Cytotoxic T lymphocytes (CTLs) are a subset of αβT-cells that usually express the CD8 co-receptor and have the ability to directly kill infected cells.
As a major part of the adaptive immune system, T-cells scan the intracellular environment in order to target and destroy infected cells. Small peptide fragments, representing the entire cellular content, are transported to the cell surface as pMHC, allowing T-cell surface expressed antigen specific αβTCRs to scan for foreign signals. T-cells interact with a large number of different cell types and recognise a diverse array of pathogens. This diversity has lead to distinct antigen recognition pathways which generate the appropriate T-cell response. These antigen recognition pathways can be subdivided according to the class of MHC presenting the antigenic peptide. MHCI present 8-13 mer antigenic peptides derived from intracellular pathogens such as viruses and tumours to CTLs . CTL recognition can lead to the release of cytotoxic granules, the release of lymphokines and the activation of apoptotic pathways via the FAS/FASL interaction to destroy the infected cell. Thus, CTL are our main defence against viruses and tumours.
CTL responses to disease are initiated through the interaction between the TCR, on the surface of a T-cell, and protein fragments derived from ‘foreign’ invaders that are presented by pMHCI on the surface of infected cells. Once a CTL has identified a cell expressing a ‘foreign’ pMHCI, the infected cell is eliminated. Understanding these mechanisms that underlie CTL antigen recognition and activation are vital for understanding and treating disease.