Platelet function was restored in recipients of β3-transduced marrow. (A) Aggregation was measured ex vivo following incubation of washed platelets with fibrinogen and a cocktail of activation agonists (ADP, epinephrine, and PAR4). Platelets from β3-transduced marrow recipients A to D as well as β3^–/–, β3^+/–, and β3^+/+ control samples aggregated in direct correlation with the level of β3 on their platelets. These results were observed for each mouse in at least 2 separate experiments. (B) Aggregation was measured ex vivo following a 30-minute pretreatment of platelets at 37°C with αIIbβ3 and αvβ3 complex–specific antibody, 7E3 (known to inhibit platelet aggregation),¹⁶  followed by incubation of washed platelets with human fibrinogen and a cocktail of platelet activation agonist (ADP, epinephrine, and PAR4). Shown is the aggregation profile of a mixture of platelets from β3-transduced marrow recipients E to F, which was increasingly inhibited with higher concentrations of 7E3 (0-50 μg/mL). This result represents the outcome of 3 separate experiments. Aggregation was not inhibited with nonspecific mouse Ig. (C) In vivo platelet function was examined by light microscopic analysis of fixed lung tissue stained with trichrome following intravenous injection of a platelet agonist (ADP) into mice (magnification, 400×). Thromboemboli (blue, arrows) formed in the pulmonary blood vessels (BV) of β3^+/– and β3^+/+ controls, while platelets in β3^–/– animals were unable to form emboli. In contrast to results with β3^–/– mice, platelets within transplant recipient C formed emboli that occluded the pulmonary blood vessels. A indicates alveolus; AD, alveolar duct; and TB, terminal bronchiole. This result represents the outcome observed after viewing several sections of each lung from 8 controls (3 β3^–/–, 2 β3^+/–, and 3 β3^+/+ mice) and 3 mice expressing human β3. Images were captured with a Nikon Eclipse TS100 microscope (Nikon, Tokyo, Japan) using a 40×/0.55 numeric aperture objective.