Citation:
Hart PH. Sun-immune connection. Nat Rev Immunol. 2019;19(11):661
Abstract:
Exposure to ultraviolet radiation (UVR) damages skin cell DNA but skin cancers develop because UVR also affects the immune system. How does this occur? In 1983, De Fabo and Noonan identified a unique photoreceptor in skin — urocanic acid (UCA) — that is an important intermediary by which UV wavelengths of 250–320 nm lead to systemic immunosuppression. Importantly, the characteristics of UVR-induced skin tumour development matched those of UVR-mediated reduction in contact hypersensitivity (CHS) responses in mice with an intact epidermis. Furthermore, the dose–response relationship between UVR exposure and reduced CHS responses was very similar to the absorption spectrum of UCA, a major component of the epidermis, which isomerizes from the trans to the cis form upon irradiation.