Abstract
BackgroundHuman herpesvirus-6 (HHV-6) is a β-herpesvirus with 90% seroprevalence that infects and establishes latency in the central nervous system. Two HHV-6 variants are known: HHV-6A and HHV-6B. Active infection or reactivation of HHV-6 in the brain is associated with neurological disorders, including epilepsy, encephalitis, and multiple sclerosis. In a preliminary study, we found HHV-6B DNA in resected brain tissue from patients with mesial temporal lobe epilepsy (MTLE) and have localized viral antigen to glial fibrillary acidic protein (GFAP)–positive glia in the same brain sections. We sought, first, to determine the extent of HHV-6 infection in brain material resected from MTLE and non-MTLE patients; and second, to establish in vitro primary astrocyte cultures from freshly resected brain material and determine expression of glutamate transporters.Methods and FindingsHHV-6B infection in astrocytes and brain specimens was investigated in resected brain material from MTLE and non-MTLE patients using PCR and immunofluorescence. HHV-6B viral DNA was detected by TaqMan PCR in brain resections from 11 of 16 (69%) additional patients with MTLE and from zero of seven (0%) additional patients without MTLE. All brain regions that tested positive by HHV-6B variant-specific TaqMan PCR were positive for viral DNA by nested PCR. Primary astrocytes were isolated and cultured from seven epilepsy brain resections and astrocyte purity was defined by GFAP reactivity. HHV-6 gp116/54/64 antigen was detected in primary cultured GFAP-positive astrocytes from resected tissue that was HHV-6 DNA positive—the first demonstration of an ex vivo HHV-6–infected astrocyte culture isolated from HHV-6–positive brain material. Previous work has shown that MTLE is related to glutamate transporter dysfunction. We infected astrocyte cultures in vitro with HHV-6 and found a marked decrease in glutamate transporter EAAT-2 expression.ConclusionsOverall, we have now detected HHV-6B in 15 of 24 patients with mesial temporal sclerosis/MTLE, in contrast to zero of 14 with other syndromes. Our results suggest a potential etiology and pathogenic mechanism for MTLE.
Highlights
Human herpesvirus-6 (HHV-6) is a b-herpesvirus first isolated in 1986 from immunosuppressed patients with lymphoproliferative disorders and HIV infection [1]
Primary astrocytes were isolated from fresh brain material obtained during epilepsy brain resection
Range of HHV-6 in normal peripheral blood mononuclear cells (PBMC) has been reported to be 100 copies/106 cells [15], and no statistical difference was observed in quantitative HHV-6B levels in PBMCs isolated from patients with mesial temporal lobe epilepsy (MTLE) compared with those in patients without MTLE
Summary
Human herpesvirus-6 (HHV-6) is a b-herpesvirus first isolated in 1986 from immunosuppressed patients with lymphoproliferative disorders and HIV infection [1]. HHV-6 can establish lifelong latency, with the viral genome persisting in peripheral blood mononuclear cells (PBMCs), salivary glands [4], and the central nervous system (CNS) [5]. HHV-6A has been implicated in multiple sclerosis, and is associated with viral persistence and reactivation in the CNS [9,10]. Active infection or reactivation of HHV-6 in the brain is associated with neurological disorders, including epilepsy, encephalitis, and multiple sclerosis. When the electrical disturbance spreads across the whole brain (a generalized seizure), there may be loss of consciousness and/or the whole body may become rigid or jerk. Head injuries or brain tumors can trigger epilepsy, the cause of most cases of epilepsy is unknown
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