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Autoimmune hepatitis (AIH; previously called lupoid hepatitis, chronic active hepatitis) predominantly affects women (75% of cases). The disease manifests by an increase in bilirubin, liver enzymes and immunoglobulins, by characteristic histological changes (liver biopsy shows necrosis of the parenchyma cells with lymphocyte and plasma cell infiltration) and the presence of various autoantibodies. The disease can occur from early childhood up to old age, but is most frequent in young to middle adulthood. In Western Europe the incidence of AIH is 1.9 cases per 100,000 inhabitants per year. Untreated, AIH soon develops into liver cirrhosis. However, with low-dose immunosuppressive therapy administered in good time and consistently right up until death, patients have a normal life expectancy. In the differential diagnosis, an infection with hepatitis viruses must be ruled out through the investigation of the appropriate serological parameters.
Circulating autoantibodies have come to play a significant role in the diagnosis of AIH. They occur in the majority of patients, although their role in pathogenesis is debatable. There is no clear correlation between the disease activity or prognosis and the antibody titer.
The following autoantibodies are associated with AIH: antibodies against cell nuclei (ANA), native DNA, smooth muscle (ASMA, most important target antigen: F-actin), soluble liver antigen/ liver-pancreas antigen (SLA/LP), liver-kidney microsomes (LKM-1, target antigen: cytochrome P450 IID6) and liver cytosolic antigen type 1 (LC-1, target antigen: formiminotransferase cyclodeaminase). The autoantibodies against SLA/LP that can today be detected by various EUROIMMUN enzyme immunoassays have the highest diagnostic accuracy of all antibodies involved in AIH. Anti-SLA/LP antibodies occur in AIH either alone or together with other autoantibodies. Their prevalence is only between 10 and 30%, but the predictive value is almost 100%. Essentially, every positive finding is evidence of autoimmune hepatitis (as long as the corresponding clinical symptoms are present).
Furthermore, high concentrations of autoantibodies against smooth muscles (ASMA) indicate AIH. One part of the antibodies is directed against conformational epitopes of F-actin, which are only present in frozen tissue sections or tissue cells and cannot therefore be detected by ELISA or Westernblot. In contrast to other ASMA, antibodies against F-actin are a very specific marker for type 1 AIH. With the cell line VSM47 (vascular smooth muscle) the microfilamentous (MF) fluorescence pattern can be easily and clearly differentiated from non-MF patterns, thus facilitating the diagnosis of type 1 AIH.