Antibodies to cultured rat heart cells in sera of patients with rheumatoid arthritis.

Since heart lesions occur in many patients with rheumatoid arthritis (RA), sera from these patients were tested with an indirect fluorescent technique for antibodies reactive with rat heart cell cultures. Of 27 sera 22 had reactivity with non-muscle (nM) cells and 3 reacted with cultured beating muscle cells (M). Positive sera reactive with nM cells exerted complement-dependent cell cytotoxicity towards M cells. The nM antibodies were found to belong predominantly to the IgG class. They displayed no cross-reactivity with bovine collagen, human and bovine serum proteins, or human and sheep red blood cells. The relationship of these antibodies to the pathogenesis of RA heart lesions remains to be determined.