Why doesn't our immune systems attack us?

Autoimmune disease: Your body's immune system protects you from disease and infection. But if you have an autoimmune disease, your immune system attacks healthy cells in your body by mistake. Autoimmune diseases can affect many parts of the body. These diseases tend to run in families. Women - particularly african-american, hispanic-american, and native-american women - have a higher risk for some autoimmune diseases.