Antibodies against Phosphorylcholine among New Guineans Compared to Swedes: An Aspect of the Hygiene/Missing Old Friends Hypothesis

Total adiponectin in indigenous Melanesians on Kitava

OBJECTIVES

Experimental and small human studies have indicated that high total adiponectin levels have beneficial cardiometabolic effects. In contrast, however, high total adiponectin levels are also associated with higher all-cause and cardiovascular mortality in thoroughly adjusted epidemiological studies. To gain further insight into these seemingly contradictory results, we report results on total adiponectin from the indigenous Melanesian population of Kitava, Trobriand Islands, Papua New Guinea, where an apparent absence of cardiometabolic disease has been previously reported.

METHODS

Fasting levels of serum total adiponectin were measured cross-sectionally in ≥40-year-old Kitavans (n = 102) and Swedish controls matched for age and sex (n = 108). Multivariable linear regression was used for the analysis of associations with total adiponectin when controlled for group, sex, smoking, hypertension and/or type 2 diabetes, age, and body mass index.

RESULTS

Total adiponectin was lower for Kitavans compared to Swedish controls (Median [Mdn] 4.6 μg/mL, range 1.0-206 μg/mL and Mdn 9.7 μg/mL, range 3.1-104 μg/mL, respectively, r = .64, p < .001). Lower total adiponectin was associated with Kitavan group, male sex (only in Swedish controls), smoking (only in Kitavans and Swedish controls combined), younger age (not in Swedish controls), higher BMI, lower total, low-density lipoprotein, high-density lipoprotein (HDL) (only in Kitavans and Swedish controls combined), and non-HDL cholesterol, and higher anti-PC IgG (only in Kitavans and Swedish controls combined).

CONCLUSION

Total adiponectin in Kitavans was significantly lower than in Swedish controls.

Systemic lupus erythematosus and cardiovascular disease

The prognosis in systemic lupus erythematosus (SLE) has improved due to better treatment and care, but cardiovascular disease (CVD) still remains an important clinical problem, since the risk of CVD in SLE is much higher than among controls. Atherosclerosis is the main cause of CVD in the general population, and in SLE, increased atherosclerosis, especially the prevalence of atherosclerotic plaques, has been demonstrated. Atherosclerosis is an inflammatory condition, where immunity plays an important role. Interestingly, oxidized low-density lipoprotein, defective clearance of dead cells, and inflammation, with a pro-inflammatory T-cell profile are characteristics of both atherosclerosis and SLE. In addition to atherosclerosis as an underlying cause of CVD in SLE, there are also other non-mutually exclusive mechanisms, and the most important of these are antiphospholipid antibodies (aPL) leading to the antiphospholipid antibody syndrome with both arterial and venous thrombosis. aPL can cause direct pro-inflammatory and prothrombotic effects on endothelial and other cells and also interfere with the coagulation, for example, by inhibiting annexin A5 from its antithrombotic and protective effects. Antibodies against phosphorylcholine (anti-PC) and other small lipid-related epitopes, sometimes called natural antibodies, are negatively associated with CVD and atherosclerosis in SLE. Taken together, a combination of traditional risk factors such as hypertension and dyslipidemia, and nontraditional ones, especially aPL, inflammation, and low anti-PC are implicated in the increased risk of CVD in SLE. Close monitoring of both traditional risk factors and nontraditional ones, including treatment of disease manifestations, not lest renal disease in SLE, is warranted.

Antibodies in action: the role of humoral immunity in the fight against atherosclerosis

The sequestering of oxidation-modified low-density lipoprotein by macrophages results in the accumulation of fatty deposits within the walls of arteries. Necrosis of these cells causes a release of intercellular epitopes and the activation of the adaptive immune system, which we predict leads to robust autoantibody production. T cells produce cytokines that act in the plaque environment and further stimulate B cell antibody production. B cells in atherosclerosis meanwhile have a mixed role based on subclass. The current model is that B-1 cells produce protective IgM antibodies in response to oxidation-specific epitopes that work to control plaque formation, while follicular B-2 cells produce class-switched antibodies (IgG, IgA, and IgE) which exacerbate the disease. Over the course of this review, we discuss further the validation of these protective antibodies while evaluating the current dogma regarding class-switched antibodies in atherosclerosis. There are several contradictory findings regarding the involvement of class-switched antibodies in the disease. We hypothesize that this is due to antigen-specificity, and not simply isotype, being important, and that a closer evaluation of these antibodies' targets should be conducted. We propose that specific antibodies may have therapeutical potential in preventing and controlling plaque development within a clinical setting.

Antibodies against phosphorylcholine and protection against atherosclerosis, cardiovascular disease and chronic inflammation

INTRODUCTION

Chronic inflammatory diseases include cardiovascular disease (CVD) atherosclerosis, rheumatic and autoimmune diseases, and others, constitute a large part of the disease burden. It is therefore of major importance to improve understanding of underlying mechanisms, prediction and treatment.

AREAS COVERED

Broad fields including atherosclerosis, immunology and inflammation are covered, through searches on Pubmed and background knowledge. Phosphorylcholine (PC) is both a danger associated molecular pattern (DAMP), present on oxidized LDL (OxLDL) in atherosclerotic lesions and dead cells, and a pathogen associated molecular pattern (PAMP), present on microorganisms. IgM and IgG1 antibodies against PC (anti-PC) are associated with protection in several chronic inflammatory conditions, especially in CVD and atherosclerosis where most research has been done. PC-immunization ameliorates atherosclerosis in animal models and several potential underlying mechanisms have been proposed, including anti-inflammatory, decreased uptake of OxLDL in the artery wall, promotion of T regulatory cells. Anti-PC develops during the first years of life. Low levels of IgM and IgG1 anti-PC may be caused by lack of exposure to microorganisms, including nematodes and helminths among others.

EXPERT OPINION

anti-PC could improve prediction of clinical outcome and raising anti-PC could be developed into a novel therapy.

Antibodies Against Phosphorylcholine Among 60-Year-Olds: Clinical Role and Simulated Interactions

Aims

Antibodies against phosphorylcholine (anti-PC) are implicated as protection markers in atherosclerosis, cardiovascular disease (CVD), and other chronic inflammatory conditions. Mostly, these studies have been focused on IgM. In this study, we determined IgG, IgG1, and IgG2 anti-PC among 60-year-olds.

Methods

Based on a 7-year follow-up of 60-year-olds (2,039 men and 2,193 women) from Stockholm County, we performed a nested case-control study of 209 incident CVD cases with 620 age- and sex-matched controls. Anti-PC was determined using ELISA. We predicted the binding affinity of PC with our fully human, in-house-produced IgG1 anti-PC clones (i.e., A01, D05, and E01) using the molecular docking and molecular dynamics simulation approach, to retrieve information regarding binding properties to PC.

Results

After adjustment for confounders, IgG and IgG2 anti-PC showed some significant associations, but IgG1 anti-PC was much stronger as a protection marker. IgG1 anti-PC was associated with an increased risk of CVD below 33rd, 25th, and 10th percentile and of stroke below 33rd and 25th, and of myocardial infarction (MI) below 10th percentile. Among men, a strong association with stroke was determined below the 33rd percentile [HR 9.20, CI (2.22–38.12); p = 0.0022]. D05 clone has higher binding affinity followed by E01 and A01 using molecular docking and further have been confirmed during the course of 100 ns simulation. The stability of the D05 clone with PC was substantially higher.

Conclusion

IgG1 anti-PC was a stronger protection marker than IgG anti-PC and IgG2 anti-PC and also separately for men. The molecular modeling approach helps in identifying the intrinsic properties of anti-PC clones and atomistic interactions with PC.

Mini Review: Structure and Function of Nematode Phosphorylcholine-Containing Glycoconjugates

An unusual aspect of the biology of nematodes is the covalent attachment of phosphorylcholine (PC) to carbohydrate in glycoconjugates. Investigation of the structure of these molecules by ever-increasingly sophisticated analytical procedures has revealed that PC is generally in phosphodiester linkage with C6 of N-acetylglucosamine (GlcNAc) in both N-type glycans and glycosphingolipids. Up to five PC groups have been detected in the former, being located on both antenna and core GlcNAc. The PC donor for transfer to carbohydrate appears to be phosphatidylcholine but the enzyme responsible for transfer remains to be identified. Work primarily involving the PC-containing Acanthocheilonema viteae secreted product ES-62, has shown that the PC attached to nematode N-glycans possesses a range of immunomodulatory properties, subverting for example, pro-inflammatory signalling in various immune system cell-types including lymphocytes, mast cells, dendritic cells and macrophages. This has led to the generation of PC-based ES-62 small molecule analogues (SMAs), which mirror the parent molecule in preventing the initiation or progression of disease in mouse models of a number of human conditions associated with aberrant inflammatory responses. These include rheumatoid arthritis, systemic lupus erythematosus and lung and skin allergy such that the SMAs are considered to have widespread therapeutic potential.

Antibodies against phosphorylcholine in hospitalized versus non-hospitalized obese subjects

Obesity associates with reduced life expectancy, type 2 diabetes, hypertension and cardiovascular disease, and is characterized by chronic inflammation. Phosphorylcholine (PC) is an epitope on oxidized low-density lipoprotein, dead cells and some microorganisms. Antibodies against PC (anti-PC) have anti-inflammatory properties. Here, we explored the role of anti-PC in hospitalized versus non-hospitalized obese. One-hundred-and-twenty-eight obese (BMI ≥ 30 kg/m²) individuals (59.8 (± 5.5) years, 53.9% women) from the Malmö Diet and Cancer Cardiovascular Cohort were examined and IgM, IgG1 and IgG2 anti-PC were analyzed by ELISA. Individuals with at least one recorded history of hospitalization prior to study baseline were considered hospitalized obese (HO). Associations between IgM, IgG1 and IgG2 anti-PC and HO (n = 32)/non-hospitalized obese (NHO) (n = 96), but also with metabolic syndrome and diabetes were analysed using logistic regressions. Both IgM and IgG1 anti-PC were inversely associated with HO, also after controlling for age and sex. When further adjusted for waist circumference, systolic blood pressure, glucose levels and smoking status, only IgG1 anti-PC remained significantly associated with HO. In multivariate models, each 1 standard deviation of increment in anti-PC IgG1 levels was inversely associated with prevalence of HO (odds ratio 0.57; CI 95% 0.33–0.98; p = 0.044). IgG2 anti-PC did not show any associations with HO. Low levels of IgM and IgG1 anti-PC are associated with higher risk of being a HO individual independent of sex and age, IgG1 anti-PC also independently of diabetes and metabolic syndrome. The anti-inflammatory properties of these antibodies may be related to inflammation in obesity and its complications.

Higher levels of anti-phosphorylcholine autoantibodies in early rheumatoid arthritis indicate lower risk of incident cardiovascular events

Background

The increased risk of cardiovascular events (CVE) in rheumatoid arthritis (RA) is not fully explained by traditional risk factors. Immuno-inflammatory mechanisms and autoantibodies could be involved in the pathogenesis of atherosclerotic disease. It has been suggested that anti-phosphorylcholine antibodies (anti-PC) of the IgM subclass may have atheroprotective effects. Here, we aimed to investigate the association between levels of IgM anti-PC antibodies with CVE in patients with early RA.

Methods

The study population was derived from the BARFOT early RA cohort, recruited in 1994–1999. The outcome of incident CVE (AMI, angina pectoris, coronary intervention, ischemic stroke, TIA) was tracked through the Swedish Hospital Discharge and the National Cause of Death Registries. Sera collected at inclusion and the 2-year visit were analyzed with ELISA to determine levels of anti-PC IgM. The Kaplan-Meier estimates and Cox proportional hazards regression models were used to compare CV outcome in the groups categorized by baseline median level of IgM anti-PC.

Results

In all, 653 patients with early RA, 68% women, mean (SD) age 54.8 (14.7) years, DAS28 5.2 (1.3), 68% seropositive, and without prevalent CVD, were included. During the follow-up of mean 11.7 years, 141 incident CVE were recorded.

Baseline IgM anti-PC above median was associated with a reduction in risk of incident CVE in patients aged below 55 years at inclusion, HR 0.360 (95% CI, 0.142–0.916); in males, HR 0.558 (0.325–0.958); in patients with BMI above 30 kg/m², HR 0.235 (0.065–0.842); and in those who did not achieve DAS28 remission at 1 year, HR 0.592 (0.379–0.924). The pattern of associations was confirmed in the models with AUC IgM anti-PC over 2 years.

Conclusion

Protective effects of higher levels of innate IgM anti-PC autoantibodies on CVE were detected in younger patients with RA and those at high risk of CVE: males, presence of obesity, and non-remission at 1 year.

Potential natural immunization against atherosclerosis in hibernating bears

Brown bears (Ursus arctos) hibernate for 5-6 months during winter, but despite kidney insufficiency, dyslipidemia and inactivity they do not seem to develop atherosclerosis or cardiovascular disease (CVD). IgM antibodies against phosphorylcholine (anti-PC) and malondialdehyde (anti-MDA) are associated with less atherosclerosis, CVD and mortality in uremia in humans and have anti-inflammatory and other potentially protective properties. PC but not MDA is exposed on different types of microorganisms. We determine anti-PC and anti-MDA in brown bears in summer and winter. Paired serum samples from 12 free ranging Swedish brown bears were collected during hibernation in winter and during active state in summer and analyzed for IgM, IgG, IgG1/2 and IgA anti-PC and anti-MDA by enzyme linked immunosorbent assay (ELISA). When determined as arbitrary units (median set at 100 for summer samples), significantly raised levels were observed in winter for anti-PC subclasses and isotypes, and for IgA anti-PC the difference was striking; 100 IQR (85.9-107.9) vs 782.3, IQR (422.8-1586.0; p < 0.001). In contrast, subclasses and isotypes of anti-MDA were significantly lower in winter except IgA anti-MDA, which was not detectable. Anti-PCs are significantly raised during hibernation in brown bears; especially IgA anti-PC was strikingly high. In contrast, anti-MDA titers was decreased during hibernation. Our observation may represent natural immunization with microorganisms during a vulnerable period and could have therapeutic implications for prevention of atherosclerosis.

C-reactive protein in traditional melanesians on Kitava

Background

Population-based levels of the chronic low-grade systemic inflammation biomarker, C-reactive protein (CRP), vary widely among traditional populations, despite their apparent absence of chronic conditions associated with chronic low-grade systemic inflammation, such as type 2 diabetes, metabolic syndrome and cardiovascular disease. We have previously reported an apparent absence of aforementioned conditions amongst the traditional Melanesian horticulturalists of Kitava, Trobriand Islands, Papua New Guinea. Our objective in this study was to clarify associations between chronic low-grade systemic inflammation and chronic cardiometabolic conditions by measuring CRP in a Kitava population sample. For comparison purposes, CRP was also measured in Swedish controls matched for age and gender.

Methods

Fasting levels of serum CRP were measured cross-sectionally in ≥ 40-year-old Kitavans (N = 79) and Swedish controls (N = 83).

Results

CRP was lower for Kitavans compared to Swedish controls (Mdn 0.5 mg/L range 0.1—48 mg/L and Mdn 1.1 mg/L range 0.1—33 mg/L, respectively, r = .18 p = .02). Among Kitavans, there were small negative associations between lnCRP for CRP values < 10 and total, low-density lipoprotein (LDL) and non-high-density lipoprotein (non-HDL) cholesterol. Among Swedish controls, associations of lnCRP for CRP values < 10 were medium positive with weight, body mass index, waist circumference, hip circumference and waist-hip ratio and low positive with triglyceride, total cholesterol-HDL cholesterol ratio, triglyceride-HDL cholesterol ratio and serum insulin.

Conclusions

Chronic low-grade systemic inflammation, measured as CRP, was lower among Kitavans compared to Swedish controls, indicating a lower and average cardiovascular risk, respectively, for these populations.

Antibodies against Phosphorylcholine and Malondialdehyde during the First Two Years of Life

Abs against phosphorylcholine (anti-PC) and Abs against malondialdehyde (anti-MDA) may be protective in chronic inflammation, like atherosclerosis and cardiovascular disease. It is not known how they develop early in life. Ab titers were measured using ELISA in healthy women (n = 105; born into life study) and their children. Plasma samples were collected from the mothers before conception and from the children at birth as well as at 1 and 2 y after birth. Extracted Abs were compared using a proteomics de novo sequencing approach. It was observed that children were born with very low levels of IgM anti-PC, whereas IgM anti-MDA was present at birth. Both IgM anti-PC and anti-MDA increased during the first 2 y of life, but IgM anti-PC in contrast to IgM anti-MDA was still significantly lower than in the mothers. IgG anti-PC decreased after 1 y but reached similar levels as mothers' after 2 y, whereas IgG anti-MDA reached similar levels as mothers' already after 1 y. Proteomics peptide sequencing analysis indicated large peptide sequence variation without specific clone expression during the early stage of life compared with the adult stage for which specific peptide sequences dominated. IgM anti-PC levels develop much slower than anti-MDA and are still relatively low at 2 y. We hypothesize that anti-PC is developed by a combination of preprogramming and exposure to the external world, in which infectious agents may play a role. For anti-MDA, preprogramming is likely to play a major role and at an earlier stage than for anti-PC.

IgM antibodies against malondialdehyde and phosphorylcholine in different systemic rheumatic diseases

IgM antibodies against phosphorylcholine (anti-PC) and malondialdehyde (anti-MDA) may have protective properties in cardiovascular and rheumatic diseases. We here compare these antibodies in systemic rheumatic conditions and study their properties. Anti-PC and anti-MDA was measured using ELISA in patients with SLE (374), RA (354), Mixed connective tissue disease (MCTD, 77), Systemic sclerosis (SSc, 331), Sjögren's syndrome (SjS, 324), primary antiphospholipid syndrome (PAPs, 65), undifferentiated connective tissue disease (UCTD, 118) and 515 matched healthy controls (HC). Cardiovascular score (CV) was broadly defined based on clinical disease symptoms. Anti-PC and anti-MDA peptide/protein characterization were compared using a proteomics de novo sequencing approach. anti-MDA and anti-PC were extracted from total IgM. The proportion of Treg cells was determined by flow cytometry. The maximal difference between cases and controls was shown for MCTD: significantly lower IgM Anti-PC but not anti-MDA among patients (median 49.3RU/ml vs 70.4 in healthy controls, p(t-test) = 0.0037). IgM low levels were more prevalent in MCTD, SLE, SjS, SSc and UCTD. IgM anti-PC variable region profiles were different from and more homologous than anti-MDA. Anti-PC but not anti-MDA were significantly negatively correlated with CV in the whole patient group. In contrast to IgM anti-PC, anti-MDA did not promote polarization of Tregs. Taken together, Anti-PC is decreased in MCTD and also in SLE, SjS and SSc but not in other studied diseases. Anti-PC may thus differentiate between these. In contrast, anti-MDA did not show these differences between diseases studied. Anti-PC level is negatively correlated with CV in the patient group cohort. In contrast to anti-PC, anti-MDA did not promote Treg polarization. These findings could have both diagnostic and therapeutic implications, one possibility being active or passive immunization with PC in some rheumatic conditions.

Different subclasses and isotypes of antibodies against phosphorylcholine in haemodialysis patients: association with mortality

The risk of premature death is high among patients on haemodialysis (HD patients). We previously determined that immunoglobulin (Ig)M antibodies against phosphorylcholine (anti-PC) are negatively associated with increased risk of cardiovascular disease (CVD), atherosclerosis, some autoimmune diseases and mortality among HD patients in this cohort. Here, we also study other subclasses and isotypes of anti-PC in HD patients in relation to mortality, inflammation and gender. The study group is a cohort of 209 prevalent HD patients [median age = 66 years, interquartile range (IQR) = 51-74], vintage time = 29 months (IQR = 15-58; 56% men) with a mean follow-up period of 41 months (IQR = 20-60). Fifty-six per cent were men. We also divided patients into inflamed C-reactive protein (CRP) > 5·6 mg/ml and non-inflamed CRP. Antibody levels were determined by in-house enzyme-linked immunosorbent assay. IgG1 anti-PC below median was significantly associated with increased all-cause mortality (after adjustment for confounders: P = 0·02), while IgG, IgA and IgG2 anti-PC were not associated with this outcome. Among non-inflamed patients, IgM and IgG1 anti-PC were significantly associated with mortality (P = 0·047 and 0·02). IgG1 anti-PC was significantly associated with mortality among men (P = 0·03) and trending among women (P = 0·26). IgM (as previously reported) and IgG1 anti-PC are negatively associated with survival among HD patients and non-inflamed HD patients, but among inflamed patients there were no associations. IgG, IgA or IgG2 anti-PC were not associated with survival in these groups and subgroups. Further studies are needed to determine if raising anti-PC levels, especially IgM and IgG1 anti-PC, through immunization is beneficial.

Immunoglobulin G1 Antibodies Against Phosphorylcholine Are Associated With Protection in Systemic Lupus Erythematosus and Atherosclerosis: Potential Underlying Mechanisms

OBJECTIVE

Immunoglobulin M antibodies against phosphorylcholine (anti-PCs) may be protective in atherosclerosis, cardiovascular disease (CVD), and systemic lupus erythematosus (SLE). We study immunoglobulin G1 (IgG1) and immunoglobulin G2 (IgG2) anti-PCs, with a focus on atherosclerosis and SLE.

METHODS

We determined anti-PCs by using the enzyme-linked immunosorbent assay in 116 patients with SLE and 110 age- and sex-matched controls. For functional studies, we used three in-house-generated, fully human monoclonal IgG1 anti-PCs (A01, D05, and E01). Apoptosis was induced in Jurkat T cells and preincubated with A01, D05, E01, or IgG1 isotype control, and effects on efferocytosis by human macrophages were studied. Anti-PC peptide/protein characterization was determined using a proteomics de novo sequencing approach.

RESULTS

IgG1, but not IgG2, anti-PC levels were higher among patients with SLE (P = 0.02). IgG1 anti-PCs were negatively associated with Systemic Lupus International Collaborating Clinics (SLICC) damage index and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) scores (odds ratio [OR]: 2.978 [confidence interval (CI): 0.876-10.098] and OR: 5.108 [CI 1.3-20.067], respectively) and negatively associated with CVD, atherosclerotic plaques, and echolucent plaques (potentially vulnerable plaques), but the association for the two former was not significant after controlling for confounders. D05 had a maximum effect on macrophage efferocytosis efficiency, followed by A01 and E01. The monoclonal antibodies showed differential binding specificity to PC and PC-associated neoepitopes. A peptide analysis showed a difference in the complementarity-determining region 3 of the three IgG1 anti-PC clones that are crucial for recognition of PC on apoptotic cell surfaces and other neoepitopes.

CONCLUSION

IgG1 anti-PCs are negatively associated with disease activity and disease damage in SLE, but the negative association with CVD is also dependent on confounding risk factors. One potential underlying mechanism could be increased clearance of dead cells.

A genome-wide association study of IgM antibody against phosphorylcholine: shared genetics and phenotypic relationship to chronic lymphocytic leukemia

Phosphorylcholine (PC) is an epitope on oxidized low-density lipoprotein (oxLDL), apoptotic cells and several pathogens like Streptococcus pneumoniae. Immunoglobulin M against PC (IgM anti-PC) has the ability to inhibit uptake of oxLDL by macrophages and increase clearance of apoptotic cells. From our genome-wide association studies (GWASs) in four European-ancestry cohorts, six single nucleotide polymorphisms (SNPs) in 11q24.1 were discovered (in 3002 individuals) and replicated (in 646 individuals) to be associated with serum level of IgM anti-PC (the leading SNP rs35923643-G, combined β = 0.19, 95% confidence interval 0.13-0.24, P = 4.3 × 10-11). The haplotype tagged by rs35923643-G (or its proxy SNP rs735665-A) is also known as the top risk allele for chronic lymphocytic leukemia (CLL), and a main increasing allele for general IgM. By using summary GWAS results of IgM anti-PC and CLL in the polygenic risk score (PRS) analysis, PRS on the basis of IgM anti-PC risk alleles positively associated with CLL risk (explained 0.6% of CLL variance, P = 1.2 × 10-15). Functional prediction suggested that rs35923643-G might impede the binding of Runt-related transcription factor 3, a tumor suppressor playing a central role in the immune regulation of cancers. Contrary to the expectations from the shared genetics between IgM anti-PC and CLL, an inverse relationship at the phenotypic level was found in a nested case-control study (30 CLL cases with 90 age- and sex-matched controls), potentially reflecting reverse causation. The suggested function of the top variant as well as the phenotypic association between IgM anti-PC and CLL risk needs replication and motivates further studies.