The transfection of primary CD4⁺ T cells with KIR2DL1 enhances IL-2 production. (A) Expression of GFP and KIR2DL1 by naive CD4⁺ T cells transfected with pEGFP-N1/KIR2DL1 or pEGFP-N1. The percentages of positive cells are indicated. Numbers in parentheses correspond to mean fluorescence intensities. (B) Detection of IL-2 in CD3⁺CD28⁺stimulated CD4⁺/KIR2DL1⁺ or CD4⁺/GFP⁺ T cells. The percentages of positive cells are indicated, and mean fluorescence intensities are indicated in parentheses. (C) Immunoselected CD4⁺ T cells were stimulated as in panel B, stained with KIR2DL1/S1 mAbs and anti–IL-2 mAb. (D) Percentages of CD4⁺ KIR2DL1/S1⁺ or CD4⁺ KIR2DL1/S1⁻ secreting IL-2 after CD3⁺CD8⁺ stimulation are shown (mean ± SD, n = 2).