Antiphospholipid Antibodies Are Not Associated with Clinical Parameters or Prognostic Outcomes in Patients with Non-Hodgkin's Lymphoma.

BACKGROUND: Antiphospholipid antibodies (APAs) are found quite frequently in patients with non-Hodgkin's lymphoma (NHL). However, the clinical significance of these antibodies is largely unknown. This study aims to delineate the clinical and prognostic role of APAs in NHL patients. PATIENTS AND METHODS: Consecutive patients of NHL were screened for lupus anticoagulant (LA), IgG/IgM anticardiolipin antibody, and IgG/IgM anti-ß2-glycoprotein I at the time of diagnosis. Baseline investigations, staging, and treatment were done as per institutional protocol. Patients were followed up until the last known outpatient visit or death. All were screened at each visit for any thromboembolic event. The association of APA status with baseline NHL characteristics and treatment response was evaluated by univariate analysis. Kaplan-Meier survival analysis was used to compare the final outcome in patients with or without APAs. Patients who were initially APA positive were retested for the corresponding antibody at the end of chemotherapy. RESULTS: Twenty-four out of 105 patients (22.8%) were APA positive at diagnosis. The presence of APA was not significantly associated with NHL stage, histology, International Prognostic Index score, activated partial thromboplastin time, or treatment response. The median duration of follow-up was 15 months. Only four patients developed venous thrombosis; none was APA positive. There was no statistically significant difference in overall survival between the two groups (p = 0.471). Patients, who were APA positive initially, tested negative at the end of treatment, irrespective of treatment response. CONCLUSION: APAs are encountered more frequently in NHL patients than in the general population. However, APAs do not correlate with disease severity, thrombosis risk, treatment outcome, or overall survival.

Endoplasmic reticulum stress occurs in association with the extrusion of toxic extracellular vesicles from human placentae treated with antiphospholipid antibodies.

Antiphospholipid autoantibodies (aPLs), a major maternal risk factor for preeclampsia, are taken into the syncytiotrophoblast where they bind intracellular vesicles and mitochondria. Subsequently, large quantities of extracellular vesicles (EVs) extruded from syncytiotrophoblast into the maternal circulation are altered such that they cause maternal endothelial cell activation. However, the mechanism driving this change is unknown. First trimester placental explants were treated with aPL for 18 h. The EVs were then collected by different centrifugation. The levels of HSP 70, misfolded proteins, caspase 8 activity, and Mixed Lineage Kinase domain-Like (MLKL) were measured in placental explants and EVs. In addition, the levels of TNF-α and CD95 in conditioned medium were also measured. Treating placental explants with aPL caused an increase in levels of HSP 70, misfolded proteins and MLKL in placental explants and EVs. Increased activity of caspase 8 was also seen in placental explants. Higher levels of TNF-α were seen conditioned medium from aPL-treated placental explant cultures. aPLs appear to induce endoplasmic reticulum stress in the syncytiotrophoblast in a manner that involved caspase 8 and TNF-α. To avoid accumulation of the associated misfolded proteins and MLKL, the syncytiotrophoblast exports these potentially dangerous proteins in EVs. It is likely that the dangerous proteins that are loaded into placental EVs in preeclampsia contribute to dysfunction of the maternal cells.

Effects of antibodies against human parvovirus B19 on angiogenic signaling.

Human parvovirus B19 (B19V) infection has symptoms similar to those of anti­phospholipid syndrome (APS). Antibodies against B19V­VP1 unique region (VP1u) exhibit activity similar to that of anti­phospholipid antibodies (aPLs) by inducing vascular endothelial cell adhesion factors and APS­like syndrome. Previous studies have identified an effect of aPLs on angiogenesis. However, little is understood regarding the effect of anti­B19V­VP1u antibodies on angiogenesis. The present study investigated the effects of anti­B19V­VP1u antibodies on the expression of adhesion molecules and angiogenic signaling using an aPL­induced human umbilical vein endothelial cell (HUVEC) model, and trypan blue staining and western blotting. The effect of B19V­VP1u antibodies on vascular endothelial growth factor (VEGF) expression in A549 cells, another well­known model used to study angiogenesis, was also examined. Significantly higher intracellular adhesion molecule 1 expression was observed following treatments with 10% fetal calf serum (FCS), aPL immunoglobulin G (IgG), B19V­VP1u IgG or B19V­NS1 IgG, compared with in the normal human (NH) IgG­treated cells. Conversely, significantly higher vascular cellular adhesion molecule 1 was only detected in HUVECs treated with B19V­VP1u IgG. Significantly increased integrin ß1 was detected in HUVECs treated with aPL IgG or B19V­VP1u IgG, whereas no difference in integrin ß1 was observed in those treated with 10% FCS, NH IgG or B19V­NS1 IgG. No difference in AKT­mTOR­S6 ribosomal protein (S6RP) signaling was observed in HUVECs treated with B19­VP1u IgG or B19V­NS1 IgG, compared with NH IgG­treated cells. Significantly higher human inducible factor­1α was detected in HUVECs treated with 10% FCS, aPL IgG, B19V­VP1u IgG or B19V­NS1 IgG, compared with in NH IgG­treated cells. However, there was no difference in the level of VEGF observed among HUVECs treated with NH IgG, B19V­VP1u IgG or B19V­NS1 IgG. Notably, no difference in VEGF level was observed in A549 cells treated with NH IgG, aPL IgG, B19V­VP1u IgG or B19V­NS1 IgG. These findings suggest that anti­B19V­VP1u antibodies may serve a role in activating adhesion molecules, but not in AKT­mTOR­S6RP signaling.

Antiphospholipid antibodies increase the levels of mitochondrial DNA in placental extracellular vesicles: Alarmin-g for preeclampsia.

The pathogenesis of preeclampsia remains unclear but placental factors are known to play a crucial role causing maternal endothelial cell dysfunction. One potential factor is placental micro- and nano- vesicles. Antiphospholipid antibodies (aPL) increase the risk of preeclampsia ten-fold, in part by damaging the mitochondria in the syncytiotrophoblast. Since mitochondrial DNA (mtDNA) is a danger- associated molecular pattern (DAMP/alarmin) that may activate endothelial cells, the aims of the current study were to investigate whether aPL affect the number of placental vesicles extruded, their mtDNA content and their ability to activate endothelial cells. Exposure of first trimester human placental explants to aPL affected neither the number nor size of extruded micro- and nano- vesicles (n = 5), however their levels of mtDNA were increased (n = 6). These vesicles significantly activated endothelial cells (n = 5), which was prevented by blocking toll-like receptor 9 (TLR-9), a receptor for extracellular DNA. Thus, aPL may increase the risk of preeclampsia in part by increasing the amount of mtDNA associated with placental vesicles. That mitochondrial DNA is recognised as a DAMP by TLR-9 to cause endothelial cell activation, raises the possibility that placental vesicles or TLR-9 might be a target for pharmaceutical intervention to reduce the consequences of aPL in pregnancy.

Hydroxychloroquine inhibits proinflammatory signalling pathways by targeting endosomal NADPH oxidase.

OBJECTIVES: Hydroxychloroquine (HCQ) has been used for decades to treat patients with rheumatic diseases, for example, systemic lupus erythematosus (SLE), rheumatoid arthritis or the antiphospholipid syndrome (APS). We hypothesise that HCQ might target endosomal NADPH oxidase (NOX), which is involved in the signal transduction of cytokines as well as antiphospholipid antibodies (aPL). METHODS: For in vitro experiments, monocytic cells were stimulated with tumour necrosis factor α (TNFα), interleukin-1ß (IL-1ß) or a human monoclonal aPL and the activity of NOX was determined by flow cytometry. The expression of genes known to be induced by these stimuli was quantified by quantitative reverse transcription PCR. Live cell imaging was performed by confocal laser scanning microscopy. Finally, the effects of HCQ on NOX-induced signal transduction were analysed in an in vivo model of venous thrombosis. RESULTS: HCQ strongly reduces or completely prevents the induction of endosomal NOX by TNFα, IL-1ß and aPL in human monocytes and MonoMac1 cells. As a consequence, induction of downstream genes by these stimuli is reduced or abrogated. This effect of HCQ is not mediated by direct interference with the agonists but by inhibiting the translocation of the catalytic subunit of NOX2 (gp91phox) into the endosome. In vivo, HCQ protects mice from aPL-induced and NOX2-mediated thrombus formation. CONCLUSIONS: We describe here a novel mechanism of action of HCQ, that is, interference with the assembly of endosomal NOX2. Since endosomal NOX2 is involved in many inflammatory and prothrombotic signalling pathways, this activity of HCQ might explain many of its beneficial effects in rheumatic diseases including the APS.

Human extravillous trophoblasts bind but do not internalize antiphospholipid antibodies.

INTRODUCTION: Obstetric morbidity in women with antiphospholipid antibodies (aPLs) may reflect the adverse effects of aPLs on placental cells such as extravillous trophoblasts and the syncytiotrophoblast. Antiphospholipid antibodies may affect the syncytiotrophoblast after being internalised by members of the Low-density lipoprotein receptor (LDLR) family and the antigen of aPLs, ß2 glycoprotein I. AIM: This study aimed to determine whether aPL internalization was a mechanism by which aPLs adversely affect extravillous trophoblasts. METHOD: of STUDY: Fluorescently-labelled monoclonal aPLs IIC5 or ID2 were incubated with first trimester extravillous trophoblast outgrowths and visualized by microscopy. The subcellular expression of ß2 glycoprotein I and LDLR family members was investigated by live/permeabilised immunocytochemistry. RESULTS: Unlike the syncytiotrophoblast of anchoring villi, monoclonal aPLs were not internalised by extravillous trophoblasts, which expressed LDLR family members intracellularly. The aPL IIC5 bound to the surface of extravillous trophoblasts in a pattern similar to the extracellular expression of ß2 glycoprotein I. CONCLUSIONS: The mechanisms of action of aPLs are different in extravillous trophoblasts and the syncytiotrophoblast. The interaction of aPLs with the extravillous trophoblast surface, which may involve ß2 glycoprotein I, is consistent with reports that aPLs trigger intracellular signaling cascades through cell-surface receptors.

Antiphospholipid Antibodies Alter Cell-Death-Regulating Lipid Metabolites in First and Third Trimester Human Placentae.

PROBLEM: Antiphospholipid antibodies (aPL) are maternal autoantibodies that increase the risk of a woman developing preeclampsia 10-fold. aPL are internalized into the syncytiotrophoblast and increase extrusion of necrotic trophoblast debris into the maternal blood. This necrotic trophoblast debris may trigger endothelial cell dysfunction contributing to the pathogenesis of preeclampsia. We hypothesize that aPL directly affect placental metabolism, leading to increased syncytiotrophoblast death. METHODS OF STUDY: First and third trimester human placental explants were cultured with aPL, a control antibody, or media only, and placental conditioned culture media was examined by mass spectroscopy. Molecular targets of interest were investigated using qRTPCR and immunohistochemistry. RESULTS: The levels of 79 and 132 metabolites, respectively, were altered due to the treatment of first and third trimester placental explants with aPL. These included ceramides and diacylglycerols, which play important roles in cell death regulatory pathways. Antiphospholipid antibodies also decreased the expression of protein kinase C-epsilon (PRKCE) in placental explants, possibly due to the disrupted balance between ceramides and diacylglycerols caused by aPL. CONCLUSION: One mechanism by which aPL cause aberrant cell death in the syncytiotrophoblast in the first and third trimester is by disruption of placental lipid signaling and decreased expression of PRKCE.

Proof-of-concept study demonstrating the pathogenicity of affinity-purified IgG antibodies directed to domain I of ß2-glycoprotein I in a mouse model of anti-phospholipid antibody-induced thrombosis.

OBJECTIVE: IgG aPL against domain I of ß2-glycoprotein I (ß2GPI) [anti-DI (aDI)] is associated with the pathogenesis of APS, an autoimmune disease defined by thrombosis and pregnancy morbidity. To date, however, no study has demonstrated direct pathogenicity of IgG aDI in vivo. In this proof-of-concept study, we designed a novel system to affinity purify polyclonal aDI aPL in order to assess its prothrombotic ability in a well-characterized mouse microcirculation model for APS. METHODS: Two polyclonal IgG fractions were isolated from serum of a patient with APS, both with high aPL activity but differing in aDI activity (aDI-rich and aDI-poor). These IgG fractions were tested for their pathogenic ability in an in vivo mouse model of thrombosis. Male CD1 mice were injected intraperitoneally with either aDI-rich or aDI-poor IgG; as a control, IgG isolated from healthy serum was used. A pinch injury was applied to the right femoral vein and thrombus dynamics and tissue factor activity in isolated tissue were evaluated. RESULTS: Both aDI-rich and aDI-poor IgG retained aCL and anti-ß2GPI activity, while only aDI-rich IgG displayed high aDI activity, as defined by our in-house cut-offs for positivity in each assay. aDI-rich IgG induced significantly larger thrombi in vivo compared with aDI-poor IgG (P < 0.0001). Similarly, aDI-rich IgG significantly enhanced the procoagulant activity of carotid artery endothelium and peritoneal macrophages isolated from experimental animals (P < 0.01). CONCLUSION: These data directly demonstrate that the ability to cause thrombosis in vivo is concentrated in the aDI fraction of aPL.

Role of Toll-like receptors 2 and 4 in mediating endothelial dysfunction and arterial remodeling in primary arterial antiphospholipid syndrome.

OBJECTIVE: To assess the role of Toll-like receptors (TLRs) in antiphospholipid antibody (aPL)-mediated vascular abnormalities in patients with primary arterial antiphospholipid syndrome (APS). METHODS: Forty-eight subjects participated in the study. Arterial function and structure and TLR pathway activation were determined in patients with primary arterial APS and matched controls. The pathogenic effects of aPL isolated from patients were assessed in wild-type (WT) and TLR-knockout mice. RESULTS: APS patients had endothelial dysfunction, arterial stiffening, and hypertrophy, as evidenced by decreased brachial artery endothelium-dependent flow-mediated dilation (FMD) and increased aortic pulse wave velocity and carotid intima-media thickness (IMT), as compared with controls. Plasma samples from APS patients revealed decreased nitric oxide (NO) availability and a pro-oxidative, proinflammatory, and prothrombotic state illustrated by a decrease in nitrite and an increase in lipid peroxidation, tumor necrosis factor α levels, and tissue factor (TF) levels. Furthermore, TLR pathway activation was found in APS patients with increased TLR-2 and TLR-4 messenger RNA expression and increased protein levels of the activated TLR transduction protein interleukin-1 receptor-associated kinase 1 in peripheral blood mononuclear cells. Moreover, agonist-stimulated cell-surface expression of TLR-2 and TLR-4 in circulating monocytes was higher in APS patients than in controls. These changes were positively associated with IMT and negatively associated with FMD. Finally, aPL injection decreased mesenteric endothelium-dependent relaxation and increased TF expression in WT mice but not in TLR-2- or TLR-4-knockout mice. CONCLUSION: This translational study supports the notion that TLR-2 and TLR-4 play a role in mediating vascular abnormalities in patients with primary arterial APS. TLRs thus constitute a promising pharmacologic target for preventing cardiovascular complications in APS.

Receptors involved in cell activation by antiphospholipid antibodies.

The antiphospholipid syndrome (APS) is an autoimmune disease associated with arterial or venous thrombosis and/or recurrent fetal loss and is caused by pathogenic antiphospholipid antibodies (aPLA). The plasma protein ß2-glycoprotein 1 (ß2GP1) has been identified as a major target of aPLA associated with APS. Cell activation by aPLA appears to be a major pathogenic cause in the pathogenesis of APS. Receptors, co-receptors and accessory molecules are known to assist the pathogenic effects of aPLA. Members of the TLR family and the platelet receptor apolipoprotein E receptor 2' (apoER2'), a receptor belonging to the low-density lipoprotein receptor (LDL-R) family, as well as GPIbα, were identified as putative candidates for aPLA recognition. CD14, a co-receptor for TLR2 and TLR4, and annexin A2, a ubiquitous Ca2+ -binding protein that is essential for actin-dependent vesicle transport, could serve as important accessory molecules in mediating the pathogenic effects of aPLA. Finally, complement activation has been reported in association with the pathogenicity of APS. The relative contribution of these different mechanisms in the pathogenesis of APS is controversial. Here, we review the various in vivo and in vitro models that have been used to investigate the pathogenic mechanisms of aPLA in APS.

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A role for uric acid and the Nalp3 inflammasome in antiphospholipid antibody-induced IL-1ß production by human first trimester trophoblast.

Women with antiphospholipid syndrome (APS) are at risk of recurrent pregnancy loss and obstetrical disorders, such as preeclampsia and intrauterine growth restriction (IUGR). Antiphospholipid antibodies (aPL) directly target the placenta by binding beta2-glycoprotein I (ß2GPI) expressed on the trophoblast. We recently demonstrated in human first trimester trophoblast cells that anti-ß2GPI antibodies (Abs) induce the secretion of IL-1ß in a Toll-like receptor 4 (TLR4)-dependent manner. IL-1ß secretion requires processing of pro-IL-1ß and this is mediated by the inflammasome, a complex of Nalp3, apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1. The objective of this study was to determine if aPL induce IL-1ß production in trophoblast via the inflammasome. Using a human first trimester trophoblast cell line, we demonstrated that a mouse anti-ß2GPI mAb and human polyclonal aPL-IgG induce IL-1ß processing and secretion, which was partially blocked upon caspase-1 inhibition. Nalp3 and ASC knockdown also attenuated anti-ß2GPI Ab-induced IL-1ß secretion. Furthermore, aPL stimulated the production of uric acid in a TLR4-dependent manner; and inhibition of uric acid prevented aPL-induced IL-1ß production by the trophoblast. These findings demonstrate that aPL, via TLR4 activation, induce a uric acid response in human trophoblast, which in turn activates the Nalp3/ASC inflammasome leading to IL-1ß processing and secretion. This novel mechanism may account for the inflammation at the maternal-fetal interface, which causes placental dysfunction and increases the risk of adverse pregnancy outcome in patients with APS.

Phospholipid scramblase 1 expression is enhanced in patients with antiphospholipid syndrome.

OBJECTIVE: Thrombus formation is the key event of vascular manifestations in antiphospholipid syndrome (APS). Phosphatidylserine (PS) is normally sequestered in the inner leaflet of cell membranes. Externalization of PS occurs during cell activation and is essential for promoting blood coagulation and for the binding of antiphospholipid antibodies (aPL) to cells. One of the molecules involved in PS externalization is phospholipid scramblase 1 (PLSCR1). We evaluated PLSCR1 expression on monocytes from APS patients and analyzed the in vitro effect of monoclonal aPL on PLSCR1 expression. PATIENTS AND METHODS: Forty patients with APS were investigated. In vitro experiments were performed in monocyte cell lines incubated with monoclonal aPL. PLSCR1 expression was determined by quantitative real-time polymerase chain reactions. PS exposure on CD14(+) cell surface was analyzed by flow cytometry. RESULTS: Levels of full-length PLSCR1 messenger RNA (mRNA) were significantly increased in APS patients compared with healthy controls (2.4 ± 1.2 vs. 1.3 ± 0.4, respectively, p < 0.001). In cultured monocytes, interferon alpha enhanced tissue-factor expression mediated by ß2-glycoprotein-I-dependent monoclonal anticardiolipin antibody. CONCLUSIONS: Monocytes in APS patients had increased PLSCR1 mRNA expression.

Th1/Th2/Th17/Treg expression in cultured PBMCs with antiphospholipid antibodies.

The aim of this study was to evaluate the expression of T-helper cell subtypes Th1, Th2, Th17 and Treg in antiphospholipid syndrome (APS), and whether they are related to anti-cardiolipin antibody (aPL) titers. Peripheral mononuclear cells (PBMCs) were isolated from healthy donors, and incubated with aPLs. Subsequent to a 48­h incubation, PBMCs were collected and detected by flow cytometry. The results revealed that aPLs at higher concentrations may induce a significant increase in Th2 and Th17 frequencies, as opposed to a significant decrease in Th1 and Treg frequencies and the Th1/Th2 ratio. These results indicate that there is a Th1/Th2 imbalance, a Th17 upregulation and a Treg downregulation present in APS, and that these factors are positively correlated with aPL titers, suggesting a potential role of Th cells in the pathogenesis of APS.

Mitochondrial dysfunction in antiphospholipid syndrome: implications in the pathogenesis of the disease and effects of coenzyme Q(10) treatment.

The exact mechanisms underlying the role of oxidative stress in the pathogenesis and the prothrombotic or proinflammatory status of antiphospholipid syndrome (APS) remain unknown. Here, we investigate the role of oxidative stress and mitochondrial dysfunction in the proatherothrombotic status of APS patients induced by IgG-antiphospholipid antibodies and the beneficial effects of supplementing cells with coenzyme Q(10) (CoQ(10)). A significant increase in relevant prothrombotic and inflammatory parameters in 43 APS patients was found compared with 38 healthy donors. Increased peroxide production, nuclear abundance of Nrf2, antioxidant enzymatic activity, decreased intracellular glutathione, and altered mitochondrial membrane potential were found in monocytes and neutrophils from APS patients. Accelerated atherosclerosis in APS patients was found associated with their inflammatory or oxidative status. CoQ(10) preincubation of healthy monocytes before IgG-antiphospholipid antibody treatment decreased oxidative stress, the percentage of cells with altered mitochondrial membrane potential, and the induced expression of tissue factor, VEGF, and Flt1. In addition, CoQ(10) significantly improved the ultrastructural preservation of mitochondria and prevented IgG-APS-induced fission mediated by Drp-1 and Fis-1 proteins. In conclusion, the oxidative perturbation in APS patient leukocytes, which is directly related to an inflammatory and pro-atherothrombotic status, relies on alterations in mitochondrial dynamics and metabolism that may be prevented, reverted, or both by treatment with CoQ(10).

Effect of Low Molecular Weight Heparins (LMWHs) on antiphospholipid Antibodies (aPL)-mediated inhibition of endometrial angiogenesis.

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by vascular thrombosis and/or pregnancy morbidity in the presence of circulating antiphospholipid antibodies (aPL). Different pathogenic mechanisms for aPL-mediated pregnancy failure have been proposed. In particular a direct effect of aPL on both maternal and fetal side of the placental tissue has been reported, since their reactivity with ß2-glycoprotein I (ß2GPI) makes them adhere to trophoblast and human endometrial endothelial cell (HEEC) membranes. ß2GPI can be recognized by aPL that, once bound, interfere with both trophoblast functions and with the HEEC differentiation.APS patients can be successfully treated with Low Molecular Weight Heparin (LMWH). Recent reports suggest that LMWH acts through mechanisms alternative to its well known anticoagulant effect, because of its ability to bind ß2GPI. In our previous studies, we showed that LMWH is able to reduce the aPL binding to trophoblasts and restore cell invasiveness and differentiation. So far, however, no study has described its effects on endometrial angiogenesis.The aim of our research was to evaluate whether two LMWHs, tinzaparin and enoxaparin, have an effect on the aPL-inhibited endometrial angiogenesis. This prompted us to investigate: (i) in vitro HEEC angiogenesis through a Matrigel assay; (ii) VEGF secretion by ELISA; (iii) matrix metalloproteinase-2 (MMP-2) activity by gelatin zymography; (iv) Nuclear Factor-κB (NF-κB) DNA binding activity by colorimetric assay; (v) STAT-3 activation by a sandwich-ELISA kit. Furthermore, using an in vivo murine model we investigated the LMWHs effects on angiogenesis.We demonstrated that the addition of LMWHs prevents aPL-inhibited HEEC angiogenesis, both in vitro and in vivo, and is able to restore the aPL inhibited NF-κB and/or STAT-3 activity, the VEGF secretion and the MMPs activity.The demonstration of a beneficial role for LMWHs on the aPL-inhibited HEEC angiogenesis might provide additional mechanisms whereby this treatment protects early pregnancy in APS.

Effects of antiphospholipid antibodies on in vitro platelet aggregation.

Antiphospholipid antibodies contribute to the development of thrombosis, although precise mechanisms remain to be elucidated. We determined the effects of affinity-purified anti-beta(2)-glycoprotein 1 (anti-ß(2)GP1) and anti-prothrombin (anti-PT) antibodies on in vitro platelet aggregation. Adenosine diphosphate (ADP) and collagen-induced platelet aggregation were performed using platelet-rich plasma ([PRP] 250 × 10(9)/L). Antiphospholipid antibodies (1.25-10 µg/mL) were preincubated with PRP for 10 minutes at 37°C prior to the addition of agonist. Anti-ß(2)GP1 antibodies significantly reduced platelet aggregation (percentage area under the curve; %AUC) in a concentration-dependent manner using both 5 µmol/L (P < .001) and 2.5 µmol/L (P = .038) ADP but did not significantly affect the rate of aggregation. Anti-PT antibodies significantly enhanced 5 µg/mL collagen-induced platelet aggregation (%AUC; P = .034) but did not affect ADP-induced platelet aggregation. These results suggest (1) interactions and effects of antiphospholipid antibodies on platelets are agonist and concentration dependent and (2) anti-ß(2)GP1 antibodies may inhibit dense granule release and/or inhibition of the arachidonic acid pathway.

A novel pathway for human endothelial cell activation by antiphospholipid/anti-ß2 glycoprotein I antibodies.

Antiphospholipid Abs (APLAs) are associated with thrombosis and recurrent fetal loss. These Abs are primarily directed against phospholipid-binding proteins, particularly ß(2)GPI, and activate endothelial cells (ECs) in a ß(2)GPI-dependent manner after binding of ß(2)GPI to EC annexin A2. Because annexin A2 is not a transmembrane protein, the mechanisms of APLA/anti-ß(2)GPI Ab-mediated EC activation are uncertain, although a role for a TLR4/myeloid differentiation factor 88-dependent pathway leading to activation of NF-κB has been proposed. In the present study, we confirm a critical role for TLR4 in anti-ß(2)GPI Ab-mediated EC activation and demonstrate that signaling through TLR4 is mediated through the assembly of a multiprotein signaling complex on the EC surface that includes annexin A2, TLR4, calreticulin, and nucleolin. An essential role for each of these proteins in cell activation is suggested by the fact that inhibiting the expression of each using specific siRNAs blocked EC activation mediated by APLAs/anti-ß(2)GPI Abs. These results provide new evidence for novel protein-protein interactions on ECs that may contribute to EC activation and the pathogenesis of APLA/anti-ß(2)GPI-associated thrombosis and suggest potential new targets for therapeutic intervention in antiphospholipid syndrome.

Modulation of trophoblast angiogenic factor secretion by antiphospholipid antibodies is not reversed by heparin.

PROBLEM Women with antiphospholipid antibodies (aPL) are at risk of miscarriage and pre-eclampsia, obstetrical disorders associated with reduced trophoblast invasion and spiral artery transformation. aPL target the placenta by binding beta(2) -glycoprotein I (ß(2) GPI) on the trophoblast. In this study, we determined whether aPL alter the trophoblast secretion of angiogenic factors and evaluated the effect of low molecular weight heparin (LMWH) on this response. METHOD OF STUDY First-trimester trophoblast was treated with anti-ß(2) GPI antibodies with or without LMWH. Angiogenic factor secretion was measured by enzyme-linked immunosorbent assay. RESULTS Trophoblast cells produced more vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), and soluble endoglin following exposure to anti-ß(2) GPI Abs, and this occurred in both a MyD88-dependent and MyD88-independent manner. LMWH was unable to reverse the effects of the anti-ß(2) GPI Abs on trophoblast VEGF secretion, but enhanced PlGF. Strikingly, LMWH upregulated soluble fms-like tyrosine kinase receptor-1 (sFlt-1) secretion independently of aPL. CONCLUSION This study demonstrates that aPL perturb the secretion of trophoblast angiogenic factors. LMWH does not reverse this effect but exacerbates sFlt-1 secretion, a potent anti-angiogenic factor. These findings may help to explain why women with antiphospholipid syndrome, who are treated with heparin to prevent early pregnancy loss, remain at increased risk of developing late obstetrical complications, such as pre-eclampsia.

[Activation of tumor necrosis factor receptor-associated factor 6 in anti-ß2GPI/ß2GPI-induced tissue factor expression on THP-1 cells].

AIM: To investigate whether tumor necrosis factor receptor-associated factor 6 (TRAF6) is involved in anti-ß2GPI/ß2GPI-induced tissue factor (TF) expression on THP-1 cells. METHODS: The total RNA was extracted and the protein lysates were collected from THP-1 cells stimulated with anti-ß2GPI/ß2GPI complex. And then the TF expression on THP-1 cells was detected by real-time quatitative PCR (RT-qPCR) and TF activity kit. TRAF6 mRNA and its protein expression were investigated by RT-qPCR and Western blotting, respectively. The proteasome inhibitor, MG-132, was used for inhibitory assays, in order to demonstrate the effect of anti-ß2GPI/ß2GPI complex on THP-1 cells. RESULTS: The TF expression (both mRNA and activity) on THP-1 cells was significantly up-regulated with the treatment of anti-ß2GPI/ß2GPI complex (100 mg/L), compared with untreated cells(P<0.05). The TRAF6 mRNA and protein levels in THP-1 cells were also significantly increased with the treatment of anti-ß2GPI/ß2GPI complex. The expression of TRAF6 was shown in a time-dependent manner, with the maximal level at 15 minutes (mRNA) and 30 minutes (protein) respectively. All the stimulating effects of anti-ß2GPI/ß2GPI complex (100 mg/L) on THP-1 cells were inhibited by MG-132 (5 µmol/L). CONCLUSION: TRAF6 is up-regulated and contributes to TF expression on THP-1 cells induced with anti-ß2GPI/ß2GPI complex.