Paper I — 2023 January (Supplementary) (2019 Scheme) — Q10
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Paper I
2023 January (Supplementary) (2019 Scheme) · 100 marks · 180 min
Question
Type-I hyper sensitivity reaction.
Q104 marksShort Answers
Answer
Type I hypersensitivity is an immediate, IgE-mediated hypersensitivity reaction.
Mechanism
On first exposure to an allergen, B cells (with T helper cell assistance) produce IgE antibodies, which bind Fc receptors on mast cells/basophils (sensitization)
On re-exposure, allergen cross-links the bound IgE, triggering degranulation and release of mediators (histamine, prostaglandins, leukotrienes)
These mediators cause vasodilatation, increased vascular permeability, smooth muscle contraction, and mucus secretion
Phases
Immediate reaction (minutes) and late-phase reaction (2–24 hours, involving eosinophils and newly synthesized mediators)
