Shigella induces epigenetic reprogramming of zebrafish neutrophils

Trained immunity is a long-term memory of innate immune cells, generating an improved response upon re-infection. Shigella is an important human pathogen and inflammatory paradigm for which there is no effective vaccine. Using zebrafish larvae we demonstrate that after Shigella priming neutrophils are more efficient at bacterial clearance. We observe that Shigella-induced protection is non-specific and long-lasting, and is unlike training by BCG and {beta}-glucan. Analysis of histone ChIP-seq on primed neutrophils revealed that Shigella training deposits the active H3K4me3 mark on promoter regions of 1612 genes, significantly changing the epigenetic landscape of neutrophils towards enhanced microbial recognition and mitochondrial ROS production. Finally, we demonstrate that mitochondrial ROS plays a key role in enhanced antimicrobial activity of trained neutrophils. It is envisioned that signals and mechanisms we discover here can be used in other vertebrates, including humans, to suggest new therapeutic strategies involving neutrophils to control bacterial infection.