Our immune system keeps us healthy by fighting off invading pathogens while simultaneously sparing our own cells and tissues. In healthy people, the immune system is able to distinguish between the self and nonself, a concept called self-tolerance. When the body is functioning properly, the immune system maintains self-tolerance while working in the background to protect the body from infections.
In people with autoimmune disease, self-tolerance does not function correctly, causing the body to turn the powerful weapons of the immune system against self molecules, causing inflammation and injury. Autoimmune disease can be systemic, affecting multiple parts of the body, such as in diseases like systemic lupus erythematosus (SLE). They can also be organ-specific, such as in type 1 diabetes, where the immune system targets and destroys the insulin-producing cells of the pancreas.