Innate immune responses to the commensal microbiota in zebrafish

The mammalian intestine harbors a diverse community of microorganisms, known as the microbiota, that play important roles in host biology. Studies of gnotobiotic animals show that the microbiota can influence a broad range of host biological processes. Microbial dysbiosis has been found to contribute to the etiology of multiple diseases including intestinal bowel disease. A comprehensive understanding of the factors mediating these interactions could provide new therapeutic targets for the treatment and prevention of diseases.;The zebrafish permits high-resolution imaging of fluorescently labeled cells in optically transparent gnotobiotic vertebrate hosts. The zebrafish also possesses a digestive tract similar to that of mammals including a liver, pancreas, gall bladder and intestine.;Microarray comparison of germ free (GF) and zebrafish larvae colonized with a normal zebrafish microbiota (CONVD) identified processes regulated by the microbiota. We found an enrichment of genes involved in several aspects of innate immune responses. However, the host factors mediating these transcriptional responses, as well as the spatial and temporal responses, of immune cells to the gut microbiota are not understood.;The NF-κB pathway has been established as an important mediator of commensal host-microbe interactions. We generated a zebrafish transgenic line (Tg(NFkB:EGFP))that permits in vivo real-time observation of NF-κB activity. Using this line we find an up-regulation of NF-κB target genes in tissues of the digestive tract suggesting that the cells in the gastrointestinal tract are robustly responsive to the microbial environment.;Using a transgenic zebrafish line that specifically labels neutrophils, we were able to examine the impact of the intestinal microbiota on neutrophil localization, behavior, and function. We find that colonization of GF larvae induces systemic alterations in neutrophil migration and localization. Using morpholino knockdown specific to the acute phase protein serum amyloid A (saa), we identify an important anti-inflammatory role for saa in the regulation of systemic neutrophil biology in GF and CONVD zebrafish.;My work provides an unprecedented insight into the spatial and temporal patterns of innate immune responses to the microbiota. The tools and methods I developed provided a unique opportunity to identify additional cell types and signaling pathways are responsive to the microbiota.