Type I hypersensitivity is mediated by

Appeared in: NORCET 1 - 2020

Explanation

Type I hypersensitivity is also known as an immediate or anaphylactic reaction.
It is triggered when an allergen binds to IgE antibodies that are already attached to the surface of mast cells and basophils.
This binding causes the cells to degranulate and release inflammatory mediators like histamine, leading to allergic symptoms.
Clinical examples include anaphylaxis, allergic asthma, and hay fever.

Option A: IgG antibodies are the primary mediators of Type II (cytotoxic) and Type III (immune complex) hypersensitivity reactions, not Type I.
Option C: IgM antibodies, along with IgG, are involved in mediating Type II and Type III hypersensitivity reactions.
Option D: IgA is primarily found in mucosal secretions (e.g., saliva, tears, breast milk) and provides localized immunity on body surfaces.

Visual 1: Diagram - A flowchart illustrating the mechanism of Type I hypersensitivity. It should show the initial sensitization phase with IgE production and binding to mast cells, followed by the effector phase upon re-exposure, showing allergen cross-linking, mast cell degranulation, and the resulting physiological effects.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mediators of Type I hypersensitivity reactions as background academic context rather than a clinical decision trigger.
A crucial nursing responsibility during patient admission is to obtain a thorough allergy history to prevent exposure to known allergens.
Nurses must be able to rapidly recognize the signs of anaphylaxis (e.g., respiratory distress, hypotension, urticaria) and initiate emergency protocols, including the administration of epinephrine.
Patient education is vital. Nurses teach patients with severe allergies how to avoid triggers and how to use an epinephrine auto-injector (e.g., EpiPen).

How to Approach the Question

First, identify the core concept of the question, which is 'Type I hypersensitivity'.
Recall the four types of hypersensitivity reactions (Gell and Coombs classification).
Associate 'Type I' with its key characteristics: 'Immediate', 'Anaphylactic', and 'Allergy'.
Link this type to its specific immunoglobulin mediator. Remember the mnemonic 'Allerg-E' to associate Allergy/Anaphylaxis with IgE.
Systematically eliminate the other options by recalling their primary roles: IgG/IgM for Type II/III, and IgA for mucosal immunity.

Concept Tested & Keywords

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Practise the full NORCET 1 - 2020

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