IgA antihistone antibodies in isoniazid-treated tuberculosis patients.

A retrospective study of tuberculosis patients treated with isoniazid was undertaken in order to establish the prevalence and specificity of antibodies against histones, chromatin and denatured DNA. Each patient had an average of 2.7 +/- 0.4 antibody activities out of the 8 tested antigens using ELISA. These reactivities tended to be higher for non-native forms of the antigens such as denatured histones and DNA with essentially no reactivity to the (H2A-H2B)-DNA subunit of chromatin. Greater than half of the patients were isotype restricted to only IgA or IgM antihistone antibodies, and IgA antihistone antibodies were the most common and reactive. Thirty-five percent of the patients had elevated levels of one or more immunoglobulin classes, and the IgA level was strongly correlated with IgA antihistone activity. These results suggest that isoniazid treatment results in modest increases in antihistone antibodies of the specificities and class typical of drug-induced autoimmunity in the absence of lupus-like disease. The IgA antihistone predominance suggests that serum antoantibodies may be the consequence of stimulation by isoniazid of lymphocytes in the gut-associated Peyer's patches or intestinal lymphoid follicles.