Autoimmune disease is characterized by the production of autoantibodies directed against endogenous antigens.

Study: Autoantibodies to human endogenous retrovirus‐K are frequently detected in health and disease and react with multiple epitopes

This study found that people with autoimmune diseases often have antibodies that attack parts of our own DNA that look like old viruses. This supports the idea that autoimmune diseases happen when the body mistakenly attacks its own stuff.

Study: Rapid induction of autoantibodies by endogenous ovarian antigens and activated T cells: implication in autoimmune disease pathogenesis and B cell tolerance.

This study showed that when mice are exposed to a part of their own ovary protein, their immune system mistakenly makes antibodies against other parts of that same protein — proving the immune system can attack the body’s own tissues, which is what happens in autoimmune diseases.