Patterns of antihistone antibody specificity in systemic rheumatic disease. I. Systemic lupus erythematosus, mixed connective tissue disease, primary sicca syndrome, and rheumatoid arthritis with vasculitis

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Abstract
A new fluorimetric assay was used to measure the relative amounts of antibodies to individual nuclear histones in sera from 102 patients with systemic lupus erythematosus (SLE), mixed connective tissue disease, primary sicca syndrome, and rheumatoid arthritis with vasculitis. In SLE sera, the predominant responses were to histones H‐1, H‐2B, and H‐3, with marked elevations of binding to H‐1 and H‐2B in one‐third of the patients, and to H‐3 in one‐fourth; antibodies of both the IgG and IgM classes were also detected. In a few SLE sera, the pattern of histone response differed or was restricted to 1 immunoglobulin class. In mixed connective tissue disease, only 2 of 9 sera showed elevated histone binding activity, the response being predominantly to H‐3 in 1 patient and to H‐1 and H‐2B in the other. Binding to H‐2B was also prominent in 2 of 3 patients with primary sicca syndrome. The highest antihistone reactivity and the most heterogeneous response patterns were observed in patients who had rheumatoid arthritis with vasculitis; 6 of 8 of those sera had elevated histone reactivity. In SLE, the highest histone binding results were found among patients with a history of photosensitivity. Histones are closely associated with DNA in the nucleosome, and we speculate that antihistone antibodies could arise as a result of damage to DNA, induced by drugs or irradiation.