HIV-1 uses which co-receptor predominantly for infection of macrophages early in HIV disease, and which co-receptor is predominantly used by T-tropic strains in advanced AIDS?
- A CXCR4 for macrophage-tropic strains; CCR5 for T-cell tropic strains
- B CCR5 for macrophage-tropic (R5) strains; CXCR4 for T-tropic (X4) strains in late disease ✓
- C CD4 alone for macrophages; CCR5 plus CXCR4 for T-cells
- D CCR3 for macrophage infection; CCR5 for T-cell infection
Explanation
HIV-1 envelope gp120 binds CD4 first, then requires a co-receptor for membrane fusion. Early/transmitted HIV strains predominantly use CCR5 (R5-tropic/macrophage-tropic) and are responsible for most sexual transmissions. As disease progresses, viral quasi-species may switch to CXCR4 (X4-tropic/T-tropic) usage, correlating with faster CD4 decline. Maraviroc is a CCR5 antagonist that blocks R5-tropic HIV. Individuals homozygous for the CCR5-delta32 deletion are highly resistant to HIV-1 infection. This co-receptor tropism determines drug eligibility for maraviroc.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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