The immune system provides humans and animals with protection from infection. When micro-organisms such as viruses and bacteria break into the body, the immune system responds. Fevers, boils, rashes and runny noses can all be caused by fighting infection. When the infection is gone, the body returns to normal, but the immune system retains a memory of the infection. If it should encounter the same infection a second time, the response will be faster, destroying the infection more quickly, perhaps without its work even being noticed.
The work of the immune system is carried out by specialised cells. These are found in great numbers in the spleen and in the lymph nodes (glands), which is why they swell up in response to infection. But because infection may occur anywhere, cells from the immune system are spread throughout the body, and no part of the body is inaccessible to an immune response. When the immune system is activated, it causes inflammation which is recognised by people as redness, swelling, warmth and pain. It may be mild or it may be intense, and as well as being able to kill invading infections, inflammation can also destroy normal tissue.
Immune responses are supposed to be triggered by cells of the immune system recognising when infection is present. Because the ability to respond rapidly to infection affects survival, because there are many different forms of infection and because through time new ways of recognising infection have evolved, this is a very complex process that does not work perfectly. When the immune system makes a “mistake” and starts attacking itself, you have autoimmune disease.
The common forms of autoimmune disease attack a specific part of the body. For example the brain is attacked in multiple sclerosis and the retina is attacked in inflammatory eye disease or uveitis. This specificity arises by exactly the same mechanisms that allow the immune response to kill specific infections. But in contrast to an infection, parts of the body like the brain cannot be eliminated and therefore autoimmunity, once it has developed, is usually a lifelong illness. To understand and treat these diseases, we study the detail of how the immune system recognises specific tissues; our goal here is to interfere with the recognition process to stop it happening. We also study the cells that cause inflammation, to find new ways of stopping them reacting in situations such as autoimmunity where they are harmful rather than helpful.
Lindsay Nicholson.