Opposite Profiles of Complement in Antiphospholipid Syndrome (APS) and Systemic Lupus Erythematosus (SLE) Among Patients With Antiphospholipid Antibodies (aPL).

APS is the association of antiphospholipid antibodies (aPL) with thromboses and/or recurrent pregnancy loss (RPL). Among patients with SLE, one-third have aPL and 10-15% have a manifestation of secondary APS. Animal studies suggested that complement activation plays an important role in the pathogenesis of thrombosis and pregnancy loss in APS. We performed a cross-sectional study on complement proteins and genes in 525 patients with aPL. Among them, 237 experienced thromboses and 293 had SLE; 111 had both SLE and thromboses, and 106 had neither SLE nor thrombosis. Complement protein levels were determined by radial immunodiffusion for C4, C3 and factor H; and by functional ELISA for mannan binding lectin (MBL). Total C4, C4A and C4B gene copy numbers (GCN) were measured by TaqMan-based realtime PCR. Two to six copies of C4 genes are frequently present in a diploid genome, and each copy may code for an acidic C4A or a basic C4B protein. We observed significantly (a) higher protein levels of total C4, C4A, C4B, C3, and anticardiolipin (ACLA) IgG, (b) increased frequencies of lupus anticoagulant and males, and (c) decreased levels of complement factor H, MBL and ACLA-IgM among patients with thrombosis than those without thrombosis (N = 288). We also observed significantly lower GCNs of total C4 and C4A among aPL-positive patients with both SLE and thrombosis than others. By contrast, aPL-positive subjects with SLE had significantly reduced protein levels of C3, total C4, C4A, C4B and ACLA-IgG, and higher frequency of females than those without SLE. Patients with thrombosis but without SLE (N = 126), and patients with SLE but without thrombosis (N = 182) had the greatest differences in mean protein levels of C3 (p = 2.6 × 10-6), C4 (p = 2.2 × 10-9) and ACLA-IgG (p = 1.2 × 10-5). RPL occurred in 23.7% of female patients and thrombotic SLE patients had the highest frequency of RPL (41.0%; p = 3.8 × 10-10). Compared with non-RPL females, RPL had significantly higher frequency of thrombosis and elevated C4 protein levels. Female patients with homozygous C4A deficiency all experienced RPL (p = 0.0001) but the opposite was true for patients with homozygous C4B deficiency (p = 0.017). These results provide new insights and biomarkers for diagnosis and management of APS and SLE.

Plasma microparticle tissue factor activity in patients with antiphospholipid antibodies with and without clinical complications.

Antiphospholipid syndrome (APS) is defined by the association of autoantibodies to certain phospholipid-binding proteins with arterial or venous thrombosis ('AT' or 'VT', respectively), and/or pregnancy-related morbidity (PM). Antiphospholipid antibodies (aPLA) promote activation of several cell types including monocytes, resulting in procoagulant tissue factor (TF) expression that may contribute to the vascular complications. Since TF synthesis by monocytes is frequently accompanied by release of TF-bearing microparticles, we hypothesized that plasma microparticle TF activity (MP-TF) may be elevated in APS patients and contribute to thrombosis and/or PM. Platelet-poor plasma specimens were obtained from 30 patients with definite APS and 72 patients with asymptomatic aPLA from the Antiphospholipid Syndrome Collaborative Registry (APSCORE). MP-TF was measured by an in-house factor Xa generation assay. The two groups were well matched for gender, age, ethnicity, proportions with underlying SLE, and aPLA profiles. MP-TF (median and (IQR)) in asymptomatic aPLA subjects was 0.09 pg/mL (0.05-0.14) compared to 0.13 pg/mL (0.10-0.17) in APS (p < 0.001). No differences in MP-TF levels were observed between APS subjects with PM, thrombosis, or PM+thrombosis. Similarly, among subjects with either APS or asymptomatic aPLA, MP-TF did not differ in the presence or absence of underlying SLE. Prospective studies will be required to determine if plasma MP-TF activity is causally related to thrombotic or gestational complications in APS.

Drug-induced lupus anticoagulants and antiphospholipid antibodies.

Lupus anticoagulants (LA) are immunoglobulins (IgG, IgM, and/or IgA) which interfere with one or more of phospholipid-dependent in vitro coagulation tests, eg, activated partial thromboplastin time (aPTT), kaolin clotting time (KCT), dilute Russell viper venom time (dRVVT), and dilute prothrombin time (dPT). LAs may be seen in a variety of clinical settings including the primary antiphospholipid syndrome (APS), systemic lupus erythematosus (SLE), other autoimmune diseases, secondary to infections, malignancies, and in association with certain drugs. LAs associated with the antiphospholipid syndrome and other autoimmune disease recognize certain phospholipid-binding proteins (ß(2)-glycoprotein I [ß(2)GPI] or prothrombin). Many drugs have been implicated as possibly causing LAs, although the majority of such cases are limited to a select few. Drug-induced LAs are heterogeneous, differing in laboratory findings as well as related clinical complications. This paper reviews the English medical literature on drug-induced LA and potential mechanisms of induction.

Pulmonary manifestations of the antiphospholipid antibody syndrome.

A broad spectrum of pulmonary disease may occur in antiphospholipid antibody syndrome. The most common pulmonary manifestations are pulmonary thromboembolism and pulmonary hypertension. In this article the authors review these manifestations, as well as less common findings including acute respiratory distress syndrome, alveolar hemorrhage, and pulmonary capillaritis.

Use of rituximab in the antiphospholipid syndrome.

B cells are promising targets for treatment in autoimmune diseases. Rituximab, a chimeric anti-CD20 monoclonal antibody that depletes B cells, is approved for use in rheumatoid arthritis and is often used to treat refractory autoimmune thrombocytopenia. There is increasing interest in using rituximab in other autoimmune diseases, including the antiphospholipid syndrome. We reviewed the published clinical experience of rituximab use in patients with the antiphospholipid syndrome. Data are limited to case reports and small case series. In 19 of 21 reported cases, rituximab appeared to have a beneficial clinical effect. Antiphospholipid antibodies levels were significantly decreased in ten of 12 cases. Controlled clinical trials are needed to determine if rituximab is effective in the antiphospholipid syndrome.

Venous thrombosis in the antiphospholipid syndrome.

The antiphospholipid syndrome is a relatively common acquired cause of venous thrombosis. Up to 20% of cases of deep vein thrombosis, with and without pulmonary embolism, may be associated with antiphospholipid antibodies. These antibodies are typically detected in lupus anticoagulant assays and tests for anticardiolipin antibodies. Most antiphospholipid antibodies are directed against several phospholipid-binding plasma proteins. The most common antigens are beta2-glycoprotein I and prothrombin. Immunoassays using these purified antigens are now available. In addition to being markers for thrombotic risk, antiphospholipid antibodies have been shown to directly contribute to hypercoagulability in animal models and in various in vitro studies. Prevention of recurrent venous thrombosis in patients with the antiphospholipid syndrome requires long-term anticoagulation. The optimal intensity of warfarin therapy is an ongoing issue, but most clinicians currently favor a target INR in the 2.0 to 3.0 range. In certain patients, antiphospholipid antibodies may interfere with determination of the INR, requiring other approaches to monitor and adjust the warfarin dose. Low-dose aspirin is typically recommended for primary prevention of thrombosis in asymptomatic patients with moderate to high levels of antiphospholipid antibodies, although strong supporting data are lacking.

Development of an inhaled endotoxin challenge protocol for characterizing evoked cell surface phenotype and genomic responses of airway cells in allergic individuals.

BACKGROUND: Environmental exposure to endotoxin is a known cause of exacerbation of asthma. Inhaled endotoxin protocols have been used to evaluate airway cell surface phenotypes associated with antigen presentation and innate immunity in healthy volunteers, but not in allergic volunteers. OBJECTIVES: To establish the safety of challenge with low-dose endotoxin (10,000 endotoxin units) (lipopolysaccharide [LPS]) inhalation in allergic individuals, to measure airway cell surface phenotypes associated with antigen presentation and innate immunity in induced sputum (IS) after LPS challenge, and to conduct gene expression profiling in IS cells to determine which host genetic networks are modified by LPS inhalation. METHODS: Induced sputum was obtained before and 6 hours after LPS inhalation in 10 allergic volunteers (8 with asthma and 2 with rhinitis). Flow cytometry was used to examine cell surface phenotypes on IS cells. Genomic expression was analyzed on a subset of IS samples (n = 10) using microarray and ingenuity pathway analysis. RESULTS: A total of 10,000 endotoxin units of LPS induced significant up-regulation of membrane CD14, CD11b, CD16, HLA-DR, CD86, and Fcepsilon receptor 1 on sputum phagocytes and increased expression of genes that influence antigen-presenting surface molecules (HLA-DR, chemokine ligand 2 or monocyte chemoattractant protein 1, v-rel reticuloendotheliosis viral oncogene homolog, prostaglandin-endoperoxide synthase 2 or cyclooxygenase 2, and transforming growth factor beta), immune activation (CD14, interleukin 1beta, and regulated upon activation, normal T cell expressed and secreted), and inflammation (intracellular adhesion molecule 1 and inhibitory kappaBalpha). Gene profiles for nuclear factor kappaB, interleukin 1, and tumor necrosis factor pathways were also significantly affected. CONCLUSIONS: Low-dose inhaled endotoxin challenge is safe in allergic individuals with mild to moderate disease. It enhances airway cell surface phenotypes and expression of genes associated with antigen presentation, innate immunity, and inflammation. Microarray with ingenuity pathway analysis can be successfully applied to sputum cells to characterize genetic responses to inhaled exacerbants.

Gene copy-number variation and associated polymorphisms of complement component C4 in human systemic lupus erythematosus (SLE): low copy number is a risk factor for and high copy number is a protective factor against SLE susceptibility in European Americans.

Interindividual gene copy-number variation (CNV) of complement component C4 and its associated polymorphisms in gene size (long and short) and protein isotypes (C4A and C4B) probably lead to different susceptibilities to autoimmune disease. We investigated the C4 gene CNV in 1,241 European Americans, including patients with systemic lupus erythematosus (SLE), their first-degree relatives, and unrelated healthy subjects, by definitive genotyping and phenotyping techniques. The gene copy number (GCN) varied from 2 to 6 for total C4, from 0 to 5 for C4A, and from 0 to 4 for C4B. Four copies of total C4, two copies of C4A, and two copies of C4B were the most common GCN counts, but each constituted only between one-half and three-quarters of the study populations. Long C4 genes were strongly correlated with C4A (R=0.695; P<.0001). Short C4 genes were correlated with C4B (R=0.437; P<.0001). In comparison with healthy subjects, patients with SLE clearly had the GCN of total C4 and C4A shifting to the lower side. The risk of SLE disease susceptibility significantly increased among subjects with only two copies of total C4 (patients 9.3%; unrelated controls 1.5%; odds ratio [OR] = 6.514; P=.00002) but decreased in those with > or =5 copies of C4 (patients 5.79%; controls 12%; OR=0.466; P=.016). Both zero copies (OR=5.267; P=.001) and one copy (OR=1.613; P=.022) of C4A were risk factors for SLE, whereas > or =3 copies of C4A appeared to be protective (OR=0.574; P=.012). Family-based association tests suggested that a specific haplotype with a single short C4B in tight linkage disequilibrium with the -308A allele of TNFA was more likely to be transmitted to patients with SLE. This work demonstrates how gene CNV and its related polymorphisms are associated with the susceptibility to a human complex disease.

Annexin A2: better left alone.

Zhang and McCrae demonstrate that APLA/b2GPI-mediated endothelial cell activation occurs via dimerization of annexin A2 molecules on the cell surface.

Mechanisms of autoantibody-induced monocyte tissue factor expression.

The expression of tissue factor (TF) activity to flowing blood is the trigger for physiological coagulation as well as many types of thrombosis. A growing body of evidence suggests that increased tissue factor activity is a significant contributor towards the hypercoagulability associated with the antiphospholipid syndrome (APS). The increase in tissue factor activity appears to be due to increased transcription and translation of nascent tissue factor molecules but is not due to de-encryption of existing tissue factor molecules on cells. Autoantibodies and/or immune complexes circulating in APS patients appear to enhance the expression of tissue factor activity on monocytes and endothelial cells. Anti-beta2-glycoprotein I (beta2GPI) autoantibodies have been specifically implicated in the antibody-mediated enhancement of tissue factor activity. The presence of antibodies against tissue factor pathway inhibitor (TFPI) in certain APS patients suggests that negative regulation of tissue factor activity might also be impaired in these patients. Given a mechanism involving increased tissue factor activity in APS-associated thrombosis, agents specifically targeting tissue factor activity may be a novel and efficacious therapy that is safer than current approaches to the management of APS.

Characterization of monocyte tissue factor activity induced by IgG antiphospholipid antibodies and inhibition by dilazep.

Increasing evidence suggests that autoantibodies directly contribute to hypercoagulability in the antiphospholipid syndrome (APS). One proposed mechanism is the antibody-induced expression of tissue factor (TF) by blood monocytes. Dilazep, an antiplatelet agent, is an adenosine uptake inhibitor known to block induction of monocyte TF expression by bacterial lipopolysaccharide. In the current study we characterized the effects of immunoglobulin G (IgG) from patients with APS on monocyte TF activity and investigated whether dilazep is capable of blocking this effect. IgG from 13 of 16 patients with APS significantly increased monocyte TF activity, whereas normal IgG had no effect. Time-course experiments demonstrated that APS IgG-induced monocyte TF mRNA levels were maximal at 2 hours and TF activity on the cell surface was maximal at 6 hours. Dilazep inhibited antibody-induced monocyte TF activity in a dose-dependent fashion but had no effect on TF mRNA expression. The effect of dilazep was blocked by theophylline, a nonspecific adenosine receptor antagonist. In conclusion, IgG from certain patients with APS induce monocyte TF activity. Dilazep inhibits the increased expression of monocyte TF activity at a posttranscriptional level, probably by way of its effect as an adenosine uptake inhibitor. Pharmacologic agents that block monocyte TF activity may be a novel therapeutic approach in APS.

Delayed apoptotic cell clearance and lupus-like autoimmunity in mice lacking the c-mer membrane tyrosine kinase.

Mice lacking the membrane tyrosine kinase c-mer have been shown to have altered macro-phage cytokine production and defective phagocytosis of apoptotic cells despite normal phagocytosis of other particles. We show here that c-mer-deficient mice have impaired clearance of infused apoptotic cells and that they develop progressive lupus-like autoimmunity, with antibodies to chromatin, DNA, and IgG. The autoimmunity appears to be driven by endogenous antigens, with little polyclonal B cell activation. These mice should be an excellent model for studying the role of apoptotic debris as an immunogenic stimulus for systemic autoimmunity.