Blood and immunity: natural killer cell recognition: practice question

A Physiology 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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Physiology · Blood and immunity: natural killer cell recognition

Sample item

A virus-infected cell has down-regulated MHC class I to escape CD8 T cells. Which lymphocyte can still kill it, and why?

ACytotoxic T cell, which recognises cells lacking MHC class IBPlasma cell, which secretes antibody against viral peptidesCHelper T cell, which lyses infected cells through CD4DNK cell, activated because inhibitory receptors no longer sense MHC class I

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

The answer and the reasoning

D. NK cell, activated because inhibitory receptors no longer sense MHC class I

NK cells carry inhibitory receptors for MHC class I. When class I is lost from a virus-infected or tumour cell, the inhibition is removed (the missing-self response) and activating signals lead to perforin and granzyme release. CD8 T cells need peptide displayed on class I.

Option by option

A. Cytotoxic T cell, which recognises cells lacking MHC class I
CD8 T cells need peptide on MHC class I and cannot see a cell that has lost it.
B. Plasma cell, which secretes antibody against viral peptides
Plasma cells secrete antibody and do not kill cells directly.
C. Helper T cell, which lyses infected cells through CD4
Helper T cells coordinate responses and do not lyse infected cells.
D. NK cell, activated because inhibitory receptors no longer sense MHC class I (correct)
Correct. Loss of the inhibitory MHC class I signal licenses NK killing.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, NK cell, activated because inhibitory receptors no longer sense MHC class I. NK cells carry inhibitory receptors for MHC class I.

Why is "Cytotoxic T cell, which recognises cells lacking MHC class I" not the answer?

CD8 T cells need peptide on MHC class I and cannot see a cell that has lost it.

Why is "Plasma cell, which secretes antibody against viral peptides" not the answer?

Plasma cells secrete antibody and do not kill cells directly.

Why is "Helper T cell, which lyses infected cells through CD4" not the answer?

Helper T cells coordinate responses and do not lyse infected cells.

What concept does this question test?

It tests Blood and immunity: natural killer cell recognition in Physiology. When class I is lost from a virus-infected or tumour cell, the inhibition is removed (the missing-self response) and activating signals lead to perforin and granzyme release. CD8 T cells need peptide displayed on class I.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Blood and immunity: natural killer cell recognition?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.