Immunology: chimeric monoclonal antibodies: 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: chimeric monoclonal antibodies

Sample item

Rituximab and infliximab are described as chimeric monoclonal antibodies. Which part of the molecule is of mouse origin?

AThe constant regions of both chainsBThe variable regions of heavy and light chainsCOnly the complementarity determining loopsDThe Fc portion

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

The answer and the reasoning

B. The variable regions of heavy and light chains

Chimeric antibodies combine murine variable regions with human constant regions, which reduces immunogenicity relative to fully murine antibodies. Humanised antibodies retain only the murine complementarity determining regions within a human framework, and fully human antibodies have no murine sequence. Names ending in -ximab, -zumab and -umab indicate these classes.

Option by option

A. The constant regions of both chains
Constant regions are human in chimeric antibodies; making them murine would increase immunogenicity.
B. The variable regions of heavy and light chains (correct)
Correct. Mouse variable domains are joined to human constant domains in a chimeric antibody.
C. Only the complementarity determining loops
Retaining only the murine hypervariable loops describes a humanised antibody.
D. The Fc portion
The Fc portion is human, which helps effector functions and lowers immunogenicity.

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 B, The variable regions of heavy and light chains. Chimeric antibodies combine murine variable regions with human constant regions, which reduces immunogenicity relative to fully murine antibodies.

Why is "The constant regions of both chains" not the answer?

Constant regions are human in chimeric antibodies; making them murine would increase immunogenicity.

Why is "Only the complementarity determining loops" not the answer?

Retaining only the murine hypervariable loops describes a humanised antibody.

Why is "The Fc portion" not the answer?

The Fc portion is human, which helps effector functions and lowers immunogenicity.

What concept does this question test?

It tests Immunology: chimeric monoclonal antibodies in Microbiology. Humanised antibodies retain only the murine complementarity determining regions within a human framework, and fully human antibodies have no murine sequence. Names ending in -ximab, -zumab and -umab indicate these classes.

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: chimeric monoclonal antibodies?

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.