Autoimmune diseases are conditions in which the body's own tissues are targeted by the immune system. Normally, the immune system provides defense against foreign organisms such as bacteria, viruses and parasites that can harm the body. However, in autoimmune diseases, the immune system perceives normal tissues as foreign organisms against its own body and attacks them. Autoimmune diseases can often target a specific organ or tissue type. For example, there are many autoimmune diseases such as autoimmune thyroiditis for the thyroid gland, type 1 diabetes for the pancreas, and Crohn's disease for the intestines. There are also systemic autoimmune diseases that can affect multiple organs or tissues, such as lupus, rheumatoid arthritis, multiple sclerosis. Genetic predispositions and environmental factors (such as infections, smoking, stress) play a role together in the development of autoimmune diseases. Certain genetic variations or gene mutations have been found to be associated with autoimmune diseases. These genetic variations include changes in genes that play a role in regulating immune system cells or controlling immune responses. These changes may increase the risk of the immune system reacting against its own tissues. For example, the CTLA4 gene controls activation of the immune system and has been associated with autoimmune diseases such as type 1 diabetes, Graves' disease, and rheumatoid arthritis. IL-17 is produced in immune system cells and plays an important role in initiating inflammation. Excessive production of IL-17 may increase inflammation and promote the autoimmune response in the pathogenesis of autoimmune diseases.