Aminophospholipid exposure and 5-HT secretion in WAS platelets. Platelets from control and WAS patients were prepared as described in Materials and Methods. Care was taken to ensure that platelets were prepared in exactly the same way and used at the same concentration. Studies were performed on the 2 WAS platelets in comparison with platelets from 2 controls. Data have been pooled and are shown as the mean ± range. (A) Procoagulant activity. Platelets were stimulated with CRP or thrombin for 3 minutes and annexin V binding was measured by flow cytometry as described in Materials and Methods. The number of positive cells is shown in the y-axis; (B) 5-HT secretion. Platelets were stimulated with CRP (90 seconds) or thrombin (30 seconds) and 5-HT secretion was measured as described in Materials and Methods. The results are representative of 3 experiments.