Sialylation of immunoglobulin E is a determinant of allergic pathogenicity

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.

Next-generation reference interval for total IgE in the United States: A retrospective real-world analysis

OBJECTIVE

To establish a next-generation reference interval (RI) for total IgE (tIgE) and evaluate its usefulness.

METHODS

A new allergen-specific IgE (sIgE)-based tIgE RI, including a continuous RI in children, was established using the NHANES 2005-2006 project. The usefulness of the RI was evaluated by sensitivity (Sen), specificity (Spec), positive predictive value (PPV), negative predictive value (NPV), κ coefficient and consistency.

RESULTS

The new tIgE RI showed better performance in identifying allergic sensitization (Sen 0.53, Spec 0.90, PPV 0.83, NPV 0.68, κ 0.44, consistency 0.72) than allergic diseases (Sen 0.37, Spec 0.75, PPV 0.55, NPV 0.60, κ 0.13, consistency 0.59). The 2014 U.S. tIgE RI was more effective in identifying allergic diseases (consistency 0.63 vs. 0.54, P<0.001) but less accurate in identifying allergic sensitization (consistency 0.59 vs. 0.67, P<0.001) in children than in adults. The new RI improved the accuracy of identifying allergic sensitization in children to a level similar to that in adults (consistency 0.72 vs 0.73, P=0.37) and maintained its advantage in identifying allergic diseases in children (consistency 0.64 vs 0.55, P<0.001).

CONCLUSIONS

The established next-generation tIgE RI is useful for identifying allergic sensitization, especially in children.

Whence and wherefore IgE?

Despite the near ubiquitous presence of Ig-based antibodies in vertebrates, IgE is unique to mammals. How and why it emerged remains mysterious. IgE expression is greatly constrained compared to other IgH isotypes. While other IgH isotypes are relatively abundant, soluble IgE has a truncated half-life, and IgE plasma cells are mostly short-lived. Despite its rarity, IgE is consequential and can trigger life-threatening anaphylaxis. IgE production reflects a dynamic steady state with IgG memory B cells feeding short-lived IgE production. Emerging evidence suggests that IgE may also potentially be produced in longer-lived plasma cells as well, perhaps as an aberrancy stemming from its evolutionary roots from an antibody isotype that likely functioned more like IgG. As a late derivative of an ancient systemic antibody system, the benefits of IgE in mammals likely stems from the antibody system's adaptive recognition and response capability. However, the tendency for massive, systemic, and long-lived production, common to IgH isotypes like IgG, were likely not a good fit for IgE. The evolutionary derivation of IgE from an antibody system that for millions of years was good at antigen de-sensitization to now functioning as a highly specialized antigen-sensitization function required heavy restrictions on antibody production-insufficiency of which may contribute to allergic disease.

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.

Mass spectrometry-based structure-specific N-glycoproteomics and biomedical applications

N-linked glycosylation is a common posttranslational modification of proteins that results in macroheterogeneity of the modification site. However, unlike simpler modifications, N-glycosylation introduces an additional layer of complexity with tens of thousands of possible structures arising from various dimensions, including different monosaccharide compositions, sequence structures, linking structures, isomerism, and three-dimensional conformations. This results in additional microheterogeneity of the modification site of N-glycosylation, i.e., the same N-glycosylation site can be modified with different glycans with a certain stoichiometric ratio. N-glycosylation regulates the structure and function of N-glycoproteins in a site- and structure-specific manner, and differential expression of N-glycosylation under disease conditions needs to be characterized through site- and structure-specific quantitative analysis. Numerous advanced methods ranging from sample preparation to mass spectrum analysis have been developed to distinguish N-glycan structures. Chemical derivatization of monosaccharides, online liquid chromatography separation and ion mobility spectrometry enable the physical differentiation of samples. Tandem mass spectrometry further analyzes the macro/microheterogeneity of intact N-glycopeptides through the analysis of fragment ions. Moreover, the development of search engines and AI-based software has enhanced our understanding of the dissociation patterns of intact N-glycopeptides and the clinical significance of differentially expressed intact N-glycopeptides. With the help of these modern methods, structure-specific N-glycoproteomics has become an important tool with extensive applications in the biomedical field.

Venom Component Allergen IgE Measurement in the Diagnosis and Management of Insect Sting Allergy

Accurate identification of allergy-eliciting stinging insect(s) is essential to ensuring effective management of Hymenoptera venom-allergic individuals with venom-specific immunotherapy. Diagnostic testing using whole-venom extracts with skin tests and serologic-based analyses remains the first level of discrimination for honeybee versus vespid venom sensitization in patients with a positive clinical history. As a second-level evaluation, serologic testing using molecular venom allergens can further discriminate genuine sensitization (honeybee venom: Api m 1, 3, 4, and 10 vs yellow jacket venom/Polistes dominula venom Ves v 1/Pol d 1 and Ves v 5/Pol d 5) from interspecies cross-reactivity (hyaluronidases [Api m 2, Ves v 2, and Pol d 2] and dipeptidyl peptidases IV [Api m 5, Ves v 3, and Pol d 3]). Clinical laboratories use a number of singleplex, oligoplex, and multiplex immunoassays that employ both extracted whole-venom and molecular venom allergens (highlighted earlier) for confirmation of allergic venom sensitization. Established quantitative singleplex autoanalyzers have general governmental regulatory clearance worldwide for venom-allergic patient testing with maximally achievable analytical sensitivity (0.1 kUA/L) and confirmed reproducibility (interassay coefficient of variation <10%). Emerging oligoplex and multiplex (fixed-panel) assays conserve on serum and are more cost-effective, but they need regulatory clearance in some countries and are prone to higher rates of detecting asymptomatic sensitization. Ultimately, the patient's clinical history, combined with proof of sensitization, is the final arbiter in the diagnosis of Hymenoptera venom allergy.

Sialic acid in the regulation of blood cell production, differentiation and turnover

Sialic acid is a unique sugar moiety that resides in the distal and most accessible position of the glycans on mammalian cell surface and extracellular glycoproteins and glycolipids. The potential for sialic acid to obscure underlying structures has long been postulated, but the means by which such structural changes directly affect biological processes continues to be elucidated. Here, we appraise the growing body of literature detailing the importance of sialic acid for the generation, differentiation, function and death of haematopoietic cells. We conclude that sialylation is a critical post-translational modification utilized in haematopoiesis to meet the dynamic needs of the organism by enforcing rapid changes in availability of lineage-specific cell types. Though long thought to be generated only cell-autonomously within the intracellular ER-Golgi secretory apparatus, emerging data also demonstrate previously unexpected diversity in the mechanisms of sialylation. Emphasis is afforded to the mechanism of extrinsic sialylation, whereby extracellular enzymes remodel cell surface and extracellular glycans, supported by charged sugar donor molecules from activated platelets.

Impact of temperature and relative humidity variability on children's allergic diseases and critical time window identification

BACKGROUND

The effects of temperature and relative humidity on different types of children's allergic diseases have not been comprehensively evaluated so far. This study aims to assess the impact of temperature and relative humidity variability on children's allergic diseases and to identify the critical time window.

METHODS

We collected outpatient data on allergen testing in children between July 2020 and January 2022 from the Affiliated Children's Hospital of Nanjing Medical University. We defined the 1st, 10th, 90th, and 99th percentiles as extreme cold, moderate cold, moderate hot, and extreme hot for temperature, and as low, moderate high, and extreme high for relative humidity, respectively. A distributed lag nonlinear model (DLNM) combined with a binomial regression model was used to assess the possible nonlinear relationship at different periods. Subgroup analysis by gender and age was conducted.

RESULTS

We found that extreme and moderate cold temperatures were positively associated with skin allergies and total allergies (28 days: OR = 4.69, 95% CI: 2.88, 7.63; OR = 3.36, 95% CI: 2.39, 4.73) and (28 days: OR = 3.76, CI: 2.43, 5.81; OR = 2.71, 95% CI: 2.00, 3.68), respectively. Moderate and extreme hot temperatures were negatively associated with food allergies (28 days: OR = 0.13, 95% CI: 0.04, 0.41 and OR = 0.04; 95% CI: 0.01, 0.27). Low relative humidity was negatively associated with respiratory allergies, skin allergies, and total allergic diseases (28 days: OR = 0.26, 95% CI: 0.10, 0.71; OR = 0.29, 95% CI: 0.15, 0.55; and OR = 0.42, 95% CI: 0.26, 0.68). Meanwhile, extreme high relative humidity was negatively associated with respiratory allergies, and positively associated with skin allergies, food allergies, and total allergies (28 days: OR = 0.16, 95%CI: 0.07, 0.37; OR = 3.60, 95% CI: 2.52, 5.14; OR = 15.61, 95% CI: 3.23, 75.56; and OR = 2.33, 95% CI: 1.73, 3.15). A stronger relationship between temperature, relative humidity, and allergic diseases was observed in children under 5 years, specifically girls.

CONCLUSIONS

Our study provides evidence that temperature and relative humidity variability may be associated with allergic diseases, however, the directionality of the relationship differs by allergic type.

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.

Elevated level of multibranched complex glycan reveals an allergic tolerance status

BACKGROUND

Allergen immunotherapy (AIT) is the only disease-modifying therapy that can achieve immune tolerance in patients through long-term allergen stimulation. Glycans play crucial roles in allergic disease, but no information on changes in glycosylation related to an allergic tolerance status has been reported.

METHODS

Fifty-seven patients with house dust mite (HDM) allergies were enrolled. Twenty-eight patients were not treated with AIT, 19 patients had just entered the AIT maintenance treatment phase, and 10 patients had been in the AIT maintenance phase for more than 1 year. Serum protein N-glycans were analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), which included linkage-specific sialylation information.

RESULTS

Eighty-four N-glycans were identified in all three groups. Compared with the patients treated without AIT, the patients treated with AIT for a shorter time showed downregulated expression of high-mannose glycans and upregulated expression of α2,6 sialic acid. The patients treated with AIT in the maintenance phase for over 1 year, which was considered the start of immunological tolerance, showed downregulated expression of biantennary N-glycans and upregulated expression of multibranched and complex N-glycans. Nine N-glycans were changed between allergic and allergic-tolerant patients.

CONCLUSIONS

The glycan form changed from mannose to a more complex type as treatment time increased, and multibranched complex glycans have the potential to be used as a monitoring indicator of immune tolerance. This serum N-glycome analysis provided important information for a deeper understanding of AIT treatment at the molecular level.

The Exploitation of the Glycosylation Pattern in Asthma: How We Alter Ancestral Pathways to Develop New Treatments

Asthma has reached epidemic levels, yet progress in developing specific therapies is slow. One of the main reasons for this is the fact that asthma is an umbrella term for various distinct subsets. Due to its high heterogeneity, it is difficult to establish biomarkers for each subset of asthma and to propose endotype-specific treatments. This review focuses on protein glycosylation as a process activated in asthma and ways to utilize it to develop novel biomarkers and treatments. We discuss known and relevant glycoproteins whose functions control disease development. The key role of glycoproteins in processes integral to asthma, such as inflammation, tissue remodeling, and repair, justifies our interest and research in the field of glycobiology. Altering the glycosylation states of proteins contributing to asthma can change the pathological processes that we previously failed to inhibit. Special emphasis is placed on chitotriosidase 1 (CHIT1), an enzyme capable of modifying LacNAc- and LacdiNAc-containing glycans. The expression and activity of CHIT1 are induced in human diseased lungs, and its pathological role has been demonstrated by both genetic and pharmacological approaches. We propose that studying the glycosylation pattern and enzymes involved in glycosylation in asthma can help in patient stratification and in developing personalized treatment.

LeGenD: determining N-glycoprofiles using an explainable AI-leveraged model with lectin profiling

Glycosylation affects many vital functions of organisms. Therefore, its surveillance is critical from basic science to biotechnology, including biopharmaceutical development and clinical diagnostics. However, conventional glycan structure analysis faces challenges with throughput and cost. Lectins offer an alternative approach for analyzing glycans, but they only provide glycan epitopes and not full glycan structure information. To overcome these limitations, we developed LeGenD, a lectin and AI-based approach to predict N-glycan structures and determine their relative abundance in purified proteins based on lectin-binding patterns. We trained the LeGenD model using 309 glycoprofiles from 10 recombinant proteins, produced in 30 glycoengineered CHO cell lines. Our approach accurately reconstructed experimentally-measured N-glycoprofiles of bovine Fetuin B and IgG from human sera. Explanatory AI analysis with SHapley Additive exPlanations (SHAP) helped identify the critical lectins for glycoprofile predictions. Our LeGenD approach thus presents an alternative approach for N-glycan analysis.

A novel IgE epitope-specific antibodies-based sandwich ELISA for sensitive measurement of immunoreactivity changes of peanut allergen Ara h 2 in processed foods

Background

Peanut is an important source of dietary protein for human beings, but it is also recognized as one of the eight major food allergens. Binding of IgE antibodies to specific epitopes in peanut allergens plays important roles in initiating peanut-allergic reactions, and Ara h 2 is widely considered as the most potent peanut allergen and the best predictor of peanut allergy. Therefore, Ara h 2 IgE epitopes can serve as useful biomarkers for prediction of IgE-binding variations of Ara h 2 and peanut in foods. This study aimed to develop and validate an IgE epitope-specific antibodies (IgE-EsAbs)-based sandwich ELISA (sELISA) for detection of Ara h 2 and measurement of Ara h 2 IgE-immunoreactivity changes in foods.

Methods

DEAE-Sepharose Fast Flow anion-exchange chromatography combining with SDS-PAGE gel extraction were applied to purify Ara h 2 from raw peanut. Hybridoma and epitope vaccine techniques were employed to generate a monoclonal antibody against a major IgE epitope of Ara h 2 and a polyclonal antibody against 12 IgE epitopes of Ara h 2, respectively. ELISA was carried out to evaluate the target binding and specificity of the generated IgE-EsAbs. Subsequently, IgE-EsAbs-based sELISA was developed to detect Ara h 2 and its allergenic residues in food samples. The IgE-binding capacity of Ara h 2 and peanut in foods was determined by competitive ELISA. The dose-effect relationship between the Ara h 2 IgE epitope content and Ara h 2 (or peanut) IgE-binding ability was further established to validate the reliability of the developed sELISA in measuring IgE-binding variations of Ara h 2 and peanut in foods.

Results

The obtained Ara h 2 had a purity of 94.44%. Antibody characterization revealed that the IgE-EsAbs recognized the target IgE epitope(s) of Ara h 2 and exhibited high specificity. Accordingly, an IgE-EsAbs-based sELISA using these antibodies was able to detect Ara h 2 and its allergenic residues in food samples, with high sensitivity (a limit of detection of 0.98 ng/mL), accuracy (a mean bias of 0.88%), precision (relative standard deviation < 16.50%), specificity, and recovery (an average recovery of 98.28%). Moreover, the developed sELISA could predict IgE-binding variations of Ara h 2 and peanut in foods, as verified by using sera IgE derived from peanut-allergic individuals.

Conclusion

This novel immunoassay could be a user-friendly method to monitor low level of Ara h 2 and to preliminary predict in vitro potential allergenicity of Ara h 2 and peanut in processed foods.

Atopy in chronic urticaria: an important yet overlooked issue

Chronic urticaria (CU) is one of the most common dermatological diseases and has a significant impact on the quality of life of patients. However, the pathogenesis of this disease remains unclear. Autoimmunity in chronic spontaneous urticaria (CSU) has received considerable attention and has been studied previously. Atopy is an important characteristic of CU; however, it has not been fully recognized. Atopy predisposes individuals to immune responses to allergens, leading to type 2 inflammation and immunoglobulin E (IgE) overproduction. Compared with healthy individuals, patients with CU have a higher proportion of atopy, and an atopic background is correlated with the clinical characteristics of CU. The total IgE levels in patients with CU is significantly higher than those in healthy individuals. Although its level is not higher than that in classic allergic diseases, it is closely related to CU. Exogenous allergens, auto-allergens, and specific IgEs, which are closely related to atopy, have been reported, and their roles in CU pathogenesis are also being studied. Local and systemic atopic inflammation is present in patients with CU. This review summarizes the current knowledge regarding atopy and CU, speculating that there are CU subtypes, such as atopic CSU or atopic chronic inducible urticaria (CIndU) and that atopy may be involved in the pathogenesis of CU. These findings provide a new perspective for a comprehensive understanding of the clinical features of CU and further research regarding its pathogenesis.

The role of glycosylation in clinical allergy and immunology

While glycans are among the most abundant macromolecules on the cell with widespread functions, their role in immunity has historically been challenging to study. This is in part due to difficulties assimilating glycan analysis into routine approaches used to interrogate immune cell function. Despite this, recent developments have illuminated fundamental roles for glycans in host immunity. The growing field of glycoimmunology continues to leverage new tools and approaches to uncover the function of glycans and glycan-binding proteins in immunity. Here we utilize clinical vignettes to examine key roles of glycosylation in allergy, inborn errors of immunity, and autoimmunity. We will discuss the diverse functions of glycans as epitopes, as modulators of antibody function, and as regulators of immune cell function. Finally, we will highlight immune modulatory therapies that harness the critical role of glycans in the immune system.

Insights into the Structure, Metabolism, Biological Functions and Molecular Mechanisms of Sialic Acid: A Review

Sialic acid (SA) is a kind of functional monosaccharide which exists widely in edible bird's nest (EBN), milk, meat, mucous membrane surface, etc. SA is an important functional component in promoting brain development, anti-oxidation, anti-inflammation, anti-virus, anti-tumor and immune regulation. The intestinal mucosa covers the microbial community that has a significant impact on health. In the gut, SA can also regulate gut microbiota and metabolites, participating in different biological functions. The structure, source and physiological functions of SA were reviewed in this paper. The biological functions of SA through regulating key signaling pathways and target genes were discussed. In summary, SA can modulate gut microbiota and metabolites, which affect gene expressions and exert its biological activities. It is helpful to provide scientific reference for the further investigation of SA in the functional foods.

The B Cell Response and Formation of Allergenic and Anti-Allergenic Antibodies in Food Allergy

Food allergies are a growing public health concern worldwide, especially in children and young adults. Allergen-specific IgE plays a central role in the pathogenesis of food allergies, but their titers poorly correlate with allergy development. Host immune systems yield allergen-specific immunoglobulin (Ig)A, IgE and IgG subclasses with low or high affinities and differential Fc N-glycosylation patterns that can affect the allergic reaction to food in multiple ways. High-affinity IgE is required to induce strong mast cell activation eventually leading to allergic anaphylaxis, while low-affinity IgE can even inhibit the development of clinically relevant allergic symptoms. IgA and IgG antibodies can inhibit IgE-mediated mast cell activation through various mechanisms, thereby protecting IgE-positive individuals from allergy development. The production of IgE and IgG with differential allergenic potential seems to be affected by the signaling strength of individual B cell receptors, and by cytokines from T cells. This review provides an overview of the diversity of the B cell response and the diverse roles of antibodies in food allergy.

Impact of ultra-low temperature storage on serum sIgE detection and allergic disease biobank feasibility

Research has shown that the concentration and composition of biological samples may change after long-term ultra-low temperature storage. Consequently, this study examined the effect of ultra-low temperature storage on serum sIgE detection by comparing sIgE concentrations at various durations from the time of sample storage to subsequent testing. We selected 40 serum samples from the Guangzhou Medical University Affiliated First Hospital Biobank, which had been tested for house dust mites, dog hair, tobacco mold, cockroaches, and cow milk allergen sIgE. Samples were categorized by storage duration: 14 samples stored for 10 years, 12 for 5 years, and 14 for 3 years. They were also classified by sIgE positive levels: 15 samples at levels 1-2, 15 at levels 3-4, and 10 at levels 5-6. The allergen sIgE of these samples was retested using the same technology. Regardless of the type of allergen or the level of positivity, the majority of sIgE concentrations measured at the time of storage were higher than the current measurements, but the difference was not statistically significant. The correlation between the sIgE results at the time of storage and the current results was high for samples stored for 10 years (rs = 0.991, P < 0.001) and 5 years (rs = 0.964, P < 0.001). Serum allergen sIgE is stable when stored under ultra-low temperature conditions, making the construction of a biological sample bank for allergic diseases feasible. This will facilitate researchers in quickly obtaining samples, conducting technical research, and translating findings, thereby promoting the development of the field of allergy through integration of industry, academia, and research.

An update on recent developments and highlights in food allergy

While both the incidence and general awareness of food allergies is increasing, the variety and clinical availability of therapeutics remain limited. Therefore, investigations into the potential factors contributing to the development of food allergy (FA) and the mechanisms of natural tolerance or induced desensitization are required. In addition, a detailed understanding of the pathophysiology of food allergies is needed to generate compelling, enduring, and safe treatment options. New findings regarding the contribution of barrier function, the effect of emollient interventions, mechanisms of allergen recognition, and the contributions of specific immune cell subsets through rodent models and human clinical studies provide novel insights. With the first approved treatment for peanut allergy, the clinical management of FA is evolving toward less intensive, alternative approaches involving fixed doses, lower maintenance dose targets, coadministration of biologicals, adjuvants, and tolerance-inducing formulations. The ultimate goal is to improve immunotherapy and develop precision-based medicine via risk phenotyping allowing optimal treatment for each food-allergic patient.

Limosilactobacillus reuteri in immunomodulation: molecular mechanisms and potential applications

Frequent use of hormones and drugs may be associated with side-effects. Recent studies have shown that probiotics have effects on the prevention and treatment of immune-related diseases. Limosilactobacillus reuteri (L. reuteri) had regulatory effects on intestinal microbiota, host epithelial cells, immune cells, cytokines, antibodies (Ab), toll-like receptors (TLRs), tryptophan (Try) metabolism, antioxidant enzymes, and expression of related genes, and exhibits antibacterial and anti-inflammatory effects, leading to alleviation of disease symptoms. Although the specific composition of the cell-free supernatant (CFS) of L. reuteri has not been clarified, its efficacy in animal models has drawn increased attention to its potential use. This review summarizes the effects of L. reuteri on intestinal flora and immune regulation, and discusses the feasibility of its application in atopic dermatitis (AD), asthma, necrotizing enterocolitis (NEC), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS), and provides insights for the prevention and treatment of immune-related diseases.

Heightened Proinflammatory Glycosylation of Borrelia burgdorferi IgG Antibodies in Synovial Fluid in Patients With Antibiotic-Refractory Lyme Arthritis

OBJECTIVE

Terminal glycans on the Fc portion of IgG antibodies are critical for antibody-triggered, proinflammatory or antiinflammatory responses. We undertook this study to compare glycan profiles of total IgG1 and Borrelia burgdorferi (Bb)-specific IgG1 antibodies in patients with oral antibiotic-responsive or antibiotic-refractory Lyme arthritis (LA).

METHODS

Following affinity-column processing, glycan profiles of IgG antibodies were determined in serum and synovial fluid (SF) samples of 21 LA patients using glycoblotting with hydrazide glycan enrichment and determination of glycan structure by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Correlations between glycan profiles and treatment outcomes were analyzed.

RESULTS

Compared with patients with antibiotic-refractory LA, those with antibiotic-responsive LA had total and Bb-specific IgG1 antibody glycans with less intense inflammatory profiles, containing lower percentages of N-acetylglucosamine (GlcNAc) and bisecting GlcNAc and higher percentages of galactose and fucose. In contrast, patients with antibiotic-refractory LA prior to receiving IV antibiotic therapy had total IgG1 and Bb IgG1 antibodies with maximal, minimally opposed, proinflammatory glycan profiles, containing high percentages of GlcNAc and bisecting GlcNAc, intermediate percentages with galactose and fucose, and low percentages with N-acetylneuraminic acid (sialic acid). Patients with refractory LA who were first seen with synovitis after receiving IV antibiotic therapy still had Bb IgG1 antibodies with strongly inflammatory glycan profiles, but their inflammatory potential appeared to be waning.

CONCLUSION

Patients with oral antibiotic-responsive LA had Bb IgG1 antibodies with more balanced proinflammatory/antiinflammatory glycan profiles, whereas patients with antibiotic-refractory LA had Bb IgG1 antibodies with maximal, minimally opposed, proinflammatory glycan profiles. Among patients with antibiotic-refractory LA, antibodies with this unbalanced inflammatory glycan profile may have a role in sustaining maladaptive joint inflammation.

Antibody-mediated regulation of basophils: emerging views and clinical implications

An increasing number of human diseases, including allergies, infections, inflammation, and cancer, involve roles for basophils. Traditionally viewed as the rarest leukocytes that are present only in the circulation, basophils have recently emerged as important players in systemic as well as tissue-specific immune responses. Their functions are regulated by immunoglobulins (Igs), and this enables basophils to integrate diverse adaptive and innate immunity signals. IgE is well known to regulate basophil responses in the context of type 2 immunity and allergic inflammation; however, growing evidence shows that IgG, IgA, and IgD also shape specific aspects of basophil functions relevant to many human diseases. We discuss recent mechanistic advances underpinning antibody-mediated basophil responses and propose strategies for the treatment of basophil-associated disorders.

Mechanism of glycoform specificity and in vivo protection by an anti-afucosylated IgG nanobody

Immunoglobulin G (IgG) antibodies contain a complex N-glycan embedded in the hydrophobic pocket between its heavy chain protomers. This glycan contributes to the structural organization of the Fc domain and determines its specificity for Fcγ receptors, thereby dictating distinct cellular responses. The variable construction of this glycan structure leads to highly-related, but non-equivalent glycoproteins known as glycoforms. We previously reported synthetic nanobodies that distinguish IgG glycoforms. Here, we present the structure of one such nanobody, X0, in complex with the Fc fragment of afucosylated IgG1. Upon binding, the elongated CDR3 loop of X0 undergoes a conformational shift to access the buried N-glycan and acts as a 'glycan sensor', forming hydrogen bonds with the afucosylated IgG N-glycan that would otherwise be sterically hindered by the presence of a core fucose residue. Based on this structure, we designed X0 fusion constructs that disrupt pathogenic afucosylated IgG1-FcγRIIIa interactions and rescue mice in a model of dengue virus infection.

Metabolism in type 2 immune responses

The immune response is tailored to the environment in which it takes place. Immune cells sense and adapt to changes in their surroundings, and it is now appreciated that in addition to cytokines made by stromal and epithelial cells, metabolic cues provide key adaptation signals. Changes in immune cell activation states are linked to changes in cellular metabolism that support function. Furthermore, metabolites themselves can signal between as well as within cells. Here, we discuss recent progress in our understanding of how metabolic regulation relates to type 2 immunity firstly by considering specifics of metabolism within type 2 immune cells and secondly by stressing how type 2 immune cells are integrated more broadly into the metabolism of the organism as a whole.

On the complexity of IgE: The role of structural flexibility and glycosylation for binding its receptors

It is well established that immunoglobulin E (IgE) plays a crucial role in atopy by binding to two types of Fcε receptors (FcεRI and FcεRII, also known as CD23). The cross-linking of FcεRI-bound IgE on effector cells, such as basophils and mast cells, initiates the allergic response. Conversely, the binding of IgE to CD23 modulates IgE serum levels and antigen presentation. In addition to binding to FcεRs, IgE can also interact with other receptors, such as certain galectins and, in mice, some FcγRs. The binding strength of IgE to its receptors is affected by its valency and glycosylation. While FcεRI shows reduced binding to IgE immune complexes (IgE-ICs), the binding to CD23 is enhanced. There is no evidence that galectins bind IgE-ICs. On the other hand, IgE glycosylation plays a crucial role in the binding to FcεRI and galectins, whereas the binding to CD23 seems to be independent of glycosylation. In this review, we will focus on receptors that bind to IgE and examine how the glycosylation and complexation of IgE impact their binding.

Clinical features and risk factors of IgE-independent aтopic dermatitis in children

Relevance. Atopic dermatitis (AD) is an inflammatory disease characterized by a chronic course with periods of remissions and exacerbations. IgE-independent atopic dermatitis is a medical and social problem of our time, since the disease manifests itself most often in childhood and is one of the most frequent forms of dermatoses among the pediatric population. The prevalence of atopic dermatitis among children is up to 20 %, among adults - 2-8 %. Recently, there has been a significant increase in atopic diseases worldwide. The aim: to study specific features of IgE-independent atopic dermatitis in children living in a metropolis. Materials and Methods. A prospective cohort study was conducted, which included 451 children aged 5 to 14 years with a diagnosis of AD who applied for outpatient care at the Moscow Scientific and Practical Center of Dermatovenereology and Cosmetology for the period 2020-2021. All parents (guardians) have given voluntary informed consent to the participation of children in the study and the publication of personal data. Examination of patients included general clinical methods, assessment of the SCORAD index and laboratory allergological examination (total and 73 specific IgE in blood serum with the most common food and aeroallergens). In 103 (22.8 %) children (57 (55.3 %) boys and 46 (44.7 %) girls), the results of the allergological analysis did not confirm concomitant allergic sensitization. Atopic dermatitis in these children was defined as IgE-independent. Results and Discussion. Predictors of the development of IgE-independent AD were hereditary predisposition [odds ratio (OR) 2.42; 95 % confidence interval (CI) 1.12-5.25], artificial feeding [OR 4.04; 95 % CI 1.46-11.20], comorbidities [OR 1.42; 95 % CI 0.57-3.52], late onset [OR 1.67; 95 % CI 0.81-3.41]. According to the SCORAD index, the majority of patients (75.7 %) had a moderate degree of AD and no seasonality. Features of skin rashes corresponded to the age periods of the course of AD: erythematous-squamous forms with lichenification foci prevailed. For the first time, the features of IgE-independent atopic dermatitis in children were shown. The role of risk factors for the development of IgE-independent atopic dermatitis in children has been shown for the first time. Conclusion. IgE-independent type of AD can be diagnosed in every fifth child with AD. The study of risk factors will allow predicting the development of this type of disease.

Targeting intracellular Neu1 for coronavirus infection treatment

There are currently no effective therapies for COVID-19 or antivirals against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and vaccines appear less effective against new SARS-CoV-2 variants; thus, there is an urgent need to understand better the virulence mechanisms of SARS-CoV-2 and the host response to develop therapeutic agents. Herein, we show that host Neu1 regulates coronavirus replication by controlling sialylation on coronavirus nucleocapsid protein. Coronavirus nucleocapsid proteins in COVID-19 patients and in coronavirus HCoV-OC43-infected cells were heavily sialylated; this sialylation controlled the RNA-binding activity and replication of coronavirus. Neu1 overexpression increased HCoV-OC43 replication, whereas Neu1 knockdown reduced HCoV-OC43 replication. Moreover, a newly developed Neu1 inhibitor, Neu5Ac2en-OAcOMe, selectively targeted intracellular sialidase, which dramatically reduced HCoV-OC43 and SARS-CoV-2 replication in vitro and rescued mice from HCoV-OC43 infection-induced death. Our findings suggest Neu1 inhibitors could be used to limit SARS-CoV-2 replication in patients with COVID-19, making Neu1 a potential therapeutic target for COVID-19 and future coronavirus pandemics.

The maternal prenatal and offspring early-life gut microbiome of childhood asthma phenotypes

BACKGROUND

The infant fecal microbiome is known to impact subsequent asthma risk, but the environmental exposures impacting this association, the role of the maternal microbiome, and how the microbiome impacts different childhood asthma phenotypes are unknown.

METHODS

Our objective was to identify associations between features of the prenatal and early-life fecal microbiomes and child asthma phenotypes. We analyzed fecal 16 s rRNA microbiome profiling and fecal metabolomic profiling from stool samples collected from mothers during the third trimester of pregnancy (n = 120) and offspring at ages 3-6 months (n = 265), 1 (n = 436) and 3 years (n = 506) in a total of 657 mother-child pairs participating in the Vitamin D Antenatal Asthma Reduction Trial. We used clinical data from birth to age 6 years to characterize subjects with asthma as having early, transient or active asthma phenotypes. In addition to identifying specific genera that were robustly associated with asthma phenotypes in multiple covariate-adjusted models, we clustered subjects by their longitudinal microbiome composition and sought associations between fecal metabolites and relevant microbiome and clinical features.

RESULTS

Seven maternal and two infant fecal microbial taxa were robustly associated with at least one asthma phenotype, and a longitudinal gut microenvironment profile was associated with early asthma (Fisher exact test p = .03). Though mode of delivery was not directly associated with asthma, we found substantial evidence for a pathway whereby cesarean section reduces fecal Bacteroides and microbial sphingolipids, increasing susceptibility to early asthma.

CONCLUSION

Overall, our results suggest that the early-life, including prenatal, fecal microbiome modifies risk of asthma, especially asthma with onset by age 3 years.

Mechanism of glycoform specificity and protection against antibody dependent enhancement by an anti-afucosylated IgG nanobody

Immunoglobulin G (IgG) antibodies contain a single, complex N -glycan on each IgG heavy chain protomer embedded in the hydrophobic pocket between its Cγ2 domains. The presence of this glycan contributes to the structural organization of the Fc domain and determines its specificity for Fcγ receptors, thereby determining distinct cellular responses. On the Fc, the variable construction of this glycan structure leads to a family of highly-related, but non-equivalent glycoproteins known as glycoforms. We previously reported the development of synthetic nanobodies that distinguish IgG glycoforms without cross-reactivity to off-target glycoproteins or free glycans. Here, we present the X-ray crystal structure of one such nanobody, X0, in complex with its specific binding partner, the Fc fragment of afucosylated IgG1. Two X0 nanobodies bind a single afucosylated Fc homodimer at the upper Cγ2 domain, making both protein-protein and protein-carbohydrate contacts and overlapping the binding site for Fcγ receptors. Upon binding, the elongated CDR3 loop of X0 undergoes a conformational shift to access the buried N -glycan and acts as a 'glycan sensor', forming hydrogen bonds with the afucosylated IgG N -glycan that would otherwise be sterically hindered by the presence of a core fucose residue. Based on this structure, we designed X0 fusion constructs that disrupt pathogenic afucosylated IgG1-FcγRIIIa interactions and rescue mice in a model of dengue virus infection.

Immune sensing of food allergens promotes aversive behaviour

In addition to its canonical function in protecting from pathogens, the immune system can also promote behavioural alterations ^1â€"3 . The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Using a mouse food allergy model, here we show that allergic sensitization drives antigen-specific behavioural aversion. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus, and central amygdala. Food aversion requires IgE antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote aversion requires leukotrienes and growth and differentiation factor 15 (GDF15). In addition to allergen-induced aversion, we find that lipopolysaccharide-induced inflammation also resulted in IgE-dependent aversive behaviour. These findings thus point to antigen-specific behavioural modifications that likely evolved to promote niche selection to avoid unfavourable environments.

IgE glycans promote anti-IgE IgG autoantibodies that facilitate IgE serum clearance via Fc Receptors

Background

Recent studies have shown that IgE glycosylation significantly impacts the ability of IgE to bind to its high-affinity receptor FcεRI and exert effector functions. We have recently demonstrated that immunizing mice with IgE in a complex with an allergen leads to a protective, glycan-dependent anti-IgE response. However, to what extent the glycans on IgE determine the induction of those antibodies and how they facilitate serum clearance is unclear.Therefore, we investigated the role of glycan-specific anti-IgE IgG autoantibodies in regulating serum IgE levels and preventing systemic anaphylaxis by passive immunization.

Methods

Mice were immunized using glycosylated or deglycosylated IgE-allergen-immune complexes (ICs) to induce anti-IgE IgG antibodies. The anti-IgE IgG antibodies were purified and used for passive immunization.

Results

Glycosylated IgE-ICs induced a significantly higher anti-IgE IgG response and more IgG-secreting plasma cells than deglycosylated IgE-ICs. Passive immunization of IgE-sensitized mice with purified anti-IgE IgG increased the clearance of IgE and prevented systemic anaphylaxis upon allergen challenge. Anti-IgE IgG purified from the serum of mice immunized with deglycosylated IgE-ICs, led to a significantly reduced elimination and protection, confirming that the IgE glycans themselves are the primary drivers of the protectivity induced by the IgE-immune complexes.

Conclusion

IgE glycosylation is essential for a robust anti-IgE IgG response and might be an important regulator of serum IgE levels.

Cell surface expression of human RP105 depends on N-glycosylation of MD-1

For its cell surface expression, radioprotective 105 (RP105) - an orphan Toll-like receptor - must form a complex with a soluble glycoprotein called myeloid differentiation 1 (MD-1). The number of RP105-negative cells is significantly increased in patients with systemic lupus erythematosus (SLE); however, to elucidate the mechanism underlying this increase, how RP105 is expressed on the cell surface depending on MD-1 should be investigated. We demonstrated that RP105 exhibits two forms depending on MD-1 and its two N-glycosylation sites, N96 and N156. Cell surface expression of RP105 decreased in the presence of mutant MD-1 (N96Q/N156Q). Nonglycosylated MD-1 decreased the de novo cell surface expression of RP105 but not pre-expressed RP105. Thus, the N-glycans of MD-1 may represent targets for SLE therapy.

An update on anaphylaxis and urticaria

Notable scientific developments have taken place in the field of anaphylaxis and urticaria in recent years; they are highlighted in this review. Case-control studies, genome-wide association studies, and large omics analyses have promoted further insights into not only the underlying genetics but also the biomarkers of both anaphylaxis and urticaria. New evidence regarding IgE-dependent and non-IgE-dependent mechanisms of anaphylaxis and urticaria, including the Mas-related G protein-coupled receptor (MRGPR [formerly MRG]) signaling pathway, has been gained. Putative elicitors of anaphylactic reactions in the context of coronavirus disease 2019 (COVID-19) vaccination and impact of the COVID-19 pandemic on the management and course of chronic urticaria have been reported. Clinical progress has also been made regarding the severity grading and risk factors of anaphylaxis, as well as the distinction of phenotypes and elicitors of both diseases. Furthermore, novel treatment approaches for anaphylaxis and subtypes of urticaria have been assessed, with different outcome and potential for a better disease control or prevention.

Sialic acid and food allergies: The link between nutrition and immunology

Food allergies (FA), a major public health problem recognized by the World Health Organization, affect an estimated 3%-10% of adults and 8% of children worldwide. However, effective treatments for FA are still lacking. Recent advances in glycoimmunology have demonstrated the great potential of sialic acids (SAs) in the treatment of FA. SAs are a group of nine-carbon α-ketoacids usually linked to glycoproteins and glycolipids as terminal glycans. They play an essential role in modulating immune responses and may be an effective target for FA intervention. As exogenous food components, sialylated polysaccharides have anti-FA effects. In contrast, as endogenous components, SAs on immunoglobulin E and immune cell surfaces contribute to the pathogenesis of FA. Given the lack of comprehensive information on the effects of SAs on FA, we reviewed the roles of endogenous and exogenous SAs in the pathogenesis and treatment of FA. In addition, we considered the structure-function relationship of SAs to provide a theoretical basis for the development of SA-based FA treatments.

Generation and Characterization of Native and Sialic Acid-Deficient IgE

Efficient characterization of IgE antibodies and their glycan structures is required for understanding their function in allergy and in the emerging AllergoOncology field for antibody immunotherapy. We report the generation, glyco-profiling and functional analysis of native and sialic acid-deficient glyco-engineered human IgE. The antibodies produced from human embryonic kidney cells were purified via a human IgE class-specific affinity matrix and structural integrity was confirmed by SDS-PAGE and size-exclusion chromatography (SEC). Purified IgEs specific for the tumor-associated antigens Chondroitin Sulfate Proteoglycan 4 (CSPG4-IgE) and Human Epidermal Growth Factor Receptor 2 (HER2-IgE) were devoid of by-products such as free light chains. Using neuraminidase-A, we generated sialic acid-deficient CSPG4-IgE as example glyco-engineered antibody. Comparative glycan analyses of native and glyco-engineered IgEs by Hydrophilic interaction liquid chromatography (HILIC)-high performance liquid chromatography (HPLC) indicated loss of sialic acid terminal residues and differential glycan profiles. Native and glyco-engineered CSPG4-IgEs recognized Fc receptors on the surface of human FcεRI-expressing rat basophilic leukemia RBL-SX38 cells, and of CD23/FcεRII-expressing human RPMI-8866 B-lymphocytes and bound to CSPG4-expressing A2058 human melanoma cells, confirming Fab-mediated recognition. When cross-linked on the cell surface, both IgEs triggered RBL-SX38 degranulation. We demonstrate efficient generation and functional competence of recombinant native and sialic acid-deficient IgEs.

Novel peanut-specific human IgE monoclonal antibodies enable screens for inhibitors of the effector phase in food allergy

Background

10% of US residents have food allergies, including 2% with peanut allergy. Mast cell mediators released during the allergy effector phase drive allergic reactions. Therefore, targeting sensitized mast cells may prevent food allergy symptoms.

Objective

We used novel, human, allergen-specific, IgE monoclonal antibodies (mAbs) created using human hybridoma techniques to design an in vitro system to evaluate potential therapeutics targeting sensitized effector cells.

Methods

Two human IgE mAbs specific for peanut, generated through human hybridoma techniques, were used to sensitize rat basophilic leukemia (RBL) SX-38 cells expressing the human IgE receptor (FcϵRI). Beta-hexosaminidase release (a marker of degranulation), cytokine production, and phosphorylation of signal transduction proteins downstream of FcϵRI were measured after stimulation with peanut. Degranulation was also measured after engaging inhibitory receptors CD300a and Siglec-8.

Results

Peanut-specific human IgE mAbs bound FcϵRI, triggering degranulation after stimulation with peanut in RBL SX-38 cells. Sensitized RBL SX-38 cells stimulated with peanut increased levels of phosphorylated SYK and ERK, signal transduction proteins downstream of FcϵRI. Engaging inhibitory cell surface receptors CD300a or Siglec-8 blunted peanut-specific activation.

Conclusion

Allergen-specific human IgE mAbs, expressed from human hybridomas and specific for a clinically relevant food allergen, passively sensitize allergy effector cells central to the in vitro models of the effector phase of food allergy. Peanut reproducibly activates and induces degranulation of RBL SX-38 cells sensitized with peanut-specific human IgE mAbs. This system provides a unique screening tool to assess the efficacy of therapeutics that target allergy effector cells and inhibit food allergen-induced effector cell activation.

Characteristics and Roles of T Follicular Helper Cells in SARS-CoV-2 Vaccine Response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is critical to controlling the coronavirus disease 2019 (COVID-19) pandemic. However, a weak response to the vaccine and insufficient persistence of specific antibodies may threaten the global impact of mass vaccination campaigns. This study summarizes the internal factors of the body that affect the effectiveness of the SARS-CoV-2 vaccine. T follicular helper (Tfh) cells support germinal center B cells to produce vaccine-specific immunoglobulins. A reduction in the Tfh cell number and a shift in the subset phenotypes caused by multiple factors may impair the production and persistence of high-affinity antibodies. Besides efficacy differences caused by the different types of vaccines, the factors that affect vaccine effectiveness by intervening in the Tfh cell response also include age-related defects, the polarity of the body microenvironment, repeated immunization, immunodeficiency, and immunosuppressive treatments. Assessing the phenotypic distribution and activation levels of Tfh cell subsets after vaccination is helpful in predicting vaccine responses and may identify potential targets for improving vaccine effectiveness.

Induction of natural IgE by glucocorticoids

IgE mediates allergic responses by coating mast cell or basophil surfaces and inducing degranulation upon binding a specific allergen. IgE can also be spontaneously produced in the absence of foreign allergens; yet the origin, regulation, and functions of such "natural" IgE still remain largely unknown. Here, we find that glucocorticoids enhance the production of IgE in B cells both in vivo and ex vivo without antigenic challenge. Such IgE production is promoted by B cell-intrinsic glucocorticoid receptor signaling that reinforces CD40 signaling and synergizes with the IL-4/STAT6 pathway. In addition, we found that rare B cells in the mesenteric lymph nodes are responsible for the production of glucocorticoid-inducible IgE. Furthermore, locally produced glucocorticoids in the gut may induce natural IgE during perturbations of gut homeostasis, such as dysbiosis. Notably, mice preemptively treated with glucocorticoids were protected from subsequent pathogenic anaphylaxis. Together, our results suggest that glucocorticoids, classically considered to be broadly immunosuppressive, have a selective immunostimulatory role in B cells.

Impact of the mucosal milieu on antibody responses to allergens

Respiratory and digestive mucosal surfaces are continually exposed to common environmental antigens, which include potential allergens. Although innocuous in healthy individuals, allergens cause allergy in predisposed subjects and do so by triggering a pathologic T_H2 cell response that induces IgE class switching and somatic hypermutation in allergen-specific B cells. The ensuing affinity maturation and plasma cell differentiation lead to the abnormal release of high-affinity IgE that binds to powerful FcεRI receptors on basophils and mast cells. When cross-linked by allergen, FcεRI-bound IgE instigates the release of prestored and de novo-induced proinflammatory mediators. Aside from causing type I hypersensitivity reactions underlying allergy, IgE affords protection against nematodes or venoms from insects and snakes, which raises questions as to the fundamental differences between protective and pathogenic IgE responses. In this review, we discuss the impact of the mucosal environment, including the epithelial and mucus barriers, on the induction of protective IgE responses against environmental antigens. We further discuss how perturbations of these barriers may contribute to the induction of pathogenic IgE production.

Risk factors and postnatal biomarkers for acute placental inflammatory lesions and intrauterine infections in preterm infants

The purpose of this study is to explore risk factors of acute placental inflammatory lesions and the potential postnatal serum biomarkers for predicting the severity of intrauterine infection in preterm infants. We performed a retrospective analysis of premature infants with or without acute placental inflammatory lesions and their mothers by chart review for clinical data and placental histopathology. The preterm infants with acute placental inflammatory lesions had a higher rate of premature rupture of membranes (PROM), a longer duration of PROM, and a higher level of serum sialic acid (SIA) than those of the non-inflammation group (all p < 0.001). According to the different inflammatory histological structures, preterm infants with funisitis had a dominant longer duration of PROM than others (p < 0.05), and their gestational age was youngest among all the infants (p < 0.05). Furthermore, they had the highest content of serum SIA above other groups. The preterm infants in the acute histological chorioamnionitis group showed a similar trend of clinical manifestation and laboratory parameters with the funisitis group. Moreover, the closer the placental lesions were to the fetus, the lower the gestational age of preterm infants was, and the higher the serum SIA content was.

CONCLUSION

We utilized a simple and precise anatomically category method of placental inflammatory histopathology for pediatricians to distinguish the extent of fetal inflammatory response for representing early-onset infectious diseases of preterm infants. SIA might be one of the potential early-stage serum biomarkers to reflect the severe intrauterine infections and could guide the postnatal anti-infection treatment.

WHAT IS KNOWN

• Acute placental inflammatory lesion contributes to preterm birth and a series of complications in preterm infants. • C-reactive protein and interleukin-6 in neonatal blood can be used as biomarkers for potential early-onset sepsis, but they are influenced by the postnatal physiological changes of preterm infants.

WHAT IS NEW

• The value of serum sialic acids of preterm infants within 1-hour afterbirth may be one of the rapid postnatal biomarkers for evaluating the severity of intra-amniotic infection. • The closer the placental lesions are to the fetus, the higher the content of serum sialic acid is.

Post-Translational Modifications in Atopic Dermatitis: Current Research and Clinical Relevance

Atopic dermatitis (AD) is a chronic and relapsing cutaneous disorder characterized by compromised immune system, excessive inflammation, and skin barrier disruption. Post-translational modifications (PTMs) are covalent and enzymatic modifications of proteins after their translation, which have been reported to play roles in inflammatory and allergic diseases. However, less attention has been paid to the effect of PTMs on AD. This review summarized the knowledge of six major classes (including phosphorylation, acetylation, ubiquitination, SUMOylation, glycosylation, o-glycosylation, and glycation) of PTMs in AD pathogenesis and discussed the opportunities for disease management.

Blocking the inhibitory receptor programmed cell death 1 prevents allergic immune response and anaphylaxis in mice

BACKGROUND

Food allergy and acute anaphylaxis can be life-threatening. While T follicular helper (Tfh) cells play a pivotal role in the allergic immune responses, the immunologic mechanisms that regulate the production of antibodies (Abs) that mediate anaphylaxis are not fully understood.

OBJECTIVE

The aim of this study was to investigate the role of the inhibitory receptor programmed cell death protein 1 (PD-1), which is highly expressed on Tfh cells, in allergic immune responses using an animal model of peanut allergy and anaphylaxis.

METHODS

Naive wild-type mice were exposed to peanut flour intranasally and then challenged with peanut extract to induce systemic anaphylaxis. The roles of PD-1 were examined by blocking Abs and using gene-deficient animals. A hapten model and passive cutaneous anaphylaxis were used to characterize allergen-specific Abs.

RESULTS

Treatment with anti-PD-1 enhanced development of Tfh cells and germinal center B cells in mice exposed to peanut flour. Nonetheless, anti-PD-1 or its ligand fully protected mice from developing anaphylaxis. Anti-PD-1 treatment or genetic deficiency of PD-1 in CD4⁺ T cells inhibited production of peanut-specific IgE and increased the levels of IgG. The passive cutaneous anaphylaxis showed that peanut-specific Abs generated in anti-PD-1-treated animals prevented, rather than provoked, anaphylaxis when transferred to naive animals. Anti-PD-1 promoted production of Abs with low affinity for an antigen in the hapten model.

CONCLUSION

Blockade of the pathway between PD-1 and its ligand is protective against allergic immune responses. The direct interaction between Tfh cells and B cells may play a pivotal role in controlling Ab quality and clinical manifestation of allergic diseases.

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.

Immunoglobulin E response in health and disease beyond allergic disorders

Immunoglobulin E is the latest discovered of immunoglobulin family and has been long associated with anaphylaxis and worm expulsion. Immunoglobulin E, along with mast cells, basophils, and eosinophils, is also a hallmark of type 2 immunity which is dysregulated in numerous diseases such as asthma, rhinitis, atopic dermatitis, and eosinophilic esophagitis in addition to anaphylaxis as aforementioned. However, recent advances have shed light on IgE regulation and memory explaining the low level of free IgE, the scarcity of IgE plasma cells that are mainly short live and the absence of IgE memory B cells in homeostatic conditions. Furthermore, IgE was implicated in inflammatory conditions beyond allergic disorders where IgE-mediated facilitated antigen presentation can enhance cellular and humoral response against autoantigens in systemic lupus or chronic urticaria leading to more severe disease and even against neoantigen facilitating tumor cell lysis. At last, IgE was unexpectedly associated with allograft rejection or atheromatous cardiovascular diseases where precise mechanisms remain to be deciphered. The purpose of this review is to summarize these recent advances in IgE regulation, biology, and physiopathology beyond allergic diseases opening whole new fields of IgE biology to explore.

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.

The Effector Function of Allergens

Allergens are antigens that generate an IgE response (sensitization) in susceptible individuals. The allergenicity of an allergen can be thought of in terms of its ability to sensitize as well as its ability to cross-link IgE/IgE receptor complexes on mast cells and basophils leading to release of preformed and newly formed mediators (effector activity). The identity of the allergens responsible for sensitization may be different from those that elicit an allergic response. Effector activity is determined by (1) the amount of specific IgE (sIgE) and in some circumstances the ratio of sIgE to total IgE, (2) the number of high affinity receptors for IgE (FcεR1) on the cell surface, (3) the affinity of binding of sIgE for its epitope and, in a polyclonal response, the collective avidity, (4) the number and spatial relationships of IgE binding epitopes on the allergen and (5) the presence of IgG that can bind to allergen and either block binding of sIgE and/or activate low affinity IgG receptors that activate intracellular inhibitory pathways. This review will discuss these important immunologic and physical properties that contribute to the effector activity of allergens.