Ex vivo identification of CD4⁺ T cells with and without IL-1RI expression in healthy human peripheral blood. (A) Flow cytometric analysis of IL-1RI expression on CD4⁺ T cells. The number on the histogram plot indicates the frequency (%) of IL-1RI⁺ cells in total CD4⁺ T cells. (B) Flow cytometric measurement of the frequency (%) of naive (CD45RA⁺CCR7⁺), central memory (CM; CD45RA⁻CCR7⁺), and effector memory (EM; CD45RA⁻CCR7⁻) cells in IL-1RI⁺ and IL-1RI⁻ CD4⁺ T cells. Numbers in quadrants indicate the frequency of cells for each quadrant. (C) Flow cytometry of CD28, CD27, and CD62L expression on IL-1RI⁺ and IL-1R⁻ naive, CM, and EM CD4⁺ T cells. (D) RT-PCR analysis of IL1RI expression in sorted IL-1RI⁺ and IL-1RI⁻ naive and memory (CD45RA⁻CCR^+/−) CD4⁺ T cells. Results are relative to the level of expression of β-actin. Data represent the mean ± SEM of 15 (A-B) and 5 (D) donors or 8 separate experiments (C, 1 experiment per donor). *P < .05 using the paired t test.