While one tissue type predominates, others may be involved in a general misdirection of immune activity, perhaps because the specific target antigen is present in differing quantities in each of the affected tissues. There seem to be hereditary causes for autoimmunity, since these diseases tend to run in families and have genetic markers. Among the more common diseases believed to fall within this category are rheumatoid arthritis , systemic lupus erythematosus, multiple sclerosis , and psoriasis . The process of autoimmune disease is very similar to infectious disease and allergy, so that great caution is observed in placing a disorder in this class. Germs were found to cause several diseases originally thought to be autoimmune.
Allergens cause others.
Many more may be uncovered. Autoimmunity is often believed to originate with a virus infection. A chemical in the virus resembles a body chemical so closely that the immune system attacks both. Autoimmune hepatitis is similiar to viral hepatitis, a disease of the liver. It can be an acute disease that kills over a third of its victims within six months, it can persist for years, or it can return periodically.