CYTOTOXIC T-LYMPHOCYTES - SPECIFICITY, SURVEILLANCE, AND ESCAPE

The cytotoxic T lymphocyte (CTL) is a powerful component of the immune response. This chapter discusses the evidence for immune surveillance and the strategies by which target cells escape CTL recognition. The specificity that targeted viruses and cells have developed strategies to escape recognition implies strong selective pressure in vivo and indicates that these cells exert a major protective role for the host. They explore cell surfaces, monitoring major histocompatibility complex (MHC) class I molecules with their inserted peptides. Self–reactive CTLs are deleted or energized. Those that bind above a threshold affinity to class I molecules containing foreign peptides react vigorously and destroy those cells. The diversity of a class I molecule ensures that the species can cope with most foreign invaders and probably most mutant-self proteins. However, some mutant proteins may fail to evoke an immune response because no new peptides are inserted into class I human leukocyte antigen (HLA) molecules. A CTL response is stimulated but cells of viruses escape CTL recognition which is an important part of tumorigenesis. © 1992 Academic Press Inc.