Ultrastructural lesions on the surface of platelets associated with either blood coagulation or with antibody-mediated immune injury.

During blood coagulation ultrastructural lesions were produced on the platelet membrane. They were dependent on the presence of both thrombin and complement (C) and were morphologically identical to the C-dependent ultrastructural lesions (type II) seen in red cells subsequent to activation of C by the alternate mechanismmthough similar in shape they differed in size from ultrastructural lesions (type I) PRODUCED BY ACTIVATION OF C via the classic mechanismmlesions of type I were seen on the platelet surface subsequent to antibody-dependent activation of the C system.