Inflammatory response has been implicated in the host defense, wound healing, and pathogenesis of many diseases. According to the types of different stimuli, it can be further divided into infection (microbe etc.) and sterile stimuli (non-microbe) induced response. Compared to the relatively well-defined infectious inflammation, the area of sterile inflammation remains largely unknown. By generating a double fluorescent reporter zebrafish, which can distinguish macrophages and neutrophils, a platform has been established to study the sterile inflammation related innate immune response in embryonic zebrafish. The reverse and forward genetic methods were utilized to uncover the underlying mechanism of these immediate and important cellular responses.

By using reverse genetic meth...[ Read more ]

Inflammatory response has been implicated in the host defense, wound healing, and pathogenesis of many diseases. According to the types of different stimuli, it can be further divided into infection (microbe etc.) and sterile stimuli (non-microbe) induced response. Compared to the relatively well-defined infectious inflammation, the area of sterile inflammation remains largely unknown. By generating a double fluorescent reporter zebrafish, which can distinguish macrophages and neutrophils, a platform has been established to study the sterile inflammation related innate immune response in embryonic zebrafish. The reverse and forward genetic methods were utilized to uncover the underlying mechanism of these immediate and important cellular responses.

By using reverse genetic method, interleukin 1 beta (il1β) was successfully identified as a key player, which was involved in the directional migration of neutrophils during wound induced sterile inflammation in vivo. Normally, during sterile inflammation induced by tissue injury, both macrophages and neutrophils will rapidly flux into the site of inflammation. However, in il1β morphant, compared with the normal macrophage influx, neutrophils can not migrate to the wound site due to the defect of directional migration. What‘s more, we demonstrated that the Il1β signaling pathway and H₂O₂ signaling pathway were two independent pathways both of which regulate the recruitment of neutrophils during sterile inflammation but not the infection induced inflammation.

The ethylnitrosourea (ENU) mutagenesis based forward genetic screening was performed to identify mutants which had inherited defects in the proper myeloid cell behaviors and functions during normal development and sterile inflammation. The temperature sensitive nlrp10-like^HKZ329 mutant which lacked NR staining positive microglia in the brain was successfully identified. What‘s more, this mutant showed abnormal SB positive neutrophils accumulation within the wound region for more than 6 hours at restrictive temperature. A point mutation within the gene nlrp10-like on chromosome 15 that was responsible for the defect of nlrp10-like^HKZ329 mutant was identified by positional cloning. In addition, it was observed that although a quite decent number of SB positive neutrophils were trapped in the wound region for longer than 6hpa in the nlrp10-like^HKZ329 mutant, the monocytes or dendritic cells (DCs) could not flux into the wound site. Interestingly, the early myeloid development and the capability of circulating macrophages to engulf bacteria appeared normal. To our big surprise, the temperature shift experiment, from restrictive temperature to permissive temperature, could rescue the microglia in the mutant brain to a decent number within a relatively short time, 12~24 hours. More detailed observation by live imaging showed that some peripheral macrophages can migrate into the brain during temperature shift experiment in the mutant, which might partially contribute to the recovery of microglia. Collectively, based on the above data and the nature of the mutated gene reported in mouse model recently, the underlying mechanism for the failure of recruitment of tissue resident macrophages to clean apoptotic cell bodies in the brain during normal development and wound induced dead cells might be partially due to the migration defects of monocytes, macrophages or DCs.