Like many other classical autoantibodies in systemic rheumatic diseases, anti-Su antibodies were originally defined by the double immunodiffusion assay in the early 80s. However, despite its high prevalence, only a few reports on anti-Su were published in the following years and the progress in characterizing the target antigens and clinical significance was slow, probably due to its inconsistent or poor reactivity in other standard immunoassays. In 2006 the target antigen was identified as the microRNA (miRNA)-binding protein Argonaute 2 (Ago2). Ago2 is a key component of the RNA-induced silencing complex enriched in cytoplasmic foci called GW bodies. Due to preferential reactivity of human autoantibodies with native antigens, immunoprecipitation is the only method to reliably detect anti-Su/Ago2 antibodies. Anti-Su/Ago2 does not appear to have disease specificity since it is found in 10-20% of patients with various rheumatic diseases, including systemic lupus erythematosus, scleroderma, polymyositis/dermatomyositis, and Sjögren's syndrome, as well as apparently healthy individuals at lower prevalence. The clinical significance and the mechanism of production of anti-Su/Ago2 remains to be clarified.