Background: Photosensitive autoimmune diseases such as cutaneous lupus erythematosus (CLE) and dermatomyositis (DM) are characterized by UVB photosensitivity. A hallmark of these diseases is the strong type I interferon (IFN-I) gene signature in skin, yet the upstream circuits linking keratinocyte injury to leukocyte infiltration remain incompletely defined. Prior studies have largely focused on the role of keratinocytes as sources of IFN-I, but less is known about how IFN-primed keratinocytes interact with surrounding stromal cells to recruit and activate inflammatory cells.

Objectives: To define the spatial, cellular, and molecular circuit linking UV-injured keratinocytes to myeloid cell recruitment and T cell activation in CLE and DM, we aimed to (1) map the spatial relationship of keratinocytes, fibroblasts, and myeloid cells in lesional skin; (2) identify cytokine- and chemokine-mediated communication between these compartments; and (3) validate the functional impact of keratinocyte-fibroblast crosstalk on myeloid cell recruitment and activation.

Methods: We combined single-cell RNA sequencing (scRNA-seq), seqFISH+ spatial transcriptomics, cytokine perturbation experiments, and chemotaxis assays on lesional skin samples from CLE and DM patients, alongside healthy controls. In addition, as a proof of concept, we conducted mechanistic clinical trials in patients with CLE and DM, using standard in vivo UVB photoprovocation protocols.

Results: Spatial transcriptomics of lesional CLE and DM skin revealed consistent enrichment of MMP9 ⁺ CD14 ⁺ monocyte-derived cells in superficial dermis, particularly within clusters also containing keratinocytes and inflammatory fibroblasts. These MMP9 ⁺ cells were often positioned adjacent to KRT14 ⁺ basal keratinocytes, suggesting a spatially coordinated circuit linking epidermal stress to dermal immune infiltration. Using scRNA-seq and seqFISH+, we identified multiple fibroblast subpopulations, including superficial inflammatory fibroblasts that express high levels of CCL2, CCL7, and CCL8, localized to the papillary dermis and expanded in lesional tissue. Although this subset of fibroblasts was not exclusive to disease, it was quantitatively and transcriptionally distinct in CLE and DM compared to healthy controls. This activation was traced to upstream keratinocyte-derived signals. To test this, primary keratinocytes were subjected to UVB injury (100 mJ/cm ² ) and IFN-β priming. Conditioned media from these keratinocytes were used to stimulate primary dermal fibroblasts. RNA-seq analysis of treated fibroblasts showed robust induction of CCL2, CCL7, and CCL8 transcripts, with significantly stronger responses to UV+IFN-β-conditioned media compared to UV or IFN-β alone. These chemokines are potent ligands for CCR2, highly expressed by monocytes, and their induction suggests a mechanism for selective monocyte recruitment. Interestingly, fibroblast expression of CXCL12, a homeostatic chemokine known to support vascular and immune quiescence, was significantly reduced upon stimulation with UV+IFN-β keratinocyte supernatants. Direct TNF treatment of fibroblasts also downregulated CXCL12 expression, consistent with prior reports showing TNF- and IL-1–mediated suppression of CXCL12 in inflammation and dermal wound repair. These findings support the hypothesis that epithelial-derived inflammatory cues actively shift fibroblasts from a homeostatic to a pro-inflammatory phenotype. In parallel, conditioned media from UV+IFN-β–injured keratinocytes also induced activation of moDCs, increasing their surface CD83 expression and enhancing secretion of chemokines that attract lymphocytes, including CXCL10 and CCL19. Flow cytometry–based transwell migration assays confirmed that moDC-conditioned media induced robust migration of both CD4 ⁺ and CD8 ⁺ T cells, a response amplified when moDCs were primed with keratinocyte supernatants. These findings support a model in which keratinocytes initiate a multicellular circuit that propagates through stromal and myeloid compartments to recruit adaptive immune effectors. Importantly, integrative spatial analysis confirmed the colocalization of chemokine-expressing fibroblasts, activated myeloid cells, and lymphocytes within lesional skin, particularly in regions with high IFN-I module scores. Finally, in a clinical proof-of-concept study, UVB irradiation of non-lesional skin of DM and CLE patients rapidly recruits CD14+ myeloid cells to the skin, which was abrogated by anti-IFN-I treatment with anifrolumab. Together, these data establish a spatially organized, feed-forward inflammatory circuit linking keratinocyte damage, fibroblast reprogramming, and immune cell recruitment in photosensitive autoimmune disease.

Conclusions: This study uncovers a spatially organized, cytokine-driven cascade in which UV- and IFN-I–injured keratinocytes orchestrate the activation of dermal fibroblasts and myeloid cells, culminating in MMP9 ⁺ CD14 ⁺ cell recruitment and T cell activation. By integrating spatial transcriptomics, ex vivo modeling, and functional validation, we show that keratinocytes act as central initiators of inflammation, while fibroblasts serve as amplifiers that translate epithelial injury into a chemokine-rich environment supporting immune cell infiltration. Suppression of CXCL12 and induction of CCL2/CCL7/CCL8 represent critical molecular switches that may be targeted to modulate immune recruitment in CLE and DM. These findings not only elucidate a core inflammatory circuit in photosensitive autoimmunity but also identify novel stromal-immune interactions that may serve as therapeutic targets in broader interferonopathies.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: Khashayar Afshari: None declared, Yuqing Wang: None declared, Nazgol Haddadi: None declared, Carolina Salomão Lopes: None declared, Chee-Huat Linus Eng: None declared, Leah M Whiteman: None declared, Nuria Martinez: None declared, Pyae. Kyawe: None declared, Ksenia S Anufrieva: None declared, Kevin Wei: None declared, Kirsten Frieda: None declared, Ruth Vleugels: None declared, John Harris: None declared, Stefania Gallucci: None declared, Manuel Garber: None declared, Mehdi Rashighi AbbVie, Incyte, AbbVie, Biogen, AbbVie, Pfizer.