Autoimmune diseases occur when the immune system fails to distinguish self from non-self, producing antibodies (autoantibodies) or T-cells that attack the body's own tissues. Examples include rheumatoid arthritis, lupus (SLE), Type 1 diabetes, and multiple sclerosis. Anaphylaxis is a severe hypersensitivity reaction to an external antigen; prophylaxis is disease prevention; immunodeficiency involves reduced immune function.