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Human herpesvirus 6 (HHV-6) is a lymphotropic betaherpesvirus which productively infects human CD4+ T cells and monocytes. HHV-6 is the etiologic agent for exanthem subitum (roseola), and it is well-known that central nervous system complications occur frequently during the course of HHV-6-associated disease. In addition, HHV-6 has been associated with encephalitis or encephalopathy. However, very little is known about its tropism for neural cells. There are reports that HHV-6 may infect some glial cell lines, but whether it can infect any primary neural cells is not known. Our studies show that both HHV-6A (GS) and HHV-6B (Z-29) can infect highly purified primary fetal astrocytes in vitro. Infected cells showed cytopathic effects, forming giant syncytia. In dual immunofluorescence assays, the infected cells were detected by antibodies against the HHV-6 p41 nuclear antigen and glial fibrillary acidic protein, indicating that the infected cells are indeed astrocytes. PCR and Northern (RNA) blot analyses also confirmed that the astrocytes are infected by HHV-6. The progeny virus did not alter its host range and could reinfect T cells as well as primary astrocytes. These findings suggest that infection of primary human astrocytes may play a role in the neuropathogenesis of HHV-6.