HHV-6A infection induces expression of HERV-K18-encoded superantigen

Abstract Background The human endogenous retrovirus K-18 (HERV-K18) encodes a superantigen that causes deregulation of the immune system. This provirus is transcriptionally silent, but can be induced by Epstein–Barr virus (EBV) infection and IFN-α treatment. Objectives Since the herpesvirus EBV induces HERV-K18 expression in human B cells, it was of interest to determine if other herpesviruses would have similar HERV-K18 transactivation properties. Human herpesvirus (HHV)-6A, a neurotropic virus associated with multiple sclerosis, was a logical candidate for these studies. Study design HSB2 cells (HHV-6 - negative control), HSB2-ML cells (containing latent HHV-6A genome) and HSB2/HHV-6A cells (HSB-2 cells productively infected with HHV-6A) were compared for their level of HERV-K18 transcription, using quantitative RT-PCR. Results Latently infected HSB2-ML cells showed a significant increase in HERV-K18 RNA compared to the control cells. HERV-K18 expression was even greater in HSB2 cells productively infected with HHV-6A for 78 h. Conclusion These results imply that HHV-6A, either in latent form or during acute infection, directly transactivates HERV-K18. This HERV-K18 induction may be mediated through IFN-α that is produced by the HHV-6A-infected cells. The functional implications of superantigen expression are discussed.