Antiphospholipid antibodies during 6-month treatment with infliximab: a preliminary report

BACKGROUND

The introduction of tumor necrosis factor (TNF) antagonists (adalimumab, infliximab, and etanercept) was a major advance and was highly important and beneficial in most rheumatoid arthritis (RA) patients. The adverse effects of this treatment are infrequent, but include opportunistic intracellular infection (especially the reactivation of latent Mycobacterium tuberculosis); exacerbation of demyelinating disorders; and the production of various types of antibodies such as antinuclear antibodies (ANA) or double-stranded DNA autoantibodies (dsDNA) and antiphospholipid antibodies (aPL) such as anti-cardiolipin antibodies (aCL) and anti-B2GP-I antibodies (B2GP-I). The aim of the study was to determine the prevalence of aCL and B2GP-I in IgM and IgG classes, using ELISA tests, during 6 months of follow-up in patients with refractory RA successfully treated with infliximab.

MATERIAL/METHODS

We determined the prevalence of aCL and B2GP-I in IgM and IgG classes, using ELISA tests, during 6 months of follow-up in patients with refractory RA successfully treated with infliximab.

RESULTS

We observed a statistically important increase only in the group of B2GP-I IgM (p<0.05). There are contradictory results concerning the ability of infliximab to induce aPL, but most authors confirm this phenomenon.

CONCLUSIONS

Further investigations are needed to determine if the new aPL appears in patients with β2-GPI gene polymorphisms such as leucine-to-valine substitution at position 247, which can lead to a conformational changes in β2-GPI protein, leading to aPL synthesis. The role of aPL in pathogenesis of APS is still unclear, but we should remember the immunogenic aspect of TNF antagonist treatment. Therefore, we recommend early detection of aPL and observation of the patient, paying special attention to signs and symptoms of thromboembolism.

Thrombosis risk in systemic lupus erythematosus: the role of thrombophilic risk factors

OBJECTIVES

Thromboembolic episodes are frequent manifestations of systemic lupus erythematosus (SLE). Although the presence of anti-phospholipid antibodies (aPL) is known to contribute to thromboembolism (TE), the relative contribution of other TE risk factors is unknown. The aim of this study was to determine the prevalence of TE in a Caucasian SLE population, to identify the risk factors of highest importance, and to assess the clinical value of thrombophilia screening among SLE patients.

METHODS

Samples from 105 patients were analysed with a screen including aPL, activated protein C resistance, factor V Leiden (FVL) and prothrombin G20210A mutations; protein C, protein S and antithrombin activity; factor VIII (FVIII) and von Willebrand factor (vWF), and homocysteine (Hcy) levels.

RESULTS

The annual incidence of arterial and venous TE events in our SLE population was 5.4 and 12.4 per 1000, respectively. The highest risk of thrombosis was carried by the simultaneous presence of lupus anticoagulant (LA) and anti-cardiolipin (aCL) [relative risk (RR) = 4.03, 95% confidence interval (CI) 2.06-7.86] or anti-beta2-glycoprotein I antibodies (abeta2-GPI) (RR = 5.10, 95% CI 2.58-10.1). Positivity for the individual aPL tests all carried an elevated TE risk. The presence of other risk factors seemed to be of less importance.

CONCLUSIONS

In SLE patients, the presence of aPL is a more significant risk factor for the development of thrombosis than the known inherited deficiencies. Based on these data, routine screening for additional hereditary risk factors seems to be unwarranted.

Platelet adhesion to dimeric beta-glycoprotein I under conditions of flow is mediated by at least two receptors: glycoprotein Ibalpha and apolipoprotein E receptor 2'

BACKGROUND

The major antigen implicated in the antiphospholipid syndrome is beta2-glycoprotein I (beta2GPI). Dimerized beta2GPI binds to apolipoprotein E receptor 2' (apoER2') on platelets and increases platelet adhesion to collagen under conditions of flow.

AIM

To investigate whether the interaction between dimerized beta2GPI and platelets is sufficiently strong to resist shear stresses.

METHODS

We studied the interaction of platelets with immobilized dimerized beta2GPI under conditions of flow, and further analyzed the interaction using surface plasmon resonance and solid phase immunoassays.

RESULTS

We found that dimerized beta2GPI supports platelet adhesion and aggregate formation under venous flow conditions. Adhesion of platelets to dimerized beta2GPI was completely inhibited by the addition of soluble forms of both apoER2' and GPIbalpha, and the addition of receptor-associated protein and the removal of GPIbalpha from the platelet surface. GPIbalpha co-precipitated with apoER2', suggesting the presence of complexes between GPIbalpha and apoER2' on platelet membranes. The interaction between GPIbalpha and dimeric beta2GPI was of intermediate affinity (Kd = 180 nM) and Zn2+, but not Ca2+-dependent. Deletion of domain V from dimeric beta2GPI strongly reduced its binding to both GPIbalpha and apoER2'. Antibodies that inhibit the binding of thrombin to GPIbalpha inhibited platelet adhesion to dimeric beta2GPI completely, while antibodies blocking the binding of von Willebrand factor to GPIbalpha had no effect. Dimeric beta2GPI showed reduced binding to low-sulfated GPIbalpha compared to the fully sulfated form.

CONCLUSION

We show that platelets adhere to dimeric beta2GPI under both arterial and venous shear stresses. Platelets adhere via two receptors: GPIbalpha and apoER2'. These receptors are present in a complex on the platelet surface.

Autoimmune disease as a cause of reproductive failure

High-risk pregnancy is the most common clinical association with antiphospholipid antibodies; the principal manifestations are pregnancy loss and early preeclampsia. Membership in this family of antibodies is continually growing and includes antibodies against a variety of phospholipids, phospholipid-protein complexes, and phospholipid-binding proteins. The current information in the literature is inadequate to clearly implicate a subgroup of antiphospholipid antibodies or a particular pathophysiologic mechanism as being responsible for poor pregnancy outcomes. It is clear, however, that prevalent diagnostic tests for LA and aCL are extremely useful to identify many of these patients, but are inadequate for diagnosis of all patients with autoimmune pregnancy loss or to elucidate the pathophysiology. Many patients who present clinically with autoimmune-like pregnancy complications currently are negative in tests for LA or aCL, but have antibodies against annexin V, phosphatidylserine, or other relevant antigens. The greatest risk for a complicated pregnancy is conveyed by a subgroup of antibodies that affect the normal function of placental trophoblast. As clinical laboratory tests designed to detect more members of the antiphospholipid antibody family become available, understanding of this complicated disease (APS) will increase.