Some viruses have mechanisms to down-regulate MHC class I protein expression on the surface of cells in which the virus is replicating. This immune evasion strategy might prevent effector CD8...

Some viruses have mechanisms to down-regulate MHC class I protein expression on the surface of cells in which the virus is replicating. This immune evasion strategy might prevent effector CD8 cytotoxic T cells from recognizing and killing the virus-infected cells. Would this immune evasion strategy also prevent the initial activation of virus-specific CD8 T cells?

1. Yes, because no viral peptide:MHC class I complexes would form to activate CD8 T cells.


2. No, because dendritic cells would take up infected cells and cross-present viral peptides to activate CD8 T cells.


3. No, because some presentation of MHC class I complexes with viral peptides would occur before the virus could down-regulate all the surface MHC class I protein.


4. Yes, because this immune evasion strategy would also function in dendritic cells, even if the virus doesn’t replicate in dendritic cells.


5. No, because the type I interferon response induced by the virus infection will up-regulate MHC class I expression and override the immune evasion mechanism.