What is the role of allergic reactions in the pathophysiology of pediatric allergic rhinitis?

Updated: Jun 04, 2021
  • Author: Jack M Becker, MD; Chief Editor: Harumi Jyonouchi, MD  more...
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Answer

Allergic reactions require exposure and then sensitization to allergens. To be sensitized, the patient must be exposed to allergens for a period of time. Sensitization to highly allergenic indoor allergens can occur in children younger than 2 years. Sensitization to outdoor allergens usually occurs when a child is older than 3–5 years, and the average age at presentation is 9–10 years. The allergic reaction begins with the cross-linking of the allergen to 2 adjacent IgE molecules that are bound to high-affinity Fcε receptors on the surface of a mast cell. This cross-linking causes mast cells to degranulate, releasing various mediators. The best-known mediators are histamine, prostaglandin D2, tryptase, heparin, and platelet-activating factor, as well as leukotrienes and other cytokines.

These substances produce 2 types of reactions: immediate and late-phase. The immediate reactions in the nasal mucosa induce acute allergy symptoms (eg, nasal itch, clear nasal discharge, sneezing, congestion). The late-phase reaction occurs hours later, secondary to the recruitment of inflammatory cells into the tissue by the action of mediators (termed chemokines) released by the mast cell. Recruited cells are predominated by eosinophils and basophils, which, in turn, release their inflammatory mediators, leading to continuation of the cascade. In very sensitive individuals, this allergen-induced nasal inflammation causes priming of the nasal mucosa. Primed nasal mucosa becomes hyperresponsive, at which point even nonspecific triggers or small amounts of the antigen can cause significant symptoms.


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