Pathophysiology of platelet destruction in immune (idiopathic) thrombocytopenic purpura

The mechanism of platelet destruction in immune (idiopathic) thrombocytopenic purpura (ITP) is thought to involve production of autoantibody to platelet surface antigens. Once coated with antibody, circulating platelets undergo sequestration via interaction with Fc receptors of macrophages in the reticuloendothelial system. A number of questions remain about the mechanism of platelet destruction in this disease: 1) What is the nature of the stimulus to the immune system that generates antiplatelet antibodies? 2) What is the role of interactions between T-helper lymphocytes and antigen-presenting cells in ITP? 3) What role, if any, is played by the targeting of single or multiple platelet surface glycoproteins by the autoimmune response? 4) Is the site of platelet destruction, intravascular or extravascular, or the state of activation of platelets important in the destruction of platelets?