CD4 and HIV infectious disease: Previous studies have demonstrated that CD4+ T-cells are rapidly and severely depleted from the intestinal mucosa following HIV infection due to the direct effects of targeted virus infection and virus-induced Fas-mediated apoptosis, resulting in a loss of mucosal integrity and a reduced capacity to control potential pathogens at mucosal surfaces—thereby triggering local and systemic pro-inflammatory responses [214,215,216,217].