Cytotoxic T cells
A cytotoxic T cell (CD8+ T cell) is a type of lymphocyte responsible for eliminating substances that the immune system identifies as harmful. Cytotoxic T cells play a critical role in limiting infections and bacteria in the body.
Functions of cytotoxic T cells
Viruses and other bacteria attack by multiplying and spreading disease as infected cells. Once a cell is infected, there is no way for antibodies to destroy the infection; this is where cytotoxic T cells come in. Through the selection process, these cells attach to antigen-binding receptors, allowing them to monitor and destroy cells that pose a threat to the body. Depending on selection markers, a cytotoxic T cell will use one of three strategies to fight infection.
The first method that cytotoxic T cells use to fight infection is the secretion of cytokines. Cytokines are substances that activate other cells. Cytotoxic T cells release two cytokines, in particular, TNF-alpha and IFN-gamma, which facilitate macrophage activation. Macrophages attack and clean infected cells and prevent unregulated cell growth, such as that of a tumour.
Another way that cytotoxic T cells kill target cells is by releasing cytotoxic granules. These granules are sent in the direction of the target cell and contain two proteins that work together to destroy cells from the inside out. The first protein, perforin, creates holes in the membrane of the target cell. This pore is then used as an entry point for granzymes, which cleave internal cell proteins. The combination of perforin and granzymes ultimately results in the apoptosis of the target cell. Apoptosis is a programmed cell death that occurs because a cell cannot function properly. After killing the target cell, the granules are passed on to another, leaving uninfected cells completely unharmed.
The last major function of cytotoxic T cells involves an interaction between FasL and its Fas receptor. When FasL and Fas bind, they trigger a reaction that binds the signalling molecules. These molecules also cause apoptosis in the cell by destroying its functions. This interaction is different because it is also how cytotoxic T cells kill each other. After an immune response is successful, there is an excess of unnecessary cells that take up space in the body. Cytotoxic T cells have both Fas and FasL on their surface, causing them to be rapidly destroyed and eliminated after they have completed their function.
Cytotoxic T cells may be the answer to fighting diseases like cancer, hepatitis, and other life-threatening diagnoses. They are a prime candidate to aid in chemotherapy. The potential uses of cytotoxic T cells make them an integral part of biomedical research. By studying how the body can naturally defend itself against disease, we can learn how to artificially expand those tactics.