Immunology: NK cell markers: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Immunology: NK cell markers

Sample item

Flow cytometry of peripheral blood lymphocytes shows a population that is CD3 negative and positive for CD16 and CD56. Which cell is this, and what is its main function?

ARegulatory T cell, suppressing effector T cells through FOXP3BNatural killer cell, killing infected and tumour cells without prior sensitisationCHelper T cell, activating B cells through CD40 ligandDCytotoxic T cell, killing cells that present antigen on MHC class I

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Natural killer cell, killing infected and tumour cells without prior sensitisation

NK cells are large granular lymphocytes that lack CD3 and express CD16 and CD56. CD16 allows antibody-dependent cell-mediated cytotoxicity, and they kill stressed cells without MHC restriction or prior sensitisation.

Option by option

A. Regulatory T cell, suppressing effector T cells through FOXP3
Regulatory T cells express CD3, CD4, CD25 and FOXP3.
B. Natural killer cell, killing infected and tumour cells without prior sensitisation (correct)
Correct. CD3 negative with CD16 and CD56 defines the natural killer cell.
C. Helper T cell, activating B cells through CD40 ligand
Helper T cells express CD3 and CD4 and signal B cells through CD40 ligand.
D. Cytotoxic T cell, killing cells that present antigen on MHC class I
Cytotoxic T cells express CD3 and CD8 and need antigen presented on MHC class I.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Natural killer cell, killing infected and tumour cells without prior sensitisation. NK cells are large granular lymphocytes that lack CD3 and express CD16 and CD56.

Why is "Regulatory T cell, suppressing effector T cells through FOXP3" not the answer?

Regulatory T cells express CD3, CD4, CD25 and FOXP3.

Why is "Helper T cell, activating B cells through CD40 ligand" not the answer?

Helper T cells express CD3 and CD4 and signal B cells through CD40 ligand.

Why is "Cytotoxic T cell, killing cells that present antigen on MHC class I" not the answer?

Cytotoxic T cells express CD3 and CD8 and need antigen presented on MHC class I.

What concept does this question test?

It tests Immunology: NK cell markers in Microbiology. CD16 allows antibody-dependent cell-mediated cytotoxicity, and they kill stressed cells without MHC restriction or prior sensitisation.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Immunology: NK cell markers?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.