Up-regulation of MHC class I by flavivirus-induced peptide translocation into the endoplasmic reticulum.

Flavivirus infection of mammalian cells increases the cell surface expression of major histocompatibility complex (MHC) class I molecules, the recognition elements for cytotoxic T cells. Here, we show that the mechanism for flavivirus-induced up-regulation of class I MHC involves an increase in peptide supply to the endoplasmic reticulum. Flavivirus-mediated peptide supply for MHC class I assembly is independent of the peptide transporters for class I antigen presentation, since infection of class I MHC peptide transport-deficient cell lines with flaviviruses results in the cell surface expression of biologically functional class I MHC peptide complexes. The flavivirus-induced supply of antigenic peptides to the endoplasmic reticulum is not restricted to flavivirus-encoded peptides and independent of interferon. The data imply that peptide availability regulates surface expression of class I MHC restriction elements and suggests a mechanism for flavivirus-induced immunopathology.