Il-1β and Reactive Oxygen Species Differentially Regulate Neutrophil Directional Migration and Basal Random Motility in a Zebrafish Injury–Induced Inflammation Model

During inflammation, the proper inflammatory infiltration of neutrophils is crucial for the host to fight against infections and remove damaged cells and detrimental substances. IL-1β and NADPH oxidase-mediated reactive oxygen species (ROS) have been implicated to play important roles in this process. However, the cellular and molecular basis underlying the actions of IL-1β and ROS and their relationship during inflammatory response remains undefined. In this study, we use the zebrafish model to investigate these issues. We find that, similar to that of NADPH oxidase-mediated ROS signaling, the Il-1β-Myd88 pathway is required for the recruitment of neutrophils, but not macrophages, to the injury-induced inflammatory site, whereas it is dispensable for bacterial-induced inflammation. Interestingly, the Il-1β-Myd88 pathway is independent of NADPH oxidase-mediated ROS signaling and critical for the directional migration, but not the basal random movement, of neutrophils. In contrast, the NADPH oxidase-mediated ROS signaling is required for both basal random movement and directional migration of neutrophils. We further document that ectopic expression of Il-1β in zebrafish induces an inflammatory disorder, which can be suppressed by anti-inflammatory treatment. Our findings reveal that the Il-1β-Myd88 axis and NADPH oxidase-mediated ROS signaling are two independent pathways that differentially regulate neutrophil migration during sterile inflammation. In addition, Il-1β overexpressing Tg(hsp70:(m)il-1β_eGFP;lyz:DsRed2)hkz10t;nz50 transgenic zebrafish provides a useful animal model for the study of chronic inflammatory disorder and for anti-inflammatory drug discovery.