Immunology: complement: 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: complement

Sample item

An immune complex of IgG bound to antigen activates complement. Which component first binds the Fc region to start this pathway?

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

The answer and the reasoning

D. C1q

The classical pathway begins when C1q binds the Fc of IgM or IgG in an immune complex. The alternative pathway uses C3b, factor B and properdin on microbial surfaces. The lectin pathway uses mannose-binding lectin.

Option by option

  • A. Factor B

    Factor B joins C3b in the alternative pathway.

  • B. Properdin

    Properdin stabilises the alternative pathway C3 convertase.

  • C. C3b

    C3b is generated by the convertases and starts the alternative pathway loop.

  • D. C1q (correct)

    Correct. C1q initiates the classical pathway on antibody-antigen complexes.

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, C1q. The classical pathway begins when C1q binds the Fc of IgM or IgG in an immune complex.

Why is "Factor B" not the answer?

Factor B joins C3b in the alternative pathway.

Why is "Properdin" not the answer?

Properdin stabilises the alternative pathway C3 convertase.

Why is "C3b" not the answer?

C3b is generated by the convertases and starts the alternative pathway loop.

What concept does this question test?

It tests Immunology: complement in Microbiology. The alternative pathway uses C3b, factor B and properdin on microbial surfaces. The lectin pathway uses mannose-binding lectin.

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: complement?

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.