Single-cell sequencing reveals metabolic reprogramming and immune regulation underlie the maintenance of teleost granulomas.

The granuloma serves not only as a physical barrier to restrict the dissemination of intracellular pathogens but also functions as a complex immune microenvironment. However, the bioenergetics and regulatory mechanisms maintaining this architecture remain elusive in vertebrates. Here, integrating multi-tissue transcriptomics, single-cell RNA sequencing (scRNA-seq), ultrastructural imaging, and fluorescence in situ hybridization (FISH) in a largemouth bass (Micropterus salmoides)-Nocardia seriolae infection model, we resolved the metabolic and functional landscape of the granuloma. We found that across multiple tissues (head kidney, spleen, liver, kidney), the host initiates a synchronized transcriptional program that promotes macrophage differentiation into specialized epithelioid macrophages (E-Macs). Notably, E-Macs concurrently upregulated specific transporters and metabolic enzymes (e.g., laao, slc6a8), as well as oxidative phosphorylation (OXPHOS) and glycolysis genes, accompanied by mitochondrial proliferation. Functionally, E-Macs shifted from a pro-inflammatory to an immunoregulatory and pro-survival phenotype, characterized by high expression of protease inhibitors (e.g., csta) and anti-apoptotic factors (e.g., bcl2l14, ywhag1). Comparative analysis in zebrafish confirmed these metabolic and regulatory signatures are evolutionarily conserved. In conclusion, this study reveals a host survival strategy of immune regulation underpinned by metabolic adaptation, providing novel perspectives for controlling chronic granulomatous diseases in aquaculture.