Identify the type of hypersensitivity related to cell-mediated hypersensitivity.

DSSSB -28 August 2019 (Shift-2)

Pathology & Genetics

Easy

Appeared in: DSSSB -28 August 2019 (Shift-2)

Explanation

Type IV hypersensitivity is also known as delayed-type or cell-mediated hypersensitivity.
It is uniquely mediated by T-lymphocytes (specifically T-helper 1 and cytotoxic T-cells) and macrophages, not by antibodies like the other types.
The reaction has a characteristic delayed onset, typically appearing 24 to 72 hours after exposure to the antigen.
Classic examples include the tuberculin (PPD) skin test for tuberculosis, contact dermatitis from substances like poison ivy or nickel, and transplant rejection.

Option A: Type I hypersensitivity is an immediate reaction mediated by IgE antibodies, mast cells, and basophils. It is not cell-mediated.
Option B: Type III hypersensitivity is caused by the deposition of antigen-antibody (immune) complexes in tissues, which is a form of antibody-mediated response, not cell-mediated.
Option D: Type II hypersensitivity is a cytotoxic reaction where IgG or IgM antibodies bind directly to antigens on cell surfaces, leading to cell destruction. It is antibody-mediated.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Gell and Coombs classification of hypersensitivity reactions as background academic context rather than a clinical decision trigger.
Understanding the different hypersensitivity types is crucial for nurses to recognize and manage patient reactions. For instance, knowing Type IV is delayed explains why a PPD test for tuberculosis is read 48-72 hours after placement, not immediately.
This knowledge is vital for patient education, such as explaining to a patient why a rash from poison ivy (contact dermatitis, a Type IV reaction) appears a day or two after exposure and not right away.
What if? If a patient develops hives, wheezing, and hypotension minutes after receiving a new antibiotic, the nurse should recognize this as a potential Type I (anaphylactic) reaction, not a delayed Type IV reaction. This correct identification prompts immediate emergency intervention, such as administering epinephrine, which is life-saving.

How to Approach the Question

First, identify the key phrase in the question: 'cell-mediated hypersensitivity'.
Recall the Gell and Coombs classification, which divides hypersensitivity reactions into four types.
Mentally separate the antibody-mediated reactions (Types I, II, and III) from the cell-mediated one.
Directly associate the term 'cell-mediated' with Type IV hypersensitivity.
Confirm your choice by quickly reviewing the other options and confirming they are antibody-mediated (Type I is IgE, Type II is cytotoxic IgG/IgM, Type III is immune complex).

Concept Tested & Keywords

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