Which type of hypersensitivity is mediated by T cells that provoke an inflammatory reaction against exogenous or endogenous antigens?

Appeared in: MP NHM CHO-2024 (Shift-1)

Explanation

Type-IV hypersensitivity is a delayed, cell-mediated immune response.
It is uniquely mediated by T-lymphocytes (T cells), not antibodies, which distinguishes it from Types I, II, and III.
Upon antigen exposure, sensitized T cells release cytokines that cause inflammation and tissue damage, with symptoms typically appearing after 24 to 72 hours.
Classic examples include the tuberculin skin test (Mantoux), contact dermatitis (e.g., from poison ivy), and transplant rejection.

Option A: Type-I hypersensitivity is an immediate reaction mediated by IgE antibodies and mast cells, not T cells.
Option B: Type-II hypersensitivity is a cytotoxic reaction mediated by IgG and IgM antibodies that bind directly to antigens on a cell's surface.
Option C: Type-III hypersensitivity is caused by the deposition of antigen-antibody (immune) complexes in tissues, which then triggers inflammation.

Visual 1: Diagram - A comparative flowchart illustrating the four types of hypersensitivity reactions, highlighting the key mediators (IgE, IgG/IgM, T-cells) and onset time for each.

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 types of hypersensitivity is crucial for nurses in identifying, managing, and educating patients about allergic reactions, autoimmune diseases, and transplant-related complications.
A nurse administering a tuberculin (Mantoux) test must instruct the patient to return in 48-72 hours for a reading, as the underlying Type-IV reaction is delayed and will not be visible immediately.
What if? If a patient developed hives, wheezing, and hypotension within minutes of receiving a penicillin injection, the nurse should suspect a Type-I (anaphylactic) reaction and initiate emergency protocols, not a Type-IV reaction.

How to Approach the Question

First, identify the core of the question: it asks for the hypersensitivity reaction mediated by 'T cells'.
Recall the Gell and Coombs classification, which categorizes hypersensitivity reactions into four types based on their mechanism.
Systematically review the primary mediators for each type: Type I is IgE-mediated, Type II is antibody-dependent cytotoxic (IgG/IgM), and Type III is immune complex-mediated (IgG/IgM).
Recognize that Type IV is distinct as it is 'cell-mediated' or 'delayed-type' and involves T-lymphocytes.
Based on this direct recall, select the option corresponding to Type IV.

Concept Tested & Keywords

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Practise the full MP NHM CHO-2024 (Shift-1)

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