Autoantibody to U3 nucleolar ribonucleoprotein (fibrillarin) in patients with systemic sclerosis.

To determine the clinical significance of serum antibodies to the U3 small nuclear ribonucleoprotein particle ([U3]snRNP), we studied sera from 416 patients with systemic sclerosis (SSc) and 264 controls, using immunofluorescence and immunoprecipitation assays. The presence of serum anti-(U3)snRNP was highly specific to SSc, was found more frequently in blacks, and was associated with skeletal muscle disease and primary pulmonary arterial hypertension. These antibodies may identify one or more unusual clinical subsets of SSc.