(A) CCR6 and CD39 expression on CD4⁺Foxp3⁺ T cells from WT and Il1rn^–/– mouse synovial tissue by flow cytometry (n = 6). (B) Frequency of CD39 and CCR6 on Foxp3⁺ T cells from synovial tissue. (C–H) Il1rn^–/– mice were treated with anti–IL-1β (αIL-1β) or isotype-matched IgG (n = 5) (5 mg/kg i.p. once per week) for 2 weeks either at weaning (early treatment, n = 5) or 14 days after (late treatment n = 5). (C) Foxp3 and IL-17 expression by CD4⁺ T cells from synovial tissue harvested 35 days after weaning by flow cytometry (n = 5). (D) Frequency of CD4⁺Foxp3^– and CD4⁺Foxp3⁺ cells expressing IL-17 from synovial tissue harvested 35 days after weaning (n = 5 per group). (E) Foxp3 and RORγt expression by CD4⁺ cells from synovial tissue by flow cytometry (n = 5, late treatment n = 3). (F) Frequency of CD4⁺Foxp3^– and CD4⁺Foxp3⁺ cells expressing RORγt (n = 5 per group, late treatment n = 3). (G and H) Foxp3⁺ cells from WT mice or Il1rn^–/– mice treated with anti–IL-1β or isotype-matched IgG were cocultured with WT Foxp3^– cells (n = 5 per group). (G) Proliferation of CD3⁺Foxp3^– cells following 72 hours of coculture. (H) Percentage of divided WT CD3⁺Foxp3^– cells. (I and J) Foxp3⁺ cells from WT mice or Il1rn^–/– mice treated with anti–IL-1β or isotype-matched IgG were cocultured with Foxp3^eGFP– cells from a donor of the same strain (n = 5 per group). (I) Foxp3^– cell proliferation following 72 hours of coculture. (J) Percentage of divided WT Foxp3^– cells. Data are expressed as mean ± SEM. Statistical significance was determined using 1-way ANOVA (B, D, F, and H).