Autoimmune diseases arise from an abnormal immune response of the body against substances and tissues normally present in the body (autoimmunity). This may be restricted to certain organs (e.g. in autoimmune thyroiditis) or involve a particular tissue in different places (e.g. Goodpasture's disease which may affect the basement membrane in both the lung and the kidney). The treatment of autoimmune diseases is typically with immunosuppression—medication that decreases the immune response. A large number of autoimmune diseases are recognised.
For a disease to be regarded as an autoimmune disease it needs to answer to Witebsky's postulates (first formulated by Ernst Witebsky and colleagues in 1957 and modified in 1994):