Active anaphylaxis in IgE-deficient mice

IgE-Mediated Activation of Mast Cells and Basophils in Health and Disease

Type 2-mediated immune responses protect the body against environmental threats at barrier surfaces, such as large parasites and environmental toxins, and facilitate the repair of inflammatory tissue damage. However, maladaptive responses to typically nonpathogenic substances, commonly known as allergens, can lead to the development of allergic diseases. Type 2 immunity involves a series of prototype TH2 cytokines (IL-4, IL-5, IL-13) and alarmins (IL-33, TSLP) that promote the generation of adaptive CD4+ helper Type 2 cells and humoral products such as allergen-specific IgE. Mast cells and basophils are integral players in this network, serving as primary effectors of IgE-mediated responses. These cells bind IgE via high-affinity IgE receptors (FcεRI) expressed on their surface and, upon activation by allergens, release a variety of mediators that regulate tissue responses, attract and modulate other inflammatory cells, and contribute to tissue repair. Here, we review the biology and effector mechanisms of these cells, focusing primarily on their role in mediating IgE responses in both physiological and pathological contexts.

Pathogenic and Nonpathogenic Antibody Responses in Allergic Diseases

Allergen-specific antibodies, particularly of the IgE class, are a hallmark of many allergic diseases. Yet paradoxically, (1) a proportion of healthy individuals possess allergen-specific IgE without clinical signs of allergy; (2) some, but not all, allergic individuals develop a more severe disease over time or fail to respond to allergen-specific immunotherapy; and (3) allergen-specific IgG antibodies can inhibit IgE-mediated responses but they can also induce allergic reactions. In this review, we discuss the occurrence of and transition between nonpathogenic and pathogenic allergen-specific antibody responses in the light of a two-stage model. We recapitulate different factors and scenarios that may induce different inflammatory conditions and qualitatively distinct allergen-specific T- and B-cell responses, influencing IgE origins and affinities, IgE/IgG(4) ratios, IgG effector functions, antibody glycosylation patterns, Fc and glycan-binding receptor expression and involvement, and ultimately their propensity to elicit allergic responses. Differences in these antibody characteristics may determine the onset of symptomatic allergy and the severity or remission of the disease.

Psychological Stress-Induced Local Immune Response to Food Antigens Increases Pain Signaling Across the Gut in Mice

BACKGROUND AND AIMS

We recently showed that a bacterial infection can break oral tolerance to food and lead to immunoglobulin E (IgE)-dependent mast cell activation and food-induced abdominal pain, which could constitute an important pathogenic mechanism in postinfectious irritable bowel syndrome (IBS). Here, we investigated whether similar immune mechanisms in response to psychological stress lead to food-evoked pain signaling, and thus potentially explain the pathophysiology in a larger group of patients with IBS.

METHODS

Mice were exposed to ovalbumin (OVA) during water avoidance stress (WAS) and re-exposed to OVA 5 weeks later. Nociception was evaluated by visceromotor responses and afferent nerve recordings to intestinal distension, and patch-clamp recordings of sensory neurons incubated with intestinal supernatants. The role of IgE and type 2 immunity was evaluated using pharmacologic and genetic approaches.

RESULTS

Re-exposure to OVA increased pain signaling in the colon and small intestine only in mice exposed to OVA during WAS, in the absence of systemic allergy. OVA-induced increases in pain responses depended on mast cells, IgE, and signal transducer and activator of transcription 6 signaling. Notably, incubation of sensory neurons with ileum and colon supernatants from WAS/OVA+OVA mice lowered their threshold of excitability. Finally, treatment with histamine receptor H1 antagonist pyrilamine blocked the increased sensory neuron excitability, and reduced ileal afferent nerve firing to distension in WAS/OVA+OVA mice.

CONCLUSIONS

Psychological stress induces a type 2 immune response to food antigens, with IgE-mediated mast cell activation and increased pain signaling in the small intestine and colon in response to food. These findings may explain the potential role of psychological stress in food-induced symptoms in IBS.

Beyond classical immunity: Mast cells as signal converters between tissues and neurons

Mast cells are regarded as effectors in immune defense against parasites and venoms and play an essential role in the pathology of allergic diseases. More recently, mast cells have been shown to receive stimuli derived from type 2 immunity, tissue damage, stress, and inflammation. Mast cells then rapidly convert these diverse signals into appropriate, organ-specific protective reflexes that can limit inflammation or reduce tissue damage. In this review, we consider functions of mast cells in sensations-such as pain, itch, and nausea-arising from tissue insults and inflammation and the ensuing protective responses. In light of emerging data highlighting the involvement of mast cells in neuroimmune communication, we also propose that mast cells are "signal converters" linking immunological and tissue states with nervous system responses.

Life-threatening antibodies: The discovery of anaphylaxis

It was at the turn of the 20th century, that immune serum was found both to save children dying from toxins of deadly pathogens, and to kill a dog within minutes following an injection of harmless doses of sea anemone toxins. This means that, before being formally identified in immune serum, antibodies were already known to be both protective and pathogenic. For this provocative finding, Charles Richet was awarded the 1913 Nobel Prize in Physiology or Medicine. Because, as its name said, anaphylaxis was understood as "the contrary of protection," unique mechanisms were found to explain it. Because, as its name did not initially say but finally said, allergy was understood as a reaction "other" than immunity, its symptoms were explained by mechanisms similar to those that explained anaphylaxis. We examined here the intricate relationships between anaphylaxis, allergy and immunity. Progressively anaphylaxis became one among other pathological effects of an immune response, and allergy an inflammatory disease among others. Looking at antibodies back in the past enables us not only to learn where they come from, but also to follow trends that contributed to shape immunology, some of which may persist in today's immunological thinking and say something about the future.

Type 2-polarized memory B cells hold allergen-specific IgE memory

Allergen-specific immunoglobulin E (IgE) antibodies mediate pathology in diseases such as allergic rhinitis and food allergy. Memory B cells (MBCs) contribute to circulating IgE by regenerating IgE-producing plasma cells upon allergen encounter. Here, we report a population of type 2-polarized MBCs defined as CD23hi, IL-4Rαhi, and CD32low at both the transcriptional and surface protein levels. These MBC2s are enriched in IgG1- and IgG4-expressing cells while constitutively expressing germline transcripts for IgE. Allergen-specific B cells from patients with allergic rhinitis and food allergy were enriched in MBC2s. Furthermore, MBC2s generated allergen-specific IgE during sublingual immunotherapy, thereby identifying these cells as a major reservoir for IgE. The identification of MBC2s provides insights into the maintenance of IgE memory, which is detrimental in allergic diseases but could be beneficial in protection against venoms and helminths.

TGFβ prevents IgE-mediated allergic disease by restraining T follicular helper 2 differentiation

Allergic diseases are common, affecting more than 20% of the population. Genetic variants in the TGFβ pathway are strongly associated with atopy. To interrogate the mechanisms underlying this association, we examined patients and mice with Loeys-Dietz syndrome (LDS) who harbor missense mutations in the kinase domain of TGFΒR1/2. We demonstrate that LDS mutations lead to reduced TGFβ signaling and elevated total and allergen-specific IgE, despite the presence of wild-type T regulatory cells in a chimera model. Germinal center activity was enhanced in LDS and characterized by a selective increase in type 2 follicular helper T cells (TFH2). Expression of Pik3cg was increased in LDS TFH cells and associated with reduced levels of the transcriptional repressor SnoN. PI3Kγ/mTOR signaling in LDS naïve CD4+ T cells was elevated after T cell receptor cross-linking, and pharmacologic inhibition of PI3Kγ or mTOR prevented exaggerated TFH2 and antigen-specific IgE responses after oral antigen exposure in an adoptive transfer model. Naïve CD4+ T cells from nonsyndromic allergic individuals also displayed decreased TGFβ signaling, suggesting that our mechanistic discoveries may be broadly relevant to allergic patients in general. Thus, TGFβ plays a conserved, T cell-intrinsic, and nonredundant role in restraining TFH2 development via the PI3Kγ/mTOR pathway and thereby protects against allergic disease.

Mast cells link immune sensing to antigen-avoidance behaviour

The physiological functions of mast cells remain largely an enigma. In the context of barrier damage, mast cells are integrated in type 2 immunity and, together with immunoglobulin E (IgE), promote allergic diseases. Allergic symptoms may, however, facilitate expulsion of allergens, toxins and parasites and trigger future antigen avoidance1-3. Here, we show that antigen-specific avoidance behaviour in inbred mice4,5 is critically dependent on mast cells; hence, we identify the immunological sensor cell linking antigen recognition to avoidance behaviour. Avoidance prevented antigen-driven adaptive, innate and mucosal immune activation and inflammation in the stomach and small intestine. Avoidance was IgE dependent, promoted by Th2 cytokines in the immunization phase and by IgE in the execution phase. Mucosal mast cells lining the stomach and small intestine rapidly sensed antigen ingestion. We interrogated potential signalling routes between mast cells and the brain using mutant mice, pharmacological inhibition, neural activity recordings and vagotomy. Inhibition of leukotriene synthesis impaired avoidance, but overall no single pathway interruption completely abrogated avoidance, indicating complex regulation. Collectively, the stage for antigen avoidance is set when adaptive immunity equips mast cells with IgE as a telltale of past immune responses. On subsequent antigen ingestion, mast cells signal termination of antigen intake. Prevention of immunopathology-causing, continuous and futile responses against per se innocuous antigens or of repeated ingestion of toxins through mast-cell-mediated antigen-avoidance behaviour may be an important arm of immunity.

Immune sensing of food allergens promotes avoidance behaviour

In addition to its canonical function of protection from pathogens, the immune system can also alter behaviour1,2. The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Here, using mouse models of food allergy, we show that allergic sensitization drives antigen-specific avoidance behaviour. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus and central amygdala. Allergen avoidance requires immunoglobulin E (IgE) antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote avoidance requires cysteinyl leukotrienes and growth and differentiation factor 15. Finally, a comparison of C57BL/6 and BALB/c mouse strains revealed a strong effect of the genetic background on the avoidance behaviour. These findings thus point to antigen-specific behavioural modifications that probably evolved to promote niche selection to avoid unfavourable environments.

Clinacanthus nutans aqueous leaves extract exerts anti-allergic activity in preclinical anaphylactic models via alternative IgG pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Allergy is mediated by the crosslinking of immunoglobulins (Ig) -E or -G to their respective receptors, which degranulates mast cells, macrophages, basophils, or neutrophils, releasing allergy-causing mediators. The removal of these mediators such as histamine, platelet-activating factor (PAF) and interleukins (ILs) released by effector cells will alleviate allergy. Clinacanthus nutans (C. nutans), an herbal plant in Southeast Asia, is used traditionally to treat skin rash, an allergic symptom. Previously, we have reported that C. nutans aqueous leaves extract (CNAE) was able to suppress the release of β-hexosaminidase and histamine but not interleukin-4 (IL-4) and tumor necrosis factor-alpha (TNF-α) in the IgE-induced mast cell degranulation model at 5 mg/mL and above. We also found that CNAE could protect rats against ovalbumin-challenged active systemic anaphylaxis (OVA-ASA) through the downregulation and upregulation of certain metabolites using proton nuclear magnetic resonance (¹H-NMR) metabolomics approach.

AIM OF THE STUDY

As allergy could be mediated by both IgE and IgG, we further evaluated the anti-allergy potential of CNAE in both in vitro model of IgG-induced macrophage activation and in vivo anaphylaxis models to further dissect the mechanism of action underlying the anti-allergic properties of CNAE.

MATERIAL & METHODS

The anti-allergy potential of CNAE was evaluated in in vivo anaphylaxis models of ovalbumin-challenged active systemic anaphylaxis (OVA-ASA) and IgE-challenged passive systemic anaphylaxis (PSA) using Sprague Dawley rats as well as IgG-challenged passive systemic anaphylaxis (IgG-PSA) using C57BL/6 mice. Meanwhile, in vitro model of IgG-induced macrophage activation model was performed using IC-21 macrophages. The release of soluble mediators from both IgE and IgG-mediated pathways were measured using enzyme-linked immunosorbent assay (ELISA). The signaling molecules targeted by CNAE were identified by performing Western blot.

RESULTS

IgG, platelet-activating factor (PAF) and IL-6 was suppressed by CNAE in OVA-ASA, but not IgE. In addition, CNAE significantly suppressed PAF and IL-6 in IgG-PSA but did not suppress histamine, IL-4 and leukotrienes C₄ (LTC₄) in IgE-PSA. CNAE also inhibited IL-6 and TNF-α by inhibiting the phosphorylation of ERK1/2 in the IgG-induced macrophage activation model.

CONCLUSION

Overall, our findings supported that CNAE exerts its anti-allergic properties by suppressing the IgG pathway and its mediators by inhibiting ERK1/2 phosphorylation, thus providing scientific evidence supporting its traditional use in managing allergy.

Immune sensing of food allergens promotes aversive behaviour

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

Mast cells in food allergy: Inducing immediate reactions and shaping long-term immunity

Mast cells are distributed throughout the gastrointestinal tract and function as the main effector cells of IgE-mediated allergic reactions to foods. Allergen-induced cross-linking of IgE antibodies bound to high-affinity IgE receptors, FcεRI, on the surface of mast cells triggers their activation, resulting in the release of mediators of immediate hypersensitivity. These mediators rapidly induce both local gastrointestinal and systemic physiological responses including anaphylaxis. Emerging evidence has revealed that, in addition to inciting immediate reactions, mast cells are key regulators of adaptive immunity to foods. In the gastrointestinal mucosa they provide the priming cytokines that initiate and, over time, consolidate adaptive T_H2 responses to ingested allergens as well as TNF and chemokines that orchestrate the recruitment of tissue-infiltrating leukocytes that drive type 2 tissue inflammation. Patients with atopic dermatitis have increased intestinal mast cell numbers and are at a greater risk for food allergy. Recent studies have uncovered a skin-gut axis in which epicutaneous allergen exposure drives intestinal mast cell expansion. The activating effects of IgE antibodies in mast cells are countered by food-specific IgG antibodies that signal via the inhibitory IgG receptor, FcγR2b, suppressing both immediate allergic reactions to foods and the type 2 immune adjuvant activity of mast cells.

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.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Dendritic cell immunoreceptor drives atopic dermatitis by modulating oxidized CaMKII-involved mast cell activation

Allergens have been identified as potential triggers in patients with atopic dermatitis (AD). AD patients are highly sensitive to cockroach allergen. The underlying mechanism, however, remains undetermined. Here, we established a cockroach allergen-induced AD-like mouse model and demonstrated that repeated exposure to cockroach allergen led to aggravated mouse skin inflammation, characterized by increased type 2 immunity, type 2 innate lymphoid cells (ILC2s), and mast cells. Increased skin mast cells were also observed in AD patients. AD mice with mast cell-deficient mice (kitW-sh/W-sh) showed diminished skin inflammation, suggesting that mast cells are required in allergen-induced skin inflammation. Furthermore, dendritic cell immuno-receptor (DCIR) is up-regulated in skin mast cells of AD patients and mediates allergen binding and uptake. DCIR-/- mice or reconstituted kitW-sh/W-sh mice with DCIR-/- mast cells showed a significant reduction in AD-like inflammation. Both in vitro and in vivo analyses demonstrated that DCIR-/- mast cells had reduced IgE-mediated mast cell activation and passive cutaneous anaphylaxis. Mechanistically, DCIR regulates allergen-induced IgE-mediated mast cell ROS generation and oxidation of calmodulin kinase II (ox-CaMKII). ROS-resistant CaMKII (MM-VVδ) prevents allergen-induced mast cell activation and inflammatory mediator release. Our study reveals a previously unrecognized DCIR-ROS-CaMKII axis that controls allergen-induced mast cell activation and AD-like inflammation.

Mouse Models of Food Allergy in the Pursuit of Novel Treatment Modalities

The prevalence of IgE-mediated food allergies has increased dramatically in the past three decades, now affecting up to 10% of the US population. IgE-mediated food allergy is an immunologic disease, involving a variety of cells, including B and T cells, mast cells, basophils, ILC2s, and epithelial cells. Mouse models of food allergy mimic the overall immunologic processes known to exist in humans. Due to the limitations of invasive sampling of human tissue and the similarities of the human and mouse immune systems, comprehensive pathogenesis studies of food allergy have been performed in mouse models. Mouse models have been effective in elucidating the roles of non-oral routes of sensitization and identifying key cells and molecules involved in allergic sensitization. Furthermore, the development of novel therapeutic approaches for food allergy has been accelerated through the use of pre-clinical mouse models. Despite the groundbreaking findings stemming from research in mice, there are continued efforts to improve the translational utility of these models. Here, we highlight the achievements in understanding food allergy development and efforts to bring novel treatment approaches into clinical trials.

Naturally occurring hypothermia promotes survival in severe anaphylaxis

Although hypothermia has received substantial attention as an indicator of severity in anaphylaxis, it has been neglected from the perspective of whether it could act as a disease-modifying factor in this condition. Here, the impact of naturally occurring (spontaneous) hypothermia on anaphylaxis was evaluated in a murine model of ovalbumin (OVA)-induced allergy. Nonextreme changes in the ambient temperature (T_a) were used to modulate the magnitude of spontaneous hypothermia. At a T_a of 24°C, challenge with OVA intraperitoneally or intravenously resulted in a rapid, transient fall in body core temperature, which reached its nadir 4-6°C below baseline in 30 min. This hypothermic response was largely attenuated when the mice were kept at a T_a of 34°C. The T_a-dependent attenuation of hypothermia resulted in a survival rate of only 30%, as opposed to survival of 100% in the condition that favored the development of hypothermia. The protective effect of hypothermia did not involve changes in the rate of mast cell degranulation, as assessed by the concentration of mast cell protease-1 in bodily fluids. On the other hand, hypothermia improved oxygenation of the brain and kidneys, as indicated by higher NAD⁺/NADH ratios. Therefore, it is plausible to propose that naturally occurring hypothermia makes organs more resistant to the anaphylactic insult.

Non-IgE-mediated anaphylaxis

Anaphylaxis is a rapidly evolving, acute, life-threatening reaction that occurs rapidly on contact with a trigger. Anaphylaxis is classically defined as an allergen-driven process that induces specific IgE and the activation of mast cells and basophils through the cross-linking of IgE receptors. However, it is clear that non-IgE-mediated pathways can induce symptoms indistinguishable from those of classic anaphylaxis, and their activation could explain the severity of IgE-mediated anaphylaxis. Indeed, mast cells and basophils can be activated by antibodies against IgE or their receptors, by molecules such as anaphylatoxins, or through G-coupled receptors. Some other allergens can induce antibodies of class IgG that can activate neutrophils to produce a molecule similar to histamine to induce anaphylaxis. Finally, some inflammatory mediators such as bradykinin or prostaglandin can also modulate mast cell and basophil activation as well as directly cause vasodilation and bronchoconstriction, resulting in anaphylaxis-like reactions.

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.

Local immune response to food antigens drives meal-induced abdominal pain

Up to 20% of people worldwide develop gastrointestinal symptoms following a meal¹, leading to decreased quality of life, substantial morbidity and high medical costs. Although the interest of both the scientific and lay communities in this issue has increased markedly in recent years, with the worldwide introduction of gluten-free and other diets, the underlying mechanisms of food-induced abdominal complaints remain largely unknown. Here we show that a bacterial infection and bacterial toxins can trigger an immune response that leads to the production of dietary-antigen-specific IgE antibodies in mice, which are limited to the intestine. Following subsequent oral ingestion of the respective dietary antigen, an IgE- and mast-cell-dependent mechanism induced increased visceral pain. This aberrant pain signalling resulted from histamine receptor H₁-mediated sensitization of visceral afferents. Moreover, injection of food antigens (gluten, wheat, soy and milk) into the rectosigmoid mucosa of patients with irritable bowel syndrome induced local oedema and mast cell activation. Our results identify and characterize a peripheral mechanism that underlies food-induced abdominal pain, thereby creating new possibilities for the treatment of irritable bowel syndrome and related abdominal pain disorders.

Basophils and IgE contribute to mixed connective tissue disease development

BACKGROUND

Mixed connective tissue disease (MCTD) is a rare and complex autoimmune disease that presents mixed features with other connective tissue diseases, such as systemic lupus erythematosus, systemic sclerosis, and myositis. It is characterized by high levels of anti-U1 small nuclear ribonucleoprotein 70k autoantibodies and a high incidence of life-threatening pulmonary involvement. The pathophysiology of MCTD is not well understood, and no specific treatment is yet available for the patients. Basophils and IgE play a role in the development of systemic lupus erythematosus and thus represent new therapeutic targets for systemic lupus erythematosus and other diseases involving basophils and IgE in their pathogenesis.

OBJECTIVE

We sought to investigate the role of basophils and IgE in the pathophysiology of MCTD.

METHODS

Basophil activation status and the presence of autoreactive IgE were assessed in peripheral blood of a cohort of patients with MCTD and in an MCTD-like mouse model. Basophil depletion and IgE-deficient animals were used to investigate the contribution of basophils and IgE in the lung pathology development of this mouse model.

RESULTS

Patients with MCTD have a peripheral basopenia and activated blood basophils overexpressing C-C chemokine receptor 3. Autoreactive IgE raised against the main MCTD autoantigen U1 small nuclear ribonucleoprotein 70k were found in nearly 80% of the patients from the cohort. Basophil activation and IgE anti-U1 small nuclear ribonucleoprotein 70k were also observed in the MCTD-like mouse model along with basophil accumulation in lymph nodes and lungs. Basophil depletion dampened lung pathology, and IgE deficiency prevented its development.

CONCLUSIONS

Basophils and IgE contribute to MCTD pathophysiology and represent new candidate therapeutic targets for patients with MCTD.

IgE and IgG Antibodies as Regulators of Mast Cell and Basophil Functions in Food Allergy

Food allergy is a major health issue, affecting the lives of 8% of U.S. children and their families. There is an urgent need to identify the environmental and endogenous signals that induce and sustain allergic responses to ingested allergens. Acute reactions to foods are triggered by the activation of mast cells and basophils, both of which release inflammatory mediators that lead to a range of clinical manifestations, including gastrointestinal, cutaneous, and respiratory reactions as well as systemic anaphylaxis. Both of these innate effector cell types express the high affinity IgE receptor, FcϵRI, on their surface and are armed for adaptive antigen recognition by very-tightly bound IgE antibodies which, when cross-linked by polyvalent allergen, trigger degranulation. These cells also express inhibitory receptors, including the IgG Fc receptor, FcγRIIb, that suppress their IgE-mediated activation. Recent studies have shown that natural resolution of food allergies is associated with increasing food-specific IgG levels. Furthermore, oral immunotherapy, the sequential administration of incrementally increasing doses of food allergen, is accompanied by the strong induction of allergen-specific IgG antibodies in both human subjects and murine models. These can deliver inhibitory signals via FcγRIIb that block IgE-induced immediate food reactions. In addition to their role in mediating immediate hypersensitivity reactions, mast cells and basophils serve separate but critical functions as adjuvants for type 2 immunity in food allergy. Mast cells and basophils, activated by IgE, are key sources of IL-4 that tilts the immune balance away from tolerance and towards type 2 immunity by promoting the induction of Th2 cells along with the innate effectors of type 2 immunity, ILC2s, while suppressing the development of regulatory T cells and driving their subversion to a pathogenic pro-Th2 phenotype. This adjuvant effect of mast cells and basophils is suppressed when inhibitory signals are delivered by IgG antibodies signaling via FcγRIIb. This review summarizes current understanding of the immunoregulatory effects of mast cells and basophils and how these functions are modulated by IgE and IgG antibodies. Understanding these pathways could provide important insights into innovative strategies for preventing and/or reversing food allergy in patients.

Perturbations to Homeostasis in Experimental Models Revealed Innate Pathways Driving Food Allergy

While type 2 immunity has been conventionally viewed as beneficial against helminths, venoms, and poisons, and harmful in allergy, contemporary research has uncovered its critical role in the maintenance of homeostasis. The initiation of a type 2 immune response involves an intricate crosstalk between structural and immune cells. Structural cells react to physical and chemical tissue perturbations by secreting alarmins, which signal the innate immune system to restore homeostasis. This pathway acts autonomously in the context of sterile injury and in the presence of foreign antigen initiates an adaptive Th2 response that is beneficial in the context of venoms, toxins, and helminths, but not food allergens. The investigation of the triggers and mechanisms underlying food allergic sensitization in humans is elusive because sensitization is a silent process. Therefore, the central construct driving food allergy modeling is based on introducing perturbations of tissue homeostasis along with an allergen which will result in an immunological and clinical phenotype that is consistent with that observed in humans. The collective evidence from multiple models has revealed the pre-eminent role of innate cells and molecules in the elicitation of allergic sensitization. We posit that, with the expanding use of technologies capable of producing formidable datasets, models of food allergy will continue to have an indispensable role to delineate mechanisms and establish causal relationships.

IgE and mast cells: The endogenous adjuvant

Mast cells and IgE are most familiar as the effectors of type I hypersensitivity reactions including anaphylaxis. It is becoming clear however that this pair has important immunomodulatory effects on innate and adaptive cells of the immune system. In this purview, they act as endogenous adjuvants to ignite evolving immune responses, promote the transition of allergic disease into chronic illness and disrupt the development of active mechanisms of tolerance to ingested foods. Suppression of IgE-mediated mast cell activation can be exerted by molecules targeting IgE, FcɛRI or signaling kinases including Syk, or by IgG antibodies acting via inhibitory Fcγ receptors. In 2015 we reviewed the evidence for the adjuvant functions of mast cells. This update includes the original text, incorporates some important developments in the field over the past five years and discusses how interventions targeting these pathways might have promise in the development of strategies to treat allergic disease.

IgE Effector Mechanisms, in Concert with Mast Cells, Contribute to Acquired Host Defense against Staphylococcusaureus

Allergies are considered to represent mal-directed type 2 immune responses against mostly innocuous exogenous compounds. Immunoglobulin E (IgE) antibodies are a characteristic feature of allergies and mediate hypersensitivity against allergens through activation of effector cells, particularly mast cells (MCs). Although the physiological functions of this dangerous branch of immunity have remained enigmatic, recent evidence shows that allergic immune reactions can help to protect against the toxicity of venoms. Because bacteria are a potent alternative source of toxins, we assessed the possible role of allergy-like type 2 immunity in antibacterial host defense. We discovered that the adaptive immune response against Staphylococcus aureus (SA) skin infection substantially improved systemic host defense against secondary SA infections in mice. Moreover, this acquired protection depended on IgE effector mechanisms and MCs. Importantly, our results reveal a previously unknown physiological function of allergic immune responses, IgE antibodies, and MCs in host defense against a pathogenic bacterium.

The Fyn-Stat5 cascade is required for Fcγ receptor-mediated mast cell function

Mast cells, well established effectors in allergic disease, can be activated by numerous stimuli. We previously found that the Fyn-Stat5B pathway is critical for FcεRI-stimulated mast cell function. Because IgG receptors employ similar signaling pathways, we investigated Fyn-Stat5B function downstream of FcγR. We report that FcγR elicits Fyn-dependent Stat5B tyrosine phosphorylation in mast cells. As we previously found for Fyn kinase, Stat5B is indispensable for IgG-mediated mast cell cytokine expression and secretion. However, Stat5B KO macrophages responded normally to FcγR signaling, indicating a lineage-restricted role for Stat5B. This was consistent in vivo, since passive FcγR activation induced anaphylaxis in a macrophage-dominated response even when Stat5B was deleted. We further investigated this lineage restriction using the K/BxN model of inflammatory arthritis. This model exhibits a rapid and transient mast cell-dependent joint inflammation followed days later by a macrophage- and neutrophil-dependent response. Consistent with our hypothesis, Fyn or Stat5B deficiency did not protect mice from late joint swelling, but greatly reduced the early mast cell-dependent response. This was associated with decreased joint and plasma histamine. We conclude that Fyn-Stat5B is a linage-restricted pathway critical for IgG-mediated mast cell responses.

Limonene-induced activation of A2A adenosine receptors reduces airway inflammation and reactivity in a mouse model of asthma

Animal models of asthma have shown that limonene, a naturally occurring terpene in citrus fruits, can reduce inflammation and airway reactivity. However, the mechanism of these effects is unknown. We first performed computational and molecular docking analyses that showed limonene could bind to both A_2A and A_2B receptors. The pharmacological studies were carried out with A_2A adenosine receptor knock-out (A_2AKO) and wild-type (WT) mice using ovalbumin (OVA) to generate the asthma phenotype. We investigated the effects of limonene on lung inflammation and airway responsiveness to methacholine (MCh) and NECA (nonselective adenosine analog) by administering limonene as an inhalation prior to OVA aerosol challenges in one group of allergic mice for both WT and KO. In whole-body plethysmography studies, we observed that airway responsiveness to MCh in WT SEN group was significantly lowered upon limonene treatment but no effect was observed in A_2AKO. Limonene also attenuated NECA-induced airway responsiveness in WT allergic mice with no effect being observed in A_2AKO groups. Differential BAL analysis showed that limonene reduced levels of eosinophils in allergic WT mice but not in A_2AKO. However, limonene reduced neutrophils in sensitized A_2AKO mice, suggesting that it may activate A_2B receptors as well. These data indicate that limonene-induced reduction in airway inflammation and airway reactivity occurs mainly via activation of A_2AAR but A_2B receptors may also play a supporting role.

Mast cell degranulation and histamine release during A/H5N1 influenza infection in influenza-sensitized mice

Here we evaluate the role of mast cells in infection with influenza A/H5N1 virus in immunized mice. CBA mice were immunized intramuscularly with formalin-inactivated A/Vietnam/1194/2004 (H5N1)NIBRG-14 (H5N1). Serum samples were obtained on days 7, 12, 14, 21 after immunization. At day 14, the mice were infected intranasally with the A/Indonesia/5/2005 (H5N1)IDCDC-RG2 (H5N1) influenza virus with half of the animals receiving a mixture of the antihistamines. 67% of the vaccinated mice were protected from the lethality compared to 43% in the PBS-immunized group. Administration of antihistamines increased survival up to 85%–95%. Immunohistochemical examination using CD117 staining of the lungs demonstrated a larger quantity of activated mast cells after infection of immunized mice compared to mock-immunized mice. This was correlated to increased histamine level in the lungs and blood. Our experimental results suggest the involvement of mast cells and the histamine they produce in the pathogenesis of influenza infection in case of incomplete formation of the immune response to vaccination and mismatch of the vaccine and infection influenza viruses.

Mast cells and IgE in defense against lethality of venoms: Possible "benefit" of allergy[]

Physicians think of mast cells and IgE primarily in the context of allergic disorders, including fatal anaphylaxis. This 'bad side' of mast cells and IgE is so well accepted that it can be difficult to think of them in other contexts, particularly those in which they may have beneficial functions. However, there is evidence that mast cells and IgE, as well as basophils (circulating granulocytes whose functions partially overlap with those of mast cells), can contribute to host defense as components of adaptive type 2 immune responses to helminths, ticks and certain other parasites. Accordingly, allergies often are conceptualized as "misdirected" type 2 immune responses, in which IgE antibodies are produced against any of a diverse group of apparently harmless antigens, and against components of animal venoms. Indeed, certain unfortunate patients who have become sensitized to venoms develop severe IgE-associated allergic reactions, including fatal anaphylaxis, upon subsequent venom exposure. In this review, we will describe evidence that mast cells can enhance innate resistance, and survival, to challenge with reptile or arthropod venoms during a first exposure to such venoms. We also will discuss findings indicating that, in mice surviving an initial encounter with venom, acquired type 2 immune responses, IgE antibodies, the high affinity IgE receptor (FcεRI), and mast cells can contribute to acquired resistance to the lethal effects of both honeybee venom and Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against venoms and perhaps other noxious substances.

IgE Contributes to Atherosclerosis and Obesity by Affecting Macrophage Polarization, Macrophage Protein Network, and Foam Cell Formation

OBJECTIVE

By binding to its high-affinity receptor FcεR1, IgE activates mast cells, macrophages, and other inflammatory and vascular cells. Recent studies support an essential role of IgE in cardiometabolic diseases. Plasma IgE level is an independent predictor of human coronary heart disease. Yet, a direct role of IgE and its mechanisms in cardiometabolic diseases remain incompletely understood. Approach and Results: Using atherosclerosis prone Apoe^-/- mice and IgE-deficient Ige^-/- mice, we demonstrated that IgE deficiency reduced atherosclerosis lesion burden, lesion lipid deposition, smooth muscle cell and endothelial cell contents, chemokine MCP (monocyte chemoattractant protein)-1 expression and macrophage accumulation. IgE deficiency also reduced bodyweight gain and increased glucose and insulin sensitivities with significantly reduced plasma cholesterol, triglyceride, insulin, and inflammatory cytokines and chemokines, including IL (interleukin)-6, IFN (interferon)-γ, and MCP-1. From atherosclerotic lesions and peritoneal macrophages from Apoe^-/-Ige^-/- mice that consumed an atherogenic diet, we detected reduced expression of M1 macrophage markers (CD68, MCP-1, TNF [tumor necrosis factor]-α, IL-6, and iNOS [inducible nitric oxide synthase]) but increased expression of M2 macrophage markers (Arg [arginase]-1 and IL-10) and macrophage-sterol-responsive-network molecules (complement C3, lipoprotein lipase, LDLR [low-density lipoprotein receptor]-related protein 1, and TFR [transferrin]) that suppress macrophage foam cell formation. These IgE activities can be reproduced in bone marrow-derived macrophages from wild-type mice, but muted in cells from FcεR1-deficient mice, or blocked by anti-IgE antibody or complement C3 deficiency.

CONCLUSIONS

IgE deficiency protects mice from diet-induced atherosclerosis, obesity, glucose tolerance, and insulin resistance by regulating macrophage polarization, macrophage-sterol-responsive-network gene expression, and foam cell formation.

Inflammation-induced IgE promotes epithelial hyperplasia and tumour growth

IgE is the least abundant circulating antibody class but is constitutively present in healthy tissues bound to resident cells via its high-affinity receptor, FcεRI. The physiological role of endogenous IgE antibodies is unclear but it has been suggested that they provide host protection against a variety of noxious environmental substances and parasitic infections at epithelial barrier surfaces. Here we show, in mice, that skin inflammation enhances levels of IgE antibodies that have natural specificities and a repertoire, VDJ rearrangements and CDRH3 characteristics similar to those of IgE antibodies in healthy tissue. IgE-bearing basophils are recruited to inflamed skin via CXCL12 and thymic stromal lymphopoietin (TSLP)/IL-3-dependent upregulation of CXCR4. In the inflamed skin, IgE/FcεRI-signalling in basophils promotes epithelial cell growth and differentiation, partly through histamine engagement of H1R and H4R. Furthermore, this IgE response strongly drives tumour outgrowth of epithelial cells harbouring oncogenic mutation. These findings indicate that natural IgE antibodies support skin barrier defences, but that during chronic tissue inflammation this role may be subverted to promote tumour growth.

Dynamics of Platelet Behaviors as Defenders and Guardians: Accumulations in Liver, Lung, and Spleen in Mice

Systemic platelet behaviors in experimental animals are often assessed by infusion of isotope-labeled platelets and measuring them under anesthesia. However, such procedures alter, therefore may not reveal, real-life platelet behaviors. 5-Hydroxytryptamine (5HT or serotonin) is present within limited cell-types, including platelets. In our studies, by measuring 5HT as a platelet-marker in non-anesthetized mice, we identified stimulation- and time-dependent accumulations in liver, lung, and/or spleen as important systemic platelet behaviors. For example, intravenous, intraperitoneal, or intragingival injection of lipopolysaccharide (LPS, a cell-wall component of Gram-negative bacteria), interleukin (IL)-1, or tumor necrosis factor (TNF)-α induced hepatic platelet accumulation (HPA) and platelet translocation into the sinusoidal and perisinusoidal spaces or hepatocytes themselves. These events occurred "within a few hours" of the injection, caused hypoglycemia, and exhibited protective or causal effects on hepatitis. Intravenous injection of larger doses of LPS into normal mice, or intravenous antigen-challenge to sensitized mice, induced pulmonary platelet accumulation (PPA), as well as HPA. These reactions occurred "within a few min" of the LPS injection or antigen challenge and resulted in shock. Intravenous injection of 5HT or a catecholamine induced a rapid PPA "within 6 s." Intravenous LPS injection, within a minute, increased the pulmonary catecholamines that mediate the LPS-induced PPA. Macrophage-depletion from liver and spleen induced "day-scale" splenic platelet accumulation, suggesting the spleen is involved in clearing senescent platelets. These findings indicate the usefulness of 5HT as a marker of platelet behaviors, and provide a basis for a discussion of the roles of platelets as both "defenders" and "guardians."

Neutrophil Extracellular Traps in Autoimmunity and Allergy: Immune Complexes at Work

Neutrophil extracellular traps (NETs) have been initially described as main actors in host defense owing to their ability to immobilize and sometimes kill microorganisms. Subsequent studies have demonstrated their implication in the pathophysiology of various diseases, due to the toxic effects of their main components on surrounding tissues. Several distinct NETosis pathways have been described in response to various triggers. Among these triggers, IgG immune complexes (IC) play an important role since they induce robust NET release upon binding to activating FcγRs on neutrophils. Few in vitro studies have documented the mechanisms of IC-induced NET release and evidence about the partners involved is controversial. In vivo, animal models and clinical studies have strongly suggested the importance of IgG IC-induced NET release for autoimmunity and anaphylaxis. In this review, we will focus on two autoimmune diseases in which NETs are undoubtedly major players, systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). We will also discuss anaphylaxis as another example of disease recently associated with IC-induced NET release. Understanding the role of IC-induced NETs in these settings will pave the way for new diagnostic tools and therapeutic strategies.

History of Histamine-Releasing Factor (HRF)/Translationally Controlled Tumor Protein (TCTP) Including a Potential Therapeutic Target in Asthma and Allergy

Histamine-releasing factor (HRF) also known as translationally controlled tumor protein (TCTP) is a highly conserved, ubiquitous protein that has both intracellular and extracellular functions. Here we will highlight the subcloning of the molecule, its clinical implications, as well as an inducible-transgenic mouse. Particular attention will be paid to its extracellular functioning and its potential role as a therapeutic target in asthma and allergy. The cells and the cytokines that are produced when stimulated or primed by HRF/TCTP will be detailed as well as the downstream signaling pathway that HRF/TCTP elicits. While it was originally thought that HRF/TCTP interacted with IgE, the finding that cells not binding IgE also respond to HRF/TCTP called this interaction into question. HRF/TCTP or at least its mouse counterpart appears to interact with some, but not all IgE and IgG molecules. HRF/TCTP has been shown to activate multiple human cells including basophils, eosinophils, T cells, and B cells. Since many of the cells that are activated by HRF/TCTP participate in the allergic response, the extracellular functions of HRF/TCTP could exacerbate the allergic, inflammatory cascade. Particularly exciting is that small molecule agonists of the phosphatase SHIP-1 have been shown to modulate the P13 kinase/AKT pathway and may control inflammatory disorders. This review discusses this possibility in light of HRF/TCTP.

An IgG-induced neutrophil activation pathway contributes to human drug-induced anaphylaxis

Anaphylaxis is a systemic acute hypersensitivity reaction that is considered to depend on allergen-specific immunoglobulin E (IgE) antibodies and histamine release by mast cells and basophils. Nevertheless, allergen-specific IgG antibodies have been proposed to contribute when the allergen is an abundant circulating large molecule, e.g., after infusions of therapeutic antibodies or dextran. Data from animal models demonstrate a pathway involving platelet-activating factor (PAF) release by monocytes/macrophages and neutrophils activated via their Fc gamma receptors (FcγRs). We hypothesized that such a pathway may also apply to small drugs and could be responsible for non–IgE-mediated anaphylaxis and influence anaphylaxis severity in humans. We prospectively conducted a multicentric study of 86 patients with suspected anaphylaxis to neuromuscular-blocking agents (NMBAs) during general anesthesia and 86 matched controls. We found that concentrations of anti-NMBA IgG and markers of FcγR activation, PAF release, and neutrophil activation correlated with anaphylaxis severity. Neutrophils underwent degranulation and NETosis early after anaphylaxis onset, and plasma-purified anti-NMBA IgG triggered neutrophil activation ex vivo in the presence of NMBA. Neutrophil activation could also be observed in patients lacking evidence of classical IgE-dependent anaphylaxis. This study supports the existence of an IgG-neutrophil pathway in human NMBA-induced anaphylaxis, which may aggravate anaphylaxis in combination with the IgE pathway or underlie anaphylaxis in the absence of specific IgE. These results reconcile clinical and experimental data on the role of antibody classes in anaphylaxis and could inform diagnostic approaches to NMBA-induced acute hypersensitivity reactions.

The effects of human parvovirus VP1 unique region in a mouse model of allergic asthma

Evidence has indicated that viral infection increases the risk of developing asthma. Although the association of human parvovirus B19 (B19V) or human bocavirus (HBoV) with respiratory diseases has been reported, little is known about the influence of the B19V-VP1u and HBoV-VP1u proteins on the symptoms of asthma. Herein, we investigated the systemic influence of subcutaneously injected B19V-VP1u and HBoV-VP1u recombinant proteins in an OVA-sensitized asthmatic mouse model. A significantly higher Penh ratio and IgE level were detected in the serum, bronchoalveolar lavage fluid (BALF) and the supernatant of a lymphocyte culture from mice treated with HBoV-VP1u or B19V-VP1u than in a lymphocyte culture from OVA-sensitized mice. Significantly higher levels of serum and BALF IgE, total IgG, IgG1, OVA-specific IgE and OVA-specific IgG1 were detected in mice treated with HBoV-VP1u or B19V-VP1u than in OVA-sensitized mice. Conversely, a significantly lower IgG2a level was detected in mice from the HBoV-VP1u or B19V-VP1u groups than in mice from the OVA group. The mice treated with HBoV-VP1u or B19V-VP1u exhibited more significant lung inflammatory indices, including elevated serum and BALF IL-4, IL-5, IL-10 and IL-13 levels; BALF lymphocyte, neutrophil and eosinophil counts, MMP-9 and MMP-2 activity; and the amount of lymphocyte infiltration, relative to those in the control mice or in those sensitized with OVA. These findings demonstrate that the subcutaneous injection of HBoV-VP1u or B19V-VP1u proteins in OVA-sensitized mice result in elevated asthmatic indices and suggest that human parvoviruses may increase the risk of developing airway inflammation in a mouse model of asthma.

Relationship between various cytokines implicated in asthma

Asthma is a complex disorder involving immunologic, environmental, genetic and other factors. Today, asthma is the most common disease encountered in clinical medicine in both children and adults worldwide. Asthma is characterized by increased responsiveness of the tracheobronchial tree resulting in chronic swelling and inflammation of the airways recognized to be controlled by the T-helper 2 (Th2) lymphocytes, which secrete cytokines to increase the production of IgE by B cells. There are many cytokines implicated in the development of the chronic inflammatory processes that are often observed in asthma. Ultimately, these cytokines cause the release of mediators such as histamine and leukotrienes (LT), which in turn promote airway remodeling, bronchial hyperresponsiveness and bronchoconstriction. The CD4⁺ T-lymphocytes from the airways of asthmatics express a panel of cytokines that represent the Th2 cells. The knowledge derived from numerous experimental and clinical studies have allowed physicians and scientists to understand the normal functions of these cytokines and their roles in the pathogenesis of asthma. The main focus of this review is to accentuate the relationship between various cytokines implicated in human asthma. However, some key findings from animal models will be highlighted to support the discoveries from clinical studies.

Experimental protocol for development of adjuvant-free murine chronic model of allergic asthma

BACKGROUND

Mouse models of allergic asthma play a crucial role in exploring of asthma pathogenesis and testing of novel anti-inflammatory drugs. Widely used acute asthma models usually developed with adjuvant (aluminum hydroxide (alum)) do not reproduce one of the main asthma feature - airway remodeling while chronic asthma model mimic the pathophysiology of human disease. Moreover, the use of alum causes distress in experimental animals and impedes the test of adjuvant-containing drugs. In this study, we aimed to develop a chronic adjuvant-free asthma model with pronounced asthmatic phenotype.

METHODS

Female BALB/c mice were divided into 3 groups. The first group was sensitized with intraperitoneal injections of ovalbumin (OVA) emulsified in aluminum hydroxide on days 0, 14, 28 followed by two stages of intranasally challenge with OVA on days 41-43 and 62-64. The second group was subcutaneously sensitized with the same dose of OVA without adjuvant and challenged on the same days. The third group (negative control) included mice which did not received any kind of treatment (i.e. sensitization and challenge). Serum levels of OVA-specific IgE, IgG2a and IgG1 antibodies were detected by ELISA. Airway hyper-responsiveness was measured by non-invasive plethysmography on days 44 and 65. Bronchoalveolar lavage fluids (BALF) sampled in all groups on days 45 and 66 were analyzed by light microscopy. The left lung was removed for histological analysis. The IL-4 and IFNγ mRNA expression in BALF cells was evaluated by RT-PCR.

RESULTS

The OVA-specific IgE antibody response was two-fold increased in mice from adjuvant-free group compared to the adjuvant group that reflects reorientation of immune response towards Th2 phenotype. At the same time, the level of OVA-specific IgG1 and IgG2a antibodies was increased in the adjuvant group. Airway hyperresponsiveness to methacholine in mice of both experimental groups was two-fold higher than in control. Analysis of cell composition in BAL has shown a significant increase in eosinophil count in both experimental groups that indicate the development of allergic inflammation. Lung histology revealed airway remodeling in both experimental groups including goblet cell hyperplasia/metaplasia, thickening of airway walls, collagen deposition in the wall of distal airways. Additionally, the tendency to develop hypertrophy of bronchial smooth muscle layer was observed. Study of gene expression in BAL cells revealed the increase of IL-4 level in both adjuvant and adjuvant-free groups while IFNγ expression in both experimental groups was similar to control group.

CONCLUSION

We have developed a chronic adjuvant-free mouse asthma model which possesses all necessary features of the disease including airway remodeling and is more suitable for pre-clinical evaluation of novel therapeutic approaches including adjuvant-containing drugs.

Identification of Soluble Mediators in IgG-Mediated Anaphylaxis via Fcγ Receptor: A Meta-Analysis

Background: Anaphylaxis is an acute and life-threatening allergic response. Classically and most commonly, it can be mediated by the crosslinking of allergens to immunoglobulin E (IgE)- high affinity IgE receptor (FcεRI) complex found mostly on mast cells. However, there is another pathway of anaphylaxis that is less well-studied. This pathway known as the alternative pathway is mediated by IgG and its Fc gamma receptor (Fcγ). Though it was not documented in human anaphylaxis, a few studies have found that IgG-mediated anaphylaxis can happen as demonstrated in rodent models of anaphylaxis. In these studies, a variety of soluble mediators were being evaluated and they differ from each study which causes confusion in the suitability, and reliability of choice of soluble mediators to be analyzed for diagnosis or therapeutic purposes. Hence, the objective of this meta-analysis is to identify the potential soluble mediators that are involved in an IgG-mediated anaphylaxis reaction.

Methods: Studies related to IgG-mediated anaphylaxis were sourced from five search engines namely PubMed, Scopus, Ovid, Cochrane Library, and Center for Agricultural Bioscience International (CABI) regardless of publication year. Relevant studies were then reviewed based on specific inclusion factors. The means and standard deviations of each soluble mediator studied were then extracted using ImageJ or Get Data Graph Digitiser software and the data were subjected to meta-analysis.

Results: From our findings, we found that histamine, serotonin, platelet activating factor (PAF), β-hexosaminidase, leukotriene C4 (LTC₄), mucosal mast cell protease-1 (MMCP-1), interleukins (IL)-4,−6, and−13; tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein-1α (MIP-1α) were often being analyzed. Out of these soluble mediators, histamine, PAF, β-hexosaminidase, IL-6, and−13, MIP-1α and TNF-α were more significant with positive effect size and p < 0.001. As study effect was relatively small, we performed publication bias and found that there was publication bias and this could be due to the small sample size studied.

Conclusion: As such, we proposed that through meta-analysis, the potential soluble mediators involved in rodent IgG-mediated anaphylaxis to be histamine, PAF, β-hexosaminidase, IL-6 and−13 and MIP-1α, and TNF-α but will require further studies with larger sample size.

The soluble isoform of human FcɛRI is an endogenous inhibitor of IgE-mediated mast cell responses

BACKGROUND

The soluble isoform of FcɛRI, the high-affinity IgE receptor (sFcεRI), is a protein of the IgE network with poorly defined functions.

OBJECTIVE

To define cellular sources and signals that result in the production of human sFcεRI and study its in vivo functions.

METHODS

FcεRI-transfected human cell lines (MelJuso), human monocyte-derived dendritic cells (moDCs), and murine bone marrow-derived mast cells (MC) were stimulated by FcεRI cross-linking and release of sFcεRI was analyzed (ELISA, Western Blot). Lysosomal-associated membrane protein 1 degranulation assays and human basophil activation tests (BATs) were used to study IgE-dependent activation. Recombinant sFcεRI (rsFcεRI) was used to assess its role in murine models of anaphylaxis with WT (wild-type) and IgE^-/- (IgE-deficient) mice.

RESULTS

Antigen-specific cross-linking of IgE-loaded FcɛRI on MelJuso cells that express the trimeric or tetrameric receptor isoform induced the production of sFcεRI. Using MCs and moDCs, we confirmed that IgE/FcɛRI activation induces sFcɛRI release. We demonstrated that generation of sFcɛRI requires Src phosphorylation and endo/lysosomal acidification. In experimental mouse models, sFcɛRI diminishes the severity of IgE-mediated anaphylaxis. BATs confirmed that, comparable to the anti-IgE monoclonal antibody omalizumab, sFcɛRI is an inhibitor of the human innate IgE effector axis, implying that sFcɛRI and omalizumab potentially inhibit each other in vivo.

CONCLUSION

sFcɛRI is produced after antigen-specific IgE/FcɛRI-mediated activation signals and functions as an endogenous inhibitor of IgE loading to FcɛRI and IgE-mediated activation. Our results imply, therefore, that sFcɛRI contributes to a negative regulatory feedback loop that aims at preventing overshooting responses after IgE-mediated immune activation.

IgG1+ B-cell immunity predates IgE responses in epicutaneous sensitization to foods

BACKGROUND

The generation of IgE-mediated food allergy in humans is silent and only diagnosed upon manifestation of clinical symptoms. While experimental models have been used to investigate some mechanisms of allergic sensitization, the generation of humoral immunity and memory remains to be elucidated. Here, we defined the evolution of allergen-specific B-cell responses during epicutaneous sensitization to foods.

METHODS

Wild-type and genetic knockout animals, and drug or antibody strategies for cell depletion and immunoglobulin signaling blockade were used to investigate epicutaneous sensitization and disease progression; we analyzed allergen-specific germinal centers and IgG1⁺ memory B cells by flow cytometry, evaluated humoral responses, and determined clinical reactivity (anaphylaxis).

RESULTS

Epicutaneous sensitization caused microscopic skin damage, inflammation, and recruitment of activated dendritic cells to the draining lymph nodes. This process generated allergen-specific IgG1⁺ germinal center B cells, serum IgG1, and anaphylaxis that was mediated by the alternative pathway. Whether we used peanut and/or ovalbumin from the egg white for sensitization, the allergen-specific IgG1⁺ memory compartment predominantly exhibited an immature, pro-germinal center phenotype (PDL-2^- CD80^- CD35⁺ CD73⁺ ). Subsequent subclinical exposures to the allergen induced IgE⁺ germinal center B cells, serum IgE, and likely activated the classical pathway of anaphylaxis.

CONCLUSIONS

Our data demonstrate that IgG1⁺ B-cell immunity against food allergens in epicutaneous sensitization precedes the generation of IgE responses. Therefore, the assessment of allergen-specific cellular and humoral IgG1⁺ immunity may help to identify individuals at risk of developing IgE-mediated food allergy and hence provide a window for therapeutic interventions.

Antigen-Specific Human Monoclonal Antibodies from Transgenic Mice

Due to the difficulties found when generating fully human monoclonal antibodies (mAbs) by the traditional method, several efforts have attempted to overcome these problems, with varying levels of success. One approach has been the development of transgenic mice carrying immunoglobulin (Ig) genes in germline configuration. The engineered mouse genome can undergo productive rearrangement in the B-cell population, with the generation of mouse B lymphocytes expressing human Ig (hIg) chains. To avoid the expression of mouse heavy or light chains, the endogenous mouse Ig (mIg) loci must be silenced by gene-targeting techniques. Subsequently, to obtain antigen-specific mAbs, conventional immunization protocols can be followed and the mAb technique used (fusion of activated B cells with mouse myeloma cells, screening, cloning, freezing, and testing) with these animThis chapter summarizes the most common chromatographic mAb andals expressing human Ig genes. This chapter describes the type of transgenic-knockout mice generated for various research groups, provides examples of human mAbs developed by research groups and companies, and includes protocols of immunization, generation, production, and purification of human mAbs from such mice. In addition, it also addresses the problems detected, and includes some of the methods that can be used to analyze functional activities with human mAbs.

The anti-penicillin antibodies levels in sensitive and insensitive people to intradermal skin test

BACKGROUND

The hypersensitivity reaction to penicillin is a public health problem. Immunological responses to penicillin and other beta-lactam antibiotics can be classified into immediate and non-immediate responses. The immediate hypersensitivity is mediated by IgE; however, the non-immediate sensitivity is facilitated by other isotypes of antibody or T lymphocytes.

OBJECTIVE

This research detected the non-IgE antibody value against penicillin in allergic and normal people.

METHODS

Thirty-eight samples from patients with positive or negative intradermal skin testing results of penicillin allergy were included in this study. The total antibody and IgM levels against penicillin G were defined by in-house ELISA test.

RESULTS

The results showed a significant (P< 0.05) elevation in total immunoglobulin and non-IgM anti-penicillin antibody of sensitive groups; however, the anti-penicillin IgM was significantly greater in non-sensitive peoples.

CONCLUSIONS

Although the sensitized people to penicillin cannot be certainly detected with the total antibody, specific IgG and IgM value against penicillin, these values are good indicators for prediction of immediate and late response of the immune system to penicillin.