A delayed hypersensitivity reaction is primarily mediated by which component of the immune system?

NORCET 1 - 2020

Applied Microbiology & Infection control

Easy

Appeared in: NORCET 1 - 2020

Explanation

Delayed hypersensitivity is classified as a Type IV reaction according to the Gell and Coombs classification.
This type of reaction is uniquely cell-mediated, meaning it is driven by immune cells rather than antibodies.
The primary cells involved are sensitized T-lymphocytes (T-cells), which recognize the antigen and orchestrate an inflammatory response.
The term 'delayed' refers to the fact that the reaction takes 24 to 72 hours to manifest, unlike immediate allergic reactions.
A classic example is the induration (hardening) of the skin seen in a positive tuberculin (Mantoux) test.

Option A: IgE antibodies are the hallmark of Type I (immediate) hypersensitivity reactions, not delayed reactions.
Option B: This is a general term. Specific circulating antibodies like IgG and IgM mediate Type II and Type III reactions, but not Type IV (delayed) hypersensitivity.
Option C: Mast cells and basophils are the effector cells in Type I (immediate) hypersensitivity, activated by IgE antibodies.

Visual 1: Diagram: The four types of hypersensitivity reactions (Gell and Coombs classification), illustrating the key cells and immune mediators for each type (IgE for Type I, IgG/IgM for II/III, T-cells for IV).
Visual 2: Infographic: A comparative timeline showing the onset of symptoms for immediate (Type I) versus delayed (Type IV) hypersensitivity reactions, highlighting the difference in speed.
Visual 3: Illustration: The mechanism of a tuberculin skin test, showing antigen-presenting cells, T-cell activation, and the resulting localized inflammation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types of Hypersensitivity Reactions as background academic context rather than a clinical decision trigger.
Nurses frequently manage conditions involving Type IV hypersensitivity, such as contact dermatitis from latex gloves or medications, and must educate patients on avoiding triggers.
The tuberculin (Mantoux) skin test, a common screening tool for tuberculosis, relies on a Type IV reaction. Nurses administer the test and must accurately interpret the results based on the size of induration after 48-72 hours.
Understanding the difference between reaction types is critical for patient safety. A Type I reaction (e.g., to penicillin) can be life-threatening and requires immediate intervention, while a Type IV reaction (e.g., a rash from the same drug) develops slowly and is managed differently.

How to Approach the Question

First, identify the key phrase in the question: 'delayed hypersensitivity reaction'.
Recall the four types of hypersensitivity reactions (Gell and Coombs classification).
Associate the term 'delayed' specifically with Type IV hypersensitivity.
Remember the fundamental distinction: Types I, II, and III are primarily mediated by antibodies, whereas Type IV is cell-mediated.
Evaluate the options based on this distinction. 'Sensitized T-lymphocytes' are the key players in cell-mediated immunity.
Systematically eliminate the other options by linking them to their correct hypersensitivity types: IgE and mast cells are for Type I, and circulating antibodies are for Types II and III.

Concept Tested & Keywords

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