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module menu icon Pathophysiology

  • Exposure to potential allergens (e.g. grass pollen, animal dander) in susceptible individuals, leads to formation of allergen-specific immunoglobulin E (IgE) antibodies that bind to the surface of mast cells. On subsequent exposure, the specific allergen interacts with the IgE on the mast cells resulting in the release of chemical mediators including histamine, leukotrienes and prostaglandins. These cause immediate nasal itching, sneezing, vascular dilatation and glandular secretion experienced as congestion and rhinorrhoea.
  • A late-phase reaction follows several hours later, mediated by eosinophils and other inflammatory cells. This results in persistence of characteristic symptoms – sneezing, rhinorrhoea, nasal itching and obstruction. Upper airway inflammation provokes bronchial hyper-reactivity so cough, wheezing and shortness of breath can also be present.
  • Allergens are foreign proteins (e.g. those at the centre of a pollen grain, in the animal saliva present on animal hair and fur, in the faecal pellets of house dust mites and cockroaches and those found in nuts or grains). Metals (e.g. nickel, chromium) and acrylates (e.g. in dental fillings or gel nails) can also elicit an immunological response.
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