Autoantibodies and their antigens in autoimmune hepatitis

Autoantibody detection assists in the diagnosis and allows differentiation of autoimmune hepatitis (AIH) type 1 (AIH-1), characterized by antinuclear antibody (ANA) and/or smooth muscle antibody (SMA), and type 2 (AIH-2), distinguished by the presence of antibodies to liver-kidney microsome type 1 (anti-LKM1) and/or antibodies to liver cytosol type 1 (anti-LC1). Detection of atypical perinuclear antineutrophil cytoplasmic antibodies (pANCA) and anti-soluble liver antigen (SLA) antibodies can act as an additional pointer toward the diagnosis of AIH, particularly in the absence of the conventional autoantibodies. Routine autoantibody testing by indirect immunofluorescence has been recently complemented by molecular assays based on purified or recombinant antigens. Although the AIH-1-specific ANA and SMA targets need better definition, those of anti-LKM1 and anti-LC1 in AIH-2 have been clearly identified; the fine specificity of antibody reactivity and its clinical relevance to disease pathogenesis are the focus of ongoing investigation. This article critically discusses the current knowledge of the diagnostic and clinical significance of AIH-related autoantibody reactivities, focusing on key issues that the physician needs to be aware of to be able to request the appropriate testing and to interpret correctly the laboratory results within the clinical context of the patient.