Agalactosyl IgG: an aid to differential diagnosis in early synovitis

IgG glycans in health and disease: Prediction, intervention, prognosis, and therapy

Immunoglobulin (IgG) glycosylation is a complex enzymatically controlled process, essential for the structure and function of IgG. IgG glycome is relatively stable in the state of homeostasis, yet its alterations have been associated with aging, pollution and toxic exposure, as well as various diseases, including autoimmune and inflammatory diseases, cardiometabolic diseases, infectious diseases and cancer. IgG is also an effector molecule directly involved in the inflammation processes included in the pathogenesis of many diseases. Numerous recently published studies support the idea that IgG N-glycosylation fine-tunes the immune response and plays a significant role in chronic inflammation. This makes it a promising novel biomarker of biological age, and a prognostic, diagnostic and treatment evaluation tool. Here we provide an overview of the current state of knowledge regarding the IgG glycosylation in health and disease, and its potential applications in pro-active prevention and monitoring of various health interventions.

Immunoglobulin G N-glycan Biomarkers for Autoimmune Diseases: Current State and a Glycoinformatics Perspective

The effective treatment of autoimmune disorders can greatly benefit from disease-specific biomarkers that are functionally involved in immune system regulation and can be collected through minimally invasive procedures. In this regard, human serum IgG N-glycans are promising for uncovering disease predisposition and monitoring progression, and for the identification of specific molecular targets for advanced therapies. In particular, the IgG N-glycome in diseased tissues is considered to be disease-dependent; thus, specific glycan structures may be involved in the pathophysiology of autoimmune diseases. This study provides a critical overview of the literature on human IgG N-glycomics, with a focus on the identification of disease-specific glycan alterations. In order to expedite the establishment of clinically-relevant N-glycan biomarkers, the employment of advanced computational tools for the interpretation of clinical data and their relationship with the underlying molecular mechanisms may be critical. Glycoinformatics tools, including artificial intelligence and systems glycobiology approaches, are reviewed for their potential to provide insight into patient stratification and disease etiology. Challenges in the integration of such glycoinformatics approaches in N-glycan biomarker research are critically discussed.

The Expression of Non-Coding RNAs and Their Target Molecules in Rheumatoid Arthritis: A Molecular Basis for Rheumatoid Pathogenesis and Its Potential Clinical Applications

Rheumatoid arthritis (RA) is a typical autoimmune-mediated rheumatic disease presenting as a chronic synovitis in the joint. The chronic synovial inflammation is characterized by hyper-vascularity and extravasation of various immune-related cells to form lymphoid aggregates where an intimate cross-talk among innate and adaptive immune cells takes place. These interactions facilitate production of abundant proinflammatory cytokines, chemokines and growth factors for the proliferation/maturation/differentiation of B lymphocytes to become plasma cells. Finally, the autoantibodies against denatured immunoglobulin G (rheumatoid factors), EB virus nuclear antigens (EBNAs) and citrullinated protein (ACPAs) are produced to trigger the development of RA. Furthermore, it is documented that gene mutations, abnormal epigenetic regulation of peptidylarginine deiminase genes 2 and 4 (PADI2 and PADI4), and thereby the induced autoantibodies against PAD2 and PAD4 are implicated in ACPA production in RA patients. The aberrant expressions of non-coding RNAs (ncRNAs) including microRNAs (miRs) and long non-coding RNAs (lncRNAs) in the immune system undoubtedly derange the mRNA expressions of cytokines/chemokines/growth factors. In the present review, we will discuss in detail the expression of these ncRNAs and their target molecules participating in developing RA, and the potential biomarkers for the disease, its diagnosis, cardiovascular complications and therapeutic response. Finally, we propose some prospective investigations for unraveling the conundrums of rheumatoid pathogenesis.

Immunoglobulin G Glycosylation in Diseases

Changes in immunoglobulin G (IgG) glycosylation pattern have been observed in a vast array of auto- and alloimmune, infectious, cardiometabolic, malignant, and other diseases. This chapter contains an updated catalog of over 140 studies within which IgG glycosylation analysis was performed in a disease setting. Since the composition of IgG glycans is known to modulate its effector functions, it is suggested that a changed IgG glycosylation pattern in patients might be involved in disease development and progression, representing a predisposition and/or a functional effector in disease pathology. In contrast to the glycopattern of bulk serum IgG, which likely relates to the systemic inflammatory background, the glycosylation profile of antigen-specific IgG probably plays a direct role in disease pathology in several infectious and allo- and autoimmune antibody-dependent diseases. Depending on the specifics of any given disease, IgG glycosylation read-out might therefore in the future be developed into a useful clinical biomarker or a supplementary to currently used biomarkers.

Glycosylation deficiency of lipopolysaccharide-binding protein and corticosteroid-binding globulin associated with activity and response to treatment for rheumatoid arthritis

BACKGROUND

Serum protein glycosylation is an area of investigation in inflammatory arthritic disorders such as rheumatoid arthritis (RA). Indeed, some studies highlighted abnormalities of protein glycosylation in RA. Considering the numerous types of enzymes, monosaccharides and glycosidic linkages, glycosylation is one of the most complex post translational modifications. By this work, we started with a preliminary screening of glycoproteins in serum from RA patients and controls.

METHODS

In order to isolate glycoproteins from serum, lectin wheat germ agglutinin was used and quantitative differences between patients and controls were investigated by LC-MS/MS. Consequently, we focused our attention on two glycoproteins found in this explorative phase: corticosteroid-binding globulin (CBG) and lipopolysaccharide-binding protein (LBP). The subsequent validation with immunoassays was widened to a larger number of early RA (ERA) patients (n = 90) and well-matched healthy controls (n = 90).

RESULTS

We observed a significant reduction of CBG and LBP glycosylation in ERA patients compared with healthy controls. Further, after 12 months of treatment, glycosylated CBG and LBP levels increased both to values comparable to those of controls. In addition, these changes were correlated with clinical parameters.

CONCLUSIONS

This study enables to observe that glycosylation changes of CBG and LBP are related to RA disease activity and its response to treatment.

Low galactosylation of IgG associates with higher risk for future diagnosis of rheumatoid arthritis during 10 years of follow-up

Antibodies are known to have an important role in the development of rheumatoid arthritis (RA), one of the most prevalent chronic inflammatory diseases which primarily involves the joints. Most RA patients develop autoantibodies against immunoglobulin G (IgG) and changes in IgG glycosylation have been associated with RA. We undertook this study to determine whether altered IgG glycosylation precedes the disease diagnosis. We studied IgG glycosylation in RA in two prospective cohorts (N = 14,749) by measuring 28 IgG glycan traits in 179 subjects who developed RA within 10-years follow-up and 358 matched controls. Ultra-performance liquid chromatography method based on hydrophilic interactions (HILIC-UPLC) was used to analyse IgG glycans. Future RA diagnosis associated with traits related to lower galactosylation and sialylation of IgG when comparing the cases to the matched controls. In RA cases, these traits did not correlate with the time between being recruited to the study and being diagnosed with RA (median time 4.31 years). The difference in IgG glycosylation was relatively stable and present years before diagnosis. This indicates that long-acting factors affecting IgG glycome composition are among the underlying mechanisms of RA and that decreased galactosylation is a pre-existing risk factor involved in the disease development.

Glycan analysis of colorectal cancer samples reveals stage-dependent changes in CEA glycosylation patterns

Background

Carcinoembryonic antigen (CEA) is a glycoprotein associated with colorectal cancer (CRC). While the functions of its gene and protein have been fully characterized, its post-translational modifications in the context of CRC development remain undefined.

Methods

To show the correlation between the different stages of CRC development and changes in the glycosylation patterns of CEA, we analyzed CEA in tumor tissues (CEA-T) and paired tumor-adjacent normal tissues (CEA-A) from 53 colorectal cancer patients using a high-density lectin microarray containing 56 plant lectins.

Results

We detected higher expression levels of fucose, mannose and Thomsen–Friedenreich antigen, and lower expression levels of N-acetylgalactosamine, N-acetylglucosamine, galactose, branched and bisecting N-glycans on CEA in the tumor tissues relative to the tumor-adjacent normal tissues. Furthermore, a combinatorial assessment of 9 lectins is sufficient to distinguish CRC tumor tissues from tumor-adjacent normal tissues with 83% sensitivity and ~ 90% specificity. Moreover, the levels of N-acetylgalactosamine, mannose, galactose, N-acetylglucosamine on CEA showed a downward trend after first experiencing an increase at Stage II with the stages of CRC.

Conclusions

Our insights into the changing CEA glycosylation patterns and their role in the development of CRC highlight the importance of glycan variants on CEA for early clinical detection and staging of CRC.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9182-4) contains supplementary material, which is available to authorized users.

Changes of glycosylation of IgG in rheumatoid arthritis patients treated with methotrexate

PURPOSE

In patients with active rheumatoid arthritis (RA) decrease of galactosylation is correlated with disease activity. The aim of our study was to evaluate an effect of methotrexate therapy on glycosylation disturbances of IgG in RA patients.

MATERIALS/METHODS

IgG glycosylation in 40 patients with active RA treated with methotrexate for 12 months prior to and after treatment were compared. The control group consisted of 20 healthy volunteers. IgG glycosylation was assessed using biotinylated lectins and immunosorbent ELISA assay. For galactose specificity Datura stramonium lectin (DSA), for sialic acid Sambucus nigra (SNA) and Maackia amurensis (MAA) and for fucose residue Areulia auranta (AAA) lectins were used.

RESULTS

In RA-cases N-glycan galactosylation and sialylation of IgG before treatment were significantly lower than in healthy subjects (for DSA, MAA lectins p<0.001 and SNA p<0.05). Significant increase of IgG galactosylation and sialylation in RA patients after therapy (for DSA, MAA and SNA lectin p<0.05) was detected. Moreover the glycosylation disturbances of N-glycan IgG were strongly associated with changes of disease activity based on disease activity score. For fucose residues significantly higher absorbency of AAA lectin in RA patients before treatment was observed compared to control subjects (p<0.05) and slightly, not significantly decreased after MTX therapy.

CONCLUSIONS

Defect of galactosylation of IgG in RA patients is a useful marker of disease activity that may be used for the assessment of therapy effectiveness. The role of IgG fucosylation and sialylation in RA pathogenesis has still to be determined.

Measuring decreased serum IgG sialylation: a novel clinical biomarker of lupus

Introduction

The aim of this work was to develop a simple assay to distinguish between patients with rheumatoid arthritis (RA) and patients with systemic lupus erythematosus (SLE) by measuring the serum sialylated IgG (SAIgG).

Methods

Using a newly established SNA-based ELISA method, we compared the sialylation of immunoglobulin G (IgG) from a healthy control group ( n = 41), RA patients ( n = 30), SLE patients ( n = 45), patients with neuropsychiatric SLE (NPSLE) ( n = 30) and patients with juvenile idiopathic arthritis (JIA) ( n = 32).

Results

The average SAIgG level in healthy control individuals, RA patients, JIA patients, SLE patients and NPSLE patients was 0.64 ± 0.17, 0.82 ± 0.33, 0.69 ± 0.23, 0.12 ± 0.02 and 0.03 ± 0.01 mg/ml, respectively. The ratio of sialylated IgG to total IgG was significantly decreased in the SLE group (1.88 ± 0.32%) compared with the healthy population (4.64 ± 0.90%).

Conclusion

In summary, while the mean serum SAIgG level of RA and JIA patients was similar to that of the healthy population, there was a significant decrease in the serum SAIgG of both SLE groups tested, whereby the level of the NPSLE population group was the lowest.

Anti-citrullinated protein antibodies acquire a pro-inflammatory Fc glycosylation phenotype prior to the onset of rheumatoid arthritis

OBJECTIVE

To determine whether anticitrullinated protein antibodies (ACPA) exhibit specific changes in Fc glycosylation prior to the onset of arthritis.

METHODS

Serum samples of patients with ACPA-positive arthralgia (n=183) were collected at baseline and at various time points of follow-up. 105 patients developed arthritis after a median of 12 months (IQR 6-24) and were classified as having either rheumatoid arthritis (RA, n=48) or undifferentiated arthritis (UA, n=57) based on the 1987 American College of Rheumatology (ACR) criteria. ACPA and total serum IgG were isolated by affinity purification and cleaved by trypsin. ACPA-IgG1 Fc-glycopeptides were subsequently analysed by nano-liquid chromatography mass spectrometry and compared to those of total IgG1.

RESULTS

At baseline, ACPA-IgG1 and total IgG1 from arthralgia patients displayed similar Fc glycosylation patterns. By contrast, at the onset of arthritis, ACPA exhibited a decrease in galactose residues in RA patients, but not in UA patients. This decrease occurred around 3 months prior to diagnosis and was paralleled by an increase in systemic inflammation (erythrocyte sedimentation rate). Galactosylation of total IgG1 was also decreased in RA, but this did not precede the onset of arthritis. Interestingly, we additionally noted a higher degree of ACPA-IgG1 Fc core fucosylation at baseline as compared with total IgG1, which further increased prior to diagnosis.

CONCLUSIONS

ACPA display significant changes in Fc galactosylation and fucosylation prior to the onset of RA. These changes towards a more pro-inflammatory phenotype could be involved in driving the disease process.

The analysis of the human plasma N-glycome in endometriosis patients

OBJECTIVE

Analysis of the plasma N-glycome in endometriosis patients compared with controls.

STUDY DESIGN

In a case-control study, blood samples were collected from patients who underwent either diagnostic or operative laparoscopy between 2008 and 2011 in the Semmelweis University, Budapest, I. Department of Obstetrics and Gynaecology. From these patients, 92 with endometriosis (30 stage I-II and 62 stage III-IV, including altogether 18 deep infiltrating cases) and 62 controls were selected for glycan analysis. After release, plasma N-glycans were subjected to hydrophilic interaction high performance liquid chromatography, which resulted in 19 chromatographic glycan peaks (GP). The abundances of the GPs were compared between the study groups. For statistical analysis a non-parametric test, the Mann-Whitney-U test, was used.

RESULTS

We found a statistically significant decrease of GP1 and increase of GP14, GP17 and GP18 in endometriosis patients. The latter peaks consist of glycans which play a role in inflammatory processes and malignancy. We also found significant differences in GP2, GP4, GP6, and GP9 between controls and the different endometriosis stage groups. The observed alterations in GP2, GP4 and GP6 may be related to altered glycosylation and remodelling of the glycan branches of the IgG molecule. The alterations of GP9 are presumably associated with changes of transferrin glycosylation. Furthermore we detected a highly significant decrease of GP1 in patients with deep infiltrating endometriosis compared with controls.

CONCLUSIONS

This is the first analysis of the plasma N-glycome in endometriosis. The observed changes in GP14, GP17 and GP18 and in GP2, GP4, GP6 and GP9 provide new aspects to the pathophysiology of the disease and the alterations of the GP1 may serve as a new potential marker in the future.

N-glycomic biomarkers of biological aging and longevity: a link with inflammaging

Glycosylation is a frequent co/post-translational modification of proteins which modulates a variety of biological functions. The analysis of N-glycome, i.e. the sugar chains N-linked to asparagine, identified new candidate biomarkers of aging such as N-glycans devoid of galactose residues on their branches, in a variety of human and experimental model systems, such as healthy old people, centenarians and their offspring and caloric restricted mice. These agalactosylated biantennary structures mainly decorate Asn297 of Fc portion of IgG (IgG-G0), and are present also in patients affected by progeroid syndromes and a variety of autoimmune/inflammatory diseases. IgG-G0 exert a pro-inflammatory effect through different mechanisms, including the lectin pathway of complement, binding to Fcγ receptors and formation of autoantibody aggregates. The age-related accumulation of IgG-G0 can contribute to inflammaging, the low-grade pro-inflammatory status that characterizes elderly, by creating a vicious loop in which inflammation is responsible for the production of aberrantly glycosylated IgG which, in turn, would activate the immune system, exacerbating inflammation. Moreover, recent data suggest that the N-glycomic shift observed in aging could be related not only to inflammation but also to alteration of important metabolic pathways. Thus, altered N-glycans are both powerful markers of aging and possible contributors to its pathogenesis.

The role of sialic acid as a modulator of the anti-inflammatory activity of IgG

Immunoglobulin G (IgG) molecules can have two completely opposing activities. They can be very potent pro-inflammatory mediators on the one hand, directing the effector functions of the innate immune system towards infected cells, tumor cells or healthy tissues in the case of autoimmune diseases. On the other hand, a mixture of IgG molecules purified from the blood of ten thousands of healthy donors is used as an anti-inflammatory treatment for many autoimmune diseases since several decades. It has become evident only recently that certain residues in the sugar moiety attached to the IgG constant fragment can dramatically alter the pro- and anti-inflammatory activities of IgG. This review will focus on sialic acid residues as a modulator of the anti-inflammatory activity and provide an overview of situations where serum IgG glycosylation and sialylation is altered and which molecular and cellular pathways may be involved in this immunomodulatory pathway.

Impact of Glycosylation on Effector Functions of Therapeutic IgG

Human IgG has only one conserved glycosylation site located in the Cγ2 domain of the Fc region that accounts for the presence of two sugar moieties per IgG. These IgG sugar cores play a critical role in a number of IgG effector functions. In the present review, we describe the main characteristics of IgG Fc glycosylation and some abnormalities of serum IgG glycosylation. We also discuss how glycosylation impacts on monoclonal antibodies (mAbs) and IVIg effector functions and how these molecules can be engineered. Several therapeutic antibodies have now been engineered to be no- or low-fucose antibodies and are currently tested in clinical trials. They exhibit an increased binding to activating FcγRIIIA and trigger a strong antibody-dependent cell cytotoxicity (ADCC) as compared to their highly-fucosylated counterparts. They represent a new generation of therapeutic antibodies that are likely to show a better clinical efficacy in patients, notably in cancer patients where cytotoxic antibodies are needed.

Anti-citrullinated peptide antibody assays and their role in the diagnosis of rheumatoid arthritis

Increasingly, assays for the detection of anti-citrullinated peptide antibodies (ACPA) are used in RA diagnosis. This review summarizes the biologic basis and development of ACPA assays, available ACPA assays and their performance characteristics, and diagnostic properties of ACPA alone and compared to rheumatoid factor (RF) in early RA. We also review correlations, precision, costs and cost-effectiveness, availability, stability and reproducibility of the available assays. Taken together, data indicate that ACPA has a higher specificity than RF for early RA, good predictive validity, high sensitivity, apparent cost-effectiveness and good stability and reproducibility. Given its superior performance characteristics and increasing availability, ACPA is emerging as the most useful single assay for the diagnosis of RA.

Autoantibodies to cyclic citrullinated peptide 2 (CCP2) are superior to other potential diagnostic biomarkers for predicting rheumatoid arthritis in early undifferentiated arthritis

We evaluated the diagnostic value of anti-cyclic citrullinated peptide 2 (anti-CCP2) antibodies and other potential diagnostic biomarkers (IgM rheumatoid factor, anti-agalactosyl IgG antibodies, matrix metalloproteinase 3, C-reactive protein) for predicting early development of rheumatoid arthritis (RA). Patients were defined as having recent-onset undifferentiated arthritis (UA) if they had developed arthritis in two or more joints within the previous 2 years and could not be classified with a well-defined arthropathy. Baseline levels of biomarkers were measured in blood samples collected at the entry of the study and the patients were followed for 1 year to monitor development of RA. Diagnoses of RA and non-RA arthropathies were made according to individual standard diagnostic criteria. A total of 146 patients were enrolled in the study. In the follow-up year, 18 patients developed RA, 54 developed non-RA arthropathies, and 60 remained in the UA category. The sensitivity and specificity of the presence of anti-CCP2 antibodies for the diagnosis of RA were 83.3 and 93.0%, respectively. The positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of anti-CCP2 antibodies for RA (65.2, 97.2, and 91.7%, respectively) were higher than for any other biomarker. Combination of anti-CCP2 with any other biomarker only slightly improved each diagnostic value compared to the presence of anti-CCP2 alone. Among the anti-CCP2-positive patients, the average titer was significantly higher in those with RA than in non-RA or UA patients (163.7 +/- 138.4 vs 55.2 +/- 72.0 U/ml, p = 0.017). Anti-CCP2 antibodies are superior to any other single biomarker for predicting early development of RA in patients with recent-onset UA and the diagnostic value of anti-CCP2 alone is similar to that for biomarker combinations. Moreover, the anti-CCP2 antibody titer is useful to discriminate between patients at high risk for early developing RA from those at risk of developing non-RA arthropathies.

The changes in monosaccharide composition of immunoglobulin G in the course of rheumatoid arthritis

The objective of this study was to determine whether galactosylation of immunoglobulin G (IgG) in patients with rheumatoid arthritis (RA) correlates with severity and duration of illness. Serum IgG glycosylation from 50 patients with RA in comparison with 30 healthy controls was analyzed. IgG from sera was isolated and monosaccharide composition was determined by means of gas chromatography. Ratio of galactose to mannose content was calculated. Patients were divided into groups according to three different criteria: disease duration, severity of RA (disease activity score index), and radiological degree of advancement of illness according to Steinbrocker. In patients with RA, significant decrease (p<0,01) of galactose ratio was observed in comparison with healthy control. In patients with long duration of RA (more than 15 years), significant decrease of galactose (p<0.05) ratio in comparison with patients who have had arthritis for less then 5 years was observed. For the group of patients with severe RA, we found reduction of galactose (p<0.001) ratio vs the group of patients in remission. For those patients who had radiological stage IV according to Steinbrocker, IgG galactose (p<0.01) content per oligosaccharide chain were also more decreased than in those patients who had stage I RA. Decreased galactosylation and of IgG in RA was observed. The lack of this carbohydrate component of IgG correlates with severity and duration of RA and could be used in monitoring the progression in early arthritis.

Hypogalactosylation of serum IgG in patients with coeliac disease

Coeliac disease (CD) is described as an autoimmune enteropathy associated with the presence of IgG and IgA antigliadin and antitransglutaminase autoantibodies. While of diagnostic significance, the role of these autoantibodies in the immunopathogenesis of CD is elucidated. An inappropriate T cell immune response to gluten is also involved in the pathogenesis of CD, as evidenced by autoantibody switching. The N-glycans released from serum IgG of CD patients and three groups of healthy controls, of differing age ranges, were analysed by NH2-high performance liquid chromatography (HPLC). The fucosylated biantennary N- glycans were the most abundant neutral oligosaccharides; in particular, the agalacto form (G0F) showed a mean value of 42% (s.d. +/- 7.4), 30% (s.d. +/- 5.9), 26% (s.d. +/- 4.2) and 35% (s.d. +/- 6.8) for CD patients, healthy children, healthy adults under 40 and healthy adults over 40 years old, respectively. The ratio of asialo agalacto fucosylated biantenna to asialo monogalacto fucosylated biantenna (G0F)/(G1F) for CD patients showed a significant increase compared to healthy children (P < 0.0002), healthy adults under 40 (P < 0.0002) and healthy adults over 40 years old (P < 0.01). Hypogalactosylation was more pronounced for CD patients than for the patients with other autoimmune diseases such as rheumatoid arthritis or psoriatic arthritis.

Binding of rheumatoid and lupus synovial fluids and sera-derived human IgG rheumatoid factor to degalactosylated IgG

BACKGROUND

Altered glycosylation of immunoglobulin G (IgG) has been demonstrated in patients with rheumatoid arthritis (RA). Specificity of IgG rheumatoid factor (RF) in recognizing degalactosylated IgG (Fab)(2) and Fc was analyzed in the present study.

METHODS

(Fab)(2) and Fc fragments were prepared from IgG of normal healthy subjects. Enzymes, including peptide-N-glycosidase (PNGase), neuraminidase, and beta-1,4-galactosidase, were used to digest (Fab)(2) and Fc fragments. Binding capacity of IgG RF from patients with RA, systemic lupus erythematosus (SLE), and from healthy subjects to (Fab)(2) and Fc treated with glycosidase, was measured with immunoassay.

RESULTS

Treating (Fab)(2) and Fc with PNGase significantly diminished their binding capacity to IgG RFs. Degalactosylated (Fab)(2) revealed higher affinity to IgG RF in all tested groups. Fc lacking terminal galactose on oligosaccharide chains showed elevated binding with synovial IgG RF of RA patients. However, lesser binding was observed in sera of patients with RA and SLE.

CONCLUSIONS

Our data suggest that IgG molecules containing less terminal galactose on their oligosaccharide moieties are preferentially recognized by IgG RF. Furthermore, IgG RF display alternative binding specificity to degalactosylated (Fab)(2) and Fc in synovial fluids and sera of RA patients.

Value of laboratory tests in early prediction of rheumatoid arthritis

OBJECTIVE

To determine which laboratory test or tests at presentation best predicted a diagnosis of rheumatoid arthritis (RA) 2 years later.

METHODS

Two hundred seventy patients with early arthritis seen in 7 hospitals underwent comprehensive evaluations at 6-month intervals for 2 years, when the diagnosis of RA was assessed by 5 rheumatologists. The sensitivity and specificity of each test at the first visit for discriminating between RA (38%, n = 98) and non-RA patients were determined. Optimal cutoffs for continuous tests were derived from receiver operating characteristic curves. Sensitivity and specificity of test combinations selected by multiple logistic regression were determined.

RESULTS

IgM rheumatoid factor (RF) by enzyme-linked immunosorbent assay, IgG-antikeratin antibody (AKA), and latex test had the strongest associations with RA. These 3 tests formed the most powerful combination for distinguishing RA from non-RA.

CONCLUSION

IgM-RF, IgG-AKA, and the latex test are the best laboratory tests for discriminating between patients with and without RA. Combining these tests slightly improves diagnostic value.

Established rheumatoid arthritis

Currently the diagnosis of rheumatoid arthritis (RA) may be difficult; the ACR criteria appear most sensitive and specific in long-standing disease. Without clear definition or diagnostic criteria for early disease it is difficult to define late or established RA. The distinction between early and established RA has been further blurred by recent imaging studies that suggest even in what is currently termed early disease, there is evidence of joint damage. The natural history of RA suggests that most patients with clinic-diagnosed RA have a progressively disabling course, but evidence is growing that modern therapeutic strategies result in better long-term outcomes, especially when applied early in the disease course. In established disease, quantitative markers such as C-reactive protein (CRP) give prognostic information, but in the pre-erosive, early phase of the disease the qualitative markers such as rheumatoid factor (RF) and shared epitope are crucial. As rheumatologists, our major aims must remain: (1) to diagnose the disease as early as possible; (2) to identify those patients with poor prognosis who will benefit most from targeted therapy; and (3) to aim for more intensive disease control irrespective of disease duration.

Glycosylation differences between the normal and pathogenic prion protein isoforms

Prion protein consists of an ensemble of glycosylated variants or glycoforms. The enzymes that direct oligosaccharide processing, and hence control the glycan profile for any given glycoprotein, are often exquisitely sensitive to other events taking place within the cell in which the glycoprotein is expressed. Alterations in the populations of sugars attached to proteins can reflect changes caused, for example, by developmental processes or by disease. Here we report that normal (PrP(C)) and pathogenic (PrP(Sc)) prion proteins (PrP) from Syrian hamsters contain the same set of at least 52 bi-, tri-, and tetraantennary N-linked oligosaccharides, although the relative proportions of individual glycans differ. This conservation of structure suggests that the conversion of PrP(C) into PrP(Sc) is not confined to a subset of PrPs that contain specific sugars. Compared with PrP(C), PrP(Sc) contains decreased levels of glycans with bisecting GlcNAc residues and increased levels of tri- and tetraantennary sugars. This change is consistent with a decrease in the activity of N-acetylglucosaminyltransferase III (GnTIII) toward PrP(C) in cells where PrP(Sc) is formed and argues that, in at least some cells forming PrP(Sc), the glycosylation machinery has been perturbed. The reduction in GnTIII activity is intriguing both with respect to the pathogenesis of the prion disease and the replication pathway for prions.

Sugar printing rheumatic diseases: a potential method for disease differentiation using immunoglobulin G oligosaccharides

OBJECTIVE

To look for oligosaccharide structural variants of IgG that may be unique to specific rheumatic diseases.

METHODS

Using normal-phase high-performance liquid chromatography technology, a comparison was made of the oligosaccharide pools released from serum IgG from patients with systemic lupus erythematosus (SLE) (n = 10), ankylosing spondylitis (AS) (n = 10), primary Sjögren's syndrome (n = 6), juvenile chronic arthritis (JCA) (n = 13), psoriatic arthritis (n = 9), rheumatoid arthritis (RA) (n = 5), and healthy control individuals (n = 19).

RESULTS

The oligosaccharide pools were resolved into 13 peaks and the relative proportions of the peaks in each disease group was significantly different from that in healthy controls (P < 0.0001-0.05). A characteristic serum IgG oligosaccharide profile, or sugar print, for each of the rheumatic diseases was found. The sugar prints exhibited a range of glycosylation patterns whereby all RA (P < 0.0001) and JCA (P < 0.006) patients had predominantly agalactosyl structures, while SLE (P < 0.03-0.0001) and AS (P < 0.025-0.0001) patients had predominantly digalactosyl structures.

CONCLUSION

The data suggest that each disease is associated with a specific mechanism that gives rise to alterations in the normal glycosylation pattern of IgG. Sugar printing of IgG is therefore a potential means for the differentiation of rheumatic diseases and may provide insight into disease pathogenesis.

Changes in the galactose content of IgG during humoral immune responses

The Fc region of IgG bears two oligosaccharides of variable composition. The serum level of one variant which lacks terminal galactose and sialic acid (agalactosyl IgG) is raised in a number of autoimmune diseases and animal models thereof. Here it is shown that such changes in IgG glycosylation occur during non-pathological humoral immune responses. It was found that if specific pathogen free (SPF) CBA/Ca mice are transferred from a sterile to a conventional environment, their levels of total serum IgG rise whereas the degree of IgG galactosylation falls. Next, mice were immunised with bovine serum albumin (BSA) in incomplete Freund's adjuvant. As anti-BSA titres rose the antibodies became less galactosylated and later, as the titres fell, the antibodies became more galactosylated. By contrast, there was little or no variation in the relative galactosylation of total IgG. It is considered that the galactosylation of IgG antibodies varies during an immune response.

Prenatal alcohol exposure affects galactosyltransferase activity and glycoconjugates in the Golgi apparatus of fetal rat hepatocytes

Prenatal exposure to alcohol affects the morphological, structural, and functional features of the Golgi apparatus (GA), thus altering the glycosylation process in fetal hepatocytes. To elucidate the cellular mechanisms underlying these alterations, we have studied the effect of alcohol exposure in utero on the activity of liver galactosyltransferase, an enzyme involved in the glycosylation process, and on the hepatic glycoprotein sugar composition. For this, livers from 21-day-old fetuses obtained from control and ethanol-fed rats were used. Galactosyltransferase (GT) activity was determined in isolated GA cis and trans fractions. Colloidal gold-labeled lectin cytochemistry was used to analyze sugar residues in hepatocytes at the subcellular level. Finally, the integrity of the GA after alcohol treatment was assessed by electron microscopy and by evaluating the distribution of the Golgi beta-COP, a protein involved in vesicular trafficking. Prenatal alcohol exposure induces a significant increase in both liver weight and total protein content in the trans Golgi. Moreover, this treatment decreases the activity of galactosyltransferase, increases alpha-L-Fuc residues, and reduces the number of alpha-Man, GlcNAc(beta1,4,GlcNAc)1,2, GalNAc alpha1,3GalNAc, alpha-GalNAc, and a-Gal residues. Alcohol exposure also causes the Golgi cisternae to disappear in about 30% of the hepatocytes, and reduces 75% the number of anti-Golgi beta-COP protein binding sites. Our results suggest that the decrease in galactosyltransferase activity, the alterations in the oligosaccharide chain composition, and the reduction in the amount of Golgi beta-COP protein could be involved in the alterations in the glycosylation process, as well as in the accumulation of hepatic proteins observed after prenatal alcohol exposure. These alterations could contribute, therefore, to the alcohol-induced injury in the developing liver.

Can we predict aggressive disease?

This chapter will describe the reasons why prognostic factors that predict aggressive disease are helpful and what the problems are in interpreting studies in this field. A summary of cohort studies on prognosis of patients with early rheumatoid arthritis are presented. This is done separately for studies predicting radiographic damage, functional outcome and mortality. The overall conclusions of these studies and the value they have for the clinician are demonstrated.

Analysis of different glycosylation states in IgG subclasses

Altered IgG glycosylation affects certain immunological activities of human IgG. Enzyme-linked lectin assays (ELLA) were developed for detecting the glycosylation on IgG and its individual subclasses in sera from healthy controls. Biotinylated Sambucus nigra, Ricinus communis agglutinin I and Bandeiraea simplicifolia II were used to detect the terminal sialic acid (SA), galactose (Gal) and N-acetylglucosamine (GlcNAc) sugar residues, respectively on the captured IgG. A mild oxidation step of the anti-IgG-coated plates obviated background reaction with the lectins. Terminal glycosylation varied significantly with age. The old age group (> 65 years) had less SA in IgG1, and IgG2, when compared to young (0-19 years) and adult (20-39 years) groups, respectively. Also the old age group had less Gal in IgG2, IgG3 and IgG4 subclasses compared to the adult group, and to the young group in the case of IgG3. This ELLA system may be a valuable tool in the detection of glycosylation disorders in patients' sera.

On the interaction between agalactosyl IgG and Fc gamma receptors

One of the serum abnormalities observed in autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is the occurrence of IgG that lacks the terminal galactose on asparagine-linked biantennary complex type oligosaccharides [Gal(0)-IgG] located in the CH2 domain. Additionally, IgG without glycosylation is known to be defective in several effector functions due to a reduced ability to bind to its specific receptors (Fc gamma R). It has thus been speculated that, by analogy with unglycosylated IgG, Gal(0)-IgG may also be functionally impaired or exert altered effector mechanisms. If this were true, Gal(0)-IgG could contribute to the phenotype of above-mentioned autoimmune diseases, like impaired immune complex clearance and defective down-regulation of activated B cells. Here, we show by three different methods that the interaction of Gal(0)-IgG and normally glycosylated IgG with the low-affinity Fc gamma RII (CD32) is indistinguishable with respect both to binding and receptor-mediated signalling. These data argue against a prominent role for Fc gamma R-dependent Gal(0)-IgG interactions in the etiology or pathogenesis of autoimmune diseases.

Changes in agalactosyl IgG levels correlate with radiological progression in early rheumatoid arthritis

Immunoglobulin G-lacking galactose (Gal[0]) appears to be helpful in differential diagnosis of early synovitis, and correlates with disease activity in rheumatoid arthritis (RA). Its utility for RA monitoring and prognosis has been evaluated in the present study. Forty-eight patients with early RA were observed for 3 years. Hand radiographs were assessed according to Larsen and results were expressed as damage score (DS) and progression of damage score (PDS). Gal[0], DS, and PDS were evaluated at the onset of the study and after 1 and 3 years. The average values of Gal[0] in RA patients at the onset of the observation were significantly higher as compared to healthy controls (0.43 +/- 0.22 vs. -0.03 +/- 0.09, P < 0.05). The findings of Gal[0] after a 3-year follow-up were also higher as compared to healthy controls (0.37 +/- 0.21 vs. -0.03 +/- 0.09, P < 0.05). Radiological progression (PDS > 15) was observed in 16 patients. This group was characterized by a constantly high level of Gal[0]. The level of Gal[0] in patients without or with moderate radiological progression (PDS < 15) was significantly lower at the onset of the study and remained low during the observation. The relationship between Gal[0] and radiological progression was shown. The data thus far obtained suggest that Gal[0] may serve as an indicator for the disease course in patients with RA. Secondly, we cannot exclude the possibility that the constantly elevated level of Gal[0] causes erosions.

Agalactosyl IgG and beta-1,4-galactosyltransferase gene expression in rheumatoid arthritis patients and in the arthritis-prone MRL lpr/lpr mouse

Reduced galactosylation of immunoglobulin G (IgG) is well documented in rheumatoid arthritis (RA), but the reason for this defect is still unknown. There is some evidence supporting a defect in the biosynthetic pathway, and a reduction in the level of beta-1,4-galactosyltransferase (beta-1,4-GalTase) enzyme activity. Since glycosyltransferases are, in general, regulated at the level of transcription, we have measured the level of beta-1,4-GalTase gene expression in B cells from patients with RA and normal control individuals. We found no significant difference in mRNA levels for the transferase in these two groups (P > 0.7). MRL/Mp-lpr/lpr (MRL-lpr) mice develop a spontaneous arthritis with increased levels of agalactosyl IgG (G0). In spite of a significant reduction in the level of beta-1,4-GalTase mRNA in total spleen lymphocytes from MRL-lpr mice compared with the congenic MRL/Mp-(+/+) (MRL-(+/+) mice and with CBA/Ca mice, we found comparable levels of the beta-1,4-GalTase mRNA in purified B cells from both spleen and lymph nodes of the three strains. Amongst the lymphoid compartments examined, the spleen and peripheral blood were found to be the major contributors of G0 in MRL-lpr mice. These data indicate that in neither human RA, nor in an animal model of this disease, is reduced IgG galactosylation caused by impaired expression of the beta-1,4-GalTase gene in B lymphocytes. Furthermore, splenic B cells, which have normal levels of beta-1,4-GalTase mRNA, appear to be a major source of G0 in MRL-lpr mice.

Raised levels of agalactosyl IgG in childhood tuberculosis

Raised levels of agalactosyl immunoglobulin G (IgG) have been found in adults with tuberculosis, Crohn's disease and rheumatoid arthritis, and recent evidence, both circumstantial and experimental, suggests that it has distinct functional properties that play a role in pathogenesis. Since tuberculosis in infants is strikingly different from the disease seen in adults, but switches to the adult form at adrenarche or puberty, we documented the association of agalactosyl IgG with tuberculosis in childhood between the ages of 0 and 16 years. Sera were collected from 99 children diagnosed as cases of tuberculosis in Istanbul, Turkey, and compared with levels in non-tuberculous controls. The percentage of agalactosyl IgG was significantly raised in children with tuberculosis overall (P < 0.001, Mann-Whitney U test) and in all age groups except for children over 12 years old, whose numbers were too small to be meaningful. Therefore the differences between adult and childhood tuberculosis are not due to a difference in the tendency for agalactosyl IgG to be produced at different ages. The percentage of agalactosyl IgG may be useful for monitoring the progress of individual complicated cases.

Immunoglobulin G galactosylation deficiency determined by isoelectric focusing and lectin affinoblotting in differential diagnosis of rheumatoid arthritis

IgG galactosylation deficiency in patients with rheumatoid arthritis (RA) can be detected by isoelectric focusing (IEF)/lectin affinoblotting. We analyzed IgG glycosylation in patients with early arthritis (n = 50) and healthy controls in order to determine the clinical value of this parameter in differential diagnosis of RA. A significant correlation between the IgG galactosylation defect at disease onset and the diagnosis of RA during the follow-up was observed. Involvement of other clinical parameters (erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor) did not improve the predictive value of IgG galactosylation changes.

The Serum Level of Agalactosyl IgG in Rheumatoid Arthritis Patients Treated with Methotrexate

To verify the hypothesis that methotrexate may affect the serum level of agalactosyl IgG (IgG[0]) we followed the changes in IgG galactosylation patterns in a cohort of rheumatoid arthritis patients treated with either methotrexate (MTX) or nonsteroidal antiinflammatory drugs (NSAID).

The average values of IgG[0] in RA patients at the beginning of the observation were significantly higher as compared to healthy controls (0.45 ± 0.39 vs. −0.03 ± 0.09, p<0.05). The findings of IgG[0] after one-year follow-up were also higher as compared to healthy controls (0.38 ± 0.39 vs. −0.03 ± 0.09, p<0.05).

We did not notice any statistically significant difference in IgG[0] between MTX and NSAID treated patients at the beginning of the study (0.49 ± 0.42 vs. 0.42 ± 0.38, NS). However, during one-year MTX treatment IgG[0] significantly dropped (0.49 ± 0.42 vs. 0.25 ± 0.24, p<0.01). We did not establish any fluctuation in IgG[0] in the group of patients treated with NSAID (0.42 ± 0.38 vs. 0.46 ± 0.45, NS).

The data thus far obtained suggest that IgG[0] may serve as an indicator for the disease course in patients with RA. Secondly, the clinical improvement and IgG[0] decrease after methotrexate implies, that the immunoregulatory abnormality in RA may be susceptible to correction by immunotherapy.

Agalactosyl IgG and materno-fetal transmission of autoimmune neonatal lupus

Neither the incidence nor the severity of neonatal autoimmune disease correlates with maternal or neonatal autoantibody titres. However, there is now evidence that the agalactosyl [Gal(0)] fractions of autoantibodies are the most pathogenic. We found that systemic lupus erythematosus (SLE) mothers whose infants developed congenital heart block (CHB) had higher %Gal(0) at the end of pregnancy than did mothers of unaffected infants (P < 0.05) or control mothers (P < 0.01). Similarly, affected infants had higher %Gal(0) than control infants (P < 0.01). Then we studied the Gal(0) content of the anti-Ro and we found that it was higher in affected neonates than in unaffected neonates (P < 0.05), though there was no difference between the corresponding groups of mothers by this criterion. We propose that agalactosyl IgG may have a regulatory or effector role and that the risk of neonates developing maternal autoantibody-mediated disorders may be related to the quantity of agalacotsyl autoantibody present at birth, rather than to its absolute titre.

Rheumatoid factor avidity in patients with rheumatoid arthritis: identification of pathogenic RFs which correlate with disease parameters and with the gal(0) glycoform of IgG

The standard ELISA for measuring rheumatoid factor (RF) binding was modified by treatment after the RF-Fc interaction with 2 M guanidine, which allowed a measurement of the avidity of the interaction. Incubation with 4 M guanidine eliminated RF binding. There was a direct correlation (r = 0.99) between the avidity as measured by the modified guanidine ELISA, and the dissociation constant for monoclonal RFs, as measured by competitive ELISA. Of the seropositive rheumatoid arthritis (RA) patients tested, 47% had high-avidity RFs (> or = 8% RF binding remaining after guanidine treatment). Tender joint count scores were significantly higher in the high avidity group (p = 0.05), whereas there was no significant difference in the ages, disease duration, sedimentation rate, RF titer or serum Ig levels compared to those with low-avidity RFs. Additionally 58% of those with high-avidity RFs had subcutaneous nodules, compared to 40% of the low-avidity group. A significantly higher number of nodules was present in the high-avidity RF group compared to those with low-avidity RFs (p = 0.03). Interestingly, the RF avidity was significantly higher in isolated immune complexes (IC), compared to that in circulating IgM RFs (p = 0.01). The RF avidity correlated with the presence of the glycoform of IgG lacking galactose in both circulating and IC-derived IgG (p = 0.003 and 0.009 respectively). Information about the strength of binding to Fc identifies a subgroup of IgM RFs that are likely pathological in patients with RA, as well as a specific glycoform of the target antigen.

Does it take sugar? A clinical role for measuring the glycosylation of IgG?

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Distinct oligosaccharide content of rheumatoid arthritis-derived immune complexes

OBJECTIVE

To investigate the association between glycosylation and immune complex formation in various disease groups.

METHODS

Immune complexes and IgG were isolated from serum and their carbohydrate content evaluated in a dot-blot assay using specifically binding lectins.

RESULTS

Significantly more N-acetylglucosamine was detected in complexes from patients with rheumatoid arthritis (RA) than in those from patients with systemic lupus erythematosus, Crohn's disease, or infectious endocarditis, or from normal controls (P < 0.001). The immune complex concentration in the circulation was strongly associated with N-acetylglucosamine levels (P < 0.001 by chi-square analysis).

CONCLUSION

The composition of immune complexes from RA patients is distinct in carbohydrate content from those found in other disease groups.

Detection of immunoglobulin G glycosylation changes in patients with rheumatoid arthritis by means of isoelectric focusing and lectin-affinoblotting

Patients with rheumatoid arthritis have a reduced prevalence of immunoglobulin G (IgG) oligosaccharide chains terminating in galactose, thus exposing N-acetylglucosamine. We analyzed IgG glycosylation in patients with rheumatoid arthritis, patients with early synovitis, and in controls by means of isoelectric focusing and lectin-affinoblotting. The ratio of N-terminal N-acetylglucosamine and galactose was determined using specific biotin-labeled lectins. The IgG glycosylation state may well be of clinical value in the differential diagnosis of patients presenting with early synovitis.

Abnormalities in the glycosylation of IgG and its clinical utility

It is approximately ten years since the first detailed analysis of the variation in oligosaccharide structures attached to human serum IgG was published [1]. This study also showed that the percentage incidence of agalactosyl structures on the bi-antennary oligosaccharide complex linked to the Fc region, was increased in patients with rheumatoid arthritis. An earlier study [2], published in abstract from only, had also suggested that this was the case but was never followed up. In this review the considerable amount of work that has explored the clinical relevance of abnormalities in the glycosylation of IgG is analysed critically.

Agalactosyl IgG and antibody specificity in rheumatoid arthritis, tuberculosis, systemic lupus erythematosus and myasthenia gravis

Agalactosyl IgG (Gal(0) is a glycoform lacking terminal galactose from the oligosaccharides situated on the Fc. The percentage of circulating IgG that is Gal(0) is increased in a a number of autoimmune diseases, and in certain chronic infections associated with autoantibody production. However it is not known whether this represents decreased galactosylation of all IgG, or an increase in the relative concentration of a subset of agalactosyl antibodies of specificity relevant to the disease process. Since there is currently no way to separate agalactosyl from galactosylated IgG, we devised an assay for the relative degree of galactosylation of antibody to tetanus toxoid (TT), an antigen irrelevant to the diseases studied, and compared this value with the %Gal(0) of the whole circulating IgG. In rheumatoid arthritis (RA) and tuberculosis (TB), a raised %Gal(0) in serum IgG was reflected in a parallel rise in the extent to which antibody to TT was agalactosyl. In SLE a rise in %Gal(0) was seen in the presence of very little rise in agalactosyl anti-TT, and in myasthenia gravis (MG), where serum %Gal(0) is normal, an abnormally low percentage of the anti-TT was agalactosyl. These results imply that in RA and TB a systemic influence is downregulating the galactosylation even of irrelevant IgG. However in SLE and MG antibodies of specificities not studied here must be responsible for the %Gal(0) found in serum. It remains to be seen whether these are the autoantibodies involved in the disease process.