Antibodies are proteins that guard against substances—such as bacteria, fungi, viruses and toxins—that enter your body like foreign invaders. They protect you by attaching to those invaders (also known as antigens) and triggering your body's natural immune response to destroy them.You can think of autoantibodies as misguided—or pathogenic—antibodies. Instead of reacting to the antigen, they respond to your body's own proteins, leading—in some cases—to an abnormal immune response that attacks the cells, tissues and organs of your body and contribute to the development of autoantibody diseases. More than 200 million people worldwide are living with an autoantibody disease, which occurs when the body attacks its own cells, tissues and proteins.