Lupus is a disease of the immune system that can affect joints, skin, kidneys, blood, and other parts of the body. The immune system is your body’s natural defense against infections, such as bacteria and viruses. In most cases the term “lupus” refers to the form known as systemic lupus erythematous, or SLE for short. Today1.5 to 2 million Americans live with some form of lupus according to Lupus Foundation of America, and it is now known to be an autoimmune disease. About 70 percent of the people who have lupus have the systemic form that affects multiple systems in your body.