Antibodies to cytoplasmic intermediate filaments in rheumatic diseases

Antibodies to 2 types of cytoplasmic intermediate filaments (IMF)--vimentin and cytokeratin filaments--were assayed in sera from various rheumatic diseases by indirect immunofluorescence using cultured human embryonic fibroblasts and an epithelial cell line, PtK 2, as substrates. These antibodies belonged mainly to the IgM class and were detected in most of the sera. Vimentin filament antibodies of IgG or IgA class were frequent in Sjögren's syndrome (43%). Antibodies to another type of IMF, cytokeratin filaments, were also more prevalent in Sjögren's syndrome (64%) than in systemic lupus erythematosus (50%), rheumatoid arthritis (46%) and other hospital patients (8%). Our results show that intermediate filaments are a major target for autoantibodies in rheumatic diseases, especially in Sjögren's syndrome. The presence of intermediate filament IgA antibodies suggest that the stimulus for their production lies at epithelial surfaces.