HIV virions bind to host T cells through which receptors?

• A. CD4 and CD8
• B. CD4 and the IL-2 receptor
• C. CD4 and CCR5
• D. CD8 and CCR2

Answer: (C)

HIV entry into T cells requires two interactions: the CD4 receptor and a chemokine coreceptor. The viral envelope protein gp120 first binds to CD4 on the surface of helper T cells, which triggers a conformational change that lets gp120 engage a coreceptor. Most strains in early infection use CCR5 as this coreceptor. Once both CD4 and CCR5 are engaged, gp41 mediates fusion of the viral and cell membranes, allowing entry of the virus. This is why the combination of CD4 with CCR5 is the key receptor pairing for HIV entry. Other options don’t fit because CD8 is not used as a coreceptor, the IL-2 receptor is not involved, and CCR2 is not the HIV coreceptor. (Note: some later-stage strains can use CXCR4 instead of CCR5, but CCR5 is the classic coreceptor associated with initial infection.)