Human herpesvirus 6 downregulates major histocompatibility complex class Iin dendritic cells

The expression of major histocompatibility complex (MHC) class I, class II, CD1a, and; CD 83 in dendritic cells (DCs) after infection with human herpe svirus 6 (HHV-6) was examined. Whereas there was no significant change in t he expression of CD1a, CD83, and: MHC class 11 in infected DCs, MHC class I expression was downregulated after infection with HHV-6 variant A but not HHV-B3. The expression of HHV-6 immediate-early or early genes was required for the downregulation of MHC class I. The de novo synthesis of MHC class I was greatly suppressed by infection with HHV-6A in DCs, while its rate of degradation was only slightly elevated. These results suggest that HHV-6A may escape from the host immune system in DCs by causing the downregulation of MHC class I synthesis. (C) 2001 Wiley-Liss, Inc.