Paper I — 2022 July (Supplementary) (2019 Scheme) — Q10

Paper I

2022 July (Supplementary) (2019 Scheme) · 100 marks · 180 min

Question

Type 1 Hypersensitivity reaction

Q104 marksShort Answers★✓

Answer

Type I hypersensitivity is an immediate, IgE-mediated hypersensitivity reaction.

Mechanism

• On first exposure to an allergen, B cells produce IgE antibodies, which bind to Fc receptors on mast cells and basophils (sensitization)
• On re-exposure, the allergen cross-links the bound IgE molecules, triggering mast cell/basophil degranulation
• Released mediators (histamine, prostaglandins, leukotrienes) cause vasodilatation, increased vascular permeability, smooth muscle contraction, and mucus secretion

Phases

• Immediate reaction: Occurs within minutes, mediated by pre-formed mediators (histamine)
• Late-phase reaction: Occurs 2–24 hours later, mediated by newly synthesized mediators (leukotrienes, cytokines) and recruited eosinophils/other inflammatory cells

Examples

• Anaphylaxis
• Allergic rhinitis (hay fever)
• Bronchial asthma
• Urticaria/angioedema
• Food allergies

Related Concepts

1. 1Type I Hypersensitivity

Other Years Asked

1. 1Type-I hyper sensitivity reaction.2023 January (Supplementary) (2019 Scheme)Short Answer · 4 marks
2. 2Release of which of the following chemical mediators is most likely responsible for this finding2024 December (Supplementary) (2019 Scheme)MCQ · 1 mark
3. 3Which of the following immunoglobulins play a major role in this reaction2024 December (Supplementary) (2019 Scheme)MCQ · 1 mark
4. 4Type I hypersensitivity reaction mediated by ------------------- antibody2024 March (Supplementary) (2019 Scheme)1 mark
5. 5The hypersensitivity reaction associated with this condition is2024 December (Supplementary) (2019 Scheme)MCQ · 1 mark
6. 6Which of the following cytokine is NOT secreted by TH2 cells2024 December (Supplementary) (2019 Scheme)MCQ · 1 mark