Discovery of RoSSA Antigens

In 1961, two precipitating autoantibody specificities known as SjD and SjT were described in patients with Sjogren's syndrome (Anderson et al. 1961). SjD antigen was reported to be insensitive to trypsin or heat treatment, whereas SjT antigen could be destroyed by the same treatment. In 1969, Clark et al. (Clark et al. 1969) reported a novel antibody specificity known as Ro in 40% of patients with SLE. The Ro antigen was described as a protease-, RNase-, and DNase-resistant cytoplasmic antigen observed in various tissue extracts. Six years later, in 1975, Alspaugh and Tan (Alspaugh and Tan 1975) described precipitin lines for two distinct autoantibody specificities termed "SSA"and "SSB" occurring predominantly in serum from patients with Sjogren's syndrome. It was not until 1979 that SSA and Ro were shown to be identical (Alspaugh and Maddison 1979); since then, this antigen system has been referred to as Ro/SSA. However, in the research areas of molecular biology and cell biology, this system is exclusively referred to as Ro ribonucleoprotein (RoRNP), since Ro antigens were shown to be associated with small RNAs (Lerner et al. 1981). Within the RoRNP complex, human serum containing anti-Ro/SSA antibodies recognizes two proteins with the molecular weight of 52 and 60 kDa (Fig. 24.1C). The 60-kDa Ro/SSA protein binds to a subpopulation of small RNAs, termed "hY RNAs" (Wolin and Steitz 1984). Antibodies to the Ro-associated RNA molecule hY5 RNA have also been detected (Granger et al. 1996), supporting the importance of the whole RoRNP particle in the autoimmune response.

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