Regulation of MHC Class I by Viruses

Originally recognized for their role in triggering T cell responses that caused the rejection of transplanted tissue, it is now known that MHC-encoded molecules are involved in immunesurveillance and antigen presentation to T lymphocytes. These MHC molecules act as “signposts” that displays fragmented pieces of an antigen (viral proteins in virus-infected cells or mutated proteins in tumor cells) on the host cell surface. Because viruses can infect virtually all nucleated cells, class I molecules are constitutively expressed on almost all nucleated cells. The association of antigenic peptides and MHC molecules is a saturable interaction and once formed, persist for a sufficiently long time to be recognized by the few T cells specific for the antigen as they circulate through. The outcome of TC cells-mediated killing of the virus-infected cells is usually via apoptosis.