Quantitative detection of DNA damage in cells after exposure to ionizing radiation by means of an improved immunochemical assay.

A simple, sensitive and fast immunochemical method has been developed to quantify the amount of DNA damage in cells of human blood after in vitro exposure to ionizing radiation. The technique is based on the enhancement of the radiation-induced single-strandedness, which occurs in DNA regions flanking strand breaks, by a controlled further unwinding of the DNA in an alkaline solution. Subsequently, the DNA is attached to the wall of polystryene cups by passive adsorption. DNA damage is then quantified by determining the extent of single-strandedness with a monoclonal antibody, D1B, directed against single-stranded DNA. D1B binding is assayed with a 'second' antibody, labelled with either an enzyme or europium. The latter gives slightly more reproducible results. No radioactive labelling of DNA is required and the assay takes only 3.5 h after the collection of blood. Damage can be detected after doses as low as 0.5 Gy. The potential broader application of the method is discussed.