IL-12R expression by CD4⁺CD28^null T cells.

CD4⁺CD28^null T cells constitutively express high levels of the IL-12 receptor. (A) The expression of the IL-12R on PBMCs was determined by 3-color flow cytometry. A representative histogram gated on CD4⁺CD28⁺ T cells (dotted line) and CD4⁺CD28^null T cells (solid line) is shown. (B) The mean fluorescence intensity of IL-12Rβ1 staining was significantly higher on the CD4⁺CD28^null T-cell subset. This result was consistent in all 10 individuals analyzed (P < .001). (C) IL-12Rβ2 cell surface expression was absent on resting CD4⁺ T cells, on both the CD4⁺CD28⁺ (dotted line) and the CD4⁺CD28^null T-cell subsets (solid line). (D-E) Cultured CD4⁺CD28^null T-cell clones and polyclonal CD4⁺CD28^null T-cell lines were examined by 4-color flow cytometry. A representative histogram of 13 clones (panel D) and 11 lines (panel E) is shown for IL-12Rβ1 (dotted line) and IL-12Rβ2 (solid line) expression. All CD4⁺CD28^null T-cell lines and clones expressed both receptor chains. In all histograms, the shaded area represents staining with an isotype control mAb.