Rescue of thrombus formation in HPS6^−/− mice by infusion of WT platelets. Washed platelets isolated from WT mice were infused into HPS6^−/− mice to a final approximate concentration of 10% to 20% of the total mouse platelet count. Platelet-specific anti-CD42b antibody and fibrin-specific mouse anti-human fibrin monoclonal antibody were infused to detect platelets and fibrin during in vivo thrombus formation initiated by laser-induced injury. (A) Representative images of the fluorescence associated with fibrin (green) and platelets (red) over 180 seconds after laser-induced vessel wall injury in an HPS6^−/− mouse (left) and an HPS6^−/− mouse treated with WT mouse platelets (right). (B) Median integrated platelet fluorescence intensity as a function of time in the absence (red) and presence (dark red) of WT platelets. (C) Median integrated fibrin fluorescence intensity as a function of time in the absence (green) and presence (dark green) of WT platelets. Under identical experimental conditions, a nonblocking anti-PDI antibody was employed instead of the fibrin-specific monoclonal antibody to visualize PDI. (D) Median integrated platelet fluorescence intensity as a function of time in the absence (gray) and presence (black) of infused WT platelets. (E) Median integrated PDI fluorescence intensity as a function of time in the absence (gray) and presence (black) of infused WT platelets. Data in panels B-E are from 30 thrombi in 3 mice for each condition. (F) Distribution of calcein-labeled WT donor platelets in a developing thrombus following their infusion into an HPS6^−/− mouse. (G) Distribution of calcein-labeled WT donor platelets in a developing thrombus following their infusion into a WT mouse. Donor WT platelets, green; platelets, red; merge, yellow.