Topical vitamin e inhibition of immunosuppression and tumorigenesis induced by ultraviolet irradiation

Abstract

Ultraviolet (UV) irradiation of C3H/HeN mice induces skin cancer and an immunosuppression that prevents the host from rejecting antigenic UV‐induced tumors. The capacity of topical vitamin E (dl‐α‐tocopherol) to prevent photocarcinogenesis or the immunosuppression induced by UV irradiation were assessed. Skin cancer incidence in UV‐irradiated mice was 81 % at 33 weeks after the first UV exposure; application to mice of 25 mg vitamin E three times per week for three weeks before UV irradiation, and throughout the experiment, reduced this incidence to 42% (p = 0.0065, log rank test). Immuno‐enhancement by vitamin E was assessed by comparing levels of immunosuppression by splenocytes from normal or UV‐irradiated mice, with and without topical vitamin E treatment. Transfer of splenocytes from UV‐irradiated mice to naive mice prevented the recipients from rejecting a UV‐induced tumor challenge, whereas splenocytes from UV‐irradiated mice treated with vitamin E did not prevent recipients from rejecting a similar tumor challenge. Phenotypic analysis of splenocytes used in the passive transfer assay, conducted with a biotin‐avidin‐immunoperoxidase technique, revealed that vitamin E treatment of mice undergoing UV irradiation prevented the UV‐induced down regulation of la expression in splenocytes and increased the proportion of Lyt‐2⁺ and L3T4⁺ splenocytes. Therefore, chronically applied vitamin E can effectively reduce cancer formation and immunosuppression induced by UV irradiation. Prevention of UV‐induced down regulation of la expression may have contributed to this immunomodulation.