IL-36R is highly expressed and functional in naive CD4⁺ T cells. CD44^loCD62L^hi naive CD4⁺ T cells (Th0 cells) were FACS sorted and polarized or not under Th1, Th2, or Th17 cell conditions for 5 days. Total mRNA was isolated from naive Th cells directly after the sort and from Th1, Th2, and Th17 differentiated cells for analyses by quantitative RT-PCR. Results represent (A) IL-36R, (B) IL-1R1, (C) IL-18Rα, and (D) ST2 mRNA expression levels relative to GAPDH. Error bars represent the SD of the mean of 3 independent experiments. (E-F) Naive T cells from WT and IL-36R^−/− mice (4 × 10⁴ cells per well) were sorted and cultured in 96-well plates precoated with anti-CD3 and anti-CD28 mAb and incubated for 72 hours in the absence (Medium) or presence of IL-36R ligands, IL-1β, IL-33, IL-18, IL-12, or LPS (100 ng/mL). (E) IL-2 secretion in culture supernatants was determined by ELISA. (F) Proliferative responses were assessed by [3H]-thymidine incorporation. Data are shown from one of 3 independent experiments with similar results. Error bars represent the SD of triplicates in the same experiment. *P < .05 (Student t test); IL-36R agonist stimulation significantly differs from unstimulated cells.