A novel macrophage subtype present in mycobacterial granulomas maintain a protective immune environment by reducing excessive inflammation (PRJCA027270)

Granulomas play a crucial role in the pathology of tuberculosis, but the immune environment governing their formation remains largely unknown. To explore the dynamic changes in the immune microenvironment during the formation of tuberculous granulomas, we infected adult zebrafish with Mycobacterium marinum (M. m) and then examined uninfected and infected kidneys, as well as large and small granulomas in the kidneys. Single-cell transcriptomic sequencing identified a new infection-induced subset of grn2+ macrophages. Depletion of these macrophages with the nitroreductase-metronidazole ablation system resulted in shortened zebrafish survival after infection, increased bacterial load and more granulomas, especially necrotic granulomas. Depletion of grn2+ macrophages also produced a denser granuloma structure with fewer T cells and showed that grn2+ macrophages can differentiate from grn2- macrophages in situ. RNA-seq and flow cytometry analysis revealed that depletion of grn2+ macrophages led to upregulated inflammatory signaling pathways, including tnfa and il1ß, and increased macrophage lytic cell death. This novel subset of grn2+ macrophages present in developing granulomas can suppress excessive inflammatory responses to alleviate macrophage lytic death, reduce tissue damage, promote T cell infiltration and ultimately help control mycobacterial growth in vivo.