The SS-A/Ro antigen

Abstract

In 1961 Anderson et al. [1] described two precipitating autoantibody specificities known as SjD and SjT from patients with Sjögren’s syndrome. SjD antigen was reported to be insensitive to trypsin or heat treatment while SjT antigen could be destroyed by the same treatment. In 1969 Clark et al. [2] reported a novel antibody specificity known as Ro in 40% of patients with systemic lupus erythematosus (SLE) and the Ro antigen was described as a protease-, RNase-, and DNase-resistant cytoplasmic antigen observed in various tissue extracts. Aware of the work of Anderson et al. [1], Alspaugh and Tan [3] in 1975 described precipitin lines for two distinct autoantibody specificities known as SS-A and SS-B occurring predominantly in patients with Sjögren’s syndrome (SS). Both SS-A and SS-B were characterized as trypsin-sensitive but RNase- and DNase-resistant nuclear antigens. It was not until 1979 that SS-A and Ro were shown to be identical as reported by Alspaugh and Maddison [4] and since then this antigen system has been referred to as SS-A/Ro or Ro/SS-A. However, in the area of molecular and cell biology, this system is often referred to as Ro ribonucleoprotein (Ro RNP) probably because of the report of Lerner et al. [5] showing the association of Ro antigens with small RNAs. It is clear now that human sera containing anti-SS-A/Ro antibodies recognize two proteins of 52 and 60kD and the latter is bound to Ro RNAs known as hY RNAs. Several recent reviews on the SS-A/Ro autoantibody-antigen system have been published [6–10]. Another protein, calreticulin, was initially reported to be the 60-kD SS-A/Ro protein [11, 12]. However more recent work revealed that calreticulin is an unrelated autoantigen [13].