Immunology: serum sickness: 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: serum sickness

Sample item

Nine days after receiving equine anti-snake venom, a farmer develops fever, urticaria, joint pains and proteinuria, with a low serum C3. What is the underlying mechanism?

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

The answer and the reasoning

D. Circulating immune complex deposition

Serum sickness is a systemic type III hypersensitivity. Antibody to foreign serum protein forms circulating complexes after about 7 to 14 days, which deposit in vessels, joints and kidneys and consume complement. The primary exposure explains the delay compared with anaphylaxis.

Option by option

  • A. Sensitised T cells releasing cytokines

    T cell-mediated disease is type IV and does not lower complement.

  • B. Cytotoxic antibody against red cells

    Cytotoxic antibody against cells is type II and would not give vasculitic features.

  • C. IgE binding to mast cells

    IgE-mediated anaphylaxis appears within minutes of exposure.

  • D. Circulating immune complex deposition (correct)

    Correct. Circulating immune complexes cause serum sickness.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Circulating immune complex deposition. Serum sickness is a systemic type III hypersensitivity.

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

T cell-mediated disease is type IV and does not lower complement.

Why is "Cytotoxic antibody against red cells" not the answer?

Cytotoxic antibody against cells is type II and would not give vasculitic features.

Why is "IgE binding to mast cells" not the answer?

IgE-mediated anaphylaxis appears within minutes of exposure.

What concept does this question test?

It tests Immunology: serum sickness in Microbiology. Antibody to foreign serum protein forms circulating complexes after about 7 to 14 days, which deposit in vessels, joints and kidneys and consume complement. The primary exposure explains the delay compared with anaphylaxis.

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: serum sickness?

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.