Th17 Cytokines in Autoimmunity

The human immune system is composed of several organs and many diff erent cell types that protect the body against any parti cle that is not part of the body, the non-self. Mostly, these will be invading pathogens or cancer cells. The immune system can be divided into two main components: an innate component and an adapti ve component (fi gure 1). These two components do not operate separately, but are in fact closely linked and depend upon each other. When the body is invaded by pathogens, cells of the innate immune system are quickly acti vated to limit the infecti on. However, they are not specifi c for one type of anti gen; rather they respond to epitopes present on many diff erent pathogens, like pepti doglycans and lipopolysaccharides, which have been strongly conserved during evoluti on. Contrary to the innate immune system, cells of the adapti ve immune system are highly specifi c for one parti cular epitope or anti gen. Development of this specifi c response takes several days, but leads to a much stronger and long lasti ng immune response. Furthermore, the high specifi city provides the possibility of developing memory cells that will be able to respond more quickly if a similar pathogen invades the body again.