The human body has a built-in protector from all things foreign: the immune system. Normally, it works to recognize any foreign invader and sets in motion a process of helping the body get rid of the offending bug and get better. But for reasons scientists are only beginning to understand, the immune system sometimes sets its sights on the person it is designed to protect. That is the heart of autoimmune diseases, and there are more than 100 of them. Autoimmune diseases can target any part of the body, including the nervous, gastrointestinal and endocrine systems, as well as skin and other connective tissues, eyes, blood and blood vessels. Women seem to be at greater risk for autoimmune diseases. At the Feinstein Institute, researchers are hard at work studying rheumatoid arthritis, lupus, thyroid disease and diabetes, as well as natural and innate immunity. The federal government estimates that there may be 50 million Americans living with an autoimmune disease.