Platelet activation depends on C3 but not on C5. Flow cytometry detection of VWF (A), P-selectin (B), and PS exposure (C) on convulxin (Cvx)–stimulated platelets in PRP from C3^−/− mice and respective WT controls in the absence or presence of PACMA31 (25 μM) (n = 6-11). Similarly, flow cytometry detection of VWF (D), P-selectin (E), and PS exposure (F) on Cvx-stimulated platelets in PRP from C5^−/− mice and respective WT controls in the absence or presence of PACMA 31 (25 μM) (n = 5-11). VWF and P-selection surface expression are shown as linear arbitrary units (AU). PS exposure data are shown as percentage of annexin V+ platelets. Data are presented as mean ± SD and were analyzed by 2-way ANOVA followed by Tukey's multiple comparisons test. *P < .05; **P < .01; ***P < .001. FITC, fluorescein isothiocyanate; n.s., not significant.