[New method of isolating components of immune complexes, using the example of rheumatoid arthritis].

Immune complexes were precipitated under defined conditions using polyethleneglycol. The precipitation was subjected to the first electrophoresis under nondecomposed conditions for immune complexes. In this way IgG can essentially be separated from the immune complexes which remain in the place where they were applied. In a second electrophoresis, the broken immune complexes were fractionated into IgM and IgG bands. These were analysed for antibody activity by means of hemagglutination and immunofluorescent methods. In serum of 20 rheumatoid arthritis patients, we could detect in the IgM fraction of the immune complexes the rheumatoid factor, an antinuclear antibody, and a new unknown antibody directed against cell plasma membranes of human muscle cells and endothelial cells. The importance of this new antibody in the pathogenesis was discussed.