Death is generally a word with unpleasant or upsetting connotations, but when it comes to your body cells, death can be a very positive thing. Apoptosis is the scientific name for cell death, and it is happening constantly.
You only need think of one extremely common disease to realise how important apoptosis is. During their lifetime, over a third of people will suffer from cancer; a disease which develops when apoptosis goes wrong. Tumour cells interrupt the usual process of cell death, causing uncontrolled cell division and resulting in cancerous growths. Some cancer drugs even work by inducing the orderly and controlled process of apoptosis in tumour cells.
Cell death is also vital to combat common infections, including those caused by viruses. Viruses are tiny, and during infection they live inside body cells where they can replicate. Body cells always display fragments of the cell’s inner proteins on their surface, which will include foreign viral proteins when the cell is infected. When Killer T cells, a type of immune cell, recognise one of these surface proteins as being from a virus, the body cell is killed. The Killer T cell injects toxic granules into the infected cell, which trigger apoptosis – the viral particles are destroyed along with the body cell, helping to eliminate the infection.
So what happens if apoptosis cannot go ahead? One example is a rare and life threatening disease called Familial Hemophagocytic Lymphohistiocytosis (FHL). In FHL, genetic mutations mean that the toxic granules released by Killer T cells are unable to enter the target cell, and therefore fail to induce apoptosis. Because virally-infected cells cannot be destroyed, the virus spreads quicker and the immune system cannot resolve the infection. This lack of apoptosis causes serious problems – half of people with FHL will die from it.
From these examples of cancer and viral infections, it is clear that when it comes to your body cells, death can be a very good thing. Without apoptosis, infections cannot be resolved and uncontrollable cell division leading to tumours can occur. Hopefully in the future, the body’s own cell death process of apoptosis will be further harnessed as a technique for controlling and treating diseases such as cancer.