Monoclonal Anticardiolipin Antibodies Research Articles

Antiphospholipid antibodies may impair factor XIIa–dependent activation of fibrinolysis in pregnancy: in vitro evidence with human endothelial cells in culture and monoclonal anticardiolipin antibodies

The purpose of this study was to analyze the in vitro activation of the contact complex with the use of human umbilical vein endothelial cells (HUVEC) in culture and monoclonal anticardiolipin antibodies (MaCL). Cultured HUVECs were incubated with pooled plasma from third-trimester pregnant women with the addition (20 mg/mL) of MaCL with anti-beta-2 glycoprotein I activity that was obtained from patients with antiphospholipid syndrome (APS), MaCL from an individual without APS, or from a control patient with immunoglobulin M without aCL activity. Supernatants were evaluated. Activated factors XII and VII, prothrombin-fragment 1 + 2, urokinase-type plasminogen activator (UPA), and differentiating 2 chain UPA were determined. In the cultured HUVEC supernatants, the addition of MaCL increased activated factor VII and prothrombin-fragment 1 + 2, did not modify UPA, and decreased activated factor XII and differentiating 2 chain UPA, in comparison with samples with control immunoglobulin M added. The MaCL without APS activity did not change any parameter that was evaluated. MaCL with anti-beta-2 activity that was obtained from patients with APS may interfere in the activation of the contact complex during pregnancy.

The putative role of cytokines in the induction of primary anti-phospholipid syndrome in mice.

Antiphospholipid syndrome (APLS) is characterized by thrombocytopenia, thromboembolic phenomena and recurrent fetal loss, associated with anti-cardiolipin antibodies (ACA) and/or lupus anticoagulant. The syndrome may be primary or may be associated with other conditions such as systemic lupus erythematosus (SLE). In this study we induced primary APLS following immunization of BALB/c mice with a human monoclonal ACA (H-3). Analysis of the cytokine profile of the mice with experimental APLS indicated low production of IL-2, IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) by concanavalin A (Con A)-stimulated splenocytes of H-3 immunized mice. It seems that the low levels of IL-3 and GM-CSF have a potential role in the fetal loss of the APLS. Whatever the mechanism of IL-3 and GM-CSF in preventing fetal loss, these results may have therapeutic bearing on the reproductive outcome in women and other species with APLS.

Some Recent Insights into the Prothrombogenic Mechanisms of Antiphospholipid Antibodies

Antiphospholipid antibodies (aPL) are a heterogeneous group of autoantibodies, detected in the sera of patients with both autoimmune and various non-autoimmune diseases. They are also detected in subjects with no overt underlying disease - the primary antiphosphilipid syndrome (PAPS). High titers of APL are associated with arterial and venous thrombosis, recurrent fetal loss and thrombocytopenia. There have been many suggestions explaining the potential mechanisms of the procoagulant effect of aPL. These include endothelial cell (EC) activation; increased adhesion molecule expression; inhibition of EC prostacyclin release, increased leucocyte adhesion to EC, downregulation of thrombomodulin expression. APL induce the procoagulant activity of monocytes via increased tissue factor expression and directly stimulate platelet hyperactivity with resultant production of enhanced amounts of the proaggregatory molecule of TXA(2). In vitro studies show that prepro-endothelin-1 mRNA is induced by human monoclonal anticardiolipin antibodies and this might contribute to vasospasm, and, ultimately, to arterial occlusion. The hypercoagulable state in APS patients is associated with alterations in the protein C/S pathway. It is suggested that aPL may impair the protein C anticoagulant system. Acquired protein C and protein S deficiency is described in patients with APS. Beta2- glycoprotein I, (Beta2-GPI) a natural anticoagulant, is involved in the regulation of protein S anticoagulant activity by preventing the binding of protein S to C4b-binding protein. APL were shown to inhibit this effect of Beta2- GP I. As the group of aPL is very heterogeneous, it is unlikely that a single mechanism is responsible for the thrombogenic activity of all aPLs associated with thrombosis.

Human monoclonal IgG anticardiolipin antibodies induce nitric oxide synthase expression

Objective Antiphospholipid antibodies are associated with increased risk of thrombosis, particularly as in antiphospholipid syndrome. This study aims to determine the acute effects of anticardiolipin antibodies on nitric oxide production and vascular function. Methods Ex vivo aortic rings from male Sprague Dawley rats were incubated with IgG monoclonal anticardiolipin antibody (IS4) or a non-specific IgG control. In organ baths, response to phenylephrine and acetlycholine was determined alone and with nitro- l-arginine methyl ester ( l-NAME), 1400 W, d-arginine, l-arginine, sodium nitroprusside and cardiolipin. In vivo antibodies were injected into anaesthetised, spontaneously breathing male Sprague Dawley rats. Haemodynamic variables and serum nitric oxide were measured. Immunohistochemistry for iNOS and eNOS was performed in kidney vessels. Results Phenylepherine contraction was decreased in the IS4 group compared to controls ( p < 0.001). l-NAME, 1400 W and cardiolipin, abolished this effect. l-Arginine caused significant relaxation in the IS4 group ( p = 0.005). Mean arterial pressure in rats injected with IS4 was reduced compared to IgG and saline controls ( p < 0.001). NO in plasma increased significantly after IS4 administration ( p < 0.001). Immunohistochemistry showed increased iNOS expression in kidney arteries in the IS4 group, with no change in eNOS. Conclusion Anticardiolipin antibodies induce NO production acutely via increased expression of iNOS in both ex vivo and in vivo models.

Effects of beta2-glycoprotein I and monoclonal anticardiolipin antibodies in platelet interaction with subendothelium under flow conditions.

To evaluate whether the effect of human monoclonal anticardiolipin antibodies (aCL) on platelet interaction with the subendothelium under flow conditions is dependent on beta(2)-glycoprotein I (beta(2)GPI). Three monoclonal IgM aCL with anti-beta(2)GPI activity (TM1B3, GR1D5, and EY2C9) obtained from patients with antiphospholipid syndrome, a monoclonal aCL with lupus anticoagulant activity but without anti-beta(2)GPI activity (FRO) obtained from a patient with a splenic lymphoma, and a control monoclonal IgM without aCL activity were used. TM1B3, GR1D5, EY2C9, FRO, and control IgM (30 microg/ml) were added to reconstituted blood containing gel-filtered platelets (200 x 10(9)/liter), factor VIII (100 units/dl), and fibrinogen (1.5 gm/liter). Samples were perfused (wall-shear rate 800 seconds(-1)), with and without the addition of purified beta(2)GPI (20 microg/ml), through annular chambers containing collagen-rich denuded vascular segments, and the percentages of surface covered by platelets and by thrombi were evaluated. No differences in the percentages of surface covered by platelets and by thrombi were observed among samples with TM1B3, GR1D5, EY2C9, FRO, and control IgM added when reconstituted blood samples without beta(2)GPI were used. However, a significant increase in the percentage of surface covered by platelets was observed in the presence of TM1B3, GR1D5, and EY2C9 but not in the presence of FRO when samples containing beta(2)GPI were used. Increased thrombi formation was induced by TM1B3 and GR1D5 but not by EY2C9 or FRO in samples with added beta(2)GPI. Monoclonal aCL require anti-beta(2)GPI activity to promote platelet interaction with the subendothelium under flow conditions.

Revisiting the anticardiolipin test and its standardization.

Although the importance of the anticardiolipin test in diagnosis of antiphospholipid syndrome (APS) is widely accepted, there remains much misunderstanding about the strengths and weaknesses of this assay. Several disorders result in formation of low levels of the antibody, hence the anticardiolipin test is not specific when results are low positive. In general, the higher the anticardiolipin level the greater the likelihood of a diagnosis of APS. Hence there have been numerous efforts to enable reproducible measurement of anticardiolipin levels. Standard calibrators were introduced to construct calibration curves from which levels of unknown samples can be derived. Those standard calibrators were made by mixing varying quantities of high positive with normal sera. More recently, calibrators derived from monoclonal anticardiolipin antibodies have been introduced. There are advantages and disadvantages with both types of calibrators. Determination of a precise and reproducible anticardiolipin level is difficult, whatever the calibrators used, because the assay is dependent on several variable components, any of which may fail on any given day. Utilization of a semi-quantitative measure (low, medium, high) may suffice in most clinical settings and would be less subject to error. Validated ELISA kits may offer greater reproducibility, since there is less variability than bench assays set up in very different laboratories. Whether using a kit or a bench assay, meticulous attention to detail offers the best opportunity for precision and reproducibility.

The effects of a human IgM monoclonal anticardiolipin antibody on pregnancy in a transgenic mouse model.

The clinical features of antiphospholipid (or Hughes') syndrome (APS) are most commonly seen in individuals who have raised levels of IgG anticardiolipin antibodies. Most murine models of the syndrome have involved the administration of such antibodies to normal mice. However, APS can occur in the presence of raised levels of serum IgM anticardiolipin antibodies alone. The present study was designed to see if an IgM monoclonal antibody can induce changes in mice similar to those seen in human APS. This antibody, BH1, has previously been derived from a patient with primary APS. In its ligand-binding and idiotypic characteristics it is representative of antiphospholipid antibodies (aPL) found in the serum of patients with APS. In order to minimise the immune response to human IgM, we used transgenic mice (F15) which express, and are predicted to be tolerant of, human immunoglobulin mu chains. The features of APS may develop more readily in individuals who have an existing autoimmune disorder, such as systemic lupus erythematosus (SLE). We therefore crossed these transgenic mice with New Zealand Black (NZB, SLE-prone) mice, and used the progeny (F15 x NZB/F1) in our experiments. Twenty-four F15 x NZB/F1 mice were given BH1, or a control IgM antibody, (A5566) immediately preceding and then three times during pregnancy. There was a reduction in the mean number of foetuses in animals given BH1 compared with those given A5566 (8.6 vs 11.0; P < 0.05), and a similar reduction in mean total foetal weight per pregnancy (9.05 vs 12.73 g; P < 0.05). Two mice showed a marked reduction in platelet count. No evidence of thrombosis was detected macroscopically or histologically. Our results show a lower incidence of APS-type features compared to previous studies in which mice have been administered aPL. This may be because BH1 is an IgM antibody. Nevertheless, the data support the concept that IgM aPL of particular ligand-binding specificities may have a direct pathogenetic role in certain cases of human APS.

Two-dimensional electrophoresis and mass spectrometry identification of proteins bound by a murine monoclonal anti-cardiolipin antibody: a powerful technique to characterize the cross-reactivity of a single autoantibody.

Antigenic cross-reactivity, i.e., the capacity of a single antibody to react with apparently dissimilar structures, is a common characteristic of autoantibodies produced during systemic lupus erythematosus (SLE), an autoimmune disease developed by humans and certain strains of mice. Characterization of the extent of cross-reactivity of SLE-related autoantibodies may help identify the immunogenic stimulus, or stimuli, of autoantibody-secreting B-lymphocytes. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was combined with mass spectrometry (MS) to identify cell proteins recognized by a single monoclonal autoantibody (mAb 4B7), derived from an (NZW x BXSB)F1 mouse and selected based on its capacity to react with cardiolipin, that binds to elements in the cytoplasm and nucleoli of HEp-2 cells as assessed by indirect immunofluorescence assay. Proteins from HL-60 extract were separated by 1-D and 2-D PAGE. Western blotting with mAb 4B7 after SDS-PAGE revealed four bands, two intensely labeled at 35 and 32 kDa, and two weaker ones at 20 and 60 kDa; three spots were detected after 2-D PAGE. After trypsin in-gel digestion of the three protein spots, MS yielded representative matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) Reflector or quadrupole-time of flight (Q-TOF) spectra. The three corresponding proteins were identified as the nucleolar phosphoprotein B23 (nucleophosmin), heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2) and the 60 kDa Ro/SS-A RNP. Thus, these results showed that 2-D PAGE combined with MS constitutes a sensitive and powerful technique to characterize the full extent of cross-reactivity of a single mAb and may constitute a new approach to further characterize the immunogenic cellular components involved in the breakage of B-cell tolerance observed in SLE.

Two-dimensional electrophresis and mass spectrometry identification of proteins bound by a murine monoclonal anti-cardiolipin antibody: A powerful technique to characterize the cross-reactivity of a single autoantibody

Two-dimensional electrophresis and mass spectrometry identification of proteins bound by a murine monoclonal anti-cardiolipin antibody: A powerful technique to characterize the cross-reactivity of a single autoantibody

Effects of beta2-glycoprotein I and monoclonal anticardiolipin antibodies on extrinsic fibrinolysis.

Antiphospholipid antibodies (aPLs) are associated with an increased incidence of thrombosis, but the mechanisms responsible for thrombosis are unclear. The present study investigated the effect of both beta2-glycoprotein I (beta2-GPI) and aPLs on the activity of extrinsic fibrinolysis. The remaining tissue-plasminogen activator (t-PA) of the sample consisting of beta2-GPI, two-chain recombinant t-PA, plasminogen activator inhibitor (PAI) -1 was measured by a chromogenic assay using synthetic substrate S-2251, Glu-plasminogen, and soluble fibrin monomer. Without PAI-1, beta2-GPI did not affect t-PA activity. When 14.3 ng/ml PAI-1 was added to 3.6 U/ml t-PA, the remaining t-PA activity was increased from 48.9% to 60.4% by the addition of beta2-GPI (190 microg/ml). The effect of beta2-GPI did not require phospholipids. The beta2-GPI seems to protect t-PA activity from the inhibition by PAI-1. When monoclonal anticardiolipin antibodies (aCLs), EY1C8, and EY2C9, which were established from a patient with antiphospholipid syndrome, were further added to the mixture with a diluted phospholipid (Platelin) to investigate the influence of aPL, the remaining t-PA activity decreased to 50.1 and 80.7%. Monoclonal aCLs appeared to inhibit the effect of beta2-GPI, that is, these monoclonals inhibited the fibrinolytic activity by an elevation in PAI-1 activity. These results suggest the possibility that the impairment of fibrinolytic activity by aCLs is one of reasons for the increased incidence in thrombosis in patients with aCLs.

Neurological dysfunction associated with antiphospholipid syndrome: histopathological brain findings of thrombotic changes in a mouse model.

The aim of this work was to study the pathological processes underlying neurological dysfunctions displayed by BALB/C mice induced with experimental antiphospholipid syndrome (APS), as we have previously reported. Experimental APS was induced in female BALB/C mice by immunization with a pathogenic monoclonal anticardiolipin (aCL) antibody, H-3 (n=10), or an irrelevant immunoglobulin in controls (n=10). Mice immunized with H-3 developed clinical and neurological manifestations of APS, including: embryo resorption, thrombocytopenia neurological defects and behavioral disturbances. In mouse sera, the titer of various autoantibodies were elevated, including: anti-phospholipids (aPLs), anti-2 glycoprotein-I (β2GPI), anti-endothelial cell antibodies (AECA) and low titer of anti-dsDNA antibodies. Five months after APS induction, mice were sacrificed and brain tissue specimens were processed for hematoxylin and eosin (H&E), immunofluorescence staining and transmission electron microscopy (TEM). H&E staining of cortical tissue derived from all APS mice revealed mild inflammation, localized mainly in the meninges. Prominent IgG deposits in the large vessel walls and perivascular IgG leakage were observed by immunofluorescence. No large thrombi were observed in large vessels. However, EM evaluation of cerebral tissue revealed pathological changes in the microvessels. Thrombotic occlusion of capillaries in combination with mild inflammation was the main finding and may underlie the neurological defects displayed by mice with APS.

Functional Analyses of Patient-derived IgG Monoclonal Anticardiolipin Antibodies Using In Vivo Thrombosis and In Vivo Microcirculation Models

Antiphospholipid antibodies (aPL) have been associated with thrombosis and pregnancy losses in patients diagnosed with antiphospholipid syndrome (APS) and enhance thrombus formation in vivo in mice, but the mechanism of thrombosis by aPL is not completely understood. It has been proposed that aPL may affect endothelial cell (EC) function and/or induce their activation, transforming their anticoagulant surface into procoagulant, thus predisposing to thrombosis. It has been proposed that aPL may affect EC cell function and/or induce their activation, transforming their anticoagulant surface into procoagulant, thus predisposing to thrombosis. This study proposes to test the hypotheses that some IgG anticardiolipins (IgG aCL) with thrombogenic properties in mice, exert their effects through activation of endothelium. We studied seven patient-derived monoclonal aCL for their thrombogenic properties in an in vivo pinch-induced thrombosis model, and their functional activities in activating EC by analyzing in vivo leukocyte adhesion to endothelium in microcirculation in venules in exposed murine cremaster muscle and in vitro adhesion molecule expression in cultured EC. The binding of the monoclonal aCL to EC was also tested. In addition to the previous identified thrombogenic IS2, four of the five new more IgG monoclonal aCL (from two patients) were found to be thrombogenic. Of these five thrombogenic aCL, three caused more in vivo leukocyte adhesion to EC in microcirculation, as compared to that induced by the H2 control human monoclonal IgG, and enhanced expression of adhesion molecules (particularly VCAM-1) on cultured EC. These data show that about 2/3 patient-derived IgG monoclonal aCL are thrombogenic and suggest that some thrombogenic IgG aCL exert their effects through activating EC.

Functional Analyses of Patient-derived IgG Monoclonal Anticardiolipin Antibodies Using In Vivo Thrombosis and In Vivo Microcirculation Models

SummaryAntiphospholipid antibodies (aPL) have been associated with thrombosis and pregnancy losses in patients diagnosed with antiphospholipid syndrome (APS) and enhance thrombus formation in vivo in mice, but the mechanism of thrombosis by aPL is not completely understood. It has been proposed that aPL may affect endothelial cell (EC) function and/or induce their activation, transforming their anticoagulant surface into procoagulant, thus predisposing to thrombosis. It has been proposed that aPL may affect EC cell function and/or induce their activation, transforming their anticoagulant surface into procoagulant, thus predisposing to thrombosis. This study proposes to test the hypotheses that some IgG anticardiolipins (IgG aCL) with thrombogenic properties in mice, exert their effects through activation of endothelium. We studied seven patient-derived monoclonal aCL for their thrombogenic properties in an in vivo pinch-induced thrombosis model, and their functional activities in activating EC by analyzing in vivo leukocyte adhesion to endothelium in microcirculation in venules in exposed murine cremaster muscle and in vitro adhesion molecule expression in cultured EC. The binding of the monoclonal aCL to EC was also tested. In addition to the previous identified thrombogenic IS2, four of the five new more IgG monoclonal aCL (from two patients) were found to be thrombogenic. Of these five thrombogenic aCL, three caused more in vivo leukocyte adhesion to EC in microcirculation, as compared to that induced by the H2 control human monoclonal IgG, and enhanced expression of adhesion molecules (particularly VCAM-1) on cultured EC. These data show that about 2/3 patientderived IgG monoclonal aCL are thrombogenic and suggest that some thrombogenic IgG aCL exert their effects through activating EC. Abbreviations: aCL, anticardiolipin antibodies; aPL, antiphospholipid antibodies; APS, antiphospholipid syndrome; CL, cardiolipin; dRVVT, dilute Russell’s viper venom time; EC, endothelial cells; ELISA, enzyme-linked immunosorbent assay; GP, glycoprotein; h, hour; HUVEC, human umbilicalvein endothelial cells; ICAM, intercellular adhesion molecule; KCT, kaolin clotting time; LA, lupus anticoagulant; PBS, phosphate-buffered saline; PL, phospholipid; sq, square; TBS, Tris-buffered saline; VCAM, vascular cell adhesion molecule; PMBC, peripheral mononuclear blood cells

The putative mechanism of thrombosis in antiphospholipid syndrome: impairment of the protein C and the fibrinolytic systems by monoclonal anticardiolipin antibodies.

The mechanism of thrombosis in patients with antiphospholipid syndrome is not clear. To investigate it, we examined the effect of monoclonal anticardiolipin (aCL) antibodies and beta2-glycoprotein I (beta2-GPI), which is required for formation of the aCL epitopes, on activated protein C (APC) and on fibrinolytic activity. First, APC activities were measured in the presence and absence of beta2-GPI or gamma M immunoglobulin (IgM) monoclonal aCLs (EY1C8 and EY2C9), or both, established from peripheral blood lymphocytes obtained from a patient with aCL. beta2-GPI exhibited a procoagulant activity by inhibiting APC activity as well as an anticoagulant activity by inhibiting thrombin generation. Any further inhibition of APC activity was caused by monoclonal aCL, and then only in the presence of beta2-GPI. The remaining tissue plasminogen activator (t-PA) of the sample consisting of beta2-GPI, two-chain recombinant t-PA, and plasminogen activator inhibitor (PAI)-1 was measured by a chromogenic assay using the synthetic substrate S-2251, Glu-plasminogen, and soluble fibrin monomer. beta2-GPI protected t-PA activity from inhibition by PAI-1. However, monoclonal aCLs (EY1C8 and EY2C9) inhibited the effect of beta2-GPI on fibrinolytic activity; that is, monoclonal aCLs inhibited fibrinolytic activity by elevating PAI-1 activity. Thrombosis in patients with aCL can be explained in part by both the inhibition of APC anticoagulant activity and the impairment of fibrinolytic activity by aCL.

The BH1 idiotype defines a population of anticardiolipin antibodies closely associated with the antiphospholipid syndrome.

A human IgM monoclonal anticardiolipin antibody - BH1 - has previously been described, which has characteristics typical of antiphospholipid antibodies in the serum of patients with antiphospholipid syndrome (APS). It appears to be idiotypically distinct from other human monoclonal autoantibodies of different or overlapping ligand-binding specificities derived from patients with related conditions. To determine whether the idiotype of BH1 is expressed on particular populations of antibodies (antiphospholipid and anti-beta2-glucoprotein I) in the serum of patients with APS and other conditions. Sera from patients with APS (9), systemic lupus erythematosus without APS ('uncomplicated SLE' -9), and rheumatoid arthritis (RA 15), and from normal controls (15) were tested by enzyme-linked immunosorbent assay (ELISA) for reactivity with cardiolipin, beta2 glycoprotein I (beta2GPI), and a polyclonal anti-idiotype raised against BH1 (RIdBH1). Absorption experiments were subsequently performed on selected sera using micelles of cardiolipin or phosphatidyl choline. Eight out of nine patients with APS were positive for binding to RIdBH1 (IgG and/or IgM), while only one patient with uncomplicated SLE and none of the patients with RA or the healthy controls were positive. Although all of the patients with APS were positive for binding to beta2GPI, there was poor correlation between these results and levels of binding to cardiolipin and RIdBH1. Absorption of sera from patients with APS by cardolipin micelles resulted in a median reduction in IgG anticardiolipin and anti-beta2GPI activity of 81.6% and 6.3% respectively. For those sera positive for IgG reactivity with RIdBH1 the median reduction in this activity was 79.4%. Antibodies eluted from selected micelles showed activity against cardiolipin, beta2GPI and RIdBH1. Three anticardiolipin-positive sera from patients with RA were similarly absorbed; however the eluted antibodies failed to bind to RIdBH1. Absorption of all these sera with phosphatidyl choline resulted in no significant reduction in any of these activities. The BH1 idiotype defines a population of serum antibodies associated with features of APS. The antibody response in this condition, though diverse, may include the expression of a restricted group of variable region genes.

Beta2-glycoprotein I is necessary to inhibit protein C activity by monoclonal anticardiolipin antibodies.

To clarify mechanisms of the thrombosis associated with anticardiolipin antibodies (aCL), we examined the effects on activated protein C (APC) of monoclonal aCL and beta2-glycoprotein I (beta2GPI), which is required for formation of the epitopes of aCL. We developed the chromogenic assay, in which the degradation of coagulation factor Va by APC is reflected in the reduced generation of thrombin from prothrombin, using soybean trypsin inhibitor to inhibit APC. APC activities were measured in the presence and absence of 3.4 microM beta2GPI and/or 2.5 microg/ml of IgM monoclonal aCL (EY2C9 and EY1C8) established from peripheral blood lymphocytes obtained from a patient with aCL. Without APC, the formed thrombin activity decreased by the addition of 3.4 microM beta2GPI. When 12.8 nM APC was added, beta2GPI partially reversed the APC-induced inhibition of thrombin generation in a concentration-dependent manner. With 3.4 microM beta2GPI, the thrombin generation in monoclonal aCL (2.5 microg/ml) decreased to 77.1-80.2% by the addition of 12.8 nM APC, but the values were above that in the control IgM (72.7%). Without beta2GPI, the APC activity was unaffected by the addition of monoclonal aCL. Beta2-glycoprotein I exhibits procoagulant activity by inhibiting APC activity and anticoagulant activity by inhibiting thrombin generation. Any further inhibition of APC activity was caused by monoclonal aCL and only in the presence of beta2GPI.

Effects of human monoclonal anticardiolipin antibodies on platelet function and on tissue factor expression on monocytes.

To investigate the effect of human monoclonal anticardiolipin antibodies (aCL) on platelet interaction with the subendothelium under flow conditions and on tissue factor (TF) expression on normal monocytes. Three monoclonal IgM aCL (TM1B3, GR1D5, and EY2C9) and 2 affinity-purified IgM aCL were studied. Immunoglobulins were added to normal blood and perfused through chambers containing denuded vascular segments. Platelet interactions were morphometrically evaluated by determining the percentage of total surface covered by platelets (PCS) or by large aggregates of thrombi platelets (TP). Expression of TF on monocytes was measured after immunoglobulin incubation with normal mononuclear cells. Significant increases in the total PCS and expression of TF were observed using all aCL. Increased levels of TP were induced by all aCL except EY2C9 (obtained from a patient without thrombosis). Previous incubations of these aCL with subendothelial surfaces did not increase platelet interaction. The effects of aCL on platelet function may help to explain the pathophysiology of thrombosis in the antiphospholipid syndrome.

Thrombogenic properties of antiphospholipid antibodies do not depend on their binding to beta2 glycoprotein 1 (beta2GP1) alone.

Immunization of mice with beta2glycoprotein 1 (beta2GP1) induces production of antiphospholipid (aPL) antibodies, which were shown to have thrombus enhancing properties in an experimental mouse model, indicating that these antibodies are thrombogenic in vivo. To determine whether the thrombogenic effect of murine antiphospholipid antibodies is due to their aPL or their anti-beta2GP1 activity, we injected mice with murine monoclonal anticardiolipin (aCL) and anti-beta2GP1 antibodies. Effects of these antibodies on thrombus formation, was evaluated utilizing a mouse model which enables kinetics of thrombus formation to be studied. The results of this study showed that the size of the thrombus in animals injected with murine aCL antibodies was larger than that in control groups. There was no difference in thrombus kinetics between anti-beta2GP1 injected mice and controls, suggesting that the thrombogenic effect of aPL antibodies is not related to their anti-beta2GP1 activity alone. Mice receiving monoclonal antibodies with both aCL and anti-beta2GP1 activity, also increase thrombus size when compared with controls. These data indicate that murine aCL, but not anti-beta2GP1, antibodies are thrombogenic in vivo.

Reactivity patterns of antiphosphilipid antibodies and endothelial cells: Effect of antiendothelial antibodies on cell migration

Antiphospholipid syndrome (APS) is characterized by the presence of a heterogenous class of antibodies directed against phospholipids and associated with high occurrence of thrombotic complications. Antiendothelial cell antibodies (AECAs) have been identified in various autoimmune disorders including APS, but their reactivity patterns remain unclear. We used eluted endothelial membrane-bound antibodies (EC eluates) to investigate possible cross-reactivity of AECAs and their pathogenic effects on endothelial cell integrity. The heterogenous and nonspecific nature of AECAs was confirmed by our finding that they cross-react with fibroblasts and platelets and bind to cardiolipin. In addition, platelet-bound antibodies from sera of patients with APS reacted with endothelial cells. A dose-dependent binding of human monoclonal anticardiolipin antibody was demonstrated, but this antibody did not compete with AECAs in EC eluates, indicating that only small portion of AECAs are directed against cardiolipin. Although sera from APS patients prolonged coagulation tests, EC eluates did not affect coagulation, suggesting that AECAs may belong to antiphospholipid antibodies subsets that does not interfere with coagulation. Vascular damage is a common feature of autoimmune disorders associated with AECAs. Possible effects of AECAs on vascular perturbance were investigated by cytotoxicity, attachment, and migration assays. Although AECAs were not shown to be cytotoxic or to affect cell attachment, sera from APS patients caused reduced cellular migration (by 30%), and EC eluates caused even more significant inhibition (by 50%). These findings suggest possible interference of AECAs in vascular repair mechanisms and provide an explanation for the thrombotic complications frequently seen in APS patients.

Arterial disease and thrombosis in the antiphospholipid syndrome: a pathogenic role for endothelin 1.

To explore a possible correlation between endothelin 1 (ET-1), the most potent endothelium-derived contracting factor that modulates vascular smooth muscle tone, and arterial disease in patients with the antiphospholipid syndrome (APS). Plasma levels of ET-1 were measured in APS patients with (n = 16) and without (n = 11) arterial thrombosis and in non-APS patients with arterial thrombosis (n = 9). In addition, steady-state prepro-ET-1 messenger RNA (mRNA) levels were determined in endothelial cells treated with a range of human monoclonal anticardiolipin antibodies (aCL) (as anti-beta2-glycoprotein I antibodies) by semiquantitative 32P-dCTP-labeled reverse transcription-polymerase chain reaction. Compared with healthy controls, markedly increased plasma levels of ET-1 were found in APS patients with arterial thrombosis (2.00 +/- 0.87 versus 0.96 +/- 0.37 pg/ml; P = 0.0001) but not in other groups. Three human monoclonal aCL induced prepro-ET-1 mRNA levels significantly more than did control monoclonal antibody lacking aCL activity. Plasma ET-1 levels correlated significantly with a history of arterial thrombosis in patients with APS. Prepro-ET-1 mRNA was induced by human monoclonal aCL in the in vitro experimental system. The induction of ET-1 by antiphospholipid antibodies might contribute to increased arterial tone, leading to vasospasm and, ultimately, to arterial occlusion.