THP-1 phagocytosis of CM-G–labeled platelets. The platelets were incubated with either (A) autoantibody-negative sera samples 1 to 4 or (B) autoantibody-positive sera samples 5 to 8 and either no LPS (□) or 0.1 μg LPS (■) and incubated with THP-1 cells. The data are presented as the mean phagocytic index (± SD) from 4 independent experiments and were calculated as in Figure 1. The numbers on the x-axes refer to the human serum sample number, and IgG antiplatelet autoantibody titers in panel B are shown above the bars for each sera sample. Statistical significance (P values) by a paired t test is shown.