CD4 and HIV-1 infection: It is highly vulnerable to HIV-1 infection [7], [22], related to the subjacent lamina propria which, in health, is densely populated with activated memory T-cells expressing both CD4 and both HIV-1 co-receptors CCR5 and CXCR4, as well as dendritic cells (DCs) and macrophages [6], [7], [22], [66], [67].