Autoantibodies against platelet glycoprotein Ib in patients with chronic immune thrombocytopenic purpura

The present studies provide direct evidence that some patients with chronic immune thrombocytopenic purpura (ITP) have autoantibodies reactive with platelet glycoprotein Ib ( GPIb ). Microtiter wells coated with a monoclonal antibody that recognized GPIb were reacted with either platelet extract or a control cell extract. After washing and incubating with test plasma, well-bound IgG was quantitated using radioactive anti-IgG. When compared to plasma from normal subjects, plasma from 3 of 106 patients with chronic ITP had significantly increased quantities of IgG bound to microtiter wells reacted with platelet extracts. Negative results were obtained with the remaining 103 patients with chronic ITP and 59 patients with a variety of other platelet disorders. Plasma from two of the three positive patients precipitated a protein from 125I-surface-labeled platelet extract with a molecular weight similar to GPlb . One of the three patients with anti- GPlb antibody also had demonstrable autoantibodies to the platelet glycoprotein llb / llla complex.     

Autoantibodies and autoantigens in chronic immune thrombocytopenic purpura

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disorder in which antiplatelet autoantibodies bind to antigens on the surface of platelets, resulting in their destruction. The newer antigen-specific (phase III) assays can detect platelet-associated and plasma autoantibodies in approximately 75% and 50% of patients, respectively. Antiplatelet autoantibodies bind to both platelets and megakaryocytes and preliminary evidence suggests that they not only cause platelet destruction but can also decrease platelet production either by interfering with megakaryocyte proliferation/maturation or by causing intramedullary platelet destruction. Autoantibodies are capable of activating complement and causing platelet phagocytosis both in vitro and in vivo. Many platelet-associated and plasma autoantibodies from ITP patients are light chain-restricted, which suggests a clonal origin. Approximately 75% of platelet autoantigens are localized to either the platelet glycoprotein (GP) IIb/IIIa or Ib/IX complex. Inhibition of the binding of autoantibodies from several ITP patients by either another ITP autoantibody or by a monoclonal anti-GPIIb/IIIa antibody suggests that the antigenic repertoire in chronic ITP may be limited. Most autoantigens on GPIIb/IIIa appear to be conformational since they are dependent on the presence of divalent cations. A variety of new investigative techniques have localized a few autoantigens to specific regions of the cytoplasmic or extracellular regions of both GPIIb/IIIa and GPIb/IX.     

Autoantibodies against platelet glycoproteins in autoimmune thrombocytopenic purpura: their clinical significance and response to treatment

Autoantibodies against platelet glycoproteins (GP) have been demonstrated in patients with autoimmune thrombocytopenic purpura (ATP). However, their clinical and pathogenetic significance as well as their response to immunosuppressive treatment is unknown. Using an immunobead assay capable of measuring autoantibodies against GPIIb-IIIa and GPIb-IX, we studied 58 adult patients with active ATP (platelet count < 150 x 10(9)/L) and 26 patients with ATP in remission (platelet count > 150 x 10(9)/L and without any therapy at time of investigation). Platelet-associated autoantibodies were detected in 39 of 53 patients with active ATP (73.6%) and in 2 of 26 patients in remission (7.7%). Circulating plasma autoantibodies were noted in 17 of 58 patients in the group with active disease (29.3%) and in none of the patients in remission. Twelve patients with active ATP and autoantibodies against GPIIb-IIIa were studied prospectively during treatment with corticosteroids. Of eight patients whose platelet count normalized during treatment, platelet-associated and plasma antibodies decreased significantly in two or became undetectable in six. In contrast, of four patients whose platelet counts were unchanged or increased moderately, we noted no significant change in antibodies. Moreover, autoantibodies reappeared in two responding patients at the time of relapse. The effect of high-dose intravenous immunoglobulin was studied in six active ATP patients with antiglycoprotein autoantibodies and refractoriness to prednisone. In one patient who developed a sustained remission after IvIgG, platelet-associated and plasma antibodies to GPIIb-IIIa decreased and became undetectable. In contrast, two patients who had only a transient rise of the platelet count after IvIgG showed no significant change in autoantibody. In three unresponsive patients, autoantibodies were without change in two and decreased transiently in one patient. We conclude that in ATP the presence of autoantibodies to GPIIb-IIIa and GPIb-IX is related to the activity of the disease. Corticosteroids may inhibit autoantibody formation in some ATP patients, whereas during the early response to IvIgG, autoantibody production may not be affected.     

Autoantibodies to the presumptive cytoplasmic domain of platelet glycoprotein IIIa in patients with chronic immune thrombocytopenic purpura.

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disorder due to autoantibodies against platelets that result in their destruction. In some patients, these autoantibodies bind to platelet glycoprotein (GP) IIIa. With the aim of better defining the antigenic epitopes, plasma from 13 selected patients with chronic ITP known to have anti-GPIIb/IIIa autoantibodies was tested for reactivity with nine synthetic peptides corresponding to different regions of the GP IIIa molecule. Of these plasmas, five bound significantly (P less than .001) with either peptide 8 (amino acids 721-744) or peptide 9 (amino acids 742-762), which together form most of the carboxyterminal region presumed to be the cytoplasmic domain. Three of these positive plasmas, were tested further. In two of these positive plasmas, the anti-peptide antibodies represented greater than 80% of the detectable circulating autoantibody. To further evaluate the importance of the carboxyterminal region as an antigenic site, the chronic ITP plasmas were tested against Chinese hamster ovary cells transfected with GPIIb and either whole GPIIIa or GPIIIa lacking amino acids 728 to 762. Ten of the 13 plasmas required the presence of this region for significant autoantibody binding. We conclude that the carboxyterminal region is an important area for stimulating antiplatelet autoantibody formation in some patients with chronic ITP. It is not known whether these autoantibodies to the presumed cytoplasmic domain play an important role in the pathogenesis of the disease or occur as a secondary phenomenon during the course of platelet destruction.     

Autoantibodies to platelet glycoproteins in patients with disease-related immune thrombocytopenia

Although increased platelet destruction and elevated platelet-associated IgG have been shown in patients with lymphomas and various autoimmune diseases, such as systemic lupus erythematosus (SLE), there have been few studies evaluating autoantibodies against platelet-specific antigens. We evaluated 24 patients retrospectively with disease-related thrombocytopenia (12 with lymphoproliferative diseases and 12 with various autoimmune disorders) using a recently reported antigen-specific assay. Autoantibodies against platelet GPIIb/IIIa or GPIb/IX were noted in 15 of the 24 patients (10 of 12 with autoimmune disease and five of 12 with lymphoproliferative disorders). Platelet-associated autoantibodies were present in 60% and plasma autoantibodies in 33%. Anti-GPIIb/IIIa autoantibodies were much more common than those against GPIb/IX. In one patient each with thrombocytopenia and either SLE or myasthenia gravis, absorption of plasma with platelets completely removed the anti-GPIIb/IIIa autoantibodies, but did not affect the level of anti-cochlear autoantibody involved with immune-mediated hearing loss in the SLE patient or the anti-acetylcholine receptor autoantibody in the myasthenic patient. These findings show that, in some cases of disease-related immune thrombocytopenia, autoantibodies against GPIIb/IIIa or GPIb/IX can be detected similar to those seen in chronic ITP. As shown in two patients with multiple autoimmune manifestations, the various autoantibodies have diverse specificities and do not crossreact.     

Bleeding manifestations in severely thrombocytopenic children with immune thrombocytopenic purpura

OBJECTIVE: To report the observations on various bleeding manifestations in children with immune thrombocytopenic purpura (ITP) having severe thrombocytopenia (platelet count (PC) < 20,000/microl) and to compare the differences in bleeding manifestations at levels of PC at < 10,000/microl compared with between 10,000 and 20,000/microl. STUDY DESIGN: It is a retrospective analysis of bleeding manifestations in children with ITP (n = 58) having severe thrombocytopenia recorded between July 1999 and June 2002. A total of 164 episodes of severe thrombocytopenia were observed. During 31 episodes (18.9%), no bleeding manifestations were observed. When bleeding was observed cutaneous bleeds were the commonest manifestations occurring in 124 episodes. Of these 124 instances, in 82 (66.1%) episodes only cutaneous bleeding was observed while in remaining 42 (33.9%) episodes cutaneous bleeding was associated with other bleeding sites. Other common bleeds observed included epistaxis 22 (13.4%), oral bleeding 21 (12.8%) and gastro-intestinal bleeding 5 (3.04%). Comparison of the bleeding manifestations during episodes when the PC was < 10,000/microl and those between 10,000 and 20,000/microl showed that in 76.6% episodes with the count at > 10,000/microl no or only cutaneous bleeds were observed (clinically mild disease) compared to 59.45% episodes with episodes having PC < 10,000/microl (z score 2.37, p < 0.05). There was no statistically significant difference in proportion of patients having clinically mild disease during acute or chronic phase of the disease. CONCLUSION: During episodes of severe thrombocytopenia, most children have clinically mild disease. When the PC is < 10,000/microl clinically mild disease is observed less often compared to episodes with PC 10,000-20,000/microl. Based on these observations, it can be recommended that during severe thrombocytopenia, particularly when the PC is between 10,000-20,22,000/microl, patients can be safely managed with watchful waiting without any specific therapeutic intervention.     

Refractory chronic immune thrombocytopenic purpura in a child with acute lymphoblastic leukemia

Immune thrombocytopenic purpura (ITP) has been associated with several hematologic malignancies such as Hodgkin and non-Hodgkin lymphomas and chronic lymphocytic leukemia, but it is rare in children with acute lymphoblastic leukemia (ALL). Here, we report a 7-year-old girl with chronic ITP during early intensive phase of chemotherapy for ALL. She underwent splenectomy because thrombocytopenia had persisted even after treatment with intravenous immunoglobulin (IVIG), steroids, vincristine, rituximab, and anti-D antibody. After splenectomy, her platelet count had recovered, and maintenance therapy could be resumed with a support of IVIG. To our knowledge, this is the first child case of chronic ITP during chemotherapy for ALL and splenectomy was effective in this patient.     

Autoantibodies against platelet glycoproteins in critically ill patients with thrombocytopenia

PURPOSE: The aim of the study was to investigate immunologic causes of thrombocytopenia in critically ill patients, especially causes that were related to platelet-associated IgG antibodies. SUBJECTS AND METHODS: All patients admitted to two intensive care units between May 1 and October 30, 1997, who developed thrombocytopenia (less than 100 x 10(9) platelets/L) were studied prospectively. We measured platelet-associated IgG with a radioimmunoassay using I(125)-labeled polyclonal antihuman IgG. Characterization of platelet-associated IgG was assessed with a monoclonal antibody immobilization of platelet antigen. Circulating immune complexes were also assayed. RESULTS: Of the 61 patients with thrombocytopenia, elevated platelet-associated IgG was found in 18 (30%). Associated antiplatelet autoantibodies (glycoprotein IIb/IIIa) were detected in 4 patients, circulating autoantibodies (glycoprotein Ib/IX) were detected in sera from 2 patients, and circulating immune complexes were detected in 3 patients. The nature of the platelet-associated IgG could not be determined in 10 patients. Elevated platelet-associated IgG was associated with sepsis and previous cardiopulmonary bypass. Thrombocytopenic patients with elevated platelet-associated IgG had a lower nadir platelet count (58 +/- 27 x 10(9)/L vs 74 +/- 24 x 10(9)/L, P = 0.03). CONCLUSION: Elevated platelet-associated IgG, some of which are platelet autoantibodies, is frequent in thrombocytopenic patients with sepsis or after cardiopulmonary bypass.     

Autoantibodies against platelet glycoprotein Ib/IX: a frequent finding in autoimmune thrombocytopenic purpura

Many autoantibodies involved in the pathogenesis of autoimmune thrombocytopenic purpura (AITP) are directed against epitopes on platelet glycoproteins (GP). These autoantibodies are a specific diagnostic characteristic of patients with AITP. In this study, the relative frequency of antibodies against GPs IIb/IIIa and Ib/IX was assessed in sera from 81 AITP patients with a glycoprotein-specific enzyme immunoassay (MAIPA assay) using monoclonal antibodies against these platelet GPs. All sera contained platelet-specific antibodies which had been detected by platelet immunofluorescence. Of the 81 antibodies tested, 58 (72%) reacted with at least one of the platelet GPs studied. Autoantibodies against GPIb/IX were as common as antibodies against the GPIIb/IIIa complex. The same ratio of specificities was observed on autologous platelets of an independent cohort of 29 patients. The epitope of three autoantibodies against GPIb/IX and of mab Gi10, a monoclonal antibody, which inhibits binding of these autoantibodies, was further characterized. Severity of thrombocytopenia was not related to the GP specificity of the autoantibody. The observation that in 23 (28%) of these sera the antigenic determinants could not be assigned to the glycoproteins under investigation suggests that platelet autoantibodies may react with other GPs or other membrane constituents, e.g. glycolipids.     

Intracranial hemorrhage in children with immune thrombocytopenic purpura

 We sent questionnaires to hospitals in Japan in order to study the incidence and conditions of intracranial hemorrhage (ICH) in children with immune thrombocytopenic purpura (ITP). From 1980 to 1995, 11 cases of ICH were reported in eight patients with ITP at 35 institutions. One patient had ICH four times, but only one patient died of the condition. From 1990 through 1995, ICH occurred in four (0.52%) of 772 patients with ITP. None of the patients died. The platelet count when ICH occurred was 5.2±3.7×10⁹/l (mean±SD) (n=11). Four of the eight patients (1980–1995) had received active treatment [e.g. intravenous immunoglobulin G (i.v. IgG)] immediately before ICH occurred. In seven cases (1980–1995), possible causes of ICH, including menstruation (n=2) and viral infections (n=3), were identified. Systemic lupus erythematosus (SLE) later developed in three patients. Although the incidence of ICH in children with ITP has not decreased compared with the rates in earlier studies, the mortality rate has decreased markedly. Our results suggest that menstruation, infection, and risk factors for progression to SLE may help to predict ICH in children with ITP. Large-scale prospective trials are needed to identify risk factors for ICH. Received: 24 June 1999 / Accepted: 26 May 2000     

Interleukin 4, interleukin 6 and interleukin 10 polymorphisms in children with acute and chronic immune thrombocytopenic purpura

Immune thrombocytopenic purpura (ITP) is an immune-mediated disorder. We investigated the polymorphisms of interleukin (IL)-4 intron 3, IL-6 (-572 G/C), and IL-10 (-627 C/A) in 50 children with acute ITP, 30 children with chronic TIP, and 100 healthy individuals. There were significant differences in the RP1/RP2 genotype proportion (P = 0.04) and the RP2 allelic frequency (P = 0.03) of IL-4 intron 3 and the A/C genotype proportion (P = 0.01) of IL-10 (-627) between children with chronic ITP and controls. This finding suggests that the IL-4 intron 3 and IL-10 (-627) polymorphisms contribute to the susceptibility of developing childhood chronic ITP.     

Pathogenesis of chronic immune thrombocytopenic purpura

PURPOSE OF REVIEW: This article summarizes recent insights into the pathophysiology of immune thrombocytopenic purpura, a disorder in which autoantibodies against cell-specific glycoproteins (GPIIb-IIIa, GPIb-IX and others) accelerate platelet destruction. RECENT FINDINGS: Autoantibodies are produced by a limited number of B-cell clones. Platelet antibodies may also impair megakaryocyte development and platelet turnover, thromobopoietin levels are normal or only modestly increased and a compensatory increase in platelet production is not effective in many patients. Patients may show impaired immune regulation manifested by increased proliferation of helper T lymphocytes. Cytotoxic T lymphocytes from patients can lyse platelets in vitro. If cytotoxic T lymphocytes are also capable of perturbing megakaryocyte function, this mechanism may contribute to impaired platelet production. Polymorphisms in the Fcgamma-RIIIa gene may correlate with response to certain forms of therapy and similar genetic approaches may help to identify subsets of patients that differ in their natural history and response to various interventions. SUMMARY: Better understanding of autoantibody development, inhibition of thrombopoiesis and Fcgamma receptor and other polymorphisms will assume increased importance in elucidating the pathogenesis and targeting treatment of chronic immune thrombocytopenic purpura.     

Characterization of platelet glycoproteins and platelet/endothelial cell antibodies in patients with thrombotic thrombocytopenic purpura

Platelets and sera from 12 patients with thrombotic thrombocytopenic purpura (TTP) and 12 healthy normal control subjects were examined. As determined by quantitative flow cytometry, prior to plasma exchange therapy platelet surface glycoprotein (GP) Ib levels were similar in TTP patients and normal controls (mean 20 188 and 20 226 molecules/platelet, respectively). Platelets from patients with TTP did, however, have significantly reduced levels of GPIIb/IIIa prior to plasmapheresis (mean 36 348 v 52 505 molecules/platelet in controls; P = 0.0004) and of GPIV (mean 13 321 v 26 212 molecules/platelet in controls; P = 0.0002). An increase in activated platelets, as determined by CD62 expression, was observed in 82% of patients. Increased platelet-associated immunoglobulins and/or complement was also seen in approximately 60% of the patients. In general, with return of platelet counts to normal levels following seven plasmaphereses, the above abnormalities were reversed, although often not to normal levels. Western blot analysis indicated the presence of antibodies reactive to platelet GPIV (88 kD) in 70% of pretreatment sera from patients with TTP; a similar band was observed in 80% of patient sera against microvascular endothelial cells. Immunofluorescence microscopic examination indicated the presence of antibody in pretreatment sera from patients with TTP to microvascular (73%) and large vessel (36%) endothelial cells. As measured by an indirect flow cytometric assay, pretreatment sera from 55% of patients with TTP were reactive with large vessel endothelial cells and 100% reacted with microvascular endothelial cells; reactivity was significantly greater against the microvascular endothelial cells (P = 0.0048) and was reduced following plasma exchange therapy. These results indicate abnormalities in platelet glycoprotein expression in TTP and suggest that anti-platelet and anti-endothelial cell antibodies play a role in the thrombocytopenia and vasculitis characteristic of this disorder.     

Antibodies against platelet membrane glycoproteins

Glycocalicin has been proposed as the common platelet receptor for both ristocetin-human VIIIR:WF and thrombin-induced platelet aggregation. Platelets which have lost glycocalicin do not respond to either ristocetin-human VIIIR:WF or bovine VIIIR:WF. Using antibodies to the platelet membrane glycoproteins Ia and Ib, IIb and IIIa, and glycocalicin we show that the Fab' fragments of anti-glycoproteins Ia and Ib and anti-glycocalicin IgG totally inhibited bovine VIIIR:WF-induced platelet aggregation, while those from anti-glycoproteins IIb and IIIa IgG were without effect. Thrombin-induced platelet aggregation was strongly inhibited by the Fab' fragments of anti-glycoproteins Ia and Ib IgG and anti-glycocalicin IgG, indicating that these glycoproteins play a major role in thrombin-platelet interaction. Fab' fragments of anti-glycoproteins IIb and IIIa IgG inhibited thrombin-induced platelet aggregation to a lesser extent implying that these glycoproteins are also somehow involved in the platelet response to thrombin perhaps as fibrinogen receptors. The data presented here give further support to the proposal that ristocetin-human VIIIR:WF and bovine VIIIR:WF share a common receptor on the platelet surface and indicate that this structure plays an important role in thrombin-induced platelet responses.     

Investigation of megakaryocyte apoptosis in children with acute and chronic idiopathic thrombocytopenic purpura

OBJECTIVE: Although the platelet destruction shows a primary role in the thrombocytopenia of idiopathic thrombocytopenic purpura (ITP), it has been demonstrated that impaired platelet production may also contribute to the severity of thrombocytopenia in ITP. The present study examined megakaryocyte apoptosis in bone marrow aspirates of children with acute and chronic ITP and investigated the role of megakaryocyte apoptosis in ITP pathophysiology. METHODS: Thirteen children diagnosed with acute ITP and eight children diagnosed with chronic ITP comprised the study group. Ten children, who were hospitalized for scoliosis operation but healthy otherwise, comprised the control group. In all children, megakaryocytes were isolated from the same amount of bone marrow aspirate samples using MACS CD61 MicroBeads (Miltenyl Biotec, Auburn, CA, USA). Megakaryocyte apoptosis was studied with transferase-mediated d-UTP-bitin nick end-labeling method. RESULTS: Isolated megakaryocyte counts did not differ significantly between acute ITP, chronic ITP and control groups. The percentage of apoptotic megakaryocytes did not differ significantly between acute ITP group and control group and between chronic ITP group and control group. The percentage of apoptotic megakaryocytes in patients with chronic ITP was significantly lower than the patients with acute ITP. There was no correlation between the percentage of apoptotic megakaryocytes and platelet counts of the cases. CONCLUSIONS: Increased megakaryocytic apoptosis does not play a role in the pathogenesis of dysmegakaryopoiesis and impaired platelet production in children with ITP. Decreased megakaryocyte apoptosis in cases with chronic ITP may be due to suppression of megakaryocyte maturation, as the terminal phase of the megakaryocyte lifespan is characterized by the onset of apoptosis.     

Diagnosis of immune thrombocytopenic purpura in children

PURPOSE OF REVIEW: This review updates the differential diagnosis between inherited and acquired immune thrombocytopenic purpura as well as clinical practice on the initial diagnosis of children with the disease. RECENT FINDINGS: A diagnosis of immune thrombocytopenic purpura may be based on an evaluation of the history, physical findings such as petechiae, bruising and mucous membrane bleeding, examination of peripheral blood films stained with Wright's or May-Grünwald-Giemsa, determination of blood counts, platelet size and appearance. Recently, diagnostic assays have been developed to detect platelet-bound antibodies. The sensitivity of these assays, however, is suboptimal, with a positive predictive value of 80-83%. If the diagnosis of immune thrombocytopenic purpura is in question due to the presence of atypical features, or if a patient with findings typical of the disease does not respond to therapy, bone marrow aspiration and biopsy are indicated to confirm the diagnosis. SUMMARY: The diagnosis of immune thrombocytopenic purpura is a process of elimination of other sources of thrombocytopenia. If the criteria discussed above are inconclusive and if the patient does not respond to therapy in 6-12 months (this is especially true in children) then a bone marrow aspiration is required to confirm the diagnosis, especially before initiating corticosteroid therapy.     

Helicobacter pylori eradication in patients with chronic immune thrombocytopenic purpura

AIM:To assess the effect of Helicobacter pylori(H.pylori)eradication on platelet counts in patients with chronic immune thrombocytopenic purpura(cITP).METHODS:A total of 36 cITP patients were included in the study.The diagnosis of H.pylori was done by rapid urease test and Giemsa staining of the gastric biopsy specimen.All H.pylori positive patients received standard triple therapy for 14 d and were subjected for repeat endoscopy at 6 wk.Patients who continued to be positive for H.pylori on second endoscopyreceived second line salvage therapy.All the patients were assessed for platelet response at 6 wk,3rd and 6th months.RESULTS:Of the 36 patients,17 were positive for H.pylori infection and eradication was achieved in16 patients.The mean baseline platelet count in the eradicated patients was 88615.38±30117.93/mm3and platelet count after eradication at 6 wk,3 mo and6 mo was 143230.77±52437.51/mm3(P=0.003),152562.50±52892.3/mm3(P=0.0001),150187.50±41796.68/mm3(P=0.0001)respectively and in the negative patients,the mean baseline count was71000.00±33216.46/mm3 and at 6 wk,3rd and 6th month follow up was 137631.58±74364.13/mm3(P=0.001),125578.95±71472.1/mm3(P=0.005),77210.53±56892.28/mm3(P=0.684)respectively.CONCLUSION:Eradication of H.pylori leads to increase in platelet counts in patients with cITP and can be recommended as a complementary treatment with conventional therapy.     

Mapping helper T-cell epitopes on platelet membrane glycoprotein IIIa in chronic autoimmune thrombocytopenic purpura

Chronic autoimmune thrombocytopenic purpura (AITP) is associated with autoantibodies specific for platelet membrane components, often including glycoprotein GPIIIa. T helper (Th) cells reactive with GPIIIa, which are capable of driving the autoantibody response, are activated in AITP, and the aim here was to map the epitopes that they recognize. Peripheral blood mononuclear cells (PBMCs) were obtained from 31 patients with AITP and 30 control donors and stimulated with a panel of 86 overlapping synthetic 15-mer peptides spanning the complete sequence of GPIIIa. One or more peptides elicited recall proliferation by PBMCs from 28 of the patients, and, typically, multiple sequences were stimulatory. In contrast, responses in healthy control donors were rare (chi-square test = 115.967; P 相似文献   

Circulating thrombopoietin level in chronic immune thrombocytopenic purpura

The circulating thrombopoietin (TPO) level in 43 patients with chronic immune thrombocytopenic purpura (ITP) was examined by an ELISA system. The TPO level (mean±SD) in ITP patients was mildly elevated (1.86±1.17 fmol/ml) compared to that in normal subjects (0.76±0.21), and was within the normal range in 30% of ITP patients. In contrast, the TPO level in patients with aplastic anaemia was very high, 12.35±6.42 fmol/ml. There was no correlation between TPO level and platelet count in ITP patients. Splenectomy was performed in two ITP patients, after which platelet counts increased to normal levels and TPO levels showed a transient increase. These data suggest that reactive TPO production against thrombocytopenia in ITP is small when compared to that in aplastic anaemia. Relative endogenous TPO deficiency may play some role in the pathophysiology of thrombocytopenia in ITP patients.