NEFL and HIV infectious disease: In HIV infection, CSF NFL levels are elevated both in early and later infection in individuals with and without neurocognitive impairment (Jessen Krut et al. 2014; Peluso et al. 2013), although levels are highest in HAD (Abdulle et al. 2007; Gisslen et al. 2007; Mellgren et al. 2007).