Immunology: T cell anergy and co-stimulation: 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: T cell anergy and co-stimulation

Sample item

A naive CD4 T cell binds peptide on MHC class II of an antigen-presenting cell that is not activated and expresses no B7 molecules. What is the most likely outcome for the T cell?

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

The answer and the reasoning

C. Anergy, because signal 1 occurs without CD28 co-stimulation

T cell activation needs signal 1 through the T cell receptor and signal 2 through CD28 binding B7. Antigen recognition without co-stimulation leaves the cell unresponsive, a mechanism of peripheral tolerance.

Option by option

  • A. Full activation with IL-2 secretion and clonal expansion

    Full activation requires both signals, and signal 2 is missing here.

  • B. Immediate apoptosis through perforin and granzyme

    Perforin and granzyme are weapons of cytotoxic cells and do not kill the helper T cell.

  • C. Anergy, because signal 1 occurs without CD28 co-stimulation (correct)

    Correct. Signal 1 without CD28-B7 co-stimulation produces anergy.

  • D. Differentiation into a Th1 effector cell

    Effector differentiation needs activation and cytokines such as IL-12, not a resting presenting cell.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Anergy, because signal 1 occurs without CD28 co-stimulation. T cell activation needs signal 1 through the T cell receptor and signal 2 through CD28 binding B7.

Why is "Full activation with IL-2 secretion and clonal expansion" not the answer?

Full activation requires both signals, and signal 2 is missing here.

Why is "Immediate apoptosis through perforin and granzyme" not the answer?

Perforin and granzyme are weapons of cytotoxic cells and do not kill the helper T cell.

Why is "Differentiation into a Th1 effector cell" not the answer?

Effector differentiation needs activation and cytokines such as IL-12, not a resting presenting cell.

What concept does this question test?

It tests Immunology: T cell anergy and co-stimulation in Microbiology. Antigen recognition without co-stimulation leaves the cell unresponsive, a mechanism of peripheral tolerance.

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 Immunology: T cell anergy and co-stimulation?

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.