CD4 and infection: The chemokine receptors CCR5 and CXCR4 are critical coreceptors that facilitate the entry of HIV-1 into host cells, with the former the method of entry early in infection whilst the latter becomes more dominant late in chronic infection.438,439 Initially, the viral protein gp120 binds to the CD4 receptor on the host cell surface which triggers a conformational change in gp120 to expose the chemokine-coreceptor binding sites.