In type I (immediate) hypersensitivity, the sensitisation phase involves:

• A Formation of IgG antibodies against the antigen that activate complement
• B Cytotoxic T lymphocyte priming against tissue antigens
• C Th2-driven IgE production that binds to high-affinity FcεRI receptors on mast cells and basophils ✓
• D Macrophage engulfment of antigen leading to granuloma formation

Explanation

In type I hypersensitivity, initial allergen exposure induces Th2 cell activation and cytokine secretion (IL-4, IL-13) that drive B cells to switch to IgE production. IgE antibodies bind high-affinity FcεRI receptors on mast cells and basophils, sensitising the individual. Re-exposure crosslinks FcεRI-bound IgE, triggering mast cell degranulation and the early-phase response (histamine, leukotrienes, prostaglandins).

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.