Virology: HIV co-receptors: 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 · Virology: HIV co-receptors

Sample item

A person who is homozygous for the CCR5-delta32 deletion remains HIV negative despite repeated high-risk exposure. What explains this resistance?

AAbsence of the co-receptor needed for entry of R5-tropic strainsBDefective reverse transcriptase in the host cellsCLoss of the integrase enzyme in circulating virusDAbsence of the CD4 receptor on T cells

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

The answer and the reasoning

A. Absence of the co-receptor needed for entry of R5-tropic strains

HIV entry needs binding of gp120 to CD4 followed by a co-receptor, CCR5 for macrophage-tropic strains that dominate transmission and CXCR4 for T-tropic strains. People lacking CCR5 are largely protected against R5 strains. Maraviroc is a drug that blocks this co-receptor.

Option by option

A. Absence of the co-receptor needed for entry of R5-tropic strains (correct)
Correct. Without CCR5, R5-tropic virus cannot complete entry.
B. Defective reverse transcriptase in the host cells
Reverse transcriptase is a viral enzyme and not a host one.
C. Loss of the integrase enzyme in circulating virus
Integrase is a viral enzyme and is not affected by a host gene deletion.
D. Absence of the CD4 receptor on T cells
CD4 expression is normal in these people.

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 A, Absence of the co-receptor needed for entry of R5-tropic strains. HIV entry needs binding of gp120 to CD4 followed by a co-receptor, CCR5 for macrophage-tropic strains that dominate transmission and CXCR4 for T-tropic strains.

Why is "Defective reverse transcriptase in the host cells" not the answer?

Reverse transcriptase is a viral enzyme and not a host one.

Why is "Loss of the integrase enzyme in circulating virus" not the answer?

Integrase is a viral enzyme and is not affected by a host gene deletion.

Why is "Absence of the CD4 receptor on T cells" not the answer?

CD4 expression is normal in these people.

What concept does this question test?

It tests Virology: HIV co-receptors in Microbiology. People lacking CCR5 are largely protected against R5 strains. Maraviroc is a drug that blocks this co-receptor.

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 Virology: HIV co-receptors?

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.