Research Article: Association of Human Herpesvirus-6B with Mesial Temporal Lobe Epilepsy

Date Published: May 29, 2007

Publisher: Public Library of Science

Author(s): Julie Fotheringham, Donatella Donati, Nahid Akhyani, Anna Fogdell-Hahn, Alexander Vortmeyer, John D Heiss, Elizabeth Williams, Steven Weinstein, Derek A Bruce, William D Gaillard, Susumu Sato, William H Theodore, Steven Jacobson, Manuel Graeber

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.

Partial Text: Human herpesvirus-6 (HHV-6) is a β-herpesvirus first isolated in 1986 from immunosuppressed patients with lymphoproliferative disorders and HIV infection [1]. HHV-6 infects most humans between 6 and 12 mo of age [2], and more than 90% of the general population is seropositive [3]. After primary infection, 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-6 DNA has been detected in the cerebrospinal fluid of children during primary infection and subsequent to infection, indicating CNS viral persistence [6]. HHV-6 reactivation may contribute to disease in immunosuppressed patients following bone marrow or solid-organ transplantation, and in those with chronic fatigue syndrome [7,8].

This study demonstrates persistent HHV-6B infection in most patients with MTS-MTLE, but no detectable infection in patients with other pathology and constitutes the first report of primary isolation and maintenance of virus-infected astrocytes from the human brain. In addition, we provide direct evidence for an etiological link of a ubiquitous human herpesvirus in a subset of patients with intractable MTLE with MTS, a syndrome of unknown origin. Active HHV-6 infection was confirmed by the detection of viral DNA, mRNA viral transcripts, and viral protein expression in human primary astrocytes isolated and cultured from resected brain tissue from patients with MTLE. HHV-6B in MTS-MTLE is unlikely to be a consequence of nonspecific inflammation or seizures, since none of the patients without MTLE patients, all of whom had intractable epilepsy, were positive for virus. Moreover, there was no evidence for inflammatory changes in any of the HHV-6B–positive patients.



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