A 25-year-old woman receives a penicillin injection and develops urticaria, bronchospasm, and hypotension within minutes. Which IgE-mediated cell type degranulates to cause these immediate hypersensitivity (Type I) manifestations?

• A Eosinophils and basophils only
• B Macrophages and dendritic cells
• C Neutrophils and NK cells
• D Mast cells and basophils ✓

Explanation

In Type I (immediate) hypersensitivity, allergen cross-links IgE bound to high-affinity FcεRI receptors on mast cells and basophils, triggering immediate degranulation releasing histamine, tryptase, and heparin. Mast cells are tissue-resident (skin, mucosae, submucosa) and basophils circulate in blood; both mediate the acute anaphylactic response. Eosinophils participate in the late-phase reaction but not the immediate degranulation.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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