PD-1 expressing cells produce more IFN-γ in response to polyclonal stimulation in comparison to PD-1⁻ CD4⁺ T cells. Cryopreserved PBMCs were thawed and cultured for 5 hours in the presence of PMA, ionomycin, and Brefeldin-A. The percentage of IFN-γ (A), TNF-α (B), IL-2 (C), IL-4 (D), and IL-17 (E) expression within PD-1⁺ (filled symbols) and PD-1⁻ (open symbols) CD4⁺ T lymphocytes in HIV⁺ (controls and IRIS) patients were measured before and 3 months after ART initiation, as well as in healthy donors (HD). Symbols represent frequencies of cytokine-producing cells after PMA/ionomycin stimulation minus background cytokine production in unstimulated controls.