Immune pathophysiology of autoimmune thrombocytopenic purpura

Chronic autoimmune thrombocytopenic purpura (AITP) is an immune-mediated, bleeding disorder in which platelets are opsonized by autoantibodies and prematurely destroyed by phagocytic cells in the reticuloendothelial system. It is classed as an organ-specific autoimmune disease primarily mediated by immunoglobulin G (IgG) autoantibodies and its etiology appears to be similar to that observed for other organ-specific autoimmune diseases. Th1 cells are important in the process, and the costimulation of Th1 cells and B cells takes place in a cytokine milieu that is reminiscent of a proinflammatory process. Chronic AITP has classically been treated with nonspecific, immunosuppressive regimens (e.g., steroids). One of the most significant developments in the treatment of AITP in the last 20 years has been the use of intravenous immunoglobulin (IVIg) and anti-D preparations. These treatments confer benefit to patients with AITP by significantly raising platelet counts. Despite this, their exact mechanisms of action remain elusive. This review focuses on cell-mediated and cytokine abnormalities within AITP, and presents data related to the mechanism of action of anti-D.