utoantibodies to the Ro (SS-A) and La (SS-B) ribonucleoprotein antigens are found commonly in the sera of patients with SjΕ‘grenΓs syndrome (SS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), or overlaps between these diseases. The prevalence of anti-Ro antibodies varies between 50% and 90% in patients with SS (according to the method used to detect them and criteria used to define the disease), between 30% and 50% in patients with SLE and between 20% and 30% in patients with RA (reviewed in Refs 1 and 2). Similarly, anti-La antibodies are often found in the sera of patients with SjΕ‘grenΓs syndrome: immunoprecipitation detects anti-La antibodies in ~35% of patients, whereas ELISA gives positive results for up to 85% patients. However, anti-La antibodies are less commonly present (18Γ28%) in the sera of patients with SLE (Refs 1, 2).
The presence of these antibodies is not simply a matter of academic interest. Anti-Ro antibodies have been eluted from the kidneys of patients with SLE (Ref. 3), but are more commonly associated with photosensitive rashes 4 . Antibodies to Ro and La appear to predispose patients with SLE to the development of SjΕ‘grenΓs syndrome 2 . These antibodies can cross the placenta and induce (in about one in 20 cases) neonatal lupus erythematosus (NLE) 5 , which is characterized by a transient skin rash and a cardiac conduction defect that can be permanent. Not surprisingly, therefore, many investiga-