Serum Smooth Muscle Antibodies (SMA).

Serum smooth muscle antibodies (SMA) react with different components of the cytoskeletal network (microfilaments, microtubuli, intermediate filaments). They can be detected in autoimmune (autoimmune hepatitis, coeliac disease) and non-autoimmune diseases (chronic viral hepatitis). IgG SMA with anti-actin specificity are regarded commonly as a sensitive and very specific marker of type 1 autoimmune hepatitis (AIH-1), being found in up to 80% of cases. The mechanism through which they appear and the pathogenic role remain to establish. Recently, anti-actin SMA of the IgA class have been found in coeliac disease (CD). Their detection is strictly associated with villous atrophy and seems to be predective of a severe enteropathy. Indirect immunofluorescence is the standard technique to detect SMA but its interpretation is largely dependent on the observer's experience.