Blood and immunity: serum sickness: 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: serum sickness

Sample item

A man develops fever, an urticarial rash, joint pains and a fall in serum C3 eight days after receiving horse-derived antivenom. Which immune mechanism underlies his illness?

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

The answer and the reasoning

D. Soluble antigen-antibody complexes deposited with complement activation

Serum sickness is a type III hypersensitivity. Antibody made against the foreign protein forms circulating immune complexes that lodge in vessels, joints and kidney, activate complement and consume C3 around a week after exposure.

Option by option

  • A. Sensitised T cells releasing cytokines at the antigen site

    Sensitised T cells mediate type IV hypersensitivity after 48 to 72 hours.

  • B. Antibody directed against antigens fixed on cell surfaces

    Antibody against fixed cell surface antigens is type II hypersensitivity.

  • C. Mast cell degranulation after cross-linking of IgE

    IgE-mediated mast cell degranulation is type I and occurs within minutes.

  • D. Soluble antigen-antibody complexes deposited with complement activation (correct)

    Correct. Type III reactions are caused by immune complexes and complement consumption.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, Soluble antigen-antibody complexes deposited with complement activation. Serum sickness is a type III hypersensitivity.

Why is "Sensitised T cells releasing cytokines at the antigen site" not the answer?

Sensitised T cells mediate type IV hypersensitivity after 48 to 72 hours.

Why is "Antibody directed against antigens fixed on cell surfaces" not the answer?

Antibody against fixed cell surface antigens is type II hypersensitivity.

Why is "Mast cell degranulation after cross-linking of IgE" not the answer?

IgE-mediated mast cell degranulation is type I and occurs within minutes.

What concept does this question test?

It tests Blood and immunity: serum sickness in Physiology. Antibody made against the foreign protein forms circulating immune complexes that lodge in vessels, joints and kidney, activate complement and consume C3 around a week after exposure.

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 Blood and immunity: serum sickness?

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.