Ultraviolet light induces HERV expression to activate RIG‐I signalling pathway in keratinocytes.

Skin inflammation and photosensitivity are common in lupus erythematosus (LE) patients, and ultraviolet (UV) light is a known trigger of skin and possibly systemic inflammation in systemic lupus erythematosus (SLE) and discoid lupus erythematosus (DLE) patients. Type I interferons (IFN) are upregulated in LE skin after UV exposure; however, the mechanisms to explain UVB‐induced inflammation remain unclear. Here, we demonstrated that UVB irradiation‐induced activation of human endogenous retroviruses (HERVs) plays a major role in the immune response. UVB‐induced HERV‐associated dsRNA transcription and subsequent activation of the innate antiviral RIG‐I/MDA5/IRF7 pathway led to downstream transcription of interferon‐stimulated genes, which promotes UVB‐induced apoptosis and proliferation inhibition in keratinocytes through RIG‐I and MDA5 pathways. Our findings indicate that UVB irradiation induces HERV‐dsRNA overexpression, and the dsRNA‐sensing innate immunity pathway promotes type I IFN production, which may be a potential mechanism of skin inflammatory response and skin lesion of SLE/DLE. [ABSTRACT FROM AUTHOR]