An autoimmune disease is a condition in which the immune system mistakenly attacks and destroys healthy body tissue. This occurs because the immune system fails to recognize that certain cells or proteins are actually part of the body, leading it to produce antibodies against them. As a result, various organs and systems can be affected, causing symptoms ranging from mild to severe. Some common autoimmune diseases include rheumatoid arthritis, lupus, multiple sclerosis, type 1 diabetes, and celiac disease. Treatment typically involves managing the symptoms and may also involve therapies that suppress or modulate the immune system to prevent further damage.