Higher frequencies of PD-1 expressing cells are found in IRIS patients before ART initiation. The percentage of PD-1 expression within CD4⁺ T and CD8⁺ T lymphocytes in HIV⁺ controls (open symbols) and HIV⁺ IRIS patients (filled symbols) were measured before and after ART initiation (A-B). Representative dot plots showing PD-1 expression on CD4⁺ T cells throughout study follow-up. Upper dot plots represent a single HIV⁺ control patient and lower dot plots represent a single HIV⁺ patient who developed one IRIS episode (C). The percentage of PD-1 expression within the effector memory compartment of CD4⁺ T and CD8⁺ T cells in HIV⁺ controls (open symbols) and HIV⁺ IRIS patients (filled symbols) were measured before and after ART initiation (D-E). Percentage of PD-1⁺Ki67⁺ expression within CD4⁺ T lymphocytes was measured before and 1, 3, 6, and 12 months after ART initiation. The dotted line represents median of the given measurement from healthy donors (F). The shaded area represents the IQR of the time of initiation of IRIS episodes, and dotted lines represent median of the given measurements from healthy donors (A-B, D-F). Symbols represent changes in the frequency of PD-1⁺Ki67⁺ cells among CD4⁺ T cells in individual patients from baseline to month 1 after ART initiation (G).