Figure 2. Photoprotection against thymine dimers by 1,25(OH)2D3 and Bufalin in human keratinocytes. DNA damage was assessed using a monoclonal antibody to thymine dimers,182 immunohistochemistry and image analysis as previously described89,94 at 3 h after UV irradiation, in human keratinocytes treated with vehicle, 1,25(OH)2D3 or three concentrations of bufalin and expressed as positively stained nuclei as a percent of total nuclei. The graph illustrates pooled data from a minimum of four independent experiments. *** denotes a significant difference compared with vehicle (***p < 0.001), ^, ^^, ^^^ denotes a significant difference compared with 10−9M bufalin (^p < 0.05, ^^p < 0.01, ^^^p < 0.001).