aPL-induced thrombosis requires C3 but not C5. (A) Representative images of thrombi developing in the flow-restricted vessels of the indicated mouse strains and (B) quantification of thrombus size 3 hours after aPL injection. Data are median, interquartile range, and range. *P = .0346; **P = .0042; ***P = .0009; 1-way ANOVA followed by the Dunnett multiple-comparison test. In panel A, platelets are depicted in red and nucleated cells in green. Scale bars = 100 μm.