The phenomenon by which T cells recognize foreign antigens in the context of specific MHC alleles is termed MHC restriction, and the specific MHC molecule is termed the restriction element. The most common source of foreign peptides presented by class I molecules is viral infection, in the course of which peptides from viral proteins enter the class I pathway. Other examples of intracellularly generated peptides that can be presented by class I molecules in an immunogenic manner include peptides derived from nonviral intracellular infectious agents (e.g., Listeria, Plasmodium), tumor antigens, minor histocompatibility antigens, and ceain autoantigens. Ref: Nepom G.T. (2012). Chapter 315. The Major Histocompatibility Complex. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.