Which immunoglobulin is primarily responsible for mediating a Type I hypersensitivity reaction?

SCTIMST Staff Nurse - 2015 (Set-A)

Applied Microbiology & Infection control

Easy

Appeared in: SCTIMST Staff Nurse - 2015 (Set-A)

Explanation

Type I hypersensitivity is an immediate allergic reaction mediated by IgE.
During the sensitization phase, IgE antibodies are produced and bind to the surface of mast cells and basophils.
Upon re-exposure to the allergen, it cross-links the bound IgE, triggering the release of inflammatory mediators like histamine.
This release of mediators causes the classic symptoms of allergy, such as vasodilation, bronchospasm, and edema.

Option A: IgG is primarily involved in Type II (cytotoxic) and Type III (immune complex-mediated) hypersensitivity reactions, not Type I.
Option B: Like IgG, IgM is a key mediator in Type II and Type III hypersensitivity reactions. It is also the first antibody produced in a primary immune response.
Option D: IgA is the main immunoglobulin found in mucosal secretions and is responsible for mucosal immunity, providing a first line of defense in the gut and respiratory tract.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Type I Hypersensitivity and Immunoglobulins as background academic context rather than a clinical decision trigger.
Understanding that IgE mediates Type I reactions is fundamental for nurses to recognize and manage allergic conditions, from mild hay fever to life-threatening anaphylaxis.
Nurses play a crucial role in patient education, teaching individuals with severe allergies how to avoid triggers and correctly use an epinephrine auto-injector (e.g., EpiPen) in an emergency.
What if? If a patient develops a rash 48-72 hours after wearing a new metal watch, the reaction is likely a Type IV (delayed-type) hypersensitivity mediated by T-cells, not IgE. The nursing intervention would focus on topical corticosteroids and advising the patient to avoid contact with the metal (likely nickel).

How to Approach the Question

First, identify the core concepts in the question: 'Type I hypersensitivity' and 'immunoglobulin'.
This is a factual recall question. Your goal is to retrieve the specific antibody class associated with this type of reaction.
Mentally review the four types of hypersensitivity reactions and their primary mediators.
Recall or use a mnemonic (e.g., ACID for Types I-IV: Allergic, Cytotoxic, Immune complex, Delayed) to associate Type I with 'Allergic' and its mediator, IgE.
Evaluate the options: IgG and IgM are linked to Types II and III. IgA is linked to mucosal immunity.
Select the option that correctly pairs Type I hypersensitivity with its immunoglobulin mediator.

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