IMMUNOSUPPRESSION INDUCED BY CHRONIC SOLAR-SIMULATED IRRADIATION IN HUMANS AND ITS PREVENTION BY SUNSCREENS

We examined in humans the effects of skin exposure either to UVB + UVA radiations or to UVA alone on the delayed-type hypersensitivity (DTH) , in order to assess both the local and systemicaly induced immunosupp ression. We then studied the efficacy of sunscreens in preventing the photoimmunosuppression. DTH was measured by using a Multitest kit (Pas teur/Merieux) which provides an interesting means to evaluate photoimm unosuppression without sensitizing volunteers. DTH tests were performe d before and after UV exposure on an exposed area (local and systemic suppression) and on an unexposed area (systemic suppression). For this purpose, 3 groups of 10 to 12 healthy subjects received 10 exposures of UVB + UVA light onto the anterior and posterior aspects of the body ; one group was exposed to UV light without product and the other two were exposed after being applied either a UVB or a UVB + UVA wide spec trum sunscreen (both with the same SPF 9). The total UVB + UVA dose re ceived corresponded to 14.5 individual minimal erythemal dose (MED) wi thout product and 13 MED multiplied by half the SPF value where a suns creen product was applied. A fourth group of 11 subjects received 12 e xposures of WA Light without sunscreen with a cumulated UVA dose of 35 0 J/cm(2). A control group of 12 subjects allowed to check the variabi lity of reactivity to the Multitest without UV exposure. The responses to the DTH test were significantly reduced by UVB + UVA and UVA in th e groups without susncreen protection. In both cases, the immunosuppre ssion was found both local and systemic. Under UVB + UVA exposure the UVB sunscreen fails to provide local and systemic immunoprotection. Th e UVB + UVA sunscreen having the same SPF but also providing and adequ ate protection in the UVA range significantly reduces the local UV ind uced immunosuppression and prevents the sytemic effects. The role of U VA in the photoimmunosuppression phenomenon is clearly shown in this s tudy together with the need for sunproducts protecting in both UVB and UVA.