The cells which lack the common characteristic surface markers that can be found on B or T lymphocytes are ca… - BTSC Staff Nurse 31 July-2025

BTSC Staff Nurse 31 July-2025

Applied Physiology

Easy

Appeared in: BTSC Staff Nurse 31 July-2025

Explanation

Natural Killer (NK) cells are a distinct lineage of lymphocytes, separate from B and T cells.
The defining feature of NK cells is the absence of the B-cell receptor (BCR) and T-cell receptor (TCR) complexes, meaning they lack key markers like CD19/CD20 (B cells) and CD3 (T cells).
NK cells are identified by their own characteristic surface markers, most commonly CD16 and CD56.
This unique profile allows them to function as part of the innate immune system, providing rapid defense against virally infected cells and tumors without prior sensitization.

Option A: Phagocytes are a functional class of cells, not a specific lymphocyte lineage. This category includes cells like macrophages and neutrophils, which are defined by their ability to engulf particles.
Option B: Granulocytes (neutrophils, eosinophils, basophils) are a category of white blood cells characterized by the presence of granules in their cytoplasm. They belong to the myeloid lineage, not the lymphoid lineage.
Option D: Mast cells are tissue-resident immune cells that play a central role in allergic (Type I hypersensitivity) reactions by releasing histamine. They are not a subtype of circulating lymphocytes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Differentiation of lymphocyte subtypes based on surface markers as background academic context rather than a clinical decision trigger.
The identification of lymphocyte subsets by their surface markers using a technique called flow cytometry is a cornerstone of modern hematology and immunology. It is essential for diagnosing and classifying leukemias, lymphomas, and immunodeficiency disorders.
Because of their innate ability to kill cancerous cells, NK cells are a major focus of cancer immunotherapy research. Therapies are being developed to enhance NK cell activity or use them to directly target tumors.
What if? If a patient's lab report showed a normal total lymphocyte count but a selective absence of CD16+/CD56+ cells, the nurse should anticipate that the patient has an NK cell deficiency. This places them at a significantly higher risk for severe viral infections (especially herpesviruses) and certain malignancies, requiring protective measures and close monitoring.

How to Approach the Question

First, identify the core concept of the question. It asks to identify a specific cell type based on the absence of certain markers.
Note the keywords: 'lack', 'surface markers', 'B or T lymphocytes'. This points to a cell that is related to lymphocytes but is not a typical B or T cell.
Recall the three main types of lymphocytes: B cells, T cells, and Natural Killer (NK) cells.
Access your knowledge of the defining surface markers for each type. T cells are defined by the T-cell receptor (TCR) and the CD3 complex. B cells are defined by the B-cell receptor (BCR) and markers like CD19 and CD20.
Consider the options in light of this knowledge. NK cells are famously known as the 'third population' of lymphocytes that are defined by the lack of these specific T and B cell markers.
Evaluate the other options to confirm your choice. Phagocytes, granulocytes, and mast cells are different categories of immune cells and are not subtypes of lymphocytes distinguished in this manner.

Concept Tested & Keywords

Concept Tested: Differentiation of lymphocyte subtypes based on surface markers.
Stem keywords: cells, lack, surface markers, B or T lymphocytes
Lead-in keywords: are called
Negative lead-in flag: false

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