Immunology: secondary antibody response: 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: secondary antibody response

Sample item

A child receives a first dose of tetanus toxoid and develops a slowly rising, mainly IgM antibody response. At a booster four weeks later, IgG antitoxin appears within days at a much higher level. Which feature explains the booster response?

ATransplacental passage of maternal IgGBPersistence of IgM from the first doseCMemory B cells with class-switched, high-affinity receptorsDA larger pool of naive B cells

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

The answer and the reasoning

C. Memory B cells with class-switched, high-affinity receptors

The first exposure generates memory B and T cells. On re-exposure these respond faster, with a shorter lag, higher titres and mainly IgG of higher affinity, which is the anamnestic response that boosters exploit.

Option by option

A. Transplacental passage of maternal IgG
Maternal IgG protects newborns and does not explain a booster response in a child.
B. Persistence of IgM from the first dose
IgM has a short half-life and does not produce a high IgG rise.
C. Memory B cells with class-switched, high-affinity receptors (correct)
Correct. Memory B cells produce a rapid, high-titre IgG response on re-exposure.
D. A larger pool of naive B cells
Naive B cells give a primary-type slow response and are not expanded for the booster.

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.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Memory B cells with class-switched, high-affinity receptors. The first exposure generates memory B and T cells.

Why is "Transplacental passage of maternal IgG" not the answer?

Maternal IgG protects newborns and does not explain a booster response in a child.

Why is "Persistence of IgM from the first dose" not the answer?

IgM has a short half-life and does not produce a high IgG rise.

Why is "A larger pool of naive B cells" not the answer?

Naive B cells give a primary-type slow response and are not expanded for the booster.

What concept does this question test?

It tests Immunology: secondary antibody response in Microbiology. On re-exposure these respond faster, with a shorter lag, higher titres and mainly IgG of higher affinity, which is the anamnestic response that boosters exploit.

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: secondary antibody response?

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.