Anti‐nuclear matrix antibodies in mixed connective tissue disease

Abstract

Purified serum antibodies of patients suffering from mixed connective tissue disease were tested for their immunological specificity against nuclear constituents of HeLa S3 [human cervical epitheloid carcinoma] cells. In the direct immunofluorescent staining technique, using cells and nuclei as targets, a typical speckled intranuclear staining pattern was obtained, that persisted after degradation and extraction of all nucleic acids and their associated proteins. This treatment of nuclei with detergents, DNase, RNase and high salt concentrations left intact only the so-called nuclear matrix which is an intranuclear proteinaceous network. Further proof that nuclear matrix proteins were targets of the autoimmune reaction was obtained after separation of these proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis and electrophoretic transfer to nitrocellulose (blotting). A specific number of blot-transferred matrix proteins reacted with purified serum antibodies of 10 patients with mixed connective tissue disease; this reaction was negative with normal healthy individuals. IgG preparations of 7 patients with systemic lupus erythematosus showed a weak, if any, reaction with matrix constituents. Obviously, in some connective tissue diseases serum antibodies are expressed which are directed to specific nuclear matrix antigens.