Type I hypersensitivity is mediated by?

Appeared in: AIIMS Patna NO - 2020

Explanation

Type I hypersensitivity is also known as an immediate or anaphylactic reaction.
It is mediated by Immunoglobulin E (IgE) antibodies, which are produced in response to an initial exposure to an allergen.
Upon re-exposure, the allergen binds to IgE on the surface of mast cells and basophils, triggering the release of histamine and other inflammatory mediators.
This rapid release of mediators causes the classic symptoms of allergy, ranging from mild hay fever to life-threatening anaphylaxis.

Option A: IgG is the primary antibody involved in Type II (cytotoxic) and Type III (immune complex) hypersensitivity reactions, not Type I.
Option C: Like IgG, IgM is a key mediator in Type II and Type III hypersensitivity reactions. It is the first antibody produced in a primary immune response but is not the main driver of Type I reactions.
Option D: IgA is the main immunoglobulin found in mucosal secretions (e.g., saliva, tears, and respiratory/gastrointestinal tracts), where it provides localized immunity. It does not mediate systemic Type I reactions.

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 as background academic context rather than a clinical decision trigger.
Rapid recognition of anaphylaxis, a severe Type I reaction, is a critical nursing skill. Symptoms include respiratory distress, hypotension, hives, and angioedema.
Nurses must be prepared to administer emergency treatment for anaphylaxis, which includes epinephrine, antihistamines, corticosteroids, and airway management.
Patient education is key. Nurses should teach patients with known 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 in the question: 'Type I hypersensitivity'.
Recall the classification of the four types of hypersensitivity reactions and their primary mediators.
Associate 'Type I' with 'Immediate', 'Anaphylactic', and 'Allergy'.
Remember the specific immunoglobulin linked to this type of reaction. A common mnemonic is to link the 'E' in IgE with 'Emergency' or 'Allergy'.
Evaluate the options. IgG and IgM are linked to Types II and III. IgA is linked to mucosal immunity. This leaves IgE as the correct answer for Type I.

Concept Tested & Keywords

QNmU3gA-uWPyAwWK-exrfG

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

E6 Pharmacology Katzung 16e p. 1522-1524

E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 1 (1-214) p. 160-162

Practise the full AIIMS Patna NO - 2020

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