Viral Evasions

When virusus infect a cell ,the proteins produced in the cytosol by the virus can be degraded by proteosome and trasported into ER though the TAP transporter ,the presence of these peptide in the ER allows them to loaded on to MHC class 1 molecules and evetully trasported to surface of the cell where it can be recognised by CD8 T cells .

Certain viruses are developed a stargeries to prevent their detection by cytotoxic t cells,Many of the statergies involve in preventing peptide derived from the virus from entering the ER and being loaded in MHC Class I molecules.

For example herpes simplex virus 1 codes a protein IPC47 that has ability to block peptide binding to the cytosol surface of the TAP transporter,In this way transport of viral peptides into the ER is prevented ,consequently these peptides cannot be loaded into MHC class I molecules.This results in reduced expression of peptide loaded MHC on surface of the infected cell.Cell is not killed and therfore virus can replicate sucessfully.