DIFFERENTIAL-EFFECTS OF SUNSCREENS ON UVB-INDUCED IMMUNOMODULATION INHUMANS

Ultraviolet radiation has been shown to suppress the (skin) immune sys tem both in animal species and in humans, Whether sunscreens can preve nt immunosuppression is a matter of debate. This study investigated th e protective capacity of a commercial sunscreen lotion in humans. Part of the right arm of healthy volunteers was exposed to erythemagenic u ltraviolet B doses of 160 mJ per cm(2) for four consecutive days. Befo re irradiation, sunscreen was applied either directly onto the skin or onto a piece of quartz fixed to the skin (to avoid penetration of the sunscreen in the epidermis where it cannot block the photoisomerizati on of trans-urocanic acid in cis-urocanic acid in the stratum corneum) . The control group was irradiated without prior application of sunscr een, Four h after the last irradiation, epidermal sheets were obtained by the suction-blister method from both arms and epidermal cells were used as stimulator cells in the mixed epidermal cell lymphocyte react ion, Responses directed to epidermal cells derived from irradiated ski n were expressed as percentages of responses directed to epidermal cel ls derived from the nonirradiated left arm, The mixed epidermal cell l ymphocyte reaction responses in the control group were found to be sig nificantly increased (205%). This enhancement of the mixed epidermal c ell lymphocyte reaction responses was associated with an influx of CD3 6(+)DR(+) macrophages in the irradiated skin, Application of the sunsc reen, either onto a piece of quartz or directly onto the skin, prevent ed the increase of the mixed epidermal cell lymphocyte reaction respon ses and the influx of CD36(+)DR(+) cells, In an earlier study, volunte ers were exposed three times weekly to suberythemagenic doses of ultra violet B over 4 wk, resulting in mixed epidermal cell lymphocyte react ion responses that were decreased to 20%. The same sunscreen was not a ble to prevent this suppression, These contradicting results indicate that the protective effect of sunscreens with respect to ultraviolet-i nduced immunomodulation is critically dependent on the choice of ultra violet treatment.