Widespread monoclonal IgE antibody convergence to an immunodominant, proanaphylactic Ara h 2 epitope in peanut allergy.

BACKGROUND: Despite their central role in peanut allergy, human monoclonal IgE antibodies have eluded characterization. OBJECTIVE: We sought to define the sequences, affinities, clonality, and functional properties of human monoclonal IgE antibodies in peanut allergy. METHODS: We applied our single-cell RNA sequencing-based SEQ SIFTER discovery platform to samples from allergic individuals who varied by age, sex, ethnicity, and geographic location in order to understand commonalities in the human IgE response to peanut allergens. Select antibodies were then recombinantly expressed and characterized for their allergen and epitope specificity, affinity, and functional properties. RESULTS: We found striking convergent evolution of IgE monoclonal antibodies (mAbs) from several clonal families comprising both memory B cells and plasmablasts. These antibodies bound with subnanomolar affinity to the immunodominant peanut allergen Ara h 2, specifically a linear, repetitive motif. Further characterization of these mAbs revealed their ability to single-handedly cause affinity-dependent degranulation of human mast cells and systemic anaphylaxis on peanut allergen challenge in humanized mice. Finally, we demonstrated that these mAbs, reengineered as IgGs, inhibit significant, but variable, amounts of Ara h 2- and peanut-mediated degranulation of mast cells sensitized with allergic plasma. CONCLUSIONS: Convergent evolution of IgE mAbs in peanut allergy is a common phenomenon that can reveal immunodominant epitopes on major allergenic proteins. Understanding the functional properties of these molecules is key to developing therapeutics, such as competitive IgG inhibitors, that are able to stoichiometrically outcompete endogenous IgE for allergen and thereby prevent allergic cascade in cases of accidental allergen exposure.

Autoreactive IgE: Pathogenic role and therapeutic target in autoimmune diseases.

Autoimmunity is the break of tolerance to self-antigens that leads to organ-specific or systemic diseases often characterized by the presence of pathogenic autoreactive antibodies (AAb) produced by plasmablast and/or plasma cells. AAb are prevalent in the general population and not systematically associated with clinical symptoms. In contrast, in some individuals, these AAb are pathogenic and drive the development of signs and symptoms of antibody-mediated autoimmune diseases (AbAID). AAb production, isotype profiles, and glycosylations are promoted by pro-inflammatory triggers linked to genetic, environmental, and hormonal parameters. Recent evidence supports a role for pathogenic AAb of the IgE isotype in a number of AbAID. Autoreactive IgE can drive the activation of mast cells, basophils, and other types of FcεRI-bearing cells and may play a role in promoting autoantibody production and other pro-inflammatory pathways. In this review, we discuss the current knowledge on the pathogenicity of autoreactive IgE in AbAID and their status as therapeutic targets. We also highlight unresolved issues including the need for assays that reproducibly quantify IgE AAbs, to validate their diagnostic and prognostic value, and to further study their pathophysiological contributions to AbAID.

Landscape of mast cell populations across organs in mice and humans.

Mast cells (MCs) are tissue-resident immune cells that exhibit homeostatic and neuron-associated functions. Here, we combined whole-tissue imaging and single-cell RNA sequencing datasets to generate a pan-organ analysis of MCs in mice and humans at steady state. In mice, we identify two mutually exclusive MC populations, MrgprB2+ connective tissue-type MCs and MrgprB2neg mucosal-type MCs, with specific transcriptomic core signatures. While MrgprB2+ MCs develop in utero independently of the bone marrow, MrgprB2neg MCs develop after birth and are renewed by bone marrow progenitors. In humans, we unbiasedly identify seven MC subsets (MC1-7) distributed across 12 organs with different transcriptomic core signatures. MC1 are preferentially enriched in the bladder, MC2 in the lungs, and MC4, MC6, and MC7 in the skin. Conversely, MC3 and MC5 are shared by most organs but not skin. This comprehensive analysis offers valuable insights into the natural diversity of MC subtypes in both mice and humans.

Healthcare resource consumption prior to asthma-related death: a nationwide descriptive study.

BACKGROUND: Although asthma mortality declined sharply until the mid-2000s, a stagnation in mortality has been observed over the past decade in different countries. OBJECTIVE: The objective of this study is to describe healthcare resource consumption for patients who died from asthma in France. METHOD: This study was conducted using data from the French National Health Data System. Patients who died from asthma between 2013 and 2017 were identified by the ICD10 codes J45 and J46. Health care consumption data were collected. Patients were categorized into four categories according to age: ⩾75, (18-75), (12-18), (0-12). Daily doses of ICS were categorized according to GINA guidelines. RESULTS: A total of 3829 patients were included. No ICS or an inadequate ICS dose was observed in 43.8%, 50.6%, 48.1%, and 54.0% of patients aged ⩾75, (18-74), (12-18), and (0-12) years, respectively. Dispensation of six or more SABA canisters was observed in 37.2%, 49.0%, and 70.3% of patients aged of ⩾75, (18-75), and (12-18) years, respectively. Omalizumab dispensation rate was very low [1.1% and 2.8% in patients aged ⩾75 and (18-75) years)]. The proportion of patients with a pulmonologist office visit was 13.8% and 14.6% in patients ⩾75 and (18-75) years, respectively. A lung function test was noted in only 18.6%, 28.3%, and 25.9% of patients ⩾75, (18-75) and (12-18) years, respectively. CONCLUSION: Half of the patients who died from asthma received inadequate ICS doses and only a small proportion had access to biological therapies. Less than 15% were referred to a specialist.

IgG Subclass-Dependent Pulmonary Antigen Retention during Acute IgG-Dependent Systemic Anaphylaxis in Mice.

Mouse models of active systemic anaphylaxis rely predominantly on IgG Abs forming IgG-allergen immune complexes that induce IgG receptor-expressing neutrophils and monocytes/macrophages to release potent mediators, leading to systemic effects. Whether anaphylaxis initiates locally or systemically remains unknown. In this study, we aimed at identifying the anatomical location of IgG-allergen immune complexes during anaphylaxis. Active systemic anaphylaxis was induced following immunization with BSA and i.v. challenge with fluorescently labeled BSA. Ag retention across different organs was examined using whole-body fluorescence imaging, comparing immunized and naive animals. Various mouse models and in vivo deletion strategies were employed to determine the contribution of IgG receptors, complement component C1q, myeloid cell types, and anaphylaxis mediators. We found that following challenge, Ag diffused systemically, but specifically accumulated in the lungs of mice sensitized to that Ag, where it formed large Ab-dependent aggregates in the vasculature. Ag retention in the lungs did not rely on IgG receptors, C1q, neutrophils, or macrophages. IgG2a-mediated, but neither IgG1- nor IgG2b-mediated, passive systemic anaphylaxis led to Ag retention in the lung. Neutrophils and monocytes significantly accumulated in the lungs after challenge and captured high amounts of Ag, which led to downmodulation of surface IgG receptors and triggered their activation. Thus, within minutes of systemic injection in sensitized mice, Ag formed aggregates in the lung and liver vasculature, but accumulated specifically and dose-dependently in the lung. Neutrophils and monocytes recruited to the lung captured Ag and became activated. However, Ag aggregation in the lung vasculature was not necessary for anaphylaxis induction.

Pharmacological approaches to target type 2 cytokines in asthma.

Asthma is the most common chronic lung disease, affecting more than 250 million people worldwide. The heterogeneity of asthma phenotypes represents a challenge for adequate assessment and treatment of the disease. However, approximately 50% of asthma patients present with chronic type 2 inflammation initiated by alarmins, such as IL-33 and thymic stromal lymphopoietin (TSLP), and driven by the TH2 interleukins IL-4, IL-5 and IL-13. These cytokines have therefore become important therapeutic targets in asthma. Here, we discuss current knowledge on the structure and functions of these cytokines in asthma. We review preclinical and clinical data obtained with monoclonal antibodies (mAbs) targeting these cytokines or their receptors, as well as novel strategies under development, including bispecific mAbs, designed ankyrin repeat proteins (DARPins), small molecule inhibitors and vaccines targeting type 2 cytokines.

IgE antibodies increase honeybee venom responsiveness and detoxification efficiency of mast cells.

BACKGROUND: In contrast to their clearly defined roles in allergic diseases, the physiologic functions of Immunoglobulin E antibodies (IgEs) and mast cells (MCs) remain enigmatic. Recent research supports the toxin hypothesis, showing that MCs and IgE-related type 2 immune responses can enhance host defense against certain noxious substances, including honeybee venom (BV). However, the mechanisms by which MCs can interfere with BV toxicity are unknown. In this study, we assessed the role of IgE and certain MC products in MC-mediated BV detoxification. METHODS: We applied in vitro and in vivo fluorescence microscopyimaging, and flow cytometry, fibroblast-based toxicity assays and mass spectrometry to investigate IgE-mediated detoxification of BV cytotoxicity by mouse and human MCs in vitro. Pharmacologic strategies to interfere with MC-derived heparin and proteases helped to define the importance of specific detoxification mechanisms. RESULTS: Venom-specific IgE increased the degranulation and cytokine responses of MCs to BV in vitro. Passive serum sensitization enhanced MC degranulation in vivo. IgE-activated mouse or human MCs exhibited enhanced potential for detoxifying BV by both proteolytic degradation and heparin-related interference with toxicity. Mediators released by IgE-activated human MCs efficiently degraded multiple BV toxins. CONCLUSIONS: Our results both reveal that IgE sensitization enhances the MC's ability to detoxify BV and also assign efficient toxin-neutralizing activity to MC-derived heparin and proteases. Our study thus highlights the potential importance of IgE, MCs, and particular MC products in defense against BV.

Neutrophil-specific gain-of-function mutations in Nlrp3 promote development of cryopyrin-associated periodic syndrome.

Gain-of-function mutations in NLRP3 are responsible for a spectrum of autoinflammatory diseases collectively referred to as "cryopyrin-associated periodic syndromes" (CAPS). Treatment of CAPS patients with IL-1-targeted therapies is effective, confirming a central pathogenic role for IL-1ß. However, the specific myeloid cell population(s) exhibiting inflammasome activity and sustained IL-1ß production in CAPS remains elusive. Previous reports suggested an important role for mast cells (MCs) in this process. Here, we report that, in mice, gain-of-function mutations in Nlrp3 restricted to neutrophils, and to a lesser extent macrophages/dendritic cells, but not MCs, are sufficient to trigger severe CAPS. Furthermore, in patients with clinically established CAPS, we show that skin-infiltrating neutrophils represent a substantial biological source of IL-1ß. Together, our data indicate that neutrophils, rather than MCs, can represent the main cellular drivers of CAPS pathology.

Dual vaccination against IL-4 and IL-13 protects against chronic allergic asthma in mice.

Allergic asthma is characterized by elevated levels of IgE antibodies, type 2 cytokines such as interleukin-4 (IL-4) and IL-13, airway hyperresponsiveness (AHR), mucus hypersecretion and eosinophilia. Approved therapeutic monoclonal antibodies targeting IgE or IL-4/IL-13 reduce asthma symptoms but require costly lifelong administrations. Here, we develop conjugate vaccines against mouse IL-4 and IL-13, and demonstrate their prophylactic and therapeutic efficacy in reducing IgE levels, AHR, eosinophilia and mucus production in mouse models of asthma analyzed up to 15 weeks after initial vaccination. More importantly, we also test similar vaccines specific for human IL-4/IL-13 in mice expressing human IL-4/IL-13 and the related receptor, IL-4Rα, to find efficient neutralization of both cytokines and reduced IgE levels for at least 11 weeks post-vaccination. Our results imply that dual IL-4/IL-13 vaccination may represent a cost-effective, long-term therapeutic strategy for the treatment of allergic asthma as demonstrated in mouse models, although additional studies are warranted to assess its safety and feasibility.

Comment on "Tumor-initiating cells establish an IL-33-TGF-ß niche signaling loop to promote cancer progression".

Taniguchi et al (Research Articles, 17 July 2020, p. 269) claim that the cytokine interleukin-33 induces accumulation of tumor-associated macrophages expressing the immunoglobulin E receptor FcεRI. Although these findings hold great therapeutic promise, we provide evidence that the anti-FcεRI antibody used in this study is not specific for FcεRI on macrophages, which raises concerns about the validity of some of the conclusions.

IgE in the pathophysiology and therapy of food allergy.

Food allergy is becoming a major public health issue, with no regulatory approved therapy to date. Food allergy symptoms range from skin rash and gastrointestinal symptoms to anaphylaxis, a potentially fatal systemic allergic shock reaction. IgE antibodies are thought to contribute importantly to key features of food allergy and anaphylaxis, and measurement of allergen-specific IgE is fundamental in diagnosing food allergy. This review will discuss recent advances in the regulation of IgE production and IgE repertoires in food allergy. We will describe the current understanding of the role of IgE and its high-affinity receptor FcεRI in food allergy and anaphylaxis, by reviewing insights gained from analyses of mouse models. Finally, we will review data derived from clinical studies of the effect of anti-IgE therapeutic monoclonal antibodies (mAbs) in food allergy, and recent insight on the efficiency and mechanisms through which these mAbs block IgE effector functions.