Antigen receptors are present on which cells?

AIIMS CRE, SNO-2024

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

Both T and B lymphocytes are the principal cells of the adaptive immune system, characterized by specificity and memory.
To achieve specificity, each T and B cell expresses a unique surface receptor that can bind to a specific antigen.
B cells possess B-cell receptors (BCRs), which are membrane-anchored immunoglobulins that recognize intact antigens.
T cells possess T-cell receptors (TCRs), which recognize processed peptide fragments of antigens presented by MHC molecules on other cells.

Option A: This option is incomplete. While T cells do have antigen receptors (TCRs), B cells also have antigen receptors (BCRs), making this statement only partially true.
Option B: This option is incomplete. While B cells have antigen receptors (BCRs), T cells are also a core part of the adaptive immune response and have their own antigen receptors (TCRs).
Option D: Red blood cells (erythrocytes) lack a nucleus and most organelles, and their primary function is oxygen transport. They have surface molecules called antigens (like A, B, Rh) that determine blood type, but they do not have receptors to recognize and respond to foreign pathogens.

Visual 1: Diagram: A B-cell showing the membrane-bound B-cell receptor (BCR) or surface immunoglobulin, capable of binding to a whole, intact antigen.
Visual 2: Diagram: A T-cell showing the T-cell receptor (TCR) interacting with an antigen-presenting cell (APC). The diagram should illustrate that the TCR only recognizes a processed antigen fragment presented on an MHC molecule.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Antigen recognition by lymphocytes as background academic context rather than a clinical decision trigger.
Understanding that both T and B cells have antigen receptors is fundamental to immunology and explains how vaccines work by stimulating specific lymphocytes to create long-lasting memory.
Dysfunction in antigen receptor signaling or self-recognition can lead to autoimmune diseases, where the immune system mistakenly attacks the body's own tissues (e.g., rheumatoid arthritis, lupus).
What if? If a person had a genetic defect preventing the formation of functional T-cell receptors (like in some forms of Severe Combined Immunodeficiency - SCID), they would have a severely compromised immune system, unable to mount a cell-mediated response, leaving them vulnerable to many infections.

How to Approach the Question

First, identify the core concept of the question, which is the location of 'antigen receptors'.
Recall the major cells of the adaptive immune system: T lymphocytes and B lymphocytes.
Consider the primary function of these cells. Both T and B cells must recognize specific foreign invaders (antigens) to initiate an immune response.
This recognition process requires specific receptors. Therefore, it is logical that both cell types would possess them.
Evaluate the options based on this understanding. 'T cells only' and 'B cells only' are too restrictive. 'Red blood cells' are primarily for oxygen transport and have surface antigens for blood typing, not immune recognition receptors.
Conclude that 'Both T and B cells' is the only option that correctly identifies the key players of the adaptive immune response that use antigen receptors.

Concept Tested & Keywords

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