A single exposure of human skin in vivo to UV-SSR, UVA or UVA1 radiation results in different alterations of density and/or morphology of LCs. All these alterations may impair the antigen-presenting function of LCs leading to an alteration of immune response.

Simulated UV daylight is a relevant new tool for daily photoprotection studies.

It is increasingly accepted that sunscreens should protect against ultraviolet radiation (UVR)-induced immunosuppression, with an index of protection that can be compared with the sun protection factor (SPF). Five groups of immunoprotection researchers met to discuss the status of immune protection factor (IPF) evaluation in human skin in vivo. Current methods rely on a suncreen's inhibition of UVR-induced local suppression of the contact hypersensitivity (CHS) response or the delayed-type hypersensitivity (DTH) response, using either the induction or the elicitation arms of these responses. The induction arm of the CHS response has the advantage of being sensitive to a single sub-erythemal exposure of solar-simulating radiation (SSR) that allows a direct comparison with the SPF. This approach, which necessitates sensitization, requires a large number of volunteers and is too labor intensive and time consuming to become a routine method. The elicitation arm of the CHS or DTH responses exploits prior sensitization to contact or recall antigens and has the advantage of being possible to apply on small groups of volunteers. Some current protocols, however, require repeat SSR exposures, which invalidates a direct comparison with SPF that is based on a single exposure. There is a need for a new simpler method of IPF that will have to be validated against existing models.

Ultraviolet radiation-induced immunosuppression is thought to play a part in skin cancer. Several studies have indicated that sunscreens that are designed to protect against erythema failed to give comparable protection against ultraviolet radiation-induced immunosuppression. One possible reason for this discrepancy is inadequate ultraviolet A protection. This study evaluated the level of immunoprotection in mice afforded by two broad-spectrum sunscreens with the same sun protection factor, but with different ultraviolet A protection factors. Both sunscreens contained the same ultraviolet B and ultraviolet A filters, in the same vehicle, but at different concentrations. Solar simulated radiation dose-response curves for erythema, edema, and systemic suppression of contact hypersensitivity were generated and used to derive protection factors for each end-point. The results of three different techniques for determining immune protection factor were compared. A comparison of the two sunscreens showed that the protection factor for erythema in mice was similar to that determined in humans (sun protection factor) but the protection factor for edema in mice was lower. Both sunscreens protected against suppression of contact hypersensitivity but the product with the higher ultraviolet A-protection factor showed significantly greater protection. The three techniques for determining immunoprotection gave very similar results for a given sunscreen, but immune protection factor was always lower than sun protection factor. These data suggest that sun protection factor may not predict the ability of sunscreens to protect the immune system and that a measure of ultraviolet A protection may also be necessary.

No abstract