P. L. Meroni

Antiphospholipid antibodies affect trophoblast gonadotropin secretion and invasiveness by binding directly and through adhered β2‐glycoprotein I

OBJECTIVEnTo investigate the in vitro ability of antiphospholipid antibodies (aPL) to bind human trophoblast cells and to affect gonadotropin secretion and invasiveness.nnnMETHODSnAntiphospholipid antibody IgG from women with recurrent miscarriages, beta2-glycoprotein I (beta2GPI)-independent IgG aPL human monoclonal antibody (mAb) (519), and IgM anti-beta2GPI human mAb (TMIG2) were investigated for their binding to trophoblasts cultured for various amounts of time, their ability to affect invasiveness of Matrigel-coated filters, and their release of human chorionic gonadotropin (hCG).nnnRESULTSnPolyclonal IgG aPL, as well as mAb 519 and TMIG2, bound to trophoblasts, the highest binding being found when cells displayed the greatest amount of syncytium formation. TM1G2 binding was found to be betaGPI dependent. Both polyclonal and monoclonal aPL, but not the controls, significantly reduced hCG release and Matrigel invasiveness.nnnCONCLUSIONnThese findings suggest that aPL recognition of both anionic PL and adhered beta2GPI on trophoblast cell structures might represent a potential pathogenetic mechanism for defective placentation in women with the antiphospholipid syndrome.

Antibodies to endothelial cells in primary vasculitides mediate in vitro endothelial cytotoxicity in the presence of normal peripheral blood mononuclear cells

Twenty-eight out of 62 patients with Wegeners granulomatosis and micropolyarteritis display circulating antiendothelial cell antibodies (AECA) detectable by a cell surface radioimmunoassay. These antibodies do not induce an in vitro endothelial damage either alone or in the presence of fresh complement; however, 50% of IgG-AECA positive sera can be cytotoxic in the presence of human normal peripheral blood mononuclear cells (PBM) at high effector/target ratios. The specificity of the PBM-mediated cytotoxicity is supported by the absence of the phenomenon in AECA negative sera, by the disappearance of the lytic effect after absorption of AECA, and by the finding that cellular-mediated cytotoxicity can be reproduced by purified IgG-AECA positive fractions. On the contrary, polymorphonuclear leukocytes or adherent mononuclear cells are not involved in such a cytotoxic activity. AECA seem to be directed against determinants consitutively expressed on the endothelial surface since the activation of endothelial cells by interleukin-1 beta or interferon-gamma affects neither the antibody binding nor their ability to mediate 51Cr release in the presence of PBM. These findings favor the hypothesis for a possible direct pathogenetic role of circulating AECA in the in vivo vascular damage.

Antiphospholipid antibodies as cause of pregnancy loss

Antiphospholipid antibodies detected by lupus anticoagulant, anticardiolipin or anti-beta2 glycoprotein I assays were associated with fetal loss. Rather than being diagnostic tools only, antiphospholipid antibodies are thought to be pathogenic. The strongest demonstration of their pathogenic role lies in the ability to induce fetal resorptions - the experimental equivalents of the human fetal losses - when passively infused in pregnant naive animals. However, still debated is how the antibodies might induce the obstetrical manifestations. Thrombotic events at the placental levels might be related to endothelial cell activation, inhibition of protein C/S system and fibrinolysis as well as to Annexin V displacement. However, the thrombophilic state apparently cannot explain all the miscarriages and a direct antibody-mediated damage on the trophoblast has been suggested. During differentiation to syncytium, trophoblasts express cell membrane anionic phospholipids that can bind beta2 glycoprotein I, the main cationic phospholipid binding protein recognized by the antiphospholipid antibodies. Adhered b2-glycoprotein I might be recognized by the antibodies that, once bound, strongly interfere with in vitro trophoblast cell maturation so resulting in a defective placentation. These mechanisms have been suggested to play a role in early fetal loss, while thrombotic events would be responsible for miscarriages late in the pregnancy.

β2-Glycoprotein I as a 'cofactor' for anti-phospholipid reactivity with endothelial cells

β2-glycoprotein I (β2GPI) is a cofactor for anti-phospholipid (aPL) binding to cardiolipin (CL)-coated plates. β2GPI is also able to bind to endothelial cell (EC) membranes as supported by in-vivo as well as by in-vitro studies. The PL-binding site in the fifth domain of the molecule is involved in the adhesion to endothelium. Actually, specific mutations in this molecular portion abolish endothelium binding and a synthetic peptide spanning the sequence Glu274 –Cys288 of the CL-binding site displays comparable adhesion to EC monolayers. Heparan sulphate appears to be one of the anionic EC membrane structures with which cationic β2GPI interacts, as supported by studies with heparitinase-treated EC. β2GPI binding to EC might be related to its activity as endothelial growth factor or as a lipid-carrying glycoprotein. Adhesion of β2GPI to endothelial membranes offers suitable epitopes for circulating aPL that, once bound, can induce cell activation

Decreased expression of heparin-binding epidermal growth factor-like growth factor as a newly identified pathogenic mechanism of antiphospholipid-mediated defective placentation

OBJECTIVEnHeparin-binding epidermal growth factor-like growth factor (HB-EGF) plays a role in blastocyst implantation and is down-regulated in preeclampsia and in hypertensive pregnancy disorders associated with defective extravillous trophoblast invasion. Defective placentation and severe preeclampsia are also features of the antiphospholipid syndrome (APS). The purpose of this study was to investigate whether abnormal HB-EGF expression plays a pathogenic role in antiphospholipid antibody (aPL)-mediated defective placentation.nnnMETHODSnHB-EGF expression in placental tissue was evaluated by Western blotting and messenger RNA analysis in normal and APS placentae. Polyclonal IgG fractions or monoclonal beta(2)-glycoprotein I-dependent aPL and their respective controls were investigated for the following 4 features: their binding to human trophoblast monolayers, as determined by cell enzyme-linked immunosorbent assay (ELISA); their effect on HB-EGF expression by Western blotting in trophoblast cell extracts as well as by ELISA as a protein secreted in the culture supernatants; their inhibitory effect on in vitro trophoblast invasiveness, as evaluated by Matrigel assay; and their inhibitory effect on matrix metalloproteinase (MMP) levels, as measured by gelatin zymography. Experiments were also performed in the presence of serial concentrations of heparin or recombinant HB-EGF.nnnRESULTSnPlacental APS tissue displayed reduced expression of HB-EGF. Polyclonal and monoclonal aPL bound to trophoblast monolayers and significantly reduced the in vitro synthesis and secretion of HB-EGF. Heparin inhibited aPL binding and restored HB-EGF expression in a dose-dependent manner. Addition of recombinant HB-EGF reduced the in vitro aPL-induced inhibition of Matrigel invasiveness as well as MMP-2 levels.nnnCONCLUSIONnThese preliminary findings suggest that the reduction of aPL-mediated HB-EGF represents an additional mechanism that is responsible for the defective placentation associated with APS and that heparin protects from aPL-induced damage by inhibiting antibody binding.

Anti-phospholipid antibody mediated fetal loss: still an open question from a pathogenic point of view:

Antiphospholipid antibodies (aPL) are associated with recurrent miscarriages and pregnancy complications, however their pathogenic mechanisms are still matter of research. Thrombotic events at the placental level cannot explain all of the clinical manifestations. It has been suggested that aPL may be responsible for a local acute inflammatory response mediated by complement activation and neutrophil infiltration eventually leading to fetal loss. However histological and immunohistological studies on human placental samples do support such a mechanism only in part and with no any clear relationship with the pregnancy outcome. A direct effect of aPL on both maternal and fetal placental tissues has been reported through the reactivity of the antibodies with beta2 glycoprotein I (β2GPI) expressed on the cell membranes. These events do not require an inflammatory response and can be in part related to the inhibition of growth factors favouring a physiological placentation. Understanding the different pathogenic mechanisms of aPL-associated miscarriages may help in improving our therapeutic approach particularly in recurrent cases not responsive to the usual treatment. Lupus (2010) 19, 453—456.

Venous thromboembolism in the antiphospholipid syndrome: management guidelines for secondary prophylaxis.

Venous thromboembolism(VTE) in patients suffering from the antiphospholipidsyndrome (APS) has been reported in almost any location of the vessel tree and the risk of recurrences has been found in several studies to be more closely associated with the presence of lupus anticoagulant than with the positivity for anti-cardiolipin antibodies. The thrombophilic state of APS raises the problem of the secondary prophylaxis to avoid VTE recurrences. For APS patients with VTE, published data appear to support a longer warfarin treatment if compared with the standard management of anti-phospholipid (aPL)-negative patients with VTE. The question of how long oral anticoagulant treatment should be continued for APS patients, however, remains unanswered. Concerning the intensity of anticoagulation, several authors recommend a target international normalized ratio (INR) between 3.0 and 4.0 to efficiently protect from VTE recurrences.A recentdecisionanalysisstudy does support such a suggestion. On the contrary, in a few prospective studies regimens with lower target INRs appear to be effective, and some authors therefore recommend a target INR of between 2.0 and 3.0. Specific large and prospective trials are needed to address this question. Until such information becomes available, individualized treatment according to the patient’s individual risk factors for both bleeding and thrombosis is the general practice.

Aspirin-interleukin-3 interrelationships in patients with anti-phospholipid syndrome.

PROBLEM: Previously we reported on the generation of experimental anti‐phospholipid syndrome (APS) in mice. These models were employed to evaluate the efficacy of various novel therapeutic modalities including interleukin‐3 (IL‐3) and low dose aspirin. The efficacy of the latter was found to be interrelated. Low dose aspirin is capable of inhibiting the activity of the enzyme cyclooxygenase which is responsible for the metabolism of arachidonic acid towards the production of prostaglandins. This shifts the metabolism of arachidonic acid to the other pathway and leads to an overproduction of leukotrienes. The leukotrienes act as stimulators of IL‐3 production, a positive cytokine in pregnancy which enhances placental and fetal development. In the current study we evaluated the IL‐3 levels in pregnant women with APS and expanded our knowledge on the interrelationships between aspirin, arachidonic acid metabolites and IL‐3 in the human system.

Modulation of Endothelial Cell Function by Antiphospholipid Antibodies

β2-glycoprotein I (β2-GP-I) the plasma cofactor for anti-phospholipid antibodies adheres on the endothelial surfaces and can be recognized by anti-β2-GP-I antibodies naturally occurring in patients with the anti-phospholipid syndrome. As for the cofactor binding to cardiolipin- or gamma irradiated-plates, the endothelial binding is mediated by the so-called phospholipid binding site, a cationic structure able to react with anionic molecules. Endothelial monolayers appear to represent a substrate able to bind β2-GP-I and to present it in a suitable manner in order to allow the binding of anti-β2-GP-I β2 antibodies. The complex between β2-GP-I and the respective antibodies induce an endothelial cell activation as demonstrated by the up-regulation of adhesion molecule expression, the secretion of proinflammatory cytokines and the modulation of arachidonic acid metabolism. Taken together these findings strongly sustain a pivotal role for β2-GP-I in allowing antibody deposition on the endothelium and in affecting endothelial cell functions potentially responsible for a procoagulant state.

Enrichment of IgG anti-DNA-producing lymphoblastoid cell lines by antigen-coated immunomagnetic beads

In this paper we describe the establishment of four anti-DNA-producing lymphoblastoid cell lines (LCL) by Epstein-Barr virus (EBV) infection of peripheral blood B-cells from a patient with systemic lupus erythematosus. The LCL showed a heterogeneous cell composition: the frequencies of cells in active proliferation, cells secreting IgG or IgM, and cells effectively producing IgG or IgM anti-DNA were estimated by limiting dilution analysis. The cells producing anti-DNA antibodies were a small fraction of the whole cell population constituting the LCL. In order to enrich the fraction of cells producing the desired antibody we performed a positive selection by DNA-coated immunomagnetic beads. Results show that in two out of three IgG anti-DNA-secreting LCL the frequency of DNA-producing cells increased after incubation with DNA-coated beads. At variance, IgM anti-DNA-secreting cells were completely lost after immunomagnetic separation. This approach could represent a further tool to obtain better fusion partners to construct stable hybrids secreting human monoclonal antibodies. The advantages of the presented technique would be: (a) removing of the fraction of low-affinity IgM-producing cells, which is often prevalent in EBV-induced LCL; and (b) the enrichment of IgG anti-DNA producing cells, which better represent the antibodies involved in the pathogenesis of the disease.