CD40LG and Alzheimer disease: Therefore, the clinical biomarker of HSV-1 exposure (i.e., IgG seropositivity) is likely to be linked to impaired memory and other cognitive measures, while biomarkers of HSV-1 reactivation or productive infection (i.e., high IgG levels or IgM seropositivity) is linked to AD (Letenneur et al., 2008; Lovheim et al., 2015a; Warren-Gash et al., 2019).