Effects of cholesterol loading in vitro on the activation of WT and SR-BI^−/− platelets. WT or SR-BI^−/− platelets were isolated by gel-filtration from pooled blood of WT chimeras and loaded with increasing amounts of cholesterol in vitro by incubation with cholesterol-chelated MβCD. Incubation with αCD was used as control. (A-C) After cholesterol loading platelets were stimulated with ADP, thrombin, or convulxin (CVX), and platelet integrin α_Πbβ₃ activation was determined by FACS analysis. (D) After cholesterol loading, platelets were stained with 50 μg/mL filipin to label unesterified cholesterol and analyzed by flow cytometry. Data are presented as mean ± SEM of measurements after 3 separate cholesterol loading, which were repeated twice. *P < .05, **P < .01, ***P < .001, compared with the same platelets without cholesterol loading. ^#P < .05, ^##P < .01, ^###P < .001, compared with WT platelets with the same concentration of cholesterol loading.