The Case for Modeling Human Infection in Zebrafish

Abstract

Zebrafish (Danio rerio) larvae are widely recognized for studying host-pathogen interactions in vivo because of their optical transparency, genetic manipulability, and translational potential. The development of the zebrafish immune system is well understood, thereby use of larvae enables investigation solely in the context of innate immunity. As a result, infection of zebrafish with natural fish pathogens including Mycobacterium marinum has significantly advanced our understanding of bacterial pathogenesis and vertebrate host defense. However, new work using a variety of human pathogens (bacterial, viral, and fungal) has illuminated the versatility of the zebrafish infection model, revealing unexpected and important concepts underlying infectious disease. We propose that this knowledge can inform studies in higher animal models and help to develop treatments to combat human infection. Why Use Zebrafish to Study Human Infection?Zebrafish have been used for almost 30 years as a model to study developmental biology because larvae are optically accessible and develop rapidly [1]. Zebrafish are also genetically tractable, and enable investigation of innate immune responses in isolation from adaptive immunity -which does not develop fully until 4 weeks post-fertilization [2][3][4]. Despite anatomical differences between zebrafish and humans, zebrafish can be used to investigate human infection by injecting a corresponding site that best suits the research question (Figure 1A, Key Figure). As a result, zebrafish have become an important animal model to study host-pathogen interactions in vivo. Mycobacterium marinum, a natural pathogen of zebrafish that causes a tuberculosis-like disease, is a paradigm for investigating host-pathogen interactions in vivo and has significantly contributed to our understanding of human infection with Mycobacterium tuberculosis (reviewed in [5]). For example, M. marinum infection in zebrafish has shown that the virulence determinant RD1 (region of difference 1) induces the aggregation of infected macrophages to form granulomas characteristic of tuberculosis [6], that modulation of host tumor necrosis factor (TNF) levels by leukotriene A4 hydrolase (LTA4H) can have both protective and pathological roles [7,8] and that macrophage necrosis in granulomas depends on an inter-organelle signaling circuit induced by TNF [65].Zebrafish share extensive genomic homology to humans, and >80% of human genes associated with diseases are present in zebrafish [4]. Importantly, counterparts of mammalian pathogen recognition receptors (PRRs), such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domainlike receptors (NLRs), as well as downstream signaling components, have been demonstrated to play important roles in zebrafish host defense [9]. In this opinion article we examine recent literature showing how infection of zebrafish with human bacterial, viral, and fungal pathogens can be used to discover fundamental concepts underlying human infection (Figure 1).

Determining macrophage versus neutrophil contributions to innate immunity using larval zebrafish

“…Excellent recent zebrafish innate immunity reviews have focused on findings related to the specific functions of macrophages (Yoshida et al, 2017;Torraca et al, 2014) or neutrophils (Henry et al, 2013;Harvie and Huttenlocher, 2015), or immunity in specific contexts such as infection (Gomes and Mostowy, 2019;Rosowski et al, 2018b;Masud et al, 2017). The purpose of this Review is to provide a broader view of the role of these cell types in diverse biological situations, and to compare and contrast different depletion methods to perhaps explain disparate results and interpretations in the literature.…”

Shigella sonneiinfection of zebrafish reveals that O-antigen mediates neutrophil tolerance and dysentery incidence

“…Except for non-human primates, there is no mammalian model that fully recapitulates human shigellosis. The zebrafish model is increasingly being used to study human bacterial pathogens in vivo , including S. flexneri [18, 19]. The major pathogenic events that lead to shigellosis in humans (i.e., macrophage cell death, invasion and multiplication within epithelial cells, cell-to-cell spread, inflammatory destruction of the host epithelium) are recapitulated in a zebrafish model of S. flexneri infection [20].…”

In vivocontrol ofToxoplasma gondiiby zebrafish macrophages

“…GRA2 staining and CLEM of replicating tachyzoites strongly suggests PV formation and is indicative of normal type I parasite behavior as demonstrated in vitro using tissue culture cells and in vivo using other animal models (39). The zebrafish HBV is well established to investigate host response to infection (30)(31)(32). We do not observe Toxoplasma dissemination from the HBV and this allows us to monitor leukocyte-parasite interactions in a localized area.…”

“…Zebrafish infection models for studying eukaryotic parasites and other human pathogens are beginning to emerge (31,32,38). In this study, we establish a novel Toxoplasma infection model using zebrafish larvae to explore host-parasite interaction in vivo.…”

“…Therefore, to complement in vivo murine studies, a novel animal model can benefit analysis of Toxoplasma control on a cellular and molecular level. Zebrafish are a well-established model for studying infection and immunity (29)(30)(31)(32). Coupled with their optical accessibility during early development, zebrafish larvae are highly suited for non-invasive study of Toxoplasma infection and host response in real-time in vivo (31,32).…”