Tolerant beekeepers display venom-specific functional IgG4 antibodies in the absence of specific IgE

Exploring the depths of IgG4: insights into autoimmunity and novel treatments

IgG4 subclass antibodies represent the rarest subclass of IgG antibodies, comprising only 3-5% of antibodies circulating in the bloodstream. These antibodies possess unique structural features, notably their ability to undergo a process known as fragment-antigen binding (Fab)-arm exchange, wherein they exchange half-molecules with other IgG4 antibodies. Functionally, IgG4 antibodies primarily block and exert immunomodulatory effects, particularly in the context of IgE isotype-mediated hypersensitivity reactions. In the context of disease, IgG4 antibodies are prominently observed in various autoimmune diseases combined under the term IgG4 autoimmune diseases (IgG4-AID). These diseases include myasthenia gravis (MG) with autoantibodies against muscle-specific tyrosine kinase (MuSK), nodo-paranodopathies with autoantibodies against paranodal and nodal proteins, pemphigus vulgaris and foliaceus with antibodies against desmoglein and encephalitis with antibodies against LGI1/CASPR2. Additionally, IgG4 antibodies are a prominent feature in the rare entity of IgG4 related disease (IgG4-RD). Intriguingly, both IgG4-AID and IgG4-RD demonstrate a remarkable responsiveness to anti-CD20-mediated B cell depletion therapy (BCDT), suggesting shared underlying immunopathologies. This review aims to provide a comprehensive exploration of B cells, antibody subclasses, and their general properties before examining the distinctive characteristics of IgG4 subclass antibodies in the context of health, IgG4-AID and IgG4-RD. Furthermore, we will examine potential therapeutic strategies for these conditions, with a special focus on leveraging insights gained from anti-CD20-mediated BCDT. Through this analysis, we aim to enhance our understanding of the pathogenesis of IgG4-mediated diseases and identify promising possibilities for targeted therapeutic intervention.

Immunoglobulin G4 in eosinophilic esophagitis: Immune complex formation and correlation with disease activity

BACKGROUND

Recent studies have shown deposition of immunoglobulin G4 (IgG4) and food proteins in the esophageal mucosa of eosinophilic esophagitis (EoE) patients. Our aims were to assess whether co-localization of IgG4 and major cow's milk proteins (CMPs) was associated with EoE disease activity and to investigate the proteins enriched in proximity to IgG4 deposits.

METHODS

This study included adult subjects with EoE (n = 13) and non-EoE controls (n = 5). Esophageal biopsies were immunofluorescence stained for IgG4 and CMPs. Co-localization in paired samples from active disease and remission was assessed and compared to controls. The proteome surrounding IgG4 deposits was evaluated by the novel technique, AutoSTOMP. IgG4-food protein interactions were confirmed with co-immunoprecipitation and mass spectrometry.

RESULTS

IgG4-CMP co-localization was higher in the active EoE group compared to paired remission samples (Bos d 4, p = .02; Bos d 5, p = .002; Bos d 8, p = .002). Co-localization was also significantly higher in the active EoE group compared to non-EoE controls (Bos d 4, p = .0013; Bos d 5, p = .0007; Bos d 8, p = .0013). AutoSTOMP identified eosinophil-derived proteins (PRG 2 and 3, EPX, RNASE3) and calpain-14 in IgG4-enriched areas. Co-immunoprecipitation and mass spectrometry confirmed IgG4 binding to multiple food allergens.

CONCLUSION

These findings further contribute to the understanding of the interaction of IgG4 with food antigens as it relates to EoE disease activity. These data strongly suggest the immune complex formation of IgG4 and major cow's milk proteins. These immune complexes may have a potential role in the pathophysiology of EoE by contributing to eosinophil activation and disease progression.

Updates and Recent Advances on Venom Immunotherapy

Purpose of Review

Venom immunotherapy has been utilized to treat Hymenoptera venom allergy since the 1920s. Over the last century, significant advances in the fields of immunology and genetics have led to improvements in the practice of venom immunotherapy. This review encompasses recent advances in the use of venom immunotherapy to provide precise, patient-centered care.

Recent Findings

Research about the mechanism of action of venom immunotherapy continues to highlight the modification of both the innate and adaptive immune systems. Molecular techniques have allowed for the identification of specific venom allergens to improve the diagnostic accuracy and safety of venom immunotherapy. Research continues to support the safety of accelerated schedules which can impact the cost, adherence, and quality of life for patients receiving this treatment modality. Finally, significant advances have led to the elucidation of risk factors that place patients at risk for reactions during and after venom immunotherapy. Creation of risk profiles for venom-allergic patients can thus inform the process of immunotherapy in order to provide personalized and precise care.

Summary

Significant progress in the use of venom immunotherapy makes the practice a dynamic and active field for continued research. Future research needs to build on these recent advances to continue to optimize and enhance this life-saving treatment.

Food antigen consumption and disease activity affect food-specific IgG4 levels in patients with eosinophilic esophagitis (EoE)

INTRODUCTION

High levels of serum food-specific IgG4 (sIgG4) have been reported in patients with EoE. The objective of this study was to examine whether serum sIgG4 levels to foods and aeroallergens are higher in EoE patients than allergic controls and to investigate the association between sIgG4 and EoE clinical characteristics.

METHODS

This was a case-control study nested in a prospective EoE Cohort. EoE cases were defined per consensus guidelines, and controls were individuals with symptoms who were confirmed to be EoE-negative on upper endoscopy. Demographic and clinical information was prospectively collected. Serum IgE and sIgG4 were measured to foods and aeroallergens by ImmunoCAP. Mean levels of sIgG4 were compared between cases and controls, and logistic regression models were used to examine predictors of elevated milk sIgG4 levels.

RESULTS

The analysis included 123 individuals (EoE n = 93, control n = 30) with a similar distribution of allergic disease between EoE patients and controls (86% vs. 93%; p = .30). EoE patients had significantly higher sIgG4 levels to all allergens evaluated, with the exception of birch (p = .24). Milk sIgG4 levels were independently associated with milk consumption (OR 4.95; p = .01) and the presence of sIgE to milk (OR 4.23; p = .008).

CONCLUSION

Serum sIgG4 levels to food and aeroallergen proteins were higher in patients with EoE than non-EoE controls, and higher levels of milk sIgG4 were independently associated with milk consumption and the presence of sIgE to milk proteins. Whether sIgG4 plays a pathogenic role in EoE or could be used as an EoE biomarker remains unknown and warrants further study.

Reported Cases and Diagnostics of Occupational Insect Allergy: A Systematic Review

A significant part of adult-onset asthma is caused by occupational exposure to both high- and low-molecular-mass agents. Insects are occasionally described to cause occupational allergy in professions including anglers and fishers, laboratory workers, employees of aquaculture companies, farmers, bakers, sericulture workers and pet shop workers. Occupational insect allergies are often respiratory, causing asthma or rhinoconjunctivitis, but can be cutaneous as well. The European Union recently approved three insect species for human consumption, enabling an industry to develop where more employees could be exposed to insect products. This review overviews knowledge on occupational insect allergy risks and the tools used to diagnose employees. Despite the limited availability of commercial occupational insect allergy diagnostics, 60.9% of 164 included reports used skin prick tests and 63.4% of reports used specific IgE tests. In 21.9% of reports, a more elaborate diagnosis of occupational asthma was made by specific inhalation challenges or peak expiratory flow measurements at the workplace. In some work environments, 57% of employees were sensitized, and no less than 60% of employees reported work-related symptoms. Further development and optimization of specific diagnostics, together with strong primary prevention, may be vital to the health conditions of workers in the developing insect industry.

Allergen immunotherapy: past, present and future

Allergen immunotherapy is a form of therapeutic vaccination for established IgE-mediated hypersensitivity to common allergen sources such as pollens, house dust mites and the venom of stinging insects. The classical protocol, introduced in 1911, involves repeated subcutaneous injection of increasing amounts of allergen extract, followed by maintenance injections over a period of 3 years, achieving a form of allergen-specific tolerance that provides clinical benefit for years after its discontinuation. More recently, administration through the sublingual route has emerged as an effective, safe alternative. Oral immunotherapy for peanut allergy induces effective ‘desensitization’ but not long-term tolerance. Research and clinical trials over the past few decades have elucidated the mechanisms underlying immunotherapy-induced tolerance, involving a reduction of allergen-specific T helper 2 (T_H2) cells, an induction of regulatory T and B cells, and production of IgG and IgA ‘blocking’ antibodies. To better harness these mechanisms, novel strategies are being explored to achieve safer, effective, more convenient regimens and more durable long-term tolerance; these include alternative routes for current immunotherapy approaches, novel adjuvants, use of recombinant allergens (including hypoallergenic variants) and combination of allergens with immune modifiers or monoclonal antibodies targeting the T_H2 cell pathway.

Durham and Shamji review the history and future of allergen immunotherapy for established IgE-mediated hypersensitivity to common allergens. They describe the mechanisms of immunotherapy-induced tolerance and the new strategies being explored to achieve safer, more effective, long-term tolerance.

On the role of allergen-specific IgG subclasses for blocking human basophil activation

Successful treatment of IgE mediated allergies by allergen-specific immunotherapy (AIT) usually correlates with the induction of allergen-specific IgG4. However, it is not clear whether IgG4 prevents the allergic reaction more efficiently than other IgG subclasses. Here we aimed to compare allergen-specific monoclonal IgG1 and IgG4 antibodies in their capacity to inhibit type I allergic reactions by engaging FcγRIIb. We found that IgG1, which is the dominant subclass induced by viruses, binds with a similar affinity to the FcγRIIb as IgG4 and is comparable at blocking human basophil activation from allergic patients; both by neutralizing the allergen as well as engaging the inhibitory receptor FcγRIIb. Hence, the IgG subclass plays a limited role for the protective efficacy of AIT even if IgG4 is considered the best correlate of protection, most likely simply because it is the dominant subclass induced by classical AITs.

Natural and Induced Tolerance to Hymenoptera Venom: A Single Mechanism?

Inducing tolerance in Hymenoptera-allergic patients, bee venom immunotherapy (BVIT) is a widely accepted method to treat severe allergy to bee stings. In order to increase the existing knowledge on the underlying immunological mechanisms and look for possible biomarkers predictive of efficacy, a group of 20 bee-venom-allergic patients (AG) were thoroughly examined during their first year of BVIT. In addition, the results of treated patients with those of an untreated group of 20 tolerant beekeepers (TG) who had previously shown a firm suppressor-regulatory profile were compared. Tolerance in AG patients was invariably associated with a significant regulatory response characterised by the expansion of Helios− subpopulation and increased IL-10, specific IgG4 (sIgG4), and kynurenine levels. Although specific IgE (sIgE) levels increased transiently, surprisingly, the T helper type 2 (Th2) population and IL-4 levels rose significantly after one year of immunotherapy. Thus, the picture of two parallel phenomena emerges: a tolerogenic response and an allergenic one. Comparing these results with those obtained from the TG, different immunological mechanisms appear to govern natural and acquired tolerance to immunotherapy. Of particular interest, the kynurenine levels and T regulatory (Treg) Helios− population could be proposed as new biomarkers of response to BVIT.

Tumor-B-cell interactions promote isotype switching to an immunosuppressive IgG4 antibody response through upregulation of IL-10 in triple negative breast cancers

Background

Triple negative breast cancer (TNBC) is an aggressive breast cancer for which there is currently no targeted therapy. Tumor-infiltrating B-cells (TIB) have been observed in tumor tissues of TNBC patients, but their functional role is unclear. IgG4 is one of four antibody subclasses of IgG expressed and secreted by B cells. Unlike other IgG isotypes, IgG4 has an immunosuppressive function and is induced by Th2-type cytokines. In cancers such as melanoma, IgG4 has been linked with advanced disease and poor patient survival. Therefore, we sought to determine if IgG4 + B cells are present and determine the mechanisms driving isotype switching in TNBC.

Methods

We performed co-culture assays to examine expression of Th2 cytokines by TNBC cells with and without the presence of B cells. We also performed in vitro class switching experiments with peripheral B cells with and without co-culture with TNBC cells in the presence or absence of an IL-10 blocking antibody. We examined expression of CD20+ TIB, IgG4 and Th2 cytokines by immunohistochemistry in 152 TNBC samples. Statistical analysis was done using Log-Rank and Cox-proportional hazards tests.

Results

Our findings indicate that B cells interact with TNBC to drive chronic inflammatory responses through increased expression of inflammatory cytokines including the TH2 cytokines IL-4 and IL-10. In vitro class switching studies show that interactions between TNBC cell lines and B cells drive isotype switching to the IgG4 isotype in an IL-10 dependent manner. In patient tissues, expression of IgG4 correlates with CD20 and tumor expression of IL-10. Both IgG4 and tumor IL-10 are associated to shorter recurrence free survival (RFS) and overall survival (OS) in TNBC. In a multi-variant analysis, IL-10 was associated with poor outcomes indicating that tumor IL-10 may drive immune escape.

Conclusions

These findings indicate that interactions between TIB and TNBC results in activation of chronic inflammatory signals such as IL-10 and IL-4 that drive class switching to an IgG4 + subtype which may suppress antibody driven immune responses. The presence of IgG4 + B cells may serve as a biomarker for poor prognosis.

Demographic patterns of human antibody levels to Simulium damnosum s.l. saliva in onchocerciasis-endemic areas: An indicator of exposure to vector bites

BACKGROUND

In onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure.

METHODOLOGY/PRINCIPAL FINDINGS

Recently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses.

CONCLUSIONS/SIGNIFICANCE

The decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.

Eosinophilic Esophagitis and IgG4: Is There a Relationship?

Our knowledge of the pathophysiology of eosinophilic esophagitis is constantly evolving. There is significant association between eosinophilic esophagitis and atopy; however, multiple studies have refuted the role of IgE in its pathogenesis. Instead, new data have demonstrated an elevated IgG4 level in patients with eosinophilic esophagitis. We review the current understanding of eosinophilic esophagitis pathogenesis and highlight the increasing evidence for the role of IgG4.

Significance of high serum IgG4 in complete or non-full-fledged IgG4-related disease-a retrospective investigation of 845 patients and its clinical relevance

OBJECTIVE

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized heterogeneous, subacute, and usually silent autoimmune disease involving many organs with protean manifestations. However, high IgG4 in serum is not necessarily indicating an IgG4-RD. The aims of this study were to investigate the clinical relevance of high serum IgG4 level in IgG4-RD or non IgG4-RD patients, and to see if IgG4-RD in Taiwan differs from that in other parts of the world.

METHODS

Eight hundred forty-five patients with high IgG4 were retrospectively reviewed from January 2002 to May 2020 in Taipei Veteran General Hospital. Two hundred sixty-seven patients fulfilled IgG4-RD criteria and were categorized into pancreato-hepato-biliary disease, retroperitoneal fibrosis and/or aortitis, head/neck-limited disease, classic Mikulicz syndrome with systemic involvement, CNS-limited disease, sclerosing vasculitis, skin-limited disease, and sensorineural hearing disease. These manifestations were correlated to smoking, atopy, hyper-IgE/eosinophilia, aging, malignancies, and hypocomplementemia. Five hundred seventy-eight patients were not fulfilling the criteria but were also analyzed for the prevalence of allergy, malignancy, connective tissue diseases, lung diseases, and infections.

RESULTS

In IgG4-RD patients, 124 (46.4%) smoked. Top 4 clinical subtypes included Mikulicz syndrome with systemic involvement (33.3%), pancreato-hepatobiliary disease (31.4%), head/neck disease (19.4%), and retroperitoneal fibrosis/aortitis (12.7%). Top 4 co-morbid conditions included high serum IgE/eosinophilia (46.2%), hypocomplementemia (34%), malignancies (13.4%), and allergy (13.4%). Pancreato-biliary disease was associated with high IgE/eosinophilia (r² = 0.380, P = 0.025) and malignancy (r² = 0.211, P = 0.027), Miculicz syndrome with allergy (r² = 0.396, P < 0.01) and high IgE/eosinophil (r² = 0.396, P < 0.01), CNS diseases (r² = 0.973, P = 0.035) and sclerosing vasculitis (r² = 1, P < 0.01) with advanced age respectively, with the latter being also related to atopy and high IgE/eosinophilia (r² = 1, p < 0.01).

CONCLUSION

Smoking may precipitate IgG4-RD. IgG4-RD with pancreato-hepatobiliary disease is closely related to allergy and neoplasm, and those with Mikulicz syndrome may result from atopy. Elderly IgG4-RD patients tend to develop CNS pathology parallel to advancing of age. The disease may probably be originated from an unknown mechanism that may sporadically evolve into malignancies.

B regulatory cells in allergy

B cells have classically been recognized for their unique and indispensable role in the production of antibodies. Their potential as immunoregulatory cells with anti-inflammatory functions has received increasing attention during the last two decades. Herein, we highlight pioneering studies in the field of regulatory B cell (Breg) research. We will review the literature on Bregs with a particular focus on their role in the regulation of allergic inflammation.

IgG Antibody Responses to the Aedes albopictus 34k2 Salivary Protein as Novel Candidate Marker of Human Exposure to the Tiger Mosquito

Mosquitoes of the Aedes genus transmit arboviruses of great importance to human health as dengue, chikungunya, Zika and yellow fever. The tiger mosquito Aedes albopictus can play an important role as arboviral vector, especially when Aedes aegypti is absent or present at low levels. Remarkably, the rapid worldwide spreading of the tiger mosquito is expanding the risk of arboviral transmission also to temperate areas, and the autochthonous cases of chikungunya, dengue and Zika in Europe emphasize the need for improved monitoring and control. Proteomic and transcriptomic studies on blood feeding arthropod salivary proteins paved the way toward the exploitation of genus-specific mosquito salivary proteins for the development of novel tools to evaluate human exposure to mosquito bites. We previously found that the culicine-specific 34k2 salivary protein from Ae. albopictus (al34k2) evokes specific IgG responses in experimentally exposed mice, and provided preliminary evidence of its immunogenicity to humans. In this study we measured IgG responses to al34k2 and to Ae. albopictus salivary gland protein extracts (SGE) in individuals naturally exposed to the tiger mosquito. Sera were collected in two areas of Northeast Italy (Padova and Belluno) during two different time periods: at the end of the low- and shortly after the high-density mosquito seasons. Anti-SGE and anti-al34k2 IgG levels increased after the summer period of exposure to mosquito bites and were higher in Padova as compared to Belluno. An age-dependent decrease of anti-saliva IgG responses was found especially in Padova, an area with at least 25 years history of Ae. albopictus colonization. Moreover, a weak correlation between anti-saliva IgG levels and individual perception of mosquito bites by study participants was found. Finally, determination of anti-al34k2 IgG1 and IgG4 levels indicated a large predominance of IgG1 antibodies. Overall, this study provides a convincing indication that antibody responses to al34k2 may be regarded as a reliable candidate marker to detect temporal and/or spatial variation of human exposure to Ae. albopictus; a serological tool of this kind may prove useful both for epidemiological studies and to estimate the effectiveness of anti-vectorial measures.

Allergic Anaphylactic Risk in Farming Activities: A Systematic Review

Allergic disorders in the agriculture sector are very common among farm workers, causing many injuries and occupational diseases every year. Agricultural employees are exposed to multiple conditions and various allergenic substances, which could be related to onset of anaphylactic reactions. This systematic review highlights the main clinical manifestation, the allergens that are mostly involved and the main activities that are usually involved. This research includes articles published on the major databases (PubMed, Cochrane Library, Scopus), using a combination of keywords. The online search yielded 489 references; after selection, by the authors, 36 articles (nine reviews and 27 original articles) were analyzed. From this analysis, the main clinical problems that were diagnosed in this category were respiratory (ranging from rhinitis to asthma) and dermatological (eczema, dermatitis, hives) in nature, with a wide symptomatology (from a simple local reaction to anaphylaxis). The main activities associated with these allergic conditions are harvesting or cultivation of fruit and cereals, beekeepers and people working in greenhouses. Finally, in addition to the allergens already known, new ones have emerged, including triticale, wine, spider and biological dust. For these reasons, in the agricultural sector, research needs to be amplified, considering new sectors, new technologies and new products, and ensuring a system of prevention to reduce this risk.

Autoimmune Pathology in Myasthenia Gravis Disease Subtypes Is Governed by Divergent Mechanisms of Immunopathology

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

Hymenoptera Venom Allergy: How Does Venom Immunotherapy Prevent Anaphylaxis From Bee and Wasp Stings?

Hymenoptera stings may cause both local and systemic allergic reactions and even life threatening anaphylaxis. Along with pharmaceutical drugs and foods, hymenoptera venom is one of the most common causes of anaphylaxis in humans. To date, no parameter has been identified that may predict which sensitized people will have a future systemic sting reaction (SSR), however some risk factors, such as mastocytosis and age >40 years are known. Venom immunotherapy (VIT) is the most effective method of treatment for people who had SSR, which is shown to be effective even after discontinuation of the therapy. Development of peripheral tolerance is the main mechanism during immunotherapy. It is mediated by the production of blocking IgG/IgG4 antibodies that may inhibit IgE dependent reactions through both high affinity (FcεRI) and low affinity (FcεRII) IgE receptors on mast cells, basophils and B cells. The generation of antigen specific regulatory T cells produces IL-10 and suppresses Th2 immunity and the immune responses shift toward a Th1-type response. B regulatory cells are also involved in the production of IL-10 and the development of long term immune tolerance. During VIT the number of effector cells in target organs also decreases, such as mast cells, basophils, innate type 2 lymphocytes and eosinophils. Several meta-analyses and randomized controlled studies have proved that VIT is effective for preventing SSR to a sting and improves the quality of life. In this review, the risk of SSR in venom allergy and how VIT changed this risk are discussed.

Randomized controlled trial demonstrating the benefits of delta inulin adjuvanted immunotherapy in patients with bee venom allergy

Background

Allergic reactions to Hymenoptera insect stings remain a major global clinical problem. Although effective, parenteral desensitization regimens require use of costly venom extracts and require frequent visits over extended periods of time.

Objective

Adjuvants are commonly used to enhance the efficacy of infectious disease vaccines, and this study asked whether Advax (Vaxine Pty Ltd, Adelaide, Australia), a novel noninflammatory polysaccharide adjuvant, might provide similar benefits for allergy desensitization.

Methods

A randomized, controlled phase 1/2 trial was undertaken in 27 adults with a history of rapid-onset systemic allergic reactions to honeybee stings and positive specific IgE levels to evaluate the safety and efficacy of honeybee venom immunotherapy (HBVIT) combined with Advax adjuvant. Venom immunotherapy (VIT) was administered monthly for 30 months after achievement of maintenance doses.

Results

Advax-adjuvanted HBVIT was well tolerated. Around week 14 of VIT, specific IgG₄ responses peaked in both groups but increased earlier, peaked higher, and were better maintained through the end of the study in the Advax-adjuvanted arm. Several different patterns of serologic response to VIT were seen; some subjects had a dominant IgG₄ response, some had a combined IgG₄ and IgG₁ response, and some had an exclusively IgG₁ response. In some subjects specific IgE levels increased during the induction phase and then decreased, whereas in others specific IgE levels progressively decreased from the start of VIT.

Conclusion

Advax adjuvant favorably enhanced the immunogenicity of HBVIT, with an early and prolonged switch to specific IgG₄ production. The ability of Advax adjuvant to enhance VIT efficacy warrants further study.

Mucosal IgE immune responses in respiratory diseases

IgE is the less abundant immunoglobulin isotype in serum and displays higher affinity for its cognate Fc receptor (FcεRI) than the rest of antibody isotypes. Moreover, the class switch recombination and the generation of memory responses remarkably differ between IgE and other isotypes. Importantly, class switch recombination to IgE can occur in the mucosae, preferentially through the sequential switching from IgG. Therefore, resident effector cells get rapidly sensitized, and free IgE can be found in mucosal secretions. All these aspects explain the involvement of IgE in respiratory diseases. In allergic rhinitis and allergic asthma, the IgE-sensitization to environmental allergens triggers an eosinophilic inflammation of the airway mucosa of atopic patients. In recent years, growing evidence indicates that some non-atopic patients with nasal reactivity to allergens display nasal eosinophilic inflammation, which could be triggered by the local production of allergen-specific IgE. This phenotype has been termed local allergic rhinitis. Mucosal IgE is also implicated in the pathophysiology of chronic rhinosinusitis with nasal polyps, even though the mechanisms for IgE synthesis might differ in this case. The role of IgE as mediator of airway diseases identify this marker as a therapeutic target. Some biologicals antagonize IgE-mediated inflammation of the airway mucosa, but they have not shown a beneficial long-term effect after discontinuation. In contrast, allergen immunotherapy does not only control the symptoms of airway allergy, but it also induces a long-lasting effect after discontinuation, thus modifying the natural course of the disease.

Measurement of Specific IgG4 Anti-mouse Urine Antibodies

IgG₄ and its role in immune tolerance has been investigated widely. Symptom reduction and improved clinical outcomes in immunotherapy trials are associated with significant increases in allergen-specific IgG₄ antibodies. Natural immune tolerance observed in beekeepers and cat owners has also been associated with elevated levels of bee venom and cat allergen-specific IgG₄, respectively. Functionally, allergen-specific IgG₄ has been shown to reduce the binding of IgE-allergen complexes to B cells, a key step in the initiation of the type 1 hypersensitivity allergic response. In laboratory animal allergy, IgG₄ has been described as a "protective/blocking" antibody. However, a consensus on the exact relationship between exposure, IgG₄, and tolerance has yet to be reached. In this chapter, we review the factors that require consideration when developing an ELISA for the quantification of allergen-specific IgG₄.

Structural Analysis of Recent Allergen-Antibody Complexes and Future Directions

PURPOSE OF REVIEW

Allergen-antibody complexes are extremely valuable in describing the detailed molecular features of epitopes. This review summarizes insights gained from recently published co-structures and what obstacles impede the acquisition of further data.

RECENT FINDINGS

Structural epitope data helped define the epitopes of two anti-Fel d 1 antibodies undergoing phase I clinical trials, providing a greater level of detail than was possible through hydrogen-deuterium exchange protection studies. Separately, a human camelid-like antibody structure with lysozyme described several unique features in a long variable loop that interacted with the active site cleft of Gal d 4. Finally, a co-structure conclusively demonstrated that Phl p 7 could function as a superantigen and that an antibody could simultaneously recognize two epitopes. These remarkable assertions would not have been possible without visualization of the complex. Only three new complexes have appeared in the last few years, suggesting that there are major impediments to traditional production and crystallization. The structural data was extremely valuable in describing epitopes. New techniques like cryo-EM may provide an alternative to crystallography.

Specific IgG4 antibodies to cow's milk proteins in pediatric patients with eosinophilic esophagitis

BACKGROUND

Allergen-specific IgG₄ (sIgG₄) antibodies are often associated with tolerance, but sIgG₄ antibodies to causally relevant foods have been reported recently in adults with eosinophilic esophagitis (EoE). Prevalence and levels of food sIgG₄ are not well established in the general pediatric population.

OBJECTIVE

We sought to investigate serum food sIgG₄ with component diagnostics in children with EoE and children from an unselected birth cohort and to explore the effects of sex, age, and milk consumption on sIgG₄ levels.

METHODS

Sera from 71 pediatric patients with EoE and 210 early adolescent children from an unselected birth cohort (Project Viva) were assayed for sIgG₄ and specific IgE (sIgE) to major cow's milk (CM) proteins (α-lactalbumin, β-lactoglobulin, and caseins) and to wheat, soy, egg, and peanut proteins.

RESULTS

In the EoE cohort high-titer sIgG₄ (≥10 μg/mL) to CM proteins was more common than in control sera and achieved odds ratios for EoE ranging from 5.5 to 8.4. sIgE levels to CM proteins were mostly 4 IU/mL or less in patients with EoE, such that sIgG₄/sIgE ratios were often 10,000 or greater. When adjusted for age and milk consumption, high-titer sIgG₄ to CM proteins was strongly associated with EoE, with an odds ratio of greater than 20 to all 3 CM proteins in boys.

CONCLUSIONS

sIgG₄ to CM proteins are common and high titer in children with EoE. Although it is not clear that this response is pathogenic, sIgG₄ levels imply that these antibodies are an important feature of the local immune response that gives rise to EoE.

IgG4 Characteristics and Functions in Cancer Immunity

IgG4 is the least abundant subclass of IgG in normal human serum, but elevated IgG4 levels are triggered in response to a chronic antigenic stimulus and inflammation. Since the immune system is exposed to tumor-associated antigens over a relatively long period of time, and tumors notoriously promote inflammation, it is unsurprising that IgG4 has been implicated in certain tumor types. Despite differing from other IgG subclasses by only a few amino acids, IgG4 possesses unique structural characteristics that may be responsible for its poor effector function potency and immunomodulatory properties. We describe the unique attributes of IgG4 that may be responsible for these regulatory functions, particularly in the cancer context. We discuss the inflammatory conditions in tumors that support IgG4, the emerging and proposed mechanisms by which IgG4 may contribute to tumor-associated escape from immune surveillance and implications for cancer immunotherapy.

Agreement of skin test with IL-4 production and CD40L expression by T cells upon immunotherapy of subjects with systemic reactions to Hymenoptera stings

Venom immunotherapy is the only curative intervention for subjects with Hymenoptera venom allergy who suffering systemic reactions upon bee or wasp stings. Venom immunotherapy can restore normal immunity against venom allergens, as well as providing to allergic subjects a lifetime tolerance against venoms. Nevertheless, it is necessary using safety assays to monitoring the development of tolerance in the VIT protocols to avoid fatal anaphylactic reactions. The purpose of this study was to assess the modifications in several markers of tolerance induction in subjects with Hymenoptera venom allergy undergoing immunotherapy. The studies were performed at baseline time and after six month of VIT. Intradermal skin tests, basophil activation tests, specific IgE levels; and the T-cell markers (IL-4 and IFN-γ producing cells; and expression of the surface activation markers CD40L and CTLA-4) were assayed. At six month of immunotherapy all parameters studied had significant alterations. All decreased, except the IFN-γ producing cells. In addition, modifications in intradermal skin test showed a significant correlation with both, CD40L expression on CD4 T lymphocytes (p=0.043) and IL-4 producing T lymphocytes (p=0.012). Neither basophil activation test nor serum levels of sIgE demonstrated any correlation with the immunological parameters studied nor among them. These results suggest that both IL-4 production and CD40L expression could be two good indicators of the beneficial effects of venom immunotherapy which translate into skin tests.

Chronic cat allergen exposure induces a TH2 cell-dependent IgG4 response related to low sensitization

BACKGROUND

In human subjects, allergen tolerance has been observed after high-dose allergen exposure or after completed allergen immunotherapy, which is related to the accumulation of anti-inflammatory IgG4. However, the specific T-cell response that leads to IgG4 induction during chronic allergen exposure remains poorly understood.

OBJECTIVE

We sought to evaluate the relationship between cat allergen-specific T-cell frequency, cat allergen-specific IgE and IgG4 titers, and clinical status in adults with cat allergy with and without cat ownership and the cellular mechanism by which IgG4 is produced.

METHODS

Fel d 1-, Fel d 4-, Fel d 7-, and Fel d 8-specific T-cell responses were characterized by CD154 expression after antigen stimulation.

RESULTS

In allergic subjects without cat ownership, the frequency of cat allergen (Fel d 1 and Fel d 4)-specific TH2 (sTH2) cells correlates with higher IgE levels and is linked to asthma. Paradoxically, we observed that subjects with cat allergy and chronic cat exposure maintain a high frequency of sTH2 cells, which correlates with higher IgG4 levels and low sensitization. B cells from allergic, but not nonallergic subjects, are able to produce IgG4 after cognate interactions with sTH2 clones and Fel d 1 peptide or the Fel d 1 recombinant protein.

CONCLUSION

These experiments suggest that (1) allergen-experienced B cells with the capacity to produce IgG4 are present in allergic subjects and (2) cat allergen exposure induces an IgG4 response in a TH2 cell-dependent manner. Thus IgG4 accumulation could be mediated by chronic activation of the TH2 response, which in turn drives desensitization.

Allergen-Specific Cytokine Polarization Protects Shetland Ponies against Culicoides obsoletus-Induced Insect Bite Hypersensitivity

The immunological mechanisms explaining development of an allergy in some individuals and not in others remain incompletely understood. Insect bite hypersensitivity (IBH) is a common, seasonal, IgE-mediated, pruritic skin disorder that affects considerable proportions of horses of different breeds, which is caused by bites of the insect Culicoides obsoletus (C. obsoletus). We investigated the allergen-specific immune status of individual horses that had either been diagnosed to be healthy or to suffer of IBH. Following intradermal allergen injection, skin biopsies were taken of IBH-affected and healthy ponies and cytokine expression was determined by RT-PCR. In addition, allergen-specific antibody titers were measured and cytokine expression of in vitro stimulated, allergen-specific CD4 T-cells was determined. 24 hrs after allergen injection, a significant increase in mRNA expression of the type-2 cytokine IL-4 was observed in the skin of IBH-affected Shetland ponies. In the skin of healthy ponies, however, an increase in IFNγ mRNA expression was found. Analysis of allergen-specific antibody titers revealed that all animals produced allergen-specific antibodies, and allergen-specific stimulation of CD4 T-cells revealed a significant higher percentage of IFNγ-expressing CD4 T-cells in healthy ponies compared to IBH-affected ponies. These data indicate that horses not affected by IBH, in contrast to the so far established dogma, are not immunologically ignorant but have a Th1-skewed allergen-specific immune response that appears to protect against IBH-associated symptoms. To our knowledge this is the first demonstration of a natural situation, in which an allergen-specific immune skewing is protective in an allergic disorder.

IgG4 and IgE transcripts in childhood allergic asthma reflect divergent antigen-driven selection

The physiologic function of the "odd" Ab IgG4 remains enigmatic. IgG4 mediates immunotolerance, as, for example, during specific immunotherapy of allergies, but it mediates tissue damage in autoimmune pemphigus vulgaris and "IgG4-related disease." Approximately half of the circulating IgG4 molecules are bispecific owing to their unique ability to exchange half-molecules. Better understanding of the interrelation between IgG4 and IgE repertoires may yield insight into the pathogenesis of allergies and into potential novel therapies that modulate IgG4 responses. We aimed to compare the selective forces that forge the IgG4 and IgE repertoires in allergic asthma. Using an IgG4-specific RT-PCR, we amplified, cloned, and sequenced IgG4 H chain transcripts of PBMCs from 10 children with allergic asthma. We obtained 558 functional IgG4 sequences, of which 286 were unique. Compared with previously published unique IgE transcripts from the same blood samples, the somatic mutation rate was significantly enhanced in IgG4 transcripts (62 versus 83%; p < 0.001), whereas fewer IgG4 sequences displayed statistical evidence of Ag-driven selection (p < 0.001). On average, the hypervariable CDRH3 region was four nucleotides shorter in IgG4 than in IgE transcripts (p < 0.001). IgG4 transcripts in the circulation of children with allergic asthma reflect some characteristics of classical Ag-driven B2 immune responses but display less indication of Ag selection than do IgE transcripts. Although allergen-specific IgG4 can block IgE-mediated allergen presentation and degranulation of mast cells, key factors that influence the Ag-binding properties of the Ab differ between the overall repertoires of circulating IgG4- and IgE-expressing cells.

Rat-specific IgG and IgG₄ antibodies associated with inhibition of IgE-allergen complex binding in laboratory animal workers

OBJECTIVES

The relationship between exposure to rodent allergens and laboratory animal allergy is complex; at highest allergen exposures there is an attenuation of sensitisation and symptoms which are associated with increased levels of rat-specific immunoglobulin (Ig)G and IgG4 antibodies. We set out to examine whether the increased levels of rat-specific IgG and IgG4 antibodies that we have previously observed at high allergen exposure in our cohort of laboratory animal workers play a functional role through blockage of the binding of IgE-allergen complex binding to CD23 receptors on B cells.

METHODS

Cross-sectional survey of laboratory animal workers (n=776) in six UK pharmaceutical companies were surveyed. IgE-allergen complex binding to B cells was measured in 703 (97.9%) eligible employees; their exposure was categorised by either job group or number of rats handled daily.

RESULTS

We observed a significant decrease in IgE-allergen complex binding to B cells with increasing quartiles of both rat-specific IgG and IgG4 antibodies (p<0.001). IgE-allergen complex binding to B cells was lower in workers with high allergen exposure, and significantly so (p=0.033) in the subgroup with highest exposures but no work-related chest symptoms.

CONCLUSIONS

These findings demonstrate a functional role for rat-specific IgG/G4 antibodies in laboratory animal workers, similar to that observed in patients treated with high dose immunotherapy who become clinically tolerant, suggesting a potential explanation for the attenuation of risk at highest allergen exposures.

Effects of a honeybee sting on the serum free amino acid profile in humans

The aim of this study was to assess the response to a honeybee venom by analyzing serum levels of 34 free amino acids. Another goal of this study was to apply complex analytic-bioinformatic-clinical strategy based on up-to-date achievements of mass spectrometry in metabolomic profiling. The amino acid profiles were determined using hybrid triple quadrupole/linear ion trap mass spectrometer coupled with a liquid chromatography instrument. Serum samples were collected from 27 beekeepers within 3 hours after they were stung and after a minimum of 6 weeks following the last sting. The differences in amino acid profiles were evaluated using MetaboAnalyst and ROCCET web portals. Chemometric tests showed statistically significant differences in the levels of L-glutamine (Gln), L-glutamic acid (Glu), L-methionine (Met) and 3-methyl-L-histidine (3MHis) between the two analyzed groups of serum samples. Gln and Glu appeared to be the most important metabolites for distinguishing the beekeepers tested shortly after a bee sting from those tested at least 6 weeks later. The role of some amino acids in the response of an organism to the honeybee sting was also discussed. This study indicated that proposed methodology may allow to identify the individuals just after the sting and those who were stung at least 6 weeks earlier. The results we obtained will contribute to better understanding of the human body response to the honeybee sting.

Advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insects in 2013

This review highlights some of the research advances in anaphylaxis; hypersensitivity reactions to foods, drugs, and insects; and allergic skin diseases that were reported in the Journal in 2013. Studies on food allergy suggest that (1) 7.6% of the US population is affected, (2) a "healthy" early diet might prevent food allergy, (3) the skin might be an important route of sensitization, (4) allergen component testing might aid diagnosis, (5) the prognosis of milk allergy might be predictable through early testing, (6) oral or sublingual immunotherapy show promise but also have caveats, and (7) preclinical studies show promising alternative modes of immunotherapy and desensitization. Studies on eosinophilic esophagitis show a relationship to connective tissue disorders and that dietary management is an effective treatment for adults. Markers of anaphylaxis severity have been determined and might inform potential diagnostics and therapeutic targets. Insights on serum tests for drug and insect sting allergy might result in improved diagnostics. Genetic and immune-mediated defects in skin epithelial differentiation contribute to the severity of atopic dermatitis. Novel management approaches to treatment of chronic urticaria, including use of omalizumab, are being identified.

Allergen immunotherapy and tolerance

Successful allergen-specific immunotherapy (AIT) is associated with a marked decrease in symptoms on allergen exposure, a reduced requirement for 'rescue' anti-allergic drugs and improvement in patients' quality of life. These benefits persist for at least several years following discontinuation of immunotherapy - the hallmark of clinical and immunological tolerance. AIT has been shown to modulate both innate and adaptive immunological responses. Early suppression of innate effector cells of allergic inflammation (mast cells, basophils), regulation of pro-allergic T helper 2 type (Th 2) responses and IgE+ B cell responses have been shown to occur both in the tissue and in the peripheral blood during AIT. The allergen-tolerant state is associated with local and systemic induction of distinct populations of allergen-specific T regulatory cells including IL-10+ Tregs (Tr1 cells), TGF-β+ Tregs and FoxP3+ memory T regs. B cells are switched in favour of producing IgG (particularly IgG4) antibodies and associated blocking activity for IgE-dependent events, including basophil activation and IgE-facilitated allergen binding to B cells. An induction of IL-10+ B regulatory cells and alterations in dendritic cell subsets have also recently been described. These events are followed by the induction of T regulatory cells, suppression of allergen-specific T cell proliferation and immune deviation from Th2 in favour of Th1 responses. Alternative mechanisms of tolerance include apoptosis/deletion of antigen-specific memory Th2 cells and/or a failure of co-stimulation leading to T cell anergy.