Novel aspects of autoantibodies to the PM/Scl complex: Clinical, genetic and diagnostic insights

A characteristic feature of patients suffering from connective tissue diseases such as polymyositis (PM), dermatomyositis, systemic sclerosis (scleroderma, SSc, Scl), systemic lupus erythematosus or overlap syndromes thereof are anti-nuclear antibodies and anti-nucleolar antibodies. Antibodies to the PM/Scl complex, also known as the human exosome complex, belong to the anti-nucleolar antibodies and are mainly found in patients with PM/SSc overlap syndrome and related diseases. Until recently, the detection of anti-PM/Scl antibodies was laborious and relied largely on indirect immunofluorescence and immunodiffusion techniques. With the identification and characterization of the autoantigens, especially PM/Scl-75, PM/Scl-100 and a synthetic peptide (PM1-Alpha) thereof, newly developed assays based on recombinant proteins and peptides have allowed the development of a new generation of anti-PM/Scl tests with high sensitivity and specificity. These novel assays (i.e. ELISA, line immunoassays and protein arrays) enable testing for anti-PM/Scl in modern, automated, multi-parametric assay settings. The present review focuses on recent insights on anti-PM/Scl autoantibodies with special emphasis on clinical, genetic and diagnostic aspects.