Phagocytosis of Antibody-Coated Platelets by Human Granulocytes

To determine whether anti-platelet antibodies act as opsonins to promote phagocytosis of sensitized platelets, normal human platelets were exposed to a variety of serums containing anti-platelet antibodies, and then incubated with autologous granulocytes. Phagocytosis was observed microscopically, by uptake of 51Cr-labeled platelets, and by initial rate of reduction of nitroblue tetrazolium. Phagocytosis and the initial rate of dye reduction were increased as compared to control serums, by serums from 14 patients with idiopathic thrombocytopenic purpura, from 13 patients refractory to platelet transfusion, and from rabbits immunized with washed human platelets. The opsonic activities of serums from patients with idiopathic thrombocytopenic purpura persisted after treatment with steroids or splenectomy. Thus antibody-mediated phagocytosis may be important in the pathogenesis of idiopathic thrombocytopenic purpura and in the clearance of sensitized platelets. (N Engl J Med 290:989–993, 1974)