Pathophysiology of immune thrombocytopenic purpura: a bird s-eye view

Immune thrombocytopenic purpura (ITP) is a common autoimmune disorder resulting in isolated thrombocytopenia. It is a bleeding disorder characterized by low platelet counts due to decreased platelet production as well as increased platelet destruction by autoimmune mechanisms. ITP can present either alone (primary) or in the setting of other conditions (secondary) such as infections or altered immune states. ITP is associated with a loss of tolerance to platelet antigens and a phenotype of accelerated platelet destruction and impaired platelet production. Although the etiology of ITP remains unknown, complex dysregulation of the immune system is observed in ITP patients. Antiplatelet antibodies mediate accelerated clearance from the circulation in large part via the reticuloendothelial (monocytic phagocytic) system. In addition, cellular immunity is perturbed and T-cell and cytokine profiles are significantly shifted toward a type 1 and Th17 proinflammatory immune response with impaired regulatory compartment, including Tregs and Bregs, have been reported, suggesting a generalized immune dysregulation in ITP. Understanding how Th1/Th17/Treg differentiation and expansion are controlled is central to uncovering how autoimmunity may be sustained in ITP.