Dissociation of immune responses to the ss‐a (ro) 52‐kd and 60‐kd polypeptides in systemic lupus erythematosus and sjögren's syndrome

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Abstract
The cellular RNA particle SS‐A (Ro) is a target of autoimmune response in many patients with Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). Recent immunologic, biochemical, and DNA cloning studies have shown that the SS‐A particle consists of at least 2 polypeptide components, of 52 kd and 60 kd. Immunodiffusion analysis of 60 sera from patients with primary SS revealed 47 (78%) to be SS‐A precipitin positive. Western blotting studies of the sera showed 3 groups of reactivities: 22 (47%) possessed autoantibodies against both the 60‐kd and the 52‐kd polypeptides, 19 (40%) reacted only with the 52‐kd protein, and 6 (13%) were nonreactive in Western blots although positive in immunodiffusion. Fifty‐one of 90 SLE sera (57%) were SS‐A precipitin positive by immunodiffusion. In Western blots, 24 (47%) possessed antibodies against both the 60‐kd and the 52‐kd antigens, while 9 (18%) reacted only with the 60‐kd protein. Eighteen (35%) were nonreactive by Western blot, although positive by immunodiffusion. Antibody to the 52‐kd antigen without concomitant antibody to the 60‐kd antigen was seen only in patients with primary SS, whereas antibody to the 60‐kd antigen without concomitant antibody to the 52‐kd antigen was seen only in SLE patients. Although antibodies to SS‐A are detected in both SS and SLE, our findings show that there is dissociation of immune responses to the 2 component antigens of the particle, which may be evidence of different events initiating the autoimmune process in these diseases.