When the body interprets the thyroid tissue as threat
The thyroid gland itself can become a target of an aberrant immune system. Normally, the immune system develops antibodies that protect you from harmful viruses and bacteria. In autoimmune diseases autoantibodies attack the body’s own tissue,12 resulting in diseases such as Hashimoto’s thyroiditis and Graves’ disease.
Wood LC, Cooper DS, and Ridgway EC. Your Thyroid. Ballantine Books Trade Paperback Edition. New York 2006