Abnormalities of the bone marrow immune microenvironment in patients with immune thrombocytopenia.

Immune thrombocytopenia (ITP) is an acquired autoimmune disease. Although antiplatelet antibodies are considered as the primary immunologic defect in these patients, dysfunctional cellular immunity is also important in the pathophysiology of ITP. Peripheral T cell abnormalities have been demonstrated in patients with ITP; however, whether the impaired bone marrow (BM) microenvironment, specifically the BM immune microenvironment, is involved in the pathogenesis of ITP remains unknown. In this study, the compartments of the BM immune microenvironment and BM vascular microenvironment were analyzed in 26 untreated patients with ITP and 26 healthy donors (HD). Subsets of T cells in the BM immune microenvironment, including Th1, Th2, Tc1, Tc2, Th17, and Treg cells, were analyzed via flow cytometry. BM endothelial cells and perivascular cells, which are key elements of the vascular microenvironment, were analyzed via flow cytometry as well as hematoxylin-eosin (H&E) and immunohistochemical (IHC) staining in situ. Elements of the BM vascular microenvironment were found to be normal in patients with ITP, but abnormal characteristics of the BM immune microenvironment, including excessive polarization in Th1, Tc1, and Th17 cells and a remarkable decrease in Treg cells, were observed in patients with ITP. Therefore, a deregulated T cell response in the BM microenvironment might play an important role in the pathogenesis of ITP.