TLR7 promotes Th1 polarization in immune thrombocytopenia

Gut microbiome composition and dysbiosis in immune thrombocytopenia: A review of literature

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by excessive reticuloendothelial platelet destruction and inadequate compensatory platelet production. However, the pathogenesis of ITP is relatively complex, and its exact mechanisms and etiology have not been definitively established. The gut microbiome, namely a diverse community of symbiotic microorganisms residing in the gastrointestinal system, affects health through involvement in human metabolism, immune modulation, and maintaining physiological balance. Emerging evidence reveals that the gut microbiome composition differs in patients with ITP compared to healthy individuals, which is related with platelet count, disease duration, and response to treatment. These findings suggest that the microbiome and metabolome profiles of individuals could unveil a new pathway for aiding diagnosis, predicting prognosis, assessing treatment response, and formulating personalized therapeutic approaches for ITP. However, due to controversial reports, definitive conclusions cannot be drawn, and further investigations are needed.

β2-adrenergic receptor agonist corrects immune thrombocytopenia by reestablishing the homeostasis of T cell differentiation

BACKGROUND

The sympathetic nerve is known to regulate immune responses in autoimmunity. Aberrant T cell immunity plays a vital role in immune thrombocytopenia (ITP) pathogenesis. The spleen is the primary site of platelet destruction. However, little is known whether and how splenic sympathetic innervation and neuroimmune modulation contribute to ITP pathogenesis.

OBJECTIVES

To determine the sympathetic distribution in the spleen of ITP mice and the association between splenic sympathetic nerves and T cell immunity in ITP development, and to evaluate the treatment potential of β2-adrenergic receptor (β2-AR) in ITP.

METHODS

Chemical sympathectomy was performed in an ITP mouse model with 6-hydroxydopamine and treated with β2-AR agonists to evaluate the effects of sympathetic denervation and activation.

RESULTS

Decreased sympathetic innervation in the spleen of ITP mice was observed. Significantly increased percentages of Th1 and Tc1 cells and reduced percentages of regulatory T cells (Tregs) were also observed in ITP mice with chemical sympathectomy (ITP-syx mice) relative to mice without sympathectomy (controls). Expression of genes associated with Th1, including IFN-γ and IRF8, was significantly upregulated, whereas genes associated with Tregs, including Foxp3 and CTLA4, were significantly downregulated in ITP-syx mice compared with controls. Furthermore, β2-AR restored the percentage of Tregs and increased platelet counts at days 7 and 14 in ITP mice.

CONCLUSION

Our findings indicate that decreased sympathetic distribution contributes to ITP pathogenesis by disturbing the homeostasis of T cells and that β2-AR agonists have potential as a novel treatment for ITP.

The immunomodulatory activity of Chenopodium ambrosioides reduces the parasite burden and hepatic granulomatous inflammation in Schistosoma mansoni-infection

ETHNOPHARMACOLOGICAL RELEVANCE

Folk medicine reports have described the use of Chenopodium ambrosioides as an anti-inflammatory, analgesic, and anthelmintic herb. These effects, including its activity against intestinal worms, are already scientifically observed. However, the immunological mechanisms of this species in the treatment of Schistosoma mansoni infection are unknown.

AIM OF THE STUDY

To evaluate the immunological and anti-Schistosoma mansoni effects of a crude Chenopodium ambrosioides hydro-alcoholic extract (HCE).

MATERIALS AND METHODS

For the in vitro analysis, cercariae and adult worms were exposed to different concentrations (0 to 10,000 μg/mL) of the HCE. For the in vivo evaluation, Swiss mice were infected with 50 cercariae of S. mansoni and separated into groups according to treatment as follows: a negative control (without treatment), a positive control (treated with Praziquantel®), HCE1 Group (treated with HCE during the cutaneous phase), HCE2 Group (treated with HCE during the lung phase), HCE3 Group (treated with HCE during the young worm phase), and HCE4 Group (treated with HCE during the adult worm phase). The animals treated with HCE received daily doses of 50 mg/kg, by gavage, for seven days, corresponding to the different developmental stages of S. mansoni. For comparison, a clean control group (uninfected and untreated) was also included. All animals were euthanized 60 days post-infection to allow the following assessments to be performed: a complete blood cells count, counts of eggs in the feces and liver, the quantification of cytokines and IgE levels, histopathological evaluations of the livers, and the analysis of inflammatory mediators.

RESULTS

HCE treatment increased the mortality of cercariae and adult worms in vitro. The HCE treatment in vivo reduced the eggs in feces and liver. The number and area of liver granulomas, independent of the phase of treatment, were also reduced. The treatment with HCE reduced the percentage of circulating eosinophils, IgE, IFN-γ, TNF-α, and IL-4. In contrast, the treatment with the HCE, dependent on the phase, increased IL-10 levels and the number of peritoneal and bone marrow cells, mainly of T lymphocytes, B lymphocytes, and macrophages. This effect could be due to secondary compounds presents in this extract, such as kaempferol, quercetin and derivatives.

CONCLUSIONS

This study demonstrates that Chenopodium ambrosioides has antiparasitic and immunomodulatory activity against the different phases of schistosomiasis, reducing the granulomatous inflammatory profile caused by the infection and, consequently, improving the disease prognosis.

Escape from X chromosome inactivation and female bias of autoimmune diseases

Generally, autoimmune diseases are more prevalent in females than males. Various predisposing factors, including female sex hormones, X chromosome genes, and the microbiome have been implicated in the female bias of autoimmune diseases. During embryogenesis, one of the X chromosomes in the females is transcriptionally inactivated, in a process called X chromosome inactivation (XCI). This equalizes the impact of two X chromosomes in the females. However, some genes escape from XCI, providing a basis for the dual expression dosage of the given gene in the females. In the present review, the contribution of the escape genes to the female bias of autoimmune diseases will be discussed.

Potential T Cell-Intrinsic Regulatory Roles for IRF5 via Cytokine Modulation in T Helper Subset Differentiation and Function

Interferon Regulatory Factor 5 (IRF5) is one of nine members of the IRF family of transcription factors. Although initially discovered as a key regulator of the type I interferon and pro-inflammatory cytokine arm of the innate immune response, IRF5 has now been found to also mediate pathways involved in cell growth and differentiation, apoptosis, metabolic homeostasis and tumor suppression. Hyperactivation of IRF5 has been implicated in numerous autoimmune diseases, chief among them systemic lupus erythematosus (SLE). SLE is a heterogeneous autoimmune disease in which patients often share similar characteristics in terms of autoantibody production and strong genetic risk factors, yet also possess unique disease signatures. IRF5 pathogenic alleles contribute one of the strongest risk factors for SLE disease development. Multiple models of murine lupus have shown that loss of Irf5 is protective against disease development. In an attempt to elucidate the regulatory role(s) of IRF5 in driving SLE pathogenesis, labs have begun to examine the function of IRF5 in several immune cell types, including B cells, macrophages, and dendritic cells. A somewhat untouched area of research on IRF5 is in T cells, even though Irf5 knockout mice were reported to have skewing of T cell subsets from T helper 1 (Th1) and T helper 17 (Th17) toward T helper 2 (Th2), indicating a potential role for IRF5 in T cell regulation. However, most studies attributed this T cell phenotype in Irf5 knockout mice to dysregulation of antigen presenting cell function rather than an intrinsic role for IRF5 in T cells. In this review, we offer a different interpretation of the literature. The role of IRF5 in T cells, specifically its control of T cell effector polarization and the resultant T cell-mediated cytokine production, has yet to be elucidated. A strong understanding of the regulatory role(s) of this key transcription factor in T cells is necessary for us to grasp the full picture of the complex pathogenesis of autoimmune diseases like SLE.

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.

TLR7 Modulated T Cell Response in the Mesenteric Lymph Node of Schistosoma japonicum-Infected C57BL/6 Mice

Toll-like receptors (TLRs) play an important role in regulating immune responses during pathogen infection. However, roles of TLRs on T cells reside in the mesenteric lymph node (MLN) were not be fully elucidated in the course of S. japonicum infection. In this study, T lymphocytes from the mesenteric lymph node (MLN) of S. japonicum-infected mice were isolated and the expression and roles of TLR2, TLR3, TLR4, and TLR7 on both CD4⁺ and CD8⁺ T cells were compared. We found that the expression of TLR7 was increased in the MLN cells of S. japonicum-infected mice, particularly in CD4⁺ and CD8⁺ T cells (P < 0.05). R848, a TLR7 agonist, could enhance the production of IFN-γ from MLN T cells of infected mice (P < 0.05), especially in CD8⁺ T cells (P < 0.01). In TLR7 gene knockedout (KO) mice, the S. japonicum infection caused a significant decrease (P < 0.05) of the expression of CD25 and CD69, as well as the production of IFN-γ and IL-4 inducted by PMA plus ionomycin on both CD4⁺ and CD8⁺ T cells. Furthermore, the decreased level of IFN-γ and IL-4 in the supernatants of SEA- or SWA-stimulated mesenteric lymphocytes was detected (P < 0.05). Our results indicated that S. japonicum infection could induce the TLR7 expression on T cells in the MLN of C57BL/6 mice, and TLR7 mediates T cell response in the early phase of infection.

In Vitro Transcribed mRNA Vaccines with Programmable Stimulation of Innate Immunity

In vitro transcribed (IVT) mRNA is an appealing platform for next generation vaccines, as it can be manufactured rapidly at large scale to meet emerging pathogens. However, its performance as a robust vaccine is strengthened by supplemental immune stimulation, which is typically provided by adjuvant formulations that facilitate delivery and stimulate immune responses. Here, we present a strategy for increasing translation of a model IVT mRNA vaccine while simultaneously modulating its immune-stimulatory properties in a programmable fashion, without relying on delivery vehicle formulations. Substitution of uridine with the modified base N1-methylpseudouridine reduces the intrinsic immune stimulation of the IVT mRNA and enhances antigen translation. Tethering adjuvants to naked IVT mRNA through antisense nucleotides boosts the immunostimulatory properties of adjuvants in vitro, without impairing transgene production or adjuvant activity. In vivo, intramuscular injection of tethered IVT mRNA-TLR7 agonists leads to enhanced local immune responses, and to antigen-specific cell-mediated and humoral responses. We believe this system represents a potential platform compatible with any adjuvant of interest to enable specific programmable stimulation of immune responses.

Transplantation of bone-marrow-derived mesenchymal stem cells into a murine model of immune thrombocytopenia

: Several reports have demonstrated T regulatory cells may play an important role in the pathophysiology of immune thrombocytopenia (ITP). As the immunomodulator, bone-marrow-derived mesenchymal stem cells (MSCs) (BM-MSCs) regulate T regulatory cells and show therapeutic effects on autoimmune diseases. However, it is not clear how BM-MSCs affect ITP. In this study, we explored the specific effects of BM-MSCs on ITP in mice. Using a murine model of ITP, mice were randomly divided into three groups: normal control group, ITP control group and ITP and BM-MSCs group. Platelet (PLT) levels were monitored by an automatic blood cell counter, and T regulatory cells were analyzed by flow cytometry. Compared with the untreated ITP mice, the PLT level of the ITP mice was significantly increased after BM-MSCs treatment. In the BM-MSCs group, T regulatory cells were significantly decreased. These findings demonstrate that bone-marrow-derived MSCs are effective in improving PLT levels and reducing the T regulatory cells mediating proinflammatory response in ITP mice.

The expression profile of toll-like receptor signaling molecules in CD19(+) B cells from patients with primary immune thrombocytopenia

BACKGROUND

B cells play a critical role in the pathogenesis of immune thrombocytopenia (ITP), and toll-like receptor (TLR) signaling is essential for the activation of autoreactive B cells. The objective of this study was to investigate the expression profile of TLR signaling molecules in circulating and splenic CD19(+) B cells isolated from ITP patients.

METHODS

CD19(+) B cells were magnetically isolated from peripheral blood and splenocytes. Human Toll-Like Receptor Signaling Pathway RT(2) Profiler™ PCR Array was used to determine the differences in mRNA expression of 84 TLR signaling pathway genes between ITP patients and controls. Flow cytometry was used to investigate intracellular expression of cytokines (IL-1β and IL-10).

RESULTS

A total of 31 genes involving TLR signaling pathways were differentially transcribed in circulating CD19(+) B cells, among which 27 were up-regulated in ITP. By comparison, differentially transcribed genes amounted to 39 in splenic B cells in ITP, among which only two were down-regulated. Up to 18 TLR signaling molecules exhibited up-regulated transcriptional levels both in splenic B cells and in circulating B cells in ITP. However, Only IL-10 and IL-1β were significantly upregulated in both the circulating and splenic B cells of patients with ITP. Intracellular staining of IL-10 and IL-1β confirmed the results of PCR Array.

CONCLUSIONS

The expression of TLRs and downstream cytokines, including IL-10 and IL-1β, is up-regulated in circulating and splenic B cells in ITP patients, suggesting that activated TLR signaling pathways in B cells may play dual roles in the pathophysiology of primary ITP.

Type I IFN Contributes to the Phenotype of Unc93b1D34A/D34A Mice by Regulating TLR7 Expression in B Cells and Dendritic Cells

TLR7 recognizes pathogen-derived and self-derived RNA, and thus a regulatory system for control of the TLR7 response is required to avoid excessive activation. Unc93 homolog B1 (Unc93B1) is a regulator of TLR7 that controls the TLR7 response by transporting TLR7 from the endoplasmic reticulum to endolysosomes. We have previously shown that a D34A mutation in Unc93B1 induces hyperactivation of TLR7, and that Unc93b1(D34A/D34A) mice (D34A mice) have systemic inflammation spontaneously. In this study, we examined the roles of inflammatory cytokines such as IFN-γ, IL-17A, and type I IFNs to understand the mechanism underlying the phenotype in D34A mice. mRNAs for IFN-γ and IL-I7A in CD4(+) T cells increased, but inflammatory phenotype manifesting as thrombocytopenia and splenomegaly was still observed in Ifng(-/-) or Il17a(-/-) D34A mice. In contrast to T cell-derived cytokines, Ifnar1(-/-) D34A mice showed an ameliorated phenotype with lower expression of TLR7 in B cells and conventional dendritic cells (cDCs). The amount of TLR7 decreased in B cells from Ifnar1(-/-) D34A mice, but the percentage of TLR7(+) cells decreased among CD8α(-) cDCs. In conclusion, type I IFNs maintain expression of TLR7 in B cells and cDCs in different ways; total amount of TLR7 is kept in B cells and TLR7(+) population is retained among cDCs. Our results suggested that these TLR7-expressing cells are activated initially and influence TLR7-dependent systemic inflammation.

Biomarkers for immune thrombocytopenia

Immune thrombocytopenia is an autoimmune disease with abnormal biomarkers. Immune thrombocytopenia pathogenesis is a complicated process in which the patient’s immune system is activated by platelet autoantigens resulting in immune mediated platelet destruction or suppression of platelet production. The autoantibodies produced by autoreactive B cells against self antigens are considered to play a crucial role. In addition, biomarkers such as transforming growth factor-beta1,Toll-like receptors,T helper 1 andT helper 2 cytokine bias, Notch signaling and abnormal biomarker in megakaryocyte maturation are involved in the pathogenesis of this disease. With the genomewide association study on immune thrombocytopenia, more biomarkers will be founded in the future. They may provides a theoretical basis for the mechanism and treatment of immune thrombocytopenia.

Platelet destruction in immune thrombocytopenia. Understanding the mechanisms

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by isolated thrombocytopenia. A dysfunctional proliferation of autoreactive T cells is suggested to be responsible for the loss of tolerance to self-platelet antigens in ITP patients. Autoreactive T cells induce uncontrolled proliferation of autoantibody producing B cells leading to persistent anti-platelet autoimmunity in some ITP patients. The autoimmune response causes an increased destruction of platelets by antibody-mediated phagocytosis, complement activation but also by T cell mediated cytotoxicity. In addition, abnormalities in thrombopoiesis and insufficient platelet production due to antibody or T cell mediated megakaryocyte inhibition and destruction contribute to the pathophysiology of ITP. These various effector cell responses may account for the heterogeneity in the clinical manifestation of ITP and also, to success or failure of different treatment strategies. A better understanding of the mechanisms behind ITP will hopefully allow for better diagnostic and, particularly, therapeutic strategies in the future.

STAT1 single nucleotide polymorphisms and susceptibility to immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder. One of the key mediators of IFN-γ signaling is the signal transducer and activator of transcription 1 protein (STAT1). We evaluated the relationship between STAT1 gene single nucleotide polymorphisms (SNPs) and the associated risk of ITP in a prospective case-control study. A total of 548 children were recruited: 328 children with ITP and 220 healthy children as sex- and age-matched normal controls. The Sequenom MassArray system (Sequenom, San Diego, CA) was used to detect three SNPs genotypes in the STAT1 gene: rs10208033, rs12693591, and rs1467199. There is a statistically significant difference in STAT1 rs1467199 allele frequencies with comparison of each of the four clinical subgroups of ITP patients to the normal controls (p = 0.0432). Also, newly diagnosed ITP patients and chronic ITP patients demonstrate significant different genotypes (χ(2 )= 8.511, p = 0.0142) and allelic frequency (p = 0.0055). Although a positive STAT1 rs1467199 genotype subgroups to the STAT1 mRNA expression level cannot be established, there is a weak correlation between STAT1 mRNA level and the activity ratio of Type 1 T helper lymphocyte and Type 2 T helper lymphocyte (Th1/Th2 ratio) (p = 0.0544); correlation with IFN-γ alone did not reach statistical significance (p = 0.1715). The findings in our study suggest that STAT1 rs1467199 SNP plays a potential role in the IFN-γ dependent development of autoimmunity in children with ITP. The important clinical implication of STAT1 SNPs testing as a predictor of pediatric chronic ITP will be validated in future molecular and protein functional analysis.

Amelioration of murine passive immune thrombocytopenia by IVIg and a therapeutic monoclonal CD44 antibody does not require the Myd88 signaling pathway

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by a low platelet count and the production of anti-platelet antibodies. The majority of ITP patients have antibodies to platelet integrin α_IIbβ₃ (GPIIbIIIa) which can direct platelet phagocytosis by macrophages. One effective treatment for patients with ITP is intravenous immunoglobulin (IVIg) which rapidly reverses thrombocytopenia. The exact mechanism of IVIg action in human patients is unclear, although in mouse models of passive ITP, IVIg can rapidly increase platelet counts in the absence of adaptive immunity. Another antibody therapeutic that can similarly increase platelet counts independent of adaptive immunity are CD44 antibodies. Toll-like receptors (TLRs) are pattern recognition receptors which play a central role in helping direct the innate immune system. Dendritic cells, which are notable for their expression of TLRs, have been directly implicated in IVIg function as an initiator cell, while CD44 can associate with TLR2 and TLR4. We therefore questioned whether IVIg, or the therapeutic CD44 antibody KM114, mediate their ameliorative effects in a manner dependent upon normal TLR function. Here, we demonstrate that the TLR4 agonist LPS does not inhibit IVIg or KM114 amelioration of antibody-induced thrombocytopenia, and that these therapeutics do not ameliorate LPS-induced thrombocytopenia. IVIg was able to significantly ameliorate murine ITP in C3H/HeJ mice which have defective TLR4. All known murine TLRs except TLR3 utilize the Myd88 adapter protein to drive TLR signaling. Employing Myd88 deficient mice, we found that both IVIg and KM114 ameliorate murine ITP in Myd88 deficient mice to the same extent as normal mice. Thus both IVIg and anti-CD44 antibody can mediate their ameliorative effects in murine passive ITP independent of the Myd88 signaling pathway. These data help shed light on the mechanism of action of IVIg and KM114 in the amelioration of murine ITP.

CD16+ monocytes control T-cell subset development in immune thrombocytopenia

Immune thrombocytopenia (ITP) results from decreased platelet production and accelerated platelet destruction. Impaired CD4(+) regulatory T-cell (Treg) compartment and skewed Th1 and possibly Th17 responses have been described in ITP patients. The trigger for aberrant T-cell polarization remains unknown. Because monocytes have a critical role in development and polarization of T-cell subsets, we explored the contribution of monocyte subsets in control of Treg and Th development in patients with ITP. Unlike circulating classic CD14(hi)CD16(-) subpopulation, the CD16(+) monocyte subset was expanded in ITP patients with low platelet counts on thrombopoietic agents and positively correlated with T-cell CD4(+)IFN-γ(+) levels, but negatively with circulating CD4(+)CD25(hi)Foxp3(+) and IL-17(+) Th cells. Using a coculture model, we found that CD16(+) ITP monocytes promoted the expansion of IFN-γ(+)CD4(+) cells and concomitantly inhibited the proliferation of Tregs and IL-17(+) Th cells. Th-1-polarizing cytokine IL-12, secreted after direct contact of patient T-cell and CD16(+) monocytes, was responsible for the inhibitory effect on Treg and IL-17(+)CD4(+) cell proliferation. Our findings are consistent with ITP CD16(+) monocytes promoting Th1 development, which in turn negatively regulates IL-17 and Treg induction. This underscores the critical role of CD16(+) monocytes in the generation of potentially pathogenic Th responses in ITP.

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.