Micro & Immunology · patient case question
In the earliest stage of HIV infection of a host cell, which enzyme is essential?
Patient case: HIV, and a Platelet Count of 18,000
Patient: 42-year-old male
Chief Complaint: Sore mouth and a broken tooth requiring extraction.
Background: HIV positive for eleven years. Recently changed antiretroviral regimen. Brings recent laboratory results.
Medications: Antiretroviral therapy
Vital Signs: BP 122/76 mmHg · HR 78 bpm · RR 16 · T 98.6°F
Findings: Laboratory: CD4 410 cells/µL, viral load undetectable, haemoglobin 13.1 g/dL, PLATELETS 18,000/µL, INR 1.0. Intraorally, removable white plaques on the buccal mucosa and palate that leave an erythematous base when scraped.
Show answer and explanation
Correct answer: A. Reverse transcriptase
- A. CORRECT. HIV is a RETROVIRUS with a single-stranded RNA genome. Immediately after entry and uncoating, REVERSE TRANSCRIPTASE transcribes the viral RNA into double-stranded DNA — the step that must occur first, and the step that defines the retroviral family. It has no proofreading capacity, which is the source of HIV's extraordinary mutation rate and its capacity to develop resistance.
- B. Protease acts LAST, cleaving the gag-pol polyprotein into functional proteins during virion maturation. Protease inhibitors block the final step.
- C. Host DNA polymerase is used later, after integration, to transcribe from the integrated provirus — but it is a host enzyme and not the defining early viral step.
- D. Integrase acts AFTER reverse transcription, inserting the newly made viral DNA into the host genome. It is the second enzymatic step, not the first.
Note: The replication sequence maps directly onto the drug classes: entry (maraviroc, enfuvirtide) → reverse transcription (zidovudine, tenofovir, efavirenz) → integration (raltegravir, dolutegravir) → maturation (ritonavir, darunavir).
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