Mathematical analysis of the relative contributions of decreased production and increased peripheral destruction in idiopathic thrombocytopenic purpura and implications in splenectomy

We utilize a model of platelet concentration kinetics and bone marrow production based on three terms (a constant loss term, a random loss term and a higher order loss term) to compare a hypoplastic bone marrow patient and a patient with Idiopathic Thrombocytopenic Purpura (ITP) for the same platelet concentration. We compare this model to published data and show that in many ITP patients there is an overall decrease in platelet production. However, for almost all cases of ITP there is an increase in peripheral platelet destruction, even in those cases where total bone marrow production is less than that in a normal individual or is severely depressed. We are able to graphically depict the variable contributions of decreased production and increased peripheral destruction in patients with ITP and hence give insight into their relative contributions in a given patient. We apply a unique feature of our model, the newly postulated destruction term proportional to the platelet concentration squared (the higher order loss term), to explain cases of antibody negative ITP. Application of our model to data on patients splenectomized as treatment for ITP shows promise in predicting which patients are likely to respond.     

Pathway of Toll-like receptor 7/B cell activating factor/B cell activating factor receptor plays a role in immune thrombocytopenia in vivo

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by anti-platelet autoantibody-mediated platelet destruction. Antigen-presenting cell (APC) dysfunction is considered to play crucial roles in ITP. However, how APC affects autoreactive B cells in ITP is still unknown. Using a mouse model of immune thrombocytopenia, we demonstrated an increase in levels of TLR7 in splenic mononuclear cells (SMCs). Using both TLR7 agonist and TLR7 silencing lentivirus, we found stimulation of TLR7 decreased platelet counts and increased levels of platelet-associated IgG (PAIgG) in ITP mice, which correlates TLR7 with platelet destruction by autoantibodies. Levels of serum BAFF increased significantly in ITP mice and stimulation of TLR7 promoted secretion of BAFF. Among the three BAFF receptors, only BAFF receptor (BAFF-R) increased in ITP mice. However, activation of TLR7 showed no effect on the expression of BAFF receptors. These findings indicate that upregulation of TLR7 may augment BAFF secretion by APC and through ligation of BAFF-R promote autoreactive B cell survival and thus anti-platelet autoantibody production. The pathway of TLR7/BAFF/BAFF-R provides us with an explanation of how activation of APC affects autoantibody production by B cells in ITP and thus might provide a reasonable therapeutic strategy for ITP.     

Chronic idiopathic thrombocytopenic purpura (ITP): molecular mechanisms and implications for therapy

Chronic idiopathic thrombocytopenic purpura (ITP) is an immune-mediated disorder in which platelets are prematurely destroyed in the reticuloendothelial system by platelet autoantibodies. However, it is becoming clear that the pivotal process of the humoral immune response in the pathogenesis of the disorder is a complex interaction between antigen-presenting cells, T cells and B cells. Furthermore, it is increasingly evident that regulatory T cells play an important role and that T-cell-mediated cytotoxicity contributes to the destruction of platelets in ITP. Different new approaches to immunotherapy in chronic ITP have been explored, including use of anti-CD20, anti-CD154 and anti-CD52 antibodies. So far, these therapies have been antigen-nonspecific and the risk of general immunosuppression is a concern. Thus, improving our understanding of the interaction and relative contribution of humoral and cell-mediated mechanisms is essential for developing antigen-specific immunotherapies for the treatment of this disorder. This review aims to elucidate the current status of knowledge of the cellular and humoral immune components of chronic ITP, together with the implications of this knowledge for therapy.     

A murine model for human immune thrombocytopenic purpura and comparative analysis of multiple gene expression in bone marrow and spleen

Homeostasis of platelet number in human and other mammals is well maintained for prevention of minor bleeding and for other immunological functions,but the exact molecular mechanism responsible for immune thrombocytopenic purpura(ITP) has not been fully understood.In an effort to identify genetic factors involved in initiation of platelet production in response to bleeding injury or platelet destruction,we have successfully generated an animal model of human ITP via intraperitoneal injection of anti-platele...     

Prediction of the effect of immunoglobulin therapy in ITP

The correlation between the response to high-dose immunoglobulin therapy (IVIg) and the sequestration pattern of Indium-labeled platelets (In-PLT) in the body was studied in 9 patients with chronic idiopathic thrombocytopenic purpura (ITP). Patients that has prominent platelet sequestration in the spleen responded to IVIg. In these patients, splenic sequestration decreased by 20-30% after IVIg without significant changes in hepatic sequestration. This finding suggests that the blocking of splenic Fc receptors with immunoglobulin minimized the destruction of sensitized platelets. However, patients who had almost equal platelet sequestration in the liver and spleen did not respond to IVIg. In these patients, hepatic sequestration decreased after IVIg, whereas splenic sequestration increased. Thus, it appears that estimating the platelet sequestration pattern using In-PLT is useful for predicting the effects of IVIg.     

Danazol in chronic idiopathic thrombocytopenic purpura resistant to corticosteroids

16 patients (11 women and 5 men) with chronic idiopathic thrombocytopenic purpura (ITP) were treated for 3-6 months with Danazol in a daily dose of 300 mg. In 6 women and 1 man an increase in blood platelet count was observed and in all but 2 patients clinical symptoms of haemorrhagic diathesis disappeared. The platelet factor 3 availability and circulating immune complexes level determined before and after 2 months therapy disclosed normalization of both tests in the majority of patients. This amelioration in immunological tests in several, but not in all patients, coincided with platelet count increase. Side-effects were negligible. The authors conclude that Danazol may be of valuable in the management of chronic refractory to corticosteroids ITP patients and that its possible mechanism of action may be an interaction with the immunologic pathways of blood platelet destruction.     

DNA methyltransferase 3B (DNMT3B − 579 G > T) promotor polymorphism and the susceptibility to pediatric immune thrombocytopenic purpura in Egypt

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease characterized by increased platelet destruction. Although the etiology of ITP remains unclear, it is accepted that both environmental and genetic factors play an important role in the development of the disease. The present study aimed at exploring a novel molecular determinant that may influence the susceptibility and course of ITP in Egyptian children. To achieve our aim, genotyping of DNMT3B − 579 G > T promotor polymorphism by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) assay. The current study was conducted on 140 ITP patients and 150 age and gender matched healthy controls. The results obtained revealed that DNMT3B − 579 TT homotype was significantly higher in ITP patients and conferred almost three fold increased risk of ITP (OR = 3.16, 95%CI = 1.73–5.79). There was no statistically significant difference between ITP patients with wild or mutant genotypes as regards their clinical or laboratory data. Furthermore, there was no statistical difference in the distribution of DNMT3B − 579 G > T genotypes between acute and chronic ITP patients. In conclusion, DNMT3B − 579 G > T promotor polymorphism represents a novel genetic risk factor for ITP but not a predictor for tendency to chronicity in pediatric ITP in Egypt.     

Changes in Follicular Helper T Cells in Idiopathic Thrombocytopenic Purpura Patients

Background: Idiopathic thrombocytopenic purpura (ITP) is a primary autoimmune disease with a decreased platelet count caused by platelet destruction mediated mainly by platelet antibodies. T follicular helper (TFH) cells have demonstrated important roles in autoimmune diseases. The aim of this study is to explore the might role of TFH cells in the patients of ITP.Methods: Twenty-three ITP patients and 12 healthy controls (HC) were enrolled in this study. The frequency of circulating TFH cells in both the patients and HC was analyzed by flow cytometry. Serum interleukin (IL)-21 and IL-6 levels were measured using ELISA, and platelet antibodies were tested using a solid phase technique. Additionally, IL-21, IL-6, Bcl-6 and c-Maf mRNA expressions in peripheral blood mononuclear cells (PBMCs) were detected using real-time PCR.Results: The percentages of circulating CXCR5⁺ CD4⁺TFH cells with ICOS^high or PD-1^high expression were significantly higher in the ITP patients than in the HC. Moreover, the frequencies of circulating CXCR5⁺ CD4⁺TFH cells with inducible costimulator (ICOS)^high or programmed death-1 (PD-1)^high expression were notably higher in ITP with platelet-antibody-positive ( ITP (+) ) patients than in ITP with platelet-antibody-negative ( ITP (-) ) patients and HC, as were the serum IL-21 and IL-6 levels (significant). Moreover, a positive correlation was found between the CXCR5⁺CD4⁺TFH cells with ICOS^high or PD-1^high expression and the serum IL-21 levels of ITP (+) patients. Additionally, the mRNA expression levels of IL-21, IL-6, Bcl-6 and c-Maf were significantly increased in ITP patients, especially in ITP (+) patients.Conclusions: This study demonstrated TFH cells and effector molecules might play an important role in the pathogenesis of ITP, which are possible therapeutic targets in ITP patients.     

Efficacy of Amifostine in Treating Patients with Idiopathic Thrombocytopenia Purpura

Idiopathic Thrombocytopenic Purpura (ITP) is an autoimmune disease characterized by the production of antibodies against platelet surface antigens, resulting in platelet destruction. ITP is generally treated using glucocorticoids, splenectomy, immunosuppressants, platelet transfusions, and also rituxan and rituximab. However, as these treatments are not effective in some refractory ITP patients, especially the elderly, who are also at greater risk of cerebral hemorrhage, we have undertaken this study to find a safe and effective way of treating these patients. In a clinical protocol, we have examined the efficacy of the cytoprotective adjuvant, amifostine, on 24 ITP patients, consisting of 21 Chinese (age: 13–92 years), and 3 Caucasians (age: 46–73 years). In order to prevent the side effects associated with amifostine treatment, an alternative dosing and anti-emetic regimen was developed as part of this protocol, which significantly improved patient acceptance. The protocol consisted of daily intravenous infusions of amifostine 5 × 400 mg per week, for a total of 4–5 weeks. All the patients experienced a long-lasting and continuing remission, defined as platelet counts greater than 100,000. Two patients relapsed: one after an upper respiratory tract infection, and another due to Helicobacter pylori. However, both these patients had complete remission, after they were treated again with amifostine. In this clinical study, we report for the first time, the successful use of amifostine for ITP treatment in refractory patients. In conclusion, amifostine may have good therapeutic effect on ITP patients, especially in refractory and/or elderly. The long-term clinical outcome and the mechanism of action of this drug still need further investigation.     

Effects of urinary extracts from patients with idiopathic thrombocytopenic purpura or aplastic anemia on rodent platelet production and megakaryocytopoiesis

Urinary extracts from idiopathic thrombocytopenic purpura (ITP) patients, aplastic anemia (AA) patients and normal subjects were investigated for their effects on in vivo platelet production, and both in vitro and in vivo megakaryocytopoiesis in rodents. Daily intraperitoneal injection of 1.2 absorbance units (AU, A278) of urinary protein for three consecutive days induced statistically significant increases in rat blood platelet numbers. This increase was observed for 1 of 4 ITP urinary extracts and for all 3 AA urinary extracts, and occurred 24 h after the final injection. In vitro levels of megakaryocyte colony-stimulating factor (Meg-CSF) in ITP urinary extracts were similar to those of normal urinary extracts, and were in dramatic contrast to the markedly elevated levels of Meg-CSF in extracts from AA urine. A single intraperitoneal injection of 0.5 AU of AA urinary protein induced a significant increase in spleen-derived megakaryocyte colony-forming cells (CFU-meg) 48 h past injection. In the group injected with ITP urinary extract, CFU-meg levels remained within normal limits. These results provide evidence that urinary extracts of ITP patients do not contain increased levels of Meg-CSF and a factor which directly stimulates in vivo CFU-meg production, and that the decrease in circulating platelet numbers that is characteristic of ITP patients is not a primary in vivo determinant in the elaboration of these factors.     

Potentiation of tumor necrosis factor-alpha-mediated cytotoxicity of mast cells by their production of nitric oxide

Nitric oxide (NO or endothelium-derived relaxing factor) has many of biologic actions, including the maintenance of blood pressure, inhibition of platelet aggregation, and cytotoxicity by phagocytic cells. Several cell types produce NO from L-arginine. Given recent emphasis on mast cell (MC)-dependent TNF-alpha-mediated cytotoxicity, we investigated the role of NO in rat peritoneal MC (PMC)-and intestinal mucosal mast cell-mediated cytotoxicity. MC cytotoxicity against the TNF alpha-sensitive target, WEHI-164, was potentiated by L-arginine. The NO competitive inhibitors, N omega-nitro-L-arginine and NG-methyl-L-arginine, diminished the cytotoxicity of rat PMC by 27 and 17%, respectively. However, hemoglobin, which binds to NO, inhibited the cytotoxic activity of PMC by 49% in the presence of 1 mM L-arginine and by 24% in L-arginine-free medium. The latter suggests that PMC use intracellular stores of L-arginine to produce NO. Neither hemoglobin nor NO metabolites affected human rTNF-alpha cytotoxicity. Furthermore, sodium nitroprusside, with its free radical NO group, restored PMC cytotoxicity in L-arginine-free medium to the level observed in 1 mM L-arginine medium. Studies with a platelet aggregation bioassay and various NO inhibitors confirmed that PMC produce NO. In addition, increased levels of NO2- were observed in medium of A23187, TNF-alpha, or WEHI-164-stimulated PMC.     

The humoral regulation of megakaryocytopoiesis and platelet production in vivo

We examined the effects of the urinary extracts from aplastic anemia (AA) patients, idiopathic thrombocytopenic purpura (ITP) patients, and normal subjects on murine megakaryocyte/platelet production in vivo and in vitro. In the first study, single doses of AA urinary protein (65%-90% ethanol precipitate) were individually injected intraperitoneally into rats and mice. Blood platelet counts in rats increased significantly 24 hours after the injection. Total megakaryocyte colony-forming units (CFU-Meg) in mouse spleens increased by 24 hours postinjection, peaked at 48 hours and returned to normal levels at 96 hours. Changes in the number of megakaryocyte colonies showed similar patterns of increasing, peaking and returning to normal levels postinjection. In the second study, we compared the effects of some urinary extracts on murine megakaryocyte/platelet production. These observations provided the evidence that AA urinary extracts contain a factor that directly stimulates megakaryocyte progenitor cell proliferation in mouse spleen in vivo as well as the release of platelets from megakaryocytes, and ITP urinary extracts do not contain increased levels of Meg-CSF and/or some other factor that directly stimulates CFU-Meg in vivo, and the decreased blood platelet mass that is clinically characteristic of ITP is not a primary in vivo determinant of the elaboration of these factors.     

Ral GTPases regulate cell-mediated cytotoxicity in NK cells

NK cells are key components of the immune response to virally infected and tumor cells. Recognition of target cells initiates a series of events in NK cells that culminates in target destruction via directed secretion of lytic granules. Ral proteins are members of the Ras superfamily of small GTPases; they regulate vesicular trafficking and polarized granule secretion in several cell types. In this study, we address the role of Ral GTPases in cell-mediated cytotoxicity. Using a human NK cell line and human primary NK cells, we show that both Ral isoforms, RalA and RalB, are activated rapidly after target cell recognition. Furthermore, silencing of RalA and RalB impaired NK cell cytotoxicity. RalA regulated granule polarization toward the immunological synapse and the subsequent process of degranulation, whereas RalB regulated degranulation but not polarization of lytic granules. Analysis of the molecular mechanism indicated that Ral activation in NK cells leads to assembly of the exocyst, a protein complex involved in polarized secretion. This assembly is required for degranulation, as interference with expression of the exocyst component Sec5 led to reduced degranulation and impaired cytotoxicity in NK cells. Our results thus identify a role for Ral in cell-mediated cytotoxicity, implicating these GTPases in lymphocyte function.     

Cutting edge: a role for the adaptor protein LAT in human NK cell-mediated cytotoxicity

Stimulation of NK cell-mediated cytotoxicity involves the coupling of proximal Src and Syk family protein tyrosine kinases to downstream effectors. However, the mechanisms linking these second messenger pathways are incompletely understood. Here, we describe a key role for the LAT (p36) adaptor protein in human NK cell activation. LAT is tyrosine phosphorylated upon stimulation of NK cells through FcgammaRIII receptors and following direct contact with NK-sensitive target cells. This NK stimulation induces the association of LAT with several phosphotyrosine-containing proteins. In addition to the biochemical evidence showing LAT involvement in NK cell activation, a genetic model shows that LAT is required for FcR-dependent phosphorylation of phospholipase C-gamma. Furthermore, overexpression of LAT in NK cells leads to increased Ab-dependent cell-mediated cytotoxicity and "natural cytotoxicity," thus demonstrating a functional role for LAT in NK cells. These data suggest that LAT is an important adaptor protein for the regulation of human NK cell-mediated cytotoxicity.     

The control of megakaryocyte ploidy and platelet production: biology and pathology

Following experimental platelet destruction in animals, large platelets, which are more hemostatically active, are produced before any change in bone marrow megakaryocyte DNA content. When platelet production is stimulated by administration of i.v. vincristine in rats, megakaryocyte ploidy is increased, but mean platelet volume is unchanged. When platelet production and destruction are both stimulated by chronic hypoxia or administration of anti-platelet serum, mean platelet volume and megakaryocyte DNA content are both increased. Since platelet volume is determined primarily at thrombopoiesis, these results imply that mean platelet volume and megakaryocyte DNA content are under separate hormonal control. Therefore, it has been postulated that changes in mean platelet volume occur following changes in platelet production rate, whereas changes in megakaryocyte ploidy are associated with an increased rate of platelet production. In myocardial infarction, platelets have increased mean volume and reduced bleeding time more than in controls. In addition, men with myocardial infarction have increased megakaryocyte size and increased DNA content when compared to controls. These changes are similar to those observed in rabbits following cholesterol feeding. If megakaryocyte polyploidy and mean platelet volume are under separate hormonal control, this suggests that in myocardial infarction, both hormones are active--one stimulating an increased platelet size, the other stimulating the increased megakaryocyte DNA content. In contrast, patients with lymphoma exhibiting a secondary thrombocytosis have no change in mean platelet volume. However, these subjects also have larger bone marrow megakaryocytes when compared to controls. The relation between megakaryocyte size and ploidy implies that the DNA content of these cells is increased in lymphoma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human monoclonal autoantibodies to characterize platelet antigens in immune-mediated thrombocytopenia

Idiopathic thrombocytopenic purpura is characterized by antiplatelet antibodies which mediate the rapid destruction of these cells by the reticuloendothelial cell system. Low serum titers of autoantibodies and the polyclonal nature of human serum make it difficult to identify platelet target antigens with plasma antibodies. To circumvent these problems, we have utilized the techniques of EBV transformation and somatic cell hybridization in order to isolate human monoclonal antibodies from patients with ITP. In this paper we describe the use of human monoclonal autoantibodies to characterize an activation specific antigen on GPIIIa and an autoantigen on the GPIb complex. Ultimately, we hope to determine whether these autoantibodies emerge from a pool of naturally occurring antibodies to activation or senescence antigens, or are triggered by environmental agents such as bacteria or virus, which are comprised of antigens similar to those found on the platelet membrane.     

Disulfide linked pyrazole derivatives inhibit phagocytosis of opsonized blood cells

Immune thrombocytopenia (ITP) is caused by production of an autoantibody to autologous platelets. ITP can be treated either by reducing platelet destruction or by increasing platelet production. Fcγ receptor mediated phagocytosis of the opsonized blood cells is a well-accepted mechanism for the underlying pathogenesis of ITP and inhibition of this phagocytosis process with small molecules is a potential strategy for the development of drugs against ITP. A broad screen indicated that 4-methyl-1-phenyl-pyrazole derivative (1) could inhibit the phagocytosis of opsonized blood cells with weak potency. We reveal here the discovery of the polysulfide products, synthesis of various 1-phenyl-pyrazole derivatives, and the biological evaluation of pyrazole derivatives as inhibitors of phagocytosis for potential use as therapeutics for ITP. Substitution at C4 of the pyrazole moiety in the disulfide-bridged dimers influenced the potency in the increasing order of 10 ? 11 ? 16 < 19 < 20. A novel scaffold, 20 with an IC₅₀ of 100 nM inhibiting opsonized blood cell phagocytosis was identified as a potential candidate for further studies. Confirmation of the disulfide bridge additionally provides clues for the non-thiol or non-disulfide bridge carrying ligands targeting ITP and other similar disorders.     

Autoantibodies in chronic ITP

Chronic ITP is a syndrome of destructive thrombocytopenia due in most cases to antiplatelet autoantibodies. In the present studies we have studied 74 patients with chronic ITP using a new immunobead assay. Of these, 59 (79.7%) had demonstrable platelet-associated autoantibodies: 48 against platelet glycoprotein IIb/IIIa and 11 against glycoprotein Ib/IX. Plasma autoantibodies were studied in all patients and 32 (43.2%) had positive results; in each case the patient also had platelet-associated autoantibodies directed to the same antigen. We conclude that the majority of patients with chronic ITP have autoantibodies against platelet membrane glycoproteins and that the immunobead assay is a sensitive and reproducible method for their detection which is applicable to the routine hospital laboratory.     

Ability of plasma from patients with immune thrombocytopenic purpura (ITP) to promote the growth of megakaryocyte progenitors from normal bone marrow.

The ability of plasma from ITP patients (before and after splenectomy) to support the growth of megakaryocyte progenitors was compared with that from healthy subjects. Plasma Factor Index-Megakaryocyte PFI-Mk (ITP) which expressed resultant colony growth was significantly lower before splenectomy, but it normalized after splenectomy. (PFI-Mk) (ITP) did not relate neither to megakaryocyte nor to platelet counts. A positive correlation has been observed between megakaryocyte and platelet numbers in healthy subjects and in ITP patients after splenectomy, but not before splenectomy. The proportion of immature megakaryocytes was markedly higher in ITP marrow before splenectomy. This study indicates, that in ITP apart from antibodies directed to platelets and megakarocytes a low plasma stimulatory activity affected megakaryocytopoiesis.     

ITP in pregnancy: use of the bleeding time as an indicator for treatment

ITP is a relatively common disorder seen in pregnancy. Current recommendations for management of patient with ITP recommend maintaining the platelet count above 50 x 10(9)/L and the bleeding time less than 20 min. It has been well documented that the bleeding time in ITP is disproportionately shortened in many patients relative to the platelet count. We present a prospective study of 24 ITP patients in whom the bleeding time was used as an indicator for therapeutic intervention in pregnancy. Indications for therapy with prednisone and/or intravenous gammaglobulin were the following: significant clinical hemorrhage due to thrombocytopenia; bleeding time of greater than 20 min at the baseline platelet count; for normalization of hemostasis prior to delivery or surgical procedure. Caesarean section was performed only in cases in which there were obstetrical indications for this mode of delivery or when the fetal platelet count (obtained by fetal scalp vein sample) was less than 50 x 10(9)/L. Of 24 patients with ITP, eight had significant thrombocytopenia (platelet count less than 50 x 10(9)/L) throughout pregnancy. Only two patients required prolonged prednisone therapy. Both suffered side effects of chronic prednisone administration. Four patients were treated with prednisone for a short course (10-14 days) at term to improve hemostasis for delivery. One patient was treated with intravenous gammaglobulin at term in an effort to prevent severe neonatal thrombocytopenia. Seven patients required caesarean section; the remaining 17 patients underwent vaginal delivery. Only one minor bleeding complication was seen - a small wound hematoma post caesarean section. In summary, using the bleeding time as an indicator for therapeutic intervention, treatment of ITP in pregnancy can be minimized. Thus, therapy related toxicity can be avoided.