The specificity of disease-associated anti-fibrillarin autoantibodies compared with that of HgCl2-induced autoantibodies

Autoantibodies against nucleolar components are a common serological feature of patients suffering from scleroderma, a collagen vascular autoimmune disease. An important target of these autoantibodies is a protein with an apparent molecular weight of 36 kDa and a pI value of 8.5, located in the dense fibrillar component of the nucleolus and therefore termed fibrillarin. Animal models in which abundant anti-nucleolar antibodies appear spontaneously have not yet been described; however, high levels of anti-fibrillarin antibodies can be induced by treating susceptible strains of mice with sub-toxic amounts of mercuric chloride. In this study, we have analysed the specificity of anti-fibrillarin autoantibodies of human and murine origin. Our results suggest that both species have similar, if not identical conformational epitopes that are the target of anti-fibrillarin autoantibodies; these epitopes require the presence of a 30-kDa fragment of the fibrillarin molecule. Post-translational modifications such as the dimethylation of arginines in the N terminus of the protein are not essential for antibody recognition.