Reversible changes in serum immunoglobulin galactosylation during the immune response and treatment of inflammatory autoimmune arthritis

Tailored therapeutic decision of rheumatoid arthritis using proteomic strategies: how to start and when to stop?

Unpredictable treatment responses have been an obstacle for the successful management of rheumatoid arthritis. Although numerous serum proteins have been proposed, there is a lack of integrative survey to compare their relevance in predicting treatment outcomes in rheumatoid arthritis. Also, little is known about their applications in various treatment stages, such as dose modification, drug switching or withdrawal. Here we present an in-depth exploration of the potential usefulness of serum proteins in clinical decision-making and unveil the spectrum of immunopathology underlying responders to different drugs. Patients with robust autoimmunity and inflammation are more responsive to biological treatments and prone to relapse during treatment de-escalation. Moreover, the concentration changes of serum proteins at the beginning of the treatments possibly assist early recognition of treatment responders. With a better understanding of the relationship between the serum proteome and treatment responses, personalized medicine in rheumatoid arthritis will be more achievable in the near future.

Autoimmune pre-disease

Approximately 5% of the world-wide population is affected by autoimmune diseases. Overall, autoimmune diseases are still difficult to treat, impose a high burden on patients, and have a significant economic impact. Like other complex diseases, e.g., cancer, autoimmune diseases develop over several years. Decisive steps in the development of autoimmune diseases are (i) the development of autoantigen-specific lymphocytes and (often) autoantibodies and (ii) potentially clinical disease manifestation at a later stage. However, not all healthy individuals with autoantibodies develop disease manifestations. Identifying autoantibody-positive healthy individuals and monitoring and inhibiting their switch to inflammatory autoimmune disease conditions are currently in their infancy. The switch from harmless to inflammatory autoantigen-specific T and B-cell and autoantibody responses seems to be the hallmark for the decisive factor in inflammatory autoimmune disease conditions. Accordingly, biomarkers allowing us to predict this progression would have a significant impact. Several factors, such as genetics and the environment, especially diet, smoking, exposure to pollutants, infections, stress, and shift work, might influence the progression from harmless to inflammatory autoimmune conditions. To inspire research directed at defining and ultimately targeting autoimmune predisease, here, we review published evidence underlying the progression from health to autoimmune predisease and ultimately to clinically manifest inflammatory autoimmune disease, addressing the following 3 questions: (i) what is the current status, (ii) what is missing, (iii) and what are the future perspectives for defining and modulating autoimmune predisease.

Distinct Longitudinal Changes in Immunoglobulin G N-Glycosylation Associate with Therapy Response in Chronic Inflammatory Diseases

Immunosuppressants and biologicals are widely used therapeutics for various chronic inflammatory diseases (CID). To gain more detailed insight into their downstream effects, we examined their impact on serum immunoglobulin G (IgG) glycosylation. We analyzed IgG subclass-specific fragment crystallizable (Fc) N-glycosylation in patients suffering from various CID using the LC-MS approach. Firstly, we compared IgG Fc N-glycosylation between 128 CID patients and 204 healthy controls. Our results replicated previously observed CID-related decrease in IgG Fc galactosylation (adjusted p-value range 1.70 × 10⁻²–5.95 × 10⁻²²) and sialylation (adjusted p-value range 1.85 × 10⁻²–1.71 × 10⁻¹⁸). Secondly, to assess changes in IgG Fc N-glycosylation associated with therapy and remission status, we compared 139 CID patients receiving either azathioprine, infliximab, or vedolizumab therapy. We observed an increase in IgG Fc galactosylation (adjusted p-value range 1.98 × 10⁻²–1.30 × 10⁻¹⁵) and sialylation (adjusted p-value range 3.28 × 10⁻⁶–4.34 × 10⁻¹⁸) during the treatment. Furthermore, patients who reached remission displayed increased Fc galactosylation levels (p-value range 2.25 × 10⁻²–5.44 × 10⁻³) in comparison to patients with active disease. In conclusion, the alterations in IgG Fc glycosylation and the fact these changes are even more pronounced in patients who achieved remission, suggest modulation of IgG inflammatory potential associated with CID therapy.

IgG N-Glycosylation from Patients with Pemphigus Treated with Rituximab

Pemphigus is a life-threatening auto-immune blistering disease of the skin and mucous membrane that is caused by the production of auto-antibodies (auto-Abs) directed against adhesion proteins: desmoglein 1 and 3. We demonstrated in the “Ritux3” trial, the high efficacy of rituximab, an anti-CD20 recombinant monoclonal antibody, as the first-line treatment for pemphigus. However, 25% of patients relapsed during the six-month period after rituximab treatment. These early relapses were associated with a lower decrease in anti-desmoglein auto-Abs after the initial cycle of rituximab. The N-glycosylation of immunoglobulin-G (IgG) can affect their affinity for Fc receptors and their serum half-life. We hypothesized that the extended half-life of Abs could be related to modifications of IgG N-glycans. The IgG N-glycome from pemphigus patients and its evolution under rituximab treatment were analyzed. Pemphigus patients presented a different IgG N-glycome than healthy donors, with less galactosylated, sialylated N-glycans, as well as a lower level of N-glycans bearing an additional N-acetylglucosamine. IgG N-glycome from patients who achieved clinical remission was not different to the one observed at baseline. Moreover, our study did not identify the N-glycans profile as discriminating between relapsing and non-relapsing patients. We report that pemphigus patients present a specific IgG N-glycome. The changes observed in these patients could be a biomarker of autoimmunity susceptibility rather than a sign of inflammation.

Changes of IgG N-Glycosylation in Thyroid Autoimmunity: The Modulatory Effect of Methimazole in Graves' Disease and the Association With the Severity of Inflammation in Hashimoto's Thyroiditis

The N-glycome of immunoglobulin G (IgG), the most abundant glycoprotein in human blood serum, reflects pathological conditions of autoimmunity and is sensitive to medicines applied in disease therapy. Due to the high sensitivity of N-glycosylation, the IgG N-glycan profile may serve as an indicator of an ongoing inflammatory process. The IgG structure and its effector functions are strongly dependent on the composition of N-glycans attached to the Fc fragment, and the binding of antigens is regulated by Fab sugar moieties. Because of the crucial role of N-glycans in IgG function, remodeling of its N-oligosaccharides can induce pathological changes that ultimately contribute to the development of autoimmunity; restoration of their physiological structure is critical to the reduction of disease symptoms. Our recently published data have shown that the pathology of autoimmune thyroid diseases (AITDs), including Hashimoto’s thyroiditis (HT) and Graves’ disease (GD), is accompanied by alterations of the composition of IgG N-glycans. The present study is a more in-depth investigation of IgG glycosylation in both AITDs, designed to determine the relationship between the severity of thyroid inflammation and IgG N-glycan structures in HT, and to assess the impact of immunosuppressive therapy on the N-glycan profile in GD patients. The study material consisted of human serum samples collected from donors with elevated anti-thyroglobulin (Tg) and/or anti-thyroperoxidase (TPO) IgGs without symptoms of hypothyroidism (n=68), HT patients characterized by high autoantibody titers and advanced destruction of the thyroid gland (n=113), GD patients with up-regulated IgG against thyroid-stimulating hormone receptor (TSHR) before (n=62) and after (n=47) stabilization of TSH level as a result of methimazole therapy (study groups), and healthy donors (control group, n=90). IgG was isolated from blood serum using protein G affinity chromatography. N-glycans were released from IgG by PNGase F digestion and analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) after 2-aminobenzamide (2-AB) labeling. UPLC-MS chromatograms were integrated into 25 peaks (GP) in the Waters UNIFI Scientific Information System, and N-glycans were assigned based on the glucose unit values and mass-to-charge ratios (m/z) of the detected ions. The Kruskal-Wallis non-parametric test was used to determine the statistical significance of the results (p<0.05). The obtained results suggest that modifications of IgG sialylation, galactosylation and core-fucosylation are associated with the severity of HT symptoms. Methimazole therapy implemented in GD patients affected the IgG N-glycan profile; as a result, the content of the sialylated and galactosylated oligosaccharides with core fucose differed after treatment. Our results suggest that N-glycosylation of IgG undergoes dynamic changes during the intensification of thyroiditis in HT, and that in GD autoimmunity it is affected significantly by immunosuppressive therapy.

Ig Glycosylation in Ulcerative Colitis: It's Time for New Biomarkers

Background: Ulcerative colitis (UC) is a chronic relapsing disease, which needs a continue monitoring, especially during biological therapies. An increasing number of patients is treated with anti-Tumor Necrosis factor (TNF) drugs, and current research is focalized to identify biomarkers able to monitor the disease and to predict therapeutic outcome.

Methods: We enrolled consecutive UC patients treated with anti-TNF, naïve to biologic drugs. Therapeutic outcome was evaluated after 54 weeks of treatment in terms of clinical remission (Partial Mayo Score -PMS- <2) and mucosal healing (Mayo Endoscopic Score <2). On serum samples collected at baseline and after 54 weeks of treatment, a Lectin-based ELISA assay was performed, and specific glycosylation patterns were evaluated by biotin-labelled lectins. We have also collected 21 healthy controls (NHS) samples, age and sex-matched.

Results: Out of 44 UC patients enrolled, 22 achieved clinical remission and mucosal healing after 54 weeks. At baseline, when Protein A was used as coating, UC patients non-responders showed a reduced reactivity to Jacalin (JAC) in comparison with NHS (p = 0.04). After one year of treatment, a decrease in JAC binding was seen only in responders, in comparison with baseline (p = 0.04). When JAC binding was tested selecting IgG by means of Fab anti-IgG Fab, UC patients displayed an increased reactivity after anti-TNF therapy (p < 0,0001 vs controls). At baseline, PMS inversely correlates with JAC binding when Fab anti-IgG Fab was used in solid phase (r² = 0,2211; p = 0,0033). Patients with higher PMS at baseline (PMS ≥5) presented lower binding capacity for JAC in comparison with NHS and with lower PMS patients (p = 0,0135 and p = 0,0089, respectively).

Conclusion: Ig glycosylation was correlated with clinical and endoscopic activity in patients with UC. JAC protein A-selected Ig showed a possible role in predicting therapeutic effectiveness. If these data would be confirmed, Ig glycosylation could be used as biomarker in UC.

Immunoglobulin G Glycosylation Changes in Aging and Other Inflammatory Conditions

Among the multiple roles played by protein glycosylation, the fine regulation of biological interactions is one of the most important. The asparagine 297 (Asn₂₉₇) of IgG heavy chains is decorated by a diantennary glycan bearing a number of galactose and sialic acid residues on the branches ranging from 0 to 2. In addition, the structure can present core-linked fucose and/or a bisecting GlcNAc. In many inflammatory and autoimmune conditions, as well as in metabolic, cardiovascular, infectious, and neoplastic diseases, the IgG Asn₂₉₇-linked glycan becomes less sialylated and less galactosylated, leading to increased expression of glycans terminating with GlcNAc. These conditions alter also the presence of core-fucose and bisecting GlcNAc. Importantly, similar glycomic alterations are observed in aging. The common condition, shared by the above-mentioned pathological conditions and aging, is a low-grade, chronic, asymptomatic inflammatory state which, in the case of aging, is known as inflammaging. Glycomic alterations associated with inflammatory diseases often precede disease onset and follow remission. The aberrantly glycosylated IgG glycans associated with inflammation and aging can sustain inflammation through different mechanisms, fueling a vicious loop. These include complement activation, Fcγ receptor binding, binding to lectin receptors on antigen-presenting cells, and autoantibody reactivity. The complex molecular bases of the glycomic changes associated with inflammation and aging are still poorly understood.

Sialylated Immunoglobulins for the Treatment of Immuno-Inflammatory Diseases

Immunoglobulins are the potent effector proteins of the humoral immune response. In the course of evolution, immunoglobulins have formed extremely diverse types of molecular structures with antigen-recognizing, antigen-binding, and effector functions embedded in a single molecule. Polysaccharide moiety of immunoglobulins plays the essential role in immunoglobulin functioning. There is growing evidence that the carbohydrate composition of immunoglobulin-linked glycans, and especially their terminal sialic acid residues, provide a key effect on the effector functions of immunoglobulins. Possibly, sialylation of Fc glycan is a common mechanism of IgG anti-inflammatory action in vivo. Thus, the post-translational modification (glycosylation) of immunoglobulins opens up significant possibilities in the diagnosis of both immunological and inflammatory disorders and in their therapies. This review is focused on the analysis of glycosylation of immunoglobulins, which can be a promising addition to improve existing strategies for the diagnosis and treatment of various immuno-inflammatory diseases.

IgG-Fc glycosylation before and after rituximab treatment in immune thrombocytopenia

The interactions of antibodies with myeloid Fcγ receptors and the complement system are regulated by an Asn297-linked glycan in the Fc portion of IgG. Alterations of serum IgG-Fc glycosylation have been reported in various autoimmune diseases, and correlate with treatment response and disease activity. We hypothesized that IgG-Fc glycosylation is altered in immune thrombocytopenia (ITP) and associates with response to anti-CD20 monoclonal antibody treatment (rituximab). IgG-Fc glycosylation was analyzed by liquid chromatography-mass spectrometry. We found that IgG-Fc glycosylation was identical between refractory ITP patients (HOVON64 trial; N = 108) and healthy controls (N = 120). Two months after rituximab treatment, we observed a shift in Fc glycosylation, with a mean 1.7% reduction in galactosylation for IgG1 and IgG4 and a mean 1.5% increase for bisection in IgG1, IgG2/3 and IgG4 (adjusted p < 1.7 × 10⁻³ and p < 2 × 10⁻⁴, respectively). Neither baseline nor longitudinal changes in IgG-Fc glycosylation after rituximab were associated with clinical treatment response. We conclude that IgG-Fc glycosylation in refractory ITP is similar to healthy controls and does not predict treatment responses to rituximab. The observed changes two months after treatment suggest that rituximab may influence total serum IgG-Fc glycosylation. Overall, our study suggests that the pathophysiology of refractory ITP may differ from other autoimmune diseases.

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.

IgG Fc Glycosylation Patterns of Preterm Infants Differ With Gestational Age

Preterm infants acquire reduced amounts of Immunoglobulin G (IgG) via trans-placental transfer as compared to term infants which might explain their high susceptibility for infections. The reduced amount of IgG antibodies also results in a lower amount of anti-inflammatory Fc N-galactosylated and -sialylated IgG antibodies. This reduction or, even more, a qualitative shift in the type of IgG Fc glycosylation might contribute to the increased risk for sustained inflammatory diseases in preterm infants. It was the aim of our explorative study to investigate the IgG Fc glycosylation patterns in preterm infants of different gestational ages compared to term infants and mothers of preterm infants. In plasma samples of preterm infants (n = 38), we investigated IgG concentrations by use of ELISA. Furthermore, we analyzed IgG Fc glycosylation patterns in plasma of preterm infants (n = 86, 23-34 weeks of gestation), term infants (n = 15) and mothers from preterm infants (n = 41) using high performance liquid chromatography. Extremely low gestational age infants (born < 28 weeks of gestation during second trimester) had reduced IgG concentrations and decreased proportions of galactosylated (84.5 vs. 88.4%), sialylated (14.5 vs. 17.9%) and bisecting N-acetylglucosamine-containing (8.4 vs. 10.8%) IgG Fc N-linked glycans as compared to preterm infants born ≥28 weeks of gestation (during third trimester) and term infants. Increased non-galactosylated (agalactosylated, 16.9 vs. 10.6%) IgG Fc N-linked glycans were associated with the development of chronic inflammatory bronchopulmonary dysplasia (BPD). However, mothers of preterm infants born during second or third trimester of pregnancy did not show significant differences in IgG Fc glycosylation patterns. Thus, the IgG Fc glycosylation patterns of preterm infants depend on their gestational age. Although lack of bisecting N-acetylglucosamine has been associated with less inflammatory effector functions, the decreased IgG Fc galactosylation and sialylation with lower gestational age suggest a rather pro-inflammatory pattern. The difference in IgG Fc glycosylation patterns between preterm infants and mothers of preterm infants suggests a selective enrichment of IgG glyco forms in preterm infants, which might contribute to or result of the development of sustained inflammatory diseases like BPD.

Measurement of Neutral and Sialylated IgG N-Glycome at Asn-297 by CE-LIF to Assess Hypogalactosylation in Rheumatoid Arthritis

Modulations in immunoglobulin G (IgG) N-glycosylation have been observed in many human diseases including chronic inflammatory diseases such as rheumatoid arthritis and also cancer. In this chapter, we describe how to determine hypogalactosylation for clinical samples, namely the sample preparation of IgG N-glycans at Asn-297 as well as the measurement of neutral and sialylated N-glycans by capillary electrophoresis coupled with laser-induced fluorescence (CE-LIF).This semiautomated protocol describes the isolation polyclonal antibodies from serum, the separation of IgG-Fc glycopeptides from IgG antigen-binding fragment by pepsin digestion. Afterward, enzymatically released IgG-Fc N-glycans are cleaned up using a polyaromatic adsorbent resin followed by carbon purification. Sialic acids are then derivatized prior to glycan labeling. As a result, the agalactosylated N-glycan A2 does not co-migrate with sialylated N-glycans, which refines the measurement of hypogalactosylation by CE-LIF.

Mechanical strain determines the site-specific localization of inflammation and tissue damage in arthritis

Many pro-inflammatory pathways leading to arthritis have global effects on the immune system rather than only acting locally in joints. The reason behind the regional and patchy distribution of arthritis represents a longstanding paradox. Here we show that biomechanical loading acts as a decisive factor in the transition from systemic autoimmunity to joint inflammation. Distribution of inflammation and erosive disease is confined to mechano-sensitive regions with a unique microanatomy. Curiously, this pathway relies on stromal cells but not adaptive immunity. Mechano-stimulation of mesenchymal cells induces CXCL1 and CCL2 for the recruitment of classical monocytes, which can differentiate into bone-resorbing osteoclasts. Genetic ablation of CCL2 or pharmacologic targeting of its receptor CCR2 abates mechanically-induced exacerbation of arthritis, indicating that stress-induced chemokine release by mesenchymal cells and chemo-attraction of monocytes determines preferential homing of arthritis to certain hot spots. Thus, mechanical strain controls the site-specific localisation of inflammation and tissue damage in arthritis.

Endoglycosidase S Enables a Highly Simplified Clinical Chemistry Procedure for Direct Assessment of Serum IgG Undergalactosylation in Chronic Inflammatory Disease

Over the past 30 years, it has been firmly established that a wide spectrum of (autoimmune) diseases such as rheumatoid arthritis, Crohn's and lupus, but also other pathologies like alcoholic and non-alcoholic steatohepatitis (ASH and NASH) are driven by chronic inflammation and are hallmarked by a reduced level of serum IgG galactosylation. IgG (under)galactosylation is a promising biomarker to assess disease severity, and monitor and adjust therapy. However, this biomarker has not been implemented in routine clinical chemistry because of a complex analytical procedure that necessitates IgG purification, which is difficult to perform and validate at high throughput. We addressed this issue by using endo-β-N-acetylglucosaminidase from Streptococcus pyogenes (endoS) to specifically release Fc N-glycans in whole serum. The entire assay can be completed in a few hours and only entails adding endoS and labeling the glycans with APTS. Glycans are then readily analyzed through capillary electrophoresis. We demonstrate in two independent patient cohorts that IgG undergalactosylation levels obtained with this assay correlate very well with scores calculated from PNGaseF-released glycans of purified antibodies. Our new assay allows to directly and specifically measure the degree of IgG galactosylation in serum through a fast and completely liquid phase protocol, without the requirement for antibody purification. This should help advancing this biomarker toward clinical implementation.

Sialylated Autoantigen-Reactive IgG Antibodies Attenuate Disease Development in Autoimmune Mouse Models of Lupus Nephritis and Rheumatoid Arthritis

Pro- and anti-inflammatory effector functions of IgG antibodies (Abs) depend on their subclass and Fc glycosylation pattern. Accumulation of non-galactosylated (agalactosylated; G0) IgG Abs in the serum of rheumatoid arthritis and systemic lupus erythematosus (SLE) patients reflects severity of the diseases. In contrast, sialylated IgG Abs are responsible for anti-inflammatory effects of the intravenous immunoglobulin (pooled human serum IgG from healthy donors), administered in high doses (2 g/kg) to treat autoimmune patients. However, whether low amounts of sialylated autoantigen-reactive IgG Abs can also inhibit autoimmune diseases is hardly investigated. Here, we explore whether sialylated autoantigen-reactive IgG Abs can inhibit autoimmune pathology in different mouse models. We found that sialylated IgG auto-Abs fail to induce inflammation and lupus nephritis in a B cell receptor (BCR) transgenic lupus model, but instead are associated with lower frequencies of pathogenic Th1, Th17 and B cell responses. In accordance, the transfer of small amounts of immune complexes containing sialylated IgG Abs was sufficient to attenuate the development of nephritis. We further showed that administration of sialylated collagen type II (Col II)-specific IgG Abs attenuated the disease symptoms in a model of Col II-induced arthritis and reduced pathogenic Th17 cell and autoantigen-specific IgG Ab responses. We conclude that sialylated autoantigen-specific IgG Abs may represent a promising tool for treating pathogenic T and B cell immune responses in autoimmune diseases.

Glycome Patterns of Perfusate in Livers Before Transplantation Associate With Primary Nonfunction

BACKGROUND & AIMS

Primary nonfunction (PNF) is a rare complication after liver transplantation that requires urgent retransplantation. PNF is associated with livers from extended criteria donors. Clinical and biochemical factors have not been identified that reliably associate with graft function after liver transplantation. Serum patterns of N-glycans associate with changes in the liver. We analyzed perfusate from grafted liver to identify protein glycosylation patterns associated with PNF.

METHODS

We performed a prospective study of consecutive patients who underwent liver transplantation (66 patients, from 1 center, in the derivation set, and 56 patients, from 2 centers, in the validation set) in Belgium, from October 1, 2011, through April 30, 2017. All donor grafts were transported using cold static storage, and perfusate samples were collected from the livers by flushing of hepatic veins before transplantation. Protein-linked N-glycans were isolated from perfusate samples and analyzed with a multicapillary electrophoresis-based ABI3130 sequencer. We compared glycan patterns between patients with vs without PNF of transplanted livers. PNF was defined as the need for urgent retransplantation when a graft had no evidence of function, after exclusion of other causes, such as hepatic artery thrombosis or acute cellular rejection.

RESULTS

The relative abundance of a single glycan, agalacto core-alpha-1,6-fucosylated biantennary glycan (NGA2F) was significantly increased in perfusate of livers given to 4 patients who developed PNF after liver transplantation compared with livers given to patients who did not develop PNF. Level of NGA2F identified patients with PNF with 100% accuracy. This glycomarker was the only factor associated with PNF in multivariate analysis in the derivation and the validation sets (P < .0001).

CONCLUSIONS

In an analysis of patients who underwent liver transplantation, we associated graft perfusate level of glycan NGA2F present on perfusate proteins with development of PNF with 100% accuracy, and validated this finding in a separate cohort of patients. This biomarker might be used to assess grafts before transplantation, especially when high-risk organs are under consideration.

Hypogalactosylation of immunoglobulin G in rheumatoid arthritis: relationship to HLA-DRB1 shared epitope, anticitrullinated protein antibodies, rheumatoid factor, and correlation with inflammatory activity

Background

Galactosylation of immunoglobulin G (IgG) is reduced in rheumatoid arthritis (RA) and assumed to correlate with inflammation and altered humoral immunity. IgG hypogalactosylation also increases with age. To investigate dependencies in more detail, we compared IgG hypogalactosylation between patients with RA, patients with axial spondyloarthritis (axSpA), and healthy control subjects (HC), and we studied it in RA on the background of HLA-DRB1 shared epitope (SE), anticitrullinated protein antibodies (ACPA), and/or rheumatoid factor (RF) status.

Methods

Patients with RA (n = 178), patients with axSpA (n = 126), and HC (n = 119) were characterized clinically, and serum IgG galactosylation was determined by capillary electrophoresis. Markers of disease activity, genetic susceptibility, and serologic response included C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), DAS28, SE, HLA-B27, ACPA, and RF. Expression of glycosylation enzymes, including beta 1–4 galactosyltransferase (B4GALT3) activity, were estimated from transcriptome data for B-cell development (GSE19599) and differentiation to plasma cells (GSE12366).

Results

IgG hypogalactosylation was restricted to RA and associated with increasing CRP levels (p < 0.0001). In axSpA, IgG hypogalactosylation was comparable to HC and only marginally increased upon elevated CRP. Restriction to RA was maintained after correction for CRP and age. Treatment with sulfasalazine resulted in significantly reduced IgG hypogalactosylation (p = 0.003) even after adjusting for age, sex, and CRP (p = 0.009). SE-negative/ACPA-negative RA exhibited significantly less IgG hypogalactosylation than all other strata (vs SE-negative/ACPA-positive, p = 0.009; vs SE-positive/ACPA-negative, p = 0.04; vs SE-positive/ACPA-positive, p < 0.02); however, this indicated a trend only after Bonferroni correction for multiple testing. In SE-positive/ACPA-negative RA IgG hypogalactosylation was comparable to ACPA-positive subsets. The relationship between IgG hypogalactosylation and disease activity was significantly different between strata defined by SE (CRP, p = 0.0003, p_Bonferroni = 0.0036) and RF (CRP, p < 0.0001, p_Bonferroni < 0.0012), whereas ACPA strata revealed only a nonsignificant trend (p = 0.15). Gene expression data indicated that the key enzyme for galactosylation of immunoglobulins, B4GALT3, is expressed at lower levels in B cells than in plasma cells.

Conclusions

Increased IgG hypogalactosylation in RA but not in axSpA points to humoral immune response as a precondition. Reduced B4GALT3 expression in B cells compared with plasma cells supports relatedness to early B-cell triggering. The differential influence of RA treatment on IgG hypogalactosylation renders it a potential diagnostic target for further studies.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1540-0) contains supplementary material, which is available to authorized users.

Glycobiology of Aging

Glycosylation is one of the most frequent post-translational modification of proteins. Many membrane and secreted proteins are decorated by sugar chains mainly linked to asparagine (N-linked) or to serine or threonine (O-linked). The biosynthesis of the sugar chains is mainly controlled by the activity of their biosynthetic enzymes: the glycosyltransferases. Glycosylation plays multiple roles, including the fine regulation of the biological activity of glycoproteins. Inflammaging is a chronic low grade inflammatory status associated with aging, probably caused by the continuous exposure of the immune system to inflammatory stimuli of endogenous and exogenous origin. The aging-associated glycosylation changes often resemble those observed in inflammatory conditions. One of the most reproducible markers of calendar and biological aging is the presence of N-glycans lacking terminal galactose residues linked to Asn₂₉₇ of IgG heavy chains (IgG-G0). Although the mechanism(s) generating IgG-G0 remain unclear, their presence in a variety of inflammatory conditions suggests a link with inflammaging. In addition, these aberrantly glycosylated IgG can exert a pro-inflammatory effect through different mechanisms, triggering a self-fueling inflammatory loop. A strong association with aging has been documented also for the plasmatic forms of glycosyltrasferases B4GALT1 and ST6GAL1, although their role in the extracellular glycosylation of antibodies does not appear likely. Siglecs, are a group of sialic acid binding mammalian lectins which mainly act as inhibitory receptors on the surface of immune cells. In general activity of Siglecs appears to be associated with long life, probably because of their ability to restrain aging-associated inflammation.

Altered glycan accessibility on native immunoglobulin G complexes in early rheumatoid arthritis and its changes during therapy

The goal of this study was to investigate the glycosylation profile of native immunoglobulin (Ig)G present in serum immune complexes in patients with rheumatoid arthritis (RA). To accomplish this, lectin binding assays, detecting the accessibility of glycans present on IgG-containing immune complexes by biotinylated lectins, were employed. Lectins capturing fucosyl residues (AAL), fucosylated tri-mannose N-glycan core sites (LCA), terminal sialic acid residues (SNA) and O-glycosidically linked galactose/N-acetylgalactosamine (GalNac-L) were used. Patients with recent-onset RA at baseline and after 3-year follow-up were investigated. We found that native IgG was complexed significantly more often with IgM, C1q, C3c and C-reactive protein (CRP) in RA patients, suggesting alterations of the native structure of IgG. The total accessibility of fucose residues on captured immune complexes to the respective lectin was significantly higher in patients with RA. Moreover, fucose accessibility on IgG-containing immune complexes correlated positively with the levels of antibodies to cyclic citrullinated peptides (anti-CCP). We also observed a significantly higher accessibility to sialic acid residues and galactose/GalNAc glyco-epitopes in native complexed IgG of patients with RA at baseline. While sialic acid accessibility increased during treatment, the accessibility of galactose/GalNAc decreased. Hence, successful treatment of RA was associated with an increase in the SNA/GalNAc-L ratio. Interestingly, the SNA/GalNAc-L ratio in particular rises after glucocorticoid treatment. In summary, this study shows the exposure of glycans in native complexed IgG of patients with early RA, revealing particular glycosylation patterns and its changes following pharmaceutical treatment.

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.

Loci associated with N-glycosylation of human IgG are not associated with rheumatoid arthritis: a Mendelian randomisation study

OBJECTIVES

A recent study identified 16 genetic variants associated with N-glycosylation of human IgG. Several of the genomic regions where these single nucleotide polymorphisms (SNPs) reside have also been associated with autoimmune disease (AID) susceptibility, suggesting there may be pleiotropy (genetic sharing) between loci controlling both N-glycosylation and AIDs. We investigated this by testing variants associated with levels of IgG N-glycosylation for association with rheumatoid arthritis (RA) susceptibility using a Mendelian randomisation study, and testing a subset of these variants in a less well-powered study of treatment response and severity.

METHODS

SNPs showing association with IgG N-glycosylation were analysed for association with RA susceptibility in 14 361 RA cases and 43 923 controls. Five SNPs were tested for association with response to anti-tumour necrosis factor (TNF) therapy in 1081 RA patient samples and for association with radiological disease severity in 342 patients.

RESULTS

Only one SNP (rs9296009) associated with N-glycosylation showed an association (p=6.92×10(-266)) with RA susceptibility, although this was due to linkage disequilibrium with causal human leukocyte antigen (HLA) variants. Four regions of the genome harboured SNPs associated with both traits (shared loci); although statistical analysis indicated that the associations observed for the two traits are independent. No SNPs showed association with response to anti-TNF therapy. One SNP rs12342831 was modestly associated with Larsen score (p=0.05).

CONCLUSIONS

In a large, well-powered cohort of RA patients, we show SNPs driving levels of N-glycosylation have no association with RA susceptibility, indicating colocalisation of associated SNPs are not necessarily indicative of a shared genetic background or a role for glycosylation in disease susceptibility.

Altered glycosylation of complexed native IgG molecules is associated with disease activity of systemic lupus erythematosus

In addition to the redundancy of the receptors for the Fc portion of immunoglobulins, glycans result in potential ligands for a plethora of lectin receptors found in immune effector cells. Here we analysed the exposure of glycans containing fucosyl residues and the fucosylated tri-mannose N-type core by complexed native IgG in longitudinal serum samples of well-characterized patients with systemic lupus erythematosus. Consecutive serum samples of a cohort of 15 patients with systemic lupus erythematosus during periods of increased disease activity and remission were analysed. All patients fulfilled the 1982 American College of Rheumatology classification criteria. Sera of 15 sex- and age-matched normal healthy blood donors served as controls. The levels and type of glycosylation of complexed random IgG was measured with lectin enzyme-immunosorbent assays. After specifically gathering IgG complexes from sera, biotinylated lectins Aleuria aurantia lectin and Lens culinaris agglutinin were employed to detect IgG-associated fucosyl residues and the fucosylated tri-mannose N-glycan core, respectively. In sandwich-ELISAs, IgG-associated IgM, IgA, C1q, C3c and C-reactive protein (CRP) were detected as candidates for IgG immune complex constituents. We studied associations of the glycan of complexed IgG and disease activity according to the physician's global assessment of disease activity and the systemic lupus erythematosus disease activity index 2000 documented at the moment of blood taking. Our results showed significantly higher levels of Aleuria aurantia lectin and Lens culinaris agglutinin binding sites exposed on IgG complexes of patients with systemic lupus erythematosus than on those of normal healthy blood donors. Disease activity in systemic lupus erythematosus correlated with higher exposure of Aleuria aurantia lectin-reactive fucosyl residues by immobilized IgG complexes. Top levels of Aleuria aurantia lectin-reactivity were found in samples taken during the highest activity of systemic lupus erythematosus. Our results show that native circulating IgG complexes from active systemic lupus erythematosus patients expose fucosyl residues and their glycan core is accessible to soluble lectins. Two putative mechanisms may contribute to the increased exposure of these glycans: (1) the canonical N-glycosylation site of the IgG-CH2 domain; (2) an IgG binding non-IgG molecule, like complement or C-reactive protein. In both cases the complexed IgG may be alternatively targeted to lectin receptors of effector cells, e.g. dendritic cells.

Lack of galactosylation enhances the pathogenic activity of IgG1 but Not IgG2a anti-erythrocyte autoantibodies

IgG bears asparagine-linked oligosaccharide side chains in the Fc region. Variations in their extent of galactosylation and sialylation could modulate IgG Fc-dependent effector functions, and hence Ab activity. However, it has not yet been clarified whether the pathogenic potential of IgG autoantibodies is consistently enhanced by the absence of galactose residues per se or the lack of terminal sialylation, which is dependent on galactosylation. Moreover, it remains to be defined whether the increased pathogenicity of agalactosylated IgG is related to activation of the complement pathway by mannose-binding lectin, as suggested by in vitro studies. Using a murine model of autoimmune hemolytic anemia, we defined the contribution of galactosylation or sialylation to the pathogenic activity of IgG1 and IgG2a anti-erythrocyte class-switch variants of 34-3C monoclonal autoantibody. We generated their degalactosylated or highly sialylated glycovariants and compared their pathogenic effects with those of highly galactosylated or desialylated counterparts. Our results demonstrated that lack of galactosylation, but not sialylation, enhanced the pathogenic activity of 34-3C IgG1, but not IgG2a autoantibodies. Moreover, analysis of in vivo complement activation and of the pathogenic activity in mice deficient in C3 or IgG FcRs excluded the implication of mannose-binding lectin-mediated complement activation in the enhanced pathogenic effect of agalactosylated IgG1 anti-erythrocyte autoantibodies.

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.

Anti-rhesus D prophylaxis in pregnant women is based on sialylated IgG antibodies

Red blood cells (RBCs) from a rhesus D (RhD)-positive fetus that reach the bloodstream of an RhD-negative pregnant woman during birth can induce a pathogenic antibody (Ab) response against the RhD-positive RBCs, leading to fetal hemolytic disease in subsequent pregnancies. To prevent a pathogenic immune reaction, the RhD-negative mother receives serum immunoglobulin G (IgG) containing polyclonal RhD-specific IgG Abs that is purified from healthy RhD-negative men immunized with RhD-positive RBCs. However, the protective mechanism of these polyclonal RhD-specific IgG Abs is unclear. It has become increasingly clear that the effector function of IgG Abs is regulated by the glycan pattern linked to the Fc region of IgG Abs. Non-fucosylated (afucosylated) IgG Abs have a higher affinity for activating Fc gamma receptors, and thus induce a stronger Ab-dependent cellular cytotoxicity (ADCC) reaction than do fucosylated IgG Abs. Agalactosylated and asialylated, autoantigen-specific serum IgG Abs correlate with pro-inflammatory immune responses and disease activity in patients with rheumatoid arthritis. In contrast, galactosylated and sialylated IgG Abs are immunosuppressive and inhibit in form of immune complexes (ICs) dendritic cell (DC) maturation and pro-inflammatory T and B cell immune responses in an antigen-specific manner. However, the galactosylation and sialylation levels of the protective polyclonal RhD-specific IgG Abs are unknown. Here, we purified RhD-specific IgG Abs from the approved commercial product Rhophylac® (CSL Behring) and found that these RhD-specific IgG Abs were even more galactosylated and sialylated than the total Rhophylac® IgG Abs. This result suggests that these galactosylated and sialylated polyclonal RhD-specific IgG Abs are immunosuppressive and induce tolerance against RhD, which would be in strong contrast to a low fucosylated, low galactosylated and low sialylated monoclonal RhD-specific IgG Ab developed to prevent fetal hemolytic disease that has recently passed a clinical phase II study.

Glycosylation status of serum in inflammatory arthritis in response to anti-TNF treatment

OBJECTIVE

Glycosylation is the most common post-translational modification and is altered in disease. The typical glycosylation change in patients with inflammatory arthritis (IA) is a decrease in galactosylation levels on IgG. The aim of this study is to evaluate the effect of anti-TNF therapy on whole serum glycosylation from IA patients and determine whether these alterations in the glycome change upon treatment of the disease.

METHODS

Serum samples were collected from 54 IA patients before treatment and at 1 and 12 months after commencing anti-TNF therapy. N-linked glycans from whole serum samples were analysed using a high-throughput hydrophilic interaction liquid chromatography-based method.

RESULTS

Glycosylation on the serum proteins of IA patients changed significantly with anti-TNF treatment. We observed an increase in galactosylated glycans from IgG, also an increase in core-fucosylated biantennary galactosylated glycans and a decrease in sialylated triantennary glycans with and without outer arm fucose. This increase in galactosylated IgG glycans suggests a reversing of the N-glycome towards normal healthy profiles. These changes are strongly correlated with decreasing CRP, suggesting a link between glycosylation changes and decreases in inflammatory processes.

CONCLUSION

Glycosylation changes in the serum of IA patients on anti-TNF therapy are strongly associated with a decrease in inflammatory processes and reflect the effect of anti-TNF on the immune system.

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.

Multiple juvenile idiopathic arthritis subtypes demonstrate proinflammatory IgG glycosylation

OBJECTIVE

Rheumatoid arthritis is associated with an excess of agalactosylated (G0) IgG that is considered relatively proinflammatory. Assessment of this association in juvenile idiopathic arthritis (JIA) is complicated by age-dependent IgG glycan variation. The aim of this study was to conduct the first large-scale survey of IgG glycans in healthy children and patients with JIA, with a focus on early childhood, the time of peak JIA incidence.

METHODS

IgG glycans from healthy children and disease-modifying antirheumatic drug-naive patients with JIA were characterized using high-performance liquid chromatography. Agalactosylated glycans were quantitated with reference to monogalactosylated (G1) species. Associations were sought between the G0:G1 ratio and disease characteristics.

RESULTS

Among healthy children ages 9 months to 16 years (n = 165), the G0:G1 ratio was highly age dependent, with the ratio peaking to 1.19 in children younger than age 3 years and declining to a nadir of 0.83 after age 10 years (Spearman's ρ = 0.60, P < 0.0001). In patients with JIA (n = 141), the G0:G1 ratio was elevated compared with that in control subjects (1.32 versus 1.02; P < 0.0001). The G0:G1 ratio corrected for age was abnormally high in all JIA subtypes (enthesitis-related arthritis was not assessed), most strikingly in systemic JIA. Glycosylation aberrancy was comparable in patients with and those without antinuclear antibodies and in both early- and late-onset disease and exhibited at most a weak correlation with markers of inflammation.

CONCLUSION

IgG glycosylation is skewed toward proinflammatory G0 variants in healthy children, in particular during the first few years of life. This deviation is exaggerated in patients with JIA. The role for IgG glycan variation in immune function in children, including the predilection of JIA for early childhood, remains to be defined.

Tregitope update: mechanism of action parallels IVIg

In the course of screening immunoglobulin G (IgG) sequences for T cell epitopes, we identified novel Treg epitope peptides, now called Tregitopes, contained in the highly conserved framework regions of Fab and Fc. Tregitopes may provide one explanation for the expansion and stimulation of Treg cells following intravenous immunoglobulin (IVIg) therapy. Their distinguishing characteristics include in silico signatures that suggest high-affinity binding to multiple human HLA class II DR and conservation across IgG isotypes and mammalian species with only minor amino acid modifications. Tregitopes induce expansion of CD4(+)/CD25(hi)/FoxP3(+) T cells and suppress immune responses to co-incubated antigens in vitro. By comparing the human IgG Tregitopes (hTregitopes 167 and 289, located in the IgG CH1 and CH2 domains) and Fab to murine sequences, we identified class II-restricted murine Tregitope homologs (mTregitopes). In vivo, mTregitopes suppress inflammation and reproducibly induce Tregs to expand. In vitro studies suggest that the Tregitope mechanism of action is to induce Tregs to respond, leading to production of regulatory signals, followed by modulation of dendritic cell phenotype. The identification of Treg epitopes in IgG suggests that additional Tregitopes may also be present in other autologous proteins; methods for identifying and validating such peptides are described here. The discovery of Tregitopes in IgG and other autologous proteins may lead to the development of new insights as to the role of Tregs in autoimmune diseases.

Serum protein N-glycosylation in paediatric non-alcoholic fatty liver disease

OBJECTIVE

We have previously shown the potential of glycomics to distinguish patients with steatosis from patients with non-alcoholic steatohepatitis (NASH) in an adult population. The pattern of disease in paediatric patients is distinct from adults. The objective of this study was to characterize the N -glycomic profile of children with varying degrees of non-alcoholic fatty liver disease (NAFLD) and identify potential biomarker profiles of disease.

METHODS

Serum protein N-glycosylation patterns of 51 paediatric NAFLD patients were assessed with deoxyribonucleic acid sequencer-assisted fluorophore-assisted capillary electrophoresis and compared with histology.

RESULTS

Peak 1 (NGA2F) is the most significantly elevated N-glycan in paediatric NASH patients with peak 5 (NA2) demonstrating the largest decrease. The logarithmically transformed ratio of peak 1 to peak 5 was -0.85 (standard deviation [SD] 0.22) in patients with steatosis and borderline NASH and -0.73 (SD 0.12) in NASH (P = 0.02). The biomarker correlated well with the amount of lobular inflammation with a consistent increase of marker score in ascending stage of lobular inflammation. There was also a trend in differentiating patients with significant fibrosis ≥F2; -0.74 (SD 0.13) from patients with no/minimal fibrosis <F2; -0.86 (SD 0.24), P = 0.06. Analysis of the N-glycans on immunoglobulin G confirmed the undergalactosylation status typical for chronic inflammatory conditions.

CONCLUSIONS

This study is the first glycomic analysis performed in a paediatric NAFLD population. In agreement with the results obtained in adults, B cells play a dominant role in the N-glycan alterations of paediatric NASH patients.

N-glycan based biomarker distinguishing non-alcoholic steatohepatitis from steatosis independently of fibrosis

BACKGROUND

Non-alcoholic fatty liver disease is a spectrum of disorders ranging from steatosis to non-alcoholic steatohepatitis (NASH). Steatosis of the liver is benign, whereas NASH can progress to cirrhosis or even hepatocellular carcinoma. Currently, a liver biopsy is the only validated method to distinct NASH from steatosis.

AIM

The objective of this study was to identify a biomarker specific for NASH based on the N-glycosylation of serum proteins.

METHODS

N-glycosylation patterns were assessed using DNA sequencer-assisted fluorophore-assisted capillary electrophoresis and compared with histology.

RESULTS

Initially, a glycomarker (log[NGA2F]/[NA2]) was developed based on the results obtained in 51 obese non-alcoholic patients scheduled for bariatric surgery. Multivariate analysis showed that our glycomarker had the lowest P-value of all biomarkers in distinguishing NASH from steatosis (P=0.069). The glycomarker was validated in a cohort of 224 non-alcoholic fatty liver disease patients. In both pilot and validation study, glycomarker score increased in ascending amount of lobular inflammation (single-factor ANOVA, P ≤ 0.001 and P=0.012, respectively). The N-glycan profile of immunoglobulin G in the NASH population confirmed the significantly increased undergalactosylation present in these patients.

CONCLUSION

Our glycomarker specifically recognises liver inflammation in obese individuals which is the main trigger for the development of steatohepatitis and can differentiate between steatosis and NASH.

Hypogalactosylation of serum N-glycans fails to predict clinical response to methotrexate and TNF inhibition in rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is associated with hypogalactosylation of immunoglobulin G (IgG). We examined whether a proxy measure for galactosylation of IgG N-glycans could predict response to therapy or was differentially affected by methotrexate (MTX) or TNF blockade.

Methods

Using a previously defined normal phase high-performance liquid chromatography approach, we ascertained the galactosylation status of whole serum N-glycans in two well-defined RA clinical cohorts: the Autoimmune Biomarkers Collaborative Network (n = 98) and Nested I (n = 64). The ratio of agalactosylated to monogalactosylated N-glycans in serum (sG0/G1) was determined before and during therapy with MTX or TNF inhibition and correlated with anticitrullinated peptide antibody (ACPA) status and clinical response as assessed by 28-joint Disease Activity Score utilizing C-reactive peptide and European League Against Rheumatism response criteria.

Results

RA patients from both cohorts exhibited elevation of sG0/G1 at baseline. Improvement in clinical scores correlated with a reduction in sG0/G1 (Spearman's ρ = 0.31 to 0.37; P < 0.05 for each cohort). However, pretreatment sG0/G1 was not predictive of clinical response. Changes in sG0/G1 were similar in the MTX and TNF inhibitor groups. Corrected for disease activity, ACPA positivity correlated with higher sG0/G1.

Conclusions

Baseline serum N-glycan hypogalactosylation, an index previously correlated with hypogalactosylation of IgG N-glycans, did not distinguish patients with rheumatoid arthritis who were likely to experience a favorable clinical response to MTX or TNF blockade. Clinical improvement was associated with partial glycan normalization. ACPA-positive patients demonstrated enhanced N-glycan aberrancy compared with ACPA-negative patients.

B cells in cardiac transplants: from clinical questions to experimental models

After many years of debate, there is now general agreement that B cells can participate in the immune response to cardiac transplants. Acute antibody-mediated rejection (AMR) is the best defined manifestation of B cell responses, but diagnostic and mechanistic questions still surround AMR. Many complement dependent mechanisms of antibody-mediated injury have been elucidated. C5 has become a therapeutic target that may not just truncate complement activation, but also may tip the balance away from inflammation by altering macrophage function. Additional complement independent effects have been identified. These may escape diagnosis and progress to chronic graft injury. The function of B cell infiltrates in cardiac transplants is even more enigmatic. Nodular endocardial infiltrates that contain B cells and plasma cells have been described in protocol biopsies of cardiac transplants for decades, but an understanding of their significance is still evolving based on more critical morphological and molecular evaluation of these infiltrates. A range of infiltrates containing B cells has also been described in the epicardial fat in transplants with advanced chronic rejection. B cells have been observed in endocardial and epicardial tertiary lymphoid nodules, but their impact on antigen presentation or antibody production remains to be determined. Experimental models in small and large animals suggest that B cells could be essential for the formation of lymphoid nodules through cytokine production. Similarly, the role of proinflammatory adipokines in the formation or function of epicardial lymphoid nodules has not been studied. These clinical observations provide critical questions to be addressed in experimental models.

Alterations of serum protein N-glycosylation in two mouse models of chronic liver disease are hepatocyte and not B cell driven

N-glycosylation of immunoglobulin G (IgG) has an important impact on the modification of the total serum N-glycome in chronic liver patients. Our aim was to determine the role and magnitude of the alterations in which hepatocytes and B cells are involved in two mouse models of chronic liver disease. Common bile duct ligation (CBDL) and subcutaneous injections with CCl(4) were induced in B cell-deficient and wild-type (WT) mice. IgG depletion was performed with beads covered with protein A/G and the depletions were evaluated by SDS-PAGE and Western blot analysis. N-glycan analysis was performed by improved DSA-FACE technology. Structural analysis of the mouse serum N-glycans was performed by exoglycosidase digests and MALDI-TOF mass spectrometry of permethylated glycans. The alterations seen in B cell-deficient mice closely resembled the alterations in WT mice, in both the CBDL and the CCl(4) models. N-glycan analysis of the IgG fraction in both mouse models revealed different changes compared with humans. Overall, the impact of IgG glycosylation on total serum glycosylation was marginal. Interestingly, the amount of fibrosis present in CBDL B cell-deficient mice was significantly increased compared with CBDL WT mice, whereas the opposite was true for the CCl(4) model as determined by Sirius red staining. However, this had no major effect on the alteration of N-glycosylation of serum proteins. Alterations of total serum N-glycome in mouse models of chronic liver disease are hepatocyte-driven. Undergalactosylation of IgG is not present in mouse models of chronic liver disease.

The lectin riddle: glycoproteins fractionated from complex mixtures have similar glycomic profiles

One common method used for analyzing the glycoproteome is chromatography using multiple lectins that display different affinities toward oligosaccharide structures. Much has been done to determine lectin affinity using standard glycoproteins with known glycosylation; however, a knowledge of the selectivity and specificity of lectins exposed to complex mixtures of proteins is required if they are to be used as a means of studying the glycoproteome. In the present study, three lectins (Concanavalin A, Jacalin, and Wheat Germ Agglutinin) were used to fractionate glycoproteins from two different complex environments: (1) cell membranes and (2) plasma. Reproducible enrichment of glycoproteins from these samples has been shown to result from the combined use of these lectins. However, the global glycan profiles of the released N- and O-linked oligosaccharides from the glycoproteins retained by the lectins, and from those glycoproteins that did not bind, using both these complex samples, were found to be very similar. That is, although the lectins selectively and reproducibly retained some glycoproteins, other proteins with the same attached oligosaccharide structures did not bind. Some small N- and O-glycan differences were observed in the bound fractions but there was little absolute specificity toward individual oligosaccharide structures known to have high affinity to these lectins. These data indicate that lectins are useful for fractionating glycoproteins from complex mixtures, but that the overall glycoproteome is not isolated by this approach.

Antibody-mediated rejection: emergence of animal models to answer clinical questions

Decades of experiments in small animals had tipped the balance of opinion away from antibodies as a cause of transplant rejection. However, clinical experience, especially with sensitized patients, has convinced basic immunologists of the need to develop models to investigate mechanisms underlying antibody-mediated rejection (AMR). This resurgent interest has resulted in several new rodent models to investigate antibody-mediated mechanisms of heart and renal allograft injury, but satisfactory models of chronic AMR remain more elusive. Nevertheless, these new studies have begun to reveal many insights into the molecular and pathological sequelae of antibody binding to the allograft endothelium. In addition, complement-independent and complement-dependent effects of antibodies on endothelial cells have been identified in vitro. As small animal models become better defined, it is anticipated that they will be more widely used to answer further questions concerning mechanisms of antibody-mediated tissue injury as well as to design therapeutic interventions.

Impact of elevation of total bilirubin level and etiology of the liver disease on serum N-glycosylation patterns in mice and humans

The GlycoFibroTest and GlycoCirrhoTest are noninvasive alternatives for liver biopsy that can be used as a follow-up tool for fibrosis patients and to diagnose cirrhotic patients, respectively. These tests are based on the altered N-glycosylation of total serum protein. Our aim was to investigate the impact of etiology on the alteration of N-glycosylation and whether other characteristics of liver patients could have an influence on N-glycosylation. In human liver patients, no specific alteration could be found to make a distinction according to etiological factor, although alcoholic patients had a significant higher mean value for the GlycoCirrhoTest. Undergalactosylation did not show a significantly different quantitative alteration in the cirrhotic and noncirrhotic population of all etiologies. Importantly, patients with an elevation of total bilirubin level (>2 mg/dl) had a strong increase of glycans modified with alpha1-6 fucose. The fucosylation index was therefore significantly higher in fibrosis/cirrhosis and hepatocellular carcinoma patients with elevated total bilirubin levels irrespective of etiology. Furthermore, in a multiple linear regression analysis, only markers for cholestasis significantly correlated with the fucosylation index. In mouse models of chronic liver disease, the fucosylation index was uniquely significantly increased in mice that were induced with a common bile duct ligation. Mice that were chronically injected with CCl(4) did not show this increase. Apart from this difference, common changes characteristic to fibrosis development in mice were observed. Finally, mice induced with a partial portal vein ligation did not show biological relevant changes indicating that portal hypertension does not contribute to the alteration of N-glycosylation.

GlycoFibroTest is a highly performant liver fibrosis biomarker derived from DNA sequencer-based serum protein glycomics

Liver fibrosis is currently assessed by liver biopsy, a costly and rather cumbersome procedure that is unsuitable for frequent patient monitoring, which drives research into biomarkers for this purpose. To investigate whether the serum N-glycome contains information suitable for this goal, we developed a 96-well plate-based serum N-glycomics sample preparation protocol that only involves fluid transfer steps and incubations in a PCR thermocycler yielding 8-aminopyrene-1,3,6-trisulfonic acid-labeled N-glycans. These N-glycans are then ready for analysis on the capillary electrophoresis-based DNA sequencers that are the current standard in clinical genetics laboratories worldwide. Subsequently we performed a multicenter, blinded study of 376 consecutive chronic hepatitis C virus patients for which liver biopsies and extensive serum biochemistry data were available. Among patients, the METAVIR fibrosis stage distribution was as follows: 10.6% F0, 44.4% F1, 20.5% F2, 18.4% F3, and 6.1% F4. We found that the ratio of two N-glycans, here called GlycoFibroTest, correlates with the histological fibrosis stage equally well as FibroTest (rho = 0.4-0.5 in F1-F4), which is used in the clinic today. Finally using affinity chromatography we depleted sera of immunoglobulin G, and this resulted in a complete removal of the undergalactosylated biantennary glycans from the N-glycome, which are partially determining GlycoFibroTest.

GlycoFibroTest is a highly performant liver fibrosis biomarker derived from DNA sequencer-based serum protein glycomics

Liver fibrosis is currently assessed by liver biopsy, a costly and rather cumbersome procedure that is unsuitable for frequent patient monitoring, which drives research into biomarkers for this purpose. To investigate whether the serum N-glycome contains information suitable for this goal, we developed a 96-well plate-based serum N-glycomics sample preparation protocol that only involves fluid transfer steps and incubations in a PCR thermocycler yielding 8-aminopyrene-1,3,6-trisulfonic acid-labeled N-glycans. These N-glycans are then ready for analysis on the capillary electrophoresis-based DNA sequencers that are the current standard in clinical genetics laboratories worldwide. Subsequently we performed a multicenter, blinded study of 376 consecutive chronic hepatitis C virus patients for which liver biopsies and extensive serum biochemistry data were available. Among patients, the METAVIR fibrosis stage distribution was as follows: 10.6% F0, 44.4% F1, 20.5% F2, 18.4% F3, and 6.1% F4. We found that the ratio of two N-glycans, here called GlycoFibroTest, correlates with the histological fibrosis stage equally well as FibroTest (rho = 0.4-0.5 in F1-F4), which is used in the clinic today. Finally using affinity chromatography we depleted sera of immunoglobulin G, and this resulted in a complete removal of the undergalactosylated biantennary glycans from the N-glycome, which are partially determining GlycoFibroTest.