The platelet-activating factor pathway in food allergy and anaphylaxis

Secretory and Membrane-Associated Biomarkers of Mast Cell Activation and Proliferation

Mast cells (MCs) are immune cells distributed in many organs and tissues and involved in the pathogenesis of allergic and inflammatory diseases as a major source of pro-inflammatory and vasoactive mediators. MC-related disorders are heterogeneous conditions characterized by the proliferation of MC within tissues and/or MC hyper-reactivity that leads to the uncontrolled release of mediators. MC disorders include mastocytosis, a clonal disease characterized by tissue MC proliferation, and MC activation syndromes that can be primary (clonal), secondary (related to allergic disorders), or idiopathic. Diagnosis of MC disorders is difficult because symptoms are transient, unpredictable, and unspecific, and because these conditions mimic many other diseases. Validation of markers of MC activation in vivo will be useful to allow faster diagnosis and better management of MC disorders. Tryptase, being the most specific MC product, is a widely used biomarker of proliferation and activation. Other mediators, such as histamine, cysteinyl leukotrienes, and prostaglandin D2, are unstable molecules and have limitations in their assays. Surface MC markers, detected by flow cytometry, are useful for the identification of neoplastic MC in mastocytosis but, so far, none of them has been validated as a biomarker of MC activation. Further studies are needed to identify useful biomarkers of MC activation in vivo.

Pathophysiological, Cellular, and Molecular Events of the Vascular System in Anaphylaxis

Anaphylaxis is a systemic hypersensitivity reaction that can be life threatening. Mechanistically, it results from the immune activation and release of a variety of mediators that give rise to the signs and symptoms of this pathological event. For years, most of the research in anaphylaxis has focused on the contribution of the immune component. However, approaches that shed light on the participation of other cellular and molecular agents are necessary. Among them, the vascular niche receives the various signals (e.g., histamine) that elicit the range of anaphylactic events. Cardiovascular manifestations such as increased vascular permeability, vasodilation, hypotension, vasoconstriction, and cardiac alterations are crucial in the pathophysiology of anaphylaxis and are highly involved to the development of the most severe cases. Specifically, the endothelium, vascular smooth muscle cells, and their molecular signaling outcomes play an essential role downstream of the immune reaction. Therefore, in this review, we synthesized the vascular changes observed during anaphylaxis as well as its cellular and molecular components. As the risk of anaphylaxis exists both in clinical procedures and in routine life, increasing our knowledge of the vascular physiology and their molecular mechanism will enable us to improve the clinical management and how to treat or prevent anaphylaxis.

Key Message

Anaphylaxis, the most severe allergic reaction, involves a variety of immune and non-immune molecular signals that give rise to its pathophysiological manifestations. Importantly, the vascular system is engaged in processes relevant to anaphylactic events such as increased vascular permeability, vasodilation, hypotension, vasoconstriction, and decreased cardiac output. The novelty of this review focuses on the fact that new studies will greatly improve the understanding of anaphylaxis when viewed from a vascular molecular angle and specifically from the endothelium. This knowledge will improve therapeutic options to treat or prevent anaphylaxis.

Pathophysiology of Immunologic and Nonimmunologic Systemic Reactions Including Anaphylaxis

There is a myriad of immunologic and nonimmunologic pathways by which the clinical phenotype of anaphylaxis can be produced. An understanding of these pathways is essential for the prevention as well as the treatment of anaphylactic episodes.

Metabolomic profiling revealed altered lipid metabolite levels in childhood food allergy

BACKGROUND

The pathophysiology of childhood food allergy (FA) and its natural history are poorly understood. Clarification of the underlying mechanism may help identify novel biomarkers and strategies for clinical intervention in children with FA.

OBJECTIVE

This study aimed to identify metabolites associated with the development and resolution of FA.

METHODS

The metabolomic profiles of 20 children with FA and 20 healthy controls were assessed by liquid chromatography-tandem mass spectrometry. Comparative analysis was performed to identify metabolites associated with FA and FA resolution. For subjects with FA, serum samples were collected at the time of diagnosis and after resolution to identify the changes in metabolite levels. The selected metabolites were then quantified in a quantification cohort to validate the results. Finally, genome-wide association analysis of the metabolite levels was performed.

RESULTS

The study demonstrated a significantly higher level of sphingolipid metabolites and a lower level of acylcarnitine metabolites in children with FA than those in healthy controls. At diagnosis, subjects with resolving FA had a significantly high level of omega-3 metabolites and a low level of platelet-activating factors compared to persistent FA. However, the level of omega-3 metabolites decreased in children with resolving FA but increased in children with persistent FA during the same time. The quantification data of omega-3-derived resolvins, platelet-activating factor, and platelet-activating factor acetylhydrolase activity further supported these results.

CONCLUSION

The lipid metabolite profile is closely related to childhood FA and FA resolution. This study suggests potential predictive biomarkers and provides insight into the mechanisms underlying childhood FA.

Mechanisms Governing Anaphylaxis: Inflammatory Cells, Mediators, Endothelial Gap Junctions and Beyond

Anaphylaxis is a severe, acute, life-threatening multisystem allergic reaction resulting from the release of a plethora of mediators from mast cells culminating in serious respiratory, cardiovascular and mucocutaneous manifestations that can be fatal. Medications, foods, latex, exercise, hormones (progesterone), and clonal mast cell disorders may be responsible. More recently, novel syndromes such as delayed reactions to red meat and hereditary alpha tryptasemia have been described. Anaphylaxis manifests as sudden onset urticaria, pruritus, flushing, erythema, angioedema (lips, tongue, airways, periphery), myocardial dysfunction (hypovolemia, distributive or mixed shock and arrhythmias), rhinitis, wheezing and stridor. Vomiting, diarrhea, scrotal edema, uterine cramps, vaginal bleeding, urinary incontinence, dizziness, seizures, confusion, and syncope may occur. The traditional (or classical) pathway is mediated via T cells, Th2 cytokines (such as IL-4 and 5), B cell production of IgE and subsequent crosslinking of the high affinity IgE receptor (FcεRI) on mast cells and basophils by IgE-antigen complexes, culminating in mast cell and basophil degranulation. Degranulation results in the release of preformed mediators (histamine, heparin, tryptase, chymase, carboxypeptidase, cathepsin G and tumor necrosis factor alpha (TNF-α), and of de novo synthesized ones such as lipid mediators (cysteinyl leukotrienes), platelet activating factor (PAF), cytokines and growth factors such as vascular endothelial growth factor (VEGF). Of these, histamine, tryptase, cathepsin G, TNF-α, LTC₄, PAF and VEGF can increase vascular permeability. Recent data suggest that mast cell-derived histamine and PAF can activate nitric oxide production from endothelium and set into motion a signaling cascade that leads to dilatation of blood vessels and dysfunction of the endothelial barrier. The latter, characterized by the opening of adherens junctions, leads to increased capillary permeability and fluid extravasation. These changes contribute to airway edema, hypovolemia, and distributive shock, with potentially fatal consequences. In this review, besides mechanisms (endotypes) underlying IgE-mediated anaphylaxis, we also provide a brief overview of IgG-, complement-, contact system-, cytokine- and mast cell-mediated reactions that can result in phenotypes resembling IgE-mediated anaphylaxis. Such classifications can lead the way to precision medicine approaches to the management of this complex disease.

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.

Do Corticosteroids Prevent Biphasic Anaphylaxis?

Anaphylaxis is a severe hypersensitivity reaction that is rapid in onset and can result in death. The pattern of an anaphylactic reaction can be uniphasic (or monophasic), biphasic (also called delayed or late phase), or refractory in nature. The most widely cited definition of biphasic anaphylaxis is a recurrence of anaphylactic symptoms after initial resolution despite no further exposure to the trigger. Corticosteroids are thought by some to prevent the development of biphasic symptoms and, therefore, commonly used in the emergency treatment of anaphylaxis but this has not been systemtically analyzed. In this review, Ovid MEDLINE, Ovid EMBASE, Web of Science, and Scopus were searched for articles using "anaphylaxis" combined with the key terms "biphasic" and/or "corticosteroids" and/or "epinephrine." A total of 31 appropriate studies were identified. Biphasic anaphylactic reactions are more likely to occur in moderate to severe anaphylaxis or when anaphylaxis is not treated with timely epinephrine. Because of the potential detrimental adverse effects of corticosteroids and lack of compelling evidence demonstrating an effective role in reducing anaphylaxis severity or preventing biphasic anaphylaxis, we do not advocate for their routine use in anaphylaxis.

Serum Diamine Oxidase in Pseudoallergy in the Pediatric Population

Histamine intolerance (pseudoallergy) is a poorly investigated type of food hypersensitivity. The main enzyme responsible for histamine degradation in the extracellular matrix is diamine oxidase (DAO). Disturbances in the concentration or activity of DAO may lead to the development of clinical signs of allergy. The aim of the present work was to assess the DAO concentration, peripheral blood morphology, lymphocytes phenotyping (CD3+, CD4+, CD8+, CD19+, NK cells, NKT cells, and activated T-cells), and natural regulatory Treg (nTregs) cell population (CD4+, CD25+, CD127low, and FoxP3) in 34 pediatric patients with histamine-dependent syndromes. Patients were divided into two groups: classical allergy and pseudoallergy on the basis of IgE concentration. The investigation was based on the analysis of peripheral blood samples. A significantly lower serum DAO, both total and specific IgE, concentration was found in the pseudoallergy group compared with the allergy group. There were no significant differences in blood morphology or lymphocyte populations. A similar level of nTreg lymphocytes was also found in both groups, although it was lower than that present in healthy individuals. The findings suggest that the serum DAO is responsible for the symptoms of histamine intolerance. Moreover, a general decrease in nTreg cells in comparison with healthy individuals may lead to symptom aggravation.