Plasma viral load is negatively correlated with expression of CD25 by FOXP3⁺ T cells. (A-B) High-magnification confocal micrograph of a FOXP3 (green) and CD25 (red) double-positive cell (A) and a FOXP3 (green) single-positive cell (B). Microbar in bottom right corner indicates 10 μm. Images were acquired using a Leica confocal scanner TCS SP II, coupled to a Leica DMR microscope (Leica, Wetzlar, Germany) using a 63×/0.75 NA oil objective. The staining reactions were developed using streptavidin-conjugated fluorophores (Alexa Fluor 488 and 594; Molecular Probes, Eugene, OR). (C) Plasma viral load was negatively correlated to the expression of CD25 by FOXP3⁺ T cells (r = –0.96, P = .003; Spearman correlation). This characterization was done in 7 HIV-infected patients across a wide span of viral loads (5 HIVprogs and 2 HIVnps were included in the analysis).