Construction of a multi-tissue immune atlas for Chinese tongue sole (Cynoglossus semilaevis) reveals granulocyte functional adaptation and underlying regulatory mechanisms.

Innate immunity in teleost fish relies heavily on granulocytes for host defense. However, how these cells functionally adapt to distinct tissue microenvironments remains poorly understood. To address this, we constructed a multi-tissue immune atlas for Cynoglossus semilaevis by integrating single-cell RNA sequencing (scRNA-seq) data from blood, liver, spleen, and head kidney. We identified five transcriptionally distinct granulocyte subsets (Gr1-Gr5), each with divergent roles in inflammation, immunoregulation, and complement activity; moreover, these subsets exhibited tissue-specific distributions. Pseudotime analysis revealed a bifurcated developmental trajectory from a shared progenitor pool residing in the head kidney and spleen, characterized by the dynamic expression of the cxcr2/cxcr4 axis and branch-specific transcription factors. While sharing core metabolic pathways, granulocyte subsets displayed tissue-specific adaptations and an inferred communication strategy involving a conserved cd44b-mediated module. Our findings systematically characterize the patterns of granulocyte adaptation in a teleost model, providing insights into fish immunology and aquaculture disease control.