Expression of IL-2Rα, IL-2Rβ, and IL-2Rγ by CD4 T lymphocytes and monocytes. PBMC from blood collected on heparin were treated by MoAbs 33B3 (anti–IL-2Rα), CF1 (anti–IL-2Rβ), and 3B5 (anti–IL-2Rγ). Further characterization of the two populations was achieved by treatment with anti-CD14 and anti-CD28 MoAbs. FITC-labeled Fab fragment anti-IgG was used to stain the cells, followed by PE-conjugated anti-CD4 MoAb. Quadrant settings distinguishing positive immunofluorescence from background fluorescence were determined by staining with isotype-matched control MoAbs: solid horizontal line for lymphocytes and dotted horizontal line for monocytes. The vertical dotted line separates CD4 low (monocytes) from CD4 high (lymphocytes) cells. The percentage of positive cells for the different markers is indicated.