Reactivity of anti-histone antibodies induced by procainamide and hydralazine

Sera from patients with procainamide (Pr)- or hydralazine (Hy)-induced lupus were examined for anti-histone antibodies by an immunofluorescence assay using histonerecostituted mouse kidney sections and by a solid-phase radioimmunoassay using polystyrene tubes coated with purified histones. Distinct differences were observed between Pr sera and Hy sera. Pr sera were uniformly positive in the immunofluorescence assay on histone-reconstituted tissue sections, but all Hy sera were negative. In solidphase radioimmunoassay, both Pr and Hy sera showed anti-histone activity with Pr sera demonstrating strong reactions with H2A-H2B histone complex but Hy sera demonstrating weak reactions. The difference in the immunofluorescence assay could in most but not all instances be attributed to this difference in anti-H2A-H2B activity. Antibodies were not detected to DNA or to nonhistone nuclear antigens Sm, nuclear ribonucleoprotein, and SS-B La . The results indicate that both Pr and Hy induce antibodies to histones and that anti-histone antibodies induced by Pr differ both quantitatively and qualitatively from those induced by Hy.