Cellular FXIII in Human Macrophage-Derived Foam Cells.

Macrophages express the A subunit of coagulation factor XIII (FXIII-A), a transglutaminase which cross-links proteins through Nε-(γ-L-glutamyl)-L-lysyl iso-peptide bonds. Macrophages are major cellular constituents of the atherosclerotic plaque; they may stabilize the plaque by cross-linking structural proteins and they may become transformed into foam cells by accumulating oxidized LDL (oxLDL). The combination of oxLDL staining by Oil Red O and immunofluorescent staining for FXIII-A demonstrated that FXIII-A is retained during the transformation of cultured human macrophages into foam cells. ELISA and Western blotting techniques revealed that the transformation of macrophages into foam cells elevated the intracellular FXIII-A content. This phenomenon seems specific for macrophage-derived foam cells; the transformation of vascular smooth muscle cells into foam cells fails to induce a similar effect. FXIII-A containing macrophages are abundant in the atherosclerotic plaque and FXIII-A is also present in the extracellular compartment. The protein cross-linking activity of FXIII-A in the plaque was demonstrated using an antibody labeling the iso-peptide bonds. Cells showing combined staining for FXIII-A and oxLDL in tissue sections demonstrated that FXIII-A-containing macrophages within the atherosclerotic plaque are also transformed into foam cells. Such cells may contribute to the formation of lipid core and the plaque structurization.

The Effect of Activated FXIII, a Transglutaminase, on Vascular Smooth Muscle Cells.

Plasma factor XIII (pFXIII) is a heterotetramer of FXIII-A and FXIII-B subunits. The cellular form (cFXIII), a dimer of FXIII-A, is present in a number of cell types. Activated FXIII (FXIIIa), a transglutaminase, plays an important role in clot stabilization, wound healing, angiogenesis and maintenance of pregnancy. It has a direct effect on vascular endothelial cells and fibroblasts, which have been implicated in the development of atherosclerotic plaques. Our aim was to explore the effect of FXIIIa on human aortic smooth muscle cells (HAoSMCs), another major cell type in the atherosclerotic plaque. Osteoblastic transformation induced by Pi and Ca2+ failed to elicit the expression of cFXIII in HAoSMCs. EZ4U, CCK-8 and CytoSelect Wound Healing assays were used to investigate cell proliferation and migration. The Sircol Collagen Assay Kit was used to monitor collagen secretion. Thrombospondin-1 (TSP-1) levels were measured by ELISA. Cell-associated TSP-1 was detected by the immunofluorescence technique. The TSP-1 mRNA level was estimated by RT-qPCR. Activated recombinant cFXIII (rFXIIIa) increased cell proliferation and collagen secretion. In parallel, a 67% decrease in TSP-1 concentration in the medium and a 2.5-fold increase in cells were observed. TSP-1 mRNA did not change significantly. These effects of FXIIIa might contribute to the pathogenesis of atherosclerotic plaques.

Effect of factor XIII levels and polymorphisms on the risk of myocardial infarction in young patients.

Factor XIII (FXIII) stabilizes and protects the fibrin network. Its role in myocardial infarction (MI) is still to be clarified. To evaluate the association of FXIII levels with MI in young patients and to investigate how the FXIII-A p.Val34Leu, FXIII-B p.His95Arg, and IVS11, c.1952 + 144 C>G (Intron K) polymorphisms influence FXIII levels and MI risk. Patients with ST elevation MI below 40 years of age (MI, n = 119), age-matched clinical controls (CC, n = 101) without MI and coronary artery disease, and healthy controls (HC, n = 120) were investigated for FXIII activity, FXIII-A2B2, FXIII-B concentrations and for the polymorphisms. FXIII activity and FXIII-A2B2 antigen were significantly elevated in MI. FXIII activity and antigen were significantly elevated in Arg95, while decreased in Intron K "G" carriers. Smoking had an independent increasing effect on FXIII activity and FXIII-A2B2 antigen. Intron K C>G polymorphism significantly decreased the risk of MI in patients with elevated fibrinogen. Among the investigated factors Intron K C>G polymorphism and smoking have the most powerful effect on FXIII levels and on the risk of MI in the young. The effect of smoking on coronary thrombus formation may partially be attributed to its FXIII increasing effect.

Regulation of plasma factor XIII levels in healthy individuals; a major impact by subunit B intron K c.1952+144 C>G polymorphism.

BACKGROUND: The regulation of plasma factor XIII (FXIII) levels in healthy individuals has been only partially explored. The identification of major non-genetic and genetic regulatory factors might provide important information on the contribution of FXIII to the risk of cardio/cerebrovascular diseases. OBJECTIVES: To determine the effect of age, smoking, BMI, fibrinogen concentration on plasma FXIII activity, complex FXIII antigen (FXIII-A2B2) and total FXIII-B subunit (tFXIII-B) level, to correlate FXIII-B level with the other two FXIII parameters and to assess the variation of FXIII levels in carriers of major FXIII subunit polymorphisms. METHODS: 268 healthy individuals were enrolled in the study. FXIII activity was measured by the ammonia release assay; FXIII-A2B2 and tFXIII-B were determined by ELISAs. FXIII-A p.Val34Leu, FXIII-B p.His95Arg and FXIII-B intron K c.1952+144 C>G polymorphisms were identified by RT-PCR using melting point analysis with fluorescence resonance energy transfer detection. RESULTS: All investigated FXIII parameters showed significant positive correlation with age and fibrinogen level; gender and BMI influenced only tFXIII-B. A highly significant positive correlation was demonstrated between tFXIII-B and the other FXIII parameters. FXIII-A p.Val34Leu polymorphism had only slight, if any effect on FXIII levels. The FXIII-B Arg95 allele moderately increased all three FXIII parameters, but the effect became statistically significant only after adjustment. The FXIII-B intron K G allele drastically decreased FXIII levels, and it seemed to be in synergism with the FXIII-A Leu34 allele. CONCLUSIONS: Plasma FXIII levels are subjected to multifactorial regulation, in which age, fibrinogen level and FXIII-B intron K polymorphism are major determinants.

The lack of aspirin resistance in patients with coronary artery disease.

BACKGROUND: Aspirin resistance established by different laboratory methods is still a debated problem. Using COX1 specific methods no aspirin resistance was detected among healthy volunteers. Here we tested the effect of chronic aspirin treatment on platelets from patients with stable coronary artery disease. The expression of COX2 mRNA in platelets and its influences on the effect of aspirin was also investigated. METHODS: One hundred and forty four patients were enrolled in the study. The direct measurement of COX1 acetylation was carried out by monoclonal antibodies specific to acetylated and non-acetylated COX1 (acCOX1 and nacCOX1) using Western blotting technique. Arachidonic acid (AA) induced TXB2 production by platelets was measured by competitive immunoassay. AA induced platelet aggregation, ATP secretion and VerifyNow Aspirin Assay were also performed. COX2 and COX1 mRNA expression in platelets were measured in 56 patients by RT-qPCR. RESULTS: In 138 patients only acCOX1 was detected, in the remaining six patients nacCOX1 disappeared after a compliance period. AA induced TXB2 production by platelets was very low in all patients including the 6 patients after compliance. AA induced platelet aggregation, secretion and with a few exceptions the VerifyNow Assay also demonstrated the effect of aspirin. Smoking, diabetes mellitus and inflammatory conditions did not influence the results. The very low amount of COX2 mRNA detected in 39 % of the investigated platelets did not influence the effect of aspirin. CONCLUSIONS: No aspirin resistance was detected among patients with stable coronary artery disease. COX2 expression in platelets did not influence the effect of aspirin.

Comparison of a new P2Y12 receptor specific platelet aggregation test with other laboratory methods in stroke patients on clopidogrel monotherapy.

BACKGROUND: Clinical studies suggest that 10-50% of patients are resistant to clopidogrel therapy. ADP induced platelet aggregation, a widely used test to monitor clopidogrel therapy, is affected by aspirin and is not specific for the P2Y12 receptor inhibited by clopidogrel. OBJECTIVES: To develop a P2Y12-specific platelet aggregation test and to compare it with other methods used for monitoring clopidogrel therapy. PATIENTS/METHODS: Study population included 111 patients with the history of ischemic stroke being on clopidogrel monotherapy and 140 controls. The effect of clopidogrel was tested by a newly developed ADP(PGE1) aggregation test in which prostaglandin E1 treated platelets are used. Results of conventional ADP induced platelet aggregation, VerifyNow P2Y12 assay and ADP(PGE1) aggregation were compared to those obtained by flow cytometric analysis of vasodilator stimulated phosphoprotein (VASP) phosphorylation. Reference intervals for all assays were determined according to the guidelines of Clinical Laboratory Standards Institute. RESULTS: The P2Y12-specificity of ADP(PGE1) test was proven by comparing it with ADP aggregation in the presence of P2Y1 antagonist, adenosine 3', 5'-diphosphate. The method was not influenced by aspirin treatment. Approximately 50% of patients were clopidogrel resistant by conventional ADP aggregation and VerifyNow tests. The ADP(PGE1) method and the VASP phosphorylation assay identified 25.9% and 11.7% of patients as non-responders, respectively. ADP(PGE1) aggregation showed good correlation with VASP phosphorylation and had high diagnostic efficiency. CONCLUSION: The new ADP(PGE1) method is a reliable test for monitoring P2Y12 receptor inhibition by platelet aggregation. As a subset of patients are non-responders, monitoring clopidogrel therapy by adequate methods is essential.

Expression of coagulation factor XIII subunit A in acute promyelocytic leukemia.

Leukemic cells often express markers, which are not characteristic of their particular cell lineage. In this study, we identified the "A" subunit of coagulation factor XIII (FXIII-A) in leukemic promyelocytes in de novo AML M3 cases. The cytoplasmic presence of factor XIII-A has previously been shown only in platelets/megakaryocytes and monocytes/macrophages. Furthermore, more recently we described the presence of FXIII-A in leukemic lymphoblasts. We studied 14 patients with this rare type of acute leukemia in a period of 4 years and investigated their bone marrow samples by 3-color flow cytometry upon diagnosis, mainly focusing on FXIII-A expression of leukemic cells. We detected FXIII-A also by ELISA, Western-blot, and confocal laser scanning microscopy. This was a homogenous group of AML M3 patients with translocation t(15;17)(q22;q21) detected by fluorescence in situ hybridization (FISH). In 10 out of 14 samples, FXIII-A was detectable by flow cytometry and was coexpressed with markers characteristic for leukemic promyleocytes (CD45dim/CD13+/CD33+/CD117+/cyMPO+ and HLA-DR-/CD34-/CD14-/CD15-). Staining for the markers GPIIb and GPIX were negative, and FXIII-A was identified in the cytoplasm of the cells by confocal microscopy in a relatively high quantity, as measured by ELISA. By Western blot analysis we could identify FXIII-A in the native 82 kDa form and in cleaved forms corresponding to cleavage products observed when purified FXIII-A was treated by human neutrophil elastase. This novel expression site of FXIII-A in AML M3 can be considered as a leukemia associated immunophenotype and may have pathophysiological significance.

Factor XIII and inflammatory cells.

Factor XIII is a coagulation factor with multiple plasmatic and cellular functions part of which is outside of the field of traditional hemostasis. The aim of the review is to provide a brief summary on the relationship between coagulation factor XIII (FXIII) and the cells of the immune system. In the first part the structure and biochemical functions of plasma and cellular FXIII are briefly summarized. Then, the interaction between leukocytes and factor XIII is discussed. This part includes the activation of FXIII by human neutrophil elastase, the down-regulation of activated FXIII (FXIIIa) by granulocyte proteases within the clot, and the effect of FXIIIa on leukocytes. In the following part data on the expression and subcellular distribution of FXIII in monocytes/macrophages are summarized. Another part of the review is devoted to changes of FXIII expression during monocyte differentiation and monocyte activation by the classical or the alternative pathway. In the final part reports on the possible functions of cellular FXIII in monocytes and macrophages are evaluated.

Factor XIII: a coagulation factor with multiple plasmatic and cellular functions.

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

Factor XIII subunits in human tears; their highly elevated levels following penetrating keratoplasty.

BACKGROUND: As blood coagulation factor XIII (FXIII) is of high importance in wound healing, we determined the concentrations of FXIII A and B subunits (FXIII-A and FXIII-B) and their complex (FXIII-A(2)B(2)) in normal tears and in tears from patients undergoing penetrating keratoplasty (PKP). METHODS: FXIII complex and subunit concentrations were measured by highly sensitive chemiluminescent ELISAs in tears from 60 healthy volunteers and from 31 patients undergoing corneal transplantation. RESULTS: In non-stimulated tears from healthy volunteers, low but consistent amounts of FXIII-A and FXIII-B (medians: 2.13 µg/L and 7.22 µg/L, respectively) were measured, mostly in non-complexed form. Following stimulation of tear secretion FXIII levels moderately decreased, but if normalized to protein concentration they did not change. One day after PKP FXIII levels became highly elevated, then gradually decreased, but even on day 7 significantly exceeded pre-surgery values. The elevation of tear FXIII levels was significantly higher in PKP patients who later developed neovascularization of donor cornea. CONCLUSIONS: FXIII subunits are low concentration components of normal tear. The striking elevation of FXIII subunit and FXIII-A(2)B(2) concentrations after PKP suggests the involvement of FXIII in corneal wound healing. Perioperatively measured high FXIII levels in tears seem to represent a risk of neovascularization.

A highly sensitive chemiluminescence immunoassay for the measurement of coagulation factor XIII subunits and their complex in tears.

Blood coagulation factor XIII (FXIII) is a tetramer (A(2)B(2)) consisting of catalytic FXIII-A and carrier/protective FXIII-B subunits. Besides stabilizing fibrin and protecting it from fibrinolysis, FXIII is also involved in wound healing and angiogenesis. The latter functions could be important in body fluids other than blood. In this study highly sensitive chemiluminescent ELISAs were developed to measure low concentrations of FXIII-A, FXIII-B and FXIII-A(2)B(2) antigen levels in tiny volumes of tear. For all three assays the limit of quantitation was below 0.02 microg/L, within laboratory imprecision did not exceed 12% and the recovery was close to 100%. The calibration curves showed an excellent fitting using second order polynomial equation. In non-stimulated tears from 40 healthy volunteers a low, but consistent amount of FXIII-A and FXIII-B (medians: 1.74 microg/L and 5.73 microg/L, respectively) was measured, mostly in free non-complexed form. The respective median values normalized for tear protein concentration were 0.23 microg FXIII-A/g and 0.85 microg FXIII-B/g. There was no gender and age difference and the values showed non-Gaussian distribution. The results prove that FXIII-A and FXIII-B are low concentration components of tear proteome, which in normal conditions might play a role in the repair of corneal micro-injuries. The developed methods provide a tool for monitoring FXIII subunit and complex levels in pathological conditions.

Assessment of thrombotic risk factors predisposing to thromboembolic complications in prosthetic orthopedic surgery.

BACKGROUND: Congenital thrombophilia is responsible for thromboembolic complications despite prolonged low-molecular-weight heparin (LMWH) prophylaxis following hip and knee endoprosthesis surgery. METHODS: A series of 86 patients with hip or knee endoprosthesis surgery were assessed 1 year after operation. Antithrombin III, protein C, and protein S were determined, and the activated protein C sensitivity ratio was measured. We screened for the presence of lupus anticoagulant, factor V Leiden mutation, and polymorphism of prothrombin G20210A. The lower limb venous circulation was monitored by color Doppler ultrasonography. Pulmonary embolism (PE) was diagnosed using ventilation and perfusion scintigraphy. RESULTS: In all, 33 patients had thromboembolic complications, 18 with thrombophilia (7 with combined form). Of the 53 patients without complications 12 had thrombophilia (2 with combined form). The differences were statistically significant. The risk score, the prevalence of FV Leiden and prothrombin G20210A mutations, and lupus anticoagulant were also significantly higher in the symptomatic group. Deep vein thrombosis (DVT) developed preoperatively in 15 patients; DVT and PE in 4 patients; thrombophilia was diagnosed in 53% and 75% of these cases. In all, 17 patients had postoperative thromboembolic complications: DVT developed in nine and PE in one patient (all with thrombophilia); DVT + PE developed in seven patients (all but one had thrombophilia). CONCLUSIONS: Significant differences were found in the incidence (P < or = 0.01) of thrombophilia and the risk score (P < or = 0.02) between symptomatic and asymptomatic patients. We recommend preoperative thrombophilia screening for patients with a history or familial prevalence of thromboembolism and/or with a high risk score (> or =15). In cases of thrombophilia, the form and duration of anticoagulant treatment must be decided individually.

Binding of plasma factor XIII to thrombin-receptor activated human platelets.

Platelet-bound coagulation factor XIII (FXIII) is targeted and concentrated at the site where platelet-rich thrombi are formed. Previous studies were in disagreement about the nature of FXIII binding to platelets. In this study, thrombin-receptor activating peptide (TRAP)-stimulated human whole blood and washed platelets were analysed by flow cytometry for the binding of FXIII using a monoclonal antibody against the A subunit of FXIII (FXIII-A). Here, we demonstrate that FXIII-A positivity significantly increased on activated platelets in whole blood compared to unstimulated sample, but not in washed platelets. GPIIb/IIIa receptor plays an essential role in FXIII binding, as fibrinogen receptor antagonist eptifibatide and fibrinogen binding inhibitor RGDS tetrapeptide significantly prevented the binding of FXIII. Furthermore, stimulated platelets from a patient with severe type I Glanzmann thrombasthenia showed insignificant FXIII-A positivity versus healthy controls. In addition, basal negligible amount of FXIII on washed platelets was only slightly increased when highly purified plasma FXIII (FXIII-A(2)B(2)) was added upon platelet activation by TRAP. Similarly, no remarkable FXIII-A positivity was observed when we used FXIII-A(2)B(2) with gammaA/gammaA fibrinogen. However, gammaA/gamma' fibrinogen significantly augmented FXIII binding on TRAP-stimulated platelets in the presence of non-activated FXIII-A(2)B(2). We conclude that FXIII-A(2)B(2) of plasma origin binds to thrombin-receptor activated platelets via GPIIb/IIIa receptor-bound fibrinogen with gamma'-chain and is not capable of direct platelet binding.

[Anticoagulation with hirudin for repeat cardiac surgery in a patient with heparin induced thrombocytopaenia]. / Hirudinnal végzett alvadásgátlás heparin kiváltotta thrombocytopeniában harmadik szívmutét során.

UNLABELLED: The authors present the case of a patient with heparin induced thrombocytopaenia who needed anticoagulation during the perioperative period of a third repeat cardiac operation without transfusions. Prostacyclin pretreatment was contraindicated because of critical aortic stenosis, heparinoids could not have been used due to necessity of postoperative anticoagulation. Recombinant hirudin was applied and its effect was monitored with ekarin coagulation time. Hirudin anticoagulation was continued until the proper INR was reached in the postoperative period. There were no intra- and postoperative complications detected, and there was no need for transfusion either. On his long-term follow-up, 6.5 years after the last cardiac surgery the patients was feeling well and had no complaints. CONCLUSION: Open heart operation of a patient with heparin induced thrombocythopenia can be performed safely by total anticoagulation with lepirudin if it is conducted by ecarin clotting time.

Endothelial dysfunction and atherosclerosis in rheumatoid arthritis: a multiparametric analysis using imaging techniques and laboratory markers of inflammation and autoimmunity.

OBJECTIVE: Cardiovascular disease is a leading cause of mortality in rheumatoid arthritis (RA). Endothelial dysfunction often precedes manifest atherosclerosis. We assessed endothelial dysfunction and atherosclerosis in RA in context with laboratory markers. METHODS: Fifty-two patients with RA and 40 matched healthy controls were studied. We assessed common carotid intima-media thickness (ccIMT) and flow- (FMD) and nitroglycerine-mediated vasodilation (NMD). We also assayed numerous immunological and metabolic laboratory markers. RESULTS: FMD was significantly lower in RA (5.32% +/- 4.66%) compared to controls (8.30% +/- 3.96%) (p = 0.001). NMD was preserved in RA. ccIMT was significantly greater in patients with RA (0.63 +/- 0.14 mm) versus controls (0.54 +/- 0.15 mm) (p = 0.012). In patients with RA, ccIMT correlated with FMD% (R = -0.318, p = 0.022), age (R = 0.831, p < 0.001), and anti-dsDNA levels (R = 0.463, p = 0.006). FMD% correlated with serum interferon-gamma (IFN-gamma) levels (R = 0.516, p = 0.014). NMD% correlated inversely with the percentage of Th0 lymphocytes (R = -0.636, p = 0.006), serum immune complex (R = -0.692, p < 0.001), and IgM levels (R = -0.606, p = 0.003). Patients with RA were divided as "low" (< 0.65 mm) versus "high" (> 0.65 mm) ccIMT groups, and into "normal" (> 5%) versus "impaired" (< 5%) FMD% subsets. Low and high ccIMT groups differed significantly in age and serum interleukin 1 (IL-1) and anti-dsDNA levels. RA patients with normal versus impaired FMD% differed significantly in age, disease duration, and serum IFN-gamma levels. Lipoprotein(a) [Lp(a)] also correlated with rheumatoid factor (RF) and C-reactive protein (CRP); homocysteine (HCy) correlated with CRP and correlated inversely with folate and vitamin B12 production. Paraoxonase-1 (PON-1) activity correlated with serum tumor necrosis factor-alpha(TNF-alpha) and IL-6 levels. CONCLUSION: This was a well characterized RA population, where FMD and ccIMT were impaired, indicating early endothelial dysfunction and accelerated atherosclerosis, respectively. RA-related autoimmune-inflammatory mechanisms and metabolic factors including anti-CCP, RF, CRP, circulating immune complexes, IgM, TNF-alpha, IL-6, Th0/Th1 ratio, HCy, folate, vitamin B12, and PON-1 may all be involved in the development of vascular disease in RA. Although ccIMT and FMD, as well as some laboratory factors, have been assessed by other investigators in RA-associated atherosclerosis, our results regarding the possible involvement of anti-CCP, anti-dsDNA, Lp(a), some cytokines, and PON-1 activity are novel. Early determination of FMD% and ccIMT may be useful to assess RA patients with high cardiovascular risk.

International registry on factor XIII deficiency: a basis formed mostly on European data.

FXIII deficiency is known as one of the rarest blood coagulation disorders. In this study, the phenotypic and in part genotypic data of 104 FXIII-deficient patients recorded from 1993 - 2005 are presented. The most common bleeding symptoms were subcutaneous bleeding (57%) followed by delayed umbilical cord bleeding (56%), muscle hematoma (49%), hemorrhage after surgery (40%), hemarthrosis (36%), and intracerebral bleeding (34%). Prophylactic treatment was initiated in about 70% of all patients. FXIII-B subunit-deficient patients had a milder phenotype than patients with FXIII-A subunit deficiency. The most frequent mutation affecting the F13A gene was a splice site mutation in intron 5 (IVS5-1G>A). This mutation was found in eight (17%) of 46 analyzed families. The haplotype analysis of patients carrying the IVS5-1A allele was consistent with a founder effect. The international registry (http://www.f13-database.de) will provide clinicians and scientists working on FXIII deficiency with a helpful tool to improve patient care and direct future studies towards better understanding and treatment of the disease.

Leukemic lymphoblasts, a novel expression site of coagulation factor XIII subunit A.

Blood coagulation factor XIII (FXIII) is a protransglutaminase circulating as a tetramer formed by two types of subunits (A2B2). The intracellular dimeric form of FXIII (A2) is present in platelets, megakaryocytes, monocytes and macrophages and has been detected in mono- and megakaryocytic leukemias. The aim of our study was to investigate FXIII-A expression in newly diagnosed B cell acute lymphoblastic leukemia (ALL) samples. We examined 47 de novo ALL cases of B cell origin by triple color labeling with flow cytometry. FXIII-A was detected by a FITC conjugated monoclonal antibody combined with CD34 and CD45 staining. In selected cases FXIII-A was investigated on slides prepared from blasts and visualized with a fluorescent microscope. In addition, blasts were studied by Western blot analysis and FXIII-A was measured by a highly sensitive ELISA method. By flow cytometry 19 samples of the 47 cases were found to be FXIII-A positive. Antigen concentration was 3.11 +/- 1.19 fg/blast, while normal lymphoid precursors and mature lymphocytes from B-CLL did not contain FXIII-A. In the lysate of lymphoblasts that were positive by flow cytometry, a single band (82 kDa) corresponding to FXIII-A was detected on Western blots. Confocal laser scanning microscopic examination revealed the presence of FXIII-A in the cytoplasm of these lymphoblasts. This novel expression site of FXIII-A in leukemic lymphoblasts can be utilized as a diagnostic tool and may also gain functional significance in B-lineage ALL.

Coagulation factor XIII-A. A flow cytometric intracellular marker in the classification of acute myeloid leukemias.

The association of coagulation factors with leukocytes have been demonstrated in several previous studies. This study was designed to study the sensitivity and specificity of factor XIII subunit A (FXIII-A) labelling in cultured myeloblastic and monoblastic cell lines and to investigate the intracytoplasmic expression of FXIII-A in de novo acute myeloid leukemia (AML) samples. Myeloblastic and a monoblastic cell lines were cultured and investigated for lineage specific maturation markers and FXIII-A expression. Furthermore, FXIII-A expression was investigated in 12 normal samples (7 bone marrow and 5 peripheral blood), 86 de novo AML samples and 6 chronic myelomonocytic leukemia (CMML) samples. In the monoblastic MonoMac6 cell line the appearance of FXIII-A preceded that of CD14 while it remained negative in the myeloblastic PLB-985 cell line throughout its maturation period. Among the AML samples the average frequency of FXIII-A positive cells in myeloblastic leukemia samples was below 10%, while in M4 and M5AML samples it was above 50% and was significantly higher than the generally used CD14 marker (p < 0.0001). In the AML M4 and M5 cases, FXIII-A proved sensitive for the identification of monoblasts. FXIII-A can be considered as a reliable intracytoplasmic marker for the monocytic and megakaryocytic series and its presence is highly predictive for mono- and megakaryocytic AML and for CMML.

High-throughput scintillation proximity assay for transglutaminase activity measurement.

Members of the transglutaminase enzyme family are involved in a broad range of biological phenomena, including haemostasis, apoptosis, semen coagulation, skin formation, and wound healing. A new and rapid method for measurement of transglutaminase activity is described in this article. The enzyme links tritium-labeled putrescine to biotinylated oligoglutamine, and the tritiated peptide is bound to a streptavidin-coated microtiter plate permanently covered by a thin layer of scintillant. Only the radioisotope incorporated into the peptide substrate is close enough to the scintillant molecules for photons to be produced. The signal generation depends on the transglutaminase activity, and it can be detected by appropriate light-measuring instrumentation without separation steps. The assay is sensitive, specific, linear at concentrations of tissue transglutaminase between 0.05 and 1.6m U/ml, and suitable for high-throughput measurements.

Possible role of factor XIII subunit A in Fcgamma and complement receptor-mediated phagocytosis.

Besides its traditional role in hemostasis, factor XIII subunit A (FXIII-A) is supposed to function as a cellular transglutaminase and to be involved in certain intracellular processes, including cytoskeletal remodeling. To investigate its intracellular role, the aim of the present study was to follow changes in FXIII-A production in combination with the receptor-mediated phagocytic activities of monocytes/macrophages and to examine the phagocytic functions of monocytes in patients with FXIII-A deficiency. Human blood monocytes were isolated from the buffy coats of healthy volunteers and cultured for 4 days. The FcgammaR-mediated phagocytosis of sensitized erythrocytes (EA) and the complement receptor (CR)-mediated phagocytosis of complement-coated yeast particles were studied during monocyte/macrophage differentiation. Changes in the gene expression of FXIII-A were detected by real-time quantitative RT-PCR. FXIII-A protein production was investigated with fluorescent image analysis at single cell level and Western immunoblot analysis. Both the FcgammaR and CR-mediated phagocytosis increased during culturing, which peaked on day 3. The phagocytic activity of the cells could be markedly inhibited with monodansylcadaverine, an inhibitor of the transglutaminase-induced crosslinking of proteins. The phagocytosis of EA, complement-coated and uncoated yeast particles was found to be strongly diminished in monocytes of FXIII-A deficient patients. The phagocytic functions of cultured cells showed a change in parallel with the alterations in FXIII-A mRNA expression, as well as with that in FXIII-A in protein synthesis detected by image and Western immunoblot analyses in concert. Our results suggest that FXIII-A plays a role in the Fcgamma and complement receptor-mediated phagocytic activities of monocytes/macrophages.