CD4 and HIV infectious disease: The neuropathogenesis of HIV infection begins with the virus particles entering the central nervous system (CNS) during early infection using infected monocytes and CD4+ T lymphocytes that cross the blood–brain barrier (BBB) and subsequently have detrimental effects both directly due to viral replication and indirectly by dysregulating cellular metabolic processes (González-Scarano and Martín-García, 2005; Smith and Wilkins, 2015; Pajkrt et al., 2016).