A human herpesvirus 7 glycoprotein, U21, diverts major histocompatibility complex class I molecules to lysosomes.

All members of the herpesvirus family persist in their host throughout life. In doing so, herpesviruses exploit a surprising number of different strategies to evade the immune system. Human herpesvirus 7 (HHV-7) is a relatively recently discovered member of the herpesvirus family, and little is known about how it escapes immune detection. Here we show that HHV-7 infection results in premature degradation of major histocompatibility complex class I molecules. We identify and characterize a protein from HHV-7, U21, that binds to and diverts properly folded class I molecules to a lysosomal compartment. Thus, U21 is likely to function in the normal course of HHV-7 infection to downregulate surface class I molecules and prevent recognition of infected cells by cytotoxic T lymphocytes.