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Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature cells and natural inhibitors of adaptive immunity. Metabolic fitness of MDSC is fundamental for its suppressive activity towards effector T cells. Our previous studies showed that the number and inhibitory function of MDSCs were impaired in patients with ITP compared with healthy controls. In this study, we analyzed the effects of decitabine on MDSCs from patients with ITP, both in vitro and in vivo. We found that low-dose decitabine promoted the generation of MDSCs, and enhanced their aerobic metabolism and immunosuppressive functions. Lower expression of liver kinase 1 (LKB1) was found in MDSCs from patients with ITP, which was corrected by decitabine therapy. LKB1 shRNA transfection effectively blocked the function of MDSCs and almost offset the enhanced effect of decitabine on impaired MDSCs. Subsequently, anti-CD61 immune-sensitized splenocytes were transferred into severe combined immunodeficient mice (SCID) to induce ITP in murine models. Passive transfer of decitabine-modulated MDSCs significantly raised platelet counts compared with that of PBS-modulated MDSCs. However, when LKB1 shRNA-transfected MDSCs were transferred into SCID mice, the therapeutic effect of decitabine in alleviating thrombocytopenia was quenched. In conclusion, our study suggests that the impaired aerobic metabolism of MDSCs is involved in the pathogenesis of ITP, and the modulatory effect of decitabine on MDSC metabolism contributes to the improvement of its immunosuppressive function. This provides a possible mechanism for sustained remission elicited by low-dose decitabine in patients with ITP.

Primary immune thrombocytopenia (ITP) is an autoantibody-mediated hemorrhagic disorder where B cells play an essential role. Previous studies have focused on peripheral blood (PB), but B cells in bone marrow (BM) have not been well characterized. We aimed to explore the profile of B cell subsets and their cytokine environments in BM of ITP patients to further clarify the pathogenesis of the disease. B cell subpopulations and their cytokine/chemokine receptors were detected by flow cytometry. Plasma concentrations of cytokines/chemokines were measured by ELISA. mRNA levels of B cell-related transcription factors were determined by qPCR. Regulatory B cell (Breg) function was assessed by quantifying their inhibitory effects on monocytes and T cells in vitro. Decreased proportions of total B cells, naïve B cells and defective Bregs were observed in ITP patients compared with healthy controls (HCs), whereas elevated frequency of long-lived plasma cells was found in BM of autoantibody-positive patients. No statistical difference was observed in plasmablasts or in short-lived plasma cells between ITP patients and HCs. The immunosuppressive capacity of BM Bregs from ITP patients was considerably weaker than that from HCs. In vivo study using an active ITP murine model revealed that Breg transfusion could significantly alleviate thrombocytopenia. Moreover, over-activation of CXCL13-CXCR5 and BAFF/APRIL systems were found in ITP patient BM. Taken together, B cell subsets in BM were skewed toward a proinflammatory profile in ITP patients, suggesting the involvement of dysregulated BM B cells in the development of the disease.

Immune thrombocytopenia (ITP) is an autoimmune haemorrhagic disease, in which the overactivation of T cells is crucial in the pathogenesis. Atorvastatin (AT), a lipid-lowering medicine, has shown promising immunomodulatory effects in certain inflammatory conditions. However, the immunoregulatory role of AT in ITP remains elusive. To investigate the effect of AT in the treatment of ITP, cluster of differentiation 4 (CD4) + T cells were isolated from patients with ITP and cultured with different dosages of AT. We found that AT significantly inhibited cell proliferation, led to cell cycle arrest, induced apoptosis, and repressed the activation of CD4 + T cells in vitro. ITP murine models were then established, and results showed that AT treatment led to faster recovery of the platelet count to normal and exhibited comparable immunomodulatory function. Furthermore, we found the phosphorylation of mammalian target of rapamycin (mTOR), protein kinase B (AKT) and extracellular signal-regulated kinase (ERK), as well as activation of rat sarcoma virus (RAS) were all reduced dramatically after AT treatment in vitro. In conclusion, our present study demonstrated that AT could reinstate the functions of CD4 + T cells by inhibiting the excessive activation, proliferation, and survival of CD4 + T cells in ITP via the RAS/mitogen-activated protein kinase kinase (MEK)/ ERK and the mTOR/phosphatidylinositol-3 kinase (PI3K)/AKT pathway. Therefore, we propose that AT could be used as a potential therapeutic option for ITP by restoring the over-activated cellular immunity.