The presence of human herpes virus – 6 infection markers in the brain tissue of patients with Alzheimer’s disease: a pilot study

Human herpesvirus-6 (HHV-6) belonging to the Betaherpesvirinae subfamily of herpesvirus exhibits lymphotropic and neurotropic affinity and persists in a variety of tissues and body cells. Recent reports have linked HHV-6 infection to the development of a number of CNS disorders. The probable involvement of infectious agents in the development of Alzheimer’s disease (AD) has drawn increasing attention. In this study, the major objective was to determine the presence of HHV-6 and its target cells in the post-mortem brain tissues of AD individuals. Brain specimens of two AD patients were acquired from the McGill Brain Bank. The morphological assessment was performed on the posterior cingulate, the inferior parietal, and the lingual cerebral tissues of the right hemisphere. Monoclonal mouse anti-HHV-6 antibody was used for immunohistochemical detection of HHV-6. A quantitative analysis has further been performed to assess viral antigen expression. The immunopositivity for HHV-6A and B antigens was confirmed in all specimens studied. There were more HHV-6-positive cells in the grey matter (5.95%) than in the white matter (0.07%). In particular, neurons exhibited the greatest HHV-6 positivity, up to 26.44% across brain regions and patients. Astrocytes were the second-most often HHV-6-affected cells, up to 25.95% across brain regions and patients. In some cases, studied AD patients demonstrate up to a quarter
of HHV-6 positive neurons and astrocytes. Less prevalent antigen immunostaining has been shown in oligodendrocytes up to 1.58%. No microglial cells were shown to be positive for the HHV-6 antigen. HHV-6, primarily located in neurons and astrocytes, can have a strong impact on neural homeostasis in AD. This study is a proof of concept and provides a framework for further, more detailed research on the link between HHV-6 and AD.