What is the initial receptor/co-receptor interaction exploited by HIV to enter CD4+ T cells?

• A. Binding to CD4 without co-receptors for entry
• B. Binding to CD4 with co-receptors CCR5 or CXCR4 for entry
• C. Binding to MHC II
• D. Binding to Fc receptor

Answer: (B)

HIV entry into CD4+ T cells requires two receptor interactions. The virus first binds to the CD4 receptor on the T cell surface, and this binding enables gp120 to engage a chemokine co-receptor—either CCR5 or CXCR4. Only after this co-receptor engagement do conformational changes activate gp41, driving fusion of the viral envelope with the cell membrane and entry of the viral core. So the key interaction is CD4 binding with a co-receptor such as CCR5 or CXCR4 for entry. MHC II binding or Fc receptor involvement is not part of the entry process.