The immunoglobulin responsible for allergic reactions is:

Appeared in: AIIMS Delhi NO-2016

Explanation

IgE is the primary antibody responsible for Type I hypersensitivity reactions, which are commonly known as allergic reactions.
It binds to high-affinity receptors (FcεRI) on the surface of mast cells and basophils.
When an allergen cross-links these bound IgE molecules, it triggers the degranulation of these cells.
This degranulation releases histamine and other inflammatory mediators, causing the classic symptoms of allergy.

Option B: IgA is primarily involved in mucosal immunity and is found in body secretions like saliva, tears, and breast milk; it does not mediate systemic allergic reactions.
Option C: IgM is the first antibody produced in a primary immune response and is a large pentameric molecule effective at activating complement and agglutinating pathogens.
Option D: IgG is the most abundant antibody in the blood, provides long-term (secondary) immunity, and is involved in opsonization and complement activation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Function of Immunoglobulin E (IgE) in Allergic Reactions as background academic context rather than a clinical decision trigger.
Understanding the role of IgE is fundamental for diagnosing allergies through tests like skin prick tests or IgE blood tests (e.g., RAST).
This knowledge informs patient education on allergen avoidance and explains the mechanism of action for anti-allergic medications like antihistamines and mast cell stabilizers.
A nurse's understanding of the IgE-mediated response is critical for recognizing and rapidly managing anaphylaxis, a life-threatening allergic reaction.

How to Approach the Question

First, identify the key terms in the question: 'immunoglobulin' and 'allergic reactions'.
Recognize this as a factual recall question that tests your knowledge of the five classes of immunoglobulins and their primary functions.
Systematically review the main role of each option in your mind: IgA (mucosal), IgM (primary response), IgG (secondary response, most abundant), and IgE (allergies, parasites).
Directly match the function 'allergic reactions' to the corresponding immunoglobulin, which is IgE.

Concept Tested & Keywords

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E6 Microbiology Essentials Sastry 4e Part 1 p. 150-152

E6 Medicine Davidson Principles Practice 24e p. 104-106

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 1382-1384

Practise the full AIIMS Delhi NO-2016

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