CD4 and HIV infectious disease: Furthermore, brain function in PHIV+ youth may be impacted by lifelong HIV infection, intermittent, or ongoing viral replication in the central nervous system, ongoing neuroinflammation, irreversible central nervous system damage prior to cART initiation, and/or neurotoxic effects of cART, all of which may contribute to the varying effects of CD4% (immune status) compared to viral load (viral replication).