The cell-mediated immunity is carried out by?

AIIMS Patna NO - 2020

Microbiology

Easy

Appeared in: AIIMS Patna NO - 2020

Explanation

T-lymphocytes are the primary effector cells responsible for carrying out cell-mediated immunity.
This branch of the adaptive immune system targets and eliminates host cells that have become infected with intracellular pathogens (like viruses) or have transformed into cancer cells.
T-cells mature in the thymus and act either by directly killing the target cells (via Cytotoxic T-cells) or by activating other immune cells like macrophages (via Helper T-cells).
The overall category of T-lymphocytes includes multiple subtypes crucial for this response, such as Helper (CD4+), Cytotoxic (CD8+), Regulatory, and Memory T-cells.

Option A: Red blood cells (erythrocytes) are not part of the immune system. Their primary function is to transport oxygen from the lungs to the body's tissues and return carbon dioxide.
Option C: B-lymphocytes are the principal cells of humoral immunity, not cell-mediated immunity. They produce antibodies that circulate in body fluids to neutralize extracellular pathogens.
Option D: This answer is too specific and therefore incomplete. CD4 cells are Helper T-cells, which are a critical subtype of T-lymphocyte that orchestrate the immune response. However, cell-mediated immunity also directly involves other T-cells, most notably Cytotoxic T-cells (CD8+), which perform the actual killing of infected cells.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cell-mediated immunity vs. Humoral immunity as background academic context rather than a clinical decision trigger.
Understanding the role of T-cells is fundamental in clinical practice, especially in immunology and infectious diseases. For instance, the Human Immunodeficiency Virus (HIV) primarily targets and destroys CD4+ T-helper cells.
The depletion of CD4 cells cripples the entire adaptive immune system, particularly cell-mediated immunity, leaving the patient vulnerable to opportunistic infections and certain cancers. This is why the CD4 count is a key marker for monitoring HIV progression and the effectiveness of antiretroviral therapy (ART).
What if? If a patient has a viral infection like influenza, the cell-mediated immune response led by T-lymphocytes would be critical for clearing the infection by killing virus-infected host cells. The humoral response would be more important for preventing future infection by neutralizing free virus particles.

How to Approach the Question

This is a factual recall question testing knowledge of the basic components of the immune system.
First, identify the key term in the question: 'cell-mediated immunity'.
Recall the two major arms of adaptive immunity: humoral and cell-mediated.
Associate humoral immunity with B-lymphocytes and the production of antibodies.
Associate cell-mediated immunity with T-lymphocytes, which act directly on target cells.
Evaluate the options based on this core knowledge. Eliminate 'Red blood cells' as they are not immune cells. Differentiate 'B lymphocytes' (humoral) from 'T lymphocytes' (cell-mediated).

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