Investigators from Uppsala University in Sweden found that HHV-6 IgG reactivity was significantly lower in Alzheimer’s Disease patients compared to controls. The authors suggest reduced immunity may be one reason why past studies have found increased levels of HHV-6 DNA in the brains of Alzheimer Disease (AD) patients compared to controls.
Studies of postmortem brain tissue in AD patients have found an increased prevalence of HHV-6. Elevated rates of HSV1 DNA has also been found in patients carrying a specific ApoE genotype (Lin 2002 ). Serum from fifty Alzheimer Disease (AD) patients and 52 controls was analyzed in a multiplex assay for reactivity to four viruses. Although the HHV-6 IgG response was abnormally low, there was no difference was found for HSV1, varicella virus or cytomegalovirus reactivity.
If this impaired humoral immunity against HHV-6 causes increased HHV-6 reactivation in the brain tissue, the impact is localized because there was no difference in the low level latent HHV-6B virus found in PBMCs in patients compared to controls. This result did not agree with a previous study by Carbone et al that found HHV-6 DNA more frequently in AD patients (23%) compared to controls (4%). The Carbone study also found an increased risk of progression to AD in patients positive for HHV-6 DNA in peripheral blood at baseline (Carbone 2014).
The authors note that further study is necessary to determine whether HHV-6 might be involved in the pathogenesis of AD.
Read the full paper: Westman 2017