Single-cell characterization of skin response to a bite by West Nile virus-infected mosquito reveals fibroblast-mediated barrier to transmission

ABSTRACT Cutaneous events at the mosquito bite site that determine orthoflavivirus transmission efficiency remain largely uncharacterized. Here, we report single-cell RNA-sequencing of skin from immunocompetent mice bitten by West Nile virus-infected mosquitoes, capturing early response at a critical transmission bottleneck. Fibroblasts were the dominant cells exposed to infectious saliva. While neutrophils and Folr2 + macrophages diminished, monocyte-derived and antigen-presenting macrophages, and lymphocytes became more abundant. Cell-cell communication analysis revealed the central roles of fibroblasts and myeloid cells in induced immune-related signaling. Transcriptional profiling defined cell type-specific responses to infectious bite integrating immune modulation, skin repair and metabolic remodeling. Using in vivo gene silencing, we demonstrated that fibroblast-expressed LRRC15 (leucine rich repeat-containing 15) functions as a cutaneous restriction factor, limiting viral replication in skin, viral dissemination to draining lymph nodes, and disease severity. Collectively, our analyses provide cellular and molecular understanding of bite-initiated arboviral transmission, establishing skin-resident fibroblasts as frontline defender cells. HIGHLIGHTS Single-cell profiling captures early cutaneous response to West Nile virus-infected mosquito bites with cell type resolution. Skin-resident fibroblasts are the dominant frontline cells exposed to infectious mosquito saliva. Infectious bite reconfigures cutaneous immune cells, and activates multi-directional signaling between immune and structural skin cell types. Bite-induced fibroblast-expressed LRRC15 restricts viral transmission and attenuates disease severity.