Role of αIIbβ3, GP Ibα, and fibrinogen in M protein–induced platelet thrombus formation.
(A) Blood (donors 3-5) was mixed for 15 minutes at room temperature (22-25°C) with buffer, or 50 μg/mL of the anti-αIIbβ3 antibody LJ-CP8, or 100 μg/mL of the anti–GP Ibα antibody LJ-Ib1, and then perfused at 37°C over streptococcal M5 protein (coating solution: 100 μg/mL). The surface coverage in an area of 45 000 μm2 was measured at the indicated shear rates after 8 minutes of perfusion. Antibody titers against rM5 (anti-M5) and an M5-specific peptide sequence (anti-N23) were determined by ELISA. (B) Blood was perfused over coverslips coated first with fibrinogen (200 μg/mL) and then rM5 or rM5ΔB (100 μg/mL), or coated directly with the bacterial proteins without fibrinogen. The results represent the mean values of 2 experiments with blood from different donors (6 and 7); bars show the range of values observed. (C) Blood cells from donor 1 were washed free of plasma proteins and then resuspended with Tyrode-HEPES buffer alone or supplemented with 2 mg/mL fibrinogen before perfusion at a shear rate of 340 s−1 over glass coverslips coated with rM5. The images show the extent of surface coverage after 8 minutes of perfusion. These results are representative of those observed in 3 separate experiments.
