Priming of T cells by exogenous antigen cross-presented on MHC class I molecules.

Cross-presentation is the process whereby bone-marrow-derived antigen-presenting cells acquire, process and present exogenous antigen as peptides bound to MHC class I molecules to CD8(+) T cells. Professional antigen-presenting cells acquire cell-associated antigen predominantly in the form of protein, then process and present antigenic peptides on their surface MHC class I molecules via several mechanisms and efficiently cross-prime naïve CD8(+) T cells in vivo. This pathway is of considerable interest because it has an important role in the immune surveillance of tissues for pathogens and cancers.