Combined blockade of the histamine H1 and H4 receptor suppresses peanut-induced intestinal anaphylaxis by regulating dendritic cell function

Gene editing in allergic diseases: Identification of novel pathways and impact of deleting allergen genes

Gene editing technology has emerged as a powerful tool in all aspects of health research and continues to advance our understanding of critical and essential elements in disease pathophysiology. The clustered regularly interspaced short palindromic repeats (CRISPR) gene editing technology has been used with precision to generate gene knockouts, alter genes, and identify genes that cause disease. The full spectrum of allergic/atopic diseases, in part because of shared pathophysiology, is ripe for studies with this technology. In this way, novel culprit genes are being identified and allow for manipulation of triggering allergens to reduce allergenicity and disease. Notwithstanding current limitations on precision and potential off-target effects, newer approaches are rapidly being introduced to more fully understand specific gene functions as well as the consequences of genetic manipulation. In this review, we examine the impact of editing technologies of novel genes relevant to peanut allergy and asthma as well as how gene modification of common allergens may lead to the deletion of allergenic proteins.

Amelioration of Ovalbumin-Induced Food Allergy in Mice by Targeted Rectal and Colonic Delivery of Cyanidin-3-O-Glucoside

Targeted rectal and colonic delivery is an effective strategy to exploit the biological functions of polyphenols. This work investigated the anti-food allergy (FA) activity of cyanidin-3-O-glucoside (C3G) delivered by enteric sodium alginate in vivo. The results showed that through targeted rectal and colonic delivery, the C3G showed better results in ameliorating clinical allergic symptoms, diarrhea, and serological indicators including ovalbumin-specific IgE, histamine, and mast cell protease-1. The C3G was more efficient in enhancing the intestinal epithelial barrier by up-regulating the tight junction protein expression and promoting secretory IgA and β-defensin secretion. The improved bioactivity in regulating T helper (Th)1/Th2 immune balance in the intestinal mucosa was also observed. Compared with the intestinal microbiota structure of the model group, targeted rectal and colonic delivery of C3G was able to bring the abundance of Bacteroidota and Firmicutes close to the levels found in normal mice. Furthermore, there was an evident increase in beneficial bacteria in the intestinal flora, such as Lactobacillus and Odoribacter, and a decrease in pathogenic bacteria like Helicobacter and Turicibacter. Therefore, the anti-FA activity of C3G could be increased via targeted rectal and colonic delivery, while the mechanism might be attributed to the regulation of intestinal microecological homeostasis.

Optimizing drug inhibition of IgE-mediated anaphylaxis in mice

BACKGROUND

Administering allergens in increasing doses can temporarily suppress IgE-mediated allergy and anaphylaxis by desensitizing mast cells and basophils; however, allergen administration during desensitization therapy can itself induce allergic responses. Several small molecule drugs and nutraceuticals have been used clinically and experimentally to suppress these allergic responses.

OBJECTIVES

This study sought to optimize drug inhibition of IgE-mediated anaphylaxis.

METHODS

Several agents were tested individually and in combination for ability to suppress IgE-mediated anaphylaxis in conventional mice, FcεRIα-humanized mice, and reconstituted immunodeficient mice that have human mast cells and basophils. Hypothermia was the readout for anaphylaxis; therapeutic efficacy was measured by degree of inhibition of hypothermia. Serum mouse mast cell protease 1 level was used to measure extent of mast cell degranulation.

RESULTS

Histamine receptor 1 (HR1) antagonists, β-adrenergic agonists, and a spleen tyrosine kinase (Syk) inhibitor were best at individually inhibiting IgE-mediated anaphylaxis. A Bruton's tyrosine kinase (BTK) inhibitor, administered alone, only inhibited hypothermia when FcεRI signaling was suboptimal. Combinations of these agents could completely or nearly completely inhibit IgE-mediated hypothermia in these models. Both Syk and BTK inhibition decreased mast cell degranulation, but only Syk inhibition also blocked desensitization. Many other agents that are used clinically and experimentally had little or no beneficial effect.

CONCLUSIONS

Combinations of an HR1 antagonist, a β-adrenergic agonist, and a Syk or a BTK inhibitor protect best against IgE-mediated anaphylaxis, while an HR1 antagonist plus a β-adrenergic agonist ± a BTK antagonist is optimal for inhibiting IgE-mediated anaphylaxis without suppressing desensitization.

Antiviral Response Induced by TLR7/TLR8 Activation Inhibits HIV-1 Infection in Cord Blood Macrophages

Vertical transmission is the main mechanism of HIV-1 infection in infants, who may develop high viremia and rapidly progress to AIDS. Innate immunity agonists can control HIV-1 replication in vitro, but the protective effect in the neonatal period remains unknown. Herein, we evaluated the immunomodulatory and antiviral effects of IFN-I adjuvants on cord blood monocyte-derived macrophages upon HIV-1 infection. Despite the phenotypic and transcriptional similarities between cord blood and adult macrophages, cord blood cells were prone to viral replication when infected with HIV-1. However, treatment with CL097 efficiently promoted the antiviral and inflammatory responses and inhibited HIV-1 replication in cord blood cells in an NF-κB and autophagy activation-independent manner. Our data suggest that cord blood macrophages are able to establish antiviral responses induced by IFN-I adjuvants similar to those of their adult counterparts, revealing a potential adjuvant candidate to enhance the neonatal immune response.

The Function of the Histamine H4 Receptor in Inflammatory and Inflammation-Associated Diseases of the Gut

Histamine is a pleiotropic mediator involved in a broad spectrum of (patho)-physiological processes, one of which is the regulation of inflammation. Compounds acting on three out of the four known histamine receptors are approved for clinical use. These approved compounds comprise histamine H1-receptor (H₁R) antagonists, which are used to control allergic inflammation, antagonists at H₂R, which therapeutically decrease gastric acid release, and an antagonist at H₃R, which is indicated to treat narcolepsy. Ligands at H₄R are still being tested pre-clinically and in clinical trials of inflammatory diseases, including rheumatoid arthritis, asthma, dermatitis, and psoriasis. These trials, however, documented only moderate beneficial effects of H₄R ligands so far. Nevertheless, pre-clinically, H₄R still is subject of ongoing research, analyzing various inflammatory, allergic, and autoimmune diseases. During inflammatory reactions in gut tissues, histamine concentrations rise in affected areas, indicating its possible biological effect. Indeed, in histamine-deficient mice experimentally induced inflammation of the gut is reduced in comparison to that in histamine-competent mice. However, antagonists at H₁R, H₂R, and H₃R do not provide an effect on inflammation, supporting the idea that H₄R is responsible for the histamine effects. In the present review, we discuss the involvement of histamine and H₄R in inflammatory and inflammation-associated diseases of the gut.

The emerging role of neuroimmune interactions in atopic dermatitis and itch

Millions of people globally suffer from allergic diseases, and the cases have been rising in the past decades. One of the major manifestations of allergic diseases is itch, which is an unpleasant symptom that triggers the urge to scratch and greatly affects the quality of life. Thus, research on how sensation of itch is detected/transmitted from the contact of the allergen to the nervous system is crucial in mitigating itch. Recent studies have attempted to elucidate the mechanisms of itch in allergic diseases. Here, we aim to review the endogenous mediators released from immune/nonimmune skin cells (that are indirectly involved in the propagation of itch) and the sensory neurons that express receptors for these itch mediators that are associated with direct transmission of itch in cutaneous allergic diseases. As the mechanisms for allergic itch become clearer, new therapeutic approaches to relieve itch are likely to be developed. Recent clinical trials are testing numerous compounds that target the endogenous mediators and their receptors. These studies provide the possibility of more effective itch treatment for allergic diseases.

Dysregulation of intestinal epithelial CFTR-dependent Cl- ion transport and paracellular barrier function drives gastrointestinal symptoms of food-induced anaphylaxis in mice

Food-triggered anaphylaxis can encompass a variety of systemic and intestinal symptoms. Murine-based and clinical studies have revealed a role for histamine and H1R and H2R-pathway in the systemic response; however, the molecular processes that regulate the gastrointestinal (GI) response are not as well defined. In the present study, by utilizing an IgE-mast cell (MC)-dependent experimental model of oral antigen-induced anaphylaxis, we define the intestinal epithelial response during a food-induced anaphylactic reaction. We show that oral allergen-challenge stimulates a rapid dysregulation of intestinal epithelial transcellular and paracellular transport that was associated with the development of secretory diarrhea. Allergen-challenge induced (1) a rapid intestinal epithelial Cftr-dependent Cl- secretory response and (2) paracellular macromolecular leak that was associated with modification in epithelial intercellular junction proteins claudin-1, 2, 3 and 5, E-cadherin and desmosomal cadherins. OVA-induced Cftr-dependent Cl- secretion and junctional protein degradation was rapid occurring and was sustained for 72 h following allergen-challenge. Blockade of both the proteolytic activity and Cl- secretory response was required to alleviate intestinal symptoms of food-induced anaphylaxis. Collectively, these data suggest that the GI symptom of food-induced anaphylactic reaction, secretory diarrhea, is a consequence of CFTR-dependent Cl- secretion and proteolytic activity.

Protective Effect of Glycomacropeptide on Food Allergy with Gastrointestinal Manifestations in a Rat Model through Down-Regulation of Type 2 Immune Response

Glycomacropeptide (GMP) is a bioactive peptide derived from milk κ-casein with immune-modulatory and anti-inflammatory properties. Food allergy (FA) is an adverse immune reaction with a broad spectrum of manifestations. Allergen intake induces persistent intestinal inflammation and tissue damage. In this study, the anti-allergic activity of GMP was evaluated using a rat ovalbumin (OVA)-induced FA model with gastrointestinal manifestation. Rats were orally GMP treated from 3 days prior and during FA development. The severity of food anaphylaxis and diarrheal episodes, antibody production and histamine level were measured. Histopathological changes, inflammation and predominant cytokine profile at intestine were analyzed. Oral GMP intake decreased clinical signs and diarrhea severity induced by allergen, with a significant reduction in intestinal edema and expression level of IL-1β and TNF-α. Prophylaxis with GMP also diminished serum anti-OVA IgE and IgG1, and histamine levels. GMP treatment markedly decreased eosinophil infiltration, mast cell and goblet cell hyperplasia, total IgE expression in intestine, and prevented histological changes in villi, crypts and internal muscularis layer. The treatment effectively suppressed IL-5, IL-13 and GATA3 expression and skewed the intestinal cytokine profile toward type 1 and regulatory. These results suggest that GMP may protect against FA through down-regulating the type 2 inflammatory response.

Loratadine Alleviates Advanced Glycation End Product-Induced Activation of NLRP3 Inflammasome in Human Chondrocytes

Background

Chondrocytes in joint tissue are responsible for the synthesis and degradation of the cartilage matrix. Chondrocytes have been closely linked to the pathogenesis of osteoarthritis and cartilage damage. Targeted drug intervention directed at chondrocyte function is a promising strategy for the treatment of osteoarthritis. The effects of histamine receptor H1 (H1R) and its antagonist loratadine in osteoarthritic chondrocytes are less known.

Materials and Methods

The inhibitory effects of loratadine on NLRP3 inflammasome and the NADPH oxidase subunit NOX4 were assessed in advanced glycation end products (AGEs)-treated SW1353 chondrocytes by real-time PCR, ELISA, and Western blot experiments. The mitochondrial ROS level was measured using the specific probe MitoSOX Red. The dependent effect of loratadine on the transcriptional factor nuclear factor erythroid 2-related factor 2 (NRF2) was evaluated through an oligo-based siRNA knockdown approach and Western blot analysis.

Results

The expression of H1R was dose-responsively induced by AGEs in chondrocytes. Treatment with loratadine mitigated AGEs-induced oxidative stress, as revealed by suppressed production of mitochondrial ROS and the NADPH oxidase subunit NOX4. Loratadine treatment inhibited the expression of TxNIP and several components of the NLRP3 inflammasome complex, including NLRP3, ASC, and cleaved caspase 1 (P10). Moreover, loratadine suppressed the expression of NRF2, and the silencing of NRF2 abolished the suppressive effect of loratadine on NLRP3 inflammasome activation.

Conclusion

Our study demonstrates that loratadine protects chondrocytes from AGEs-induced TxNIP/NLRP3 inflammasome activation by modulating the expression of the transcriptional factor NRF2. This finding implies that loratadine has therapeutic potential in the treatment of osteoarthritis and cartilage injury.

Coumarin alleviates ovalbumin-induced food anaphylaxis in a mouse model by affecting mast cell function

Coumarin is an important organic heterocyclic compound with a wide range of sources in nature. It plays an important role in the drug discovery process due to its existence in diverse biologically active compounds and its broad bioactivity. In this study, the anti-allergic activity of coumarin was evaluated using an ovalbumin (OVA)-induced mouse food allergy model and an immunoglobulin (Ig)E mediated mouse bone marrow-derived mast cell (BMMC) model. Coumarin could alleviate the OVA-induced allergic symptoms, decrease the diarrhea rates, and promote the rectal temperature rise in allergic mice. Moreover, coumarin had the ability to reduce the levels of histamine and mouse mast cell proteinases, inhibit OVA-specific IgE, and significantly decrease the population of mast cells in the spleen and mesenteric lymph nodes. Coumarin could also significantly suppress mast cell-dependent passive cutaneous anaphylaxis. Additionally, the number of mature BMMCs was decreased as coumarin caused the suppression of c-KIT receptors. Furthermore, coumarin up-regulated the apoptosis of OVA-activated BMMCs in a concentration-dependent manner. In conclusion, coumarin displayed effective anti-food allergy activity via the regulation of mast cell function and numbers. Coumarin and its derivatives provide a new direction for the development of anti-food allergic drug components.

Mouse Models for Food Allergies: Where Do We Stand?

Food allergies are a steadily increasing health and economic problem. Immunologically, food allergic reactions are caused by pathological, allergen-specific Th2 responses resulting in IgE-mediated mast cell degranulation and associated inflammatory reactions. Clinically, food allergies are characterized by local inflammation of the mouth mucosa, the face, the throat, the gastrointestinal tract, are frequently paralleled by skin reactions, and can result in life-threatening anaphylactic reactions. To better understand food allergies and establish novel treatment options, mouse models are indispensable. This review discusses the available mouse food allergy models, dividing them into four categories: (1) adjuvant-free mouse models, (2) mouse models relying on adjuvants to establish allergen-specific Th2 responses, (3) mouse models using genetically-modified mouse strains to allow for easier sensitization, and (4) humanized mouse models in which different immunodeficient mouse strains are reconstituted with human immune or stem cells to investigate humanized immune responses. While most of the available mouse models can reproducibly portray the immunological parameters of food allergy (Th2 immune responses, IgE production and mast cell activation/expansion), so far, the recreation of the clinical parameters has proven more difficult. Therefore, up to now none of the available mouse models can reproduce the complete human pathology.

Attenuation of allergic responses following treatment with resveratrol in anaphylactic models and IgE-mediated mast cells

Resveratrol exists widely in plant species and has a variety of anti-oxidant, anti-inflammatory, and immunomodulatory properties. However, there have been few reports regarding its anti-food allergic activity. In this study, we demonstrated that resveratrol (isolated from Abies georgei) could decrease the release of β-hexosaminidase and histamine in rat basophilic leukemia-2H3 cells. Resveratrol was not only found to suppress the development of diarrhea, up-regulate the rectal temperature of ovalbumin-allergic mice, and decrease the serum level of specific immunoglobulin E, mouse mast cell protease-1 and histamine, but also found to decrease the population of dendritic cells, B cells and mast cells of ovalbumin -allergic mice in the spleen or mesenteric lymph node. Furthermore, resveratrol inhibited the release of β-hexosaminidase and histamine in bone marrow-derived cells and alleviated mast cell-mediated passive cutaneous anaphylaxis reactions. These findings indicated that resveratrol isolated from Abies georgei might have the potential to alleviate food hypersensitivity or allergic disease.

P-FN12, an H4R-Based Epitope Vaccine Screened by Phage Display, Regulates the Th1/Th2 Balance in Rat Allergic Rhinitis

Allergic rhinitis (AR) involves antigen-specific immune-inflammation of the nasal mucosa. Classical therapy for AR targets the histamine pathway, e.g., histamine receptor blockers. Histamine H4 receptor (H4R) was suggested as a novel therapeutic target due to its wide expression on almost all immune-related cells. A 12-mer random peptide library was used to select the specific epitope of the H4R. The phage clone showing the highest degree of activation was verified and translated to the corresponding peptide. The peptide FNKWMDCLSVTH, designated as P-FN12, was bound by H4R monoclonal antibody (mcAb) with high affinity. Moreover, the P-FN12 + CTB@Lipo-formulated vaccine, used as nasal drops, decreased allergic symptoms such as sneezing and nasal rubbing in a rat model. The level of ovalbumin (OVA)-specific immunoglobulin E (IgE) decreased significantly after vaccine administration. It also elicited increased levels of interferon (IFN)-γ and interleukin-2 (IL-2) but a decreased level of IL-4, and it elevated the T helper type 1 (Th1):T helper type 2 (Th2) cell ratio in peripheral blood mononuclear cell cultures. Our results indicated that the reduction of allergic inflammation by P-FN12-based vaccine was related to a decrease in production of OVA-specific IgE, Th2 immunity, and tissue eosinophilia. P-FN12 + CTB@Lipo is a promising vaccine that could suppress Th2 response and enhance the induction of Th1 cells in an AR model.

The Fab fragment of anti-IgE Cε2 domain prevents allergic reactions through interacting with IgE-FcεRIα complex on rat mast cells

Immunoglobulin E (IgE) plays a central role in the pathogenesis of Type I hypersensitivity through interaction with a high-affinity receptor (FcεRIα). For therapeutic applications, substantial attention has been focused recently on the blockade of the IgE interaction with FcεRIα. While exploring better options for preventing allergic diseases, we found that the Fab fragment of the rat anti-murine IgE antibody (Fab-6HD5) strongly inhibited passive cutaneous anaphylaxis (PCA) in vivo, as well as spleen tyrosine kinase (Syk) activity and β-hexosaminidase release from basophilic leukemia cells in vitro. The in vivo effects of Fab-6HD5 pre-administration were maintained over a long period of time for at least 10 days. Using flow cytometry analysis, we also found that Fab-6HD5 did not recognize the IgE Cε3 domain containing specific binding sites for FcεRIα. Furthermore, deletion-mapping studies revealed that Fab-6HD5 recognized conformational epitopes on the Cε2 domain of IgE. Given that the Cε2 domain plays a key role in stabilizing the interaction of IgE with FcRIα, our results suggest that the specific binding of Fab-6HD5 to the Cε2 domain prevents allergic reactions through destabilizing the preformed IgE-FcεRIα complex on rat mast cells. Although the present study was performed using animal models, these findings support the idea that a certain antibody directed against IgE CH domains may contribute to preventing allergic diseases through interacting with IgE-FcεRIα complex.

Markers of anaphylaxis - a systematic review

Anaphylaxis is defined as severe, life-threatening, systemic or general, immediate reaction of hypersensitivity, with repeatable symptoms caused by the dose of stimulus which is well tolerated by healthy persons. The proper diagnosis, immediate treatment and differential diagnosis are crucial for saving patient's life. However, anaphylaxis is relatively frequently misdiagnosed or confused with other clinical entities. Thus, there is a continuous need for identifying detectable markers improving the proper diagnosis of anaphylaxis. Here we presented currently known markers of anaphylaxis and discussed in more detail the most clinically valuable ones: tryptase, platelet activacting factor (PAF), PAF-acethylhydrolase, histamine and its metabolites.

Role of Histamine in Modulating the Immune Response and Inflammation

Inflammatory mediators, including cytokines, histamine, bradykinin, prostaglandins, and leukotrienes, impact the immune system, usually as proinflammatory factors. Other mediators act as regulatory components to establish homeostasis after injury or prevent the inflammatory process. Histamine, a biogenic vasoactive amine, causes symptoms such as allergies and has a pleiotropic effect that is dependent on its interaction with its four histamine receptors. In this review, we discuss the dualistic effects of histamine: how histamine affects inflammation of the immune system through the activation of intracellular pathways that induce the production of inflammatory mediators and cytokines in different immune cells and how histamine exerts regulatory functions in innate and adaptive immune responses. We also evaluate the interactions between these effects.

Deep-Sea-Derived Butyrolactone I Suppresses Ovalbumin-Induced Anaphylaxis by Regulating Mast Cell Function in a Murine Model

Deep-sea-derived butyrolactone I (BTL-I), which was identified as a type of butanolide, was isolated from Aspergillus sp. Ovalbumin (OVA)-induced BALB/c anaphylaxis was established to explore the antifood allergic activity of BTL-I. As a result, BTL-I was able to alleviate OVA-induced allergy symptoms, reduce the levels of histamine and mouse mast cell proteinases, inhibit OVA-specific IgE, and decrease the population of mast cells in the spleen and mesenteric lymph nodes. BTL-I also significantly suppressed mast-dependent passive cutaneous anaphylaxis. Additionally, the maturation of bone marrow-derived mast cells (BMMCs) declined as BTL-I caused down-regulation of c-KIT receptors. Furthermore, molecular docking analyses revealed that BTL-I interacted with the inhibitory receptor, FcγRIIB. In conclusion, the reduction of mast cell function by deep-sea-derived BTL-I as well as its interactions with the inhibitory receptor, FcγRIIB, may contribute to BTL-I-related protection against food anaphylaxis.

Influence of peanut matrix on stability of allergens in gastric-simulated digesta: 2S albumins are main contributors to the IgE reactivity of short digestion-resistant peptides

BACKGROUND

Most food allergens sensitizing via the gastrointestinal tract are stable proteins that are resistant to pepsin digestion, in particular major peanut allergens, Ara h 2 and Ara h 6. Survival of their large fragments is essential for sensitizing capacity. However, the immunoreactive proteins/peptides to which the immune system of the gastrointestinal tract is exposed during digestion of peanut proteins are unknown. Particularly, the IgE reactivity of short digestion-resistant peptides (SDRPs; <10 kDa) released by gastric digestion under standardized and physiologically relevant in vitro conditions has not been investigated.

OBJECTIVE

The aim of this study was to investigate and identify digestion products of major peanut allergens and in particular to examine IgE reactivity of SDRPs released by pepsin digestion of whole peanut grains.

METHODS

Two-dimensional gel-based proteomics and shotgun peptidomics, immunoblotting with allergen-specific antibodies from peanut-sensitized patients, enzyme-linked immunosorbent inhibition assay and ImmunoCAP tests, including far ultraviolet-circular dichroism spectroscopy were used to identify and characterize peanut digesta.

RESULTS

Ara h 2 and Ara h 6 remained mostly intact, and SDRPs from Ara h 2 were more potent in inhibiting IgE binding than Ara h 1 and Ara 3. Ara h 1 and Ara h 3 exhibited sequential digestion into a series of digestion-resistant peptides with preserved allergenic capacity. A high number of identified SDRPs from Ara h 1, Ara h 2 and Ara h 3 were part of short continuous epitope sequences and possessed substantial allergenic potential.

CONCLUSION AND CLINICAL RELEVANCE

Peanut grain digestion by oral and gastric phase enzymes generates mixture of products, where the major peanut allergens remain intact and their digested peptides have preserved allergenic capacity highlighting their important roles in allergic reactions to peanut.

Clinical Development of Histamine H4 Receptor Antagonists

The discovery of the histamine H₄ receptor (H₄R) provided a new avenue for the exploration of the physiological role of histamine, as well as providing a new drug target for the development of novel antihistamines. The first step in this process was the identification of selective antagonists to help unravel the pharmacology of the H₄R relative to other histamine receptors. The discovery of the selective H₄R antagonist JNJ 7777120 was vital for showing a role for the H₄R in inflammation and pruritus. While this compound has been very successful as a tool for understanding the function of the receptor, it has drawbacks, including a short in vivo half-life and hypoadrenocorticism toxicity in rats and dogs, that prevented advancing it into clinical studies. Further research let to the discovery of JNJ 39758979, which, similar to JNJ 7777120, was a potent and selective H₄R antagonist and showed anti-inflammatory and anti-pruritic activity preclinically. JNJ 39758979 advanced into human clinical studies and showed efficacy in reducing experimental pruritus and in patients with atopic dermatitis. However, development of this compound was terminated due to the occurrence of drug-induced agranulocytosis. This was overcome by developing another H₄R antagonist with a different chemical structure, toreforant, that does not appear to have this side effect. Toreforant has been tested in clinical studies in patients with rheumatoid arthritis, asthma, or psoriasis. In conclusions there have been many H₄R antagonists reported in the literature, but only a few have been studied in humans underscoring the difficulty in finding ligands with all of the properties necessary for testing in the clinic. Nevertheless, the clinical data to date suggests that H₄R antagonists can be beneficial in treating atopic dermatitis and pruritus.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

LPS priming in early life decreases antigen uptake of dendritic cells via NO production

Immunological mechanisms of hygiene hypothesis are expected to develop a novel strategy for allergy prevention. Although a large number of studies has investigated the relation between allergies and infection, little is known about the influence of the exposure to infections on antigen uptake by dendritic cells (DCs). In this study, we examined the effect of lipopolysaccharide (LPS) priming in early life on the antigen uptake ability of DCs by using an original mouse model. LPS priming in juvenile mice decreased the migration of antigen-capturing CD11c⁺ cells in the lymph nodes, but not in aged mice. Besides, the bone marrow-derived DCs (BMDCs) from juvenile LPS-primed mice had the poor antigen uptake ability, and constitutively produced NO through the inducible nitric oxide synthase (iNOS). Interestingly, the LPS priming-induced poor antigen uptake of BMDCs was mimicked by the NO donor, and recovered by the iNOS inhibitor. Additionally, LPS priming in juvenile mice prevented the allergic reactions, but not in aged mice. Our results suggested that an exposure to infections in early life prevents allergy through the alteration of the BM cells fate that is to induce the differentiation of BM cells into inhibitory DCs such as NO-producing DCs.

Epidemiology of severe anaphylaxis: can we use population-based data to understand anaphylaxis?

PURPOSE OF REVIEW

The observed increase in incidence of allergic disease in many regions over the past 3 decades has intensified interest in understanding the epidemiology of severe allergic reactions. We discuss the issues in collecting and interpreting these data and highlight current deficiencies in the current methods of data gathering.

RECENT FINDINGS

Anaphylaxis, as measured by hospital admission rates, is not uncommon and has increased in the United Kingdom, the United States, Canada, and Australia over the last 10-20 years. All large datasets are hampered by a large proportion of uncoded, 'unspecified' causes of anaphylaxis. Fatal anaphylaxis remains a rare event, but appears to be increasing for medication in Australia, Canada, and the United States. The rate of fatal food anaphylaxis is stable in the United Kingdom and the United States, but has increased in Australia. The age distribution for fatal food anaphylaxis is different to other causes, with data suggesting an age-related predisposition to fatal outcomes in teenagers and adults to the fourth decade of life.

SUMMARY

The increasing rates of food and medication allergy (the latter exacerbated by an ageing population) has significant implications for future fatality trends. An improved ability to accurately gather and analyse population-level anaphylaxis data in a harmonized fashion is required, so as to ultimately minimize risk and improve management.

Outstanding animal studies in allergy I. From asthma to food allergy and anaphylaxis

PURPOSE OF REVIEW

Animal models published within the past 18 months on asthma, food allergy and anaphylaxis, all conditions of rising public health concern, were reviewed.

RECENT FINDINGS

While domestic animals spontaneously develop asthma, food allergy and anaphylaxis, in animal models, divergent sensitization and challenge routes, dosages, intervals and antigens are used to induce asthmatic, food allergic or anaphylactic phenotypes. This must be considered in the interpretation of results. Instead of model antigens, gradually relevant allergens such as house dust mite in asthma, and food allergens like peanut, apple and peach in food allergy research were used. Novel engineered mouse models such as a mouse with a T-cell receptor for house dust mite allergen Der p 1, or with transgenic human hFcγR genes, facilitated the investigation of single molecules of interest. Whole-body plethysmography has become a state-of-the-art in-vivo readout in asthma research. In food allergy and anaphylaxis research, novel techniques were developed allowing real-time monitoring of in-vivo effects following allergen challenge. Networks to share tissues were established as an effort to reduce animal experiments in allergy which cannot be replaced by in-vitro measures.

SUMMARY

Natural and artificial animal models were used to explore the pathophysiology of asthma, food allergy and anaphylaxis and to improve prophylactic and therapeutic measures. Especially the novel mouse models mimicking molecular aspects of the complex immune network in asthma, food allergy and anaphylaxis will facilitate proof-of-concept studies under controlled conditions.

Multifactorial Modulation of Food-Induced Anaphylaxis

Prevalence of food-induced anaphylaxis increases progressively and occurs in an unpredictable manner, seriously affecting the quality of life of patients. Intrinsic factors including age, physiological, and genetic features of the patient as well as extrinsic factors such as the intake of drugs and exposure to environmental agents modulate this disorder. It has been proven that diseases, such as mastocytosis, defects in HLA, or filaggrin genes, increase the risk of severe allergic episodes. Certain allergen families such as storage proteins, lipid transfer proteins, or parvalbumins have also been linked to anaphylaxis. Environmental factors such as inhaled allergens or sensitization through the skin can exacerbate or trigger acute anaphylaxis. Moreover, the effect of dietary habits such as the early introduction of certain foods in the diet, and the advantage of the breastfeeding remain as yet unresolved. Interaction of allergens with the intestinal cell barrier together with a set of effector cells represents the primary pathways of food-induced anaphylaxis. After an antigen cross-links the IgEs on the membrane of effector cells, a complex intracellular signaling cascade is initiated, which leads cells to release preformed mediators stored in their granules that are responsible for the acute symptoms of anaphylaxis. Afterward, they can also rapidly synthesize lipid compounds such as prostaglandins or leukotrienes. Cytokines or chemokines are also released, leading to the recruitment and activation of immune cells in the inflammatory microenvironment. Multiple factors that affect food-induced anaphylaxis are discussed in this review, paying special attention to dietary habits and environmental and genetic conditions.

Alternative Anaphylactic Routes: The Potential Role of Macrophages

Anaphylaxis is an acute, life-threatening, multisystem syndrome resulting from the sudden release of mediators from effector cells. There are two potential pathways for anaphylaxis. The first one, IgE-dependent anaphylaxis, is induced by antigen (Ag) cross-linking of Ag-specific IgE bound to the high-affinity IgE receptor (FcεRI) on mast cells and basophils. The second one, IgG-dependent anaphylaxis is induced by Ag cross-linking of Ag-specific IgG bound to IgG receptors (FcγRI, FcγRIIA, FcγRIIB, FcγRIIC, and FcγRIIIA) on macrophages, neutrophils, and basophils. Macrophages exhibit a huge functional plasticity and are capable of exerting their scavenging, bactericidal, and regulatory functions under a wide variety of tissue conditions. Herein, we will review their potential role in the triggering and development of anaphylaxis. Thereby, macrophages, among other immune cells, play a role in both anaphylactic pathways (1) by responding to anaphylactic mediators secreted by mast cells after specific IgE cross-linking or (2) by acting as effector cells in the anaphylactic response mediated by IgG. In this review, we will go over the cellular and molecular mechanisms that take place in the above-mentioned anaphylactic pathways and will discuss the clinical implications in human allergic reactions.

IgE-associated allergic disorders: recent advances in etiology, diagnosis, and treatment

IgE-associated allergic diseases belong to the most common inflammatory conditions. Their clinical manifestation ranges from mild symptoms to life-threatening episodes. Often patients experience a reduction in physical and psychologic well-being and suffer from a decreased quality of life due to disease activity. The continuously rising number of people that are affected by an allergic condition indicates an urgent need for better diagnostics and more efficient treatment options. Recent progress in the understanding of pathophysiologic mechanisms underlying IgE-associated allergic disorders has led to the identification of novel therapeutic targets and the development of drug candidates that are currently under evaluation. In this review, we highlight studies and clinical trials, which have helped to gain further insight in the etiology of IgE-associated allergic conditions as well as advances in the development of diagnostic tools and therapeutic approaches recently published in Allergy (European Journal of Allergy and Clinical Immunology).