Autoantibodies to hmg‐17 nucleosomal protein in autoimmune rheumatic diseases

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Abstract
Objective. Previous studies have shown that serum from patients with systemic lupus erythematosus (SLE) contains antibodies directed against HMG-17, a nucleosomal nonhistone high mobility group (HMG) protein found in chromatin. The aim of the present study was to investigate any associations between the presence of antibodies to HMG-17 and clinical and serologic features of SLE. Methods. Using porcine thymus as a source, HMG-17 was purified by Sephacryl S-200 chromatography followed by high performance liquid chromatography. An enzyme-linked immunosorbent assay utilizing the purified HMG-17 as antigen was developed and was used to evaluate sera from patients with autoimmune rheumatic diseases, for the presence of autoantibodies. Results. Anti–HMG-17 antibodies were found in the serum of 34.8% of the patients with SLE, compared with 11.5% of patients with primary Sjögren's syndrome, 4.4% of patients with rheumatoid arthritis, and 4.1% of normal blood donors. Analysis of the clinical features of SLE using 2 different lupus activity indices revealed that anti-HMG-17 antibodies were more frequently found in patients with active disease. A positive correlation was also observed between anti–HMG-17 and anti-dsDNA levels, and levels of both of these autoantibodies demonstrated a negative correlation with C4. Analysis of sequentially obtained serum samples from 4 SLE patients revealed that, in 2 patients, anti-HMG-17 levels fluctuated in parallel with both disease activity and anti-dsDNA levels, and in the remaining 2, anti–HMG-17 levels fluctuated in parallel with disease activity. Conclusion. Antibodies to HMG-17 are found in patients with many different autoimmune rheumatic diseases, although they are more frequently observed in those with SLE. Their presence appears to be associated with lupus disease activity as well as with anti-dsDNA and C4 levels.