The immune system has a complex system of defense against infection. One of these defenses is the ability to make antibodies. Billions of different antibodies can be generated to protect against pneumonia, the flu, and all sorts of other infections. The immune system can also generate special immune cells called T-cells to target cells infected with viruses. Billions of possible T-cells could also be generated to help the body fight off everything from chickenpox to herpes. Most the time these defenses are carefully controlled to only target viruses and other infections — things foreign to the body. But every once in a while a mistake occurs and immune system targets a normal part of the body, like the brain, causing an autoimmune disease. Researchers do not yet know exactly what causes this overreaction of the immune system, but our research is providing valuable clues.