ACUTE EFFECTS OF LOW-FLUENCE ULTRAVIOLET-LIGHT ON HUMAN LYMPHOCYTES-T SUBSETS

The acute effects of low-fluence ultraviolet light, primarily between wavelengths 280 and 320 nm (ultraviolet B) on T-lymphocyte subsets were assessed in vitro and in vivo by quantitative cytofluorometric analysis. In vitro, 90 J/m2 of ultraviolet irradiation of human mononuclear cells produced a significant increase in the OKT4 (helper-inducer)/OKT8 (suppressor-cytotoxic) ratio (P < 0.008), due primarily to a decrease in the OKT8 subset. In vivo, 24 h after whole-body UV irradiation of human subjects with one half of a minimal erythemal dose of ultraviolet B the OKT4/OKT8 ratios again increased (P < 0.002), again with somewhat greater effects on the OKT8 subset. These results indicate that suberythemal exposure to UV light increases OKT4/OKT8 ratios in normal human subjects because of differential effects on lymphocyte subsets. They suggest that casual exposure to sunlight mediates immunologic changes in normal human subjects.