The detection of circulating autoantibodies in chronic liver disease is of great clinical importance in the differential diagnosis of chronic active hepatitis (CAH) from chronic persistent hepatitis (CPH) and is particularly useful in the diagnosis of primary biliary cirrhosis (PBC).
Smooth muscle antibodies (SMA) can be demonstrated in patients with acute and chronic hepatitis, the highest titers occurring in Chronic Active Hepatitis (CAH). All of the various forms of chronic liver disease show SMA titers not higher than 1:160, except for CAH where titers up to 1:1280 are found. The differential diagnosis of CAH in patients which chronic liver disease is facilitated by titration of SMA using the indirect immunofluorescence method with rat stomach muscularis mucosae, the most commonly recommended substrate employed in the detection of SMA.
The antigen active in CAH patients with a SMA reaction is actin. These antibodies are non organ specific and will react with any histological structures containing actin, including: capillary linings, platelets, brush borders of renal tubular epithelium and in the renal glomerular cells and the smooth muscle surrounding arteries and veins. The reactivity of SMA for CAH patients is rather broad and includes many of these "non muscle" tissues. SMA is actin specific when associated with CAH.
Tests for the detection of mitochondrial antibodies (MA) are recommended as an alternative to surgical exploration as the presence of high titer MA can provide confirmatory evidence for the diagnosis of PBC. Both CAH and PBC have many overlapping immunologic features and may represent a continuum of a single disease entity. MA titers in PBC do not appear to have any correlation with clinical activity since they do not vary with the severity or progression of the disease and cannot serve as a monitor of response to therapy or provide prognostic information. MA are present in sera of patients with a variety of liver disorders but are only present in high titer in the majority of patients with PBC.