Inflammation and repair: C3 deficiency: practice question

A Pathology 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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Pathology · Inflammation and repair: C3 deficiency

Sample item

A child has repeated severe pyogenic infections with encapsulated bacteria and an immune complex disease. Which complement component deficiency fits best?

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

The answer and the reasoning

B. C3

C3 is central to all pathways and is the major opsonin (C3b). Its deficiency causes severe recurrent pyogenic infections and immune complex disease because immune complexes are not cleared. Terminal component deficiencies mainly cause Neisseria infections.

Option by option

  • A. Factor D

    Factor D deficiency affects only the alternative pathway and gives a milder phenotype.

  • B. C3 (correct)

    Correct. Loss of C3b opsonisation allows recurrent pyogenic infection.

  • C. C5

    C5 deficiency mainly predisposes to Neisseria infections through loss of the membrane attack complex.

  • D. C9

    C9 deficiency causes few problems, mainly mild Neisseria susceptibility.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, C3. C3 is central to all pathways and is the major opsonin (C3b).

Why is "Factor D" not the answer?

Factor D deficiency affects only the alternative pathway and gives a milder phenotype.

Why is "C5" not the answer?

C5 deficiency mainly predisposes to Neisseria infections through loss of the membrane attack complex.

Why is "C9" not the answer?

C9 deficiency causes few problems, mainly mild Neisseria susceptibility.

What concept does this question test?

It tests Inflammation and repair: C3 deficiency in Pathology. Its deficiency causes severe recurrent pyogenic infections and immune complex disease because immune complexes are not cleared. Terminal component deficiencies mainly cause Neisseria infections.

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 Inflammation and repair: C3 deficiency?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.