Anastasia Lambrianides

Antibodies to apolipoprotein A-I, high-density lipoprotein, and C-reactive protein are associated with disease activity in patients with systemic lupus erythematosus

OBJECTIVE Inflammatory disease activity in patients with systemic lupus erythematosus (SLE) may affect the development of atherosclerosis, contributing to their increased risk of cardiovascular disease (CVD). This process may be mediated by anti-apolipoprotein A-I (anti-Apo A-I), anti-high-density lipoprotein (anti-HDL), and anti-C-reactive protein (anti-CRP) autoantibodies. We undertook this study to examine whether levels of these antibodies rise in association with increased SLE disease activity. METHODS IgG anti-Apo A-I, anti-HDL, and anti-CRP levels were measured in serum from the following groups: 39 patients with persistently high disease activity (British Isles Lupus Assessment Group [BILAG] A or B score) over the previous 2 years, 42 patients with persistently low disease activity (no BILAG A or B scores) over the previous 2 years, 34 healthy controls, 25 individual patients from whom paired samples (at time of disease flare and quiescence) were obtained and compared, 16 patients with newly diagnosed lupus nephritis from whom multiple samples were obtained and who were followed up prospectively for up to 2 years, and 24 patients with SLE who had experienced CVD events. RESULTS Serum levels of IgG anti-Apo A-I, anti-HDL, and anti-CRP were higher in patients with SLE than in controls. Anti-Apo A-I and anti-HDL levels, but not anti-CRP levels, were higher in patients with persistently high disease activity than in those with low disease activity. Mean levels of the 3 autoantibodies in patients who had experienced CVD events lay between the mean levels in the high and low disease activity groups. Only levels of anti-Apo A-I were significantly higher in samples obtained from individual patients during disease flares than in samples obtained during disease quiescence. In the lupus nephritis patients, anti-Apo A-I and anti-HDL levels correlated with serum levels of high avidity IgG anti-double-stranded DNA. CONCLUSION Persistent disease activity is associated with a significant increase in IgG anti-Apo A-I and anti-HDL in patients with SLE.

Effects of Polyclonal IgG Derived from Patients with Different Clinical Types of the Antiphospholipid Syndrome on Monocyte Signaling Pathways

A major mechanism of hypercoagulability in the antiphospholipid syndrome (APS) is antiphospholipid Ab-mediated upregulation of tissue factor (TF) on monocytes via activation of TLRs, p38 MAPK, and NF-κB pathways. We examined whether monocyte signaling pathways are differentially activated by IgG from patients with vascular thrombosis (VT) alone compared with IgG from patients with pregnancy morbidity (PM) alone. We purified IgG from 49 subjects. A human monocyte cell line and ex vivo healthy monocytes were treated with 100 μg/ml IgG for 6 h, and cell extracts were examined by immunoblot using Abs to p38 MAPK and NF-κB. To further investigate intracellular signaling pathways induced by these IgGs, specific inhibitors of p38 MAPK, NF-κB, TLR4, and TLR2 were used to determine their effect on TF activity. Only IgG from patients with VT but no PM (VT+/PM−) caused phosphorylation of NF-κBand p38 MAPK and upregulation of TF activity in monocytes. These effects were not seen with IgG from patients with PM alone (VT−/PM+), anti-phospholipid Ab-positive patients without APS, or healthy controls. TF upregulation caused by the VT+/PM− samples was reduced by inhibitors of p38 MAPK, NF-κB, and TLR4. The effects of VT+/PM− IgG on signaling and TF upregulation were concentrated in the fraction that bound β-2-glycoprotein I. Our findings demonstrate that IgGs from patients with diverse clinical manifestations of APS have differential effects upon phosphorylation of NF-κB and p38 MAPK and TF activity that may be mediated by differential activation of TLR4.

B cell depletion therapy for patients with systemic lupus erythaematosus results in a significant drop in anticardiolipin antibody titres

Background: B cell depletion therapy (BCDT) has recently been used with success to treat patients with rheumatoid arthritis and systemic lupus erythematosus (SLE). As antiphospholipid antibodies have been implicated in the pathogenesis of the antiphospholipid syndrome (APS), we asked the question whether BCDT affects levels of IgG anticardiolipin antibodies (aCL) in our cohort of 32 SLE patients given this treatment. Methods: We identified seven SLE patients who had undergone BCDT and had had at least two moderate positive aCL titres at least 12 weeks apart. Of these only one patient had APS. IgG aCL were measured at time 0 and 6–9 months post BCDT. Results: At time 0, the mean IgG aCL level was 20.6 standardized IgG antiphospholipid units (GPLU) (range (SD) 10–32, (10.1), normal level <5). At 6–9 months post depletion the IgG aCL levels in six of the seven patients was undetectable and in the other patient the level reduced from 25 GPLU to 15 GPLU (p<0.005, two-tailed paired t test). At baseline, only one patient had a mildly positive anti-β2-glycoprotein I (β2GPI) antibody level at 30% (compared to an in-house standard), which fell to 5% post-BCDT. Conclusions: This small observational study in patients with SLE is the first to demonstrate that BCDT results in a significant reduction in levels of IgG aCL.

Thrombin binding predicts the effects of sequence changes in a human monoclonal antiphospholipid antibody on its in vivo biologic actions.

The mechanisms by which antiphospholipid Abs (aPL) cause thrombosis are not fully understood. It is clear that binding to a number of phospholipid-associated Ags is important but it is difficult to identify which Ag-binding properties are most closely linked to the ability to cause biologic effects such as promotion of thrombosis and activation of endothelial cells. We have previously used an in vitro expression system to produce a panel of human monoclonal IgG molecules between which we engineered small differences in sequence leading to significant well-defined changes in binding properties. In this study, we assess the properties of five of these IgG molecules in assays of biologic function in vitro and in vivo. The i.p. injection of these IgG into mice subjected to a femoral vein pinch stimulus showed that only those IgG that showed strong binding to thrombin promoted in vivo venous thrombosis and leukocyte adherence. However, this finding did not hold true for the effects of these IgG on activation of cultured endothelial cells in vitro, where there was a less clear relationship between binding properties and biologic effects.

Stable expression of a recombinant human antinucleosome antibody to investigate relationships between antibody sequence, binding properties, and pathogenicity

When purified under rigorous conditions, some murine anti-double-stranded-DNA (anti-dsDNA) antibodies actually bind chromatin rather than dsDNA. This suggests that they may actually be antinucleosome antibodies that only appear to bind dsDNA when they are incompletely dissociated from nucleosomes. Experiments in murine models suggest that antibody–nucleosome complexes may play a crucial role in the pathogenesis of glomerulonephritis in systemic lupus erythematosus. Some human monoclonal anti-DNA antibodies are pathogenic when administered to mice with severe combined immunodeficiency (SCID). Our objective was to achieve stable expression of sequence-altered variants of one such antibody, B3, in Chinese hamster ovary (CHO) cells. Purified antibodies secreted by these cells were tested to investigate whether B3 is actually an antinucleosome antibody. The pathogenic effects of the antibodies were tested by implanting CHO cells secreting them into SCID mice. Purified B3 does not bind to dsDNA unless supernatant from cultured cells is added, but does bind to nucleosomes. The strength of binding to dsDNA and nucleosomes is dependent on the sequence of the light chain. Mice that received CHO cells secreting wild-type B3 developed more proteinuria and died earlier than control mice that received nonsecreting CHO cells or mice that received B3 with a single light chain mutation. However, none of the mice had histological changes or deposition of human immunoglobulin G in the kidneys. Sequence changes may alter the pathogenicity of B3, but further studies using different techniques are needed to investigate this possibility.

Evaluating the conformation of recombinant domain I of β2-glycoprotein I and its interaction with human monoclonal antibodies

Highlights ► Bacterial expressed human recombinant DI has a structure consistent with that of DI in the published β2GPI crystal structure. ► Mutating residues D8/D9 and R39 do not alter the overall DI protein fold but cause local changes in surface contour. ► Monoclonal aPL-derived antibodies and DI of β2GPI interactions are influenced by specific arginine residues in aPL and particular epitopes in DI.

Changes in regulation of human monocyte proteins in response to IgG from patients with antiphospholipid syndrome

The effects of immunoglobulin G (IgG) from patients with the antiphospholipid syndrome (APS) upon monocyte activation have not been fully characterized. We carried out a comprehensive proteomic analysis of human monocytes treated with IgG from patients with different manifestations of the APS. Using 2-dimensional differential gel electrophoresis (2D DiGE), 4 of the most significantly regulated proteins (vimentin [VIM], zinc finger CCH domain-containing protein 18, CAP Gly domain-containing linker protein 2, and myeloperoxidase) were differentially regulated in monocytes treated with thrombotic or obstetric APS IgG, compared with healthy control (HC) IgG. These findings were confirmed by comparing monocytes isolated from APS patients and HC. Anti-VIM antibodies (AVAs) were significantly increased in 11 of 27 patients (40.7%) with APS. VIM expression on HC monocytes was stimulated more strongly by APS IgG from patients with higher-avidity serum AVA. We further characterized the proteome of thrombotic APS IgG-treated monocytes using a label-free proteomics technique. Of 12 proteins identified with the most confidence, 2 overlapped with 2D DiGE and many possessed immune response, cytoskeletal, coagulation, and signal transduction functions which are all relevant to APS and may therefore provide potential new therapeutic targets of this disease.

Interactions of human monoclonal and polyclonal antiphospholipid antibodies with serine proteases involved in hemostasis

Objective To characterize the interaction between procoagulant and/or anticoagulant serine proteases and human monoclonal IgG antiphospholipid antibodies (aPL) and polyclonal IgG derived from patients with the antiphospholipid syndrome (APS). Methods Five human monoclonal IgG with small differences in their sequences were tested for binding to protein C, activated protein C, plasmin, factor VIIa (FVIIa), FIX, FIXa, and FXII. Serum levels of antithrombin and anti–activated protein C were compared in 32 patients with APS, 29 patients with systemic lupus erythematosus (SLE), and 22 healthy controls. Purified polyclonal IgG derived from APS patients with elevated levels of serum antithrombin antibodies was also tested for its functional effects on thrombin and antithrombin activity. Results Studies of monoclonal antibodies showed that sequence changes in human aPL are important in determining their ability to bind procoagulant and anticoagulant/fibrinolytic serine proteases. Mean IgG antithrombin levels were significantly elevated in patients with APS and in SLE patients with aPL but no APS (SLE/aPL+) compared to healthy controls, but anti–activated protein C levels were not increased in these patients. Moreover, IgG purified from patients with APS displayed higher avidity for thrombin and significantly inhibited antithrombin inactivation of thrombin compared with IgG from SLE/aPL+ patients. Conclusion High-avidity antithrombin antibodies, which prevent antithrombin inactivation of thrombin, distinguish patients with APS from SLE/aPL+ patients, and thus may contribute to the pathogenesis of vascular thrombosis in APS.

Structure-Function Relationships in Anti-DNA and Anti-Phospholipid Antibodies and their Relevance to the Pathogenesis of Disease

Autoantibodies are pathogenic in systemic lupus erythematosus (SLE) and the antiphospholipid syndrome (APS). These pathogenic autoantibodies are generally characterized by IgG isotype and high affinity binding to particular antigens. In SLE, antibodies to double-stranded DNA (dsDNA), nucleosomes and alpha-actinin are particularly important. In APS, pathogenic antibodies that cause thrombosis or fetal loss are particularly characterized by binding to anionic phospholipids (PL) and beta-2-glycoprotein I. Sequence analysis of human and murine monoclonal anti-dsDNA and aPL antibodies shows that high affinity for these antigens is associated with the presence of the residues arginine (Arg), asparagine (Asn) and lysine (Lys) in the complementarity determining regions (CDRs) of their heavy and light chains. In vitro expression systems have been used to create variants of the antibodies in which these amino acids have been altered. In general, removal of arginine residues reduces affinity for dsDNA, nucleosomes and anionic PL. Arginines at different positions in the sequence have different effects on binding affinity and effects on binding are not always mirrored by effects on pathogenicity. These studies, together with molecular models of antigen/antibody complexes, help us to understand exactly how pathogenic antibodies interact with antigens. Ultimately, this understanding may aid the design of therapeutic agents to block the pathogenic effects of these antibodies.