Expression of STAT4 in different hematopoietic-cell subsets. (A) Immunoblot analysis of STAT4 protein levels. Various subsets of cells as indicated were isolated from control PBMCs using positive selection with magnetic beads (Miltenyi Biotec). The level of STAT4 protein in each subset was determined as described in Figure 1E. Nondetectable STAT4 protein is presented as (-). Results shown are representative of 3 different control samples that were tested. (B) Flow cytometric analysis of STAT4 protein levels. Control PBMCs were stained with mAbs specific for lineage-associated antigens, fixed, permeabilized, and stained with anti-STAT4 Abs as described in “Methods.” Histograms represent data obtained by electronic gating on CD3⁻CD56⁺ cells (NK-cell subset; top panel), CD3⁺CD56⁻ cells (T-cell subset; middle panel), and CD3⁻CD20⁺ cells (B-cell subset; bottom panel). Logarithm of red fluorescence is displayed on the abscissa and relative cell number on the ordinate. STAT4 Ab staining is indicated by shaded histograms and control staining by open histograms. Results shown are representative of 10 different control samples that were tested. Summary data and statistics are presented in the text.