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J. Exp. Med.,
Volume 189, Number 3, February 1, 1999 531-540
By






From the * Division of Rheumatology, Department of Internal Medicine, the Anti-Ro60 autoantibodies are found in a variety of autoimmune disorders including systemic
lupus erythematosus (SLE), Sjögren's syndrome, primary biliary cirrhosis, and active hepatitis.
They are the most prevalent autoantibodies in normal individuals and in asymptomatic mothers
of infants afflicted with neonatal lupus. In the present study, immune responses to recombinant
human Ro60 (rhRo60) and recombinant mouse Ro60 (rmRo60) and selected Ro60 peptides
in non-SLE-prone mice were investigated. Multiple T and B cell epitopes were identified in
Ro60. Immunizations with either xenogeneic or autologous Ro60 induced autoantibodies to a
diverse group of autoantigens. In addition to La and Ro52, proteins in the small nuclear ribonucleoprotein (snRNP) particles such as SmA, SmB, SmD, and 70-kD U1-RNP were unexpectedly identified as targeted antigens. In the studies involving synthetic Ro60 peptides, both
human and mouse Ro60316-335 peptides, which differ in three amino acids, were found to contain dominant cross-reactive T cell determinants. Immunizations with these peptides induced autoantibodies to Ro60, La, SmD, and 70-kD U1-RNP without autoantibodies to Ro52,
SmA, or SmB. With human Ro60316-335 as the immunogen, additional autoantibodies reactive
with the Golgi complex were found. In contrast to the immunodominance of both human and
mouse Ro60316-335 peptides, the T cell determinant in human Ro60441-465 was dominant,
whereas that in the mouse peptide was cryptic. Immunization with human Ro60441-465 induced
primarily anti-peptide Abs. Mouse Ro60441-465 failed to induce an antibody response. These results show that both the nature of the immunogen and the immunogenicity of the related endogenous antigen are important in determining the specificities of the autoantibodies generated. They have significant implications for proposed mechanisms on the generation of
complex patterns of autoantibodies to a diverse group of autoantigens in SLE patients.
Department of
Microbiology, the § Departments of Psychiatric Medicine and Neurology, and the
Department of
Pathology, the University of Virginia School of Medicine, Charlottesville, Virginia 22908
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