Blood and immunity: polysaccharide vaccine response: practice question

A Physiology 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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Physiology · Blood and immunity: polysaccharide vaccine response

Sample item

Infants respond poorly to a pure capsular polysaccharide vaccine but respond well when the same polysaccharide is chemically linked to a carrier protein. What is the main reason for the improvement?

AThe carrier converts IgM to IgE in the infantBThe carrier directly activates natural killer cellsCThe carrier increases the amount of polysaccharide presented on MHC class IDThe carrier protein recruits T cell help for B cells, enabling class switching and memory

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

The answer and the reasoning

D. The carrier protein recruits T cell help for B cells, enabling class switching and memory

Pure polysaccharides are T-independent antigens that produce mainly short-lived IgM. Linking them to a protein lets B cells present carrier peptides on MHC class II to helper T cells, giving class switching, affinity maturation and memory, even in infants.

Option by option

A. The carrier converts IgM to IgE in the infant
Class switching to IgG, not IgE, is the desired outcome.
B. The carrier directly activates natural killer cells
NK cell activation is not the mechanism of conjugate vaccines.
C. The carrier increases the amount of polysaccharide presented on MHC class I
Presentation on MHC class II, not class I, is needed for T cell help to B cells.
D. The carrier protein recruits T cell help for B cells, enabling class switching and memory (correct)
Correct. The carrier protein engages helper T cells for a T-dependent response.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, The carrier protein recruits T cell help for B cells, enabling class switching and memory. Pure polysaccharides are T-independent antigens that produce mainly short-lived IgM.

Why is "The carrier converts IgM to IgE in the infant" not the answer?

Class switching to IgG, not IgE, is the desired outcome.

Why is "The carrier directly activates natural killer cells" not the answer?

NK cell activation is not the mechanism of conjugate vaccines.

Why is "The carrier increases the amount of polysaccharide presented on MHC c…" not the answer?

Presentation on MHC class II, not class I, is needed for T cell help to B cells.

What concept does this question test?

It tests Blood and immunity: polysaccharide vaccine response in Physiology. Linking them to a protein lets B cells present carrier peptides on MHC class II to helper T cells, giving class switching, affinity maturation and memory, even in infants.

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 Blood and immunity: polysaccharide vaccine response?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.