We previously demonstrated that CD1d knockout mice were resistant to ultraviolet (UV)–induced immunosuppression. Because immune suppression is a critical factor in the development of UV-induced skin cancers, we investigated the response of wild type (WT) and CD1d−/− mice to UV carcinogenesis. We found that although 100% of WT mice developed skin tumors after 45 weeks of UV irradiation, only 60% of CD1d−/− mice developed skin tumors. To investigate the mechanisms involved in the resistance of CD1d−/− mice to UV-induced carcinogenesis, we determined the time course and kinetics of keratinocyte cell death after UV irradiation. After acute UV exposure, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL)-positive keratinocytes were eliminated from the skin of WT mice by 72 h post-UV, but they still persisted until 96 h in CD1d−/− mice. The kinetics of p53 protein expression closely followed the kinetics of apoptotic cell death. Chronic UV irradiation resulted in induction of a significantly higher number of apoptotic keratinocytes in CD1d−/− than WT mice. In addition, epidermis and dermis from chronically UV-irradiated CD1d−/− mice harbored significantly fewer p53 mutations than WT mice. These results indicate that the resistance of CD1d−/− mice to UV carcinogenesis may be due to increased cell death and elimination of keratinocytes and fibroblasts containing DNA damage and p53 mutations.
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Vol. 81 • No. 1