Activation of basophils with (A) anti-IgE antibody and (B) acarids. PB cells from normal volunteers (○) or from donors with allergy against acarids (▪) were stimulated with serial dilutions of either anti-IgE antibody or acarids allergen extracts for 15 minutes at 37°C. After washing, the cells were stained with MoAb 97A6-PE and analyzed on a FACSCalibur flow cytometer. The mean fluorescence intensities of cells gated on the 97A6⁺ population are plotted against the concentrations of the stimulating agents.