Immunology: direct allorecognition: 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: direct allorecognition

Sample item

In the first weeks after a kidney transplant, a large fraction of the recipient's T cells react to the graft by recognising intact donor MHC molecules on dendritic cells that migrated out of the kidney. What is this pathway called?

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

The answer and the reasoning

D. Direct allorecognition

In direct allorecognition, recipient T cells recognise intact donor MHC peptide complexes on donor antigen-presenting cells, which are numerous and cause strong early acute cellular rejection. In indirect recognition, donor proteins are processed and presented on self MHC and drive later rejection and chronic injury.

Option by option

  • A. Superantigen activation

    Superantigens bind outside the peptide groove and cross-link MHC II to the T cell receptor beta chain, which is not graft recognition.

  • B. Indirect allorecognition

    Indirect allorecognition involves recipient antigen-presenting cells presenting processed donor peptides on self MHC.

  • C. Molecular mimicry

    Molecular mimicry refers to cross-reaction between a microbial and a self antigen.

  • D. Direct allorecognition (correct)

    Correct. Recognition of intact donor MHC on donor dendritic cells defines the direct pathway.

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 D, Direct allorecognition. In direct allorecognition, recipient T cells recognise intact donor MHC peptide complexes on donor antigen-presenting cells, which are numerous and cause strong early acute cellular rejection.

Why is "Superantigen activation" not the answer?

Superantigens bind outside the peptide groove and cross-link MHC II to the T cell receptor beta chain, which is not graft recognition.

Why is "Indirect allorecognition" not the answer?

Indirect allorecognition involves recipient antigen-presenting cells presenting processed donor peptides on self MHC.

Why is "Molecular mimicry" not the answer?

Molecular mimicry refers to cross-reaction between a microbial and a self antigen.

What concept does this question test?

It tests Immunology: direct allorecognition in Microbiology. In indirect recognition, donor proteins are processed and presented on self MHC and drive later rejection and chronic injury.

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: direct allorecognition?

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.