Serum smooth muscle autoantibodies (SMA) react with different proteins (actin, tubulin, vimentin, desmin, cytokeratins) of the cytoskeletal components (microfilaments, microtubuli, intermediate filaments). Their presence characterizes both autoimmune (type 1 autoimmune hepatitis, coeliac disease) and viral diseases (chronic hepatitis C, infectious mononucleosis). When detected at titers higher than 1:80, they are considered a sensitive marker for type I autoimmune hepatitis (AIH), being found in up to 80% of cases. Within the spectrum of SMA, antiactin antibodies are most specific for the diagnosis of type 1 AIH, but they lack evidence of pathogenetic or prognostic value. Antiactin SMA of the IgA class have been described in coeliac patients in association with more severe intestinal histology; it is still controversial whether they should be considered as a secondary epiphenomenon or have a pathogenetic relevance. At present, immunomorphological techniques are still the gold standard for SMA testing; recently, however, new immunochemical tests with purified antigens have been demonstrated to be reliable. The detection of SMA is based on indirect immunifluorescence (IIF) technique using conventional substrates, such as rodent stomach, liver and kidney, in particular, SMA reacts with the wall of small arteries present in all three tissues; analysis of the kidney reactivity is of relevance, as it allows to easily recognize three immunomorphological patterns described: SMA-V (vessels), SMA-G (glomeruli), and SMA-T (tubuli).
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)