The detection of smooth muscle antibodies reacting with intermediate filaments of desmin type.

Some human smooth muscle antibodies (SMA) react with cytoskeletal intermediate filament (IMF) antigens. The smooth muscle tissue contains two types of IMF: vimentin and desmin filaments. In this study, SMA of anti-IMF type in 52 patients' sera have been classified into anti-vimentin filament and anti-desmin filament types according to their immunofluorescence staining patterns on rat testis. This classification is based on the fact that the arterial walls of testis contains both vimentin and desmin whereas the myoid cell layer surrounding the seminiferous tubuli contains only desmin. Four out of the 52 sera gave the anti-desmin staining pattern and 40 sera showed the anti-vimentin type of staining. Thirty-two sera were further classified by using cultured human rhabdomyosarcoma (RD) cells as targets. Nine sera reacted with the intermediate filaments of the RD cells. Among these were 3 out of the 4 sera that gave the anti-desmin filament staining pattern. The anti-desmin specificity of SMA was confirmed in 1 serum by the immunoblotting technique. These results indicate that while human anti-desmin filament antibodies exist, most human SMA of anti-IMF type react with vimentin filaments.