Autoimmune hepatitis and immunoglobulin G4-associated autoimmune hepatitis

Autoimmune hepatitis (AIH) is a disease that is characterized by the presence of autoantibodies and elevated levels of serum immunoglobulin G (IgG) and hepatic enzymes. Its characteristic findings in the liver include interface hepatitis, infiltration of lymphocytes and plasma cells, and rosette formation, and is treated with immunosuppressive drugs. Autoimmune pancreatitis, a pancreatic disease caused by an autoimmune mechanism, is associated with elevated levels of serum IgG4 and the infiltration of IgG4-positive cells into the pancreatic parenchyma, and it is occasionally accompanied by systemic features. This systemic inflammatory disease characterized by the infiltration of IgG4-positive plasma cells and elevated serum IgG4 levels was recently classified as an IgG4-related disease. A few studies have reported AIH cases with infiltrated IgG4-positive plasma cells in the liver, suggesting the involvement of IgG4 in the pathogenesis of AIH. This feature was called IgG4-associated AIH and only two studies have been published. However, the diagnostic criteria of IgG4-associated AIH has not been defined and the epidemiology and clinical features remain uncertain. The degree of IgG4-positive plasma cell infiltration in the liver was different in each article. The serum IgG4 level was not elevated in one study, whereas it was severely elevated in the other. Corticosteroid therapy normalized liver enzymes in both studies. Further studies are needed to define the epidemiological features or diagnostic criteria.