Reactive oxygen species modified thymine and poly(dT) present unique epitope for human anti-DNA autoantibodies

Hydroxyl radical, one of the most potent of all reactive oxygen species has been implicated in many human degenerative diseases and is known to modify adenine and thymine in cellular DNA. In the present studies, adenine, thymine and their synthetic homopolymers poly(dA), poly(dT) were ROS-modified and subsequently used as inhibitors of native DNA binding to human anti-DNA autoantibodies. Besides nDNA, modified thymine and poly(dT) were effective inhibitors of DNA-anti-DNA antibody interaction. The relative affinity of ROS-modified poly(dT) was better than that of native DNA. Visual detection of modified thymine and poly(dT) binding to affinity purified anti-DNA IgG by an indirect band shift assay support competition inhibition data. The enhanced recognition of ROS-DNA by anti-DNA autoantibodies, as reported earlier, could be due to the ROS-induced modification of thymine.