Growth Factors of Lower Vertebrates

The goldfish primary kidney macrophage system

Miodrag (Mike) Belosevic and collaborators profoundly influenced the development of primary kidney macrophage culturing system (PKM) to study fish immunology in various aspects of comparative immunology. Their application of using PKM model, opened a new path for studying the development of macrophages, regulation of hematopoiesis, and cell specific response against various pathogens. By measuring histopathological and immunological outcomes, the biological implications of a variety of cytokines and signal transduction molecules could be elucidated with the established PKM system. A variety of growth factors mediating hematopoiesis and cytokines regulating the immune responses were functionally characterized, which served as a fundamental basis for making goldfish an excellent model to study fish immunology. Specifically, using in vivo and PKM based in vitro assays, the Belosevic lab advanced the goldfish-M. marinum model to study the anti-mycobacteria responses in teleosts, thus paving a way for the development of novel therapeutic approaches which could be applied in aquaculture settings or utilized as a model for human disease. In this review, we will look at the contribution of Dr. Mike Belosevic to teleost macrophage development, multiple cytokine functional characterization, and host-pathogen interactions.

Molecular characterization, gene expression and functional analysis of goldfish (Carassius auratus L.) macrophage colony stimulating factor 2

Background

Macrophage colony-stimulating factor 2 (MCSF-2) is an important cytokine that controls how cells of the monocyte/macrophage lineage proliferate, differentiate, and survive in vertebrates. Two isoforms of MCSF have been identified in fish, each exhibiting distinct gene organization and expression patterns. In this study, we investigated a goldfish MCSF-2 gene in terms of its immunomodulatory and functional properties.

Methods

In this study, goldfish were acclimated for 3 weeks and sedated with TMS prior to handling. Two groups of fish were used for infection experiments, and tissues from healthy goldfish were collected for RNA isolation. cDNA synthesis was performed, and primers were designed based on transcriptome database sequences. Analysis of gfMCSF-2 sequences, including nucleotide and amino acid analysis, molecular mass prediction, and signal peptide prediction, was conducted. Real-time quantitative PCR (qPCR) was used to analyze gene expression levels, while goldfish head kidney leukocytes (HKLs) were isolated using standard protocols. The expression of gfMCSF-2 in activated HKLs was investigated, and recombinant goldfish MCSF-2 was expressed and purified. Western blot analysis, cell proliferation assays, and flow cytometric analysis of HKLs were performed. Gene expression analysis of transcription factors and pro-inflammatory cytokines in goldfish head kidney leukocytes exposed to rgMCSF-2 was conducted. Statistical analysis using one-way ANOVA and Dunnett's post hoc test was applied.

Results

We performed a comparative analysis of MCSF-1 and MCSF-2 at the protein and nucleotide levels using the Needleman-Wunsch algorithm. The results revealed significant differences between the two sequences, supporting the notion that they represent distinct genes rather than isoforms of the same gene. Sequence alignment demonstrated high sequence identity with MCSF-2 homologs from fish species, particularly C. carpio, which was supported by phylogenetic analysis. Expression analysis in various goldfish tissues demonstrated differential expression levels, with the spleen exhibiting the highest expression. In goldfish head kidney leukocytes, gfMCSF-2 expression was modulated by chemical stimuli and bacterial infection, with upregulation observed in response to lipopolysaccharide (LPS) and live Aeromonas hydrophila. Recombinant gfMCSF-2 (rgMCSF-2) was successfully expressed and purified, showing the ability to stimulate cell proliferation in HKLs. Flow cytometric analysis revealed that rgMCSF-2 induced differentiation of sorted leukocytes at a specific concentration. Moreover, rgMCSF-2 treatment upregulated TNFα and IL-1β mRNA levels and influenced the expression of transcription factors, such as MafB, GATA2, and cMyb, in a time-dependent manner.

Conclusion

Collectively, by elucidating the effects of rgMCSF-2 on cell proliferation, differentiation, and the modulation of pro-inflammatory cytokines and transcription factors, our findings provided a comprehensive understanding of the potential mechanisms underlying gfMCSF-2-mediated immune regulation. These results contribute to the fundamental knowledge of MCSF-2 in teleosts and establish a foundation for further investigations on the role of gfMCSF-2 in fish immune responses.

Regulatory roles of cytokines in T and B lymphocytes-mediated immunity in teleost fish

T and B lymphocytes (T and B cells) are immune effector cells that play critical roles in adaptive immunity and defend against external pathogens in most vertebrates, including teleost fish. In mammals, the development and immune response of T and B cells is associated with cytokines including chemokines, interferons, interleukins, lymphokines, and tumor necrosis factors during pathogenic invasion or immunization. Given that teleost fish have evolved a similar adaptive immune system to mammals with T and B cells bearing unique receptors (B-cell receptors (BCRs) and T-cell receptors (TCRs)) and that cytokines in general have been identified, whether the regulatory roles of cytokines in T and B cell-mediated immunity are evolutionarily conserved between mammalians and teleost fish is a fascinating question. Thus, the purpose of this review is to summarize the current knowledge of teleost cytokines and T and B cells as well as the regulatory roles of cytokines on these two types of lymphocytes. This may provide important information on the parallelisms and dissimilarities of the functions of cytokines in bony fish versus higher vertebrates, which may aid in the evaluation and development of adaptive immunity-based vaccines or immunostimulants.

Characterization of the pro-inflammatory roles of the goldfish (Carassius auratus L.) M17 protein

The interleukin-6 family of cytokines possesses a diversity of roles with significant redundancy. The roles of these molecules have been relatively well characterized in mammals, with limited attention in other species. Progress has been made in the discovery of homologous molecules in fish. Here we report the characterization of pro-inflammatory properties of recombinant goldfish M17. Recombinant goldfish M17 enhanced phagocytosis, primed production of reactive oxygen intermediates, and was chemotactic to macrophages. Treatment of goldfish macrophages with LPS, heat-killed and live Aeromonas hydrophila resulted in higher M17 mRNA levels. Recombinant M17 (RgM17) induced dose-dependent production of IFNγ and IL-1β1 in goldfish macrophages. Furthermore, treatment of macrophages with rgM17 resulted in upregulation of transcription factors that were important in the differentiation of myeloid progenitors into monocytes/macrophages (Runx1 and GATA2). Our results indicate that goldfish M17 is an essential inflammatory cytokine for proliferation and differentiation of goldfish progenitor cells.

Blunt snout bream (Megalobrama amblycephala) MaCSF-1 contributes to proliferation, phagocytosis and immunoregulation of macrophages via MaCSF-1R

CSF-1 and CSF-1R have been well demonstrated in humans, regulating the differentiation, proliferation and survival of the mononuclear phagocyte system. However, the functional study on MaCSF-1 and MaCSF-1R from blunt snout bream (Megalobrama amblycephala) is still unknown. In the present study, we cloned and functionally characterized MaCSF-1 and MaCSF-1R. Multiple sequence alignment and phylogenetic tree analysis showed that both MaCSF-1 and MaCSF-1R were mostly close to the grass carp counterparts. Tissue distribution analysis showed that both MaCSF-1 and MaCSF-1R were widely distributed in all examined tissues, dominantly distributed in spleen, blood and head kidney tissues. Furthermore, confocal microscopy assay and flow cytometry assay showed that MaCSF-1R was the marker on the surface of macrophages. Recombinant MaCSF-1 promoted macrophage proliferation, phagocytosis and the production of IL-10. Through the pull-down experiments and indirect immunofluorescence experiments, the interaction between MaCSF-1 and MaCSF-1R was confirmed. To explore the relationship between MaCSF-1 and its receptor, MaCSF-1R and MaCSF-1R antibody was prepared. Then the MaCSF-1R blockage assay indicated that the role of MaCSF-1 on the macrophages proliferation and phagocytosis was weakened, leading the reduction of IL-10 expression level. In conclusion, MaCSF-1R is the marker on the surface of macrophage membrane; and MaCSF-1 promotes macrophage proliferation, phagocytosis, and significantly increased the expression levels of IL-10 depended on the interacting with MaCSF-1R. This study provides basal data for the biological function of MaCSF-1 and MaCSF-1R, and is valuable for the exploration of MaCSF-1 and MaCSF-1R molecular interactions.

Transcriptional Signatures of Immune, Neural, and Endocrine Functions in the Brain and Kidney of Rainbow Trout (Oncorhynchus mykiss) in Response to Aeromonas salmonicida Infection

Rainbow trout (Oncorhynchus mykiss) serves as one of the most important commercial fish with an annual production of around 800,000 tonnes. However, infectious diseases, such as furunculosis caused by Aeromonas salmonicida infection, results in great economic loss in trout culture. The brain and kidney are two important organs associated with “sickness behaviors” and immunomodulation in response to disease. Therefore, we worked with 60 trout and investigated transcriptional responses and enrichment pathways between healthy and infected trout. We observed that furunculosis resulted in the activation of toll-like receptors with neuroinflammation and neural dysfunction in the brain, which might cause the “sickness behaviors” of infected trout including anorexia and lethargy. We also showed the salmonid-specific whole genome duplication contributed to duplicated colony stimulating factor 1 (csf-1) paralogs, which play an important role in modulating brain immunomodulation. Enrichment analyses of kidneys showed up-regulated immunomodulation and down-regulated neural functions, suggesting an immune-neural interaction between the brain and kidney. Moreover, the kidney endocrine network was activated in response to A. salmonicida infection, further convincing the communications between endocrine and immune systems in regulating internal homeostasis. Our study provided a foundation for pathophysiological responses of the brain and kidney in response to furunculosis and potentially offered a reference for generating disease-resistant trout strains.

The Roles of Amphibian (Xenopus laevis) Macrophages during Chronic Frog Virus 3 Infections

Infections by Frog Virus 3 (FV3) and other ranavirus genus members are significantly contributing to global amphibian decline. The Xenopus laevis frog is an ideal research platform upon which to study the roles of distinct frog leukocyte populations during FV3 infections. Frog macrophages (MΦs) are integrally involved during FV3 infection, as they facilitate viral dissemination and persistence but also participate in immune defense against this pathogen. In turn, MΦ differentiation and functionality depend on the colony-stimulating factor-1 receptor (CSF-1R), which is ligated by CSF-1 and iterleukin-34 (IL-34) cytokines. Our past work indicated that X. laevis CSF-1 and IL-34 give rise to morphologically and functionally distinct frog MΦ subsets, and that these CSF-1- and IL-34-MΦs respectively confer susceptibility and antiviral resistance to FV3. Because FV3 targets the frog kidneys and establishes chronic infections therein, presently we examined the roles of the frog CSF-1- and IL-34-MΦs in seeding and maintaining these chronic kidney infections. Our findings indicate that the frog CSF-1-MΦs result in more prominent kidney FV3 infections, which develop into greater reservoirs of lingering FV3 marked by infiltrating leukocytes, fibrosis, and overall immunosuppressive states. Moreover, the antiviral effects of IL-34-MΦs are short-lived and are lost as FV3 infections progress.

Colony Stimulating Factor-1 and its Receptor in Gastrointestinal Malignant Tumors

Gastrointestinal malignant tumor is the fourth most common cancer in the world and the second cause of cancer death. Due to the susceptibility to lymphatic metastasis and liver metastasis, the prognosis of advanced tumor patients is still poor till now. With the development of tumor molecular biology, the tumor microenvironment and the cytokines, which are closely related to the proliferation, infiltration and metastasis, have become a research hotspot in life sciences. Colony stimulating factor-1 (CSF-1), a polypeptide chain cytokine, and its receptor CSF-1R are reported to play important roles in regulating tumor-associated macrophages in tumor microenvironment and participating in the occurrence and development in diversities of cancers. Targeted inhibition of the CSF-1/CSF-1R signal axis has broad application prospects in cancer immunotherapy. Here, we reviewed the biological characters of CSF-1/CSF-1R and their relationship with gastrointestinal malignancies.

Macrophage colony stimulating factor (MCSF) of Japanese flounder (Paralichthys olivaceus): Immunoregulatory property, anti-infectious function, and interaction with MCSF receptor

Macrophage colony-stimulating factor (MCSF) is an essential growth factor to control the proliferation, differentiation and survival of the macrophage lineage in vertebrates. Sequences of MCSF have been identified in multiple teleost species, however, the functional investigations of MCSF were documented in only a few species. In this study, we examined the biological activity and the immunomodulatory property of a MCSF homologue, PoMCSF, from Japanese flounder (Paralichthys olivaceus). Structural analysis showed that PoMCSF possesses conserved structural characteristics of MCSF proteins, including a signal peptide, a CSF-1 domain, and a transmembrane region closed to the C-terminal. Under normal physiological condition, PoMCSF expression distributes in all the examined tissues, the highest three tissues are blood, muscle, and head kidney. When infected by extracellular and intracellular bacterial pathogens and viral pathogen, the PoMCSF expression patterns vary with different types of microbial pathogens infection and different immune tissues. In vitro experiment showed recombinant PoMCSF promoted the activity of macrophage. In vivo experiment indicated that PoMCSF overexpression boosted the defensive ability of flounder against Edwardsiella piscicida, a severe fish pathogen that infects multiple species of economically important fish, and regulated the expression of multiple immune-related genes. To explore the relationship between PoMCSF and its receptor PoMCSFR, anti-PoMCSFR antibody was prepared and PoMCSFR knockdown was conducted. The neutralization assay showed that when PoMCSFR was neutralized by its antibody, the role of PoMCSF on host defense against E. piscicida was weakened. Knockdown of PoMCSFR impaired the phagocytic capacity of macrophages. Collectively, these findings suggest that PoMCSF plays a crucial role in the immune defense system of Japanese flounder and the effect of PoMCSF is dependent on PoMCSFR. This study provides new insights into the biological activity of MCSF and the relationship between MCSF and MCSFR in teleost.

A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

The amphibian (Xenopus laevis) colony-stimulating factor-1 and interleukin-34-derived macrophages possess disparate pathogen recognition capacities

Pathogens such as the Frog Virus 3 (FV3) ranavirus are contributing to the worldwide amphibian declines. While amphibian macrophages (Mϕs) are central to the immune defenses against these viruses, the pathogen recognition capacities of disparate amphibian Mϕ subsets remain unexplored. In turn, Mϕ differentiation and functionality are interdependent on the colony-stimulating factor-1 receptor (CSF-1R), which is ligated by colony-stimulating factor-1 (CSF-1) and the unrelated interleukin-34 (IL-34) cytokines. Notably, the Xenopus laevis frog CSF-1- and IL-34-derived Mϕs are functionally distinct, and while the CSF-1-Mϕs are more susceptible to FV3, the IL-34-Mϕs are highly resistant to this pathogen. Here, we elucidate the pathogen recognition capacities of CSF-1- and IL-34-differentiated Mϕs by evaluating their baseline transcript levels of key pathogen pattern recognition receptors (PRRs). Compared to the frog CSF-1-Mϕs, their IL-34-Mϕs exhibited greater expression of PRR genes associated with viral recognition as well as PRR genes known for recognizing bacterial pathogen-associated molecular patterns (PAMPs). By contrast, the CSF-1-Mϕs displayed greater expression of toll-like receptors (TLRs) that are absent in humans. Moreover, although the two Mϕ types possessed similar expression of most downstream PRR signaling components, they exhibited distinct outcomes upon stimulation with hallmark PAMPs, as measured by their tumor necrosis factor-alpha and interferon-7 gene expression. Remarkably, stimulation with a TLR2/6 agonist conferred FV3 resistance to the otherwise susceptible CSF-1-Mϕs while treatment with a TLR9 agonist significantly ablated the IL-34-Mϕ resistance to FV3. These changes in Mϕ-FV3 susceptibility and resistance appeared to be linked to changes in their expression of key immune genes. Greater understanding of the amphibian macrophage pathogen-recognition capacities will lend to further insights into the pathogen-associated causes of the amphibian declines.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

Differentiation-dependent antiviral capacities of amphibian (Xenopus laevis) macrophages

Infections by ranaviruses such as Frog virus 3 (Fv3), are significantly contributing to worldwide amphibian population declines. Notably, amphibian macrophages (Mφs) are important to both the Fv3 infection strategies and the immune defense against this pathogen. However, the mechanisms underlying amphibian Mφ Fv3 susceptibility and resistance remain unknown. Mφ differentiation is mediated by signaling through the colony-stimulating factor-1 receptor (CSF-1R) which is now known to be bound not only by CSF-1, but also by the unrelated interleukin-34 (IL-34) cytokine. Pertinently, amphibian (Xenopus laevis) Mφs differentiated by CSF-1 and IL-34 are highly susceptible and resistant to Fv3, respectively. Accordingly, in the present work, we elucidate the facets of this Mφ Fv3 susceptibility and resistance. Because cellular resistance to viral replication is marked by expression of antiviral restriction factors, it was intuitive to find that IL-34-Mφs possess significantly greater mRNA levels of select restriction factor genes than CSF-1-Mφs. Xenopodinae amphibians have highly expanded repertoires of antiviral interferon (IFN) cytokine gene families, and our results indicated that in comparison with the X. laevis CSF-1-Mφs, the IL-34-Mφs express substantially greater transcripts of representative IFN genes, belonging to distinct gene family clades, as well as their cognate receptor genes. Finally, we demonstrate that IL-34-Mφ-conditioned supernatants confer IFN-mediated anti-Fv3 protection to the virally susceptible X. laevis kidney (A6) cell line. Together, this work underlines the differentiation pathways leading to Fv3-susceptible and -resistant amphibian Mφ populations and defines the molecular mechanisms responsible for these differences.

Evolutionary Aspects of Macrophages Polarization

Macrophages constitute a heterogeneous population of myeloid cells that are essential for maintaining homeostasis and as a first line of innate responders controlling and organizing host defenses against pathogens. Monocyte-macrophage lineage cells are among the most functionally diverse and plastic cells of the immune system. They undergo specific activation into functionally distinct phenotypes in response to immune signals and microbial products. In mammals, macrophage functional heterogeneity is defined by two activation states, M1 and M2, which represent two polar ends of a continuum exhibiting pro-inflammatory and tissue repair activities, respectively. While the ancient evolutionary origin of macrophages as phagocytic defenders is well established, the evolutionary roots of the specialized division of macrophages into subsets with polarized activation phenotypes is less well defined. Accordingly, this chapter focuses on recent advances in the understanding of the evolution of macrophage polarization and functional heterogeneity with a focus on ectothermic vertebrates.

The Function of Fish Cytokines

What is known about the biological activity of fish cytokines is reviewed. Most of the functional studies performed to date have been in teleost fish, and have focused on the induced effects of cytokine recombinant proteins, or have used loss- and gain-of-function experiments in zebrafish. Such studies begin to tell us about the role of these molecules in the regulation of fish immune responses and whether they are similar or divergent to the well-characterised functions of mammalian cytokines. This knowledge will aid our ability to determine and modulate the pathways leading to protective immunity, to improve fish health in aquaculture.

Amphibian macrophage development and antiviral defenses

Macrophage lineage cells represent the cornerstone of vertebrate physiology and immune defenses. In turn, comparative studies using non-mammalian animal models have revealed that evolutionarily distinct species have adopted diverse molecular and physiological strategies for controlling macrophage development and functions. Notably, amphibian species present a rich array of physiological and environmental adaptations, not to mention the peculiarity of metamorphosis from larval to adult stages of development, involving drastic transformation and differentiation of multiple new tissues. Thus it is not surprising that different amphibian species and their respective tadpole and adult stages have adopted unique hematopoietic strategies. Accordingly and in order to establish a more comprehensive view of these processes, here we review the hematopoietic and monopoietic strategies observed across amphibians, describe the present understanding of the molecular mechanisms driving amphibian, an in particular Xenopus laevis macrophage development and functional polarization, and discuss the roles of macrophage-lineage cells during ranavirus infections.

Goldfish (Carassius auratus L.) as a model system to study the growth factors, receptors and transcription factors that govern myelopoiesis in fish

The process of myeloid cell development (myelopoiesis) in fish has mainly been studied in three cyprinid species: zebrafish (Danio rerio), ginbuna carp (Carassius auratus langsdorfii) and goldfish (C. auratus, L.). Our studies on goldfish myelopoiesis have utilized in vitro generated primary kidney macrophage (PKM) cultures and isolated primary kidney neutrophils (PKNs) cultured overnight to study the process of macrophage (monopoiesis) and neutrophil (granulopoiesis) development and the key growth factors, receptors, and transcription factors that govern this process in vitro. The PKM culture system is unique in that all three subpopulations of macrophage development, namely progenitor cells, monocytes, and mature macrophages, are simultaneously present in culture unlike mammalian systems, allowing for the elucidation of the complex mixture of cytokines that regulate progressive and selective macrophage development from progenitor cells to fully functional mature macrophages in vitro. Furthermore, we have been able to extend our investigations to include the development of erythrocytes (erythropoiesis) and thrombocytes (thrombopoiesis) through studies focusing on the progenitor cell population isolated from the goldfish kidney. Herein, we review the in vitro goldfish model systems focusing on the characteristics of cell sub-populations, growth factors and their receptors, and transcription factors that regulate goldfish myelopoiesis.

Mechanisms of amphibian macrophage development: characterization of the Xenopus laevis colony-stimulating factor-1 receptor

Macrophage-lineage cells are indispensable to vertebrate homeostasis and immunity. In turn, macrophage development is largely regulated through colony-stimulating factor-1 (CSF1) binding to its cognate receptor (CSF1R). To study amphibian monopoiesis, we identified and characterized the X. laevis CSF1R cDNA transcript. Quantitative analysis revealed that CSF1R tissue gene expression increased with X. laevis development, with greatest transcript levels detected in the adult lung, spleen and liver tissues. Notably, considerable levels of CSF1R mRNA were also detected in the regressing tails of metamorphosing animals, suggesting macrophage involvement in this process, and in the adult bone marrow; corroborating the roles for this organ in Xenopus monopoiesis. Following animal infections with the ranavirus Frog Virus 3 (FV3), both tadpole and adult X. laevis exhibited increased kidney CSF1R gene expression. Conversely, while FV3-infected tadpoles increased their spleen and liver CSF1R mRNA levels, the FV3-challenged adults did not. Notably, FV3 induced elevated bone marrow CSF1R expression, and while stimulation of tadpoles with heat-killed E. coli had no transcriptional effects, bacterial stimulation of adult frogs resulted in significantly increased spleen, liver and bone marrow CSF1R expression. We produced the X. laevis CSF1R in recombinant form (rXlCSF1R) and determined, via in vitro cross-linking studies, that two molecules of rXlCSF1R bound the dimeric rXlCSF1. Finally, administration of rXlCSF1R abrogated the rXlCSF1-induced tadpole macrophage recruitment and differentiation as well as bacterial and FV3-elicited peritoneal leukocyte accumulation. This work marks a step towards garnering greater understanding of the unique mechanisms governing amphibian macrophage biology.

Accumulation of cells expressing macrophage colony-stimulating factor receptor gene in the ovary of a pregnant viviparous fish, Neoditrema ransonnetii (Perciformes, Embiotocidae)

Macrophage colony-stimulating factor receptor (M-CSFR), a member of the group of type III protein tyrosine kinase receptors, is expressed primarily by monocyte/macrophage lineage cells. In order to describe the distribution of macrophages at the maternal-fetal interface in Neoditrema ransonnetii, a viviparous fish species, M-CSFR cDNA was sequenced. Two sequences were obtained: NrM-CSFR1 (4381 bp, encoding 980 amino acids), and NrM-CSFR2 (3573 bp, encoding 1016 amino acids). Both the genes were expressed in the ovary of pregnant females. In situ hybridization revealed that a number of cells that were positive for NrM-CSFR1 and/or NrM-CSFR2 populated the ovigerous lamellae of the ovary during pregnancy. Following parturition, M-CSFR-positive cells disappeared from the subepithelial region of ovigerous lamellae, and were localized in perivascular tissues. These results suggest the role of M-CSFR-positive cells, which appear to be macrophages, in N. ransonnetii during pregnancy.

Biology of Bony Fish Macrophages

Macrophages are found across all vertebrate species, reside in virtually all animal tissues, and play critical roles in host protection and homeostasis. Various mechanisms determine and regulate the highly plastic functional phenotypes of macrophages, including antimicrobial host defenses (pro-inflammatory, M1-type), and resolution and repair functions (anti-inflammatory/regulatory, M2-type). The study of inflammatory macrophages in immune defense of teleosts has garnered much attention, and antimicrobial mechanisms of these cells have been extensively studied in various fish models. Intriguingly, both similarities and differences have been documented for the regulation of lower vertebrate macrophage antimicrobial defenses, as compared to what has been described in mammals. Advances in our understanding of the teleost macrophage M2 phenotypes likewise suggest functional conservation through similar and distinct regulatory strategies, compared to their mammalian counterparts. In this review, we discuss the current understanding of the molecular mechanisms governing teleost macrophage functional heterogeneity, including monopoetic development, classical macrophage inflammatory and antimicrobial responses as well as alternative macrophage polarization towards tissues repair and resolution of inflammation.

Distinct functional roles of amphibian (Xenopus laevis) colony-stimulating factor-1- and interleukin-34-derived macrophages

Although Mϕ represent the most primordial immune cell subsets, the mechanisms governing their functional heterogeneity remain poorly defined. However, it is well established that the CSF-1 cytokine contributes to monopoiesis and to this heterogeneity, whereas the unrelated IL-34 also binds the CSF-1R toward poorly understood immunologic roles. To delineate the molecular and evolutionary basis behind vertebrate Mϕ functional heterogeneity, we performed comprehensive transcriptional and functional studies of amphibian (Xenopus laevis) BM (in vitro) and PER (in vivo) Mϕ derived by rXlCSF-1 and rXlIL-34. Our findings indicate that these amphibian cytokines promote morphologically and functionally distinct Mϕ populations. Mϕ induced by rXlCSF-1 possess more robust iNOS gene expression, are substantially more phagocytic, display greater NO responses, and exhibit enhanced bactericidal capacities. By contrast, rXlIL-34-derived Mϕ express greater levels of Arg-1 and NADPH oxidase components and possess greater respiratory burst responses. Most notably, whereas CSF-1 Mϕ are highly susceptible to the emerging FV3 ranavirus, rXlIL-34 Mϕ exhibit potent antiviral activity against this pathogen, which is dependent on reactive oxygen production. This work marks an advance in our understanding of the possible mechanisms governing vertebrate Mϕ functional heterogeneity.

Recombinant goldfish thrombopoietin up-regulates expression of genes involved in thrombocyte development and synergizes with kit ligand A to promote progenitor cell proliferation and colony formation

Thrombopoietin (TPO) is the principal regulator of thrombopoiesis and promotes the proliferation, differentiation and maturation of megakaryocytic progenitor cells in mammals. In this study we report on the molecular and functional characterization of goldfish TPO. Quantitative expression analysis of goldfish tpo revealed the highest mRNA levels in heart, followed by spleen, liver, brain, intestine and kidney tissues. Significant decrease of tpo and c-mpl expressions in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, indicates that TPO is not involved in monopoiesis. Recombinant goldfish TPO (rgTPO) alone did not induce significant proliferation of progenitor cells, but TPO in cooperation with recombinant goldfish kit ligand A (rgKITLA) supported proliferation of progenitor cells in a dose-dependent manner. In response to rgTPO or a combination of rgTPO and rgKITLA, the mRNA levels of thrombopoietic markers cd41 and c-mpl as well as thrombo/erythropoietic transcription factors gata1 and lmo2 in sorted progenitor cells were up-regulated, while the mRNA levels of granulopoietic markers (cebpα and gcsfr) and the lymphoid transcription factor gata3 were down-regulated. Furthermore, rgTPO and rgKITLA synergistically stimulated thrombocytic colony-formation. Our results demonstrate that goldfish TPO has similar functions to mammalian TPO as a regulator of thrombopoiesis, and suggests a highly conserved molecular mechanism of thrombocyte development throughout evolution of vertebrates.

Grouper (Epinephelus coioides) IL-34/MCSF2 and MCSFR1/MCSFR2 were involved in mononuclear phagocytes activation against Cryptocaryon irritans infection

MCSF and its well-known receptor MCSFR had been well studied in humans, regulating the differentiation, proliferation, and survival of the mononuclear phagocyte system. IL-34, which is an alternative ligand of MCSF receptor, was recently identified as a novel cytokine and functionally overlaps with MCSF. However, the functional study of these receptors and their ligands in fish are largely unknown. In the present study, the cDNA of two potential grouper MCSFR ligands have been cloned, EcIL-34 (657 bp) and EcMCSF2 (804 bp), as well as an additional copy of grouper MCSFR, EcMCSFR2 (3141 bp). Sequence analysis showed that these three molecules had higher identities with other fish counterparts compared to mammals and their conserved structures and important functional residues were also analyzed. Tissue distribution analysis showed that EcIL-34 is dominant in brain, gill and spleen compared to EcMCSF2, which is dominant in head kidney, trunk kidney, skin, heart and muscle. EcMCSFR1 was dominant in the most tissues except head kidney and liver compared to EcMCSFR2. The different tissue distribution patterns of these two grouper MCSF receptors and their two ligands indicate the different mononuclear phagocyte differentiation and activation modes in different tissues. In Cryptocaryon irritans infected grouper, EcIL-34 and EcMCSFR2 were the most strongly up-regulated ligand and receptor in the infected sites, gill and skin. Their up-regulation confirmed the proliferation and activation of phagocytes in C. irritans infected sites, which would improve the antigen presentation and elicit the host local specific immune response. In C. irritans infected grouper head kidney, both ligands EcIL-34 and EcMCSF2 (especially EcMCSF2) were up-regulated, but both receptors EcMCSFR1 and EcMCSFR2 were down-regulated, which indicated that the phagocytes differentiation and proliferation may have occurred in this hemopoietic organ, and after that they migrated to the infected cites. The down-regulation of EcIL-34 and EcMCSF2 and no significant change of EcMCSFR1 and EcMCSFR2 in most time point of grouper spleen showed it was less involved in phagocytes response to C. irritans infection.

Control of CSF-1 induced inflammation in teleost fish by a soluble form of the CSF-1 receptor

The colony-stimulating factor-1 (CSF-1) is the principal regulator of the survival, proliferation, differentiation, and function of macrophages and their precursors, and has been shown to play a role in the etiology of inflammation. We recently identified a novel mechanism for the control of CSF-1 activity in teleost fish, through the production of an inhibitory soluble form of the CSF-1 receptor (sCSF-1R). Primary goldfish kidney macrophages selectively expressed sCSF-1R during the senescence phase, which corresponds to a defined stage of in vitro culture development where inhibition of macrophage proliferation and apoptotic cell death are prominent. In contrast, primary macrophage cultures undergoing active proliferation displayed low levels of sCSF-1R expression. Addition of purified recombinant sCSF-1R to developing primary macrophage cultures leads to a dose-dependent decrease in macrophage proliferation and inhibits macrophage antimicrobial functions including chemotaxis, phagocytosis, and production of reactive oxygen intermediates. Using a goldfish in vivo model of self-resolving peritonitis, we found that sCSF-1R plays a role in the inhibition of inflammation, following an initial acute phase of antimicrobial responses within an inflammatory site. Soluble CSF-1R inhibits pro-inflammatory cytokine production, inhibits leukocyte recruitment to the inflammatory site and decreases ROS production in a dose-dependent manner. This sCSF-1R-dependent regulation of inflammation appears to be an elegant mechanism for the control of macrophage numbers at inflammatory sites of lower vertebrates. Overall, our results provide new insights into the evolutionary origins of the CSF-1 immune regulatory axis.

Divergent antiviral roles of amphibian (Xenopus laevis) macrophages elicited by colony-stimulating factor-1 and interleukin-34

Macrophages are integral to amphibian immunity against RVs, as well as to the infection strategies of these pathogens. Although CSF-1 was considered to be the principal mediator of macrophage development, the IL-34 cytokine, which shares no sequence identity with CSF-1, is now believed to contribute to vertebrate monopoiesis. However, the respective roles of CSF-1- and IL-34-derived macrophages are still poorly understood. To delineate the contribution of these macrophage populations to amphibian immunity against the RV FV3, we identified the Xenopus laevis IL-34 and transcriptionally and functionally compared this cytokine with the previously identified X. laevis CSF-1. The X. laevis CSF-1 and IL-34 displayed strikingly nonoverlapping developmental and tissue-specific gene-expression patterns. Furthermore, only CSF-1 but not IL-34 was up-regulated in the kidneys of FV3-challenged tadpoles. Intriguingly, recombinant forms of these cytokines (rXlCSF-1, rXlIL-34) elicited morphologically distinct tadpole macrophages, and whereas rXlCSF-1 pretreatment decreased the survival of FV3-infected tadpoles, rXlIL-34 administration significantly prolonged FV3-challenged animal survival. Compared with rXlIL-34-elicited macrophages, macrophages derived by rXlCSF-1 were more phagocytic but also significantly more susceptible to in vitro FV3 infections. By contrast, rXlIL-34-derived macrophages exhibited significantly greater in vitro antiranaviral activity and displayed substantially more robust gene expression of the NADPH oxidase components (p67(phox), gp91(phox)) and type I IFN. Moreover, FV3-challenged, rXlIL-34-derived macrophages exhibited several orders of magnitude greater up-regulation of the type I IFN gene expression. This marks the first report of the disparate roles of CSF-1 and IL-34 in vertebrate antiviral immunity.

Molecular and functional characterization of erythropoietin receptor of the goldfish (Carassius auratus L.)

Erythropoietin receptor (EPOR) is a member of the class I cytokine receptor superfamily and signaling through this receptor is important for the proliferation, differentiation and survival of erythrocyte progenitor cells. This study reports on the molecular and functional characterization of goldfish EPOR. The identified goldfish EPOR sequence possesses the conserved EPOR ligand binding domain, the fibronectin domain, the class I cytokine receptor superfamily motif (WSXWS) as well as several intracellular signaling motifs characteristic of other vertebrate EPORs. The expression of epor mRNA in goldfish tissues, cell populations and cells treated with recombinant goldfish EPO (rgEPO) were evaluated by quantitative PCR revealing that goldfish epor mRNA is transcribed in both erythropoietic tissues (blood, kidney and spleen) and non-hematopoietic tissues (brain, heart and gill), as well as in immature erythrocytes. Recombinant goldfish EPOR (rgEPOR), consisting of its extracellular domain, dose-dependently inhibited proliferation of progenitor cells induced by rgEPO. In vitro binding studies indicated that rgEPO exists as monomer, dimer and/or trimmer and that rgEPOR exists as monomer and/or homodimer, and when incubated together, formed a ligand-receptor complex. Our results demonstrate that goldfish EPO/EPOR signaling has been highly conserved throughout vertebrate evolution as a required mechanism for erythrocyte development.

Gram-negative marine bacteria: structural features of lipopolysaccharides and their relevance for economically important diseases

Gram-negative marine bacteria can thrive in harsh oceanic conditions, partly because of the structural diversity of the cell wall and its components, particularly lipopolysaccharide (LPS). LPS is composed of three main parts, an O-antigen, lipid A, and a core region, all of which display immense structural variations among different bacterial species. These components not only provide cell integrity but also elicit an immune response in the host, which ranges from other marine organisms to humans. Toll-like receptor 4 and its homologs are the dedicated receptors that detect LPS and trigger the immune system to respond, often causing a wide variety of inflammatory diseases and even death. This review describes the structural organization of selected LPSes and their association with economically important diseases in marine organisms. In addition, the potential therapeutic use of LPS as an immune adjuvant in different diseases is highlighted.

Expressions of transcription factors in goldfish (Carassius auratus L.) macrophages and their progenitors

The development of macrophages is a highly regulated process requiring coordination amongst transcription factors. The presence/absence, relative levels, antagonism, or synergy of all transcription factors involved is critical to directing lineage cell fate and differentiation. While relative levels of many key myeloid transcription factors have been determined in mammalian macrophage differentiation, a similar set of studies have yet to be conducted in a teleost system. In this study, we report on the mRNA levels of transcription factors (cebpa, cjun, cmyb, egr1, gata1, gata2, gata3, lmo2, mafb, pax5, pu.1 and runx1) in sorted goldfish progenitor cells, monocytes, and macrophages from primary kidney macrophage cultures. The mRNA levels of runx1 and pu.1 were significantly higher, gata3 and pax5 mRNA levels were lower, in monocytes compared to progenitors, and the mRNA levels of cjun, egr1, gata2, gata3, mafb and pax5 were significantly decreased in macrophages compared to progenitor cells. The relative mRNA levels of the interferon regulatory factor family of transcription factors, irf1, irf2, irf5, irf7, irf8 and irf9 in sorted progenitors, monocytes and macrophages were also measured. In contrast to other irf family transcription factors examined, irf8 mRNA levels were increased in monocytes compared to progenitors by greater than three-fold, suggesting that irf8 is important for monopoiesis. Lastly, we show the differential regulation of myeloid transcription factor mRNA levels in sorted progenitor cells from 1, 2, or 3-day old cultures in response to the recombinant goldfish growth factors, rgCSF-1 and rgKITLA.

Comparative analysis of a teleost skeleton transcriptome provides insight into its regulation

An articulated endoskeleton that is calcified is a unifying innovation of the vertebrates, however the molecular basis of the structural divergence between terrestrial and aquatic vertebrates, such as teleost fish, has not been determined. In the present study long-read next generation sequencing (NGS, Roche 454 platform) was used to characterize acellular perichondral bone (vertebrae) and chondroid bone (gill arch) in the gilthead sea bream (Sparus auratus). A total of 15.97 and 14.53Mb were produced, respectively from vertebrae and gill arch cDNA libraries and yielded 32,374 and 28,371 contigs (consensus sequences) respectively. 10,455 contigs from vertebrae and 10,625 contigs from gill arches were annotated with gene ontology terms. Comparative analysis of the global transcriptome revealed 4249 unique transcripts in vertebrae, 4201 unique transcripts in the gill arches and 3700 common transcripts. Several core gene networks were conserved between the gilthead sea bream and mammalian skeleton. Transcripts for putative endocrine factors were identified in acellular gilthead sea bream bone suggesting that in common with mammalian bone it can act as an endocrine tissue. The acellular bone of the vertebra, in contrast to current opinion based on histological analysis, was responsive to a short fast and significant (p<0.05) down-regulation of several transcripts identified by NGS, osteonectin, osteocalcin, cathepsin K and IGFI occurred. In gill arches fasting caused a significant (p<0.05) down-regulation of osteocalcin and up-regulation of MMP9.

A soluble form of the CSF-1 receptor contributes to the inhibition of inflammation in a teleost fish

We previously reported on the identification of a novel soluble form of the CSF-1 receptor (sCSF-1R) in goldfish that induced dose-dependent down-regulation of macrophage proliferation. Herein, we report that sCSF-1R has a role beyond macrophage development, which extends into the control of cellular antimicrobial inflammatory responses in this lower vertebrate. Using an in vivo model of self-resolving peritonitis coupled to in vitro characterization of sCSF-1R activity, we show that sCSF-1R plays a role in the inhibition of inflammation which follows an initial acute phase of innate antimicrobial responses within an inflammatory site. In vitro, mature goldfish primary kidney macrophages but not monocytes up-regulated sCSF-1R expression upon direct contact with apoptotic cells. In vivo, sCSF-1R expression coincided with an increase in macrophage numbers that resulted from administration of apoptotic cells into the goldfish peritoneal cavity. This contrasted the decrease in sCSF-1R expression during zymosan-induced inflammatory responses in vivo. Subsequent experiments showed an anti-inflammatory effect for sCSF-1R. Leukocyte infiltration and ROS production decreased in a dose-dependent manner compared to zymosan-stimulated controls upon addition of increasing doses of recombinant sCSF-1R. Among others, sCSF-1R may contribute to the dual role that phagocytic macrophages play in the induction and regulation of inflammation. Overall, our results provide new insights into ancient mechanisms of inflammation control and, in particular, the evolutionary origins of the CSF-1 immune regulatory axis.

Colony-stimulating factor-1-responsive macrophage precursors reside in the amphibian (Xenopus laevis) bone marrow rather than the hematopoietic subcapsular liver

Macrophage precursors originate from and undergo lineage commitment within designated sites of hematopoiesis, such as the mammalian bone marrow. These cells subsequently differentiate in response to stimulation with macrophage colony-stimulating factor-1 (CSF-1). The amphibian bone marrow, unlike that of mammals, has been overlooked as a source of leukocyte precursors in favor of the liver subcapsular region, where hematopoiesis occurs in anurans. Here we report that the bone marrow rather than the liver periphery provides macrophage progenitors to the amphibian Xenopus laevis. We identified the amphibian CSF-1, examined its gene expression in developing and virally infected X. lae vis and produced it in recombinant form (rXlCSF-1). This rXlCSF-1 did not bind or elicit proliferation/differentiation of subcapsular liver cells. Surprisingly, a subpopulation of bone marrow cells engaged this growth factor and formed rXlCSF-1 concentration-dependent colonies in semisolid medium. Furthermore, rXlCSF-1-treated bone marrow (but not liver) cultures comprised of cells with characteristic macrophage morphology and high gene expression of the macrophage marker CSF-1 receptor. Together, our findings indicate that in contrast to all other vertebrates studied to date, committed Xenopus macrophage precursor populations are not present at the central site of hematopoiesis, but reside in the bone marrow.

Colony-stimulating factor-1 receptor protein expression is a specific marker for goldfish (Carassius auratus L.) macrophage progenitors and their differentiated cell types

Signaling through the colony-stimulating factor-1 receptor (CSF-1R) mediates the proliferation, differentiation, and activation of macrophages and their progenitors. In this study we report on the use of an anti-goldfish CSF-1R antibody to specifically recognize a population of CSF-1R positive cells from goldfish tissues. Furthermore, using our previously characterized primary kidney macrophage culture system, we show that CSF-1R positive cells include monocytes, macrophages, and their progenitor cells. Freshly isolated progenitor cells had a higher median florescent intensity ratio than those progenitor cells cultured for up to four days. The decrease in CSF-1R expression on the progenitor cells coincides with the appearance and development of monocytes and macrophages. Monocytes were consistently CSF-1R+ and maintained the high level of CSF-1R expression as they developed into macrophages. Like that of mammalian systems, CSF-1R is expressed on all macrophage sub-populations (progenitors, monocytes, macrophages), and CSF-1R expression increases with macrophage development in teleosts.

Pivotal Advance: Avian colony-stimulating factor 1 (CSF-1), interleukin-34 (IL-34), and CSF-1 receptor genes and gene products

Macrophages are involved in many aspects of development, host defense, pathology, and homeostasis. Their normal differentiation, proliferation, and survival are controlled by CSF-1 via the activation of the CSF1R. A recently discovered cytokine, IL-34, was shown to bind the same receptor in humans. Chicken is a widely used model organism in developmental biology, but the factors that control avian myelopoiesis have not been identified previously. The CSF-1, IL-34, and CSF1R genes in chicken and zebra finch were identified from respective genomic/cDNA sequence resources. Comparative analysis of the avian CSF1R loci revealed likely orthologs of mammalian macrophage-specific promoters and enhancers, and the CSF1R gene is expressed in the developing chick embryo in a pattern consistent with macrophage-specific expression. Chicken CSF-1 and IL-34 were expressed in HEK293 cells and shown to elicit macrophage growth from chicken BM cells in culture. Comparative sequence and co-evolution analysis across all vertebrates suggests that the two ligands interact with distinct regions of the CSF1R. These studies demonstrate that there are two separate ligands for a functional CSF1R across all vertebrates.

Molecular and functional characterization of kita and kitla of the goldfish (Carassius auratus L.)

Kit ligand and its type III tyrosine kinase receptor Kit promotes the survival, proliferation and differentiation of progenitor cells involved in mammalian myelopoiesis. In this study we report on the molecular and functional characterization of kit receptor A (kita) and kit ligand A (kitla) from the goldfish. Both kita and kitla were ubiquitously expressed in goldfish tissues, with higher mRNA levels observed in the kidney and spleen, the major hematopoietic organs of fish. Furthermore, both kita and kitla expressions decreased in a time-dependent manner in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, and the highest expressions of both the receptor and ligand were observed in sorted progenitor cell populations. Activation of mature macrophage cultures increased both kita and kitla expressions. Kit ligand A induced chemotactic response, proliferation and survival of PKM cells in a dose-dependent manner, but did not induce differentiation of early PKM cells. These results are consistent with the role of kita and kitla during myelopoiesis of higher vertebrates and suggest a conserved mechanism of macrophage development throughout vertebrates.

A comparative view on mechanisms and functions of skeletal remodelling in teleost fish, with special emphasis on osteoclasts and their function

Resorption and remodelling of skeletal tissues is required for development and growth, mechanical adaptation, repair, and mineral homeostasis of the vertebrate skeleton. Here we review for the first time the current knowledge about resorption and remodelling of the skeleton in teleost fish, the largest and most diverse group of extant vertebrates. Teleost species are increasingly used in aquaculture and as models in biomedical skeletal research. Thus, detailed knowledge is required to establish the differences and similarities between mammalian and teleost skeletal remodelling, and between distantly related species such as zebrafish (Danio rerio) and medaka (Oryzias latipes). The cellular mechanisms of differentiation and activation of osteoclasts and the functions of teleost skeletal remodelling are described. Several characteristics, related to skeletal remodelling, distinguish teleosts from mammals. These characteristics include (a) the absence of osteocytes in most species; (b) the absence of haematopoietic bone marrow tissue; (c) the abundance of small mononucleated osteoclasts performing non-lacunar (smooth) bone resorption, in addition to or instead of multinucleated osteoclasts; and (d) a phosphorus- rather than calcium-driven mineral homeostasis (mainly affecting the postcranial dermal skeleton). Furthermore, (e) skeletal resorption is often absent from particular sites, due to sparse or lacking endochondral ossification. Based on the mode of skeletal remodelling in early ontogeny of all teleosts and in later stages of development of teleosts with acellular bone we suggest a link between acellular bone and the predominance of mononucleated osteoclasts, on the one hand, and cellular bone and multinucleated osteoclasts on the other. The evolutionary origin of skeletal remodelling is discussed and whether mononucleated osteoclasts represent an ancestral type of resorbing cells. Revealing the differentiation and activation of teleost skeletal resorbing cells, in the absence of several factors that trigger mammalian osteoclast differentiation, is a current challenge. Understanding which characters of teleost bone remodelling are derived and which characters are conserved should enhance our understanding of the process in fish and may provide insights into alternative pathways of bone remodelling in mammals.

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.

Isolation and functional characterization of neutrophil-like cells, from goldfish (Carassius auratus L.) kidney

Neutrophils are one of the first cells to arrive at the site of inflammation and are central cells of innate immunity of vertebrates. Upon activation, neutrophils are capable of producing an intense respiratory burst response, they rapidly degranulate in the presence of pathogens, and deploy neutrophil extracellular traps that efficiently remove infections agents. We report on the isolation, cultivation and characterization of neutrophil-like cells isolated from the goldfish kidney. Neutrophil-like cells stained positive for acid phosphatase and Sudan black, expressed MPO, and produced a dose-dependent respiratory burst response after stimulation with phorbol esters (PMA) and calcium ionophore A23187 (CaI). Treatment of neutrophil-like cultures with PMA, CaI or zymosan induced a dose-dependent non-reversible degranulation of neutrophil-like cells. Goldfish neutrophil-like cells also exhibited a chemotactic response, degranulation, and respiratory burst response when exposed to the virulent fish pathogen, Aeromonas salmonicida A449.

Will advances in fish immunology change vaccination strategies?

This review will discuss some of the recent advances in discovering immune genes in fish, in terms of their relevance to vaccine design and development. Particular emphasis will be placed on the many cytokine and costimulatory molecules now known, with examples drawn from the mammalian literature as to their potential value for fish vaccinology. A new area of vaccine research will also be touched upon, where efficacious responses are elicited by inhibiting the natural negative regulators of immune responses, such as Treg cell products and SOCS proteins.