Antibodies of IgM subclass to phosphorylcholine and oxidized LDL are protective factors for atherosclerosis in patients with hypertension

Profile of autoantibodies against phosphorylcholine and cross-reactivity to oxidation-specific neoantigens in selective IgA deficiency with or without autoimmune diseases

Immunoglobulin A deficiency (IgAD) is considered the most common form of primary immunodeficiency. The majority of IgA-deficient individuals are considered asymptomatic, even though IgAD has been associated with an increased frequency of recurrent infections, allergy, and autoimmune diseases. In this study we evaluate the Natural autoantibodies (NatAbs) reactivity to phosphorylcholine (PC) and to some pro-inflammatory molecules in IgAD with or without autoimmune disorders. We observed that in the absence of IgA there is an enhancement of IgG subclasses functioning as NatAbs against PC. Immunoglobulin G (IgG) against lipopolysaccharide, C-reactive protein, and IgA was found in IgAD, regardless of the autoimmune manifestations. Nonetheless, IgAD patients with autoimmune disease showed significantly higher IgG reactivity against pro-inflammatory molecules, such as cardiolipin, oxidized low-density lipoproteins, and phosphatidylserine, with positive correlation between them. In conclusion, the IgG NatAbs against PC may represent a compensatory defense mechanism against infections and control excess of inflammation, explaining the asymptomatic status in the IgA deficiency.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

Vaccination for atherosclerosis

Atherosclerosis is an inflammatory disease, and several antigens have been shown to activate the immune response and affect the development of atherogenesis. This suggests that modulation of the immune system could represent a useful approach to prevent and/or treat this disorder. A vaccination approach might be a useful, effective tool in the modern arsenal of cardiovascular therapy and could possibly be used on a large scale at a low cost. Several modalities of vaccines have been tested against lipoproteins, cholesterol, molecules involved in cholesterol metabolism, atherosclerosis-associated microorganisms, and other molecules (heat shock protein, CD99, vascular endothelial growth factor-receptor, interleukin-2), with promising results. Nevertheless, a deeper understanding of the role of immunization in atherosclerosis will be essential to the use of vaccines in clinical medicine.

High plasma immunoglobulin (Ig) A and low IgG antibody titers to oxidized low-density lipoprotein are associated with markers of glucose metabolism

CONTEXT

Plasma oxidized low-density lipoprotein (OxLDL) is known to be associated with obesity, metabolic syndrome, and diabetes.

OBJECTIVE

The objective of the study was to investigate the association between plasma IgA, IgM, and IgG titers to OxLDL, phosphocholine (PC), and streptococcal cell wall polysaccharide (CWPS) and markers of glucose metabolism, type 2 diabetes, and liver adiposity.

SETTING AND PARTICIPANTS

A population-based cohort of middle-aged Finns (n = 1039) participated in the study.

DESIGN

Plasma IgM, IgG, and IgA to copper oxidized LDL (CuOx-LDL) and malondialdehyde-modified low-density lipoprotein (MDA-LDL), PC, and CWPS were determined with chemiluminescent ELISA and liver adiposity with ultrasonography.

RESULTS

IgA autoantibody titers to OxLDL and PC, but not CWPS, were positively associated with fasting blood glucose and plasma insulin levels and inversely with insulin sensitivity index. IgA to OxLDL was significantly higher (P = 0.013 for CuOx-LDL and P = 0.016 for MDA-LDL) and IgG to OxLDL significantly lower (P = 0.036 for CuOx-LDL and P = 0.001 for MDA-LDL) among the subjects with type 2 diabetes compared with subjects with normal or impaired glucose metabolism when adjusted for age, sex, body mass index, smoking, and alcohol consumption. Logistic regression analysis showed that high plasma IgA to OxLDL and low IgG to MDA-LDL were independent risk factors for type 2 diabetes. Plasma IgA titers to OxLDL demonstrated a significant association with liver adiposity (P = 0.012) and gamma-glutamyltransferase levels (P = 0.002).

CONCLUSIONS

Plasma IgA titers to OxLDL were positively and IgG titers negatively associated with markers of glucose metabolism. High plasma IgA and low IgG to OxLDL were independent risk factors for type 2 diabetes.

The Role of Immune Complexes in Atherogenesis

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis. Immune complexes (ICs) may form between these antigens and autoantibodies and via Fc receptor signaling and complement activation may modulate the inflammation in atherosclerosis. Antibody isotype may direct the role that ICs play in atherogenesis, immunoglobulin G (IgG) being potentially pro-atherogenic and immunoglobulin M (IgM) playing a protective role. Therapeutic options targeting complement activation and those which are potentially Fc-receptor mediated have been investigated in animal models, though targeting Fc receptor signaling is an area that needs further investigation.

Low levels of antibodies against phosphorylcholine predict development of stroke in a population-based study from northern Sweden

BACKGROUND AND PURPOSE

Natural immunoglobulin M antibodies specific for phosphorylcholine (anti-PC) have been implicated in atherosclerosis. We have shown previously that high levels of anti-PC predict a slower progression of atherosclerosis in humans and that low levels of anti-PC are associated with higher risk for cardiovascular disease. Here we determine the association between anti-PC and the incidence of stroke.

METHODS

Using a nested case control study design, we examined 227 incident cases (125 men and 102 women) of first-time stroke and 455 age- and sex-matched controls identified during a 13-year time period (1985 to 1999) within the population-based cohorts of the Västerbotten Intervention Project (VIP) and the World Health Organization Monitoring Trends and Determinants in Cardiovascular Disease (WHO MONICA) project in Northern Sweden. Odds ratios of stroke with 95% CIs with adjustments for age, gender, smoking, serum cholesterol, diabetes, body mass index, and blood pressure were determined. Anti-PC levels were measured using ELISA.

RESULTS

A significant association between low levels of anti-PC at baseline and incident stroke was seen for the whole group of anti-PC levels below the 30th percentile (multivariately adjusted odds ratio, 1.62; CI, 1.11 to 2.35). Analyses of gender-specific associations indicated fairly strong associations for females, especially at the lowest 30th percentile (multivariately adjusted odds ratio, 2.65; CI, 1.41 to 4.95). No associations were noted for men.

CONCLUSION

Low anti-PC is a novel independent risk marker for development of stroke. Measurements of anti-PC could be used to identify immunodeficient subjects at an increased risk for stroke. The possibility that such subjects might be targets for novel modes of treatment such as immunotherapies deserves further investigation.

Management of cardiovascular complications in systemic lupus erythematosus

Cardiovascular disease (CVD) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Patients with SLE have an excess risk compared with the general population; this is particularly pronounced in younger women with SLE who have an excess risk of over 50-fold compared with population controls. There is a higher prevalence of subclinical atherosclerosis in patients with SLE compared with controls, as demonstrated by a variety of imaging modalities discussed in this review. The causality of the excess risk of CVD and subclinical atherosclerosis is multifactorial in patients with SLE. While traditional risk factors play a role, after controlling for the traditional Framingham risk factors, the excess risk is still 7.5-fold greater than the general population. This review will also cover novel cardiovascular risk factors and some SLE-specific variables that contribute to CVD risk. This review discusses the risk factor modification and the evidence available for treatment of these risk factors in SLE. There have not yet been any published randomized, controlled trials in patients with SLE with respect to CVD risk factor modifications. Thus, the treatment and management recommendations are based largely on published guidelines for other populations at high risk for CVD.

Vaccination, atherosclerosis and systemic lupus erythematosus

Atherosclerosis is an inflammatory disease, leading to the formation of pro-inflammatory and pro-oxidative lipids that generate an immune response. Several antigens have been shown to activate the immune response and affect the development of atherogenesis. Systemic lupus erythematosus is an autoimmune and inflammatory disease strongly associated with premature development of atherosclerotic plaques. Modulation of the immune system could represent a useful approach to prevent and/or treat atherosclerosis. A vaccination-based approach might be a useful, effective tool in the modern arsenal of cardiovascular therapies and could be used on a large scale at a low cost. In non-systemic lupus erythematosus populations, vaccines against oxidized low-density lipoprotein, beta-2-glycoprotein I, heat shock proteins, lipoproteins, cholesterol, molecules involved in cholesterol metabolism, and other molecules (CD99, vascular endothelial growth factor-receptor, and interleukin-2) have been tested, with promising results. However, there are no studies of vaccination against atherosclerosis in systemic lupus erythematosus.

Natural antibodies against phosphorylcholine in cardiovascular disease

Atherosclerosis is a chronic inflammatory disease characterized by the presence of activated immune-competent cells in the lesions, producing mainly proinflammatory cytokines. Atherosclerosis is the underlying cause of cardiovascular disease (CVD), to a large extent occurring after damage and/or rupture of the atherosclerotic plaques. One major factor implicated as a cause of this immune activation is modified low-density lipoproteins (LDL), especially oxidized forms (oxLDL), which are abundant in plaques, both in foam cells and in the necrotic core. The LDL-oxidation process is very complex, and the nature of the antigens has been difficult to identify. We and others have focused on the phospholipids (PL) in oxLDL, especially oxidized forms of PL, including platelet-activating factor (PAF)-like lipids and lysophosphatidylcholine (LPC), and demonstrated that these could play a major role through proinflammatory effects. One common epitope is phosphorylcholine (PC), which is also exposed on some microorganisms (including Streptococcus pneumoneae) and on apoptotic cells. Natural IgM antibodies against PC (anti-PC) have been known for a long time, but little has been reported about their role in human disease, especially in CVD. We have demonstrated that anti-PC IgM are negatively associated with atherosclerosis development in hypertensive individuals and that low levels of anti-PC independently predict development of CVD. Anti-PC IgM could, therefore, be a novel risk marker in CVD. Animal experiments indicate that both active immunization with PC and passive immunization with anti-PC ameliorate atherosclerosis development. The possibility that anti-PC could be used therapeutically in humans deserves further study.

Antitreponemal antibodies leading to autoantibody production and protection from atherosclerosis in Kitavans from Papua New Guinea

The objective of our study was to determine the prevalence of anti-infectious agent antibodies and autoantibodies in a unique non-Westernized population from Kitava, Papua New Guinea (PNG), compared to Western populations. We matched 120 serum samples from Kitavans with 437 samples from four healthy control groups. Sera were tested for the presence of anti-infectious agent antibodies (treponema, toxoplsmosis, Epstein-Barr virus, cytomegalovirus, rubella) and autoantiobodies [anti-double-stranded (ds)DNA, anti-chromatin, anti-ribonucleoprotein (RNP), anti-SSB, anti-SSA, anti-Scl-70, anti-Smith, anti-centromer, anti-SmRNP, anti-Jo-1, and anti-ribosomal-P] using the Bio-Rad BioPlex 2200. Antitreponemal antibodies were detected in 87% of PNG sera versus 0-6% of controls (P < 0.0001). Anti-dsDNA antibodies were detected in 31% of PNG samples, which was significantly higher than in three of the control groups (<10%). The outstanding high rate of antitreponemal antibodies detected in Kitavans possibly represents prior yaws disease. A low prevalence of cardiovascular disease was previously documented in Kitavans and has been attributed, in addition to their diet, to the high prevalence of natural cardioprotective autoantibodies (the IgM-antiphosphorylcholine antibodies) in this population. Treponemal infection has been shown to induce the appearance of antiphosphorylcholine antibodies. These protective autoantibodies may cross-react with the pathogenic anti-dsDNA antibodies. Thus, it is suggested that infection with treponema is associated with the presence of protective as well as pathogenic autoantibodies.

Intravenous immunoglobulins in systemic lupus erythematosus: from the bench to the bedside

This article is an update on the clinical and research data available on systemic lupus erythematosus (SLE) and intravenous immunoglobulin (IVIg) therapy that includes some studies performed under the umbrella of the European Working Party on SLE. Various mechanisms of IVIg may play a role, some synergistically, in the modulation of SLE. Recently it has been suggested that IVIg also suppresses the expansion of autoreactive B lymphocytes through signalling of the FcgRIIB, idiotype-mediated inhibition of B cell receptors and neutralisation of cytokines such as the B cell survival factors (B cell activation factor (BAFF and APRIL). In case reports and in open trials, high-dose IVIg (2 g/kg over a 5-day period) has consistently been shown to be a beneficial and safe adjunct therapeutic agent for over 20 manifestations in patients with SLE. It can be given as a first choice of therapy in some cases, for example, in neurological involvement and in those patients who refuse certain immunosuppressive agents such as cyclophosphamide, or in patients who have concomitant infections. Furthermore, IVIg may have a steroid-sparing effect although this characteristic needs further investigation. Specific IVIg (an anti-idiotype to anti-DNA, phosphorylcholine and antiphospholipids) has been shown to be effective in experimental murine models. Hence, extractable IVIg that is directed to the specific pathogenic immunoglobulins will enable the more specific therapy for patients with lupus.

Low levels of IgM antibodies against phosphorylcholine predict development of acute myocardial infarction in a population-based cohort from northern Sweden

OBJECTIVE

Phosphorylcholine (PC) is one important epitope on oxidized low-density lipoprotein that may play an important role by contributing to the atherogenicity of oxidized low-density lipoprotein. IgM antibodies against PC (anti-PC) are present ubiquitously in the population as natural antibodies. We here determine the association between anti-PC and incidence of myocardial infarction (MI).

METHODS

We studied 462 incident cases of first events of MI and 888 age-matched and sex-matched controls identified through 13 years of follow-up (1987-1999) of participants in a population-based study from northern Sweden. Relative risks (RRs) with 95% confidence intervals (CIs) of incident MI with adjustments for age, sex, geographical region, hypertension, diabetes, BMI, smoking habits, s-cholesterol and high-sensitivity C-reactive protein were determined. Anti-PC levels were measured by enzyme-linked immunoassay.

RESULTS

Low anti-PC values were associated with increased risk of MI. Significant associations were found for values below 26.8 U/ml, corresponding to the lowest 25th percentile, and the highest association was seen below 16.9 U/ml. These results remained almost the same after adjustment for confounding factors (RR crude: 1.56, CI: 1.07-2.28 and RR adjusted: 1.69, CI: 1.09-2.54).

CONCLUSION

Low levels of natural IgM anti-PC could play an important role as risk markers for development of MI. Adjustment for common confounders only marginally affected the RR, suggesting that the addition of IgM anti-PC add independent information to the more traditional risk factors.

Low level natural antibodies against phosphorylcholine: a novel risk marker and potential mechanism in atherosclerosis and cardiovascular disease

Atherosclerosis is an inflammatory condition characterised by an abundance of activated immunocompetent cells in plaques which cause cardiovascular disease (CVD) when they rupture. Oxidized forms of low density lipoprotein (OxLDL) are a major constituent of atherosclerotic plaques and have proinflammatory effects, making oxLDL a candidate factor promoting atherosclerosis. In previous studies we and others demonstrated that platelet-activating factor (PAF)-like lipids in oxLDL may cause oxLDL-induced immune-stimulatory effects. A common denominator is phosphorylcholine (PC), a hapten-like epitope which is exposed on OxLDL and some microorganisms. We recently demonstrated that anti-PC has anti-inflammatory properties and that low levels of anti-PC predict the development of stroke and myocardial infarction. We hypothesize that low anti-PC represents a novel paradigm as a cause of chronic inflammatory diseases such as atherosclerosis where oxidized and/or inflammatory phospholipids play a role. It is possible that anti-PC can be used as a novel diagnostic tool and therapy in atherosclerotic disease.

Low levels of IgM antibodies to phosphorylcholine predict cardiovascular disease in 60-year old men: effects on uptake of oxidized LDL in macrophages as a potential mechanism

OBJECTIVE

We here determine the role of IgM antibodies against phosphorylcholine (anti-PC) in prediction of cardiovascular disease (CVD) and on macrophage uptake of Oxidized LDL (OxLDL).

METHODS

From a screening of 4232 subjects, 60-year-old (2039 men and 2193 women), 211 incident cases of CVD (myocardial infarction, ischemic stroke, or hospitalized angina pectoris) and 633 age- and sex-matched controls were identified through a 5-7 year follow-up. Serum levels of IgM anti-PC was determined by ELISA. Anti-PC was extracted from pooled human IgM and the effect of anti-PC on the uptake of OxLDL was studied by FACScan.

RESULTS

Relative risks (RR) with 95% confidence intervals (CI) by quartiles of anti-PC levels with quartile 4 set as the reference value (RR = 1.0) and adjusted for smoking, BMI, type II diabetes, hypercholesterolaemia, and high blood pressure yielded an excess risk for CVD only for those within the lowest quartile of anti-PC values with an RR of 1.37 (CI 0.87-2.16). However, for men stronger associations were noted with increasing multivariately adjusted RRs from quartile 4 to quartile 1. Subjects within quartile 1 (values below 29.7 U/ml) had a significantly increased RR of 1.96 (CI 1.09-3.55). Further adjustments for hsCRP gave essentially the same results. No excess risk was noted for women. Specific anti-PC could be extracted from IgM and these antibodies inhibited macrophage uptake of OxLDL.

CONCLUSIONS

Low IgM anti-PC could be a novel risk marker for CVD among men. One possible mechanism could be inhibition of uptake of oxLDL in macrophages.

Immunoglobulin M is required for protection against atherosclerosis in low-density lipoprotein receptor-deficient mice

BACKGROUND

Immunoglobulin M (IgM) natural antibodies bind oxidatively-modified low-density lipoprotein (LDL) and apoptotic cells and have been implicated as being important for protection against atherosclerosis. We have directly investigated the requirement for IgM by studying the effects of IgM deficiency in LDL receptor-deficient (Ldlr(-/-)) mice.

METHODS AND RESULTS

Mice deficient in serum IgM (sIgM) or complement C1q were crossed with Ldlr(-/-) mice and studied on both low-fat and high-fat semisynthetic diets. On both diets, en face and aortic root atherosclerotic lesions in sIgM.Ldlr(-/-) mice were substantially larger and more complex, with accelerated cholesterol crystal formation and increased smooth muscle cell content in aortic root lesions. Combined C1q and IgM deficiency had the same effect as IgM deficiency alone. Increased apoptosis was observed in aortic root lesions of both sIgM.Ldlr(-/-) and C1qa.Ldlr(-/-) mice. Because lesions were significantly larger in IgM-deficient mice than in the absence of C1q, IgM protective mechanisms appear to be partially independent of classical pathway activation and apoptotic cell clearance. Levels of IgG antibodies against copper-oxidized LDL were lower in sIgM.Ldlr(-/-) mice fed a high-fat diet, suggesting compensatory consumption of IgG in the absence of IgM.

CONCLUSIONS

This study provides direct evidence that IgM antibodies play a central role in protection against atherosclerosis. The mechanism appears to be at least partly independent of classical pathway complement activation by C1q.

Early atherosclerosis and IgG2 to bacteria are associated with FcgammaRIIa genotype in non-smokers

BACKGROUND

Involvement of low density lipoprotein (LDL) immune complexes (ICs) in atherogenesis has been proposed. Human FcgammaRIIa receptor (CD32) plays a crucial role in the phagocytosis of IgG(2) ICs and a functional point mutation 131His/Arg diminishes IgG(2) binding to the receptor.

STUDY DESIGN

We examined FcgammaRIIa-131His/Arg polymorphism, IgG(2) antibody titres to oxidized low-density lipoprotein (OxLDL) and Streptococcus pneumoniae cell wall polysaccharide (CWPS) and subclinical atherosclerosis in a large cohort of Finnish subjects (n = 1041).

RESULTS

Non-smoking subjects with homozygous 131His/His genotype had more premature atherosclerosis (P = 0.004) and higher IgG(2) to bacterial CWPS (P = 0.002) compared with other genotypes. Smoking subjects had significantly higher intima-media thickness (IMT) than that of non-smokers (P < 0.001) and genotype-dependent associations were indistinct. There was no association between FcgammaRIIa genotype and antibody titres to OxLDL.

CONCLUSIONS

Our data demonstrate that FcgammaRIIa 131His/Arg polymorphism is associated with subclinical atherosclerosis in non-smoking subjects. Furthermore, FcgammaRIIa genotype is associated with IgG(2) titres to bacterial CWPS, but not to OxLDL. These data propose possible involvement of FcgammaRIIa receptor in atherogenesis.

Clinical significance of the humoral immune response to modified LDL

Human low density lipoprotein (LDL) undergoes oxidation and glycation in vivo. By themselves, oxidized LDL (oxLDL) and AGE-LDL have proinflammatory properties and are considered atherogenic. But the atherogenicity of these lipoproteins are significantly increased as a consequence of the formation of immune complexes (IC) involving specific autoantibodies. OxLDL and AGE antibodies have been shown to be predominantly of the IgG1 and IgG3 isotypes. OxLDL antibodies are able to activate the complement system by the classical pathway and to induce FcR-mediated phagocytosis. In vitro and ex vivo studies performed with modified LDL-IC have proven their pro-inflammatory and atherogenic properties. Clinical studies have demonstrated that the levels of circulating modified LDL-IC correlate with parameters indicative of cardiovascular and renal disease in diabetic patients and other patient populations. The possibility that spontaneously formed or induced modified LDL antibodies (particularly IgM oxLDL antibodies) may have a protective effect has been suggested, but the data is unclear and needs to be further investigated.

Relationship of oxidized phospholipids on apolipoprotein B-100 particles to race/ethnicity, apolipoprotein(a) isoform size, and cardiovascular risk factors: results from the Dallas Heart Study

BACKGROUND

Elevated levels of oxidized phospholipids (OxPLs) on apolipoprotein B-100 particles (OxPL/apoB) are associated with cardiovascular disease and predict new cardiovascular events. Elevated lipoprotein (a) [Lp(a)] levels are a risk factor for cardiovascular disease in whites and also in blacks if they carry small apolipoprotein(a) [apo(a)] isoforms. The relationship of OxPL/apoB levels to race/ethnicity, cardiovascular risk factors, and apo(a) isoforms is not established.

METHODS AND RESULTS

OxPL/apoB levels were measured in 3481 subjects (1831 black, 1047 white, and 603 Hispanic subjects) in the Dallas Heart Study and correlated with age, sex, cardiovascular risk factors, and Lp(a) and apo(a) isoforms. Significant differences in OxPL/apoB levels were noted among racial/ethnic subgroups, with blacks having the highest levels compared with whites and Hispanics (P<0.001 for each comparison). OxPL/apoB levels generally did not correlate with age, sex, or risk factors. In the overall cohort, OxPL/apoB levels strongly correlated with Lp(a) (r=0.85, P<0.001), with the shape of the relationship demonstrating a "reverse L" shape for log-transformed values. The highest correlation was present in blacks, followed by whites and Hispanics; was dependent on apo(a) isoform size; and became progressively weaker with larger isoforms. The size of the major apo(a) isoform (number of kringle type IV repeats) was negatively associated with OxPL/apoB (r=-0.49, P<0.001) and Lp(a) (r=-0.61, P<0.001) regardless of racial/ethnic group. After adjustment for apo(a) isoform size, the relationship between OxPL/apoB and Lp(a) remained significant (r=0.67, P<0.001).

CONCLUSIONS

OxPL/apoB levels vary according to race/ethnicity, are largely independent of cardiovascular risk factors, and are inversely associated with apo(a) isoform size. The association of OxPL with small apo(a) isoforms, in which a similar relationship is present among all racial/ethnic subgroups despite differences in Lp(a) levels, may be a key determinant of cardiovascular risk.

Rheumatoid cachexia is associated with dyslipidemia and low levels of atheroprotective natural antibodies against phosphorylcholine but not with dietary fat in patients with rheumatoid arthritis: a cross-sectional study

INTRODUCTION

Patients with rheumatoid arthritis (RA) have an increased risk for cardiovascular disease (CVD) independent of traditional risk factors. The aim of this study was to analyze the associations between diet, body composition, lipids and atheroprotective natural antibodies against phosphorylcholine (anti-PC) in patients with RA.

METHODS

A total of 80 RA patients (76% women), mean age (standard deviation (SD)) 61.4 (12) years and median disease duration of 6 years, were assessed by food frequency questionnaire (FFQ), fatty acid profile in adipose tissue and whole-body dual energy x ray absorptiometry (DXA). Rheumatoid cachexia was defined as fat free mass index below the 25th percentile and fat mass index above the 50th percentile of a reference population. Blood lipids, oxidized low-density lipoprotein (oxLDL) and anti-PC levels were determined.

RESULTS

The mean body mass index for the women and men was 25.0 and 27.0, respectively. Central obesity was found in 57% of the women (waist circumference >80 cm) and in 89% of the men (waist circumference >94 cm). In all, 18% of the women and 26% of the men had rheumatoid cachexia. These patients had significantly higher total cholesterol (P < 0.033), LDL (P < 0.029), and trendwise oxLDL (P = 0.056) as well as lower anti-PC IgM (P = 0.040), higher frequency of hypertension (69%) and metabolic syndrome (25%) than those without. The patients reported a high dietary intake of saturated fat, which partly correlated with fatty acid composition in adipose tissue and significantly with disease activity. However, patients with or without cachexia did not differ with respect to dietary fat intake or intake of Mediterranean-like diet. Additionally, patients on a Mediterranean-like diet had high levels of anti-PC (P < 0.001).

CONCLUSIONS

About one in five patients with low-active RA displayed rheumatoid cachexia. This condition was associated with high levels of LDL cholesterol, low levels of atheroprotective anti-PC and high frequency of hypertension, which is of interest in the context of CVD in RA. The cachexia could not be related to diet fat intake. However, patients on a Mediterranean-like diet had high anti-PC levels in spite of similar frequency of cachexia. High anti-PC levels may provide some protection against CVD.

Anti-(apolipoprotein A-1) IgGs are associated with high levels of oxidized low-density lipoprotein in acute coronary syndrome

ApoA-1 (apolipoprotein A-1) is the main component of HDL (high-density lipoprotein) and stabilizes PON-1 (paraoxonase-1), which prevents lipid peroxidation and oxLDL (oxidized low-density lipoprotein) formation. Autoantibodies against apoA-1 [anti-(apoA-1) IgG] have been found in antiphospholipid syndrome and systemic lupus erythematosous, two diseases with an increased risk of thrombotic events, as well as in ACS (acute coronary syndrome). OxLDL levels are also elevated in these diseases. Whether anti-(apoA-1) IgGs exist in other prothrombotic conditions, such as APE (acute pulmonary embolism) and stroke, has not been studied and their potential association with oxLDL and PON-1 activity is not known. In the present study, we determined prospectively the prevalence of anti-(apoA-1) IgG in patients with ACS (n=127), APE (n=58) and stroke (n=34), and, when present, we tested their association with oxLDL levels. The prevalance of anti-(apoA-1) IgG was 11% in the ACS group, 2% in the control group and 0% in the APE and stroke groups. The ACS group had significantly higher median anti-(apoA-1) IgG titres than the other groups of patients. Patients with ACS positive for anti-(apoA-1) IgG had significantly higher median oxLDL values than those who tested negative (226.5 compared with 47.7 units/l; P<0.00001) and controls. The Spearman ranked test revealed a significant correlation between anti-(apoA-1) IgG titres and serum oxLDL levels (r=0.28, P<0.05). No association was found between PON-1 activity and oxLDL or anti-(apoA-1) IgG levels. In conclusion, anti-(apoA-1) IgG levels are positive in ACS, but not in stroke or APE. In ACS, their presence is associated with higher levels of oxLDL and is directly proportional to the serum concentration of oxLDL. These results emphasize the role of humoral autoimmunity as a mediator of inflammation and coronary atherogenesis.

Naturally occurring auto-antibodies in homeostasis and disease

Antibodies with germline or close to germline configuration exist in vertebrates, and these so-called 'naturally occurring auto-antibodies' (NAb) are directed to self and altered self components. Such NAbs have been attracting increasing interest because several of them, including some in their recombinant forms, have therapeutic potential. Whereas a large number of IgM and IgG NAbs have tissue homeostatic roles, others modulate and regulate cellular and enzyme properties. This review describes some of these NAbs and emphasizes how these low-titer, low-affinity NAbs interact with self and altered self and show functional potency in homeostasis and regulation, in addition to in diseases such as infarction and systemic inflammatory response syndrome.

Systemic lupus erythematosus and cardiovascular disease

Atherosclerosis is an inflammatory disease characterised by presence of activated immune competent cells in middle-sized and large arteries and is the major cause of cardiovascular disease (CVD). The risk of CVD is very high in systemic lupus erythematosus (SLE). SLE-related CVD and atherosclerosis are, therefore, important clinical problems but may in addition also have implications for the role of immune reactions in CVD in general. Others and we have recently demonstrated that risk factors for CVD in SLE are both traditional and non-traditional acting in concert. Traditional risk factors implicated in SLE include, for example, dyslipidemia (especially high triglycerides), hypertension, renal disease, non-traditional as inflammation, antiphospholipid antibodies (aPL) and low-density lipoprotein (LDL) oxidation are also associated with CVD in SLE. Atherothrombosis is likely to be a major underlying mechanism and is not only an increased risk of thrombosis per se. It is possible that factors like proinflammatory reactions or prothrombotic factors, such as aPL, make atherosclerotic lesions in SLE more prone to rupture than in 'normal' atherosclerosis. Whether premature atherosclerosis is a general feature of SLE or only affects a subgroup of patients is presently not clear. Treatment of patients with SLE should include a close monitoring of traditional risk factors and also the above-mentioned non-traditional for CVD.

Low levels of IgM antibodies against phosphorylcholine-A potential risk marker for ischemic stroke in men

BACKGROUND

Natural antibodies specific for phosphorylcholine (anti-PC) have been implicated as protective factors in atherosclerosis. We herein determined the relationship between IgM anti-PC and incidence of cardiovascular disease (CVD).

METHODS

We studied 349 incident cases (200 men) of first events of CVD (coronary heart disease (CHD; n=203 or ischemic stroke; n=146) and 693 age- and sex-matched controls identified through 12 years of follow-up (1991-2003) of subjects from the cardiovascular cohort within the Malmö Diet and Cancer Study. Relative risks (RR) of CVD with 95% confidence intervals (CI) of incident CVD with adjustments for age, smoking, total cholesterol and blood pressure were determined. Anti-PC-levels were measured using ELISA (Athera CVDefine).

RESULTS

As determined using Athera CVDefine, significant associations were attained with values of anti-PC below 17U/ml (corresponding to the lowest 9th percentile), which remained after taking confounders into account (RR: 1.79, 95% CI: 1.09-2.94, p=0.021). If men were studied separately, significance was evident at values below 17U/ml (RR: 2.01, 95% CI: 1.11-3.67, p=0.022), which was not the case among women. Furthermore, values below 17U/ml were also associated with ischemic stroke (RR=3.67, 95% CI: 1.34-10.1, p=0.01), but not with CHD.

CONCLUSION

Low IgM anti-PC could be a novel risk marker for development of ischemic stroke in men. Further studies are needed to establish gender and subgroup differences.

Ethnic variation in levels of circulating IgG autoantibodies to oxidised low-density lipoprotein

BACKGROUND

Oxidised low-density lipoprotein (Ox-LDL) plays a key role in atherosclerosis. Our aim was to determine whether serum autoantibodies against Ox-LDL (Ab Ox-LDL) differ by ethnic group.

DESIGN AND METHODS

Soluble serum Ab Ox-LDL levels were measured in 250 white (113 females), 169 African origin (91 females) and 196 South Asian (92 females) individuals from the Wandsworth Heart and Stroke Study (WHSS) population. All were free from coronary heart disease (CHD), stroke, other cardiovascular disease, diabetes, drug therapy for hypertension or high lipids, hormone replacement therapy or oral contraceptive pill.

RESULTS

There were no sex differences in levels of Ab Ox-LDL, but levels were higher in non-smokers (430U/L [95% CI 471-596]) than in smokers (384U/L [316-468]) (p<0.009). Age- and sex-adjusted levels of Ab Ox-LDL were higher in people of African origin and South Asians compared to whites. This difference was maintained in South Asian women following adjustment for multiple risk factors (82% [21-175]; p=0.004). Ab Ox-LDL levels were negatively associated with serum triglycerides and positively associated with sVCAM-1.

CONCLUSIONS

Higher IgG Ab to Ox-LDL are associated with higher levels of sVCAM-1 and, are elevated in female South Asian individuals who have an increased risk of atherosclerosis compared to whites.

Atherosclerosis and systemic lupus erythematosus: the role of altered lipids and of autoantibodies

The accelerated atherosclerosis that occurs in some patients with systemic lupus erythematosus (SLE) has a complex pathogenesis, including alterations in lipids, inflammation and the immune system. In this article, we review the evidence that peroxidase-related alteration of normal, protective high-density lipoprotein (HDL) converts them to pro-inflammatory HDL (piHDL), characterized by lower content of the cholesterol transport lipoprotein ApoA1 and impaired function of the antioxidant enzyme paroxonase, which prevents oxidation of low-density lipoprotein (LDL). Forty-five per cent of women with SLE have piHDL compared with 20% of patients with rheumatoid arthritis and 4% of healthy controls. The presence of piHDL increases risk for coronary artery events and carotid artery plaque. Another result of lipid oxidation in patients with SLE is generation of highly oxidized LDL and phospholipids (PL), probably stimulating antibodies to OxPL phospholipids. These antibodies along with promoting thrombosis also interfere with deposits of Annexin V onto endothelial cells, which probably promote increased instability of atherosclerotic plaque. Thus, piHDL and anti-OxPL promote plaque formation, plaque instability and thrombosis, accounting for some of the large increase in atherosclerosis and coronary artery events in SLE.

Atherogenesis and the humoral immune response to modified lipoproteins

Modified forms of LDL are immunogenic and activate both cell-mediated and humoral immune responses. Both types of responses are pro-inflammatory and are probably primary players in the perpetuation of the chronic inflammatory reaction characteristic of atherosclerosis. The immunologic response to modified LDL can be directed to MHC-II-associated peptides in the case of T helper cells, and to a variety of epitopes-modified lysine groups, modified phospholipids, proteins that become associated with oxidized LDL (such as beta2GP1)--in the case of B cell responses. T cell activation is likely to play a major role through cross-activation of macrophages. Humoral responses to modified LDL are pathogenic as a consequence of the formation of antigen-antibody complexes containing modified LDL and IgG antibodies. Those immune complexes induce cholesterol ester accumulation in macrophages and macrophage-like cells, and induce the release of pro-inflammatory cytokines, chemokines, oxygen active radicals, and matrix metalloproteinases from those cells. There is no conclusive evidence supporting a protective role for IgM antibodies in humans, possibly because autoantibodies to modified lipoproteins are predominantly of the IgG isotype.

Gluten-free vegan diet induces decreased LDL and oxidized LDL levels and raised atheroprotective natural antibodies against phosphorylcholine in patients with rheumatoid arthritis: a randomized study

Introduction

The purpose of this study was to investigate the effects of vegan diet in patients with rheumatoid arthritis (RA) on blood lipids oxidized low-density lipoprotein (oxLDL) and natural atheroprotective antibodies against phosphorylcholine (anti-PCs).

Methods

Sixty-six patients with active RA were randomly assigned to either a vegan diet free of gluten (38 patients) or a well-balanced non-vegan diet (28 patients) for 1 year. Thirty patients in the vegan group completed more than 3 months on the diet regimen. Blood lipids were analyzed by routine methods, and oxLDL and anti-PCs were analyzed by enzyme-linked immunosorbent assay. Data and serum samples were obtained at baseline and after 3 and 12 months.

Results

Mean ages were 50.0 years for the vegan group and 50.8 years for controls. Gluten-free vegan diet induced lower body mass index (BMI) and low-density lipoprotein (LDL) and higher anti-PC IgM than control diet (p < 0.005). In the vegan group, BMI, LDL, and cholesterol decreased after both 3 and 12 months (p < 0.01) and oxLDL after 3 months (p = 0.021) and trendwise after 12 months (p = 0.090). Triglycerides and high-density lipoprotein did not change. IgA anti-PC levels increased after 3 months (p = 0.027) and IgM anti-PC levels increased trendwise after 12 months (p = 0.057). There was no difference in IgG anti-PC levels. In the control diet group, IgM anti-PC levels decreased both after 3 and 12 months (p < 0.01). When separating vegan patients into clinical responders and non-responders at 12 months, the effects on oxLDL and anti-PC IgA were seen only in responders (p < 0.05).

Conclusion

A gluten-free vegan diet in RA induces changes that are potentially atheroprotective and anti-inflammatory, including decreased LDL and oxLDL levels and raised anti-PC IgM and IgA levels.

OxLDL/beta2GPI-anti-oxLDL/beta2GPI complex and atherosclerosis in SLE patients

It has been demonstrated that atherosclerosis (ATS) is enhanced in autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE). The reason for this accelerated process is still debatable and, although traditional risk factors are more prevalent in SLE patients than in general population, they do not seem to fully explain the enhanced risk. ATS has the characteristics of an autoimmune chronic disease, involving both the innate and the adaptive immunity. Moreover, it satisfies the four criteria defining an autoimmune disease, proposed by Witebsky and Rose. It has been shown that some autoantibodies, including anti-oxLDL, anti-beta(2)GPI, anti-HSP60/65, and more recently anti-oxLDL/beta(2)GPI, play a key role in the pathogenesis of ATS. However the role of these autoantibodies in accelerated ATS in SLE patients is still controversial. In fact, some of them seem to be proatherogenic and other protective; moreover, it has been demonstrated that induced oral tolerance has a protective role against ATS. We have recently observed that the levels of oxLDL/beta(2)GPI antigenic complexes and their antibodies were higher in patients with SLE than in healthy subjects, but we did not find a clear association between oxLDL/beta(2)GPI complexes and IgG or IgM anti-oxLDL/beta(2)GPI autoantibodies and subclinical ATS in SLE patients. Many other studies are required to explain the role of autoantibodies in the pathogenesis of ATS in SLE patients, because the characteristics of SLE seem to mask their effects for atherogenesis.

Newborn humans manifest autoantibodies to defined self molecules detected by antigen microarray informatics

Autoimmune diseases are often marked by autoantibodies binding to self antigens. However, many healthy persons also manifest autoantibodies that bind to self antigens, known as natural autoantibodies. In order to characterize natural autoantibodies present at birth, we used an antigen microarray (antigen chip) to analyze informatically (with clustering algorithms and correlation mapping) the natural IgM, IgA, and IgG autoantibody repertoires present in 10 pairs of sera from healthy mothers and the cords of their newborn babies. These autoantibodies were found to bind to 305 different, mostly self, molecules. We report that in utero, humans develop IgM and IgA autoantibodies to relatively uniform sets of self molecules. The global patterns of maternal IgM autoantibodies significantly diverged from those at birth, although certain reactivities remained common to both maternal and cord samples. Because maternal IgG antibodies (unlike IgM and IgA) cross the placenta, maternal and cord IgG autoantibodies showed essentially identical reactivities. We found that some self antigens that bind cord autoantibodies were among the target self antigens associated with autoimmune diseases later in life. Thus, the obviously benign autoimmunity prevalent at birth may provide the basis for the emergence of some autoimmune diseases relatively prevalent later in life.

Atheroprotective natural anti-phosphorylcholine antibodies of IgM subclass are decreased in Swedish controls as compared to non-westernized individuals from New Guinea

Objective

To determine the importance of IgM antibodies against phosphorylcholine (aPC), a novel protective factor for cardiovascular disease (CVD), in a population with a non-western life style as compared with a Swedish control group.

Methods and results

Risk factors for cardiovascular disease were determined in a group of 108 individuals aged 40–86 years from New Guinea and 108 age-and sex-matched individuals from a population based study in Sweden. Antibodies were tested by ELISA. aPC IgM levels were significantly higher among New Guineans than among Swedish controls (p < 0.0001). This difference remained significant among both men and women when controlled for LDL and blood pressure which were lower and smoking which was more prevalent in New Guineans as compared to Swedish controls (p < 0.0001). aPC IgM was significantly and negatively associated with age and systolic blood pressure among Swedish controls and with waist circumference among New Guineans. aPC IgM levels were significantly higher among women than men in both groups. The proportion of the saturated fatty acid (FA) myristic acid in serum cholesterol esters was negatively but polyunsaturated eicosapentaenoic acid and also lipoprotein (a) were positively associated with aPC IgM levels.

Conclusion

IgM-antibodies against PC, which have atheroprotective properties, are higher in a population from Kitava, New Guinea with a traditional lifestyle, than in Swedish Controls, and higher among women than men in both populations tested. Such antibodies could contribute to the low incidence of cardiovascular disease reported from Kitava and could also provide an explanation as to why women have a later onset of CVD than men.