Up-regulation of GITR and CTLA-4 following IL-2 administration. (A) Purified CD4 T cells or PBMCs were stained with allophycocyanin-conjugated anti-CD4, PE-conjugated anti-CD25, and FITC-conjugated anti-CD69, anti-GITR, or (C) anti-CD27 antibodies. Dot plots were gated on CD4⁺ T cells. (B) Purified CD4 T cells or PBMCs were stained initially with either FITC-conjugated anti-CD4 or anti-CD8 antibodies with allophycocyanin-conjugated anti-CD25 antibody, followed by intracellular staining with PE-conjugated anti-CTLA-4 antibody. The dot plots were gated on CD4⁺ or CD8⁺ T cells, respectively. The quadrants for CD69, GITR, CD27, and CTLA-4 were based on the isotype control antibodies as well as T cells that lack expression of these markers. This result is representative of 6 patients and 3 healthy donors.