The overall objective of this thesis work was to develop new insights into the etiology of scleroderma, a human systemic autoimmune disease, by analyzing the autoantibodies to centrosome antigens that develop during the disease. Centrosomes are perinuclear organelles that form microtubule arrays, including mitotic spindles that ensure the faithful segregation of chromosomes during mitosis.

These studies used a novel methodology to determine the prevalence of anti-centrosome autoantibodies in patients with scleroderma. Recombinant centrosome antigens were used to determine the antigenic specificity of anti-centrosome antibody subsets by immunoblotting. Centrosome marker antibodies were used in indirect immunofluorescence assays to distinguish centrosomes within the polymorphic staining pattern frequently given by scleroderma sera. We found that 43% of patients are autoreactive to centrosomes, a prevalence higher than has been reported for any other scleroderma autoantigen. Half of the centrosome-positive patients also had autoantibodies against other antigens used in scleroderma diagnosis. However, in the remaining half of these patients, anti-centrosome antibodies represented the sole class of autoantibodies that was detectable. Anti-centrosome antibodies were detected in only a small percentage of normal individuals and patients with other connective tissue diseases. These data suggest that anti-centrosome autoantibodies may represent a new diagnostic tool in scleroderma. Upon examination of anti-centrosome autoantibody development in an animal model, it appeared that this autoantibody specificity may develop in mice as a consequence of an infection.

An infectious agent was isolated by plaque-formation from carrier mice. Further characterization of the infectious agent was undertaken to obtain information on its physical, morphological and cytopathological properties. The infectious agent was identified by sequence and unique antigenic properties to be homologous to the pig pathogen Mycoplasma hyorhinis. When reintroduced into naive mice, the murine mycoplasma triggered anti-centrosome autoantibody development. While anti-centrosome autoantibodies of IgM isotype are part of the repertoire of naive unimmunized mice, mycoplasma infection specifically triggered the development of anti-centrosome IgG. Moreover, centrosome autoreactivity was prevented by antibiotic treatment. The autoantibody response evolved to recruit additional specificities, having IgM isotypes, reactive to endoplasmic reticulum-associated autoantigens.