UV Light Exposure Induces a Type I Interferon Dependent Activation and Migration of Inflammatory Dendritic Cells to Local Lymph Nodes

Objective Photosensitivity occurs in ~75% of lupus patients. Although ultraviolet light radiation (UVR) stimulates Type I interferon (IFN‐I) in the skin, how UVR induced skin inflammation leads to downstream effects is poorly understood. Tissue inflammation causes DC to migrate from organs to draining lymph nodes (dLN) including a recently identified inflammatory DC subset (inf cDC2) that are potent antigen presenting cells. To explore links between UVR and the early immune response, we examined DC and lymphocyte subset migration to dLNs in normal and a lupus prone mouse strains as well as the role of IFN‐I. Methods Mice received a single dose of UV (500 mJ/cm2) on the dorsal skin. Brachial and axillary dLN were harvested at 1‐ or 2‐days post UVR. Flow cytometry using the Symphony A3 cytometer and 15 color staining identified myeloid and lymphoid subsets. Statistical significance was determined by Student's t‐test. Results Higher numbers of CD64+ myeloid cells as well as inf cDC2 were detected in the dLN after UVR in B6 mice but not in Ifnar KO mice. In contrast, Trex1 mutant mice had an exaggerated IFN‐I response in the skin and a higher proportion of inf cDC2 in the dLN. Conclusions These findings reveal a previously unknown relationship between skin UVR and the migration inf cDC2 population to dLN. They highlight the role of IFN‐I in this process and the differences between Trex1 mutant and normal mice suggest this may be of relevance to lupus.