title: Sunlight-induced immunosuppression in humans is initially because of UVB, then UVA, followed by interactive effects.
abstract: Solar-simulated ultraviolet radiation (ssUV) suppresses immunity in humans. The ultraviolet B (UVB) waveband is recognized as immunosuppressive; however the relative significance of UVA to ssUV immunosuppression is unknown. We created dose and time-response curves for UVB-, UVA-, and ssUV-induced suppression of memory immunity to nickel in humans. UVB caused immunosuppression within 24 h. UVA immunosuppression required 48 h and was normalized by 72 h. UVB alone accounts for ssUV immunosuppression at 24 h, but both UVB and UVA contributed at 48 h. By 72 h neither waveband accounted for ssUV immunosuppression. An interaction between these wavebands was therefore the major contributor. To confirm this dose-response curves were used to determine immune protection factors (IPF) for sunscreens with nickel challenge 72 h following ssUV. A sunscreen with good UVA protection had an IPF twice that of a poor UVA protector, despite providing similar protection from sunburn. Thus UVA was a major contributor to ssUV-induced immunosuppression at 72 h but only with the cooperation of UVB. Hence, UVB initiates immunosuppressive signals within 24 h, followed by UVA at 48 h, then an interaction between UVB and UVA. By 72 h following ssUV exposure, neither UVB nor UVA, but an interaction between them is the major cause of sunlight-induced immunosuppression.
authors.affiliation: Discipline of Medicine (Dermatology), Melanoma and Skin Cancer Research Institute, Sydney Cancer Centre, Royal Prince Alfred Hospital at the University of Sydney, Sydney, NSW, Australia.
authors.forename: Terence S C
authors.initials: TS
authors.lastname: Poon
authors.forename: Ross St C
authors.initials: RS
authors.lastname: Barnetson
authors.forename: Gary M
authors.initials: GM
authors.lastname: Halliday
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007108:Immune Tolerance / Q000528:radiation effects*; D008875:Middle Aged; D013472:Sunlight / Q000009:adverse effects*; D013473:Sunscreening Agents / Q000494:pharmacology; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D013473:Sunscreening Agents