Sunlight-Induced Immunosuppression in Humans Is Initially Because of UVB, Then UVA, Followed by Interactive Effects  Terence S.C. Poon, Ross St C. Barnetson, Gary M. Halliday  Journal of Investigative Dermatology  Volume 125, Issue 4, Pages 840-846 (October 2005) DOI: 10.1111/j.0022-202X.2005.23894.x Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

Figure 1 Single-exposure ultraviolet (V) immunosuppression time course and dose response. In separate experiments groups of 15 nickel-allergic volunteers were irradiated with a single exposure to UVB, UVA or solar-simulated UV (ssUV). Nine different areas on the lower back of each volunteer received one of three UV doses at each of 24 h (open columns), 48 h (hatched columns) and 72 h (closed columns) prior to nickel challenge to generate dose and time responses for each of the three UV spectra. The UVA and UVB doses used were their relative contributions to the ssUV dose. The resultant erythema from the nickel CHS response at each irradiated site was read 72 h after nickel challenge using an erythema meter and subtracted from an unirradiated positive control site to calculate immunosuppression (erythema index). Mean ±SEM are shown for the 15 volunteers. A paired two-tailed Student's t test was used to compare each test site with the unirradiated control to determine whether the immunosuppression at each dose was significant, and this is shown by the p value centered above each column. Journal of Investigative Dermatology 2005 125, 840-846DOI: (10.1111/j.0022-202X.2005.23894.x) Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

Figure 2 Spectra used in this study. An Oriel 1000 W solar simulator equipped with twin 280–400 nm dichroic mirrors and an atmospheric attenuation filter produced a solar-simulated ultraviolet spectrum that closely approximates standard sunlight as defined by COLIPA. Using a ultraviolet (UV)B/UVC-blocking filter in place of the atmospheric attenuation filter produced a UVA spectrum. Two 280–320 nm dichroic mirrors were used together with the atmospheric attenuation filter to produce the UVB spectrum. The ssUV, COLIPA, and UVB spectra were normalized to 1 at 320 nm, whereas the UVA spectrum was normalized at 340 nm to enable them to be compared. Journal of Investigative Dermatology 2005 125, 840-846DOI: (10.1111/j.0022-202X.2005.23894.x) Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

Figure 3 Sunscreen B absorbs more ultraviolet A than sunscreen A. The spectral absorbance of sunscreens A and B was obtained using a Labsphere UV-1000 SPF analyzer (Labsphere, North Sutton, New Hampshire) with sunscreen applied at 2 mg per cm2 onto a quartz plate substrate profiled with the topography of human skin derived from casts of human test back skin. Journal of Investigative Dermatology 2005 125, 840-846DOI: (10.1111/j.0022-202X.2005.23894.x) Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

Figure 4 Immune protection factor determination for sunscreens with solar-simulated ultraviolet (ssUV) 72 h prior to antigen challenge. ssUV immunosuppression dose–response curves using four separate ssUV doses 72 h prior to nickel challenge on skin that was unprotected (circles) or protected with the low ultraviolet A (UVA) protecting sunscreen A (squares) or the high UVA protecting sunscreen B (triangles). Immunosuppression was calculated as the difference between an unirradiated control site and each ssUV-irradiated test site as described in the legend to Figure 2. A mean of 15 volunteers is shown. A line of best fit was obtained using linear regression analysis (solid lines). The minimal immunosuppressive dose was calculated from this line of best fit as that ssUV dose that gave 30% immunosuppression in unprotected skin, which was an immunosuppression of 21 erythemal index in this experiment (dashed lines). Journal of Investigative Dermatology 2005 125, 840-846DOI: (10.1111/j.0022-202X.2005.23894.x) Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions