Which immunological mechanism is responsible for mediating a Type I immediate hypersensitivity reaction?

Appeared in: NORCET-11 Prelims

Explanation

Type I hypersensitivity is mediated by IgE antibodies bound to mast cells.
Upon re-exposure to the allergen, cross-linking of IgE on mast cells triggers degranulation and release of chemical mediators.
This mechanism leads to rapid onset of symptoms such as urticaria, bronchospasm, and anaphylaxis.

Option A: T lymphocytes and their cytokines mediate Type IV (delayed-type) hypersensitivity, not Type I. Type IV is cell-mediated, not antibody-mediated.
Option C: IgG and IgM antibodies activating complement is the hallmark of Type II (antibody-mediated) hypersensitivity, not Type I. This leads to cell lysis or phagocytosis, not immediate allergic symptoms.
Option D: Deposition of circulating antigen-antibody complexes is the mechanism of Type III (immune complex-mediated) hypersensitivity, not Type I. This causes vasculitis and tissue injury, not immediate allergic reactions.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Immunological mechanism of Type I immediate hypersensitivity reaction as background academic context rather than a clinical decision trigger.
Nurses must recognize signs of Type I hypersensitivity (e.g., urticaria, bronchospasm, anaphylaxis) for rapid intervention.
Immediate administration of epinephrine is critical in anaphylaxis, a severe Type I reaction.
What if? If a patient develops symptoms hours to days after exposure (not immediately), consider Type III or IV hypersensitivity instead of Type I.

How to Approach the Question

Identify the hypersensitivity type in the stem (Type I = immediate, allergy, anaphylaxis).
Recall the immunological mediator for each type (Type I = IgE and mast cells).
Eliminate options involving IgG, IgM, or T cells for Type I questions.
Look for keywords like 'immediate', 'allergy', 'mast cell', and 'IgE' to guide your answer.
Use process of elimination for distractors that fit other hypersensitivity types.

Concept Tested & Keywords

Concept Tested: Immunological mechanism of Type I immediate hypersensitivity reaction
Stem keywords: Type I hypersensitivity, immediate reaction, immunological mechanism
Lead-in keywords: responsible for mediating

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E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 212-214

E6 Pharmacology Katzung 16e p. 1522-1524

Practise the full NORCET-11 Prelims

Attempt every question from this paper in a timed mock, then review the full solution for each one.