The immune system defends the body against infections and certain other diseases. It is made up of different organs, cells, and proteins known as antibodies. It identifies, attacks, and destroys germs and other foreign substances. Sometimes the immune system makes a mistake and attacks the body's own tissues or organs. This is called autoimmunity. One example of an autoimmune disease is type 1 diabetes, in which the immune system destroys the cells in the pancreas that produce insulin.