Antihistone antibodies in systemic lupus erythematosus: assay dependency and effects of ubiquitination and serum DNA.

OBJECTIVE

Antihistone antibodies occur in systemic lupus erythematosus (SLE) but there are many discrepancies in their reported prevalence, isotype, specificity and correlation with disease symptoms. We examined the role of the assay and the influence of serum DNA as possible causes of these discrepancies. In addition, we sought to confirm the presence of antibodies to ubiquitin and ubiquitinated H2A (uH2A).

METHODS

Western blot and enzyme linked immunosorbent assay (ELISA).

RESULTS

Sera displayed substantial differences between ELISA and Western blot in reactivity to individual histones when all reagents were nearly identical, indicating that subtle differences in the solid phase adsorbents have pronounced effect on histone antigenicity. No uniform pattern of antibody reactivity with the 5 histones was apparent with either assay. For most sera, digestion with DNase caused only minor decrease in binding to histones and no histone class showed particular sensitivity to this treatment. In agreement with most other studies, no significant correlation between histone binding and symptoms was found. Just 2 of 40 sera showed detectable binding to ubiquitin or uH2A.

CONCLUSION

Although IgG antihistone antibodies were detected in 53-55% of patients with SLE with active disease, the sensitivity of antibody activity to assay conditions, patient variability, and lack of correlation with symptoms compromise the clinical utility of measuring antihistone antibodies by Western blot or ELISA: We were also unable to confirm that ubiquitin and uH2A are major antigens recognized by antibodies in SLE.