Which co-receptors does HIV use to enter cells?

• A. CD4 and CCR5
• B. CD8 and CXCR4
• C. CCR5 only
• D. CCR5 and CXCR4

Answer: (D)

HIV entry requires two interactions: the primary receptor and a co-receptor. The virus first binds to CD4 on the surface of T cells or macrophages, then engages a chemokine co-receptor to fuse with the cell membrane. The chemokine co-receptors HIV uses are CCR5 and CXCR4. Depending on the viral strain, HIV can be CCR5-tropic, CXCR4-tropic, or dual-tropic, which is why both CCR5 and CXCR4 are required as co-receptors. Early infection often involves CCR5, while CXCR4 can be used later in some individuals. Genetic loss of CCR5 (CCR5-Δ32) confers resistance to CCR5-tropic viruses, underscoring the role of this co-receptor. So the best answer is that HIV can use both CCR5 and CXCR4 as co-receptors.