IL-1RI⁺ memory CD4⁺ T cells produce higher levels of IL-17 in response to TCR triggering compared with IL-1RI⁻ memory CD4⁺ T cells. (A) Flow cytometric analysis of IL-1RI expression on IL-17–producing CD4⁺ T cells. Peripheral blood mononuclear cells were stimulated for 4 hours with PMA and ionomycin (A). Mean fluorescent intensity (MFI) of IL-1RI expression on IL-17⁺CD4⁺ (IL-17⁺) and IL-17⁻CD4⁺ (IL-17⁻) T cells (A, right). (B-C) Sorted IL-1RI⁺ and IL-1RI⁻ memory CD4⁺ T cells were stimulated for 7 days (B) or indicated times (C) with anti-CD3/anti-CD28 antibody-coated beads. Cytokine production was determined using intracellular flow cytometry after 4 hours of PMA/ionomycin stimulation (B) or ELISA (C). (D) RT-PCR analysis of Th17-related genes in IL-1RI⁺ and IL-1RI⁻ memory CD4⁺ T cells that were treated for 7 days as in panel C. Numbers indicate the frequency of cells for each quadrant (B). Data represent the mean ± SEM of 10 (A), 9 (B), and 5 (C-D) donors. *Below the lower limit of detection (15 pg/mL of IL-17). P values were obtained by the paired t test.