Repeated exposures of humans to low doses of solar simulated radiation lead to limited photoadaptation and photoprotection against UVB-induced erythema and cytokine mRNA up-regulation

Abstract

Exposure of the skin to ultraviolet radiation (UVR) causes local and systemic immunosuppression [ [1] Clydesdale G.J. Dandie G.W. Muller H.K. Ultraviolet Light induced injury: immunological and inflammatory effects. Immunol Cell Biol. 2001; 79: 547-568 Crossref PubMed Scopus (445) Google Scholar ]. One major local change induced by the UVR is production of immunomodulating cytokines, including IL-1α, IL-1β, IL-6, IL-8, IL-10 and TNF-α, from keratinocytes and other target cells [ 2 Barr R.M. Walker S.L. Tsang W. Harrison G.I. Ettehadi P. Greaves M.W. et al. Suppressed alloantigen presentation, increased TNF-alpha, IL-1, IL-1 Ra, IL-10, and modulation of TNF-R in UV-irradiated human skin. J Invest Dermatol. 1999; 112: 692-698 Crossref PubMed Scopus (83) Google Scholar , 3 Brink N. Szamel M. Young A.R. Wittern K.P. Bergmann J. Comparative quantification of IL-1beta, IL-10, IL-10r, TNF-alpha and IL-7 mRNA levels in UV-irradiated human skin in vivo. Inflamm Res. 2000; 49: 290-296 Crossref PubMed Scopus (109) Google Scholar ]. Most in vivo studies have employed a single erythemal dose of UVB. In real life, many human subjects go outside for short periods of time on a daily basis during the summer months and respond by tanning and epidermal thickening. To mimic this type of exposure, we assessed the contact hypersensitivity response in individuals irradiated daily for up to 30 days with a low dose of solar simulated radiation (SSR) [ [4] Narbutt J. Lesiak A. Skibinska M. Wozniaka A. van Loveren H. Sysa-Jedrzejowska A. et al. Suppression of contact hypersensitivity after repeated exposures of humans to low doses of solar simulated radiation. Photochem Photobiol Sci. 2005; 4: 517-522 Crossref PubMed Scopus (28) Google Scholar ]. Now we extend these observations by assessing whether photoadaptation to the induction of four cutaneous cytokine mRNAs occurred as a result of repeated SSR exposures. The dose chosen represented less than 0.3 minimal erythema dose (MED) for subjects with phototypes II and III. This exposure would be achieved after approximately 15 min on a clear day around midday in summer in mid-Europe. It has been reported that the development of a tan in individuals with these phototypes offers some, although limited, protection against erythema [ [5] Sheehan J.M. Potten C.S. Young A.R. Tanning in human types II and III offers modest photoprotection against erythema. Photochem Photobiol. 1998; 68: 588-592 Crossref PubMed Scopus (78) Google Scholar ]. Therefore, we tested for development of photoprotection regarding erythema and cytokine mRNA expression by irradiating a small body area with three MEDs UVB in the subjects who had already received 10 days of SSR.