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.

An immunocompetent man in his 20s presented with a 24-hour history of severe odynophagia, nausea, vomiting and throat pain. Esophagogastroduodenoscopy (EGD) revealed severe esophagitis with ulcerated mucosa, exudative debris, haemorrhage and multiple erosions. Biopsy of the oesophageal tissue demonstrated marginated chromatin, multinucleated giant cells and molding of nuclei, consistent with herpes simplex virus esophagitis (HSE). Treatment with oral acyclovir led to the complete resolution of symptoms. The patient subsequently developed dysphagia again, 8 months later. EGD showed furrowing and concentric rings typical of eosinophilic esophagitis (EoE), a diagnosis confirmed by biopsy. Treatment with a proton pump inhibitor and swallowed topical corticosteroids led to symptomatic improvement. Thus, HSE can occur in immunocompetent hosts and on occasion, HSE may be a harbinger of EoE, as evidenced by our extensive literature review. Mechanical disruption of the mucosal barrier by viruses, facilitating food allergen penetration, and associated immunological signaling abnormalities may be responsible phenomena requiring further elucidation.