Antiphospholipid antibodies, eicosanoids and expression of endothelial cyclooxygenase-2

Endothelium as a target for antiphospholipid antibodies

Several, and not necessarily alternative, pathogenic mechanisms have been suggested to sustain the thrombophilic diathesis of the anti-phospholipid syndrome. Among them, interference of anti-phospholipid antibodies with cell acting in the coagulation cascade likely plays a major role. Anti-phospholipid antibodies have been shown to react with endothelial cells mainly by reacting with beta 2 glycoprotein I expressed on the cell membrane surface. Beta 2 glycoprotein I can adhere to endothelial cell surface through the Annexin II receptor and through negatively charged structures (heparin-like molecules) that are bound by the phospholipid-binding site of the molecule. The autoantibody binding involves a yet unknown receptor that activates a signalling pathway able to translocate NFkappaB from the cytoplasm to the nucleus and to activate genes for adhesion molecule, pro-inflammatory cytokine and Tissue Factor up-regulation. The ultimate effect is the induction of a pro-inflammatory and a pro-coagulant endothelial phenotype that has been reproduced both in vitro and in vivo experimental models. Additional effects of anti-phospholipid-mediated endothelial cell activation are the interference with the protein C/S system, with the Annexin V binding, the up-regulation of endothelin I synthesis and the induction of apoptosis. Altogether these effects cooperate in switching endothelium from an anti-coagulant to a pro-coagulant surface.

Primary anti-phospholipid antibody syndrome (APS): current concepts

Primary anti-phospholipid syndrome (APS) is a thrombophilic state characterized by recurrent arterial and venous thrombosis, recurrent pregnancy loss, and the presence of circulating anti-phospholipid antibodies that may be responsible for thrombophilia and pregnancy morbidity. Ophthalmologic features are present in 15-88% of the patients with primary APS, thus ophthalmologists are one of the first physicians to whom the patient will present. An accurate diagnosis may save the patient from recurrent, potentially life-threatening thrombosis. In the U.S.A., an estimated 35,000 new cases of APS-related venous thrombosis occur each year in a population that is several decades younger than the patient population typically affected by thrombosis. Clinical features, such as chorea, transverse myelitis, cardiac valvular lesions, and accelerated atherosclerosis, are hypothesized to be due to a direct tissue-antibody interaction and cannot be explained purely by thrombosis. The use of recently proposed, well-defined diagnostic criteria, and better standardization of laboratory assays for the anti-phospholipid antibodies should help enable epidemiological surveys to establish the prevalence of these antibodies in patients with thrombosis and in the general population. Diagnosis of APS should be considered in all patients with recurrent systemic or ocular thrombosis in the absence of known risk factors. Several well-designed prospective studies show an increased risk of thrombosis in the presence of medium to high antibody level. With ocular involvement in as many as 88% of APS patients, an ophthalmic assessment should be an integral part of the clinical work-up of any patient with suspected or confirmed APS. The presence of isolated ocular thrombophilia with persistently elevated anti-phospholipid antibodies or lupus coagulant should confirm the diagnosis of APS. Management of these patients must be a multi-disciplinary effort with either a rheumatologist or a hematologist having the overall responsibility for coordinating treatment and monitoring the patient's immune status and anticoagulation. Treatment of isolated ocular thrombophilia in the presence of moderate to high titers of antiphospholipid antibodies should be on the same principles as patients with APS to prevent recurrent ocular or cerebral thrombosis.

Antiphospholipid antibodies and the endothelium

The interaction between aPL (particularly anti-beta 2GPI antibodies) and endothelium does represent a potential pathogenetic mechanism for the thrombotic manifestations of the syndrome. The autoantibody-mediated EC activation probably plays a role in sustaining the appearance of a proadhesive, proinflammatory, and procoagulant phenotype. The heterogeneity of the APS clinical manifestations is likely linked to the varied effects that aPL can induce on ECs and to the different functions that ECs display depending on the anatomic localization.

Human anticardiolipin monoclonal autoantibodies cause placental necrosis and fetal loss in BALB/c mice

OBJECTIVE

To analyze the structure, specificity, and in vivo pathogenetic potential of 2 human anticardiolipin (aCL) monoclonal antibodies (MAb).

METHODS

Human aCL IgG MAb were generated from hybridized Epstein-Barr virus-induced B cell lines from a healthy subject (MAb 519) and from a patient with primary antiphospholipid syndrome (MAb 516). Studies of antigen-binding specificity and analysis of Ig V-gene mutations were carried out. The MAb were independently injected into mated female BALB/c mice, and their effect on pregnancy outcome was compared with that of MAb 57, a highly mutated and antigen-selected human IgG1lambda rabies virus antibody.

RESULTS

Both MAb 519 and MAb 516 utilized minimally mutated V(H)DJ(H) and VkappaJkappa gene segments and bound cardiolipin and other anionic phospholipids in the absence of beta2-glycoprotein I (beta2-GPI). The mice injected with aCL MAb displayed a significantly higher rate of fetal resorption and a significant reduction in fetal and placental weight as compared with those injected with MAb 57. These findings were accompanied by a finding of placental human IgG deposition and necrosis in the aCL MAb-treated animals.

CONCLUSION

The results of this study indicate that human aCL IgG that are beta2-GPI independent can induce pathology.

Endothelial cells as a target for antiphospholipid antibodies: role of anti-beta 2 glycoprotein I antibodies

PROBLEM

To investigate the role of the plasma cofactor for antiphospholipid antibodies in antibody binding to endothelial cells.

METHOD OF STUDY

a) Evaluation of endothelial cell binding of polyclonal and monoclonal anti-beta 2 glycoprotein I antibodies; and b) study of the effects of antibody binding: adhesion molecule expression, leukocyte adhesion, and interleukin-1 beta secretion.

RESULTS

Anti-beta 2 glycoprotein I antibodies bind endothelial cell monolayers in vitro by reacting with the cofactor adhered to the cell membranes. Antibody binding induces an up-regulation of adhesion molecules, favours leukocyte adherence, and increases interleukin-1 beta secretion. Interleukin-1 beta plays an active role to mediate adhesion molecule expression through an autocrine loop, as shown by the inhibitory effect of interleukin 1 receptor antagonist.

CONCLUSIONS

Antiphospholipid antibodies do react with endothelium through the co-factor adhered to their cell membranes and induces a pro-adhesive cell phenotype.