ADP antagonism further reduces thrombus formation after the inhibition of GPVI or α₂β₁. Blood was treated with 10B12 at 50 or 300 μg/mL, 6F1 at 20 μg/mL with or without ADP receptor antagonism (40 μM MRS2179, 20 μM AR-C69 931MX, and 1 U/mL apyrase). (A) Total surface coverage of platelets and of annexin V–positive platelets was measured (mean ± SE from 4-6 donors). **P < .01 compared with control condition. (B) Histograms of feature sizes from phase-contrast micrographs, determined as in Figure 2, where individual antibody effects are shown. Estimated numbers of platelets per feature were 1 to 2 ( ▦) , 2 to 8 (▧ ), 8 to 40 (▥) , 40 to 130 (▪), and more than 130 platelets (□). Data are means ± SE from 3 donors.