CD4 and disease arising from reactivation of latent virus: Through the binding of the viral Env glycoprotein gp120 to the CD4 receptor, followed by interaction with either CCR5 or CXCR4 cellular co-receptors and subsequent membrane fusion mediated by viral gp41, HIV-1 is able to productively infect CD4+ T lymphocytes, resulting in a latent infection in distinct CD4+ T cell differentiation stages [10].