Platelet destruction in immune thrombocytopenia. Understanding the mechanisms

The mTORC1 pathway participate in hyper-function of B cells in immune thrombocytopenia

B cell hyper-function plays an important role in the pathogenesis of immune thrombocytopenia (ITP), but the molecular mechanisms underlying such changes remain unclear. We sought to identify regulators of B cell dysfunction in ITP patients through transcriptome sequencing and the use of inhibitors. B cells were isolated from PBMC of 25 ITP patients for B cell function test and transcriptome sequencing. For the potential regulatory factors identified by transcriptome sequencing, the corresponding protein inhibitors were used to explore the regulatory effect of the regulatory factors on B cell dysfunction in vitro. In this study, increased antibody production, enhanced terminal differentiation and highly expressed costimulatory molecules CD80 and CD86 were found in B cells of patients with ITP. In addition, RNA sequencing revealed highly activated mTOR pathway in these pathogenic B cells, indicating that the mTOR pathway may be involved in B cell hyper-function. Furthermore, mTOR inhibitors rapamycin or Torin1 effectively blocked the activation of mTORC1 in B cells, resulting in reduce antibody secretion, impaired differentiation of B cells into plasmablasts and downregulation of costimulatory molecules. Interestingly, as an unspecific inhibitor of mTORC2 besides mTORC1, Torin1 did not show a stronger capacity to modulate B cell function than rapamycin, suggesting that the regulation of B cells by Torin1 may depend on blockade of mTORC1 rather than mTORC2 pathway. These results indicated that the activation of mTORC1 pathway is involved in B cell dysfunction in patients with ITP, and inhibition of mTORC1 pathway might be a potential therapeutic approach for ITP.

Investigation of the correlation between immune thrombocytopenia and T cell activity-regulated gene polymorphism using functional study

Thrombocytopenia is a condition where the platelet count is under 100 × 10⁹/L, which is caused by various disorders. However, the mechanism of thrombocytopenia is still unclear. Hence, we tried to investigate the correlation between immune thrombocytopenia (ITP) and single nucleotide polymorphisms (SNPs) of genes related to T cell activation. There were 32 ITP patients and 30 healthy controls enrolled in this study. PCR and sequencing were used to find out the significant SNPs, which we focused on the promoter region of CTLA4 and CD28. In this study, the ITP cases were divided into primary ITP group, secondary ITP group, and the combination of the two to the follow-up analysis. Moreover, dual-luciferase reporter assay was used to evaluate the transcription activity of the significant SNP. We found the − 1765_rs11571315 of CTLA4 gene was associated with primary ITP (p = 0.006), secondary ITP (p = 0.008), and the combination of the two (p = 0.003). Moreover, the −318_rs5742909 also had statistical significance in secondary ITP group that was only caused by autoimmune disease (p = 0.019). In functional study, the rs5742909 would decrease 19% of the transcription activity when it carried a T-allele at this position (p = 0.040). It was noted that CTLA4 gene polymorphism was related to ITP but not CD28. According to our results, we surmised that CTLA4 is involved in the pathogenesis of ITP, and the secondary ITP result from the lower CTLA4 expression that leads to T cell over-activation.

Primary Immune Thrombocytopenia: Novel Insights into Pathophysiology and Disease Management

Immune thrombocytopenia (ITP) is an autoimmune disorder defined by a significantly reduced number of platelets in blood circulation. Due to low levels of platelets, ITP is associated with frequent bruising and bleeding. Current evidence suggests that low platelet counts in ITP are the result of multiple factors, including impaired thrombopoiesis and variations in immune response leading to platelet destruction during pathological conditions. Patient outcomes as well as clinic presentation of the disease have largely been shown to be case-specific, hinting towards ITP rather being a group of clinical conditions sharing common symptoms. The most frequent characteristics include dysfunction in primary haemostasis and loss of immune tolerance towards platelet as well as megakaryocyte antigens. This heterogeneity in patient population and characteristics make it challenging for the clinicians to choose appropriate therapeutic regimen. Therefore, it is vital to understand the pathomechanisms behind the disease and to consider various factors including patient age, platelet count levels, co-morbidities and patient preferences before initiating therapy. This review summarizes recent developments in the pathophysiology of ITP and provides a comprehensive overview of current therapeutic strategies as well as potential future drugs for the management of ITP.

Copy-number variations in adult patients with chronic immune thrombocytopenia

OBJECTIVES

Immune thrombocytopenia (ITP) is an autoimmune disease with heterogeneous background. FCGR2C mutations were defined in one third of the patients but genetic players have not been fully elucidated yet. Although childhood ITP present as benign, ITP in adulthood is chronic disease with treatment challenges. This study aimed to focus on adult ITP patients using a whole genome genotyping that is valuable approach to identify the responsible genomic regions for the disease.

METHODS

Herein 24 adult primary-refractory for ITP patients were evaluated using HumanCytoSNP12BeadChip,Illumina. Forty-six age and sex matched healthy individuals, and ptients awith nonhematological conditions were analyzed as controls. Identified CNV regions were verified by qRTPCR. T-cell receptor beta and delta (TCRB/TCRG) clonality were assessed by heteroduplex analysis in mosaic cases.

RESULTS

Several CNV losses and gains were defined (losses:2q,7q,17q,19p, and gains: 1q,2p,3q,4q,7q,10q,12p,13q,14q,15q,17p,20q,21p,22q,Xp). Mosaic changes of different sizes (0.2-17.77Mb) were identified in five patients and three of them showed clonality. CNV regions that were unique to ITP patients were identified for the first time and among these genes, those related to immune regulation, and cellular trafficking were noteworthy. Conclusion: Identified CNV regions harbor several candidate genes, the functions of which might shed light on the pathogenesis of chronic ITP.

The Inhibitory Effect of Protamine on Platelets is Attenuated by Heparin without Inducing Thrombocytopenia in Rodents

Protamine sulfate (PS) is a polycationic protein drug obtained from the sperm of fish, and is used to reverse the anticoagulant effect of unfractionated heparin (UFH). However, the interactions between PS, UFH, and platelets are still not clear. We measured the platelet numbers and collagen-induced aggregation, P-selectin, platelet factor 4, β-thromboglobulin, prostacyclin metabolite, D-dimers, activated partial thromboplastin time, prothrombin time, anti-factor Xa, fibrinogen, thrombus weight and megakaryocytopoiesis in blood collected from mice and rats in different time points.. All of the groups were treated intravenously with vehicle, UFH, PS, or UFH with PS. We found a short-term antiplatelet activity of PS in mice and rats, and long-term platelet-independent antithrombotic activity in rats with electrically-induced thrombosis. The antiplatelet and antithrombotic potential of PS may contribute to bleeding risk in PS-overdosed patients. The inhibitory effect of PS on the platelets was attenuated by UFH without inducing thrombocytopenia. Treatment with UFH and PS did not affect the formation, number, or activation of platelets, or the thrombosis development in rodents.

Current and emerging treatments for immune thrombocytopenia

Introduction: Immune thrombocytopenia (ITP) is an autoimmune disease. Even though there are many treatments available, some patients remain resistant to multiple treatments. Therefore, it is very important to develop new treatment options. Areas covered: Here, the authors summarize several current and emerging treatments developed for ITP in recent years. They include a summary of their mechanisms of action and clinical trial results. Expert opinion: At present, the first-line treatment of ITP is glucocorticoid and intravenous immunoglobulin (IVIg). Other traditional therapies include splenectomy, thrombopoietin (TPO), rituximab and other immunosuppressive agents. The several emerging treatments developed recently for ITP may change the treatment pattern in the future.

Pulsed high-dose dexamethasone modulates Th1-/Th2-chemokine imbalance in immune thrombocytopenia

Background

Chemokines and chemokine receptors play important roles in autoimmune diseases; however, their role in immune thrombocytopenia (ITP) is unclear. High-dose dexamethasone (HD-DXM) may become a first-line therapy for adult patients with ITP, but the effect of HD-DXM on chemokines in ITP patients is unknown. Our aim was to investigate the mechanism of pulsed HD-DXM for management of ITP, specifically regarding the chemokine pathways.

Methods

Th1-/Th2-associated chemokine and chemokine receptor profiles in ITP patients before and after pulsed HD-DXM was studied. Plasma levels of CCL5 and CXCL11 (Th1-associated) and of CCL11 (Th2-associated) were determined by ELISA. Gene expression of these three chemokines and their corresponding receptors CCR5, CXCR3, and CCR3, in peripheral blood mononuclear cells (PBMCs) was determined by quantitative RT-PCR.

Results

Thirty-three of the thirty-eight ITP patients responded effectively to HD-DXM (oral, 40 mg/day, 4 days). In ITP patients, plasma CXCL11 levels increased, while CCL11 and CCL5 decreased compared to controls (P < 0.05). Similarly, gene expression of CXCL11 and its receptor CXCR3 increased, while CCL11 and CCR3 decreased (P < 0.05). CCL5 expression did not significantly change; however, expression of its receptor CCR5 increased (P < 0.05). Interestingly, in the patients who responded to pulsed HD-DXM, CXCL11 and CXCR3 expression was down-regulated, while CCL11 and CCR3 expression was up-regulated (P < 0.05). Meanwhile, CCL5 expression was up-regulated and CCR5 was down-regulated by HD-DXM (P < 0.05).

Conclusions

The abnormal profiles of Th1-/Th2-associated chemokines and chemokine receptors may play important roles in the pathogenesis of ITP. Importantly, regulating Th1 polarization by pulsed HD-DXM may represent a novel approach for immunoregulation in ITP.