Effect of IgG isolated from antiphospholipid syndrome patient sera on thrombus formation in the mouse laser injury model. Fab fragments of a rat monoclonal anti–mouse CD41 antibody conjugated to Alexa 647 (0.3 μg/g body weight) and either normal IgG (1 mg) or patient A IgG (1 mg) were infused into a wild-type mice 5 minutes before laser-induced arteriolar wall injury. (A) Representative images of the fluorescence signal associated with platelets (red) over 180 seconds after vessel injury are shown within the context of the bright-field histology. (B) The median integrated platelet fluorescence (F Platelet) associated with platelet thrombus formation in 3 wild-type mice after infusion of patient IgG (n = 25 thrombi) or control IgG (n = 25 thrombi) over 250 seconds after vessel wall injury. Gray represents patient A IgG; and black, control IgG.