Center for Immunology
University of Minnesota
Almost all cells display on their surfaces a representative sampling of the proteins they are makeing, as peptide fragments bound to cell surface class I MHC proteins. When these are self peptides they are generally ignored by the immune system. When the bound peptide is foreign, then naive CD8+ T cells that specifically recognize the peptide/MHC complex can be activated to clonally expand and differentiate to active effector cytotoxic T cells that are able to directly and rapidly kill any cell that bears the same foreign pept ide antigen. 'Foreign' peptides can include peptides derived from viral or tumor-specific proteins, and killer cells can thus provide an important arm of defense against virus infections and cancers. Activation of naive CD8+ cel ls to proliferate and differentiate, and activation of effector cells to kill the target, both involve recognition of antigen by the T cell receptor (TCR). Additional requirements for these distinct activation processes differ substantially, however. The adhesion and signaling receptors involved in these processes, and their interactions, will be reviewed and discussed.