Lupus-prone NZM2328 mice exhibit enhanced UV-induced myeloid cell recruitment and activation in a type I interferon...

Though the exact causes of systemic lupus erythematosus (SLE) remain unknown, exposure to ultraviolet (UV) light is one of the few well-known triggers of cutaneous inflammation in SLE. However, the precise cell types which contribute to the early cutaneous inflammatory response in lupus, and the ways that UV dosing and interferons modulate these findings, have not been thoroughly dissected. Here, we explore these questions using the NZM2328 spontaneous murine model of lupus. In addition, we use iNZM mice, which share the NZM2328 background but harbor a whole-body knockout of the type I interferon (IFN) receptor, and wild-type BALB/c mice. 10-13-week-old female mice of each strain were treated with acute (300 mJ/cm² x1), chronic (100 mJ/cm² daily x5 days), or no UVB, and skin was harvested and processed for bulk RNA sequencing and flow cytometry. We identify that inflammatory pathways and gene signatures related to myeloid cells - namely neutrophils and monocyte-derived dendritic cells - are a shared feature of the acute and chronic UVB response in NZM skin greater than iNZM and wild-type skin. We also verify recruitment and activation of these cells by flow cytometry in both acutely and chronically irradiated NZM and WT mice and demonstrate that these processes are dependent on type I IFN signaling. Taken together, these data indicate a skewed IFN-driven inflammatory response to both acute and chronic UVB exposure in lupus-prone skin dominated by myeloid cells, suggesting both the importance of type I IFNs and myeloid cells as therapeutic targets for photosensitive patients and highlighting the risks of even moderate UV exposure in this patient population.