Chronic ITP is an autoimmune disorder in which the patient’s immune system reacts to develop a platelet autoantigen. This results in thrombocytopenia due to immunemediated platelet destruction or suppression of platelet production.1 Platelet membrane proteins become antigenic and stimulate the immune system to produce autoantibodies and cytotoxic T-cells (Figure 1). These autoantibodies are directed
against platelet glycoprotein GPIIbIIIa or GP1b-IX, and are detected in the majority of patients. The etiology of ITP is not completely known, but has been attributed to the ability of these autoantibodies to coat circulating platelets. The antibody-coated platelets are then removed by the reticuloendothelial system (spleen and liver), resulting in thrombocytopenia. In addition, cytotoxic T-cells may destroy megakaryocte production of new platelets. Suppression of platelet production may play a role in the development of ITP as demonstrated by evidence of megakaryocyte abnormalities, improper response of the bone marrow to ongoing platelet destruction, antibody-induced inhi
bition of megakaryocyte production and maturation, and deficiencies in thrombopoietin receptor signaling. The relative importance of these different mechanisms involved in the pathogenesis of ITP remains to be elucidated.