Why does an allergic reaction to allergens like pollen or animal dander trigger immediate symptoms of sneezing, watery eyes, and bronchoconstriction?

Answer and explanation

Correct answer: B. Allergens cross-link IgE on mast cells to trigger histamine and serotonin release

  1. Step 1: An allergy is a Type I hypersensitivity reaction mediated by antibodies.
  2. Step 2: Upon initial exposure to an allergen (pollen, house dust mites, animal dander), plasma cells produce , which binds via its Fc region to high-affinity receptors on tissue mast cells and blood basophils.
  3. Step 3: Upon re-exposure, the allergen cross-links adjacent molecules, triggering explosive degranulation and release of preformed inflammatory mediators, primarily histamine and serotonin.
  4. Step 4: Histamine causes vasodilation, increased capillary permeability (edema, rhinorrhea), and smooth muscle contraction in bronchioles.
Answer
Allergens cross-link membrane-bound IgE antibodies on mast cells and basophils, triggering rapid release of histamine and serotonin
Why not the others: 'Allergens stimulate cytotoxic T-cells to lyse bronchial epithelial cells' describes Type IV cell-mediated delayed hypersensitivity; 'Allergens induce IgM antibodies to activate complement...' describes Type II cytotoxic reactions; 'Allergens bind to insulin receptors...' is unrelated to allergic pathogenesis.

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