Role of specific antibodies in M protein–induced platelet aggregation.
Surface coverage by platelets and platelet thrombi was measured in an area of 45 000 μm2 after blood perfusion at 340 s−1 over glass coverslips coated with 100 μg/mL rM5. (A) Blood from the highly reactive donor 1 was perfused after mixing with buffer (control) or the anti- FcγRIIA antibody IV.3 (20 μg/mL). (B) Blood from the poorly reactive donor 8 was perfused after mixing with buffer (control), or with polyclonal anti-M5 IgG purified from donor 1, or with the polyclonal IgG from which the anti-M protein antibodies had been removed by immunoadsorbtion. (C) Plasma-free blood cells from donor 1 were reconstituted with homologous plasma, or plasma depleted of antistreptococcal antibodies plus buffer, or depleted plasma plus either polyclonal anti-M5 IgG or immunoadsorbed IgG lacking anti-M5 antibodies, prepared as described in the legend to panel B. Where bars are displayed, the results represent the average and range of values observed in different fields of view during the same experiment.
