Inhibition of Con A mitogenesis by serum from procainamide-treated patients and patients with systemic lupus erythematosus.

Serum obtained from patients with spontaneous systemic lupus erythematosus or from patients treated at least 3 months with procainamide could specifically inhibit Con A mitogenesis of cultured peripheral blood mononuclear cells obtained from procainamide-treated patients or from normal donors. Transfer of procainamide treated patients to N-acetylprocainamide eliminated the blocking factor from their serum. The blocking factor is not procainamide itself since adding the drug to normal serum and only slight effects on mitogenesis of normal peripheral blood mononuclear cells. These data suggest that systemic lupus erythematosus and procainamide-induced lupus may differ in the relative reversibility of a regulatory defect associated with a Con A responsive population of peripheral blood mononuclear (PBM) cells.