Differences between antihistone antibodies found in systemic DILE and idiopathic SLE
In certain specialized research laboratories, the specificity of antihistone antibodies for individual histones (i.e., H1, H2A, H2B, H3, and H4), histone complexes, or intrahistone epitopes can be distinguished. Overall, antihistone antibodies in DILE tend to be much more focused on certain histone complexes than those in idiopathic SLE. For example, in procainamide-induced lupus (and most other causes of DILE), the onset of symptomatic disease has been associated with the production of IgG antibodies to the H2A-H2B-DNA complex. Although this complex is also a target in about 15% of patients with SLE, autoantibodies in idiopathic SLE are frequently directed to other individual histones (H1 and H2B) and other histone complexes. In hydralazine-induced disease, the major target is the H3 to H4 complex. In contrast to procainamide-induced lupus and SLE, autoantibodies induced by hydralazine appear to be directed more to determinants hidden within the chromatin rather than exposed on the surface.