Immunology: hybridoma selection: 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: hybridoma selection

Sample item

In producing monoclonal antibodies, mouse spleen B cells are fused with HGPRT-deficient myeloma cells and cultured in HAT medium. Why do only the hybridoma cells survive?

AHypoxanthine is toxic to unfused myeloma cellsBThymidine allows spleen B cells to grow indefinitely in cultureCAminopterin selectively kills spleen B cells but spares myeloma cellsDMyeloma cells cannot use the salvage pathway when aminopterin blocks de novo synthesis

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

The answer and the reasoning

D. Myeloma cells cannot use the salvage pathway when aminopterin blocks de novo synthesis

Aminopterin blocks the de novo purine and pyrimidine pathway, so cells must use the salvage pathway with hypoxanthine and thymidine, which needs HGPRT. Unfused myeloma cells lack HGPRT and die, and unfused spleen cells die because they have a limited life span in culture. Hybrids inherit HGPRT from the spleen cell and immortality from the myeloma cell.

Option by option

A. Hypoxanthine is toxic to unfused myeloma cells
Hypoxanthine is the substrate of the salvage pathway, not a toxin.
B. Thymidine allows spleen B cells to grow indefinitely in culture
Thymidine is a salvage pathway substrate and does not confer immortality.
C. Aminopterin selectively kills spleen B cells but spares myeloma cells
Aminopterin acts on all cells through the de novo pathway and does not discriminate spleen cells from myeloma cells.
D. Myeloma cells cannot use the salvage pathway when aminopterin blocks de novo synthesis (correct)
The enzyme defect leaves myeloma cells unable to salvage nucleotides once the de novo route is blocked.

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 D, Myeloma cells cannot use the salvage pathway when aminopterin blocks de novo synthesis. Aminopterin blocks the de novo purine and pyrimidine pathway, so cells must use the salvage pathway with hypoxanthine and thymidine, which needs HGPRT.

Why is "Hypoxanthine is toxic to unfused myeloma cells" not the answer?

Hypoxanthine is the substrate of the salvage pathway, not a toxin.

Why is "Thymidine allows spleen B cells to grow indefinitely in culture" not the answer?

Thymidine is a salvage pathway substrate and does not confer immortality.

Why is "Aminopterin selectively kills spleen B cells but spares myeloma cells" not the answer?

Aminopterin acts on all cells through the de novo pathway and does not discriminate spleen cells from myeloma cells.

What concept does this question test?

It tests Immunology: hybridoma selection in Microbiology. Unfused myeloma cells lack HGPRT and die, and unfused spleen cells die because they have a limited life span in culture. Hybrids inherit HGPRT from the spleen cell and immortality from the myeloma cell.

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: hybridoma selection?

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.