A unique phenotype of acquired Glanzmann thrombasthenia due to non-function-blocking anti-αIIbß3 autoantibodies.

Essentials Acquired Glanzmann thrombasthenia (aGT) is generally caused by function-blocking antibodies (Abs). We demonstrated a unique aGT case due to marked reduction of αIIbß3 with anti-αIIbß3 Abs. The anti-αIIbß3 Abs of the patient did not inhibit platelet function but reduced surface αIIbß3. Internalization of αIIbß3 induced by the Abs binding may be responsible for the phenotype. SUMMARY: Background Acquired Glanzmann thrombasthenia (aGT) is a bleeding disorder generally caused by function-blocking anti-αIIbß3 autoantibodies. Aim We characterize an unusual case of aGT caused by marked reduction of surface αIIbß3 with non-function-blocking anti-αIIbß3 antibodies (Abs). Methods A 72-year-old male suffering from immune thrombocytopenia since his 50s showed exacerbation of bleeding symptom despite mild thrombocytopenia. Platelet aggregation was absent with all agonists but ristocetin. Analysis of αIIbß3 expression and genetic analysis were performed. We also analyzed effects of anti-αIIbß3 Abs of the patient on platelet function and αIIbß3 expression. Results Surface αIIbß3 expression was markedly reduced to around 5% of normal, whereas his platelets contained αIIbß3 to the amount of 40-50% of normal. A substantial amount of fibrinogen was also detected in his platelets. There were no abnormalities in ITGA2B and ITGB3 cDNA. These results indicated that reduced surface αIIbß3 expression caused a GT phenotype, and active internalization of αIIbß3 was suggested. Anti-αIIbß3 IgG Abs were detected in platelet eluate and plasma. These Abs did not inhibit PAC-1 binding, indicating that the Abs were non-function-blocking. Surface αIIbß3 expression of a megakaryocytic cell line and cultured megakaryocytes tended to be impaired by incubation with the patient's Abs. After 2 years of aGT diagnosis, his bleeding symptom improved and surface αIIbß3 expression was recovered to 20% of normal with reduction of anti-αIIbß3 Abs. Conclusion We demonstrated a unique aGT phenotype due to marked reduction of surface αIIbß3. Internalization induced by anti-αIIbß3 Abs may be responsible in part for the phenotype.

A lower starting dose of eltrombopag is efficacious in Japanese patients with previously treated chronic immune thrombocytopenia.

BACKGROUND: Eltrombopag is an oral, non-peptide thrombopoietin receptor agonist that has shown efficacy and safety in chronic immune thrombocytopenia (ITP). However, ethnic differences in eltrombopag exposure have been reported: area under the curve exposure to eltrombopag was 87% greater among ITP patients of East Asian descent than among ITP patients of non-East Asian ITP descent. OBJECTIVES: To evaluate the efficacy and safety of eltrombopag by using, in Japanese ITP patients, lower starting (12.5 mg) and maximum (50 mg) doses of eltrombopag than the standard starting (50 mg) and maximum (75 mg) doses approved in the USA and Europe. PATIENTS: We examined 23 Japanese patients with previously treated chronic ITP with a platelet count of < 30,000 µL(-1) in a multicenter study comprising a randomized, double-blind, placebo-controlled phase for 6-week evaluation (15 eltrombopag, and eight placebo) and an open-label phase for 6-month evaluation (23 eltrombopag). RESULTS AND CONCLUSIONS: The response rate (platelet count of ≥ 50,000 µL(-1) ) at week 6 of the 6-week double-blind phase was 60% in eltrombopag-treated patients and 0% in placebo-treated patients. Ten of 23 patients (43.5%) responded for ≥ 75% of predefined assessment visits during the 6-month open-label phase. Notably, 22% (5/23) of patients responded to 12.5 mg of eltrombopag, which was administered within the first 3 weeks of eltrombopag treatment. Bleeding decreased with eltrombopag treatment as compared with baseline. Eltrombopag was generally well tolerated; one patient experienced a transient ischemic attack on day 9. Eltrombopag (12.5-50 mg) is effective for the management of Japanese patients with chronic ITP (NCT00540423).

STAP-2 interacts with and modulates BCR-ABL-mediated tumorigenesis.

In chronic myeloid leukemia (CML), the BCR-ABL fusion oncoprotein activates multiple pathways involved in cell survival, growth promotion and disease progression. In this report, we show that the signal-transducing adaptor protein-2 (STAP-2) is involved in BCR-ABL activity. We demonstrate that STAP-2 bound to BCR-ABL, and BCR and ABL proteins, depending on the STAP-2 Src homology 2-like domain. BCR-ABL phosphorylates STAP-2 Tyr250 and the phosphorylated STAP-2 in turn upregulated BCR-ABL phosphorylation, leading to enhanced activation of downstream signaling molecules including ERK (extracellular-signal-regulated kinase), STAT5 (signal transducer and activator of transcription 5), BCL-xL (B-cell lymphoma-extra large) and BCL-2(B-cell lymphoma 2). In addition, STAP-2 interacts with BCR-ABL to alter chemokine receptor expression leading to downregulation of CXCR4 and upregulation of CCR7. The interaction between STAP-2 and BCR-ABL plays a crucial role in conferring a growth advantage and resistance to imatinib, a BCR-ABL inhibitor, as well as tumor progression. Notably, mice injected with BCR-ABL/STAP-2-expressing Ba/F3 cells developed lymph node enlargement and hepatosplenomegaly. Moreover, suppression of STAP-2 in K562 CML cells resulted in no tumor formation in mice. Our results demonstrate a critical contribution of STAP-2 in BCR-ABL activity, and suggest that STAP-2 might be an important candidate for drug development for patients with CML. Furthermore, the expression of STAP-2 provides useful information for estimating the characteristics of individual CML clones.

C-terminal mutation of RUNX1 attenuates the DNA-damage repair response in hematopoietic stem cells.

Loss-of-function mutations of RUNX1 have been found in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDSs). Although several reports have suggested roles for RUNX1 as a tumor suppressor, its precise function remains unknown. Because gene alterations of RUNX1 by themselves do not lead to the development of leukemia in mouse models, additional mutation(s) would be required for leukemia development. Here, we report that the C-terminal deletion mutant of RUNX1, RUNX1dC, attenuates DNA-damage repair responses in hematopoietic stem/progenitor cells. γH2AX foci, which indicate the presence of DNA double-strand breaks, were more abundantly accumulated in RUNX1dC-transduced lineage(-)Sca1(+)c-kit(+) (LSK) cells than in mock-transduced LSK cells both in a steady state and after γ-ray treatment. Expression profiling by real-time -PCR array revealed RUNX1dC represses the expression of Gadd45a, a sensor of DNA stress. Furthermore, bone marrow cells from MDS/AML patients harboring the RUNX1-C-terminal mutation showed significantly lower levels of GADD45A expression compared with those from MDS/AML patients with wild-type RUNX1. As for this mechanism, we found that RUNX1 directly regulates the transcription of GADD45A and that RUNX1 and p53 synergistically activate the GADD45A transcription. Together, these results suggest Gadd45a dysfunction due to RUNX1 mutations can cause additional mutation(s) required for multi-step leukemogenesis.

Bleeding tendency and impaired platelet function in a patient carrying a heterozygous mutation in the thromboxane A2 receptor.

BACKGROUND: Thromboxane A(2) receptor (TXA(2)R) abnormality appears to dominantly disturb platelet function. OBJECTIVES: To reveal a molecular genetic defect in a patient with TXA(2)R abnormality and investigate the mechanism for the impaired response to TXA(2). PATIENT: The proband (OSP-2, PT) was a 7-year-old Japanese girl, suffering from repeated mucocutaneous bleeding. METHODS AND RESULTS: U46619 (2.5 and 10 µm)-induced platelet aggregation was remarkably impaired in the proband and her father. Immunoblots showed that TXA(2)R expression levels in their platelets were approximately 50% of controls, and nucleotide sequence analysis revealed that they were heterozygous for a novel mutation, c.167dupG in the TXA(2)R cDNA. Expression studies using Chinese hamster ovary (CHO) cells indicated that the mutation is responsible for the expression defect in TXA(2)R. We then examined α(IIb)ß(3) activation by employing an initial velocity analysis and revealed that U46619 failed to induce a sustained α(IIb)ß(3) and Rap1B activation in the proband. In addition, platelet secretion as monitored by P-selectin expression was markedly impaired in response to U46619 but not to ADP. The interaction between secreted ADP and P2Y(12) has been shown to play a critical role in the sustained α(IIb)ß(3) activation (Kamae et al. J Thromb Haemost 2006; 4: 1379). As expected, small amounts of exogenous ADP (0.5 µm) partially restored the sustained α(IIb)ß(3) activation induced by U46619. CONCLUSION: Our present data strongly suggest that the impaired platelet activation in response to U46619 in the heterozygous subject for the TXA(2)R mutation is, at least in part, as a result of the decrease in ADP secretion.

Presence of platelet-associated anti-glycoprotein (GP)VI autoantibodies and restoration of GPVI expression in patients with GPVI deficiency.

BACKGROUND: Glycoprotein (GP)VI deficiency is a rare platelet disorder with a mild bleeding tendency. However, its pathophysiology remains unclear. OBJECTIVES: We characterized a novel GPVI-deficient patient with immune thrombocytopenic purpura and searched for the presence of anti-GPVI autoantibodies in this and another patient with GPVI deficiency. METHODS AND RESULTS: A 12-year-old Japanese girl (case 1) with moderate thrombocytopenia and mild bleeding showed selectively impaired collagen-induced platelet aggregation. Flow cytometric analysis indicated that the patient had a defect in the expression of GPVI-FcRgamma. An eluate of her platelet-associated IgG contained anti-alpha(IIb)beta3 autoantibodies. Moreover, using GPVI-FcRgamma-transfected cells, we unexpectedly identified anti-GPVI antibodies against the soluble ectodomain of GPVI in the eluate, despite the patient's GPVI deficiency. In contrast, anti-GPVI antibodies were not detectable in her plasma. In another case of GPVI deficiency (case 2) without detectable plasma anti-GPVI antibodies, we again detected platelet-associated anti-GPVI antibodies. In a 2-year follow-up of case 1, the platelet count increased to within the normal range and the bleeding tendency improved. Interestingly, GPVI was again expressed on her platelets, in association with a decrease in the relative amount of anti-GPVI antibodies. CONCLUSIONS: This is the first demonstration of platelet-associated anti-GPVI antibodies in GPVI-deficient subjects, in one case with spontaneous restoration of GPVI expression. These results strongly suggest an autoimmune mechanism in GPVI deficiency.

Arteriosclerosis obliterans associated with anti-cardiolipin antibody/beta2-glycoprotein I antibodies as a strong risk factor for ischaemic heart disease in patients with systemic lupus erythematosus.

OBJECTIVE: The main objective of this study was to clarify the role of aPLs in the pathogenesis of arteriosclerosis obliterans (ASO), ischaemic heart disease (IHD) and cerebral vascular disorder (CVD) in patients with SLE. METHODS: We evaluated 155 patients with SLE by using objective tests for diagnosing ASO, IHD and CVD and laboratory tests including ELISA for aCL/beta2-glycoprotein I antibodies (aCL/beta2-GPI) and anti-phosphatidylserine/prothrombin antibodies (anti-PS/PT). RESULTS: Twenty-five (16.1%) of the 155 SLE patients were diagnosed with ASO. Both aCL/beta2-GPI and anti-PS/PT levels were significantly higher in SLE patients with ASO (mean +/- S.E., 104.3 +/- 38.8 U/ml for aCL/beta2-GPI, P < 0.01; 72.6 +/- 48.9 U/ml for anti-PS/PT, P < 0.05) than in SLE patients without ASO (22.8 +/- 9.9 U/ml for aCL/beta2-GPI; 18.3 +/- 4.4 U/ml for anti-PS/PT). Multivariate logistic analysis including aCL/beta2-GPI, anti-PS/PT and traditional risk factors (hypercholesterolaemia, hypertension and diabetes mellitus) confirmed that the presence of aCL/beta2-GPI was the most significant risk factor for ASO in SLE patients [odds ratio (OR) 3.45; 95% CI 1.40, 8.56; P < 0.01]. Furthermore, the prevalence of ASO was associated strongly with IHD (OR 11.8; 95% CI 3.45, 40.1; P < 0.0001) but not CVD (OR 1.84; 95% CI 0.65, 5.21; P = 0.25). CONCLUSIONS: The presence of aCL/beta2-GPI contributes to the risk of development of ASO, which may represent an important mechanism for the pathogenesis of IHD in patients with SLE.

Diffuse large B-cell lymphoma showing an interfollicular pattern of proliferation: a study of the Osaka Lymphoma Study Group.

AIMS: Diffuse large B-cell lymphoma (DLBCL) usually proliferates effacing lymph follicles. In occasional cases, tumour cells show an interfollicular pattern of proliferation preserving lymph follicles. The aim was to analyse clinicopathological findings in DLBCL showing an interfollicular pattern of proliferation to determine whether this type of lymphoma is a distinct entity of DLBCL. METHODS AND RESULTS: Clinicopathological findings in 12 cases of DLBCL showing an interfollicular pattern of proliferation [interfollicular group (IF)] were examined and compared with those in 30 cases of DLBCL with ordinary morphology [control group (CG)]. IF showed a significantly lower lactate dehydrogenase level and International Prognostic Index scores than CG (P = 0.023 and P < 0.01, respectively). The frequency of localized disease, clinical stage 1 and 2, in IF was higher than that in CG (P = 0.016). A morphologically polymorphous pattern of proliferation was found in seven of 12 cases (58.3%) in IF, which was higher than that in CG, five (16.7%) of 30 cases (P < 0.01). Clonality analysis with the polymerase chain reaction method revealed that all 11 IF cases examined showed a monoclonal pattern. Immunohistochemically, the majority (11 of 12) of IF cases showed a non-germinal centre B-cell phenotype and the frequency was higher than that in CG (P = 0.021). CONCLUSION: Diffuse large B-cell lymphoma with an interfollicular pattern of proliferation shows distinct clinical and pathological findings from ordinary DLBCL.

Difference between genomic actions of estrogen versus raloxifene in human ovarian cancer cell lines.

Although there is growing evidence that estrogens promote tumor progression in epithelial ovarian cancer, the molecular mechanisms accounting for this are still unclear. Selective estrogen receptor modulators (SERMs) mimic estrogen action in certain tissues while opposing it in others. The molecular mechanisms of the effects of SERMs such as raloxifene on the tumor progression of epithelial ovarian cancer are also still unclear. Here, we show that various genomic actions of estrogen differ from those of raloxifene in human ovarian cancer cell lines expressing estrogen receptor alpha (ERalpha). 17beta-Estradiol (E2) induced the gene expression of c-Myc and IGF-1 and increased the binding of ERalpha to the AP1 site of the promoters of c-Myc and IGF-1. ERalpha silencing abolished the E2-stimulated c-Myc expression. E2 induced the recruitment of co-activators such as SRC-1, SRC-3 and CBP to the promoters of c-Myc and IGF-1, and SRC-1 silencing abolished both the E2-stimulated c-Myc expression and cell-cycle progression. In contrast, although raloxifene increased the binding of ERalpha to the AP1 site of the promoters of c-Myc and IGF-1, raloxifene had no effect on the gene expression of c-Myc or IGF-1. Raloxifene induced the recruitment of co-repressors such as HDAC2, N-CoR and SMRT to the promoter of IGF-1. Thus, the difference between the genomic actions exerted by estrogen and raloxifene in human ovarian cancer cell lines expressing ERalpha appear to be dependent on the recruitment of co-regulators.

Role of DNA methylation for expression of novel stem cell marker CDCP1 in hematopoietic cells.

CDCP1, a novel stem cell marker, is expressed in hematopoietic cell line K562 but not in Jurkat. When CDCP1 promoter was transfected exogenously, Jurkat showed comparable promoter activity with K562, suggesting that the factor to enhance transcription was present but interfered to function in Jurkat. The reporter assay and si-RNA-mediated knockdown experiment revealed that zfp67, a zinc-finger protein, enhanced CDCP1 transcription. Amount of zfp67 in Jurkat was comparable with K562, but chromatin immunoprecipitation showed that zfp67 bound to CDCP1 promoter in K562 but not in Jurkat. There are CpG sequences around the promoter of CDCP1, which were heavily methylated in Jurkat but not in K562. Addition of demethylating reagent to Jurkat induced CDCP1 expression, and increased the zfp67 binding to CDCP1 promoter. Among normal hematopoietic cells such as CD34+CD38- cells, lymphocytes and granulocytes, inverse correlation between proportion of methylated CpG sequences and CDCP1 expression level was found. Demethylation of CpG sequences in lymphocytes, in which CpG sequences were heavily methylated, induced CDCP1 expression and its expression level further increased through zfp67 overexpression. The methylation of DNA appeared to regulate the cell-type-specific expression of CDCP1 through the control of interaction between chromatin DNA and transcription factors.

Critical role of ADP interaction with P2Y12 receptor in the maintenance of alpha(IIb)beta3 activation: association with Rap1B activation.

OBJECTIVE: Platelet integrin alpha(IIb)beta3 plays a crucial role in platelet aggregation, and the affinity of alpha(IIb)beta3 for fibrinogen is dynamically regulated. Employing modified ligand-binding assays, we analyzed the mechanism by which alpha(IIb)beta3 maintains its high-affinity state. METHODS AND RESULTS: Washed platelets adjusted to 50 x 10(3) microL(-1) were stimulated with 0.2 U mL(-1) thrombin or 5 microm U46619 under static conditions. After the completion of alpha(IIb)beta3 activation and granule secretion, different kinds of antagonists were added to the activated platelets. The activated alpha(IIb)beta3 was then detected by fluorescein isothiocyanate (FITC)-labeled PAC1. The addition of 1 mum AR-C69931MX (a P2Y12 antagonist) or 1 mm A3P5P (a P2Y1 antagonist) disrupted the sustained alpha(IIb)beta3 activation by approximately 92% and approximately 38%, respectively, without inhibiting CD62P or CD63 expression. Dilution of the platelet preparation to 500 microL(-1) also disrupted the sustained alpha(IIb)beta3 activation, and the disruption by such dilution was abrogated by the addition of exogenous adenosine 5'-diphosphate (ADP) in a dose-dependent fashion. The amounts of ADP released from activated platelets determined by high-performance liquid chromatography were compatible with the amounts of exogenous ADP required for the restoration. We next examined the effects of antagonists on protein kinase C (PKC) and Rap1B activation induced by 0.2 U mL(-1) thrombin. Thrombin induced long-lasting PKC and Rap1B activation. AR-C69931MX markedly inhibited Rap1B activation without inhibiting PKC activation. CONCLUSIONS: Our data indicate that the continuous interaction between released ADP and P2Y12 is critical for the maintenance of alpha(IIb)beta3 activation.

Impaired platelet function in a patient with P2Y12 deficiency caused by a mutation in the translation initiation codon.

In this study, we have identified a patient (OSP-1) with a congenital P2Y12 deficiency showing a mild bleeding tendency from her childhood and examined the role of P2Y12 in platelet function. At low concentrations of agonists OSP-1 platelets showed an impaired aggregation to several kinds of stimuli, whereas at high concentrations they showed a specifically impaired platelet aggregation to adenosine diphosphate (ADP). ADP normally induced platelet shape change and failed to inhibit PGE1-stimulated cAMP accumulation in OSP-1 platelets. Molecular genetic analysis revealed that OSP-1 was a homozygous for a mutation in the translation initiation codon (ATG to AGG) in the P2Y12 gene. Heterologous cell expression of wild-type or mutant P2Y12 confirmed that the mutation was responsible for the deficiency in P2Y12. OSP-1 platelets showed a markedly impaired platelet spreading onto immobilized fibrinogen. Real-time observations of thrombogenesis under a high shear rate (2000 s(-1)) revealed that thrombi over collagen were small and loosely packed and most of the aggregates were unable to resist against high shear stress in OSP-1. Our data suggest that secretion of endogenous ADP and subsequent P2Y12-mediated signaling are critical for platelet aggregation, platelet spreading, and as a consequence, for stabilization of thrombus.

Expression and subcellular localization of WAVE isoforms in the megakaryocyte/platelet lineage.

WAVE isoforms, which consist of WAVE-1, WAVE-2 and WAVE-3, are members of the Wiskott-Aldrich syndrome protein (WASP) family. They are implicated in the regulation of actin-cytoskeletal reorganization downsteam of the small GTPase, Rac. Since platelet attachment to extracellular matrices leads to filopodial and lamellipodial extension, we examined the expression and subcellular localization of WAVEs in platelets. Employing primary megakaryocytic cells derived from cord blood as well as megakaryocytic cell lines, we also examined their expression during megakaryocytic differentiation. Immunoblotting and immunohistochemical analysis revealed that platelets expressed WAVE-1 and WAVE-2, whereas WAVE-3 expression was hardly to be detected. WAVE-1 expression was associated with megakaryocytic differentiation, whereas WAVE-2 and WAVE-3 expression was not changed by the differentiation. In adhered platelets both WAVE-1 and WAVE-2 were localized at the edge of the lamellipodia and at the tips of filopodia. In WASP-deficient platelets we found normal lamellipodial formation and localization of WAVE-1 and WAVE-2 at the edges of lamellipodia. Furthermore, we demonstrated that WAVE-1 and WAVE-2 moved from a detergent-soluble cytosolic fraction to insoluble cytoskeleton fraction after platelet aggregation. These results suggest that WAVE-1 and WAVE-2 regulate actin reorganization during platelet spreading and aggregate formation.

Oncogenic receptor tyrosine kinase in leukemia.

Growth, survival and differentiation of hematopoietic cells are regulated by the interaction between hematopoietic growth factors and their receptors. While the defect in this interaction results in an insufficient hematopoiesis, the aberrantly elevated activation leads to the transformation of hematopoietic cells. The constitutive active mutations of receptor tyrosine kinase, such as c-Kit platelet-derived growth factor receptor (PDGFR) or fins-like tyrosine kinase 3 (Flt3), play a major role in the development of hematopoietic neoplasia. The constitutive activation is provoked by several mechanisms, such as making fusion genes by chromosomal translocations, or various mutations involving regulatory regions of the receptor. The chromosomal translocation brings the receptor intracytoplasmic domain juxtaposed to an unrelated molecule which has dimerization or multimerization motif, resulting in the constitutive dimerization of the receptor. The missense, insertion or deletion mutations in the regulatory regions, such as juxtamembrane domain, activation loop and extracellular domain, cause constitutive activation by releasing the respective auto-inhibitory functions of each regulatory region. Constitutive active receptors generate different signals quantitatively and qualitatively from wild type receptor, which mediate the oncogenic phenotype. Given the frequent involvement of constitutive active receptor tyrosine kinase in hematopoietic malignancies, targeted inhibitions of active tyrosine kinase and downstream aberrant signaling are rapidly developing novel therapeutic modality with much promise.

Anti-prothrombin antibodies combined with lupus anti-coagulant activity is an essential risk factor for venous thromboembolism in patients with systemic lupus erythematosus.

Anti-prothrombin antibodies (anti-prothrombin) and anti-beta2-glycoprotein I antibodies (anti-beta2-GP I) are the most common and characterized anti-phospholipid antibodies (aPL) detected using specific enzyme-linked immunosorbent assay (ELISA) systems. Recently, lupus anti-coagulant (LA) activity detected by a phospholipid-dependent coagulation assay was reported to be associated with anti-prothrombin and/or anti-beta2-GP I. Here we show that the co-existence of IgG anti-prothrombin and LA activity might be an essential risk factor for venous thromboembolism (VTE) in patients with systemic lupus erythematosus (SLE). We examined not only the levels of antibodies to prothrombin and anti-beta2-GP I (both IgG and IgM isotypes) using an ELISA system, but also LA activity detected using both diluted Russell's viper venom time (dRVVT) and STACLOT LA test in 124 patients with SLE. The SLE patients were divided into four groups according to the results of ELISA and LA assay results for each aPL: group A, ELISA+ and LA+ group B, ELISA+ and LA-; group C, ELISA- and LA+ group D, ELISA- and LA-. Regarding IgG anti-prothrombin, the prevalence of VTE was significantly higher in group A (16/35 cases, 45.7%, P < 0.001, Fisher's exact probability test) than in the other groups (B, 2/30, 6.7%; C, 1/22, 4.5%; D, 1/37, 2.7%). With respect to IgM anti-prothrombin and IgG or IgM anti-beta2-GP I, the prevalence of VTE was higher in both groups A and C than in group D, but no statistical difference in prevalence was found between groups A and C. Multivariate logistic regression analysis of risk factors for VTE confirmed that the co-existence of IgG anti-prothrombin and LA activity was the only significant risk factor for VTE (odds ratio, 19.13; 95% confidence intervals, 4.74-77.18).

Measurement of a newly developed thrombomodulin addition activated partial thromboplastin time assay in patients with deep venous thrombosis.

We developed a simple assay using rabbit thrombomodulin (TM) based on an activated partial thromboplastin time method, which detected the response to TM in plasma coagulation. We call it thrombomodulin addition clotting time (TACT). The anticoagulant response to TM was calculated by dividing the clotting time with TM by the clotting time with buffer solution. Results were expressed as TACT ratio, which indicates the degree of inhibition of plasma clotting by TM. Using this assay, we measured the TACT ratio in 80 patients with deep-vein thrombosis (DVT) and in 126 controls matched to the patients according to age and sex. A significant difference in the TACT ratio was observed between patients with DVT (mean 1.874) and controls (mean 1.956) (p < 0.001). Twenty- three patients (29%) had TACT ratios below the 10th percentile (1.757) of distribution of control subjects (odds ratio: 3.5; 95% confidence interval (CI): 1.7-7.2). After excluding subjects with a deficiency of protein C, protein S and antithrombin III, we found an odds ratio for DVT of 3.4 (95% CI: 1.6-7.2). These data suggest that natural anticoagulant deficiencies do not influence the TACT ratio, and our case-control study may show that the plasma of patients with DVT has a low response to TM.