During the initial phase of infection, HIV binds to CD4 receptors and co-receptors, such as chemokine (C–C motif) receptor 5 (CCR5) or chemokine (C–X–C motif) receptor 4 (CXCR4), on the host cell surface via the gp120 protein, initiating the viral infection cascade [151]. This evidence concerns the gene CD4 and infection.