Your immune system attacks your body when you have an autoimmune disease. The immune system typically protects against viruses and germs. When it detects these outside invaders, it unleashes a massive army of fighter cells to engage them. Normally, your immune system can distinguish between your own cells and foreign cells. When you have an autoimmune disease, your immune system misidentifies a portion of your body, such as your skin or joints, as alien. Autoantibodies, a class of proteins, are released and assault healthy cells. Some autoimmune illnesses only affect one organ. Pancreas damage from type 1 diabetes. Other conditions, such as systemic lupus erythematosus (SLE), or lupus, can have a global impact.