Alteration of T cell subsets and induction of suppressor T cell activity in normal subjects after exposure to sunlight.

The effects of exposure to natural sunlight on the immune system were studied in 15 normal human subjects. Exposure was for 1 hr each day for 12 days over 2 wk and tests were carried out before, on completion, and 2 wk after completion. In comparison to concurrent studies on 13 age- and sex-matched controls, sun-exposed subjects had a significant increase in their circulation of T cells recognized by OKT8 monoclonal antibodies and a decrease in OKT4 positive T cells. Suppressor T cell activity measured in pokeweed mitogen-stimulated cultures of T and B cells was significantly increased against IgG and IgM production. These changes were still evident in many of the subjects 2 weeks after completion of the sun exposure. A trend for depression of natural killer cell activity against a melanoma target cell was noted in the present study, but this did not appear as marked as that noted previously in subjects exposed to radiation in solariums. The differences between the effect of radiation from solariums and natural sunlight on the immune system may result from the higher dosage of UV-A in radiation from solariums. The results suggest that exposure to sunlight may favor the induction of suppressor pathways in response to antigenic stimuli and that this may limit immune responses against tumor cells such as melanoma. They support the idea from animal studies that systemic changes in the immune system may be an important factor in the association of UV radiation with malignancy.