) Shows cytokine secretion as measured by ELISA. Data is representative of at least 3 independent experiments. *p<0.05, **p<0.01, ***p<0.001 as determined by two-tailed, unpaired Student's t-test.

Figure 2. 13R deficiency nullifies transitional IFNγ⁺/IL17⁺ double positive cells but increases IL17⁺ single positive cells

EAE was induced in 13R^+/+ and 13R^-/- C57BL/6 mice using 100 μg MOGp, the LN and CNS were harvested at the indicated days post-disease induction, and CD4⁺MOG^tet+ T cells were analysed ex vivo for intracellular IFNγ and IL-17. (A) Shows the frequency of single as well as double cytokine producing CD4⁺MOG^tet+ T cells in both the LN and the CNS. (B) Shows the absolute cell numbers accumulated in the CNS of CD4⁺MOG^tet+ T cells producing IL-17 (left panel), IFNγ (median panel), or both (right panel). The data is compiled from 3 independent experiments. *p<0.05, **p<0.01 as determined by two-tailed, unpaired Student's t-test.

Figure 3. 13R deficiency interferes with Th17 conversion leading to reduced Th1 accumulation in the CNS

(A, B) 13R^+/+ and 13R^-/- IL-17a^cre-eYFP mice were induced for EAE with 100 μg MOGp, the LN were harvested on day 7 post-disease induction and the frequency of YFP expressing CD4⁺IL-17⁺ (A) and CD4⁺IFNγ⁺ (B) T cells was determined by flow cytometry. (C-H) LN and CNS cells were harvested on days 4, 5 and 6 (C, D) or every 6 hours beginning on day 4 as indicated (E-H) and expression of Tbet and RoRγt by CD4⁺MOG^tet+YFP⁺ cells was measured ex vivo by intracellular staining. (C, D) Show the frequency of CD4⁺MOG^tet+YFP⁺ cells expressing Tbet and/or RoRγt in the LN (C) and CNS (D). (E-H) show the mean ± SD of the absolute numbers of CD4⁺MOG^tet+YFP⁺ double positive for RoRγt and Tbet in (E, F) or Tbet single positive (G, H). Data is compiled from 3 independent experiments. *, p<0.05; **, p<0.01 as determined by two-tailed, unpaired Student's t-test.

Figure 4. 13R deficiency does not affect the frequency or function of Tregs

Thy (A), SP (B), and LN (C) were harvested from naïve 13R^+/+ and 13R^-/- mice and the frequency of CD4⁺Foxp3⁺ Treg was determined by flow cytometry. (D, E) 13R^+/+ and 13R^-/- Foxp3-GFP mice were immunized with 100 μg MOGp s.c. in PBS/CFA and on day 10 post-immunization the SP cells were used to isolate effector Th1 and Th17 cells whereas the LN cells were utilized to sort CD4⁺CD25⁺Foxp3⁺(GFP⁺) Tregs. Effector Th1 and Th17 cells from 13R^+/+ (D) and 13R^-/- (E) mice were then co-cultured with the LN Tregs from both strains and suppression of effector function was evaluated by measuring residual IFNγ and IL-17 production by ELISA. The percent of residual cytokine represent the ratio of cytokine obtained in the presence of Tregs over cytokine produced in the absence of Tregs multiplied by 100. Data is representative of at least 3 independent experiments.

Figure 5. 13R deficiency increase the sensitivity of Th1 cells to suppression by Tregs

13R^+/+ and 13R^-/- Foxp3-GFP mice were immunized with 100 μg MOGp s.c. in PBS/CFA and on day 10 post-immunization splenic effector Th1 cells from both strains were re-stimulated with PMA and ionomycin, isolated based on cytokine secretion and co-cultured with Tregs from the LN of 13R^+/+ or 13R^-/- mice. (A) Shows IFNγ production in cultures where the Th1 cells from either strain were co-cultured with Tregs from 13R^+/+ mice at Treg/Th1 ratios of 1:1 and 1:4. (B) Shows the percent residual IFNγ production obtained at the indicated Treg:Th1 ratios (see Materials and Methods). The dashed lines indicate the inhibition ratios 50 (IR₅₀), which is the Treg to T effector ratio at which the residual cytokine production is reduced by 50% (see Material and Methods). *p<0.05, **p<0.01 as determined by two-tailed, unpaired Student's t-test. (C) Shows the IR₅₀± SD for Th1 effectors obtained with Tregs from 13R^+/+ and 13R^-/- mice. The SI (sensitivity index) represents the absolute amount of IFNγ that an effector Th1 cell could not produce due to suppression by Tregs (see Material and Methods). Data is compiled from 3 independent experiments.

Figure 6. 13R deficiency diminishes the sensitivity of Th17 cells to suppression by Tregs

13R^+/+ and 13R^-/- Foxp3-GFP mice were immunized with 100 μg MOGp s.c. in PBS/CFA and on day 10 post-immunization splenic effector Th17 cells from both strains were re-stimulated with PMA and ionomycin, isolated based on cytokine secretion and co-cultured with Tregs from the LN of 13R^+/+ or 13R^-/- mice. (A) Shows IL-17 production in cultures where the Th17 cells from either strain were co-cultured with Tregs from 13R^+/+ mice at Treg/Th17 ratios of 1:1 and 1:4. (B) Shows the percent residual IL-17 production obtained at the indicated Treg:Th17 ratios. The dashed lines indicate the IR₅₀ at which the residual cytokine production is reduced by 50%. *p<0.05, **p<0.01 as determined by two-tailed, unpaired Student's t-test. (C) Shows the IR₅₀± SD for Th17 effectors obtained with Tregs from 13R^+/+ and 13R^-/- mice. The SI represents the absolute amount of IL-17 that an effector Th17 cell could not produce due to suppression by Tregs. Data is compiled from 3 independent experiments.

Figure 7. Absence of 13R increases sensitivity of Th1 effector cells to Tregs

13R^+/+ Foxp3-GFP and 13R^-/- mice were immunized with 100μg MOGp s.c. in PBS/CFA and 10 days later the SP were used to isolate effector Th1 cells. Also, the LN from 13R^+/+ Foxp3-GFP mice were utilized to sort CD4⁺CD25⁺GFP⁺(Foxp3⁺) Tregs to serve for suppression. The Th1 cells were then transferred (1 ×10⁶ Th1 cells per mouse) i.v. into Rag2^-/- C57BL/6 mice (6 mice per group) with or without Tregs (2.5 ×10⁶ cells per mouse). On day 2 after transfer the hosts were induced for EAE with 100μg MOGp. (A) Shows the mean clinical scores ± SD for hosts recipient of Th1 effector cells from 13R^+/+ mice without (13R^+/+ + Nil) or with (13R^+/+ + Tregs) Tregs. (B) Shows the mean clinical scores ± SD for hosts recipient of Th1 effector cells from 13R^-/- mice without (13R^-/- + Nil) or with (13R^-/- + Tregs) Tregs. (C) Shows comparison of the mean clinical scores ± SD of hosts recipient of Tregs and Th1 effector cells from 13R^+/+ versus 13R^-/- mice. **p<0.01 as determined by Mann-Whitney U test.

Figure 8. Absence of 13R decreases sensitivity of Th17 effector cells to Tregs

13R^+/+ Foxp3-GFP and 13R^-/- mice were immunized with 100μg MOGp s.c. in PBS/CFA and 10 days later the SP were used to isolate effector Th17 cells. Also, the LN from 13R^+/+ Foxp3-GFP mice were utilized to sort CD4⁺CD25⁺GFP⁺(Foxp3⁺) Tregs to serve for suppression. The Th17 cells were then transferred (4 ×10⁶ Th17 cells per mouse) i.v. into Rag2^-/- C57BL/6 mice (6 mice per group) with or without Tregs (2 ×10⁶ cells per mouse). On day 2 after transfer the hosts were induced for EAE with 100μg MOGp. (A) Shows the mean clinical scores ± SD for hosts recipient of Th17 effector cells from 13R^+/+ mice without (13R^+/+ + Nil) or with (13R^+/+ + Tregs) Tregs. (B) Shows the mean clinical scores ± SD for hosts recipient of Th17 effector cells from 13R^-/- mice without (13R^-/- + Nil) or with (13R^-/- + Tregs) Tregs. (C) Shows comparison of the mean clinical scores ± SD of hosts recipient of Tregs and Th17 effector cells from 13R^+/+ versus 13R^-/- mice. **p<0.01 and ***p<0.001 as determined by Mann-Whitney U test.