IL-21 up-regulates perforin expression in CD8 T cells. Perforin expression (mean ± SEM) determined by intracellular flow cytometry in total CD8 T cells from healthy controls (A) and patients with HIV (B) after 5 hours of culture with medium, IL-21 (50 ng/mL), or IL-15 (50 ng/mL). *P < .05. Perforin expression determined by mean fluorescent intensity (MFI) in purified CD3 T cells from a representative healthy control (C) and patient with HIV (D) following 5 hours of stimulation with medium, IL-21, or IL-15, and corresponding perforin mRNA expression from the same healthy control (E) and patient with HIV (F) determined by quantitative RT-PCR. The effect of CHX on cytokine-induced perforin mRNA expression (G) and perforin protein expression (H) was analyzed in purified CD3 T cells that were cultured in medium or stimulated with IL-21 (50 ng/mL), IL-15 (50 ng/mL), anti-CD3 (30 ng/mL), and the combinations for 5 hours, with (solid bars) and without (open bars) CHX (10 μg/mL) treatment. Data for perforin mRNA in T cells and percentage of perforin⁺CD8⁺ T cells from 1 representative patient of 3 patients studied are shown.