Cytotoxic T Cell - Effector Functions

Effector Functions

When exposed to infected/dysfunctional somatic cells, T_C cells release the cytotoxins perforin, granzymes, and granulysin. Perforin forms pores (aqueous channels) in the target cell's plasma membrane allowing granzymes, types of serine proteases that cleave at aspartate residues in the substrate, to enter the target cell, which then activate a series of cysteine proteases, the caspase cascade, that eventually lead to apoptosis (programed cell death). A second way to induce apoptosis is via cell-surface interactions between the T_C and the infected cell. When a T_C is activated it starts to express the surface protein FAS ligand (FasL)(Apo1L)(CD95L), which can bind to Fas (Apo1)(CD95) molecules expressed on the target cell. However, this Fas-Fas ligand interaction is thought to be more important to the disposal of unwanted T lymphocytes during their development or to the lytic activity of certain T_H cells than it is to the cytolytic activity of T_C effector cells. Engagement of Fas with FasL allows for recruitment of the death-induced signaling complex (DISC). The Fas-associated death domain (FADD) translocates with the DISC, allowing recruitment of procaspases 8 and 10. These caspases then activate the effector caspases 3, 6, and 7, leading to cleavage of death substrates such as lamin A, lamin B1, lamin B2, PARP (poly-ADP ribose polymerase), and DNAPK (DNA-activated protein kinase). The final result is apoptosis of the cell that expressed Fas.