Background/Purpose: Extracellular vesicles (EVs) are cell-derived nanoparticles that mediate cell-cell communication. EVs are implicated in photosensitive autoimmune diseases like dermatomyositis (DM) and systemic lupus (SLE), where UVB radiation can trigger systemic flares. Given UVB’s limited dermal penetration, we hypothesize that keratinocyte-derived EVs (KEVs) mediate UVB inflammation via relaying proinflammatory signals from keratinocytes (KCs) to dermal immune cells. Our prior work showed KEVs elicit inflammation in healthy control (HC) PBMCs, but specific immune cell targets remain undefined. This study identifies immune cell subsets responsive to KEVs.

Methods: HaCaT KCs were pretreated ±1 ng/mL IFN-β for 24h (to mimic DM skin), then irradiated with 0 or 75 mJ/cm² UVB and cultured overnight in EV-free media. KEVs were isolated by ultracentrifugation, resuspended in PBS, and incubated overnight with HC PBMCs. Cells were analyzed by flow cytometry.

Results: EVs from UVB-irradiated KCs (UVB-KEVs) significantly induced IFNβ compared to sham-KEVs in conventional dendritic cells (cDCs) [p=0.002], monocyte-derived dendritic cells (MoDCs) [p=0.039], macrophages [p=0.019], CD4⁺ T cells [p=0.036], CD8⁺ T cells [p=0.015], and CD19⁺ B cells [p=0.036]. A similar trend was observed in natural killer cells (NKs) [p=0.09] and plasmacytoid dendritic cells (pDCs) [p=0.149], though not significant. Notably, only EVs from IFNβ-pretreated irradiated KCs (IFNβ-KEVs) significantly stimulated IFNβ in pDCs [p=0.015] and NKs [p=0.007]. UVB-KEVs also induced IFNγ in MoDCs [p=0.034], macrophages [p=0.005], CD8⁺ T cells [p=0.047], and B cells [p=0.039], with non-significant increases in NKs [p=0.2], pDCs [p=0.06], and CD4⁺ T cells [p=0.06]. However, only IFNβ-KEVs significantly induced IFNγ in pDCs [p=0.001]. UVB-KEVs increased p-NFκB in NKs [p=0.033], CD4⁺ T cells [p=0.021], CD8⁺ T cells [p=0.029], and B cells [p=0.031], with a trend in pDCs [p=0.052]. UVB-KEVs significantly upregulated p-STING in NKs [p=0.0008], pDCs [p=0.006], MoDCs [p=0.0009], macrophages [p=0.0008], CD4⁺ T cells [p=0.017], CD8⁺ T cells [p=0.019], and B cells [p=0.01], with a similar but non-significant trend in cDCs [p=0.12]. However, IFNβ-KEVs significantly increased p-STING in cDCs [p=0.03] and more than UVB-KEVs [p=0.043]. p-STING activation was highest in macrophages and MoDCs. IFNγ was highest in pDCs (only with IFNβ-KEVs); IFNβ was most induced in cDCs and pDCs (again only by IFNβ-KEVs). IFNβ-KEVs uniquely induced both IFNβ and IFNγ in pDCs. Of note, cDCs were previously found to be enriched in DM skin of antimalarial non-responders and express high IFNβ and p-STING, and blood pDCs and cDCs in DM patients secreted more IFNβ than HCs, and pDCs are enriched in DM skin, producing high IFNβ and IFNγ.

Conclusion: UVB-KEVs trigger type I IFN production and activate STING, both upregulated in DM and SLE. Responses were more prominent in innate immune cells. IFNβ-KEVs distinctively activated cDC p-STING and drove pDC IFNβ and IFNγ, both critical in DM/SLE pathogenesis. This suggests a mechanism by which UVB triggers systemic inflammation via KEVs. Ongoing studies aim to block KEV release, dissect their cargo, and mitigate their proinflammatory effects.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/uvb-irradiated-keratinocyte-extracellular-vesicles-trigger-innate-immune-activation-via-type-i-interferons-and-sting-pathway/