SERUM AUTOANTIBODY TO THE NUCLEOLAR ANTIGEN PM-SCL - CLINICAL AND IMMUNOGENETIC ASSOCIATIONS

Objective. The inflammatory myopathies are characterized by distinctive autoantibodies that are associated with certain clinical features and immunogenetic patterns. Anti-PM-Scl is one such antibody and is found in pure myositis, myositis in overlap, and systemic sclerosis (SSc). Our purpose was to describe the clinical and immunogenetic associations of the anti-PM-Scl antibody. Methods. Serum samples from 617 patients with various connective tissue diseases were screened for anti-PM-Scl antibody by indirect immunofluorescence and Ouchterlony double immunodiffusion. Patients with anti-PM-Scl were serologically typed for HLA-DR and DQ, and the genes encoding DQalpha and DQbeta were characterized by hybridization of sequence-specific oligonucleotide to amplified genomic DNA. Results. Twenty-three patients (4%) had serum anti-PM-Scl. Sixteen had either pure myositis or myositis in overlap, 6 had SSc alone, and 1 had SSc and rheumatoid arthritis. Twenty of the antibody-positive patients had serologic HLA typing performed; 15 (75%) were HLA-DR3 positive, and 17 (85%) expressed the DQw2 allele. None of the 5 DR3 negative patients shared a unique DR or DQ antigen with the DR3 positive patients, and further DNA analysis of 10 patients (4 of whom were DR3 negative) did not reveal any unique DQ alleles. Conclusion. Anti-PM-Scl identifies a subset of patients with myositis, SSc, or an overlap of the two disorders, and this antibody has a strong but not exclusive immunogenetic association with the HLA-DR3 antigen.