Effects of solar-simulated radiation dose fractionation on CD1a+Langerhanscells and CD11b+macrophages in human skin

Background There are few human studies investigating the immunosuppressive effects of exposure to solar-simulated radiation (SSR) and its relationship with sunburn/erythema, and few comparative data on the importance of SSR e xposure regimens. Objectives To evaluate whether SSR-induced erythema is a reliable end-point for assessing damage to antigen-presenting cells (APCs) in human skin. Methods We compared the relationship between SSR-induced erythema and alter ations in epidermal CD1a+ Langerhans cells (LCs) and CD11b+ macrophages in human volunteers after single exposures to 0, 0.5, 1, 2 or 3 minimal erythe ma doses (MED). We also investigated whether SSR exposure leads to an accum ulation or accommodation of the same end-points by comparing the effects of a relatively low cumulative SSR dose (3 MED) given in varying daily dose f ractions (4 x 0.75 MED, 2 x 1.5 MED and 1 x 3 MED). Results Single SSR exposures induced a dose-dependent increase in erythema. CD1a+ LCs remaining in the irradiated epidermis showed a dose-dependent in crease in cell size and altered morphology. Significant depletion of CD1aLCs and presence of CD11b+ macrophages only occurred in sites irradiated wi th 2 MED and 3 MED. Dose fractionation had no effect on the final erythemal response but the 4 x 0.75 MED and I x 3 MED protocols were better tolerate d than 2 x 1.5 MED for alterations in CD1a+ LC and CD11b+ cell numbers. In contrast, dose fractionation protected against alterations in CD1a+ LC morp hology or cell size. Conclusions We found that erythema is a poor indicator of alterations in ep idermal APCs and that dose fractionation is an important parameter in the i mmunological effects of ultraviolet radiation.