Clinical importance of antibodies against platelet activating factor in antiphospholipid syndrome manifestations

Prevalence and Clinical Associations of Antiphospholipid Antibodies in Systemic Sclerosis: New Data From a French Cross-Sectional Study, Systematic Review, and Meta-Analysis

Objectives: Antiphospholipid antibodies (aPL) can be present in the sera of systemic sclerosis (SSc) patients. This study aimed to determine the prevalence of aPL in a cross-sectional study of SSc patients, to assess their clinical associations, to perform a systematic review of published reports and a meta-analysis to estimate the worldwide prevalence of aPL in SSc. Methods: Two-hundred and forty-nine SSc patients were consecutively tested once for lupus anticoagulant (LA), anticardiolipin (aCL), and anti-β2glycoprotein I (anti-β2GpI) antibodies. Clinical associations with aPL positivity were studied using a logistic regression model. A systematic review of the literature was carried out in PubMed and Embase. Meta-analysis was performed using number of aPL positive (at least one of the three antibodies positive) and negative patients. Meta-regression was used to study potential factors explaining the heterogeneity between studies. Results: In our cross-sectional study, aPL positivity was found in 16 patients (prevalence 6.4%; 95%CI [3.8-10.4]). In multivariate analysis, there was a significant association between aPL positivity and venous thrombosis (VT) (OR 6.25 [1.18-33.00]; p = 0.028) and miscarriage (OR 5.43; 95%CI [1.31-22.13]; p = 0.017). Twenty-four studies were included in the meta-analysis, representing a total population of 3036 SSc patients. The overall pooled prevalence of aPL in SSc was 14% (9-20) with a high degree of heterogeneity among studies. Conclusion: This study found a prevalence of aPL positivity in our SSc population of 6.4% (3.8-10.4) and an overall worldwide pooled prevalence of 14% (9-20). In our SSc population, aPL positivity was associated with VT and miscarriage. These data provide additional insights into the role of aPL in the vasculopathy observed in SSc.

Anticardiolipin and anti-beta2 glycoprotein I antibodies and lupus-like anticoagulant: prevalence and significance in systemic sclerosis

BACKGROUND

It has been suggested that both anticardiolipin (aCL) and anti-beta(2) glycoprotein I (abeta(2)GPI) antibodies may play a critical role in the pathogenesis of systemic sclerosis (SSc)-related vascular impairment.

OBJECTIVES

To evaluate the prevalence of aCL and abeta(2)GPI antibodies and lupus-like anticoagulant (LAC) in patients with SSc and healthy controls. We also investigated a possible relationship between clinical and biological variables of patients with SSc and the presence of aCL/abeta(2)GPI antibodies and/or LAC.

METHODS

Measurements of aCL and abeta(2)GPI antibodies, and LAC were performed in 69 consecutive patients with SSc and 69 age- and sex-matched controls. Clinical and biological findings were compared between patients with and without antiphospholipid antibodies.

RESULTS

aCL and abeta(2)GPI antibodies and/or LAC were detected in 13 (19%) of 69 consecutive patients with SSc; in the healthy control group, aCL antibody was found in only one (2%) subject (P = 0.0007). None of the healthy controls had abeta(2)GPI antibody and/or LAC. Moreover, pitting scars, pulmonary arterial hypertension, macrovascular involvement as well as severity of capillary impairment (using nailfold videocapillaroscopy) were more frequent in SSc patients with aCL/abeta(2)GPI antibodies and/or LAC compared with those without.

CONCLUSIONS

Our findings suggest that antiphospholipid antibodies may have a role in the genesis of vascular involvement related to SSc. Finally, the assessment of antiphospholipid antibodies (aCL and abeta(2)GPI antibodies, as well as LAC) may contribute to a better recognition of clinical features in patients with SSc; in essence, the patients with aCL/abeta(2)GPI antibodies and/or LAC may require close monitoring of vascular changes, including in particular pulmonary arterial hypertension and digital infarcts.

Antibodies elicited by the bovine lungworm, Dictyocaulus viviparus, cross-react with platelet-activating factor

Parasite N-glycans may play an important role in helminth infections. As antibodies from Dictyocaulus viviparus-infected calves strongly react with N-glycans, we investigated the characteristics of the major immunodominant glycoprotein (GP300) of this parasite. Probing of worm extracts with various lectins demonstrated unique binding of GP300 to wheat germ agglutinin. Analysis of lectin-purified GP300 revealed that the glycan was substituted with phosphorylcholine and reacted with the phosphorylcholine-specific antibody TEPC-15. Competitive enzyme-linked immunosorbent assay with GP300-coated plates and GP300-specific immunoglobulin G (IgG) in conjunction with free phosphorylcholine or TEPC-15 demonstrated that antibodies from infected calves recognized phosphorylcholine on GP300. Additional assays showed that these antibodies cross-reacted with the phosphorylcholine moiety present on platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), a proinflammatory mediator of the host. Heavily infected calves contained high levels of serum GP300-specific IgG1 but low levels of IgA and IgG2 and showed a reduced influx of eosinophils in the lungs, all consistent with a neutralization of PAF activity. In conclusion, we demonstrated that D. viviparus infection elicits GP300-specific antibodies that cross-react with PAF and may neutralize PAF function, thus limiting the development of a protective response as well as parasite-induced host pathology.

Proinflammatory high-density lipoprotein as a biomarker for atherosclerosis in patients with systemic lupus erythematosus and rheumatoid arthritis

OBJECTIVE

Women with systemic lupus erythematosus (SLE) have a 7-50-fold increased risk of coronary artery disease (CAD). In the general population, oxidized low-density lipoprotein (ox-LDL) increases the risk for CAD. Normal high-density lipoproteins (HDLs) protect LDL from oxidation; proinflammatory HDLs do not. This study was undertaken to determine whether patients with SLE, who have chronic inflammation that causes oxidative damage, have more proinflammatory HDL and higher levels of ox-LDL, thus predisposing them to atherosclerosis.

METHODS

One hundred fifty-four women with SLE, 48 women with rheumatoid arthritis (RA), and 72 healthy controls were studied. The ability of the patients' HDL to prevent oxidation of normal LDL was measured. Values >1.0 (the value assigned for LDL oxidation in the absence of HDL) after the addition of HDL indicated proinflammatory HDL. Plasma ox-LDL levels were measured as the amount of oxidation produced by the patient's LDL after the removal of HDL.

RESULTS

SLE patients had more proinflammatory HDL (mean +/- SD score 1.02 +/- 0.57, versus 0.68 +/- 0.28 in controls [P < 0.0001] and 0.81 +/- 0.22 in RA patients [P = 0.001 versus SLE patients]). A higher proportion of SLE patients had proinflammatory HDL: 44.7% of SLE patients versus 4.1% of controls and 20.1% of RA patients had scores >1.0 (P < 0.006 between all groups). Levels of ox-LDL correlated with levels of proinflammatory HDL (r = 0.37, P < 0.001). SLE patients with CAD had significantly higher proinflammatory HDL scores than patients without CAD (P < 0.001).

CONCLUSION

HDLs are proinflammatory in a significant proportion of SLE patients and are associated with elevated levels of ox-LDL. Abnormal HDLs impair the ability to prevent LDL oxidation and may predispose to atherosclerosis.

Atherosclerosis in Patients With Autoimmune Disorders

Recent findings indicate that presence of activated immune competent cells and inflammation are typical of atherosclerosis, the main cause of cardiovascular disease (CVD). The risk of CVD is very high in a prototypic autoimmune disease, systemic lupus erythematosus (SLE), and is also raised in other autoimmune diseases such as rheumatoid arthritis. Autoimmunity-related CVD and atherosclerosis are important clinical problems. They may also shed light on interactions between immune reactions and atherosclerosis development and manifestations, not least in women, who have a much higher risk of autoimmune disease than men. In general, a combination of traditional and nontraditional risk factors, including dyslipidemia (and to a varying degree, hypertension, diabetes, and smoking), inflammation, antiphospholipid antibodies (aPLs), and lipid oxidation, contribute to CVD in autoimmune diseases. Premature atherosclerosis is likely to be a major underlying mechanism, although distinctive features, if any, of autoimmunity-related atherosclerosis compared with “normal” atherosclerosis are not clear. One interesting possibility is that factors such as inflammation, neoepitopes on endothelial cells, or aPLs make atherosclerotic lesions in autoimmune disease more prone to rupture than in “normal” atherosclerosis. Some cases of autoimmunity-related CVD may be more related to thrombosis than atherosclerosis. Whether premature atherosclerosis is a general feature of autoimmune diseases such as SLE or only affects a subgroup of patients whereas others do not have an increased risk remains to be demonstrated. Treatment of patients with autoimmune disease should also include CVD aspects and be focused on traditional risk factors as well as on disease-related factors. Hopefully novel therapeutic principles will be developed that target the causes of the inflammation present in atherosclerotic lesions.

SLE, atherosclerosis and cardiovascular disease

Atherosclerosis is an inflammatory disease and the major cause of cardiovascular disease (CVD) in general. Atherosclerotic plaques are characterized by the presence of activated immune competent cells, but antigens and underlying mechanisms causing this immune activation are not well defined. During recent years and with improved treatment of acute disease manifestations, it has become clear that the risk of CVD is very high in a prototypic autoimmune disease, systemic lupus erythematosus (SLE). SLE-related CVD and atherosclerosis are important clinical problems but may in addition also shed light on how immune reactions are related to premature atherosclerosis and atherothrombosis. A combination of traditional and nontraditional risk factors, including dyslipidaemia (and to a varying degree hypertension, diabetes and smoking), inflammation, antiphospholipid antibodies (aPL) and lipid oxidation are related to CVD in SLE. Premature atherosclerosis in some form leading to atherothrombosis is likely to be a major underlying mechanism, though distinctive features if any, of SLE-related atherosclerosis when compared with 'normal' atherosclerosis are not clear. One interesting possibility is that factors such as inflammation or aPL make atherosclerotic lesions in autoimmune disease more prone to rupture than in 'normal' atherosclerosis. Whether premature atherosclerosis is a general feature of SLE or only affects a subgroup of patients remains to be demonstrated. Treatment of SLE patients should also include a close monitoring of traditional risk factors for CVD. In addition, attention should also be paid to nontraditional risk factors such as inflammation and SLE-related factors such as aPL. Hopefully novel therapeutic principles will be developed that target the causes of the inflammation and immune reactions present in atherosclerotic lesions.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Current debates in antiphospholipid syndrome: the acquired antibody-mediated thrombophilia

Antiphospholipid (APL) syndrome is the most common form of acquired thrombophilia. It can cause significant morbidity and even mortality. The term "APL antibodies" represents a heterogeneous group of antibodies associated with this disorder. Currently no single assay can identify every APL antibody. Clinically relevant APL antibodies are mainly anticardiolipin antibodies (ACA) detected by solid phase enzyme-linked immunosorbent assay (ELISA) and lupus anticoagulants (LA) demonstrated by in vitro coagulation assay. However, there are some other antibodies associated with the APL syndrome (i.e., subgroup APL antibodies). ACAs, LAs, and subgroup APL antibodies represent intersecting, but non-identical, subsets of autoantibodies. Thus, those autoantibodies may coexist or may occur independently. Any organ system and any size of vessel can be affected during the clinical course of the disease. Therefore, the APL syndrome can manifest itself in a wide variety of clinical thrombotic features. Fetal loss and pregnancy morbidity represent a specific challenge. Despite tremendous advances in the understanding of the pathogenesis of APL syndrome during the past decade, the mainstay of management is still anticoagulation. However, there is no general agreement regarding the duration and intensity of anti-coagulant therapy. In this review, we focused on the current dilemmas and their present clarifications in the wide clinicopathologic spectrum of APL syndrome and APL antibody-related distinct pathologic conditions.

Antibodies against platelet-activating factor and platelet-activating factor–like lipids are raised in women with primary recurrent abortion

OBJECTIVE

The purpose of this study was to determine the antibody levels against platelet-activating factor (PAF), PAF-like lipids lysophosphatidylcholine (LPC), cardiolipin (CL), and oxidized low-density lipoprotein (LDL) in recurrent abortion.

STUDY DESIGN

Eigthy-five women with a history of at least 3 recurrent spontaneous abortions (55 women with primary abortion [31.4+/-5.1 years old]; 30 women with secondary abortion [33+/-4.5 years old]) were compared with 48 age-matched control subjects (33+/-4.4 years old) who had delivered without complications. Antibodies were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Antibodies against PAF and antibodies against oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (oxPAPC) were raised significantly in the group with primary abortion, as compared to control subjects (P<.05) and not significantly higher than in secondary abortion; antibodies against oxidized LDL, LPC, or CL levels did not differ between groups.

CONCLUSION

Antibodies against platelet-activating factor and antibodies against platelet-activating factor-like lipid oxPAPC are associated with primary recurrent abortion and may function as novel disease markers. Whether these antibodies also are pathogenic (eg, by interacting with endothelial cells in placenta or by interfering with platelet-activating factor during embryonal development) remains to be shown.

Antiphospholipid antibodies: discovery, definitions, detection and disease

Antiphospholipid antibodies (aPL) are immunoglobulins of IgG, IgM and IgA isotypes that target phospholipid (PL) and/or PL-binding plasma proteins. Detection of aPL in the laboratory is done currently by both immunoassays and functional coagulation tests. Convention defines aPL specificity in immunoassays according to the particular PL substrate present, for example aPS represents antiphosphatidylserine antibodies. This may be technically incorrect inasmuch as a particular PL may be responsible for binding and highly concentrating a specific plasma protein, the latter then becomes the target for the aPL. The binding of beta(2)GP-I (apolipoprotein H) to the negatively charged PL, cardiolipin (CL) provides a good example of this circumstance. In contrast, aPL which specifically prolong coagulation times in in vitro are called lupus anticoagulants (LA). The precise PL target(s) of the aPL responsible for LA activities are unknown and often debated. The persistent finding of aPL in patients in association with abnormal blood clotting and a myriad of neurological, obstetrical and rheumatic disorders often compounded by autoimmune diseases has led to an established clinical diagnosis termed antiphospholipid syndrome (APS). The common denominator for these APS patients is the presence of circulating aPL on two or more occasions and the observation of events attributable to abnormal or accelerated blood clotting somewhere in vivo. The purpose of this review is to collect, collate, and consolidate information concerning aPL.

No evidence for a putative involvement of platelet-activating factor in systemic lupus erythematosus without active nephritis

BACKGROUND

Platelet-activating factor (PAF) seems to be implicated in systemic lupus erythematosus (SLE) patients with associated renal diseases.

AIMS

In this study, we ensured the role of PAF in SLE patients without renal complications.

METHODS

Blood PAF and acetylhydrolase activity, plasma soluble phospholipase A(2), and the presence of antibodies against PAF were investigated in 17 SLE patients without active nephritis and in 17 healthy controls.

RESULTS

Blood PAF levels were not different (p=0.45) between SLE patients (6.7+/-2.8 pg/ml) and healthy subjects (9.6+/-3.1 pg/ml). Plasma acetylhydrolase activity (the PAF-degrading enzyme) was significantly (p=0.03) elevated in SLE patients (57.8+/-6.4 nmol/min/ml) as compared with controls (37.9+/-2.6 nmol/min/ml). Plasma soluble phospholipase A(2) (the key enzyme for PAF formation) was not different (p=0.6) between SLE patients (59.1+/-5.1 U/ml) and controls (54.7+/-2.4 U/ml). Antibodies against PAF were detected only in 3/17 SLE patients. Flow cytometry analysis did not highlight PAF receptors on circulating leukocytes of SLE patients.

CONCLUSION

This clinical study highlights no evidence for a putative important role of PAF in SLE patients without active nephritis.