As suggested in the preceding sections, SIV and HIV infection lead to chronic immune activation, which creates a pro-inflammatory “cytokine storm.” This storm recruits and activates additional CD4+ T cells into mucosal tissues, providing the virus with a continuous supply of activated memory CD4+ T cells to infect (Mogensen et al. 2010; Wang et al. 2013). Here, CD4 is linked to HIV infectious disease.