Presence Of Platelet Autoantibodies Research Articles

Desialylation by neuraminidases in platelets, kiss of death or bittersweet?

Loss of surface sialic acid by neuraminidases is known as 'desialylation'. Platelets are desialylated in bacterial or viral infections, during storage, senescence, various mutations, platelet auto antibodies, hemostasis and shear stress. In this review the recent literature on the different sialic acid capped glycan structures will be covered as well as platelet desialylation in inherited glycan disorders and induced by external neuraminidases. Neuraminidases are released from platelet intracellular stores and translocated to the platelet surface. Apart from clearance, loss of surface sialic acid by neuraminidases ('desialylation') affects platelet signaling including ligand binding and their procoagulant function. Platelets are also desialylated in infections, various mutations, presence of platelet auto antibodies. Since platelet desialylation occurs in various healthy and pathological conditions, measuring desialylation might be a new diagnostic tool.

Anti-Platelet Antibodies Are Predominantly IgM in Childhood Immune Thrombocytopenia

IntroductionPlatelet clearance in childhood immune thrombocytopenia (ITP) is thought to occur through antibodies binding to platelet glycoproteins such as GPIIb/IIIa, Ib/IX and V. Most children recover spontaneously, but ~10% remain thrombocytopenic beyond 12 months (chronic ITP).Anti-platelet antibodies of IgG subclass have been shown in adult ITP patients. In children, limited data is available. Van Leeuwen et al. (Scand J Haematol 1981) suggested that children with chronic ITP might have class-switched platelet IgG antibodies, with superior effector functions, whereas anti-platelet IgM antibodies may be found in spontaneously recovering patients. 30% of children with ITP do not respond to intravenous immunoglobulin (IVIG) therapy, and a lower response rate to IVIG has been described in adult ITP patients with anti-platelet GPIb/IX antibodies. This association is yet unknown in children.In the present work we investigated the prevalence of autoantibodies in childhood ITP and their effect on spontaneous recovery, development of chronic disease, and resistance to IVIG therapy.MethodsWe evaluated the presence and glycoprotein specificity of platelet autoantibodies in 200 children with newly diagnosed ITP who participated in a multicenter randomized controlled trial. In this study, children aged 3 months to 16 years were allocated in a 1:1 ratio to careful observation or a single dose of IVIG, and followed clinically for 1 year. Blood samples obtained at diagnosis were analyzed by indirect platelet monoclonal antibody-specific immobilization of platelet antigens (MAIPA, for IgG and IgM) at a central reference laboratory. To correlate autoantibody levels with clinical outcomes, we investigated the association between platelet antibody profiles and spontaneous resolution of thrombocytopenia (observation arm) and response to IVIG (treatment arm).ResultsPlatelet antibodies were evaluated by incubation of patient serum with donor platelets, as the low sample volumes of children made it impossible to directly detect immunoglobulin binding to platelets of a thrombocytopenic child. At diagnosis, platelet autoantibodies of IgM subclass were found in 52% (95% confidence interval [CI], 44-60%) of patients. Glycoprotein-specific IgM antibodies to GPIIb/IIIa were most frequent (47%; 95% CI, 40-55%), followed by GPIb/IX (31%; 95% CI, 24-38%) and GPV (29%; 95% CI, 22-36%). In turn, glycoprotein-specific IgG antibodies were present in only 8% (95% CI, 4-12%) of children. Only 3 patients were positive for IgM and IgG autoantibodies at the same time. IgM anti-GPIIb/IIIa antibodies were more prevalent in young children, and correlated with lymphocytosis.There was no association between the presence of platelet autoantibodies and resolution of thrombocytopenia 1 week after diagnosis, both for patients that were allocated to observation only (P=0.45 for IgM; P=1.0 for IgG) or treated with IVIG (P=0.94 for IgM; P=0.46 for IgG). The rate of no, partial and complete response were also similar amongst antibody-positive and -negative individuals. Buchanan bleeding scores were comparable amongst patients with and without antibodies.Finally, we could not detect differences in autoantibody levels or isotype between patients who remained thrombocytopenic beyond 12 months (chronic ITP), and patients who recovered. During the 1-year follow-up period, we found no evidence of class switching from IgM to IgG, also not in children who developed chronic ITP.ConclusionsOur data show that in contrast to adult ITP, platelet antibodies in newly diagnosed childhood ITP are predominantly of IgM subclass. The spontaneous recovery and response to IVIG was not different between children with or without antibodies. DisclosuresNo relevant conflicts of interest to declare.

Differential diagnostics and correction of metabolic and immunological disorders in patients with hepatic cirrhosis, complicated hepatosplenomegalia and portal hypertension

The study of the role of the spleen in the pathogenesis of liver cirrhosis is important for treatment. Currently available literature data indicate the role of altered spleen functions in the pathogenesis of liver cirrhosis. The aim of this study was to clarify the features of the etiology and pathogenetic disorders in patients with hepatosplenomegaly. Materials and methods. We investigated the uniform elements of blood and blood serum from 58 patients with hepatosplenomegaly amid cirrhosis, portal hypertension complicated. Patients were divided into two groups depending on the antigenic load: I - patients with liver cirrhosis against the background of hepatitis viruses HBV/HCV and II - patients with autoimmune hepatitis against the background of herpes viruses CMV/VEB. Treatment of patients included the use of antiherpetic immunoglobulins and hematopoietic cord blood progenitor cells. Results. In patients of group I was detected an increase in the spontaneous oxidative activity of neutrophils and depletion of the oxidative reserve in oxygen-dependent phagocytosis. It activated the signaling pathways of pro-inflammatory cytokines IL-6 (an increase of 60 times). We found an increased content of CD22+ -plasma B-lymphocyte that elevated synthesized concentrations of IgA. In patients of group II were found an increase in the activity of C3 and a decrease in the C4-components of complement; thrombocytopenia due to the presence of platelet autoantibodies; increased synthesis of immunoglobulins IgM, IgG, increased synthesis of IFN-. All patients showed disturbances in the metabolism of amino acids in various metabolic cycles - ornithine, which disrupted the formation of urea and indicates the accumulation of ammonia, which can enhance the cytotoxic effect in group I; methionine with a violation of the formation of cystine from cysteine and the accumulation of homocysteine, which enhances the synthesis of IFN-γ, which was increased in group II by 4 times. Conclusions. Some etiological and pathogenetic features of the formation of liver cirrhosis complicated by portal hypertension and recurrent bleeding from varicose veins of the esophagus were revealed. The immunological and metabolic changes verified by us correlated with the disappearance of the clinical manifestations of the disease, improved well-being, and the absence of recurrence of bleeding.

The effect of platelet autoantibodies on the course of the disease and clinical response of patients with idiopathic thrombocytopenic purpura

In this study, we evaluated the response to treatment of 409 idiopathic thrombocytopenic purpura (ITP) patients who were tested for the presence of platelet-associated autoantibodies by direct-platelet immunofluorescence test (PIFT) and for the presence of plasma antibodies directed against the GPIIb/IIIa, GPIb and GPIa/IIa by monoclonal antibody immobilization of platelet antigens (MAIPA). In patients with platelet autoantibodies in comparison with patients without antibodies more frequently were observed the chronic form of disease (83.5%vs. 68.5%) and severe symptoms of haemorrhage diathesis (17.3%vs. 6.9%). Evaluation of the treatment response (to corticosteroids, immunosuppressive drugs and splenectomy) referred to patients with complete response, e.g. complete remission defined as platelet count of >100 x 10(9)/l for at least 2 years. The percentage of complete response in the whole population of ITP patients, both with and without autoantibodies regardless of the method of treatment, was similar (about 54%). However, the presence of platelet autoantibodies had effect on patients treated with corticosteroids: complete response approximately 71% (36/51) of patients with autoantibodies and in 60% (72/120) of patients without antibodies, as well as in patients treated with immunosuppressive drugs (cyclophosphamide, azathioprine, vincristin and vinblastin); complete response approximately 51% (11/21) of patients with autoantibodies and in 34.8% (6/17) of patients without autoantibodies. The presence of autoantibodies had no effect on the response of splenectomy patients.

Platelet activation in patients with antiphospholipid syndrome.

The binding of antiphospholipid antibodies to circulating platelets and the potential association with thrombocytopenia and platelet activation was investigated in 25 patients with primary antiphospholipid syndrome (APS). Fourteen patients had a platelet count above 150 x 10(9)/l, and 11 patients had mild to moderate thrombocytopenia of 50-150 x 10(9)/l. The presence of platelet autoantibodies was investigated by immunofluorescent binding. No correlation between the presence of autoantibodies on platelets and thrombocytopenia was found. The binding of antibodies in patients' serum and platelet eluates was investigated by performing enzyme-linked immunosorbent assays with phospholipids as antigens. In seven patients antibodies to negatively charged phospholipids were present in platelet eluates. Platelet activation was measured by flow cytometry using a fluorescein isothiocyanate (FITC) labeled monoclonal antibody to P-selectin (CD62). The binding of anti-P-selectin to patients' platelet surface P-selectin was not increased, compared with the binding to platelets obtained from normal donors. Platelet serotonin concentration in APS patients was significantly lower than that found in the platelets of normal controls. More studies are necessary to determine the exact role of antiphospholipid antibodies in the pathogenesis of thrombocytopenia, and to elucidate the cause of low serotonin levels in platelets of APS patients.

Lupus anticoagulants: strong association with the major histocompatibility complex class II and platelet antibodies.

A relationship between the presence of platelet autoantibodies and major histocompatibilty complex class II alleles was determined in 27 patients with lupus anticoagulants. Twenty-two patients had a primary antiphospholipid syndrome' and five patients had lupus erythematosus (SLE). Platelet antibodies against the platelet glycoproteins (GP) IIb/IIIa were detectable in 20 patients. Anti-GPIb/IX or -GPIV antibodies were detectable only in patients with anti-GPIIb/IIIa antibodies. An increased frequency of HLA-DQB1*06 was demonstrable in the total patient population. The association between the lupus anticoagulants and HLA-DQB1*06 was even stronger if patients also had detectable platelet antibodies. This association was also seen if patients with a history of thromboembolic disease were considered separately. However, within the patient population there was no difference between frequencies of HLA alleles detectable platelet antibodies.

High prevalence of platelet autoantibodies in patients with systemic lupus erythematosus.

The aim of this study was to determine the prevalence of platelet autoantibodies (PAA) in patients with systemic lupus erythematosus (SLE) and its correlation with clinical and other laboratory manifestations of the disease, as well as to evaluate the influence of platelet count and disease activity on the result of the test for PAA. Ninety SLE patients, 29 with thrombocytopenia, were evaluated. The presence of PAA was determined using the direct and indirect platelet suspension immunofluorescence test. A total of 166 PAA determinations were performed in the 90 patients upon entry into the study. Fifty-six of the 90 patients (62%) with SLE were positive for PAA. There were no statistically significant correlations between the presence of PAA and the different disease manifestations except for thrombocytopenia (P = 0.0005). The presence of PAA in the same patient was significantly associated with current thrombocytopenia and disease activity. It was concluded that the prevalence of PAA in SLE patients is high. All SLE patients with thrombocytopenia had PAA, although some patients with PAA had a normal platelet count. The presence of PAA in SLE patients is not synonymous with thrombocytopenia but should instead be regarded as one of the multiple serological abnormalities which may develop in these patients.

Anticoagulant-induced Pseudothrombocytopenia and Pseudoleucocytosis

Pseudothrombocytopenia (PTP) is the phenomenon of falsely low platelet counts due to in vitro platelet clumping in the presence of platelet autoantibodies and anticoagulants. We assessed anticoagulant-dependence, time course of platelet counts and impact of different counter devices on the phenomenon. Blood of 10 persons with previously recognized pronounced EDTA-dependent PTP was collected into 7 different anticoagulants and counted after different intervals in parallel in a Coulter T540 and a Coulter STKS counter and by phase contrast microscopy. With the Coulter T540 model PTP was most pronounced in blood samples anticoagulated with EDTA, Na-oxalate or Na-citrate. In the STKS counter EDTA, heparin and oxalate presented as the worst anticoagulants. The time course of platelet counts was significantly different between the two counters. Our results demonstrate that PTP is not restricted to EDTA, but is also present with other anticoagulants. In contrast, pseudoleucocytosis was observed only in EDTA-anticoagulated blood in the Coulter T540 device. We investigated the expression of platelet integrins and activation antigens on platelets of persons with anticoagulant-dependent PTP and in healthy controls without PTP. In the presence of EDTA the expression of GpIIb/IIIa was significantly reduced in the PTP subjects compared to control. Activation antigens CD62, CD63 and thrombospondin-antigen were upregulated in the presence of EDTA. These alterations in the expression of platelet antigens could also be induced on platelets of normal donors by incubation with sera of PTP subjects and EDTA.(ABSTRACT TRUNCATED AT 250 WORDS)

HIGH-DOSE INTRAVENOUS IgG IN ADULTS WITH AUTOIMMUNE THROMBOCYTOPENIA

A study of the effect of high-dose intravenous IgG in 25 adults with autoimmune thrombocytopenia confirmed the predictable rise in the platelet count seen during the infusion and previously reported in children. Unlike the data based on children, there was no sustained response unless the IgG infusion was closely associated with splenectomy. There was no correlation between the presence of platelet autoantibodies or the Ig class of the autoantibody and the pattern of response to the infusion. The initial platelet response appears to be the result of transient blockade of the reticuloendothelial system, including the macrophage Fc receptor mechanism. The long-term response in some patients requires another explanation and may be due to a more specific immunosuppressive effect of the high-dose IgG infusion. Splenectomy may have an additive effect by removing a major site of platelet autoantibody production.

Immunofluorescence microphotometry for the detection of platelet antibodies. III. Demonstration of autoantibodies against platelets.

After a survey of the literature dealing with the demonstration of platelet autoantibodies by immunofluorescence techniques, the results are given of a study in which immunofluorescence microphotometry was used for this purpose. The serum of 58, the platelets of 34, and the megakaryocytes of 2 patients with thrombocytopenia were investigated. In 21 of 52 sera (40%) in which the presence of platelet autoantibodies could be expected, positive results were obtained that could not be due to isoantibodies, either because the patients had not been pregnant and had not received blood transfusions or because the reactivity of the serum with the patient's own platelets was demonstrated. The platelets of 28 patients with thrombocytopenia not due to a platelet defect or decreased thrombopoiesis were investigated. In the platelets of 15 (54%) of these, significant differences in fluorescence were found with anti-immunoglobulin conjugate as well as with anti-IgG, -IgA, -IgM, or -complement reagents. It was concluded that in these patients in vivo sensitization of the platelets with autoantibody was demonstrated. In two patients an indication of the in vivo sensitization of the megakaryocytes was also obtained.