Differential antibody glycosylation in autoimmunity: sweet biomarker or modulator of disease activity?

The Human Lung Glycome Reveals Novel Glycan Ligands for Influenza A Virus

Glycans within human lungs are recognized by many pathogens such as influenza A virus (IAV), yet little is known about their structures. Here we present the first analysis of the N- and O- and glycosphingolipid-glycans from total human lungs, along with histological analyses of IAV binding. The N-glycome of human lung contains extremely large complex-type N-glycans with linear poly-N-acetyllactosamine (PL) [-3Galβ1-4GlcNAcβ1-]n extensions, which are predominantly terminated in α2,3-linked sialic acid. By contrast, smaller N-glycans lack PL and are enriched in α2,6-linked sialic acids. In addition, we observed large glycosphingolipid (GSL)-glycans, which also consists of linear PL, terminating in mainly α2,3-linked sialic acid. Histological staining revealed that IAV binds to sialylated and non-sialylated glycans and binding is not concordant with respect to binding by sialic acid-specific lectins. These results extend our understanding of the types of glycans that may serve as binding sites for human lung pathogens.

Profiling of Naturally Occurring Antibodies to the Thomsen-Friedenreich Antigen in Health and Cancer: The Diversity and Clinical Potential

The Thomsen-Friedenreich (TF) antigen is expressed in a majority of human tumors due to aberrant glycosylation in cancer cells. There is strong evidence that humoral immune response to TF represents an effective mechanism for the elimination of cancer cells that express TF-positive glycoconjugates. The presence of naturally occurring antibodies to tumor-associated TF and cancer-specific changes in their levels, isotype distribution and interrelation, avidity, and glycosylation profile make these Abs a convenient and ubiquitous marker for cancer diagnostics and prognostics. In this review, we attempt to summarize the latest data on the potential of TF-specific Abs for cancer diagnostics and prognostics.

Phytoestrogens protect joints in collagen induced arthritis by increasing IgG glycosylation and reducing osteoclast activation

Based on previous studies, we know that estrogen can protect the joints from arthritis development by increasing IgG glycosylation and inhibiting osteoclast activation. Phytoestrogens, especially genistein and daidzein, are structurally similar to estradiol that can bind to estrogen receptors (ERs). However, how phytoestrogens affect IgG glycosylation and osteoclast activation in vivo are not investigated so far. In this study, we used 20 mg/kg genistein or daidzein to gavage the female DBA1/J mice in collagen induced arthritis (CIA). We assessed arthritis and bone erosion by clinical scores, histopathology, and micro-CT analysis. Inflammatory cells such as neutrophils, B cells, macrophages and T cells in the peripheral blood were analyzed by flow cytometry. Phagocytic function of peritoneal macrophages was assessed by using FITC-labeled Escherichia coli. New monoclonal antibodies against CII were produced, purified and analyzed. Glycosylation levels of polyclonal and monoclonal IgG were detected by lectin-ELISA. Quantitative PCR was used to analyze the genes related to IgG glycosylation (B4galt1, St6gal1) and osteoclasts (TRAP, NFATC1, c-Fos). Expression of NF-κB and Akt signaling pathways as well as downstream transcription factors NFATc1 and c-Fos was studied by Western blot. Our results show that phytoestrogens protect mice from CIA by increasing IgG glycosylation leading to amelioration of inflammation and inhibiting the NF-κB pathway and NFATc1/c-Fos to decrease the activity of osteoclasts. In conclusion, phytoestrogens can protect bone and joints in CIA mice by increasing IgG glycosylation and inhibiting osteoclast activity.

Precision medicine in the care of rheumatoid arthritis: Focus on prediction and prevention of future clinically-apparent disease

There is an emerging understanding that an individual's risk for future rheumatoid arthritis (RA) can be determined using a combination of factors while they are still in a state where clinically-apparent inflammatory arthritis (IA) is not yet present. Indeed, this concept has underpinned several completed and ongoing prevention trials in RA. Importantly, risk factors can be divided into modifiable (e.g. smoking, exercise, dental care and diet) and non-modifiable factors (e.g. genetics, sex, age). In addition, there are now several biomarkers including autoantibodies, inflammatory markers and imaging techniques that are highly predictive of future clinically-apparent IA/RA. Although none of the prevention studies have yet provided major breakthroughs, several of them have provided valuable insights that can help to improve the design of future clinical trials and enable RA prevention. In aggregate, these findings suggest that the most accurate disease prediction models will require the combination of demographic and clinical information, biomarkers and potentially medical imaging data to identify individuals for intervention. This review summarizes some of the key aspects around precision medicine in RA with special focus on disease prediction and prevention.

Fc-Linked IgG N-Glycosylation in FcγR Knock-Out Mice

Immunoglobulin G (IgG) is the most abundant immunoglobulin isotype in the blood and is involved in the pathogenesis and progression of various diseases. Glycosylation of the IgG fragment crystallizable (Fc) region is shown to vary in different physiological and pathological states. Fc N-glycan composition can alter the effector functions of IgG by modulating its affinity for ligands, such as Fcγ receptors (FcγRs). However, it is not known whether IgG glycosylation is affected by the available repertoire of FcγRs, and if the Fc-linked N-glycome can compensate for modulation of the IgG-FcγR interaction. To explore this, we examined the subclass-specific Fc IgG glycoprofiles of healthy male and female FcγR knock-out mice on C57BL/6 and BALB/c backgrounds. We observed slight changes in IgG Fc N-glycan profiles in different knock-outs; however, it seems that the strain background and sex have a stronger effect on N-glycosylation of IgG Fc regions than the FcγR repertoire.

Deficiency of O-linked-glycosylation regulates activation of T cells and aggravates Concanavalin A-induced liver injury

OBJECTIVE

Protein glycosylation is involved in immunological recognition and immune cell activation. The role of O-glycosylation in Concanavalin A (Con A)-induced autoimmune hepatitis (AIH) was elucidated in the present study.

METHODS

Mice were intravenously injected with Con A (10 mg/kg) to establish an AIH mouse model. Here, 24 h prior to administration of Con A, experimental mice were intragastrically administrated with O-glycosylation inhibitor (benzyl-α-GalNAc) at doses of 1 and 5 mg/kg, respectively, while control mice were administrated with the same volume of saline. Before and after administration of Con A for 6 and 12 h, mice were sacrificed and their plasma and livers were collected to score liver injury. Peripheral blood, spleen, and thymus were collected for flow cytometry analysis. The expression levels of neutrophilic alkaline phosphatase-3 (NALP3) and NALP6 in liver were evaluated as well.

RESULTS

Pre-treatment with benzyl-α-GalNAc increased the serum transaminase levels and induced more infiltration and necrosis in livers of Con A administrated mice. The levels of some pro-inflammation cytokines also increased in administrated mice. In addition, pretreatment with benzyl-α-GalNAc up-regulated the expression levels of NALP3 and NALP6. And benzyl-α-GalNAc inhibited the levels of apoptosis of thymus cells and influenced activation of T cells in peripheral blood and spleen of Con A administrated mice, especially that accelerated the physiological progression of CD4⁺CD25^-CD69⁺ subset.

CONCLUSION

The present research demonstrated that benzyl-α-GalNAc aggravated Con A-induced AIH, and the role of the O-glycosylation inhibitor as the aggravation may be related to regulation of the levels of cytokines, as well as influencing proliferation of T cells.

Maternal asthma is associated with persistent changes in allergic offspring antibody glycosylation

BACKGROUND

Maternal asthma during pregnancy is considered an environmental risk factor for asthma development in children. Immunoglobulin G (IgG) antibodies that are transferred from the mother to the fetus are known to act in a pro- or anti-inflammatory manner depending on their glycosylation status.

OBJECTIVE

Using a mouse model, we examined how maternal allergic airway inflammation during pregnancy influenced offspring experimental asthma severity, as well as maternal and offspring serum IgG antibody glycosylation patterns. Additionally, the effects of maternal and offspring exposure to the same or different allergens were investigated.

METHODS

Female mice were either sham sensitized or sensitized to casein (CAS) or ovalbumin (OVA) before mating. Subsequently, allergic lung inflammation was induced in pregnant dams via aerosol allergen challenge (sham, CAS or OVA). After weaning, pups were subjected to an experimental asthma protocol using OVA. Asn-297 IgG glycosylation was analysed in maternal and offspring serum.

RESULTS

When mothers and offspring were sensitized to the same allergen (OVA-OVA), offspring had more severe experimental asthma. This was evidenced by altered antibody concentrations, increased bronchoalveolar lavage inflammatory cell influx and decreased lung tissue and lung draining lymph node regulatory T cell percentages. When mothers and offspring were sensitized to different allergens (CAS-OVA), this phenotype was no longer observed. Additionally, maternal serum from allergic mothers had significantly higher levels of pro-inflammatory IgG1, shown by decreased galactosylation and sialylation at the Asn-297 glycosylation site. Similar glycosylation patterns were observed in the serum of adult allergic offspring from allergic mothers.

CONCLUSIONS AND CLINICAL RELEVANCE

We observed a strong association between maternal experimental asthma during pregnancy, increased offspring airway inflammation and pro-inflammatory IgG glycosylation patterns in mothers and offspring. IgG glycosylation is not a standard measurement in the clinical setting, and we argue that it may be an important parameter to include in future clinical studies.

Minimal B Cell Extrinsic IgG Glycan Modifications of Pro- and Anti-Inflammatory IgG Preparations in vivo

Select residues in the biantennary sugar moiety attached to the fragment crystallizable of immunoglobulin G (IgG) antibodies can modulate IgG effector functions. Thus, afucosylated IgG glycovariants have enhanced cytotoxic activity, whereas IgG glycovariants rich in terminal sialic acid residues can trigger anti-inflammatory effects. More recent evidence suggests that terminal α2,6 linked sialic acids can be attached to antibodies post IgG secretion. These findings raise concerns for the use of therapeutic antibodies as they may change their glycosylation status in the patient and hence affect their activity. To investigate to what extent B cell extrinsic sialylation processes modify therapeutic IgG preparations in vivo, we analyzed changes in human intravenous IgG (IVIg) sialylation upon injection in mice deficient in B cells or in mice lacking the sialyltransferase 1, which catalyzes the addition of α2,6 linked sialic acid residues. By performing a time course of IgG glycan analysis with HILIC-UPLC-FLR (plus MS) and xCGE-LIF our study suggests that therapeutic IgG glycosylation is stable upon injection in vivo. Only a very small fraction of IgG molecules acquired sialic acid structures predominantly in the Fab- but not the Fc-portion upon injection in vivo, suggesting that therapeutic antibody glycosylation will remain stable upon injection in vivo.

Intense Physical Exercise Induces an Anti-inflammatory Change in IgG N-Glycosylation Profile

Exercise is known to improve many aspects of human health, including modulation of the immune system and inflammatory status. It is generally understood that exercise reduces inflammation, but there are missing links in terms of understanding the mechanisms as well as the differences between exercise modalities. N-glycosylation of immunoglobulin G (IgG) and total plasma proteins was previously shown to reflect changes in inflammatory pathways, which could provide valuable information to further clarify exercise effects. In order to further expand the understanding of the relationship between physical activity and inflammation, we examined the effect of intense exercise, in the form of repeated sprint training (RST), on IgG and total plasma proteins N-glycosylation in combination with traditionally used inflammation markers: C-reactive protein (CRP), interleukin 6 (IL-6), and leukocyte count. Twenty-nine male physical education students were separated into treatment (RST, N = 15) and control (N = 14) groups. The RST group completed a 6-week exercise protocol while the control group was instructed to refrain from organized physical activity for the duration of the study. Three blood samples were taken at different time points: prior to start of the training program, the final week of the exercise intervention (EXC), and at the end of the 4-week recovery period (REC). Following the end of the recovery period IgG N-glycosylation profiles showed anti-inflammatory changes in RST group compared to the control group, which manifested as a decrease in agalactosylated (p = 0.0473) and an increase in digalactosylated (p = 0.0473), and monosialylated (p = 0.0339) N-glycans. Plasma protein N-glycans didn’t change significantly, while traditional inflammatory markers also didn’t show significant change in inflammatory status. Observed results demonstrate the potential of intense physical exercise to reduce levels of systemic basal inflammation as well as the potential for IgG N-glycosylation to serve as a sensitive longitudinal systemic inflammation marker.

An Inflammatory Story: Antibodies in Tuberculosis Comorbidities

Mycobacterium tuberculosis (Mtb) resides in a quarter of the world's population and is the causative agent for tuberculosis (TB), the most common infectious reason of death in humans today. Although cellular immunity has been firmly established in the control of Mtb, there is growing evidence that antibodies may also modulate the infection. More specifically, certain antibody features are associated with inflammation and are divergent in different states of human infection and disease. Importantly, TB impacts not just the healthy but also those with chronic conditions. While HIV represents the quintessential comorbid condition for TB, recent epidemiological evidence shows that additional chronic conditions such as diabetes and kidney disease are rising. In fact, the prevalence of diabetes as a comorbid TB condition is now higher than that of HIV. These chronic diseases are themselves independently associated with pro-inflammatory immune states that encompass antibody profiles. This review discusses isotypes, subclasses, post-translational modifications and Fc-mediated functions of antibodies in TB infection and in the comorbid chronic conditions of HIV, diabetes, and kidney diseases. We propose that inflammatory antibody profiles, which are a marker of active TB, may be an important biomarker for detection of TB disease progression within comorbid individuals. We highlight the need for future studies to determine which inflammatory antibody profiles are the consequences of comorbidities and which may potentially contribute to TB reactivation.

The Glycosylation Site of Myelin Oligodendrocyte Glycoprotein Affects Autoantibody Recognition in a Large Proportion of Patients

Autoantibodies to myelin oligodendrocytes glycoprotein (MOG) are found in a fraction of patients with inflammatory demyelination and are detected with MOG-transfected cells. While the prototype anti-MOG mAb 8-18C5 and polyclonal anti-MOG responses from different mouse strains largely recognize the FG loop of MOG, the human anti-MOG response is more heterogeneous and human MOG-Abs recognizing different epitopes were found to be pathogenic. The aim of this study was to get further insight into details of antigen-recognition by human MOG-Abs focusing on the impact of glycosylation. MOG has one known N-glycosylation site at N31 located in the BC loop linking two beta-sheets. We compared the reactivity to wild type MOG with that toward two different mutants in which the neutral asparagine of N31 was mutated to negatively charged aspartate or to the neutral alanine. We found that around 60% of all patients (16/27) showed an altered reactivity to one or both of the mutations. We noted seven different patterns of recognition of the two glycosylation-deficient mutants by different patients. The introduced negative charge at N31 enhanced recognition in some, but reduced recognition in other patients. In 7/27 patients the neutral glycosylation-deficient mutant was recognized stronger. The folding of the extracellular domain of MOG with the formation of beta-sheets did not depend on its glycosylation as seen by circular dichroism. We determined the glycan structure of MOG produced in HEK cells by mass spectrometry. The most abundant glycoforms of MOG expressed in HEK cells are diantennary, contain a core fucose, an antennary fucose, and are decorated with α2,6 linked Neu5Ac, while details of the glycoforms of MOG in myelin remain to be identified. Together, we (1) increase the knowledge about heterogeneity of human autoantibodies to MOG, (2) show that the BC loop affects recognition in about 60% of the patients, (3) report that all patients recognized the unglycosylated protein backbone, while (4) in about 20% of the patients the attached sugar reduces autoantibody binding presumably via steric hindrance. Thus, a neutral glycosylation-deficient mutant of MOG might enhance the sensitivity to identify MOG-Abs.

GlycopeptideGraphMS: Improved Glycopeptide Detection and Identification by Exploiting Graph Theoretical Patterns in Mass and Retention Time

The leading proteomic method for identifying N-glycosylated peptides is liquid chromatography coupled with tandem fragmentation mass spectrometry (LCMS/MS) followed by spectral matching of MS/MS fragment masses to a database of possible glycan and peptide combinations. Such database-dependent approaches come with challenges such as needing high-quality informative MS/MS spectra, ignoring unexpected glycan or peptide sequences, and making incorrect assignments because some glycan combinations are equivalent in mass to amino acids. To address these challenges, we present GlycopeptideGraphMS, a graph theoretical bioinformatic approach complementary to the database-dependent method. Using the AXL receptor tyrosine kinase (AXL) as a model glycoprotein with multiple N-glycosylation sites, we show that those LCMS features that could be grouped into graph networks on the basis of glycan mass and retention time differences were actually N-glycopeptides with the same peptide backbone but different N-glycan compositions. Conversely, unglycosylated peptides did not exhibit this grouping behavior. Furthermore, MS/MS sequencing of the glycan and peptide composition of just one N-glycopeptide in the graph was sufficient to identify the rest of the N-glycopeptides in the graph. By validating the identifications with exoglycosidase cocktails and MS/MS fragmentation, we determined the experimental false discovery rate of identifications to be 2.21%. GlycopeptideGraphMS detected more than 500 unique N-glycopeptides from AXL, triple the number found by a database search with Byonic software, and detected incorrect assignments due to a nonspecific protease cleavage. This method overcomes some limitations of the database approach and is a step closer to comprehensive automated glycoproteomics.

Establishment of an international autoantibody reference standard for human anti-DFS70 antibodies: proof-of-concept study for a novel Megapool strategy by pooling individual specific sera

Background

International autoantibody standards, traditionally based on material obtained from plasmapheresis of single subjects, represent individual immune response and may not comprehend the heterogeneity of the general population. The anti-DFS70 autoantibody yields a characteristic dense fine speckled (DFS) nuclear pattern on indirect immunofluorescence assay on HEp-2 cells (HEp-2 IFA) and speaks against autoimmunity. We propose a novel strategy for developing autoantibody reference standards, based on stepwise pooling of serum samples from hundreds of individuals with anti-DFS70 antibodies.

Methods

Within a 2-year period, serum samples were selected from routine HEp-2 IFA according to the following criteria: DFS HEp-2 IFA pattern at titer ≥1:640; anti-DFS70 reactivity in three analyte-specific tests (Western blot [WB], enzyme-linked immunosorbent assay [ELISA] and chemiluminescent immunoassay [CLIA]). Aliquots of individual samples were combined into progressively larger pools with stepwise validation of intermediary pools as for individual samples. Validated intermediary pools were merged into a final pool for lyophilization.

Results

A total of 741 validated samples yielded a 750 mL final pool that was lyophilized into thousands of 200 μL-aliquots. Reconstituted aliquots yielded the expected anti-DFS70 reactivity in ELISA, CLIA and WB, as well as high-titer DFS HEp-2 IFA pattern. The appropriate anti-DFS70 reactivity of the lyophilized pool was confirmed by seven international expert centers, using HEp-2 IFA, ELISA, WB and immunoprecipitation.

Conclusions

This proof-of-concept study provides an innovative and efficient strategy to build serum reference standards for autoantibody testing. The anti-DFS70 standard will integrate the panel of standards of Autoantibody Standardization Committee (ASC, www.autoab.org), contributing to education for proper assay validation and interpretation of the DFS pattern and other HEp-2 IFA patterns.

Detecting post-translational modification signatures as potential biomarkers in clinical mass spectrometry

INTRODUCTION

Numerous diseases are caused by changes in post-translational modifications (PTMs). Therefore, the number of clinical proteomics studies that include the analysis of PTMs is increasing. Combining complementary information-for example changes in protein abundance, PTM levels, with the genome and transcriptome (proteogenomics)-holds great promise for discovering important drivers and markers of disease, as variations in copy number, expression levels, or mutations without spatial/functional/isoform information is often insufficient or even misleading. Areas covered: We discuss general considerations, requirements, pitfalls, and future perspectives in applying PTM-centric proteomics to clinical samples. This includes samples obtained from a human subject, for instance (i) bodily fluids such as plasma, urine, or cerebrospinal fluid, (ii) primary cells such as reproductive cells, blood cells, and (iii) tissue samples/biopsies. Expert commentary: PTM-centric discovery proteomics can substantially contribute to the understanding of disease mechanisms by identifying signatures with potential diagnostic or even therapeutic relevance but may require coordinated efforts of interdisciplinary and eventually multi-national consortia, such as initiated in the cancer moonshot program. Additionally, robust and standardized mass spectrometry (MS) assays-particularly targeted MS, MALDI imaging, and immuno-MALDI-may be transferred to the clinic to improve patient stratification for precision medicine, and guide therapies.

Exploring Cerebrospinal Fluid IgG N-Glycosylation as Potential Biomarker for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease for which the existing candidate biomarkers (neurofilaments) have low specificity. Changes in blood IgG N-glycosylation have been observed in several diseases, including ALS, whereas cerebrospinal fluid (CSF) IgG has been less studied. Here, we characterized N-glycans of CSF IgG from ALS patients in comparison with a control group of other neurological diseases. Cerebrospinal fluid was collected from patients with ALS (n = 26) and other neurological diseases (n = 10). N-Glycans were released from CSF purified IgG with peptide N-glycosidase F, labeled with 2-aminobenzamide and analyzed by NP-HPLC chromatography in combination with exoglycosidase digestion and MALDI-TOF mass spectrometry. The N-glycosylation profile of ALS CSF IgG consisted of diantennary N-glycans predominantly with proximal fucose and some bisecting GlcNAc; agalacto-, mono-, and digalactosylated as well as α2,6-sialylated structures were detected. Differences between ALS and control patients were observed; most relevant was the increase in ALS CSF IgG of the level of galactosylated structures defined here as Gal-index (median 46.87 and 40.50% for ALS and controls, respectively; p = 0.006). The predictive value of the Gal-index (AUC = 0.792, p = 0.007) considering ROC analysis had potential utility as a diagnostic test for ALS and was comparable to that of phosphoneurofilament heavy chain (AUC = 0.777, p = 0.011), which was used as benchmark marker for our group of patients. The results provide the basis to further explore the potential of IgG N-glycan galactosylation as biomarker for ALS by using larger cohorts of patients and controls.

Sweet SIGNs: IgG glycosylation leads the way in IVIG-mediated resolution of inflammation

A hallmark of many chronic inflammatory and autoimmune diseases is that there is an impaired resolution of inflammation and return to the steady state. The infusion of high doses of pooled serum IgG preparations from thousands of donors [intravenous immunoglobulin (IVIG) therapy] has been shown to induce resolution of inflammation in a variety of chronic inflammatory and autoimmune diseases, suggesting that IgG molecules can instruct the immune system to stop inflammatory processes and initiate the return to the steady state. The aim of this review is to discuss how insights into the mechanism of IVIG activity may help to understand the molecular and cellular pathways underlying resolution of inflammation. We will put a special emphasis on pathways dependent on the IgG FC domain and IgG sialylation, as several recent studies have provided new insights into how this glycosylation-dependent pathway modulates innate and adaptive immune responses through different sets of C-type or I-type lectins.

Emerging immunotherapies for autoimmune kidney disease

Autoimmunity is a leading cause of chronic kidney disease and loss of native and transplanted kidneys. Conventional immunosuppressive therapies can be effective but are non-specific, noncurative, and risk serious side effects such as life-threatening infection and cancer. Novel therapies and targeted interventions are urgently needed. In this brief review we explore diverse strategies currently in development and under consideration to interrupt underlying disease mechanisms in immune-mediated renal injury. Because autoantibodies are prominent in diagnosis and pathogenesis in multiple human glomerulopathies, we highlight several promising therapies that interfere with functions of early mediators (IgG and complement) of the effector arm and with an epicenter (the germinal center) for induction of humoral immunity.

The Clinical Value of Autoantibodies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a highly heterogeneous syndrome in terms of clinical presentation, progression, and response to therapy. In such a complicated context, the identification of disease-related biomarkers would be undoubtedly helpful in assisting tailored approaches for every patient. Despite remarkable efforts, however, progress in new biomarker development and validation is dramatically slow. At present, none of the candidate genetic, cellular, or molecular biomarker has yet surpassed the clinical value of RA-specific autoantibodies, including rheumatoid factor (RF) and anti-citrullinated protein autoantibodies (ACPA). Rather, recent years have witnessed significant advancements in our understanding of the multiple roles that RF and ACPA play in RA pathophysiology. This has helped clarifying the mechanistic basis of the clinical associations of autoantibodies in RA. In this short review, we will briefly summarize the effector functions of RF and ACPA, and analyse how autoantibodies may help subclassifying RA patients in terms of clinical presentation and response to therapy.

Cis interaction between sialylated FcγRIIA and the αI-domain of Mac-1 limits antibody-mediated neutrophil recruitment

Vascular-deposited IgG immune complexes promote neutrophil recruitment, but how this process is regulated is still unclear. Here we show that the CD18 integrin Mac-1, in its bent state, interacts with the IgG receptor FcγRIIA in cis to reduce the affinity of FcγRIIA for IgG and inhibit FcγRIIA-mediated neutrophil recruitment under flow. The Mac-1 rs1143679 lupus-risk variant reverses Mac-1 inhibition of FcγRIIA, as does a Mac-1 ligand and a mutation in Mac-1’s ligand binding αI-domain. Sialylated complex glycans on FcγRIIA interact with the αI-domain via divalent cations, and this interaction is required for FcγRIIA inhibition by Mac-1. Human neutrophils deficient in CD18 integrins exhibit augmented FcγRIIA-dependent recruitment to IgG-coated endothelium. In mice, CD18 integrins on neutrophils dampen IgG-mediated neutrophil accumulation in the kidney. In summary, cis interaction between sialylated FcγRIIA and the αI-domain of Mac-1 alters the threshold for IgG-mediated neutrophil recruitment. A disruption of this interaction may increase neutrophil influx in autoimmune diseases.

Deposited immune complexes (IC) promote neutrophil recruitment, but the fine tuning of this process is still unclear. Here the authors show that the cis interaction of the IC receptor, FcγRIIA and CD18 integrin, Mac-1, on the neutrophil surface modulates neutrophil adhesion, with FcγRIIA sialylation specifically implicated in this interaction.

The Utilization of Autoantibodies in Approaches to Precision Health

Precision health (PH) applied to autoimmune disease will need paradigm shifts in the use and application of autoantibodies and other biomarkers. For example, autoantibodies combined with other multi-analyte “omic” profiles will form the basis of disease prediction allowing for earlier intervention linked to disease prevention strategies, as well as earlier, effective and personalized interventions for established disease. As medical intervention moves to disease prediction and a model of “intent to PREVENT,” diagnostics will include an early symptom/risk-based, as opposed to a disease-based approach. Newer diagnostic platforms that utilize emerging megatrends such as deep learning and artificial intelligence and close the gaps in autoantibody diagnostics will benefit from paradigm shifts thereby facilitating the PH agenda.

Changes in canine serum N-glycosylation as a result of infection with the heartworm parasite Dirofilaria immitis

Filariases are diseases caused by infection with filarial nematodes and transmitted by insect vectors. The filarial roundworm Dirofilaria immitis causes heartworm disease in dogs and other carnivores. D. immitis is closely related to Onchocerca volvulus, Wuchereria bancrofti and Brugia malayi, which cause onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) in humans and are neglected tropical diseases. Serum N-glycosylation is very sensitive to both pathological infections and changes in mammalian biology due to normal aging or lifestyle choices. Here, we report significant changes in the serum N-glycosylation profiles of dogs infected with D. immitis. Our data derive from analysis of serum from dogs with established patent infections and from a longitudinal infection study. Overall, galactosylation and core fucosylation increase, while sialylation decreases in infected dog sera. We also identify individual glycan structures that change significantly in their relative abundance during infection. Notably, the abundance of the most dominant N-glycan in canine serum (biantennary, disialylated A2G2S2) decreases by over 10 percentage points during the first 6 months of infection in each dog analyzed. This is the first longitudinal study linking changes in mammalian serum N-glycome to progression of a parasitic infection.

Neutrophil-released enzymes can influence composition of circulating immune complexes in multiple sclerosis

During NET formation, the content of neutrophils granules is released into the intercellular milieu. Consisting of many proteases and ROS species, formed NETs were shown to degrade cytokines (Schauer, Nat Med, 2014); while the content of neutrophil's azurophilic granules proved to contain glycosidases, secreted upon activation (Thaysen-Andersen, JBC, 2015), and formation of autoantibodies to neutrophil beta-glucoronidase was connected with the level of anti-MPO antibodies (Ab) (Martensson, Autoimmunity, 1992). Taking into account these facts, we aimed to investigate the possibility of NET-related changes in glycan composition on circulating IgG molecules and IgG-IgM immune complexes in multiple sclerosis (MS). This autoimmune disorder still has no reliable detection markers or established ways of treatment, besides widely accepted interferon therapy, making it a particularly interesting clinical condition. By applying capture lectin-ELISA, we analysed binding of α2,6 sialyl-specific lectins SNA, PSqL, and core α1,6-fucose specific lectin AAL to circulating IgG and related complexes in five groups of MS patients: untreated (17 persons); undergoing therapy with interferon (IFN) β-1 b (15 persons), corticosteroids (methylprednisolone) (12 persons) and anti-B-cell monoclonal Ab (12 persons: Ocrelizumab, 6 persons and alemtuzumab, 6 persons). A group of 23 healthy donors served as control. Significant increase in neutrophil elastase activity, observed in the group of patients under corticosteroid treatment was also accompanied by sialyl-specific PSqL and SNA lectin binding to captured IgG molecules. Subsequent analysis demonstrated that sialic acid residues were exposed on free IgG and on circulating IgG-IgM immune complexes. Increased lectin binding was not observed for anti-myelin basic protein (one of the major autoAb in MS) Ab compared to total serum Ab. IFN therapy was accompanied by low neutrophil elastase activity and low amount of circulating immune complexes. Incubation of in vitro generated NETs with human serum revealed the digestion of high-molecular weight immune complexes with subsequent exposure of hidden glycoepitops. Obtained data indicate the potential of neutrophil-derived proteases to modify (partially degrade) circulating immune complexes leading to exposure of internal glycoepitops.

Intradomain Interactions in an NMDA Receptor Fragment Mediate N-Glycan Processing and Conformational Sampling

The structural and functional roles of highly conserved asparagine-linked (N)-glycans on the extracellular ligand-binding domain (LBD) of the N-methyl-D-aspartate receptors are poorly understood. We applied solution- and computation-based methods that identified N-glycan-mediated intradomain and interglycan interactions. Nuclear magnetic resonance (NMR) spectra of the GluN1 LBD showed clear signals corresponding to each of the three N-glycans and indicated the reducing end of glycans at N440 and N771 potentially contacted nearby amino acids. Molecular dynamics simulations identified contacts between nearby amino acids and the N440- and N771-glycans that were consistent with the NMR spectra. The distal portions of the N771-glycan also contacted the core residues of the nearby N471-glycan. This result was consistent with mass spectrometry data indicating the limited N471-glycan core fucosylation and reduced branch processing of the N771-glycan could be explained by interglycan contacts. We discuss a potential role for the GluN1 LBD N-glycans in interdomain contacts formed in NMDA receptors.

Antibody glycosylation in inflammation, disease and vaccination

Antibodies are antigen recognizing immunoglobulins with an amazingly diverse repertoire in the antigen specific domain. The diversity of the antibody response is further increased by modifications such as somatic recombination and hypermutation. Furthermore, variation in the isotype and post-translational modifications such as Fc glycosylation further increase diversity of the effector functions. In particular variations in the glycan structures contribute significantly to the functional capacities of the antibodies. This is of particular interest given the dynamic nature of these modifications that is strongly influenced by the inflammatory environment.

Intriguingly, the glycan profile of antibodies has been unravelled in great detail in inflammatory (auto)immune diseases but received only limited attention in the area of infectious diseases and vaccination. Here, we reviewed the current knowledge on immunoglobulin glycosylation and specifically focussed on studies in the field of infectious diseases and vaccination against infectious diseases, an area with a lot of interesting opportunities.

Pathogenicity of human antibodies against myelin oligodendrocyte glycoprotein

OBJECTIVE

Autoantibodies against myelin oligodendrocyte glycoprotein (MOG) occur in a proportion of patients with inflammatory demyelinating diseases of the central nervous system (CNS). We analyzed their pathogenic activity by affinity-purifying these antibodies (Abs) from patients and transferring them to experimental animals.

METHODS

Patients with Abs to MOG were identified by cell-based assay. We determined the cross-reactivity to rodent MOG and the recognized MOG epitopes. We produced the correctly folded extracellular domain of MOG and affinity-purified MOG-specific Abs from the blood of patients. These purified Abs were used to stain CNS tissue and transferred in 2 models of experimental autoimmune encephalomyelitis. Animals were analyzed histopathologically.

RESULTS

We identified 17 patients with MOG Abs from our outpatient clinic and selected 2 with a cross-reactivity to rodent MOG; both had recurrent optic neuritis. Affinity-purified Abs recognized MOG on transfected cells and stained myelin in tissue sections. The Abs from the 2 patients recognized different epitopes on MOG, the CC' and the FG loop. In both patients, these Abs persisted during our observation period of 2 to 3 years. The anti-MOG Abs from both patients were pathogenic upon intrathecal injection in 2 different rat models. Together with cognate MOG-specific T cells, these Abs enhanced T-cell infiltration; together with myelin basic protein-specific T cells, they induced demyelination associated with deposition of C9neo, resembling a multiple sclerosis type II pathology.

INTERPRETATION

MOG-specific Abs affinity purified from patients with inflammatory demyelinating disease induce pathological changes in vivo upon cotransfer with myelin-reactive T cells, suggesting that these Abs are similarly pathogenic in patients. Ann Neurol 2018;84:315-328.

IgG3 regulates tissue-like memory B cells in HIV-infected individuals

Immunoglobulin G3 (IgG3) has an uncertain role in the response to infection with and vaccination against human immunodeficiency virus (HIV). Here we describe a regulatory role for IgG3 in dampening the immune system-activating effects of chronic HIV viremia on B cells. Secreted IgG3 was bound to IgM-expressing B cells in vivo in HIV-infected chronically viremic individuals but not in early-viremic or aviremic individuals. Tissue-like memory (TLM) B cells, a population expanded by persistent HIV viremia, bound large amounts of IgG3. IgG3 induced clustering of B cell antigen receptors (BCRs) on the IgM⁺ B cells, which was mediated by direct interactions between soluble IgG3 and membrane IgM of the BCR (IgM-BCR). The inhibitory IgG receptor CD32b (FcγRIIb), complement component C1q and inflammatory biomarker CRP contributed to the binding of secreted IgG3 onto IgM-expressing B cells of HIV-infected individuals. Notably, IgG3-bound TLM B cells were refractory to IgM-BCR stimulation, thus demonstrating that IgG3 can regulate B cells during chronic activation of the immune system.

Glycosylation of random IgG distinguishes seropositive and seronegative rheumatoid arthritis

The N-glycosylation of human immunoglobulins, especially IgGs, plays a critical role in determining affinity of IgGs towards their effector (pro- and anti-inflammatory) receptors. However, it is still not clear whether altered glycosylation is involved in only antibody-dependent disorders like seropositive rheumatoid arthritis (RA) or also in pathologies with similar clinical manifestations, but no specific autoantibodies like seronegative RA. The clarification of that uncertainty was the aim of the current study. Another study aim was the detection of specific glycan forms responsible for altered exposure of native glycoepitopes. We studied sera from seropositive RA (n = 15) and seronegative RA (n = 12) patients for exposure of glycans in native IgG molecules, followed by determination of specific glycans by capillary electrophoresis with laser-induced fluorescent detection (CE-LIF). Aged-matched groups of normal healthy donors (NHD) and samples of intravenous immunoglobulin IgG preparations (IVIG) served as controls. There was significantly stronger binding of Lens culinaris agglutinin (LCA) and Aleuria aurantia lectin (AAL) lectins towards IgG from seropositive RA compared to seronegative RA or NHD. CE-LIF analysis revealed statistically significant increases in bisecting glycans FA2BG2 (p = .006) and FABG2S1 (p = .005) seropositive RA, accompanied by decrease of bisecting monogalactosylated glycan FA2(6)G1 (p = .074) and non-bisecting monosialylated glycan FA2(3)G1S1 (p = .055). The results suggest that seropositive RA is distinct from seronegative RA in terms of IgG glycan moieties, attributable to specific immunoglobulin molecules present in seropositive disease. These glycans were determined to be bisecting GlcNAc-bearing forms FA2BG2 and FABG2S1, and their appearance increased the availability of LCA and AAL lectin-binding sites in native IgG glycoepitopes.

Targeting B Cells and Plasma Cells in Autoimmune Diseases

Success with B cell depletion using rituximab has proven the concept that B lineage cells represent a valid target for the treatment of autoimmune diseases, and has promoted the development of other B cell targeting agents. Present data confirm that B cell depletion is beneficial in various autoimmune disorders and also show that it can worsen the disease course in some patients. These findings suggest that B lineage cells not only produce pathogenic autoantibodies, but also significantly contribute to the regulation of inflammation. In this review, we will discuss the multiple pro- and anti-inflammatory roles of B lineage cells play in autoimmune diseases, in the context of recent findings using B lineage targeting therapies.

IgG and leukocytes: Targets of immunomodulatory α2,6 sialic acids

ST6Gal1 is a critical sialyltransferase enzyme that controls the addition of α2,6-linked sialic acids to the termini of glycans. Attachment of sialic acids to glycoproteins as a posttranslational modification influences cellular responses, and is a well-known modifier of immune cell behavior. ST6Gal1 activity impacts processes such as: effector functions of immunoglobulin G via Fc sialylation, hematopoietic capacity by hematopoietic stem and progenitor cell surface sialylation, and lymphocyte activation thresholds though CD22 engagement and inhibition of galectins. This review summarizes recent studies that suggest α2,6 sialylation by ST6Gal1 has an immunoregulatory effect on immune reactions.