Development of antibodies to ribonucleoprotein following short-term therapy with procainamide.

An autoimmune response to certain nuclear antigens frequently develops in patients receiving prolonged therapy with procainamide. In order to define events involved in the initiation of this immune response, patients with myocardial infarction were studied early after starting procainamide and at later times. Polynucleotide antibodies and circulating polynucleotide antigens were sought by sensitive assay techniques in the sera of these patients. Very high titers of antiribonucleoprotein developed selectively in the majority of these patients after short-term therapy with procainamide. Such antibodies were infrequent in the long-term therapy group, most of whose members exhibited anti-single-strand DNA and were symptomatic with overt procainamide-induced lupus. Patients with acute myocardial infarction who did not receive procainamide did not develop anti-polynucleotide antibodies, but rather had high levels of free ribonucleoprotein antigen in their serum. Various interpretations of these data are discussed.