A transforming growth factor-beta1-mediated bystander immune suppression could be associated with remission of chronic idiopathic thrombocytopenic purpura

Platelets as an inter-player between hyperlipidaemia and atherosclerosis

Platelet hyperreactivity and hyperlipidaemia contribute significantly to atherosclerosis. Thus, it is desirable to review the platelet-hyperlipidaemia interplay and its impact on atherogenesis. Native low-density lipoprotein (nLDL) and oxidized LDL (oxLDL) are the key proatherosclerotic components of hyperlipidaemia. nLDL binds to the platelet-specific LDL receptor (LDLR) ApoE-R2', whereas oxLDL binds to the platelet-expressed scavenger receptor CD36, lectin-type oxidized LDLR 1 and scavenger receptor class A 1. Ligation of nLDL/oxLDL induces mild platelet activation and may prime platelets for other platelet agonists. Platelets, in turn, can modulate lipoprotein metabolisms. Platelets contribute to LDL oxidation by enhancing the production of reactive oxygen species and LDLR degradation via proprotein convertase subtilisin/kexin type 9 release. Platelet-released platelet factor 4 and transforming growth factor β modulate LDL uptake and foam cell formation. Thus, platelet dysfunction and hyperlipidaemia work in concert to aggravate atherogenesis. Hypolipidemic drugs modulate platelet function, whereas antiplatelet drugs influence lipid metabolism. The research prospects of the platelet-hyperlipidaemia interplay in atherosclerosis are also discussed.

In chronic lymphocytic leukemia, activation of the thrombopoietin receptor promotes T-cell inhibitory properties, contributing to immunosuppression

In chronic lymphocytic leukemia (CLL), the immune system is skewed towards a suppressive milieu. Levels of thrombopoietin (TPO), promoting cellular immune regulatory activity in immune thrombocytopenic purpura, were shown to be elevated in CLL patients. This study explored TPO as a potential immunomodulator, supporting CLL progression. We evaluated CLL cell-induced expression of TPO receptor (TPO-R) on T-cells and effects of its activation on T-cell responses. CLL cell involvement in TPO generation was also assessed. Baseline TPO-R expression on CD4 + T-cells was found to be higher in CLL patients than in healthy controls (HC). Exposure of HC-T-cells to B-cells, especially to CLL-B-cells stimulated with B-cell activating molecules, resulted in enhanced TPO-R expression on T-cells. CLL-T-cell stimulation with TPO reduced their proliferation and expanded the regulatory T-cell (Treg) population. At baseline, phosphorylation of STAT5, known to impact the Treg phenotype, was elevated in CLL-T-cells relative to those of HC. Exposure to TPO further enhanced STAT5 phosphorylation in CLL-T-cells, possibly driving the observed Treg expansion. The CLL immune milieu is involved in promotion of inhibitory features in T-cells through increased TPO-R levels and TPO-induced intracellular signaling. TPO and its signaling pathway could potentially support immunosuppression in CLL, and may emerge as novel therapeutic targets.

Interleukin-37, vascular endothelial growth factor A, and transforming growth factor-β1: promising biomarkers in primary immune thrombocytopenia

BACKGROUND

Immune thrombocytopenic purpura (ITP) is an acquired autoimmune hematologic disorder with heterogeneous bleeding manifestations. Many biomarkers such as interleukin-37 (IL-37), vascular endothelial growth factor A (VEGFA), and transforming growth factor-β1 (TGFß1) have a role in immunity, inflammation, and megakaryopoiesis.

METHODS

In the present study, immunoassay of interleukin-37 as well as the gene expression of vascular endothelial growth factor A and transforming growth factor-β1 were done in 60 primary ITP patients, 60 thrombocytopenia patients, and 60 healthy volunteers.

RESULTS

Increased IL-37 level and down regulation of VEGFA and TGFß1gene expression were detected in primary ITP patients when compared with other groups. A negative correlation was observed between IL-37 and platelet count. However, a positive correlation was observed between VEGFA and TGFß1 levels and platelet count.

CONCLUSION

Current results suggested that interleukin-37, vascular endothelial growth factor A, and transforming growth factor-β may be promising indicators in the diagnosis of ITP and detection of disease severity with inexpensive and cost-effectiveness compared to the benefits.

Recent advances in the mechanisms and treatment of immune thrombocytopenia

Primary immune thrombocytopenia is an autoimmune disease associated with a reduced peripheral blood platelet count. The phenotype is variable with some patients suffering no bleeding whilst others have severe bleeding which may be fatal. Variability in clinical behaviour and treatment responses reflects its complex underlying pathophysiology. Historically the management has relied heavily on immune suppression. Recent studies have shown that the older empirical immune suppressants fail to alter the natural history of the disease and are associated with a poor quality of life for patients. Newer treatments, such as the thrombopoietin receptor agonists, have transformed ITP care. They have high efficacy, are well tolerated and improve patients’ quality of life. A greater understanding of the underlying pathophysiology of this disorder has helped develop a number of new targeted therapies. These include inhibitors of the neonatal Fc receptor inhibitors, Bruton tyrosine kinase and complement pathway. Here we discuss the mechanisms underlying ITP and the new approach to ITP care.

Monocytes complexed to platelets differentiate into functionally deficient dendritic cells

In addition to their role in hemostasis, platelets store numerous immunoregulatory molecules such as CD40L, TGFβ, β2-microglobulin, and IL-1β and release them upon activation. Previous studies indicate that activated platelets form transient complexes with monocytes, especially in HIV infected individuals and induce a proinflammatory monocyte phenotype. Because monocytes can act as precursors of dendritic cells (DCs) during infection/inflammation as well as for generation of DC-based vaccine therapies, we evaluated the impact of activated platelets on monocyte differentiation into DCs. We observed that in vitro cultured DCs derived from platelet-monocyte complexes (PMCs) exhibit reduced levels of molecules critical to DC function (CD206, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin, CD80, CD86, CCR7) and reduced antigen uptake capacity. DCs derived from PMCs also showed reduced ability to activate naïve CD4+ and CD8+ T cells, and secrete IL-12p70 in response to CD40L stimulation, resulting in decreased ability to promote type-1 immune responses to HIV antigens. Our results indicate that formation of complexes with activated platelets can suppress the development of functional DCs from such monocytes. Disruption of PMCs in vivo via antiplatelet drugs such as Clopidogrel/Prasugrel or the application of platelet-free monocytes for DCs generation in vitro, may be used to enhance immunization and augment the immune control of HIV.

Crosstalk Between Platelets and Microbial Pathogens

Platelets, small anucleate cells circulating in the blood, are critical mediators in haemostasis and thrombosis. Interestingly, recent studies demonstrated that platelets contain both pro-inflammatory and anti-inflammatory molecules, equipping platelets with immunoregulatory function in both innate and adaptive immunity. In the context of infectious diseases, platelets are involved in early detection of invading microorganisms and are actively recruited to sites of infection. Platelets exert their effects on microbial pathogens either by direct binding to eliminate or restrict dissemination, or by shaping the subsequent host immune response. Reciprocally, many invading microbial pathogens can directly or indirectly target host platelets, altering platelet count or/and function. In addition, microbial pathogens can impact the host auto- and alloimmune responses to platelet antigens in several immune-mediated diseases, such as immune thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. In this review, we discuss the mechanisms that contribute to the bidirectional interactions between platelets and various microbial pathogens, and how these interactions hold relevant implications in the pathogenesis of many infectious diseases. The knowledge obtained from "well-studied" microbes may also help us understand the pathogenesis of emerging microbes, such as SARS-CoV-2 coronavirus.

CD4+ T cell phenotypes in the pathogenesis of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet counts due to enhanced platelet clearance and compromised production. Traditionally, ITP was regarded a B cell mediated disorder as anti-platelet antibodies are detected in most patients. The very nature of self-antigens, evident processes of isotype switching and the affinity maturation of anti-platelet antibodies indicate that B cells in order to mount anti-platelet immune response require assistance of auto-reactive CD4⁺ T cells. For a long time, ITP pathogenesis has been exclusively reviewed through the prism of the disturbed balance between Th1 and Th2 subsets of CD4⁺ T cells, however, more recently new subsets of these cells have been described including Th17, Th9, Th22, T follicular helper and regulatory T cells. In this paper, we review the current understanding of the role and immunological mechanisms by which CD4⁺ T cells contribute to the pathogenesis of ITP.

Role of Platelets in Leukocyte Recruitment and Resolution of Inflammation

Platelets are most often recognized for their crucial role in the control of acute hemorrhage. However, current research has greatly expanded the appreciation of platelets beyond their contribution to primary hemostasis, indicating that platelets also actively participate in leukocyte recruitment and the regulation of the host defense in response to exogenous pathogens and sterile injury. Early recruitment of leukocytes, especially neutrophils, is the evolutionary stronghold of the innate immune response to successfully control exogenous infections. Platelets have been shown to physically interact with different leukocyte subsets during inflammatory processes. This interaction holds far-reaching implications for the leukocyte recruitment into peripheral tissues as well as the regulation of leukocyte cell autonomous functions, including the formation and liberation of neutrophil extracellular traps. These functions critically depend on the interaction of platelets with leukocytes. The host immune response and leukocyte recruitment must be tightly regulated to avoid excessive tissue and organ damage and to avoid chronification of inflammation. Thus, platelet-leukocyte interactions and the resulting leukocyte activation and recruitment also underlies tight regulation by several inherited feedback mechanisms to limit the extend of vascular inflammation and to protect the host from collateral damage caused by overshooting immune system activation. After the acute inflammatory phase has been overcome the host defense response must eventually be terminated to allow for resolution from inflammation and restoration of tissue and organ function. Besides their essential role for leukocyte recruitment and the initiation and propagation of vascular inflammation, platelets have lately also been implicated in the resolution process. Here, their contribution to phagocyte clearance, T cell recruitment and macrophage reprogramming is also of outmost importance. This review will focus on the role of platelets in leukocyte recruitment during the initiation of the host defense and we will also discuss the participation of platelets in the resolution process after acute inflammation.

CD4+ T cells in atherosclerosis: Regulation by platelets

Atherosclerosis is an inflammatory and thrombotic disease, in which both CD4+ T cells and platelets play important roles throughout all stages of atherogenesis. CD4+ T cells are the most abundant T cells present in atherosclerotic lesions. They are primarily seen as type 1 T helper (Th1) cells, while the other CD4+ T cell subsets Th2, Th17, and regulatory T (Treg) cells are also found in the lesions with lower frequencies. CD4+ T effector cells release various cytokines, which exert paracrine or autocrine effects among different CD4+ T cell subsets and other lesional cells and subsequently modulate inflammatory processes in the lesions. Platelets are instrumental in thrombosis and haemostasis, but also play important regulatory roles in immune response, inflammation, and angiogenesis. The present review summarises the current knowledge and/or understanding on how platelets regulate recruitment, activation, differentiation, and cytokine production of different CD4+ T cell subsets, as well as impacts of the platelet-CD4+ T cell interactions on atherogenesis. The research perspectives of platelet-CD4+ T cell interaction in atherosclerosis are also discussed.

Regulatory T Cells in Patients with Idiopathic Thrombocytopenic Purpura

Objective:

Immune thrombocytopenic purpura (ITP) is an immune-mediated bleeding disorder in which platelets are opsonized by autoantibodies and destroyed by an Fc receptor-mediated phagocytosis by the reticuloendothelial system within the spleen. Autoimmune processes are also considered in the pathogenesis of this disorder. CD4+CD25+FoxP3+ regulatory T (Treg) cells and CD8+CD28- Treg cells have roles in autoimmune diseases. We investigated these regulatory cells in ITP patients.

Materials and Methods:

We included 22 ITP patients and 16 age-matched healthy subjects. CD4+CD25+FoxP3+ Treg cells and CD8+CD28- cells were investigated by three-color flow cytometry. The ratios of these cell populations to total lymphocytes were calculated. Statistical analysis was carried out with the Mann-Whitney U test.

Results:

CD4+CD25+ Treg cells were 9.69±3.70% and 12.99±5.58% in patients with ITP and controls, respectively. CD4+CD25highFoxP3+ cells were 27.72±19.74% and 27.55±23.98% in ITP patients and controls, respectively. The percentages of both of these cell types were not statistically significant when compared to the control group.

Conclusion:

We did not find any differences in ratios of CD4+CD25+FoxP3+ Treg cells or CD8+CD28- T cells in lymphocytes between patients and healthy subjects. We conclude that these circulatory cells are not different in ITP, but further studies are needed to explore the putative roles of these regulatory cells.

Relation of interleukin-10 Promoter Polymorphisms to Adult Chronic Immune Thrombocytopenic Purpura in a Cohort of Egyptian Population

BACKGROUND

Adult chronic immune thrombocytopenic purpura (chronic ITP) is an autoimmune multifactorial bleeding disorder that occurs because of enhanced peripheral platelet destruction. Treatment decisions can be challenging because the goal of treatment is to prevent severe bleeding, but the risk of bleeding can be difficult to estimate for any individual patient.

OBJECTIVE

This case-control study was planned to investigate the relationship of interleukin (IL)-10 promoter (IL-10-1082, -819 and -592) polymorphisms with the susceptibility, severity and outcome of adult chronic ITP in a cohort of Egyptian population.

SUBJECTS AND METHODS

Typing of IL-10 promoter polymorphisms was done using restriction fragment length polymorphism for 62 adult patients with chronic ITP and 73 age- and sex-matched healthy controls.

RESULTS

No significant differences were found between ITP patients and controls regarding the frequency of IL-10 promoter genotypes, alleles or haplotypes. IL-10-592 AA genotype and ATA (IL-10-1082, -819 and -592) haplotype were associated with severe ITP (p = 0.003, 0.043, respectively).

CONCLUSION

Our findings suggest that the IL-10 promoter polymorphisms are unlikely to affect the development or treatment outcome of chronic adult ITP in Egyptian population, but IL-10-592 AA genotype and IL-10 (-1082, -819 and -592) ATA haplotype may be associated with disease severity. Because ITP is a complex disease, it is recommended that a multicenter study should be done with large sample size and unified typing technique.

Imbalanced immune homeostasis in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder resulting from low platelet counts caused by inadequate production as well as increased destruction by autoimmune mechanisms. As with other autoimmune disorders, chronic ITP is characterized by perturbations of immune homeostasis with hyperactivated effector cells as well as defective regulatory arm of the adaptive immune system, which will be reviewed here. Interestingly, some ITP treatments are associated with restoring the regulatory imbalance, although it remains unclear whether the immune system is redirected to a state of tolerance once treatment is discontinued. Understanding the mechanisms that result in breakdown of immune homeostasis in ITP will help to identify novel pathways for restoring tolerance and inhibiting effector cell responses. This information can then be translated into developing therapies for averting autoimmunity not only in ITP but also many autoimmune disorders.

The nonhemostatic immune functions of platelets

Platelets are megakaryocyte-derived cellular fragments, which lack a nucleus and are the smallest circulating cells and are classically known to have a major role in supporting hemostasis. Apart from this well-established role, it is now becoming evident that platelets are also capable of conveying other important functions, such as during infection and inflammation. This paper will outline these nonhemostatic functions in two major sections termed "Platelets versus pathogens" and "Platelet-target cell communication". Platelets actively contribute to protection against invading pathogens and are capable of regulating immune functions in various target cells, all through sophisticated and efficient mechanisms. These relatively novel features will be highlighted, illustrating the multifunctional role of platelets in inflammation.

Identification of novel biomarkers in chronic immune thrombocytopenia (ITP) by microarray-based serum protein profiling

The pathological mechanisms underlying the development of immune thrombocytopenia (ITP) are unclear and its diagnosis remains a process of exclusion. Currently, there are no known specific biomarkers for ITP to support differential diagnosis and treatment decisions. Profiling of serum proteins may be valuable for identifying such biomarkers. Sera from 46 patients with primary chronic ITP and 34 healthy blood donors were analysed using a microarray of 755 antibodies. We identified 161 differentially expressed proteins. In addition to oncoproteins and tumour-suppressor proteins, including apoptosis regulator BCL2, breast cancer type 1 susceptibility protein (BRCA1), Fanconi anaemia complementation group C (FANCC) and vascular endothelial growth factor A (VEGFA), we detected six anti-nuclear autoantibodies in a subset of ITP patients: anti-PCNA, anti-SmD, anti-Ro/SSA60, anti-Ro/SSA52, anti-La/SSB and anti-RNPC antibodies. This finding may provide a rational explanation for the association of ITP with malignancies and other autoimmune diseases. While RUNX1mRNA expression in the peripheral blood mononuclear cells (PBMC) of patients was significantly downregulated, an accumulation of RUNX1 protein was observed in the platelets of ITP patients. This may indicate dysregulation of RUNX1 expression in PBMC and megakaryocytes and may lead to an imbalanced immune response and impaired thrombopoiesis. In conclusion, we provide novel insights into the pathogenic mechanisms of ITP that warrant further exploration.

Platelets in the pathogenesis of acute respiratory distress syndrome

Platelets have an emerging and incompletely understood role in a myriad of host immune responses, extending their role well beyond regulating thrombosis. Acute respiratory distress syndrome is a complex disease process characterized by a range of pathophysiologic processes including oxidative stress, lung deformation, inflammation, and intravascular coagulation. The objective of this review is to summarize existing knowledge on platelets and their putative role in the development and resolution of lung injury.

Nouvelle cuisine: platelets served with inflammation

Platelets are small cellular fragments with the primary physiological role of maintaining hemostasis. In addition to this well-described classical function, it is becoming increasingly clear that platelets have an intimate connection with infection and inflammation. This stems from several platelet characteristics, including their ability to bind infectious agents and secrete many immunomodulatory cytokines and chemokines, as well as their expression of receptors for various immune effector and regulatory functions, such as TLRs, which allow them to sense pathogen-associated molecular patterns. Furthermore, platelets contain RNA that can be nascently translated under different environmental stresses, and they are able to release membrane microparticles that can transport inflammatory cargo to inflammatory cells. Interestingly, acute infections can also result in platelet breakdown and thrombocytopenia. This report highlights these relatively new aspects of platelets and, thus, their nonhemostatic nature in an inflammatory setting.

Association of CD4(+)CD25(+)FoxP3(+) regulatory T cells with natural course of childhood chronic immune thrombocytopenic purpura

PURPOSE

The purpose of this study was to determine the frequency of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Treg) in the peripheral blood of patients with childhood chronic immune thrombocytopenic purpura (ITP) exhibiting thrombocytopenia and spontaneous remission. The findings of this study indicate the possibility of predicting spontaneous recovery and pathogenesis of childhood chronic ITP.

METHODS

Eleven children with chronic ITP (seven thrombocytopenic and four spontaneous remission cases; mean age, 8.8 years; range, 1.7-14.9 years) were enrolled in this study. Five healthy children and eight healthy adults were included as controls. The frequency of Treg was evaluated by flow cytometry in the peripheral blood.

RESULTS

In this study, four patients (36%) achieved spontaneous remission within 2.8 years (mean year; range, 1.0-4.4 years). The frequency of Treg was significantly lower in patients with persisting thrombocytopenia (0.13%±0.09%, P<0.05), than that in the patients with spontaneous remission (0.30%±0.02%), healthy adults controls (0.55%±0.44%), and healthy children controls (0.46%±0.26%). A significantly positive correlation was found between the frequency of Treg and the platelet count in children.

CONCLUSION

These data suggest that a lower frequency of Treg contributes to the breakdown of self-tolerance, and may form the basis for future development of specific immunomodulatory therapies. Furthermore, Treg frequency has prognostic implication toward the natural course and long-term outcomes of childhood chronic ITP.

Thrombocytopenia in Dengue: Interrelationship between Virus and the Imbalance between Coagulation and Fibrinolysis and Inflammatory Mediators

Dengue is an infectious disease caused by dengue virus (DENV). In general, dengue is a self-limiting acute febrile illness followed by a phase of critical defervescence, in which patients may improve or progress to a severe form. Severe illness is characterized by hemodynamic disturbances, increased vascular permeability, hypovolemia, hypotension, and shock. Thrombocytopenia and platelet dysfunction are common in both cases and are related to the clinical outcome. Different mechanisms have been hypothesized to explain DENV-associated thrombocytopenia, including the suppression of bone marrow and the peripheral destruction of platelets. Studies have shown DENV-infected hematopoietic progenitors or bone marrow stromal cells. Moreover, anti-platelet antibodies would be involved in peripheral platelet destruction as platelets interact with endothelial cells, immune cells, and/or DENV. It is not yet clear whether platelets play a role in the viral spread. Here, we focus on the mechanisms of thrombocytopenia and platelet dysfunction in DENV infection. Because platelets participate in the inflammatory and immune response by promoting cytokine, chemokine, and inflammatory mediator secretion, their relevance as "immune-like effector cells" will be discussed. Finally, an implication for platelets in plasma leakage will be also regarded, as thrombocytopenia is associated with clinical outcome and higher mortality.

Altered cytokine levels in pediatric ITP

Immune thrombocytopenia (ITP) is an autoimmune disease where platelets are destroyed prematurely. In the majority of children, the disease resolves, but in some, it becomes chronic. Cytokines are important mediators of the immune response and are known to be dysregulated in autoimmune diseases. Therefore, our aim was to investigate differences in plasma levels of cytokines between children with ITP and healthy controls. We had two cohorts of children: one Swedish with 18 children with ITP and seven healthy children and a second Chinese one with 58 children with ITP and 30 healthy children. Plasma levels of chemokine (C-X3-C motif) ligand 1 (CX3CL1), transforming growth factor β1 (TGF-β1), and interleukin 22 (IL-22) were analyzed in both cohorts using enzyme-linked immunosorbent assays (ELISAs). We found lower plasma levels of TGF-β1 and elevated levels of CX3CL1 and IL-22 in children with ITP compared with controls in both the Swedish and the Chinese cohort. In conclusion, all three cytokines differ between pediatric ITP and healthy controls and may, therefore, be potential biomarkers for the disease.

Platelets in leucocyte recruitment and function

Platelets have a longstanding recognition as an essential cellular component of the coagulation system. However, substantial research over the last decade has added another important aspect to platelet function in that they are also an integral part of the innate immune system. Complex organisms are facing a constant threat of infections by invading pathogens, and they have developed a sophisticated and elegant measure to combat this threat, namely the immune system. Leucocyte recruitment to sites of infections is an essential step at the forefront of the immune response. Platelets have been shown to be involved in several steps of this process and they are an integrated connecting element among haemostasis, host defence, and additional immunological functions (e.g. neutrophil extracellular traps formation). However, the immune system also requires a tight regulation, as an overshooting immune response carries the risk of harming the host itself. This review aims at highlighting the unique features and molecular mechanisms that allow for the interactions of platelets and leucocytes and the regulation of this process. Furthermore, this article identifies the functional relevance of these events for the immune response.

Foxp3 methylation status in children with primary immune thrombocytopenia

AIM

To investigate the status of DNA methylation in the Foxp3 promoter in pediatric ITP patients and assess the role of DNA methylation of Treg cells in the pathogenesis of ITP.

METHODS

Quantitative DNA methylation levels of Foxp3 promoter in pediatric ITP patients were detected by MassARRAY EpiTYPER. Methylation levels of Foxp3 promoter were analyzed in ITP patients and normal controls.

RESULTS

Significantly higher expression of CpG-2, CpG-3 and CpG-11.12 was observed in ITP patients compared to the controls. A subgroup analysis revealed that persistent and chronic ITP patients exhibited significantly higher CpG-6 expression than in the subgroup of newly diagnosed ITP patients. All patients who represented newly diagnosed ITP at admission were reclassified at later follow-up. In this follow-up subgroup analysis, there were significantly higher levels of CpG-6 in the persistent ITP group than that in the newly diagnosed ITP group.

CONCLUSIONS

Our results indicate that defective Treg cell activity identified in ITP might be partially mediated through hypermethylation of CpG sites in the promoter region of Foxp3.

Cytokine profile of patients with chronic immune thrombocytopenia affects platelet count recovery after Helicobacter pylori eradication

Helicobacter pylori eradication induces platelet recovery in a subgroup of patients with chronic immune thrombocytopenia (cITP), but the mechanisms involved are still not understood. We aimed to evaluate the effect of H. pylori eradication on platelet response and to identify the associated serum cytokine profile in 95 patients with cITP. Serum cytokine concentrations were determined by enzyme-linked immunosorbent assay prior to and 6 months after H. pylori eradication. Remission of cITP was observed in 17 (28·8%) of 59 patients in whom the bacterium was eradicated. Six months after treatment, a significant reduction in the concentrations of T-helper (Th) 1 and Th17 cells and an increase in T regulatory (Treg) and Th2-cell commitment cytokines were observed in patients who recovered, but not in those whose platelet count did not recover. Patients who had a platelet response to eradication of the bacteria had higher pre-treatment serum levels of γ-interferon (IFNG, IFN-γ), transforming growth factor-β (TGFB1, TGF-β) and interleukin 17 (IL17A, IL-17) than patients who did not respond, but only higher pre-treatment TGFB1 levels was independently associated with platelet response. In conclusion, amelioration of cITP after eradication of H. pylori was linked to a more efficient suppression of Th1 and Th17 response and a more pronounced Treg cell response.

A novel canine model of immune thrombocytopenia: has immune thrombocytopenia (ITP) gone to the dogs?

Canine immune thrombocytopenia (ITP) is analogous to human ITP, with similar platelet counts and heterogeneity in bleeding phenotype among affected individuals. With a goal of ultimately investigating this bleeding heterogeneity, a canine model of antibody-mediated ITP was developed. Infusion of healthy dogs with 2F9, a murine IgG2a monoclonal antibody to the canine platelet glycoprotein GPIIb (a common target of autoantibodies in ITP) resulted in profound, dose-dependent thrombocytopenia. Model dogs developed variable bleeding phenotypes, e.g. petechiae and haematuria, despite similar degrees of thrombocytopenia. 2F9 infusion was not associated with systemic inflammation, consumptive coagulopathy, or impairment of platelet function. Unexpectedly however, evaluation of cytokine profiles led to the identification of platelets as a potential source of serum interleukin-8 (IL8) in dogs. This finding was confirmed in humans with ITP, suggesting that platelet IL8 may be a previously unrecognized modulator of platelet-neutrophil crosstalk. The utility of this model will allow future study of bleeding phenotypic heterogeneity including the role of neutrophils and endothelial cells in ITP.

Platelets provoke distinct dynamics of immune responses by differentially regulating CD4+ T-cell proliferation

BACKGROUND

Platelets regulate responses of type 1 T helper (Th1), Th17, and regulatory T (Treg) cells. However, little is known about how platelets influence the dynamics of CD4(+) T-cell responses.

OBJECTIVES

To investigate the dynamics of platelet-regulated CD4(+) T-cell activation and cross-talk and their underlying mechanisms.

METHODS AND RESULTS

Human CD3/CD28-challenged CD4(+) T cells were cultured without or with autologous platelets. Th1, Th17, and Treg responses were monitored during 5 days. Platelets simultaneously enhanced activation of Th1, Th17, and Treg cells within 48-h coculture. Thereafter, platelets remained augmentative for Treg but turned suppressive for Th1/Th17 responses. Without platelets, FoxP3 blockade inhibited Treg activation, which subsequently enhanced Th1 activation. In platelet-T-cell cocultures, however, FoxP3 blockade had no effect on Treg or Th1 activation. Neutralization of platelet-derived transforming growth factor β, but not Treg-derived interleukin-10, enhanced Th1 activation. These data suggest that Treg cells have limited impact on, while platelets are the primary regulator for Th1 suppression during the second phase of coculture. Combining carboxyfluorescein succinimidyl ester and FoxP3 staining, platelets were found to enhance Treg response by promoting cell proliferation of FoxP3(+) T cells and to induce the suppression phrase of Th1 responses by inhibiting FoxP3(-) T-cell proliferation. The latter was markedly attenuated by TGFβ neutralization.

CONCLUSIONS

Platelets constantly promote Treg cell response but exert a biphasic regulation on Th1/Th17 activation, namely a transient enhancement followed by a secondary suppression. The distinct regulations are achieved by transforming growth factor β-mediated selective inhibition of FoxP3(-) T-cell proliferation. This represents a novel mechanism of platelet-regulated CD4(+) effector cell responses.

Alterations in immune cell subsets and their cytokine secretion profile in childhood idiopathic thrombocytopenic purpura (ITP)

Immune thrombocytopenic purpura (ITP) is acquired autoimmune disease in children characterized by the breakdown of immune tolerance. This work is designed to explore the contribution of different lymphocyte subsets in acute and chronic ITP children. Imbalance in the T helper type 1 (Th1)/Th2 cytokine secretion profile was investigated. The frequency of T (CD3(+), CD4(+), CD8(+)) and B (CD19(+)) lymphocytes, natural killer (NK) (CD16(+) 56(+)) and regulatory T (T(reg)) [CD4(+) CD25(+high) forkhead box protein 3 (FoxP3)(+) ] cells was investigated by flow cytometry in 35 ITP children (15 acute and 20 chronic) and 10 healthy controls. Plasma levels of Th1 cytokines [interferon (IFN-γ) and tumour necrosis factor (TNF-α)] and Th2 [interleukin (IL)-4, IL-6 and IL-10)] cytokines were measured using enzyme-linked immunosorbent assay (ELISA). The percentage of Treg (P < 0·001) and natural killer (NK) (P < 0·001) cells were significantly decreased in ITP patients compared to healthy controls. A negative correlation was reported between the percentage of T(reg) cells and development of acute (r = -0·737; P < 0·01) and chronic (r = -0·515; P < 0·01) disease. All evaluated cytokines (IFN-γ, TNF-α, IL-4, IL-6 and IL-10) were elevated significantly in ITP patients (P < 0·001, P < 0·05, P < 0·05, P < 0·05 and P < 0·001, respectively) compared to controls. In conclusion, our data shed some light on the fundamental role of immune cells and their related cytokines in ITP patients. The loss of tolerance in ITP may contribute to the dysfunction of T(regs). Understanding the role of T cell subsets will permit a better control of autoimmunity through manipulation of their cytokine network.

Transplantation of adipose-derived mesenchymal stem cells into a murine model of passive chronic immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is a bleeding disorder characterized by antibody-opsonized platelets (PLTs) being prematurely destroyed by macrophages in the reticuloendothelial system. T helper (Th) cells and different Th cytokines play an important role in the pathophysiology of ITP. As immunomodulators, adipose-derived mesenchymal stem cells (ADSCs) regulate Th cells and show therapeutic effects in autoimmune diseases. However, it is not clear how ADSCs affect ITP. In this study, we explored the specific effects of ADSCs on ITP in mice.

STUDY DESIGN AND METHODS

BALB/c mice were randomly divided into three groups: normal controls, ITP controls, and ITP with ADSC transplantation. PLT levels were monitored by an automatic blood cell counter, and the cytokines interferon-γ (IFN-γ); interleukin (IL)-2, -4, -10, and -17; and transforming growth factor-β1 (TGF-β1) were analyzed by enzyme-linked immunosorbent assays.

RESULTS

Compared to the untreated ITP mice, the PLT level of the ITP mice significantly increased after ADSC treatment. In the ADSC group, IFN-γ, IL-2, and IL-17 significantly decreased, while IL-4, IL-10, and TGF-β1 increased.

CONCLUSION

These findings constitute the first experimental evidence that ADSCs are efficacious in improving PLT levels and reducing the related Th cytokines mediating proinflammatory response in ITP mice, which may provide a scientific basis for using ADSCs as a new therapy for ITP.

Reduced expression of transforming growth factor-β1 and correlated elevation of interleukin-17 and interferon-γ in pediatric patients with chronic primary immune thrombocytopenia (ITP)

BACKGROUND

Dysregulated T helper (Th) cells are considered important in the pathophysiology of chronic primary immune thrombocytopenia (ITP). The present study investigated whether levels of Th cytokines in pediatric patients with chronic ITP were different compared with healthy controls.

PROCEDURES

Fifty-seven pediatric patients with chronic ITP and 28 healthy controls were enrolled. Patients were divided into three groups based on their platelet counts at the time of the study: (i) active disease <50 × 10(9) /l (n = 23), (ii) stable disease 50-150 × 10(9) /l (n = 23), and (iii) in remission >150 × 10(9) /l (n = 11). Plasma concentration of Th1 [interferon gamma (INF-γ), interleukin 2 (IL-2)], Th2 (IL-4, IL-10), Th3 [transforming growth factor-β1 (TGF-β1)], and Th17 (IL-17) cytokines were investigated by enzyme-linked immunosorbent assay.

RESULTS

IFN-γ was increased in patients with active (P < 0.001) and stable disease (P = 0.026) when compared with controls. The IL-17 level was significantly higher in all of the 3 patient groups. In addition, there was a positive correlation between IL-17 and IFN-γ levels in chronic ITP patients (r = 0.640, P < 0.001). Reduced TGF-β1 expression was observed in patients with active (P < 0.001) and stable disease (P = 0.001) in comparison with controls. Moreover, TGF-β1 level in patients was positively correlated with the platelet count (r = 0.355, P = 0.007).

CONCLUSIONS

Elevation of IL-17 and IFN-γ may be an important dysregulation of cellular immunity in pediatric patients with chronic ITP. The disease activity is associated with reduced production of TGF-β1.

Favorable response of chronic refractory immune thrombocytopenic purpura to mesenchymal stem cells

Seven patients with chronic refractory immune thrombocytopenic purpura (ITP) received adipose tissue-derived mesenchymal stem cells (AMSC) from haplo-identical family donors. The AMSC dose was 2.0×10(6)/kg. No side effects were noted after the AMSC infusions. Overall responses were reached in all patients and sustained response rate was 57.1% (4/7). The serum levels of transforming growth factor β1 (TGF-β1), interleukin (IL)-4, and IL-10 were significantly elevated, whereas those of interferon-γ (IFN-γ) and IL-2 were significantly decreased after AMSC administration, compared with those in the patients with active ITP. During follow-up, the cytokine profiles in patients maintaining sustained response remained stable compared with the post-treatment level, but IFN-γ and IL-2 levels were significantly increased, and those of TGF-β1, IL-4, and IL-10 were significantly reduced again in relapsed patients. AMSC therapy seems to represent reasonable salvage treatment in severe, chronic refractory ITP by causing a shift in the Th1/Th2 cytokine balance to the same levels as normal controls.

Improved regulatory T-cell activity in patients with chronic immune thrombocytopenia treated with thrombopoietic agents

Immune thrombocytopenia (ITP) is an autoantibody-mediated bleeding disorder with both accelerated platelet destruction and impaired platelet production. We and others have described impaired regulatory CD4(+)CD25(hi) T cells (Treg) numbers and/or suppressive function in ITP patients. Clinical trials using thrombopoietic agents to stimulate platelet production have shown favorable outcomes in ITP patients, but information on the immunologic responses of treated patients are lacking. We studied the immunologic profile of chronic ITP patients before (n = 10) and during treatment with thrombopoietin receptor (TPO-R) agonists (n = 9). Treg activity, as measured by suppression of proliferation of autologous CD4(+) CD25(-) cells, was improved in patients on treatment (P < .05), and the improvement correlated with reduction in interleukin-2-producing CD4(+) cells, consistent with dampening of immune responses. There was a concomitant increase in total circulating transforming growth factor-β1 (TGF-β1) levels (P = .002) in patients on treatment, and the levels of TGF-β1 correlated with the degree of improvement in platelet counts (r = .8, P = .0002). This suggests that platelets in patients on TPO-R treatment may play a role in improving Treg function, either directly or indirectly by enhanced release of TGF-β1 as a result of greater platelet turnover. In conclusion, our findings suggest that thrombopoietic agents in patients with ITP have profound effects to restore immune tolerance.

The ITP syndrome: pathogenic and clinical diversity

Immune thrombocytopenia (ITP) is mediated by platelet autoantibodies that accelerate platelet destruction and inhibit their production. Most cases are considered idiopathic, whereas others are secondary to coexisting conditions. Insights from secondary forms suggest that the proclivity to develop platelet-reactive antibodies arises through diverse mechanisms. Variability in natural history and response to therapy suggests that primary ITP is also heterogeneous. Certain cases may be secondary to persistent, sometimes inapparent, infections, accompanied by coexisting antibodies that influence outcome. Alternatively, underlying immune deficiencies may emerge. In addition, environmental and genetic factors may impact platelet turnover, propensity to bleed, and response to ITP-directed therapy. We review the pathophysiology of several common secondary forms of ITP. We suggest that primary ITP is also best thought of as an autoimmune syndrome. Better understanding of pathogenesis and tolerance checkpoint defects leading to autoantibody formation may facilitate patient-specific approaches to diagnosis and management.

Profile of Th17 cytokines (IL-17, TGF-beta, IL-6) and Th1 cytokine (IFN-gamma) in patients with immune thrombocytopenic purpura

The data on polarization of the immune system towards T helper 1 (Th1) or T helper 2 (Th2) cells in immune thrombocytopenic purpura (ITP) are limited and contradictory. Th17 characterized by the production of Interleukin 17 (IL-17) has been shown to play a crucial part in the induction of autoimmune diseases. To further investigate the role of Th cytokines in the pathogenesis of ITP, we measured the plasma concentration of three Th17-associated cytokines [IL-17, transforming growth factor-ss (TGF-ss), IL-6] and Th1 cytokine interferon-gamma (IFN-gamma) in ITP patients, and evaluated their clinical relevance. The concentration of IL-17, TGF-ss, IL-6, and IFN-gamma in plasma specimens from 29 adults with chronic ITP and 38 controls was analyzed by enzyme-linked immunosorbent assay method. No significant differences of Th17 cytokines (IL-17, TGF-ss, and IL-6) and Th1 cytokine (IFN-gamma) concentration were observed between patients with active ITP and the control group. And the IFN-gamma/IL-17 ratio representing Th1/Th17 cytokine profile was not significantly different between ITP patients and control, either. However, significantly positive correlation between IL-6 and IFN-gamma in ITP patients was observed (r = 0.48, P = 0.01). Among the ITP patients, Plasma IL-17 levels in male were marginally higher than those in female, while similar for TGF-ss, IL-6 or IFN-gamma. There was a significantly positive correlation between age and IL-6 concentration in ITP patients (r = 0.56, P = 0.0002), while no statistical significance between age and the other three cytokines. No significant correlation between cytokine concentrations and platelets or megakaryocytes number was found in ITP patients. In summary, ITP may not be associated with changes of plasma Th17 and Th1 cytokine concentrations relative to control population.

Recruitment of T cells into bone marrow of ITP patients possibly due to elevated expression of VLA-4 and CX3CR1

In idiopathic thrombocytopenic purpura (ITP), platelets are destroyed in the spleen, liver, and bone marrow (BM) by autoantibodies and cytotoxic T cells. In a DNA microarray screen of peripheral blood T cells, we found that VLA-4, CX3CR1, and CXCR4, involved in T-cell homing, had increased expression in ITP patients compared with controls. However, we only found increased protein expression of VLA-4 on T cells from peripheral blood by flow cytometry. To address a possible recruitment of T cells into the organs involved in platelet destruction, we analyzed T cells in BM. In BM, T-cell surface expression of VLA-4 and CX3CR1 was increased in ITP patients compared with controls. Furthermore, the number of CD3(+) T cells in BM, but not in blood, was increased in ITP patients compared with controls. This finding was confirmed by immunohistochemistry of BM biopsies. The number of regulatory T cells (CD4(+)/CD25(bright)) was decreased in the BM of ITP patients, whereas Fas expression was increased. In conclusion, ITP is associated with accumulation and activation of T cells in the BM. Recruitment of T cells into the target organ (eg, BM) is plausible and may be facilitated through increased VLA-4 and CX3CR1 expression. These molecules might serve as new treatment targets in ITP.

Modulation of immune response with cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin-induced anergic T cells in chronic idiopathic thrombocytopenic purpura

BACKGROUND

Platelet glycoprotein (GP)-reactive CD4+ T cells are essential for the stimulation and maintenance of antiplatelet autoantibody production in chronic idiopathic thrombocytopenic purpura (ITP). Blocking costimulatory signals could result in platelet-specific T-cell anergy.

METHODS

GP-specific CD4+ T cells from patients with ITP were made anergic using cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4-Ig). The CTLA4-Ig-induced GP-specific anergic T cells were investigated for their inhibitory function on GP-reactive T-cell proliferation and antibody production with in vitro culture systems. To further analyze their tolerizing mechanisms, we cocultured GP-anergic T cells with dendritic cells (DCs) from patients with ITP.

RESULTS

Our studies demonstrated that the anergized GP-specific T cells have profound effects on both GP-specific T-cell proliferation and antibody production. These anergic T cells exerted their suppressive effects mainly in a cell contact-dependent manner, and they were not constitutively suppressive but required specific antigen stimulation to make DCs tolerogenic. The anergic T-cell-modulated DCs could induce the autoreactive T cells to be tolerant, and this effect was not restricted to T cells of the same specificity.

CONCLUSION

Our studies demonstrate the efficacy of CTLA4-Ig in suppressing the pathologic autoimmune responses in ITP. These findings provide new insights into the underlying mechanisms of anergy induction in chronic ITP.

Correction of Th1-dominant Cytokine Profiles by High-dose Dexamethasone in Patients with Chronic Idiopathic Thrombocytopenic Purpura

To investigate the possible correcting of T helper (Th) cytokine profiles by high-dose dexamethasone (HD-DXM) therapy in chronic idiopathic thrombocytopenic purpura (ITP) with active disease, we determined the plasma levels of IFN-gamma, IL-2, IL-4, IL-10, and TGF-beta1 in 52 patients before and after oral administration of 40 mg/day DXM for four consecutive days. The cytokine levels were measured by enzyme-linked immunosorbent assay. The results showed that initial responses were reached in all patients and sustained response (SR) rate is 46.15%. The pretreatment plasma levels of both IFN-gamma and IL-2 were significantly increased and those of IL-4, IL-10, and TGF-beta1 significantly decreased, compared with those of the normal controls (P < 0.01), indicating a Th1-dominant cytokine profile typically found in ITP. After HD-DXM treatment, IFN-gamma and IL-2 were decreased (P < 0.01), whereas IL-4 and IL-10 were increased (P < 0.05). There was no significant difference between the HD-DXM-treated patients and the normal controls (P > 0.05). TGF-beta1 was also increased (P < 0.01) after HD-DXM treatment, but still lower than that of the normal controls (P < 0.05). During following-up, the cytokine profiles in the SRs remained stable compared to the posttreatment level (P > 0.05), but IFN-gamma and IL-2 levels raised up, and IL-4, IL-10, and TGF-beta1 levels reduced again in the relapsed patients (P < 0.01). Our data demonstrate that HD-DXM is an effective initial therapy for ITP, and the Th1 cytokine dominance could be corrected by HD-DXM.

Studies of chronic ITP in children and adolescents

This paper presents an ongoing study of children with chronic ITP in Sweden that addresses four specific questions: is there a subgroup of children with chronic ITP that have impaired platelet function? Do children in this subgroup have antibodies directed against surface glycoproteins that are crucial for platelet function? Can desmopressin improve the impaired platelet function in this subgroup? Do children with chronic ITP show signs of cell-mediated cytotoxicity?

Multi-dysfunctional pathophysiology in ITP

Idiopathic thrombocytopenic purpura (ITP) is an organ-specific autoimmune disorder characterized by a low platelet count and mucocutaneous bleeding. The decrease of platelets is caused by increased autoantibodies against self-antigens, particularly IgG antibodies against GPIIb/IIIa. The production of these autoantibodies by B cells depends on a number of cellular mechanisms that form a network of modulation, with T cells playing a pivotal role in pathophysiology. Delineation of the dysfunction of cellular immunity has recently been attempted. This review will focus on these recent advances applicable to ITP and to highlight how these may translate into novel approaches to treatment in the future. Multi-dysfunction in these networks may include a failure of self-antigen recognition and tolerance, involvement of abnormal cell surface molecules, altered Th1/Th2 cytokine profiles, impaired megakaryocytopoiesis and impaired cell-mediated cytotoxicity. In ITP, multi-step dysfunctions in these networks may take place that finally lead to the occurrence of the disease. Therefore, unveiling these dysfunctions is vital in understanding the pathophysiology of ITP and will finally lead to the development of new therapies to fight the disease.

Leptin and its soluble receptor in plasma of patients suffering from remitting-relapsing multiple sclerosis (MS) In vitro effects of leptin on type-1 and type-2 cytokine secretion by peripheral blood mononuclear cells, T-cells and monocytes of MS patients

Leptin is synthesized by adipocytes to regulate appetite. Leptin has also been implicated in the pathogenesis of multiple sclerosis (MS) leading to speculation about a beneficial effect of fasting to autoimmune patients. We measured plasma leptin and its soluble receptor (OB-Rs) in 52 MS patients and 50 controls. We also cultured MS and control peripheral blood mononuclear cells (PBMC), T-cells and monocytes +/- recombinant leptin (rleptin), to assess leptin's direct effect on pro- and anti-inflammatory cytokine secretion. We found similar leptin and OB-Rs plasma levels between patients and controls. Untreated patients in the acute phase or in remission, or patients treated with methylprednisolone, had lower leptin levels than patients in the acute phase or in remission receiving IFN-beta. OB-Rs levels were low in patients refractory to IFN-beta but higher in patients receiving methylprednisolone or patients in remission receiving IFN-beta. PBMC from untreated patients in the acute phase, secreted spontaneously IFN-gamma, TNF-alpha and IL-10. IFN-gamma was contributed by T-cells, TNF-alpha and IL-10 primarily by monocytes and to a lesser extent by T-cells. The overall effect of rleptin on PBMC was a net increase in IL-10 production and a net reduction in IFN-gamma production. These results do not warrant a beneficial effect of fasting to MS patients.

The Role of Autoreactive T-Cells in the Pathogenesis of Idiopathic Thrombocytopenic Purpura

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease mediated by antiplatelet autoantibodies. The major target of these autoantibodies is a platelet membrane glycoprotein, GPIIb-IIIa, which is a receptor for fibrinogen and other ligands. We recently identified CD4+ T-cells autoreactive to GPIIb-IIIa in ITP patients. These T-cells are considered pathogenic because they help B-cells produce antibodies that bind to normal platelet surfaces. GPIIb-IIIa-reactive T-cells respond to chemically reduced and tryptic peptides of GPIIb-IIIa but not to native GPIIb-IIIa, indicating that the epitopes they recognize are "cryptic" determinants generated at a subthreshold level by the processing of native GPIIb-IIIa under normal circumstances. Although GPIIb-IIIa-reactive T-cells are also detected in healthy individuals, they are activated in vivo only in ITP patients. Activation of GPIIb-IIIa-specific T-cells and the subsequent production of pathogenic anti-GPIIb-IIIa antibodies can be induced by functional antigen-presenting cells in the spleen that present cryptic GPIIb-IIIa peptides to these T-cells. The pathogenic process of ITP can be explained as a continuous loop in which B-cells produce antiplatelet autoantibodies, splenic macrophages phagocytose antibody-coated platelets and present GPIIb-IIIa-derived cryptic peptides, and GPIIb-IIIa-reactive CD4+ T-cells exert their helper activity. Further studies examining the mechanisms that induce the processing and presentation of cryptic peptides derived from the platelet antigen at disease onset will clarify how the pathogenic autoantibody response in ITP is initiated.