Advances in the Understanding and Treatment of Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by a platelet count of less than 100 x 109 platelets/L. ITP results from two distinct processes: accelerated platelet destruction and reduced platelet production. A distinction of the relative contribution of these pathologies should help guide more targeted treatment decisions. Mechanistically, decreased platelet production is caused by autoantibody-mediated damage to megakaryocytes, while increased clearance of antibody opsonized platelets has traditionally been attributed to the activity of splenic and hepatic macrophages. T cell mediated toxicity has also been described as a contributor to ITP pathogenesis. Recent observations of increased platelet apoptosis and glycoprotein desialylation associated with platelet clearance by hepatocytes provide new avenues for therapeutic intervention. The aim of ITP therapy is to attain sufficient platelet levels to achieve haemostasis. Significant improvements have been obtained with first line therapies such as corticosteroids and intravenous immunoglobulins. For unresponsive patients, second line therapies (splenectomy, rituximab, TPO receptor agonists) have proved beneficial. Nevertheless, the heterogeneous nature of ITP demands further understanding of the causal biological processes to provide personalized and more effective therapies. This chapter presents an account of the current understanding of the biology of ITP and discusses the existing and potential new treatments.

Keywords: Apoptosis, Autoantibodies, Autoimmunity, Desialylation, Immune thrombocytopenia, Immune thrombocytopenic purpura, ITP, IVIg, Megakaryocyte, Platelets, Splenectomy, Thrombopoiesis, TPO receptor agonists.