97A6 antigen expression on lung mast cells and PB basophils. To quantify the intensity of 97A6 antigen expression on basophils and mast cells, normal PB basophils (top) and lung mast cells (bottom) were analyzed by multicolor flow cytometry on a FACSCalibur. PB cells (source of basophils) were stained with MoAb 97A6 plus goat antimouse IgG-FITC, as well as with anti-CD123-PE and anti–HLA-DR-PerCP. The upper histogram results from cells gated on the CD123⁺⁺HLA-DR⁻ population. Lung mast cells were stained with MoAb 97A6 plus goat antimouse IgG-FITC and anti–c-kit-PE. The lower histogram results from cells gated on the c-kit⁺ population. Control histograms represent cells stained with IgG1 control antibodies instead of MoAb 97A6.