The Glycosylation of Human Serum IgD and IgE and the Accessibility of Identified Oligomannose Structures for Interaction with Mannan-Binding Lectin

IgE glycosylation and impact on structure and function: A systematic review

The impact of human IgE glycosylation on structure, function and disease mechanisms is not fully elucidated, and heterogeneity in different studies renders drawing conclusions challenging. Previous reviews discussed IgE glycosylation focusing on specific topics such as health versus disease, FcεR binding or impact on function. We present the first systematic review of human IgE glycosylation conducted utilizing the PRISMA guidelines. We sought to define the current consensus concerning the roles of glycosylation on structure, biology and disease. Despite diverse analytical methodologies, source, expression systems and the sparsity of data on IgE antibodies from non-allergic individuals, collectively evidence suggests differential glycosylation profiles, particularly in allergic diseases compared with healthy states, and indicates functional impact, and contributions to IgE-mediated hypersensitivities and atopic diseases. Beyond allergic diseases, dysregulated terminal glycan structures, including sialic acid, may regulate IgE metabolism. Glycan sites such as N394 may contribute to stabilizing IgE structure, with alterations in these glycans likely influencing both structure and IgE-FcεR interactions. This systematic review therefore highlights critical IgE glycosylation attributes in health and disease that may be exploitable for therapeutic intervention, and the need for novel analytics to explore pertinent research avenues.

Systematic mutational analysis reveals an essential role of N275 in IgE stability

Therapeutic antibodies have predominantly been IgG-based. However, the ongoing clinical trial of MOv18 IgE has highlighted the potential of using IgE antibodies in cancer therapy. While extensive studies targeting IgG glycosylation resulted in a rational basis for the development of enhanced biotherapeutics, IgE glycosylation remains an area with limited analyses. Previous studies on the role of IgE glycosylation present conflicting data with one study emphasizing the importance of N275 and T277 residues for FcεRI binding whereas another asserts the nonsignificance of IgE glycosylation in receptor interaction. While existing literature underscores the significance of glycans at the N275 position for binding to FcεR1 receptor and initiation of anaphylaxis, the role of other IgE glycosylation sites in folding or receptor binding remains elusive. This study systematically investigates the functional significance of N-linked glycosylation sites in the heavy chain of IgE which validates the pivotal role of N275 residue in IgE secretion and stability. Replacement of this asparagine to non-amine group moieties does not affect IgE function in vitro, yet substitution with aspartic acid compromises antibody yield. The deglycosylated IgE variant exhibits superior efficacy, challenging the conventional importance of glycosylation for effector function. In summary, our study unveils an intricate relationship between N-glycosylation sites and the structural-functional dynamics of IgE antibodies. Furthermore, it offers novel insights into the IgE scaffold, paving the way for the development of more effective and stable IgE-based therapeutics.

A Comparison of Natural and Therapeutic Anti-IgE Antibodies

Immunoglobulin E (IgE) plays a critical role for the immune system, fighting against parasites, toxins, and cancer. However, when it reacts to allergens without proper regulation, it can cause allergic reactions, including anaphylaxis, through a process initiated by effector cells such as basophils and mast cells. These cells display IgE on their surface, bound to the high-affinity IgE receptor FcεRI. A cross-linking antigen then triggers degranulation and the release of inflammatory mediators from the cells. Therapeutic monoclonal anti-IgE antibodies such as omalizumab, disrupt this process and are used to manage IgE-related conditions such as severe allergic asthma and chronic spontaneous urticaria. Interestingly, naturally occurring anti-IgE autoantibodies circulate at surprisingly high levels in healthy humans and mice and may thus be instrumental in regulating IgE activity. Although many open questions remain, recent studies have shed new light on their role as IgE regulators and their mechanism of action. Here, we summarize the latest insights on natural anti-IgE autoantibodies, and we compare their functional features to therapeutic monoclonal anti-IgE autoantibodies.

Modelling the assembly and flexibility of antibody structures

Antibodies are large protein assemblies capable of both specifically recognising antigens and engaging with other proteins and receptors to coordinate immune action. Traditionally, structural studies have been dedicated to antibody variable regions, but efforts to determine and model full-length antibody structures are emerging. Here we review the current knowledge on modelling the structures of antibody assemblies, focusing on their conformational flexibility and the challenge this poses to obtaining and evaluating structural models. Integrative modelling approaches, combining experiments (cryo-electron microscopy, mass spectrometry, etc.) and computational methods (molecular dynamics simulations, deep-learning based approaches, etc.), hold the promise to map the complex conformational landscape of full-length antibody structures.

Inhibition of pathologic immunoglobulin E in food allergy by EBF-2 and active compound berberine associated with immunometabolism regulation

Introduction

Food allergy is a significant public health problem with limited treatment options. As Food Allergy Herbal Formula 2 (FAHF-2) showed potential as a food allergy treatment, we further developed a purified version named EBF-2 and identified active compounds. We investigated the mechanisms of EBF-2 on IgE-mediated peanut (PN) allergy and its active compound, berberine, on IgE production.

Methods

IgE plasma cell line U266 cells were cultured with EBF-2 and FAHF-2, and their effects on IgE production were compared. EBF-2 was evaluated in a murine PN allergy model for its effect on PN-specific IgE production, number of IgE⁺ plasma cells, and PN anaphylaxis. Effects of berberine on IgE production, the expression of transcription factors, and mitochondrial glucose metabolism in U266 cells were evaluated.

Results

EBF-2 dose-dependently suppressed IgE production and was over 16 times more potent than FAHF-2 in IgE suppression in U266 cells. EBF-2 significantly suppressed PN-specific IgE production (70%, p<0.001) and the number of IgE-producing plasma cells in PN allergic mice, accompanied by 100% inhibition of PN-induced anaphylaxis and plasma histamine release (p<0.001) without affecting IgG1 or IgG2a production. Berberine markedly suppressed IgE production, which was associated with suppression of XBP1, BLIMP1, and STAT6 transcription factors and a reduced rate of mitochondrial oxidation in an IgE-producing plasma cell line.

Conclusions

EBF-2 and its active compound berberine are potent IgE suppressors, associated with cellular regulation of immunometabolism on IgE plasma cells, and may be a potential therapy for IgE-mediated food allergy and other allergic disorders.

Affinity-Driven Site-Specific High Mannose Modification Determines the Structural Polymerization and Function of Tetrameric IgM in a Primitive Vertebrate

Teleost tetramer IgM is the predominant Ig in the immune system and plays essential roles in host defense against microbial infection. Due to variable disulfide polymerization of the monomeric subunits, tetrameric IgM possesses considerable structural diversity. Previous work indicated that the teleost IgM H chain was fully occupied with complex-type N-glycans. However, after challenge with trinitrophenyl (TNP) Ag, the complex N-glycans in the Asn-509 site of Oreochromis niloticus IgM H chain transformed into high mannose. This study, therefore, was conducted to examine the functional roles of the affinity-related high-mannose modification in tilapia IgM. The TNP-specific IgM Ab affinity maturation was revealed in tilapia over the response. A positive correlation between TNP-specific IgM affinity and its disulfide polymerization level of isomeric structure was demonstrated. Mass spectrometric analysis indicated that the relationship between IgM affinity and disulfide polymerization was associated with the Asn-509 site-specific high-mannose modification. Furthermore, the increase of high mannose content promoted the combination of IgM and mannose receptor (MR) on the surface of phagocytes. Moreover, the increased interaction of IgM and MR amplified the phagocytic ability of phagocytes to Streptococcus agalactiae. To our knowledge, this study demonstrates that site-specific high-mannose modification associates with IgM Ab affinity and its structural disulfide polymerization and amplifies the phagocytosis of phagocytes by the combination of IgM and MR. The present study provides evidence for understanding the association of IgM structure and function during the evolution of the immune system.

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

Chronic inflammation is the main feature of many long-term inflammatory diseases such as autoimmune diseases, metabolic disorders, and cancer. There is a growing number of studies in which alterations of N-glycosylation have been observed in many pathophysiological conditions, yet studies of the underlying mechanisms that precede N-glycome changes are still sparse. Proinflammatory cytokines have been shown to alter the substrate synthesis pathways as well as the expression of glycosyltransferases required for the biosynthesis of N-glycans. The resulting N-glycosylation changes can further contribute to disease pathogenesis through modulation of various aspects of immune cell processes, including those relevant to pathogen recognition and fine-tuning the inflammatory response. This review summarizes our current knowledge of inflammation-induced N-glycosylation changes, with a particular focus on specific subsets of immune cells of innate and adaptive immunity and how these changes affect their effector functions, cell interactions, and signal transduction.

Sialylation as an Important Regulator of Antibody Function

Antibodies play a critical role in linking the adaptive immune response to the innate immune system. In humans, antibodies are categorized into five classes, IgG, IgM, IgA, IgE, and IgD, based on constant region sequence, structure, and tropism. In serum, IgG is the most abundant antibody, comprising 75% of antibodies in circulation, followed by IgA at 15%, IgM at 10%, and IgD and IgE are the least abundant. All human antibody classes are post-translationally modified by sugars. The resulting glycans take on many divergent structures and can be attached in an N-linked or O-linked manner, and are distinct by antibody class, and by position on each antibody. Many of these glycan structures on antibodies are capped by sialic acid. It is well established that the composition of the N-linked glycans on IgG exert a profound influence on its effector functions. However, recent studies have described the influence of glycans, particularly sialic acid for other antibody classes. Here, we discuss the role of glycosylation, with a focus on terminal sialylation, in the biology and function across all antibody classes. Sialylation has been shown to influence not only IgG, but IgE, IgM, and IgA biology, making it an important and unappreciated regulator of antibody function.

Bacterial lectin BambL acts as a B cell superantigen

B cell superantigens crosslink conserved domains of B cell receptors (BCRs) and cause dysregulated, polyclonal B cell activation irrespective of normal BCR-antigen complementarity. The cells typically succumb to activation-induced cell death, which can impede the adaptive immune response and favor infection. In the present study, we demonstrate that the fucose-binding lectin of Burkholderia ambifaria, BambL, bears functional resemblance to B cell superantigens. By engaging surface glycans, the bacterial lectin activated human peripheral blood B cells, which manifested in the surface expression of CD69, CD54 and CD86 but became increasingly cytotoxic at higher concentrations. The effects were sensitive to BCR pathway inhibitors and excess fucose, which corroborates a glycan-driven mode of action. Interactome analyses in a model cell line suggest BambL binds directly to glycans of the BCR and regulatory coreceptors. In vitro, BambL triggered BCR signaling and induced CD19 internalization and degradation. Owing to the lectin's six binding sites, we propose a BCR activation model in which BambL functions as a clustering hub for receptor glycans, modulates normal BCR regulation, and induces cell death through exhaustive activation.

Brilliant glycans and glycosylation: Seq and ye shall find

Proteoglycosylation is the addition of monosaccharides or glycans to the protein peptide chain. This is a common post-translational modification of proteins with a variety of biological functions. At present, more than half of all biopharmaceuticals in clinic are modified by glycosylation. Most glycoproteins are potential drug targets and biomarkers for disease diagnosis. Therefore, in-depth study of glycan structure of glycoproteins will ultimately improve the sensitivity and specificity of glycoproteins for clinical disease detection. With the deepening of research, the function and application value of glycans and glycosylation has gradually emerged. This review systematically introduces the latest research progress of glycans and glycosylation. It encompasses six cancers, four viruses, and their latest discoveries in Alzheimer's disease, allergic diseases, congenital diseases, gastrointestinal diseases, inflammation, and aging.

Concanavalin A targeting N-linked glycans in spike proteins influence viral interactions

Lectins, which exhibit viral-interaction abilities, have garnered attention in the current pandemic era as potential neutralizing agents and vaccine candidates. Viral invasion through envelope proteins is modulated by N-linked glycosylation in the spike (S) protein. This study demonstrates the biophysical aspects between lectins and high-mannose and -galactose N-glycans to provide insights into binding events.

Genomic features of humoral immunity support tolerance model in Egyptian rousette bats

Bats asymptomatically harbor many viruses that can cause severe human diseases. The Egyptian rousette bat (ERB) is the only known reservoir for Marburgviruses and Sosuga virus, making it an exceptional animal model to study antiviral mechanisms in an asymptomatic host. With this goal in mind, we constructed and annotated the immunoglobulin heavy chain locus, finding an expansion on immunoglobulin variable genes associated with protective human antibodies to different viruses. We also annotated two functional and distinct immunoglobulin epsilon genes and four distinctive functional immunoglobulin gamma genes. We described the Fc receptor repertoire in ERBs, including features that may affect activation potential, and discovered the lack of evolutionary conserved short pentraxins. These findings reinforce the hypothesis that a differential threshold of regulation and/or absence of key immune mediators may promote tolerance and decrease inflammation in ERBs.

Glycan-specific IgG anti-IgE autoantibodies are protective against allergic anaphylaxis in a murine model

BACKGROUND

IgE causes anaphylaxis in type I hypersensitivity diseases by activating degranulation of effector cells such as mast cells and basophils. The mechanisms that control IgE activity and prevent anaphylaxis under normal conditions are still enigmatic.

OBJECTIVE

We aimed to unravel how anti-IgE autoantibodies are induced and we aimed to understand their role in regulating serum IgE level and allergic anaphylaxis.

METHODS

We immunized mice with different forms of IgE and tested anti-IgE autoantibody responses and their specificities. We then analyzed the effect of those antibodies on serum kinetics and their in vitro and in vivo impact on anaphylaxis. Finally, we investigated anti-IgE autoantibodies in human sera.

RESULTS

Immunization of mice with IgE-immune complexes induced glycan-specific anti-IgE autoantibodies. The anti-IgE autoantibodies prevented effector cell sensitization, reduced total IgE serum levels, protected mice from passive and active IgE sensitization, and resulted in cross-protection against different allergens. Furthermore, glycan-specific anti-IgE autoantibodies were present in sera from subjects with allergy and subjects without allergy.

CONCLUSION

In conclusion, this study provided the first evidence that in the murine model, the serum level and anaphylactic activity of IgE may be downregulated by glycan-specific IgG anti-IgE autoantibodies.

Artesunate: A natural product-based immunomodulator involved in human complement

Complement is an important innate immune defence machinery. Once dysregulated, it is often linked to pathogenesis of diverse autoimmune diseases. Artesunate (ART) is a well-known anti-malarial compound. Recently, ART has been highlighted by its potential therapeutic effects on certain complement-related autoimmune diseases. However, the underlying mechanisms are hitherto unknown. In the present study, we found that ART mediated complement interception as validated by analysis of complement haemolytic assay. In cell-based setup using dying Jurkat cells, ART-mediated complement interception was also confirmed. Further, we newly established an ELISA system selectively allowing complement activation via the classical pathway, the lectin pathway and the alternative pathway, respectively. ELISA analysis revealed that ART dose-dependently inhibited C4 activation, C3 activation and terminal complement complex assembly via the effector pathways. ART was found to blockade C1q, C3 and C5 with a lesser extent to properdin. The interaction of ART with C1q was determined to be mediated via C1q globular head region. FACS analysis using ART-conjugated mesoporous silica particles revealed that ART specifically bound the key therapeutic targets of C1q, C3 and C5 on microparticles. In conclusion, we for the first time report the anti-complement bioactivities of ART and suggest a potential therapeutic benefit of ART in the complement-related human diseases.

The therapeutic implications of activated immune responses via the enigmatic immunoglobulin D

Immunoglobulin D (IgD) is an enigmatic antibody and the least appreciated member of the immunoglobulin (Ig) family. Since its discovery over half a century ago, the essence of its function in the immune system has been somewhat enigmatic and less well-defined than other antibody classes. Membrane-bound IgD (mIgD) is mostly recognized as B-cell receptor (BCR) while secreted IgD (sIgD) has been recently implicated in 'arming' basophils and mast cells in mucosal innate immunity. Activations of immune responses via mIgD-BCR or sIgD by specific antigens or anti-IgD antibody thereby produce a broad and complex mix of cellular, antibody and cytokine responses from both the innate and adaptive immune systems. Such broadly activated immune responses via IgD were initially deemed to potentiate and exacerbate the onset of autoimmune and allergic conditions. Paradoxically, treatments with anti-IgD antibody suppressed and ameliorated autoimmune conditions and allergic inflammations in mouse models without compromising the host's general immune defence, demonstrating a unique and novel therapeutic application for anti-IgD antibody treatment. Herein, this review endeavored to collate and summarize the evidence of the unique characteristics and features of activated immune responses via mIgD-BCR and sIgD that revealed an unappreciated immune-regulatory function of IgD in the immune system via an amplifying loop of anti-inflammatory Th2 and tolerogenic responses, and highlighted a novel therapeutic paradigm in harnessing these immune responses to treat human autoimmune and allergic conditions.

Glycosylation of Plant-Produced Immunoglobulins

Many economically important protein-based therapeutics like monoclonal antibodies are glycosylated. Due to the recognized importance of this type of posttranslational modification, glycoengineering of expression systems to obtain highly active and homogenous therapeutics is an emerging field. Although most of the monoclonal antibodies on the market are still produced in mammalian expression platforms, plants are emerging as an alternative cost-effective and scalable production platform that allows precise engineering of glycosylation to produce targeted human glycoforms at large homogeneity. Apart from producing more effective antibodies, pure glycoforms are required in efforts to link biological functions to specific glycan structures. Much is already known about the role of IgG1 glycosylation and this antibody class is the dominant recombinant format that has been expressed in plants. By contrast, little attention has been paid to the glycoengineering of recombinant IgG subtypes and the other four classes of human immunoglobulins (IgA, IgD, IgE, and IgM). Except for IgD, all these antibody classes have been expressed in plants and the glycosylation has been analyzed in a site-specific manner. Here, we summarize the current data on glycosylation of plant-produced monoclonal antibodies and discuss the findings in the light of known functions for these glycans.

Sweet Rules: Linking Glycosylation to Antibody Function

Antibodies produced upon infections with pathogenic microorganisms are essential for clearing primary infections and for providing the host with long-lasting immunity. Moreover, antibodies have become the most widely used platform for developing novel therapies against cancer and autoimmunity, requiring an in-depth understanding of how antibodies mediate their activity in vivo and which factors modulate pro- or anti-inflammatory antibody activities. Since the discovery that select residues present in the sugar domain attached to the immunoglobulin G (IgG) fragment crystallizable (Fc) region can modulate both, pro- and anti-inflammatory effector functions, a wealth of studies has focused on understanding how IgG glycosylation is regulated and how this knowledge can be used to optimize therapeutic antibody activity. With the introduction of glycoengineered afucosylated antibodies in cancer therapy and the initiation of clinical testing of highly sialylated anti-inflammatory antibodies the proof-of-concept that understanding antibody glycosylation can lead to clinical innovation has been provided. The focus of this review is to summarize recent insights into how antibody glycosylation is regulated in vivo and how select sugar residues impact IgG function.

Capillary (Gel) Electrophoresis-Based Methods for Immunoglobulin (G) Glycosylation Analysis

The in-depth characterization of protein glycosylation has become indispensable in many research fields and in the biopharmaceutical industry. Especially knowledge about modulations in immunoglobulin G (IgG) N-glycosylation and their effect on immunity enabled a better understanding of human diseases and the development of new, more effective drugs for their treatment. This chapter provides a deeper insight into capillary (gel) electrophoresis-based (C(G)E) glycan analysis, addressing its impressive performance and possibilities, its great potential regarding real high-throughput for large cohort studies, as well as its challenges and limitations. We focus on the latest developments with respect to miniaturization and mass spectrometry coupling, as well as data analysis and interpretation. The use of exoglycosidase sequencing in combination with current C(G)E technology is discussed, highlighting possible difficulties and pitfalls. The application section describes the detailed characterization of N-glycosylation, utilizing multiplexed CGE with laser-induced fluorescence detection (xCGE-LIF). Besides a comprehensive overview on antibody glycosylation by comparing species-specific IgGs and human immunoglobulins A, D, E, G, and M, the chapter comprises a comparison of therapeutic monoclonal antibodies from different production cell lines, as well as a detailed characterization of Fab and Fc glycosylation. These examples illustrate the full potential of C(G)E, resolving the smallest differences in sugar composition and structure.

Large-scale site-specific mapping of the O-GalNAc glycoproteome

Protein glycosylation is one of the most common protein modifications. A major type of protein glycosylation is O-GalNAcylation, in which GalNAc-type glycans are attached to protein Ser or Thr residues via an O-linked glycosidic bond. O-GalNAcylation is thought to play roles in protein folding, stability, trafficking and protein interactions, and identification of the site-specific O-GalNAc glycoproteome is a crucial step toward understanding the biological significance of the modification. However, lack of suitable methodology, absence of consensus sequon of O-GalNAcylation sites and complex O-GalNAc glycan structures pose analytical challenges. We recently developed a mass spectrometry-based method called extraction of O-linked glycopeptides (EXoO) that enables large-scale mapping of site-specific mucin-type O-GalNAcylation sites. Here we provide a detailed protocol for EXoO, which includes seven stages of: (1) extraction and proteolytic digestion of proteins to peptides, (2) sequential guanidination and de-salting of peptides, (3) enrichment of glycopeptides, (4) solid-phase peptide conjugation and release of O-GalNAc glycopeptides using the OpeRATOR protease, (5) liquid chromatography with tandem mass spectrometry analysis of O-GalNAc glycopeptides, (6) identification of O-GalNAc glycopeptides by database search and (7) quantification of O-GalNAc glycopeptides. Using this protocol, thousands of O-GalNAcylation sites from hundreds of glycoproteins with information regarding site-specific O-GalNAc glycan can be identified and quantified from complex samples. The protocol can be performed by a researcher with basic proteomics skills and takes about 4 d to complete.

Relative content detection of oligomannose modification of IgM heavy chain induced by TNP-antigen in an early vertebrate through nanoLC-MS/MS

N-glycan modification is reported to be important in regulating the structure and function of immunoglobulins in mammals. While, the study on teleost immunoglobulin glycosylation is still limitted. In this study, we constructed a TNP-antigen driven model, and detected the site-specific N-glycans of PBS-immunized and TNP-specific Oreochromis niloticus serum IgM through ¹⁸O-labeling and nanoLC-MS/MS. These methods are widely used for peptide enrichment and protein modification identification, but rarely used in detecting the level of N-glycosylation in teleost Igs that driven by specific antigen. The results revealed that there are four N-glycosylation sites in O.niloticus IgM heavy chain, namely, the Asn-315 site in the CH2 domain, the Asn-338 site in the CH3 domain, and the Asn-509 and Asn-551 sites in the CH4 domain, All of the four residues were efficiently N-glycosylated. After immunized with TNP-antigen, the signal strength of oligomannose in the TNP-specific IgM in primary mass spectrometry was significantly higher than that in the PBS-immunized IgM. Notably, the TNP-specific IgM had an Asn-509 site fully occupied with oligomannose, while only a small amount of oligomannose was found in the PBS-immunized IgM of this site. N-glycans in other sites were mainly complex-type with a low content of fucosylation and sialylated. The oligomannose in TNP-specific IgM was further verified to be essential for the binding of IgM and MBL. These results demonstrated that the TNP-antigen induced the site-specific oligomannose modification of O.niloticus IgM heavy chain, and played an important role in the interaction of IgM and MBL, which provided insights into the evolutionary understanding of the IgM oligomannose modification and function.

Sialylation of immunoglobulin E is a determinant of allergic pathogenicity

Approximately one-third of the world's population suffers from allergies¹. Exposure to allergens crosslinks immunoglobulin E (IgE) antibodies that are bound to mast cells and basophils, triggering the release of inflammatory mediators, including histamine². Although IgE is absolutely required for allergies, it is not understood why total and allergen-specific IgE concentrations do not reproducibly correlate with allergic disease^3-5. It is well-established that glycosylation of IgG dictates its effector function and has disease-specific patterns. However, whether IgE glycans differ in disease states or affect biological activity is completely unknown⁶. Here we perform an unbiased examination of glycosylation patterns of total IgE from individuals with a peanut allergy and from non-atopic individuals without allergies. Our analysis reveals an increase in sialic acid content on total IgE from individuals with a peanut allergy compared with non-atopic individuals. Removal of sialic acid from IgE attenuates effector-cell degranulation and anaphylaxis in several functional models of allergic disease. Therapeutic interventions-including removing sialic acid from cell-bound IgE with a neuraminidase enzyme targeted towards the IgE receptor FcεRI, and administering asialylated IgE-markedly reduce anaphylaxis. Together, these results establish IgE glycosylation, and specifically sialylation, as an important regulator of allergic disease.

Considerations for the Design of Antibody-Based Therapeutics

Antibody-based proteins have become an important class of biologic therapeutics, due in large part to the stability, specificity, and adaptability of the antibody framework. Indeed, antibodies not only have the inherent ability to bind both antigens and endogenous immune receptors but also have proven extremely amenable to protein engineering. Thus, several derivatives of the monoclonal antibody format, including bispecific antibodies, antibody-drug conjugates, and antibody fragments, have demonstrated efficacy for treating human disease, particularly in the fields of immunology and oncology. Reviewed here are considerations for the design of antibody-based therapeutics, including immunological context, therapeutic mechanisms, and engineering strategies. First, characteristics of antibodies are introduced, with emphasis on structural domains, functionally important receptors, isotypic and allotypic differences, and modifications such as glycosylation. Then, aspects of therapeutic antibody design are discussed, including identification of antigen-specific variable regions, choice of expression system, use of multispecific formats, and design of antibody derivatives based on fragmentation, oligomerization, or conjugation to other functional moieties. Finally, strategies to enhance antibody function through protein engineering are reviewed while highlighting the impact of fundamental biophysical properties on protein developability.

In Planta Glycan Engineering and Functional Activities of IgE Antibodies

Human immunoglobulin E (IgE) is the most extensively glycosylated antibody isotype so glycans attached to the seven N-glycosites (NGS) in its Fab and Fc domains may modulate its functions. However, targeted modification of glycans in multiply glycosylated proteins remains a challenge. Here, we applied an in vivo approach that allows the manipulation of IgE N-glycans, using a trastuzumab equivalent IgE (HER2-IgE) as a model. Taking advantage of plant inherent features, i.e., synthesis of largely homogeneous complex N-glycans and susceptibility to glycan engineering, we generated targeted glycoforms of HER2-IgE largely resembling those found in serum IgE. Plant-derived HER2-IgE exhibited N-glycans terminating with GlcNAc, galactose or sialic acid, lacking, or carrying core fucose and xylose. We were able to not only modulate the five NGSs naturally decorated with complex N-glycans, but to also induce targeted glycosylation at the usually unoccupied NGS6, thus increasing the overall glycosylation content of HER2-IgE. Recombinant human cell-derived HER2-IgE exhibited large N-glycan heterogeneity. All HER2-IgE variants demonstrated glycosylation-independent binding to the target antigen and the high affinity receptor FcεRI, and subsequent similar capacity to trigger mast cell degranulation. In contrast, binding to the low affinity receptor CD23 (FcεRII) was modulated by the glycan profile, with increased binding to IgE variants with glycans terminating with GlcNAc residues. Here we offer an efficient in planta approach to generate defined glycoforms on multiply glycosylated IgE, allowing the precise exploration of glycosylation-dependent activities.

IgE Glycosylation in Health and Disease

IgE are absolutely required for initiation of allergy reactions, which affect over 20% of the world's population. IgE are the least prevalent immunoglobulins in circulation with 12-h and 2-day half-lives in mouse and human serum, respectively, but an extended tissue half-life of 3-weeks bound to the surface of mast cells by the high affinity IgE receptor, FcεRI (Gould and Sutton 2008). Although the importance of glycosylation to IgG biology is well established, less is known regarding the contribution of IgE glycosylation to allergic inflammation. IgE has seven and nine N-linked glycosylation sites distributed across human and murine constant chains, respectively. Here we discuss studies that have analyzed IgE glycosylation and its function, and how IgE glycosylation contributions to health and disease.

Elevated serum activity of MBL and ficolin-2 as biomarkers for progression to hepatocellular carcinoma in chronic HCV infection

Hepatocellular carcinoma (HCC) is an uncommon but significant outcome of chronic hepatitis C virus (HCV) infection. A serum biomarker for predicting progression to HCC would have a major impact on patient monitoring and clinical management. We explored circulating liver-expressed lectins, ficolin-2, ficolin-3 and mannose binding lectin (MBL), as potential biomarkers for the development of HCC. The activity of these three lectins were analysed in HCV positive patients who developed HCC (n = 31) with comparable HCV-positive HCC-negative patients (n = 106) and healthy controls (n = 79). Serum binding activity of ficolin-2 and MBL were elevated compared to controls. Analysis of pre-HCC onset samples revealed that MBL levels were significantly elevated up to 3 years, and ficolin-2 was elevated up to 1 year, prior to diagnosis of HCC over controls. This preliminary study identifies MBL and ficolin-2 as potential biomarkers for the development of HCC in chronic HCV infection.

IgE Antibodies: From Structure to Function and Clinical Translation

Immunoglobulin E (IgE) antibodies are well known for their role in mediating allergic reactions, and their powerful effector functions activated through binding to Fc receptors FcεRI and FcεRII/CD23. Structural studies of IgE-Fc alone, and when bound to these receptors, surprisingly revealed not only an acutely bent Fc conformation, but also subtle allosteric communication between the two distant receptor-binding sites. The ability of IgE-Fc to undergo more extreme conformational changes emerged from structures of complexes with anti-IgE antibodies, including omalizumab, in clinical use for allergic disease; flexibility is clearly critical for IgE function, but may also be exploited by allosteric interference to inhibit IgE activity for therapeutic benefit. In contrast, the power of IgE may be harnessed to target cancer. Efforts to improve the effector functions of therapeutic antibodies for cancer have almost exclusively focussed on IgG1 and IgG4 subclasses, but IgE offers an extremely high affinity for FcεRI receptors on immune effector cells known to infiltrate solid tumours. Furthermore, while tumour-resident inhibitory Fc receptors can modulate the effector functions of IgG antibodies, no inhibitory IgE Fc receptors are known to exist. The development of tumour antigen-specific IgE antibodies may therefore provide an improved immune functional profile and enhanced anti-cancer efficacy. We describe proof-of-concept studies of IgE immunotherapies against solid tumours, including a range of in vitro and in vivo evaluations of efficacy and mechanisms of action, as well as ex vivo and in vivo safety studies. The first anti-cancer IgE antibody, MOv18, the clinical translation of which we discuss herein, has now reached clinical testing, offering great potential to direct this novel therapeutic modality against many other tumour-specific antigens. This review highlights how our understanding of IgE structure and function underpins these exciting clinical developments.

Improving Immunotherapy Through Glycodesign

Immunotherapy is revolutionizing health care, with the majority of high impact "drugs" approved in the past decade falling into this category of therapy. Despite considerable success, glycosylation-a key design parameter that ensures safety, optimizes biological response, and influences the pharmacokinetic properties of an immunotherapeutic-has slowed the development of this class of drugs in the past and remains challenging at present. This article describes how optimizing glycosylation through a variety of glycoengineering strategies provides enticing opportunities to not only avoid past pitfalls, but also to substantially improve immunotherapies including antibodies and recombinant proteins, and cell-based therapies. We cover design principles important for early stage pre-clinical development and also discuss how various glycoengineering strategies can augment the biomanufacturing process to ensure the overall effectiveness of immunotherapeutics.

Structure and Immune Recognition of the HIV Glycan Shield

Vaccine design efforts against the human immunodeficiency virus (HIV) have been greatly stimulated by the observation that many infected patients eventually develop highly potent broadly neutralizing antibodies (bnAbs). Importantly, these bnAbs have evolved to recognize not only the two protein components of the viral envelope protein (Env) but also the numerous glycans that form a protective barrier on the Env protein. Because Env is heavily glycosylated compared to host glycoproteins, the glycans have become targets for the antibody response. Therefore, considerable efforts have been made in developing and validating biophysical methods to elucidate the complex structure of the Env-spike glycoprotein, with its combination of glycan and protein epitopes. We illustrate here how the application of robust biophysical methods has transformed our understanding of the structure and function of the HIV Env spike and stimulated innovation in vaccine design strategies that takes into account the essential glycan components.

Neutralizing Antibodies Induced by Gene-Based Hydrodynamic Injection Have a Therapeutic Effect in Lethal Influenza Infection

The influenza virus causes annual epidemics and occasional pandemics and is thus a major public health problem. Development of vaccines and antiviral drugs is essential for controlling influenza virus infection. We previously demonstrated the use of vectored immune-prophylaxis against influenza virus infection. We generated a plasmid encoding neutralizing IgG monoclonal antibodies (mAbs) against A/PR/8/34 influenza virus (IAV) hemagglutinin (HA). We then performed electroporation of the plasmid encoding neutralizing mAbs (EP) in mice muscles and succeeded in inducing the expression of neutralizing antibodies in mouse serum. This therapy has a prophylactic effect against lethal IAV infection in mice. In this study, we established a new method of passive immunotherapy after IAV infection. We performed hydrodynamic injection of the plasmid encoding neutralizing mAbs (HD) involving rapid injection of a large volume of plasmid-DNA solution into mice via the tail vein. HD could induce neutralizing antibodies in the serum and in several mucosal tissues more rapidly than in EP. We also showed that a single HD completely protected the mice even after infection with a lethal dose of IAV. We also established other isotypes of anti-HA antibody (IgA, IgM, IgD, and IgE) and showed that like anti-HA IgG, anti-HA IgA was also effective at combating upper respiratory tract IAV infection. Passive immunotherapy with HD could thus provide a new therapeutic strategy targeting influenza virus infection.

N-glycosylation of serum proteins for the assessment of patients with IgD multiple myeloma

Background

Because glycosylation is one of the most common post-translational modifications of proteins and because changes in glycosylation have been shown to have a significant correlation with the development of many cancer types, we investigated the serum N-glycome used to diagnose, stage and evaluate the pathological outcomes in IgD multiple myeloma.

Methods

Serum samples were available for 20 patients with IgD multiple myeloma, 41 patients with light chain multiple myeloma and 42 healthy control subjects. Serum N-glycans were released and analysed using DNA sequencer-assisted fluorophore-assisted capillary electrophoresis.

Results

Characteristic changes were revealed in the serum N-glycome of IgD myeloma. In particular, three N-glycans (NG1(6)A2F, Peak3; NG1(3)A2F, Peak4; NA2FB, Peak7) showed increased clinical value. The best area under the ROC curve of NG1(6)A2F to diagnose IgD myeloma was 0.981, with a 95.0% sensitivity and 95.2% specificity, and that of NG1(3)A2F was 0.936, with a 95.0% sensitivity and 78.6% specificity. The best area under the ROC curve of NA2FB/NG1(3)A2F to differentially diagnose IgD myeloma versus light chain myeloma was 0.744, with a 95.3% sensitivity and 50.0% specificity. The level of NG1(3)A2F was correlated with the international staging system, while the higher abundance of NA2FB presented in IgD myeloma was predictive of a shorter progression-free survival.

Conclusions

The advent of serum N-glycan signatures may play a role in the diagnosis, staging and prognosis of IgD myeloma and will serve as the foundation for a precision medicine approach to this rare subtype of multiple myeloma.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3891-3) contains supplementary material, which is available to authorized users.

Modeling of Oligosaccharides within Glycoproteins from Free-Energy Landscapes

In spite of the abundance of glycoproteins in biological processes, relatively little three-dimensional structural data is available for glycan structures. Here, we study the structure and flexibility of the vast majority of mammalian oligosaccharides appearing in N- and O-glycosylated proteins using a bottom up approach. We report the conformational free-energy landscapes of all relevant glycosidic linkages as obtained from local elevation simulations and subsequent umbrella sampling. To the best of our knowledge, this represents the first complete conformational library for the construction of N- and O-glycan structures. Next, we systematically study the effect of neighboring residues, by extensively simulating all relevant trisaccharides and one tetrasaccharide. This allows for an unprecedented comparison of disaccharide linkages in large oligosaccharides. With a small number of exceptions, the conformational preferences in the larger structures are very similar as in the disaccharides. This, finally, allows us to suggest several efficient approaches to construct complete N- and O-glycans on glycoproteins, as exemplified on two relevant examples.

Thermal sensitivity and flexibility of the Cε3 domains in immunoglobulin E

Immunoglobulin E (IgE) is the antibody that plays a central role in the mechanisms of allergic diseases such as asthma. Interactions with its receptors, FcεRI on mast cells and CD23 on B cells, are mediated by the Fc region, a dimer of the Cε2, Cε3 and Cε4 domains. A sub-fragment lacking the Cε2 domains, Fcε3–4, also binds to both receptors, although receptor binding almost exclusively involves the Cε3 domains. This domain also contains the N-linked glycosylation site conserved in other isotypes. We report here the crystal structures of IgE-Fc and Fcε3–4 at the highest resolutions yet determined, 1.75 Å and 2.0 Å respectively, revealing unprecedented detail regarding the carbohydrate and its interactions with protein domains. Analysis of the crystallographic B-factors of these, together with all earlier IgE-Fc and Fcε3–4 structures, shows that the Cε3 domains exhibit the greatest intrinsic flexibility and quaternary structural variation within IgE-Fc. Intriguingly, both well-ordered carbohydrate and disordered polypeptide can be seen within the same Cε3 domain. A simplified method for comparing the quaternary structures of the Cε3 domains in free and receptor-bound IgE-Fc structures is presented, which clearly delineates the FcεRI and CD23 bound states. Importantly, differential scanning fluorimetric analysis of IgE-Fc and Fcε3–4 identifies Cε3 as the domain most susceptible to thermally-induced unfolding, and responsible for the characteristically low melting temperature of IgE.

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The Cε3 domains of IgE are most susceptible to thermally induced unfolding determined by differential scanning fluorimetry.

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The Cε3 domains are responsible for the characteristically low melting temperature of IgE.

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The Cε3 domains exhibit the greatest intrinsic flexibility.

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Quaternary structural diversity of Cε3 domains is compared across all known structures using a simplified single parameter.

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Human IgE-Fc and Fcε3–4 domain structures are determined at the highest resolutions yet reported (1.75 Å and 2.0 Å).

Immunoglobulin Glycosylation Effects in Allergy and Immunity

PURPOSE OF REVIEW

The aim of this review will be to familiarize the reader with the general area of antibody (Ab) glycosylation and to summarize the known functional roles of glycosylation and how glycan structure can contribute to various disease states with emphasis on allergic disease.

RECENT FINDINGS

Both immunoglobulin (Ig) isotype and conserved Fc glycosylation sites often dictate the downstream activity of an Ab where complexity and degree of glycosylation contribute to its ability to bind Fc receptors (FcRs) and activate complement. Most information on the effects of glycosylation center on IgG in cancer therapy and autoimmunity. In cancer therapy, glycosylation modifications that enhance affinity for activating FcRs are utilized to facilitate immune-mediated tumor cell killing. In autoimmunity, disease severity has been linked to alterations in the presence, location, and composition of Fc glycans. Significantly less is understood about the role of glycosylation in the setting of allergy and asthma. However, recent data demonstrate that glycosylation of IgE at the asparagine-394 site of Cε3 is necessary for IgE interaction with the high affinity IgE receptor but, surprisingly, glycosylation has no effect on IgE interaction with its low-affinity lectin receptor, CD23. Variations in the specific glycoform may modulate the interaction of an Ig with its receptors. Significantly more is known about the functional effects of glycosylation of IgG than for other Ig isotypes. Thus, the role of glycosylation is much better understood in the areas of autoimmunity and cancer therapy, where IgG is the dominant isotype, than in the field of allergy, where IgE predominates. Further work is needed to fully understand the role of glycan variation in IgE and other Ig isotypes with regard to the inhibition or mediation of allergic disease.

Recombinant plant-derived human IgE glycoproteomics

The increasing biotechnological interest in human IgE antibodies demands advanced systems which allow their proper expression. However, this is still a challenge due to the complexity of the molecule, particularly regarding the diverse N-glycosylation pattern. Here, we present the expression of recombinant IgE in wild type and glycan-engineered Nicotiana benthamiana plants and in-depth N-glycosylation analyses. Mass spectrometric profiling revealed that plant IgE has a site occupancy rate that ranges from non-occupied at glycosite 6 (GS6) to 100% occupancy at GS1 and 2. Similarly to human cell-derived IgE, plant versions carry complex N-glycans at GS1-5 and oligomannosidic structures at GS7. Computational modelling suggests that spatial position (or orientation) of glycans can impair processing or site occupancy on adjacent glycosites. IgE expressed in glycoengineered and wild type plants carry, respectively, GnGn and plant-typical GnGnXF structures at large homogeneity. This contrasts with the glycan diversity of HEK cell-derived IgE, carrying at least 20 different glycoforms. Importantly, IgE glycoengineering allows the control of its glycosylation, a so far unmet need when using well-established expression systems. This enables the elucidation of possible carbohydrate-dependent IgE functions.

SIGNIFICANCE

Targeted glycosylation of recombinant proteins may provide an advantage in therapeutic applications. Despite increasing biotechnological interest in IgE antibodies, knowledge and impact of glycosylation on this antibody class are scarce. With the ability to glyco-engineer recombinant IgE, we provide an important step towards the generation of IgE with other targeted N-glycans. This will facilitate detailed structure-function studies and may lead to the production of IgE with optimized activities.

Half-life of IgE in serum and skin: Consequences for anti-IgE therapy in patients with allergic disease

We present results from clinical studies on plasma infusion done in the late 1970s in patients with hypogammaglobulinemia in which we documented the short half-life of both total and allergen-specific IgE in serum. The development of specific allergic sensitization in the skin of those patients followed by the gradual decrease in sensitization over 50 days was also documented. The data are included here along with a discussion of the existing literature about the half-life of IgE in both the circulation and skin. This rostrum reinterprets the earlier clinical studies in light of new insights and mechanisms that could explain the rapid removal of IgE from the circulation. These mechanisms have clinical implications that relate to the increasing use of anti-IgE mAbs for the treatment of allergic disease.

Recombinant ArtinM activates mast cells

Background

Mast cells are hematopoietically derived cells that play a role in inflammatory processes such as allergy, as well as in the immune response against pathogens by the selective and rapid release of preformed and lipid mediators, and the delayed release of cytokines. The native homotetrameric lectin ArtinM, a D-mannose binding lectin purified from Artocarpus heterophyllus seeds, is one of several lectins that are able to activate mast cells. Besides activating mast cells, ArtinM has been shown to affect several biological responses, including immunomodulation and acceleration of wound healing. Because of the potential pharmacological application of ArtinM, a recombinant ArtinM (rArtinM) was produced in Escherichia coli. The current study evaluated the ability of rArtinM to induce mast cell degranulation and activation.

Results

The glycan binding specificity of rArtinM was similar to that of jArtinM. rArtinM, via its CRD, was able to degranulate, releasing β-hexosaminidase and TNF-α, and to promote morphological changes on the mast cell surface. Moreover, rArtinM induced the release of the newly-synthesized mediator, IL-4. rArtinM does not have a co-stimulatory effect on the FcεRI degranulation via. The IgE-dependent mast cell activation triggered by rArtinM seems to be dependent on NFkB activation.

Conclusions

The lectin rArtinM has the ability to activate and degranulate mast cells via their CRDs. The present study indicates that rArtinM is a suitable substitute for the native form, jArtinM, and that rArtinM may serve as an important and reliable pharmacological agent.

Control of B Cell Responsiveness by Isotype and Structural Elements of the Antigen Receptor

Expression of a functional B cell antigen receptor (BCR) plays a central role in regulating B cell development, maturation, and effector functions. Although IgM is solely expressed in immature B cell stages, the presence of both IgM- and IgD-BCR isotypes on mature naïve B cells raises the question of whether IgD has a unique role in B cell activation and function. While earlier studies suggested a broad functional redundancy between IgM and IgD, recent data point to an important immune regulatory role of IgD. Herein, we review these findings and discuss how the structural flexibility, mode of antigen binding, and co-receptor interactions, enable the IgD-BCR to act as a 'rheostat', regulating the activation and function of mature naïve B cells.

The Art of Destruction: Optimizing Collision Energies in Quadrupole-Time of Flight (Q-TOF) Instruments for Glycopeptide-Based Glycoproteomics

In-depth site-specific investigations of protein glycosylation are the basis for understanding the biological function of glycoproteins. Mass spectrometry-based N- and O-glycopeptide analyses enable determination of the glycosylation site, site occupancy, as well as glycan varieties present on a particular site. However, the depth of information is highly dependent on the applied analytical tools, including glycopeptide fragmentation regimes and automated data analysis. Here, we used a small set of synthetic disialylated, biantennary N-glycopeptides to systematically tune Q-TOF instrument parameters towards optimal energy stepping collision induced dissociation (CID) of glycopeptides. A linear dependency of m/z-ratio and optimal fragmentation energy was found, showing that with increasing m/z-ratio, more energy is required for glycopeptide fragmentation. Based on these optimized fragmentation parameters, a method combining lower- and higher-energy CID was developed, allowing the online acquisition of glycan and peptide-specific fragments within a single tandem MS experiment. We validated this method analyzing a set of human immunoglobulins (IgA1+2, sIgA, IgG1+2, IgE, IgD, IgM) as well as bovine fetuin. These optimized fragmentation parameters also enabled software-assisted glycopeptide assignment of both N- and O-glycopeptides including information about the most abundant glycan compositions, peptide sequence and putative structures. Twenty-six out of 30 N-glycopeptides and four out of five O-glycopeptides carrying >110 different glycoforms could be identified by this optimized LC-ESI tandem MS method with minimal user input. The Q-TOF based glycopeptide analysis platform presented here opens the way to a range of different applications in glycoproteomics research as well as biopharmaceutical development and quality control.

Glycoproteomic studies of IgE from a novel hyper IgE syndrome linked to PGM3 mutation

Glycans serve as important regulators of antibody activities and half-lives. IgE is the most heavily glycosylated antibody, but in comparison to other antibodies little is known about its glycan structure function relationships. We therefore describe the site specific IgE glycosylation from a patient with a novel hyper IgE syndrome linked to mutations in PGM3, which is an enzyme involved in synthesizing UDP-GlcNAc, a sugar donor widely required for glycosylation. A two-step method was developed to prepare two IgE samples from less than 1 mL of serum collected from a patient with PGM3 mutation and a patient with atopic dermatitis as a control subject. Then, a glycoproteomic strategy was used to study the site-specific glycosylation. No glycosylation was found at Asn264, whilst high mannose glycans were only detected at Asn275, tri-antennary glycans were exclusively observed at Asn99 and Asn252, and non-fucosylated complex glycans were detected at Asn99. The results showed similar glycosylation profiles between the two IgE samples. These observations, together with previous knowledge of IgE glycosylation, imply that IgE glycosylation is similarly regulated among healthy control, allergy and PGM3 related hyper IgE syndrome.

Human plasma protein N-glycosylation

Glycosylation is the most abundant and complex protein modification, and can have a profound structural and functional effect on the conjugate. The oligosaccharide fraction is recognized to be involved in multiple biological processes, and to affect proteins physical properties, and has consequentially been labeled a critical quality attribute of biopharmaceuticals. Additionally, due to recent advances in analytical methods and analysis software, glycosylation is targeted in the search for disease biomarkers for early diagnosis and patient stratification. Biofluids such as saliva, serum or plasma are of great use in this regard, as they are easily accessible and can provide relevant glycosylation information. Thus, as the assessment of protein glycosylation is becoming a major element in clinical and biopharmaceutical research, this review aims to convey the current state of knowledge on the N-glycosylation of the major plasma glycoproteins alpha-1-acid glycoprotein, alpha-1-antitrypsin, alpha-1B-glycoprotein, alpha-2-HS-glycoprotein, alpha-2-macroglobulin, antithrombin-III, apolipoprotein B-100, apolipoprotein D, apolipoprotein F, beta-2-glycoprotein 1, ceruloplasmin, fibrinogen, immunoglobulin (Ig) A, IgG, IgM, haptoglobin, hemopexin, histidine-rich glycoprotein, kininogen-1, serotransferrin, vitronectin, and zinc-alpha-2-glycoprotein. In addition, the less abundant immunoglobulins D and E are included because of their major relevance in immunology and biopharmaceutical research. Where available, the glycosylation is described in a site-specific manner. In the discussion, we put the glycosylation of individual proteins into perspective and speculate how the individual proteins may contribute to a total plasma N-glycosylation profile determined at the released glycan level.

A Method for Comprehensive Glycosite-Mapping and Direct Quantitation of Serum Glycoproteins

A comprehensive glycan map was constructed for the top eight abundant glycoproteins in plasma using both specific and nonspecific enzyme digestions followed by nano liquid chromatography (LC)-chip/quadrupole time-of-flight mass spectrometry (MS) analysis. Glycopeptides were identified using an in-house software tool, GPFinder. A sensitive and reproducible multiple reaction monitoring (MRM) technique on a triple quadrupole MS was developed and applied to quantify immunoglobulins G, A, M, and their site-specific glycans simultaneously and directly from human serum/plasma without protein enrichments. A total of 64 glycopeptides and 15 peptides were monitored for IgG, IgA, and IgM in a 20 min ultra high performance (UP)LC gradient. The absolute protein contents were quantified using peptide calibration curves. The glycopeptide ion abundances were normalized to the respective protein abundances to separate protein glycosylation from protein expression. This technique yields higher method reproducibility and less sample loss when compared with the quantitation method that involves protein enrichments. The absolute protein quantitation has a wide linear range (3-4 orders of magnitude) and low limit of quantitation (femtomole level). This rapid and robust quantitation technique, which provides quantitative information for both proteins and glycosylation, will further facilitate disease biomarker discoveries.

IgE immunotherapy: a novel concept with promise for the treatment of cancer

The importance of antibodies in activating immune responses against tumors is now better appreciated with the emergence of checkpoint blockade antibodies and with engineered antibody Fc domains featuring enhanced capacity to focus potent effector cells against cancer cells. Antibodies designed with Fc regions of the IgE class can confer natural, potent, long-lived immune surveillance in tissues through tenacious engagement of high-affinity cognate Fc receptors on distinct, often tumor-resident immune effector cells, and through ability to activate these cells under tumor-induced Th2-biased conditions. Here, we review the properties that make IgE a contributor to the allergic response and a critical player in the protection against parasites, which also support IgE as a novel anti-cancer modality. We discuss IgE-based active and passive immunotherapeutic approaches in disparate in vitro and in vivo model systems, collectively suggesting the potential of IgE immunotherapies in oncology. Translation toward clinical application is now in progress.

Restricted motion of the conserved immunoglobulin G1 N-glycan is essential for efficient FcγRIIIa binding

Immunoglobulin G1 (IgG1)-based therapies are widespread, and many function through interactions with low-affinity Fc γ receptors (FcγR). N-glycosylation of the IgG1 Fc domain is required for FcγR binding, though it is unclear why. Structures of the FcγR:Fc complex fail to explain this because the FcγR polypeptide does not bind the N-glycan. Here we identify a link between motion of the N-glycan and Fc:FcγRIIIa affinity that explains the N-glycan requirement. Fc F241 and F243 mutations decreased the N-glycan/polypeptide interaction and increased N-glycan mobility. The affinity of the Fc mutants for FcγRIIIa was directly proportional to the degree of glycan restriction (R(2) = 0.82). The IgG1 Fc K246F mutation stabilized the N-glycan and enhanced affinity for FcγRIIIa. Allosteric modulation of a protein/protein interaction represents a previously undescribed role for N-glycans in biology. Conserved features suggesting a similar N-glycan/aromatic interaction were also found in IgD, IgE, and IgM, but not IgA.