ABSTRACT
The principal function of the immune system is to offer protection against the invasion of exogenous antigen. However, at the same time it must also have the ability to recognize self antigen and avoid damage to host tissues. Autoimmune diseases appear to arise, however, as a result of failure of the immune system to recognize self antigen. The common autoimmune disorders collectively affect around 5% of the population, of which the most common are type 1 diabetes, autoimmune thyroid disease, and rheumatoid arthritis.
