This web page was produced as an assignment for an undergraduate course at Davidson College.
CELL-MEDIATED IMMUNE RESPONSE
The cellular response of the adaptive immune system is executed by cytotoxic T cells, macrophages, and NK (natural killer) cells.
All of these cells are "born killers" that attack and destroy infected cells.
Cytotoxic T Cells
Immature T cells are activated in the presence of antigen as presented by APCs (antigen presenting cells) such as dendritic cells.
Once activated, the T cell migrates to the site of infection and binds to the adhesion molecules on the surface of cells until it recognizes the specific antigen it was activated to kill.
The cytotoxic T cell then binds to the infected cell and releases noxious substances that penetrate the target cell membrane and destroy the cell contents, killing the cell.
These cells are serial killers, so once the cell is dead, it moves on to kill another.
Natural Killer Cells
NK cells are also serial killer cells and instead of being activated by and recognizing a particular antigen, they must receive a stop signal from the target cell in order to prevent death.
If it does not get this inhibitory signal, either because it is infected or there is some mutation preventing its presentation on the cell surface, the target cell is eliminated via the release of noxious substances by the NK cell that are similar to those release by cytotoxic T cells.