An autoimmune disease occurs when the immune system mistakenly attacks and damages healthy cells in the body. Common symptoms include fatigue, pain, fever, and respiratory issues. There are four main types of autoimmune diseases depending on which immune cells are involved in the attack. Some examples of autoimmune diseases are type 1 diabetes where the immune system attacks pancreatic cells; Graves' disease where the thyroid is attacked; and multiple sclerosis where the immune system damages the myelin sheath surrounding nerves.