Antiplatelet Autoantibodies Research Articles

Increase of C3a is Associated with Hemorrhagic Propensity in Patients with Immune Thrombocytopenia.

Complement activation is critically involved in multiple autoimmune diseases. Immune thrombocytopenia (ITP) is a hemorrhagic condition with enhanced platelet clearance caused by antiplatelet autoantibodies. However, the roles of complements C3a, C5a, and soluble C5b-9 (sC5b-9) in the hemorrhage of ITP remain unknown. Plasma C3a, C5a, and sC5b-9 levels in ITP patients were measured by enzyme-linked immunosorbent assay (ELISA). Antiplatelet autoantibodies (anti-GPIIb/IIIa and anti-GPIbα) were evaluated by modified monoclonal antibody immobilization of platelet antigen (MAIPA) assay. The severity of bleeding was assessed using the validated bleeding score for each ITP patient at onset. Levels of C3a, C5a, and sC5b-9 were significantly increased in active ITP patients, compared with those in controls (p < 0.001). However, levels of C3a, C5a, and sC5b-9 were not changed by treatment of HD-DXM. In addition, the C3a levels were correlated with the increase in bleeding scores from the patients with ITP (p < 0.05, r = 0.256). In contrast, neither platelet counts nor antiplatelet autoantibodies (anti-GPIIb/IIIa and anti-GPIbα) showed any correlation with levels of C3a, C5a, and sC5b-9. Levels of C3a, C5a, and sC5b-9 are increased in patients with ITP, suggesting a hyperactive complement system. Certain complement components, such as C3a, may contribute to hemorrhage of patients with ITP.

Regulatory and Memory B Lymphocytes in Children With Newly Diagnosed Immune Thrombocytopenia.

BackgroundImmune (idiopathic) thrombocytopenic purpura (ITP) is a primary autoimmune disease. It is characterized by a diminished peripheral platelet count (< 100 × 109/L) caused by platelet destruction with an increased risk of mucocutaneous bleeding. The diagnosis of ITP depends on clinical characteristics and the laboratory examinations conducted, as well as the ability to exclude other diseases associated with thrombocytopenia. Antiplatelet autoantibodies are responsible for platelet destruction and probably for inhibition of megakaryopoiesis. B lymphocytes participate in immune responses through production of antibodies, antigen presentation to T cells, and cytokine secretion. The aims of this study were to investigate the levels of Bregs and memory B lymphocytes in newly diagnosed pediatric ITP patients and to correlate their levels with the course of the disease.MethodsThis study was a case-control study. The study included 30 patients with acute ITP. The patients were recruited from Pediatric Clinical Hematology Unit of Children Hospital, Assiut University. In addition, 20 healthy children of comparable age and sex were taken as controls. The institutional review board approved the study and informed consents were obtained.ResultsThere is a significant alteration of B-cell homeostasis in patients with ITP.ConclusionAnalysis of Bregs and memory B cells could serve as prognostic markers and might guide therapy in ITP patients in the future.

Plasma microRNAs characterising patients with immune thrombocytopenic purpura.

Altered microRNA (miRNA) expression has been reported in patients with immune thrombocytopenic purpura (ITP). However, the detailed expression profiling of cell-free circulating miRNAs in ITP patients has not been fully investigated. In this study, we aimed to examine plasma miRNAs in ITP patients and evaluate their diagnostic values. Plasma samples from 74 ITP patients and 58 healthy controls were obtained and allocated into discovery, validation, and therapy-response sets. Initial screen with a miRNA microarray assay identified 23 miRNAs with different levels between ITP patients and healthy controls (>1.5-fold changes; p<0.01). Subsequent quantitative real-time PCR confirmed eight up-regulated miRNAs (miR-320c, miR-642b-3p, miR-1275, miR-3141, miR-4270, miR-4499, miR-4739 and miR-6126) and three down-regulated miRNAs (miR-144-3p, miR-1281 and miR-3162-3p) in ITP patients. The levels of these circulating miRNAs varied, depending on ITP subtypes, i.e. newly-diagnosed, persistent and chronic ITP, and between treatment responders and non-responders. In receiver operator characteristic analysis, 10 miRNAs had positive diagnostic values (p<0.05) when tested individually. The diagnostic value improved when the miRNAs were analysed as a panel or together with the analysis of anti-platelet autoantibodies. Plasma miR-3162-3p levels were also found to positively correlate with platelet counts in ITP patients (r=0.338, p=0.01). Our results indicate that plasma miRNA profiles are altered in ITP patients and that the differentially expressed miRNAs may be used as biomarkers to improve the diagnosis of ITP.

Ethylenediaminetetraacetic Acid (EDTA)-Induced Thrombocytopenia: A Case Report

Ethylenediaminetetraacetic Acid (EDTA)-Induced Thrombocytopenia is a fairly rare in vitro immunological mediated phenomenon characterized by a spuriously low platelet count on automated analyzers secondary to antiplatelet autoantibodies which cause platelets to aggregate in specimens ant coagulated with EDTA. The aggregations of platelets result in a false increase in leukocytes as giant platelets are counted as lymphocytes. Failure to detect this EDTA-Induced Thrombocytopenia could result in unnecessary laboratory investigations and superfluous interventions. EDTA-induced thrombocytopenia is sometimes prevented by other anticoagulants such as sodium citrate or heparin. In this article we reported a case of a 23-year-old female with EDTA-induced thrombocytopenia and a falsely increased leukocyte count confirmed by the use of a citrated tube and a peripheral smear without platelet aggregation.

Mouse immune thrombocytopenia is associated with Th1 bias and expression of activating Fcγ receptors.

Immune thrombocytopenia (ITP) is an autoimmune disease mediated by anti-platelet autoantibodies. We recently established a mouse ITP model exhibiting regulatory T-cell (Treg) deficiency, although only one-third of the Treg-deficient mice developed ITP. To clarify mechanisms involved in the emergence of platelet-specific autoimmunity in this model, we examined the T helper (Th)-cell balance and macrophage Fcγ receptor (FcγR) expression profiles in Treg-deficient mice with and without ITP. Splenocytes from both populations of Treg-deficient mice and control BALB/c mice were subjected to flow cytometry-based analyses to evaluate Th cell subset proportions and the expression of activating and inhibitory FcγRs on macrophages. In addition, IgG subclass distribution of anti-platelet autoantibodies in splenocyte culture supernatants was determined by flow cytometry using IgG subclass-specific antibodies. Treg-deficient ITP mice exhibited a significantly higher proportion of Th1 cells than either Treg-deficient non-ITP or control mice. The predominant anti-platelet autoantibody subclasses in the ITP mice were Th1-associated IgG2a and IgG2b. Furthermore, the FcγRI/FcγRIIB expression ratio in splenic macrophages was higher in the Treg-deficient ITP than in the Treg-deficient non-ITP and control mice. In summary, Th1 polarization and macrophages' activating FcγR expression profile are associated with the development of ITP in Treg-deficient mice.

Cytokine and Chemokine Levels Correlate with Apoptosis Markers in Platelets of Pediatric Patients with Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is defined as an autoimmune disease that leads to platelet clearance by macrophages. It is well known that auto-reactive B cells and CD4+ T-helper (Th) cells, and in particular their cytokines, have been associated with ITP. Cytokines and chemokines are key players in our immune response to recruit different cells, e.g. macrophages and monocytes, to respond to certain inflammatory signals. Specific cytokines (i.e. TNF-a, IFN-g) are known to induce apoptosis in nucleated blood cells.To understand the role of cytokines and chemokines in acute ITP, we studied their plasma levels in 10 pediatric ITP patients at diagnosis with a median platelet count of 3 x 109/L (range < 1 to 22 x 109/L) and compared them with controls: healthy children (n=9; platelet count > 150 x 109/L); and chemotherapy-induced thrombocytopenia patients (cTP; n=9; median platelet count of 12 x 109/L; range: 3-53 x 109/L). ITP patients fulfilled the criteria for acute ITP and presented with mild to moderate bleeding symptoms. The median age at diagnosis was 3.4 yrs (range: 1.6 - 6.5 yrs); blood samples were taken prior to treatment. Luminex technology was used to measure plasma levels of 42 cytokines and chemokines. Markers of platelet apoptosis - activated caspase-3, -8 and -9 - and of platelet activation - CD62P and CD63 expression and PAC-1 binding - were measured by flow cytometry.Distinct plasma cytokine/chemokine patterns were observed in ITP patients compared with controls. Significantly increased levels of the Th1 cell commitment cytokines TNF-α (p < 0.01) and IFN-g (p < 0.05), as well as of the Th2 cytokines IL-6 (p < 0.01), IL-10 (p < 0.01) and IL-13 (p < 0.05), were identified in ITP patients. We have previously shown that there is activation of platelet caspase-3, -8 and -9 at diagnosis in acute paediatric ITP patients compared with controls (Winkler et al, Br J Haematol 2012;156:508). In ITP patients, but not in controls, a negative correlation between eotaxin and caspase- 3 (r2 = 0.72), -8 (r2 = 0.76) and -9 (r2 = 0.53) activity were observed, as well as a negative correlations between GM-CSF and caspase-8 (r2 = 0.52) and -9 (r2 = 0.33). Furthermore, we found a correlation between IL-13 and platelet activation as measured by CD62P (r2 = 0.87) and CD63 (r2 = 0.67) expression in ITP patients but not in controls.In summary, increased plasma levels of the cytokines TNF-α, IFN-g, IL-6, IL-10, and IL-13 were observed in ITP patients at initial presentation, suggesting that these cytokines contribute to the pathogenesis of the disease. Since IL-6 and IFN-g are known to activate macrophages, while higher levels TNF-α, IL-10 and IL-13 in the plasma are signs for activated T cells, our findings are consistent with the current model of ITP, in which activated macrophages induce B and T cells to produce anti-platelet autoantibodies. Our goal is to study the interplay between the immune system and the reduction of platelet count in ITP and to further define apoptosis/activation-related pathways in ITP platelets.Furthermore, we showed a correlation in ITP patients between the chemokine eotaxin and GM-CSF with caspase-3, -8 and -9 activity, and a correlation between IL-13 and platelet activation. Our results imply, that apoptosis and platelet activation at diagnosis in ITP play a role in the development of ITP, but the underlying mechanisms are still unknown and needs to be further evaluated by increasing the patient cohort in our study. DisclosuresNo relevant conflicts of interest to declare.

B cell depleting therapy regulates splenic and circulating T follicular helper cells in immune thrombocytopenia

B cells are involved in immune thrombocytopenia (ITP) pathophysiology by producing antiplatelet auto-antibodies. However more than a half of ITP patients do not respond to B cell depletion induced by rituximab (RTX). The persistence of splenic T follicular helper cells (TFH) that we demonstrated to be expanded during ITP and to support B cell differentiation and antiplatelet antibody-production may participate to RTX inefficiency. Whereas it is well established that the survival of TFH depends on B cells in animal models, nothing is known in humans yet. To determine the effect of B cell depletion on human TFH, we quantified B cells and TFH in the spleen and in the blood from ITP patients treated or not with RTX. We showed that B cell depletion led to a dramatic decrease in splenic TFH and in CXCL13 and IL-21, two cytokines predominantly produced by TFH. The absolute count of circulating TFH and serum CXCL13 also decreased after RTX treatment, whatever the therapeutic response. Therefore, we showed that the maintenance of TFH required B cells and that TFH are not involved in the inefficiency of RTX in ITP.

Mechanisms of loss of immune tolerance in the production of antiplatelet autoantibodies in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an organ-specific autoimmune hemorrhagic disease. The etiology of ITP is still unclear, but loss of immune tolerance to platelet surface antigens is considered as a fundamental cause of ITP. Therapeutic strategies that prevent the activation and proliferation of autoreactive cells have been suggested, which includes clearance of autoreactive cells (apoptosis), receptor editing, induction of anergy and extrinsic cellular suppression. Failure at any of these steps may lead to the production of autoantibodies against platelet and megakaryocyte glycoproteins. An improved understanding of the mechanisms for autoantibody production will provide theoretical basis for optimal diagnosis and treatment of ITP. Key words: ITP; Autoantibody; Immune tolerance

The spleen dictates platelet destruction, anti-platelet antibody production, and lymphocyte distribution patterns in a murine model of immune thrombocytopenia.

For many years, splenectomy has been used to treat immune thrombocytopenia (ITP), and this procedure benefits approximately two-thirds of the treated patients. Although splenectomy may raise platelet counts, antibody-coated platelets and cytotoxic T lymphocytes appear to persist or can change over time. To better understand how the spleen may affect anti-platelet immune responses, we used a murine model of ITP demonstrating both antibody-mediated and T lymphocyte-mediated thrombocytopenia. Mice with severe combined immunodeficiency (SCID) were either splenectomized or not and transfused with splenocytes from CD61 (GPIIIa) knockout mice immunized against CD61(+) platelets. Platelet counts and anti-platelet antibody levels were performed weekly. After 4weeks, the mice were sacrificed, and lymphoid organs were harvested and examined by flow cytometry to quantify CD4(+)CD25(+)FoxP3(+) Tregs and conventional cross-presenting XCR1(+) and tolerizing SIRPα+ dendritic cells. The results indicate that compared with control non-splenectomized mice, thrombocytopenia was improved and anti-platelet antibody production was significantly diminished in all splenectomized mice that received immune splenocytes. Splenectomized SCID mice also had a marked reduction in Tregs in the thymus together with an increased proportion of both thymic dendritic cell subsets that correlated with increased platelet counts. Of interest, although splenectomy diminished anti-platelet antibody production and raised platelet counts, marrow megakaryocyte densities were still significantly reduced in mice that received immune splenocytes. These results suggest that the spleen in murine ITP not only is the primary site responsible for platelet destruction, but it also controls, to a significant extent, the antibody response against platelets and the migration patterns of lymphocyte subsets.

CD8(+) T cells induce platelet clearance in the liver via platelet desialylation in immune thrombocytopenia.

In addition to antiplatelet autoantibodies, CD8+ cytotoxic T lymphocytes (CTLs) play an important role in the increased platelet destruction in immune thrombocytopenia (ITP). Recent studies have highlighted that platelet desialylation leads to platelet clearance via hepatocyte asialoglycoprotein receptors (ASGPRs). Whether CD8+ T cells induce platelet desialylation in ITP remains unclear. Here, we investigated the cytotoxicity of CD8+ T cells towards platelets and platelet desialylation in ITP. We found that the desialylation of fresh platelets was significantly higher in ITP patients with positive cytotoxicity of CD8+ T cells than those without cytotoxicity and controls. In vitro, CD8+ T cells from ITP patients with positive cytotoxicity induced significant platelet desialylation, neuraminidase-1 expression on the platelet surface, and platelet phagocytosis by hepatocytes. To study platelet survival and clearance in vivo, CD61 knockout mice were immunized and their CD8+ splenocytes were used. Platelets co-cultured with these CD8+ splenocytes demonstrated decreased survival in the circulation and increased phagocytosis in the liver. Both neuraminidase inhibitor and ASGPRs competitor significantly improved platelet survival and abrogated platelet clearance caused by CD8+ splenocytes. These findings suggest that CD8+ T cells induce platelet desialylation and platelet clearance in the liver in ITP, which may be a novel mechanism of ITP.

What do we learn from immunomodulation in patients with immune thrombocytopenia?

Current therapeutic strategies for autoimmune diseases primarily rely on immunosuppression, but global immune suppression results in an increased risk for severe infection and malignancy. In contrast, immuomodulation is another therapeutic approach employing intrinsic or environmental regulators that exert modulatory effects by intervening multiple checkpoints of the immune system, leading to correction of dysregulated immune responses. We have learned that immunomodulation by intravenous immunoglobulin is highly efficacious and safe in patients with immune thrombocytopenia (ITP), an autoimmune disease mediated by IgG antiplatelet autoantibodies. Recently, another types of immunomodulatory treatment are also effective for ITP. These include eradication of Helicobacter pylori and thrombopoietic agents, such as thrombopoietin receptor agonists. These treatment modalities are shown to exert immunomodulatory action by suppressing multiple checkpoints of the pathogenic loop of ITP, although only certain subsets of the patients show robust responses. Understanding mechanisms underlying immunomodulation is highly useful in clarifying pathogenesis of immune-mediated diseases and developing novel therapeutic approaches.

High-dose dexamethasone vs prednisone for treatment of adult immune thrombocytopenia: a prospective multicenter randomized trial

AbstractThis study compared the efficacy and safety of high-dose dexamethasone (HD-DXM) and conventional prednisone (PDN) on the largest cohort to date as first-line strategies for newly diagnosed adult primary immune thrombocytopenia (ITP). Patients enrolled were randomized to receive DXM 40 mg/d for 4 days (n = 95, nonresponders received an additional 4-day course of DXM) or prednisone 1.0 mg/kg daily for 4 weeks and then tapered (n = 97). One or 2 courses of HD-DXM resulted in a higher incidence of overall initial response (82.1% vs 67.4%, P = .044) and complete response (50.5% vs 26.8%, P = .001) compared with prednisone. Time to response was shorter in the HD-DXM arm (P < .001), and a baseline bleeding score ≥8 was associated with a decreased likelihood of initial response. Sustained response was achieved by 40.0% of patients in the HD-DXM arm and 41.2% in the PDN arm (P = .884). Initial complete response was a positive indicator of sustained response, whereas presence of antiplatelet autoantibodies was a negative indicator. HD-DXM was generally tolerated better. We concluded that HD-DXM could be a preferred corticosteroid strategy for first-line management of adult primary ITP. This study is registered at www.clinicaltrials.gov as #NCT01356511.

Advances in Diagnosis and Treatments for Immune Thrombocytopenia.

Immune thrombocytopenia (ITP) is an acquired hemorrhagic condition characterized by the accelerated clearance of platelets caused by antiplatelet autoantibodies. A platelet count in peripheral blood <100 × 109/L is the most important criterion for the diagnosis of ITP. However, the platelet count is not the sole diagnostic criterion, and the diagnosis of ITP is dependent on additional findings. ITP can be classified into three types, namely, acute, subchronic, and persistent, based on disease duration. Conventional therapy includes corticosteroids, intravenous immunoglobulin, splenectomy, and watch-and-wait. Second-line treatments for ITP include immunosuppressive therapy [eg, anti-CD20 (rituximab)], with international guidelines, including rituximab as a second-line option. The most recently licensed drugs for ITP are the thrombopoietin receptor agonists (TRAs), such as romiplostim and eltrombopag. TRAs are associated with increased platelet counts and reductions in the number of bleeding events. TRAs are usually considered safe, effective treatments for patients with chronic ITP at risk of bleeding after failure of first-line therapies. Due to the high costs of TRAs, however, it is unclear if patients prefer these agents. In addition, some new agents are under development now. This manuscript summarizes the pathophysiology, diagnosis, and treatment of ITP. The goal of all treatment strategies for ITP is to achieve a platelet count that is associated with adequate hemostasis, rather than a normal platelet count. The decision to treat should be based on the bleeding severity, bleeding risk, activity level, likely side effects of treatment, and patient preferences.

Serum thrombopoietin and platelet antibodies in thrombocytopenic patients with chronic hepatitis C virus: clinical application of platelet indices

Background Chronic hepatitis C virus (HCV) infection is prevalent in 160 million individuals worldwide. Egypt has the highest prevalence of HCV in the world. HCV is known to cause thrombocytopenia even in the absence of overt hepatic disease. The pathophysiology of thrombocytopenia with chronic HCV is complex. Aims To evaluate serum thrombopoietin (TPO) and platelet antibodies in thrombocytopenic patients with chronic HCV and to assess the diagnostic utility of mean platelet volume (MPV) and platelet distribution width (PDW). Patients and methods The present study included 70 patients with chronic HCV with thrombocytopenia divided into two groups; 20 age-matched and sex-matched HCV patients without thrombocytopenia were also included as controls. Serum TPO, platelet autoantibodies, MPV, and PDW were measured in all participants. Results A significantly lower serum TPO level and platelet count were found with advancing degree of liver fibrosis and activity. Significantly higher MPV and PDW were found in patients with antiplatelet autoantibodies formation. The platelet count showed significant positive correlations with TPO level, MPV, and PDW, and inverse correlations with aspartate aminotransferase, alanine aminotransferase, and viral load. Conclusion The dominant mechanism in mild thrombocytopenic HCV patients was the formation of antiplatelet autoantibodies, whereas in moderate to severe thrombocytopenic patients, the dominant mechanism was combined bone marrow affection and formation of antiplatelet autoantibodies. Serum TPO level was decreased in patients with HCV-induced thrombocytopenia. MPV and PDW may be used as indicators for the dominant mechanism. Egyptian J Haematol 41:-0 ͹ 2016 The Egyptian Society of Haematology.

Immune Profiling of Immune Thrombocytopenia (ITP) Patients: Evidence for CD8 T Cell Involvement in the Disease

Introduction: Immune thrombocytopenia (ITP) is a bleeding disorder caused by an autoimmune response against platelets. In the majority of cases, ITP is thought to be caused by the presence of autoreactive B cells that produce anti-platelet autoantibodies and target platelets for destruction by phagocytic cells. However, in about 40% of ITP patients platelet autoantibodies cannot be detected and there is some evidence that cytotoxic cells might also be responsible for platelet death. Indeed, many patients repeatedly fail to respond to current immunosuppressive therapies that target B cells and their autoantibodies. As a consequence, these patients retain very low platelet counts with increased bleeding diathesis. In this study we have immunophenotyped a group of adult chronic ITP patients that have not responded to traditional immunosuppressive therapies and we identified 2 subgroups of patients with either an increase or decrease in the frequency of CD8+ T effector memory CD45RA+ cells (CD8TEMRA) compared to healthy controls.Methods: PBMCs were isolated from blood samples of 14 ITP patients with platelet counts <100x109/L and 14 matched healthy controls. The cells were phenotyped using a variety of antibodies including: CD3, CD4, CD8, CD45RA, CCR7, CD127, CD25, CD14, CD16 and CD19. In addition, at least 5x106 PBMCs were stimulated with PMA (50ng/ml) and ionomycin (1µg/ml) for 5 hours at 37°C, 5% CO2 and stained with antibodies against CD3 and CD8, then fixed and permeabilised before staining with antibodies specific to Granzyme B and Interferon-γ.Results and discussion: In our cohort of ITP patients we were able to identify two subgroups of patients based on their frequency of CD8TEMRA cells, identified as CD45RA+ CCR7- cells, gated on CD3+ CD8+ cells. Compared to healthy controls (mean=16.33%), 6/14 patients had significantly lower frequencies of CD8TEMRA cells (mean=11.31%) and 8/14 patients showed a significant increase (mean=31.50%). Interestingly, these two groups of patients also show significant differences between them in the frequency of CD19+ B cells (gated on CD3- cells), as the group with the lowest CD8TEMRA frequency showed a significant increase in B cells compared to the high CD8TEMRA group. Considering that CD8TEMRA cells are described as highly differentiated cytotoxic T cells, these results suggest that in patients with active ITP in which the CD8TEMRA population is more prevalent and the frequency of B cells is reduced, cytotoxic T cells might play an important role in platelet destruction. Although an increase in the frequency of CD8TEMRA with age has been described we did not find a correlation between these two variables in our cohort of patients. In the low CD8TEMRA group we also observed a significant increase in the frequency of T regulatory cells (Tregs) and monocytes when compared to healthy controls, whereas the trend in the high CD8TEMRA group was for frequencies closer to controls. In addition, when analysing the production of Granzyme B and Interferon-γ after a short in vitro stimulation, we found that the trend was for the CD8+ T cells in the high CD8TEMRA group to produce higher levels of both Granzyme B and Interferon-γ when compared to the patients in the low CD8TEMRA group. This would support the hypothesis that in patients with increased frequency of CD8TEMRA there has been an expansion of cells with cytotoxic properties. Further work will be required to confirm that in this cohort of patients there is a CD8+ T cell population that can specifically target and lyse platelets, thus contributing to ITP pathogenesis. DisclosuresProvan:UCB: Consultancy; GSK: Equity Ownership, Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Medimmune: Consultancy.

Stromal cell-derived factor-1 rs2297630 polymorphism associated with platelet production and treatment response in Chinese patients with chronic immune thrombocytopenia

Stromal cell-derived factor-1 (SDF-1), signaling through CXCR4, is implicated in megakaryopoiesis and platelet production. SDF-1 rs2297630 is a functional polymorphism in linkage disequilibrium with other functional variants in SDF-1. This study aimed to investigate the role of SDF-1 rs2297630 in chronic ITP. The genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism and confirmed by direct sequencing. Immature platelet fraction (IPF) was performed using Sysmex XE-2100. Anti-platelet autoantibodies were assayed by enzyme-linked immunosorbent assay. The main characteristics at diagnosis and the outcome of chronic ITP in 201 Chinese patients were retrospectively reviewed. There was no significant difference in either genotype or allelic distribution between ITP patients and the controls (p = 0.114; p = 0.787). However, both heterozygote (GA) and homozygote minor allele (AA) patients had significantly increased megakaryocyte quantity compared to homozygote genotype (GG) patients at diagnosis (p = 0.011). The mean IPF values of GA and AA genotype patients were higher than those observed in the GG genotype patients when platelet counts ≤50 × 109/L at diagnosis (p = 0.007). Patients with GA and AA genotype showed a higher response rate to standard treatments than patients with GG genotype (p < 0.001). In particular, GA and AA genotype patients had a significantly increased chance of responding to steroids, intravenous immunoglobulin (IVIG), and thrombopoietin analogs (p = 0.007; p = 0.029; p = 0.034, respectively). No significant difference was found between anti-platelet antibodies and genotypes (p = 0.296). In summary, the SDF-1 rs2297630 was associated with platelet production and treatment response in Chinese patients with chronic ITP.

Involvement of Fcα/μ Receptor in IgM Anti-Platelet, but Not Anti-Red Blood Cell Autoantibody Pathogenicity in Mice.

IgM anti-mouse platelet autoantibodies cause thrombocytopenia by mediating uptake of opsonized thrombocytes, whereas IgM anti-erythrocyte autoantibodies induce anemia through a phagocytosis-independent cell destruction. In this article, we show that infection with lactate dehydrogenase-elevating virus, a benign mouse arterivirus, exacerbates the pathogenicity of IgM anti-platelet, but not anti-erythrocyte autoantibodies. To define the role of Fcα/μ receptor (Fcα/μR) in IgM-mediated thrombocytopenia and anemia, we generated mice deficient for this receptor. These animals were resistant to IgM autoantibody-mediated thrombocytopenia, but not anemia. However, the lactate dehydrogenase-elevating virus-induced exacerbation of thrombocytopenia was not associated with enhanced Fcα/μR expression on macrophages. These results indicate that Fcα/μR is required for the pathogenicity of IgM anti-platelet autoantibodies but is not sufficient to explain the full extent of the disease in virally infected animals.

Study of a humanized inhibitory anti-platelet glycoprotein VI phage antibody from a phage antibody library

Objective: The aims of the study were to study the effect of anti-platelet glycoprotein (GP) VI auto-antibodies on platelet aggregation and use phage surface display technology to produce anti-platelet GPVI phage antibody fragment, which may be developed to inhibit platelet aggregation in the treatment of cardiovascular disease.Methods: Plasma samples from patients with immune thrombocytopenia (ITP) were screened by monoclonal antibody immobilization of the platelet antigen assay and the platelet aggregation test for anti-platelet GPVI auto-antibody with an inhibitory effect. The humanized anti-platelet GPVI phage antibody was produced by phage surface display technology. The function of the phage antibody fragment against platelet aggregation was examined by the platelet aggregation test.Results: Of 726 ITP patients, 2 (0.27%) patients’ plasma significantly inhibited platelet aggregation induced by collagen-1. After five rounds of selection, enrichment, and purification, a soluble phage antibody fragment was produced, which can inhibit platelet aggregation induced by collagen-1. The results demonstrate that only a few of the screened anti-platelet GPVI auto-antibodies showed an inhibitory effect on platelet aggregation.Discussion: A completely humanized anti-GPVI soluble phage antibody can be produced by phage surface display technology. The antibody was able to specifically block collagen-induced platelet aggregation without influencing the aggregation responses to other agonists.Conclusions: Results of the present study suggest that very few anti-platelet GPVI auto-antibodies inhibit the aggregation function of platelet. The humanized anti-platelet GPVI produced by phage surface display technology is promising to be used to inhibit platelet aggregation in the treatment of cardiovascular disease.

Dengue virus and antiplatelet autoantibodies synergistically induce haemorrhage through Nlrp3-inflammasome and FcγRIII.

Dengue haemorrhagic fever (DHF) typically occurs during secondary infections with dengue viruses (DENVs). Although it is generally accepted that antibody-dependent enhancement is the primary reason why patients with secondary infection are at an increased risk of developing DHF, a growing body of evidence shows that other mechanisms, such as the elicitation of antiplatelet autoantibodies by DENV nonstructural protein NS1, also play crucial roles in the pathogenesis of DHF. In this study, we developed a "two-hit" model of secondary DENV infection to examine the respective roles of DENV (first hit) and antiplatelet Igs (second hit) on the induction of haemorrhage. Mice were first exposed to DENV and then exposed to antiplatelet or anti-NS1 Igs 24 hours later. The two-hit treatment induced substantial haemorrhage, coagulopathy, and cytokine surge, and additional treatment with antagonists of TNF-α, IL-1, caspase-1, and FcγRIII ameliorated such effects. In addition, knockout mice lacking the Fcγ receptor III, Toll-like receptor 3, and inflammasome components Nlrp3 and caspase-1 exhibited considerably fewer pathological alterations than did wild type controls. These findings may provide new perspectives for developing feasible approaches to treat patients with DHF.

Persistent neonatal thrombocytopenia can be caused by IgA antiplatelet antibodies in breast milk of immune thrombocytopenic mothers

AbstractImmune thrombocytopenia (ITP) in pregnant women can cause neonatal thrombocytopenia by transport of antiplatelet autoantibodies across the placenta. Usually, an infant's platelet count normalizes within 2 months. We observed neonatal thrombocytopenia that persisted more than 4 months and disappeared following discontinuation of breastfeeding. The aim of our study was to discern whether breast milk of ITP mothers contained antiplatelet antibodies causing persistent thrombocytopenia. We collected milk samples from 3 groups of women: ITP group, 7 women who had ITP during pregnancy; R-ITP group, 6 women who recovered from ITP before pregnancy; and 9 healthy controls. We found increased levels of antiplatelet antibodies of the immunoglobulin A type in the milk of ITP patients compared with the other 2 groups. Similar increase was demonstrated for antibodies binding to αIIbβ3 expressed in cultured cells. Thus, transfer of antiplatelet antibodies from ITP mothers by breastfeeding can be associated with persistent neonatal thrombocytopenia.