An example of type IV hypersensitivity is?

Appeared in: AIIMS BBSR SNO - 2019

Explanation

Type IV hypersensitivity is also known as delayed-type or cell-mediated hypersensitivity.
It is mediated by T-lymphocytes (T-cells) and their cytokines, not by antibodies.
The reaction is slow to develop, typically appearing 24-72 hours after antigen exposure.
The tuberculin-type reaction, seen in the Mantoux test for tuberculosis, is the classic example of a Type IV reaction.

Option A: The Arthus reaction is a classic example of a Type III (immune complex-mediated) hypersensitivity reaction, not Type IV. It involves the deposition of antigen-antibody complexes in tissues.
Option C: Atopy refers to the genetic predisposition to develop allergic diseases like asthma and hay fever, which are manifestations of Type I (IgE-mediated) hypersensitivity.
Option D: Anaphylactic reactions are severe, systemic manifestations of Type I (immediate) hypersensitivity, mediated by IgE antibodies and mast cell degranulation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Hypersensitivity Reactions as background academic context rather than a clinical decision trigger.
Nurses must understand the delayed nature of Type IV reactions to correctly interpret diagnostic tests like the Mantoux (PPD) test for tuberculosis, which must be read 48-72 hours after administration.
Patient education is crucial for conditions like contact dermatitis (a Type IV reaction), helping patients identify and avoid triggers such as nickel, latex, or poison ivy.
Recognizing the signs of graft rejection in transplant patients, which is primarily a Type IV cell-mediated process, is a critical nursing responsibility for early intervention.

How to Approach the Question

First, identify the core concept of the question, which is 'Type IV hypersensitivity'.
Recall the key features of Type IV reactions: they are 'delayed' (taking 24-72 hours) and 'cell-mediated' (involving T-cells, not antibodies).
Evaluate each option against these features.
Analyze 'Arthus reaction': Recall this is a Type III (immune complex) reaction.
Analyze 'Tuberculin-type reaction': Recognize this as the classic example of a delayed, T-cell-mediated response.
Analyze 'Atopy' and 'Anaphylactic reaction': Identify both as examples of Type I (immediate, IgE-mediated) reactions.

Concept Tested & Keywords

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E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 1 (1-214) pp. 159-161, 163-165

E6 Microbiology Applied AnjuDhir 3e Part 2 p. 112-114

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