We have established an in vivo model for genetic analysis of the inflammatory response by generating a transgenic zebrafish line that expresses GFP under the neutrophil-specific myeloperoxidase promoter. We show that inflammation is induced after transection of the tail of zebrafish larvae and that this inflammation subsequently resolves over a similar time course to mammalian systems. Quantitative data can be generated from this model by counting of fluorescent cells or by digital image analysis. In addition, we show that the resolution of experimentally induced inflammation can be inhibited by the addition of a pancaspase inhibitor, zVD.fmk, demonstrating that experimental manipulation of the resolution of inflammation is possible in this model. IntroductionNeutrophilic inflammation is essential for the maintenance of health and life, but failure to resolve the response in a timely manner can cause irreparable tissue damage because of the release of toxic granule contents of persisting neutrophils. 1 An understanding of the genetic basis of inflammation resolution would undoubtedly provide an important basis for the development of approaches to limiting neutrophil-mediated tissue injury. To facilitate such a genetic analysis, an animal model in which the cellular components of inflammation can be readily visualized in wild-type and genetically manipulated individuals is required.Zebrafish larvae are transparent, allowing excellent visualization of fluorescent proteins in cellular processes in vivo. Zebrafish neutrophils (heterophils) are identifiable from approximately 48 hours after fertilization, 2 and the innate immune system exists in isolation from any adaptive system, which does not arise until approximately 4 weeks after fertilization. 3 A range of tools is available for the genetic manipulation of the zebrafish, as are extensive genomics resources, including a draft sequence of the entire genome. We therefore selected this species as an ideal organism for the generation of a simplified, genetically tractable model using fluorescent neutrophils to track the inflammatory response. Here, we report the generation of a transgenic zebrafish line for use in such experiments and describe the onset and resolution of inflammation in this model. We show that inflammation proceeds with kinetics similar to those in mammalian systems and that experimental manipulation of inflammation in this system is achievable and quantifiable. Materials and methodsZebrafish were maintained according to standard protocols. 4 Reagents were from Sigma (Poole, United Kingdom) unless otherwise specified. zVD.fmk was from Bachem (Weil am Rhein, Germany). MPO::GFP lineBAC (zC91B8) was modified by the use of a red recombinase system in EL250 cells (gift of Dr Neal Copeland, National Cancer Institute, Frederick, MD). 5 EGFP with an SV40 polyadenylation site (Clontech, Palo Alto, CA) was inserted at the mpo (also called mpx) ATG start site. This BAC, linearized with PI-Sce1, was used to generate stable transgenic lines according to publis...

Zebrafish are a unique model for pharmacological manipulation of physiological processes such as inflammation; they are small and permeable to many small molecular compounds, and being transparent, they permit the visualization and quantitation of the inflammatory response by observation of transgenically labeled inflammatory cell populations. Using a transgenic line specifically labeling neutrophils in vivo (mpx:GFP), we studied the effects of a range of pharmacological agents on the resolution of inflammation in vivo. These agents were selected for their ability to modulate neutrophil function and lifespan in human neutrophils in vitro. Agents delaying neutrophil apoptosis (LPS, dbcAMP, and several caspase inhibitors) all lead to a delay in resolution of neutrophilic inflammation. Reciprocally, pyocyanin and roscovitine (inducers of neutrophil apoptosis) lead to reduced neutrophil numbers. The occurrence of apoptosis was observed by time-lapse analysis and confirmed by dual staining for neutrophil-specific mpx activity (TSA staining) and an apoptotic marker (TUNEL). During inflammation, macrophages follow neutrophils into the inflamed site, and TUNEL/TSA dual-positive material can be demonstrated within macrophages, consistent with their uptake of apoptotic neutrophils. This model has several advantages over mammalian models and lends itself to the study of pharmaceutical agents modulating inflammation.

WINNING ABSTRACT: Although we are separated from zebrafish by 160 million years of evolution, we share many features of the innate and adaptive immune systems. In addition, we can manipulate the genome of zebrafish, and observe the effects on inflammation in vivo as they are transparent in their larval stages. This has exciting implications for the study of inflammatory diseases.We have established a model of inflammation in the zebrafish tail, in which caspase dependent cell death is required for resolution. For example, addition of the pan-caspase inhibitor zVD added at 4 hours after tailfin injury increases the number of neutrophils present from 6.0+/-1.0 to 28.9+/-3.3 (mean +/-s.e.m. p,0.001 n53).The transparency of the larvae makes these an ideal model for the study of in vivo inflammation, and we have generated fluorescent systems for the easy visualisation of neutrophilic inflammation and resolution in vivo.We are also performing an unbiased forward genetic screen for mutants with defective resolution of inflammation, and to date have identified 38 putative mutants. These techniques allow new approaches to understanding the molecular controls of inflammation resolution.