Immunology: lectin complement pathway: 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: lectin complement pathway

Sample item

A serum protein that binds mannose residues on the surface of a bacterium triggers cleavage of C4 and C2 through associated serine proteases, even before any specific antibody is produced. Which pathway is this?

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

The answer and the reasoning

A. Lectin pathway

The lectin pathway is started by mannose-binding lectin or ficolins attaching to carbohydrate patterns on microbes, with MASP-1 and MASP-2 cleaving C4 and C2 to form the C3 convertase C4b2a. It operates as part of innate immunity without antibody. Deficiency of the lectin predisposes infants to recurrent infections in the window after maternal antibody wanes.

Option by option

  • A. Lectin pathway (correct)

    Correct. Carbohydrate recognition by a serum lectin with MASP activation defines the lectin pathway.

  • B. Classical pathway

    The classical pathway is triggered by C1q binding antibody-antigen complexes.

  • C. Alternative pathway

    The alternative pathway starts with spontaneous hydrolysis of C3 and amplification by factors B and D.

  • D. Terminal pathway

    The terminal pathway is the common assembly of C5b to C9 into the membrane attack complex, not an initiating 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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Lectin pathway. The lectin pathway is started by mannose-binding lectin or ficolins attaching to carbohydrate patterns on microbes, with MASP-1 and MASP-2 cleaving C4 and C2 to form the C3 convertase C4b2a.

Why is "Classical pathway" not the answer?

The classical pathway is triggered by C1q binding antibody-antigen complexes.

Why is "Alternative pathway" not the answer?

The alternative pathway starts with spontaneous hydrolysis of C3 and amplification by factors B and D.

Why is "Terminal pathway" not the answer?

The terminal pathway is the common assembly of C5b to C9 into the membrane attack complex, not an initiating pathway.

What concept does this question test?

It tests Immunology: lectin complement pathway in Microbiology. It operates as part of innate immunity without antibody. Deficiency of the lectin predisposes infants to recurrent infections in the window after maternal antibody wanes.

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: lectin complement pathway?

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.