Cytotoxic T Lymphocytes

Killer T Cells

What are CTLs, or killer T-cells?

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.

What is the role of CTLs in the immune system?

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.

Killer T Cells

Why is it important to study CTLs?

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.