Immunological detection and visualization of 8-methoxypsoralen-DNA photoadducts

Monoclonal antibodies specific for DNA damaged by 8-methoxypsoralen (8-MOP) plus ultraviolet A (UVA) light were used to study adduct formation in human keratinocytes and mouse and rat skin in vivo. This antibody does not cross-react with nonmodified DNA or free 8-MOP. Sensitive competitive enzyme-linked immunosorbent assays with color or fluorescence endpoints were used to quantitate adducts on DNA isolated from treated keratinocytes or skin samples. Localization of 8-MOP-DNA adducts was studied by indirect immunofluorescence with fluorescein-conjugated anti-mouse-IgG antibodies. When cultured keratinocytes were treated with 8-MOP and UVA, immunofluorescence was localized in the nucleus. There was no fluorescence in untreated control cells or treated cells incubated with nonspecific serum. Comparison of intensity of immunofluorescence staining with quantitation of adduct levels by enzyme-linked immunosorbent assay indicated that the limit of sensitivity of the immunofluorescence technique is 9.0 fmol adduct/micrograms DNA or 2.9 adducts/10(6) nucleotides.