Single-Cell Transcriptome Profiling Reveals Conserved IFNγ-IL8 Signaling-Induced Antibacterial Neutrophil States during Bacterial Infection

Streptococcus agalactiae is a significant pathogen in both humans and animals, yet the immune cell subtype dynamics during infection remain poorly defined. Leveraging the high susceptibility and tractability of Nile tilapia (Oreochromis niloticus), 113,356 single immune cells are profiled from head kidney and spleen across multiple infection time points (0, 1, 5, 10, 75 days post-infection and 3 days post-reinfection). This single-cell transcriptomic and flow cytometry analyses revealed distinct activation and transition patterns among neutrophils, macrophages, T cells, and B cells. Neutrophils exhibited early transcriptional remodeling enriched in inflammatory and interferon gamma (IFNγ) signaling pathways. Cross-species integration identified a conserved IFNγ-driven transition toward il8⁺ neutrophils. Furthermore, recombinant interleukin-8 (IL8) enhanced antibacterial responses in tilapia and human neutrophils, while inhibition of STAT1 reduced IL8 expression. IL8 stimulation increased phagocytosis and reactive oxygen species (ROS） production, supporting its role in neutrophil-mediated bacterial clearance. Together, this findings establish IFNγ-IL8 as a conserved mechanism in vertebrate immunity and a potential target for antibacterial therapies.