Zebrafish kidney phagocytes utilize macropinocytosis and Ca+-dependent endocytic mechanisms

The Attenuation Mechanism and Live Vaccine Potential of a Low-Virulence Edwardsiella ictaluri Strain Obtained by Rifampicin Passaging Culture

The rifampicin-resistant strain E9-302 of Edwardsiella ictaluri strain 669 (WT) was generated by continuous passage on BHI agar plates containing increasing concentrations of rifampicin. E9-302 was attenuated significantly by 119 times to zebrafish Danio rerio compared to WT in terms of the 50% lethal dose (LD₅₀). Zebrafish vaccinated with E9-302 via intraperitoneal (IP) injection at a dose of 1 × 10³ CFU/fish had relative percentage survival (RPS) rates of 85.7% when challenged with wild-type E. ictaluri via IP 14 days post-vaccination (dpv). After 14 days of primary vaccination with E9-302 via immersion (IM) at a dose of 4 × 10⁷ CFU/ml, a booster IM vaccination with E9-302 at a dose of 2 × 10⁷ CFU/ml exhibited 65.2% RPS against challenge with wild-type E. ictaluri via IP 7 days later. These results indicated that the rifampicin-resistant attenuated strain E9-302 had potential as a live vaccine against E. ictaluri infection. A previously unreported amino acid site change at position 142 of the RNA polymerase (RNAP) β subunit encoded by the gene rpoB associated with rifampicin resistance was identified. Analysis of the whole-genome sequencing results revealed multiple missense mutations in the virulence-related genes esrB and sspH2 in E9-302 compared with WT, and a 189 bp mismatch in one gene, whose coding product was highly homologous to glycosyltransferase family 39 protein. This study preliminarily explored the molecular mechanism underlying the virulence attenuation of rifampicin-resistant strain E9-302 and provided a new target for the subsequent study of the pathogenic mechanism of E. ictaluri.

Trained Immunity Provides Long-Term Protection against Bacterial Infections in Channel Catfish

Beta glucan exposure induced trained immunity in channel catfish that conferred long-term protection against Edwardsiella ictaluri and Edwardsiella piscicida infections one month post exposure. Flow cytometric analyses demonstrated that isolated macrophages and neutrophils phagocytosed higher amounts of E. ictaluri and E. piscicida. Beta glucan induced changes in the distribution of histone modifications in the monomethylation and trimethylation of H3K4 and modifications in the acetylation and trimethylation of H3K27. KEGG pathway analyses revealed that these modifications affected expressions of genes controlling phagocytosis, phagosome functions and enhanced immune cell signaling. These analyses correlate the histone modifications with gene functions and to the observed enhanced phagocytosis and to the increased survival following bacterial challenge in channel catfish. These data suggest the chromatin reconfiguration that directs trained immunity as demonstrated in mammals also occurs in channel catfish. Understanding the mechanisms underlying trained immunity can help us design prophylactic and non-antibiotic based therapies and develop broad-based vaccines to limit bacterial disease outbreaks in catfish production.

Immunomodulatory Function of Polyvinylpyrrolidone (PVP)-Functionalized Gold Nanoparticles in Vibrio-Stimulated Sea Urchin Immune Cells

We investigated the role of the gold nanoparticles functionalized with polyvinylpyrrolidone (PVP–AuNPs) on the innate immune response against an acute infection caused by Vibrio anguillarum in an in vitro immunological nonmammalian next-generation model, the sea urchin Paracentrotus lividus. To profile the immunomodulatory function of PVP–AuNPs (0.1 μg mL⁻¹) in sea urchin immune cells stimulated by Vibrio (10 μg mL⁻¹) for 3 h, we focused on the baseline immunological state of the donor, and we analysed the topography, cellular metabolism, and expression of human cell surface antigens of the exposed cells, as well as the signalling leading the interaction between PVP–AuNPs and the Vibrio-stimulated cells. PVP–AuNPs are not able to silence the inflammatory signalling (TLR4/p38MAPK/NF-κB signalling) that involves the whole population of P. lividus immune cells exposed to Vibrio. However, our findings emphasise the ability of PVP–AuNPs to stimulate a subset of rare cells (defined here as Group 3) that express CD45 and CD14 antigens on their surface, which are known to be involved in immune cell maturation and macrophage activation in humans. Our evidence on how PVP–AuNPs may stimulate sea urchin immune cells represents an important starting point for planning new research work on the topic.

Specific Aptamer-Based Probe for Analyzing Biomarker MCP Entry Into Singapore Grouper Iridovirus-Infected Host Cells via Clathrin-Mediated Endocytosis

Biomarkers have important roles in various physiological functions and disease pathogenesis. As a nucleocytoplasmic DNA virus, Singapore grouper iridovirus (SGIV) causes high economic losses in the mariculture industry. Aptamer-Q5-complexed major capsid protein (MCP) in the membrane of SGIV-infected cells can be used as a specific molecular probe to investigate the crucial events of MCP endocytosis into SGIV-infected host cells during viral infection. Chlorpromazine blocks clathrin-mediated endocytosis, and MCP endocytosis into SGIV-infected cells decreased significantly when the cells were pretreated with chlorpromazine. The disruption of cellular cholesterol by methyl-β-cyclodextrin also significantly reduced MCP endocytosis. In contrast, inhibitors of key regulators of caveolae/raft-dependent endocytosis and macropinocytosis, including genistein, Na⁺/H⁺ exchanger, p21-activated kinase 1 (PAK1), myosin II, Rac1 GTPase, and protein kinase C (PKC), had no effect on MCP endocytosis. The endocytosis of the biomarker MCP is dependent on low pH and cytoskeletal actin filaments, as shown with various inhibitors (chloroquine, ammonia chloride, cytochalasin D). Therefore, MCP enters SGIV-infected host cells via clathrin-mediated endocytosis, which is dependent on dynamin, cholesterol, low pH, and cytoskeletal actin filaments. This is the first report of a specific aptamer-based probe used to analyze MCP endocytosis into SGIV-infected host cells during viral infection. This method provides a convenient strategy for exploring viral pathogenesis and facilitates the development of diagnostic tools for and therapeutic approaches to viral infection.

Modulation of azole sensitivity and filamentation by GPI15, encoding a subunit of the first GPI biosynthetic enzyme, in Candida albicans

Glycosylphosphatidylinositol (GPI)-anchored proteins are important for virulence of many pathogenic organisms including the human fungal pathogen, Candida albicans. GPI biosynthesis is initiated by a multi-subunit enzyme, GPI-N-acetylglucosaminyltransferase (GPI-GnT). We showed previously that two GPI-GnT subunits, encoded by CaGPI2 and CaGPI19, are mutually repressive. CaGPI19 also co-regulates CaERG11, the target of azoles while CaGPI2 controls Ras signaling and hyphal morphogenesis. Here, we investigated the role of a third subunit. We show that CaGpi15 is functionally homologous to Saccharomyces cerevisiae Gpi15. CaGPI15 is a master activator of CaGPI2 and CaGPI19. Hence, CaGPI15 mutants are azole-sensitive and hypofilamentous. Altering CaGPI19 or CaGPI2 expression in CaGPI15 mutant can elicit alterations in azole sensitivity via CaERG11 expression or hyphal morphogenesis, respectively. Thus, CaGPI2 and CaGPI19 function downstream of CaGPI15. One mode of regulation is via H3 acetylation of the respective GPI-GnT gene promoters by Rtt109. Azole sensitivity of GPI-GnT mutants is also due to decreased H3 acetylation at the CaERG11 promoter by Rtt109. Using double heterozygous mutants, we also show that CaGPI2 and CaGPI19 can independently activate CaGPI15. CaGPI15 mutant is more susceptible to killing by macrophages and epithelial cells and has reduced ability to damage either of these cell lines relative to the wild type strain, suggesting that it is attenuated in virulence.

Ras signaling activates glycosylphosphatidylinositol (GPI) anchor biosynthesis via the GPI-N-acetylglucosaminyltransferase (GPI-GnT) in Candida albicans

The ability of Candida albicans to switch between yeast to hyphal form is a property that is primarily associated with the invasion and virulence of this human pathogenic fungus. Several glycosylphosphatidylinositol (GPI)-anchored proteins are expressed only during hyphal morphogenesis. One of the major pathways that controls hyphal morphogenesis is the Ras-signaling pathway. We examine the cross-talk between GPI anchor biosynthesis and Ras signaling in C. albicans. We show that the first step of GPI biosynthesis is activated by Ras in C. albicans This is diametrically opposite to what is reported in Saccharomyces cerevisiae Of the two C. albicans Ras proteins, CaRas1 alone activates GPI-GnT activity; activity is further stimulated by constitutively activated CaRas1. CaRas1 localized to the cytoplasm or endoplasmic reticulum (ER) is sufficient for GPI-GnT activation. Of the six subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) that catalyze the first step of GPI biosynthesis, CaGpi2 is the key player involved in activating Ras signaling and hyphal morphogenesis. Activation of Ras signaling is independent of the catalytic competence of GPI-GnT. This too is unlike what is observed in S. cerevisiae where multiple subunits were identified as inhibiting Ras2. Fluorescence resonance energy transfer (FRET) studies indicate a specific physical interaction between CaRas1 and CaGpi2 in the ER, which would explain the ability of CaRas1 to activate GPI-GnT. CaGpi2, in turn, promotes activation of the Ras-signaling pathway and hyphal morphogenesis. The Cagpi2 mutant is also more susceptible to macrophage-mediated killing, and macrophage cells show better survival when co-cultured with Cagpi2.

Phagocytic and Bactericidal Properties of Channel Catfish Peritoneal Macrophages Exposed to Edwardsiella ictaluri Live Attenuated Vaccine and Wild-Type Strains

Edwardsiella ictaluri (E. ictaluri), a Gram-negative, intracellular, facultative bacterium, is the causative agent of enteric septicemia of catfish (ESC), which is one of the most significant diseases of farmed channel catfish. Macrophages have a critical role in major defense mechanisms against bacterial infections by migrating to the site of infection, engulfing and killing pathogens, and priming adaptive immune responses. Vaccination of catfish with E. ictaluri live attenuated vaccine (LAV) strains increased the efficiency of phagocytosis and bacterial killing in catfish peritoneal macrophages compared in vitro with macrophages from non-vaccinated fish. Recently, our group developed several protective LAV strains from E. ictaluri. However, their effects on the antigen uptake and bacterial killing in catfish macrophages have not been evaluated. In this study, we assessed the phagocytic and bactericidal activity of peritoneal macrophages in the uptake of E. ictaluri wild-type (WT) and two LAV strains. We found that phagocytosis of LAV strains was significantly higher compared to their WT counterpart in peritoneal macrophages. Moreover, the uptake of E. ictaluri opsonized with sera from vaccinated catfish was more efficient than when opsonized with sera from sham-vaccinated fish. Notably, catfish macrophages did not lose their phagocytic properties at 4°C, as described previously in mammalian and zebrafish models. Also, opsonization of E. ictaluri with inactivated sera from vaccinated and sham-vaccinated catfish decreased significantly phagocytic uptake of bacteria at 32°C, and virtually suppressed endocytosis at 4°C, suggesting the important role of complement-dependent mechanisms in catfish macrophage phagocytosis. In conclusion, our data on enhanced phagocytic capacity and effective killing ability in macrophages of vaccine strains suggested the LAVs’ advantage if processed and presented in the form of peptides to specific lymphocytes of an adaptive immune system and emphasize the importance of macrophage-mediated immunity against ESC. Furthermore, we showed the role of complement-dependent mechanisms in the phagocytic uptakes of E. ictaluri in catfish peritoneal macrophages at 4 and 32°C. Finally, LAV vaccine-induced bacterial phagocytosis and killing properties of peritoneal macrophages emphasized the importance of the innate immune responses in ESC.

Immune competence assessment in marine medaka (Orzyias melastigma)-a holistic approach for immunotoxicology

Many anthropogenic pollutants in coastal marine environments can induce immune impairments in wild fish and reduce their survival fitness. There is a pressing need to establish sensitive and high throughput in vivo tools to systematically evaluate the immunosuppressive effects of contaminants in marine teleosts. This study reviewed a battery of in vivo immune function detection technologies established for different biological hierarchies at molecular (immune function pathways and genes by next generation sequencing (NGS)), cellular (leukocytes profiles by flow cytometry), tissues/organ system (whole adult histo-array), and organism (host resistance assays (HRAs)) levels, to assess the immune competence of marine medaka Oryzias melastigma. This approach enables a holistic assessment of fish immune competence under different chemical exposure or environmental scenarios. The data obtained will also be useful to unravel the underlying immunotoxic mechanisms. Intriguingly, NGS analysis of hepatic immune gene expression profiles (male > female) are in support of the bacterial HRA findings, in which infection-induced mortality was consistently higher in females than in males. As such, reproductive stages and gender-specific responses must be taken into consideration when assessing the risk of immunotoxicants in the aquatic environment. The distinct phenotypic sexual dimorphism and short generation time (3 months) of marine medaka offer additional advantages for sex-related immunotoxicological investigation.

Intracellular uptake of macromolecules by brain lymphatic endothelial cells during zebrafish embryonic development

The lymphatic system controls fluid homeostasis and the clearance of macromolecules from interstitial compartments. In mammals brain lymphatics were only recently discovered, with significant implications for physiology and disease. We examined zebrafish for the presence of brain lymphatics and found loosely connected endothelial cells with lymphatic molecular signature covering parts of the brain without forming endothelial tubular structures. These brain lymphatic endothelial cells (BLECs) derive from venous endothelium, are distinct from macrophages, and are sensitive to loss of Vegfc. BLECs endocytose macromolecules in a selective manner, which can be blocked by injection of mannose receptor ligands. This first report on brain lymphatic endothelial cells in a vertebrate embryo identifies cells with unique features, including the uptake of macromolecules at a single cell level. Future studies will address whether this represents an uptake mechanism that is conserved in mammals and how these cells affect functions of the embryonic and adult brain.

DOI:http://dx.doi.org/10.7554/eLife.25932.001

Characterization and Vaccine Potential of Membrane Vesicles Produced by Francisella noatunensis subsp. orientalis in an Adult Zebrafish Model

Vaccine development against extracellular bacteria has been important for the sustainability of the aquaculture industry. In contrast, infections with intracellular pathogens remain largely an unresolved problem. Francisella noatunensis subsp. orientalis is a Gram-negative, facultative intracellular bacterium that causes the disease francisellosis in fish. Francisellosis is commonly characterized as a chronic granulomatous disease with high morbidity and can result in high mortality depending on the host. In this study, we explored the potential of bacterial membrane vesicles (MVs) as a vaccine agent against F. noatunensis subsp. orientalis. Bacterial MVs are spherical structures naturally released from the membrane of bacteria and are often enriched with selected bacterial components such as toxins and signaling molecules. MVs were isolated from broth-cultured F. noatunensis subsp. orientalis in the present work, and proteomic analysis by mass spectrometry revealed that MVs contained a variety of immunogenic factors, including the intracellular growth proteins IglC and IglB, known to be part of a Francisella pathogenicity island (FPI), as well as outer membrane protein OmpA, chaperonin GroEL, and chaperone ClpB. By using flow cytometry and electron microscopy, we observed that F. noatunensis subsp. orientalis mainly infects myelomonocytic cells, both in vivo and in vitro. Immunization with MVs isolated from F. noatunensis subsp. orientalis protects zebrafish from subsequent challenge with a lethal dose of F. noatunensis subsp. orientalis. To determine if MVs induce a typical acute inflammatory response, mRNA expression levels were assessed by quantitative real-time PCR. Expression of tnfa, il1b, and ifng, as well as mhcii, mpeg1.1, and ighm, was upregulated, thus confirming the immunogenic properties of F. noatunensis subsp. orientalis-derived MVs.

Comparative Analysis of Membrane Vesicles from Three Piscirickettsia salmonis Isolates Reveals Differences in Vesicle Characteristics

Membrane vesicles (MVs) are spherical particles naturally released from the membrane of Gram-negative bacteria. Bacterial MV production is associated with a range of phenotypes including biofilm formation, horizontal gene transfer, toxin delivery, modulation of host immune responses and virulence. This study reports comparative profiling of MVs from bacterial strains isolated from three widely disperse geographical areas. Mass spectrometry identified 119, 159 and 142 proteins in MVs from three different strains of Piscirickettsia salmonis isolated from salmonids in Chile (LF-89), Norway (NVI 5692) and Canada (NVI 5892), respectively. MV comparison revealed several strain-specific differences related to higher virulence capability for LF-89 MVs, both in vivo and in vitro, and stronger similarities between the NVI 5692 and NVI 5892 MV proteome. The MVs were similar in size and appearance as analyzed by electron microscopy and dynamic light scattering. The MVs from all three strains were internalized by both commercial and primary immune cell cultures, which suggest a potential role of the MVs in the bacterium’s utilization of leukocytes. When MVs were injected into an adult zebrafish infection model, an upregulation of several pro-inflammatory genes were observed in spleen and kidney, indicating a modulating effect on the immune system. The present study is the first comparative analysis of P. salmonis derived MVs, highlighting strain-specific vesicle characteristics. The results further illustrate that the MV proteome from one bacterial strain is not representative of all bacterial strains within one species.

Protective effect of a recombinant VHSV-G vaccine using poly(I:C) loaded nanoparticles as an adjuvant in zebrafish (Danio rerio) infection model

There is a constant need to increase the efficiency of vaccines in the aquaculture industry. Although several nano-based vaccine formulations have been reported, to the best of our knowledge so far only one of them have been implemented in the industry. Here we report on chitosan-poly(I:C) nanoparticles (NPs) that could be used as a non-specific adjuvant in antiviral vaccines in aquaculture. We have characterized the physical parameters of the NPs, studied the in vivo and in vitro bio-distribution of fluorescent NPs and verified NP uptake by zebrafish leucocytes. We used the zebrafish model to test the protective efficiency of the recombinant glycoprotein G (rgpG) of VHSV compared to inactivated whole virus (iV) against VHSV using NPs as an adjuvant in both formulations. In parallel we tested free poly(I:C) and rgpG (pICrgpG), and free chitosan and rgpG (CSrgpG) vaccine formulations. While the iV group (with NP adjuvant) provided the highest overall survival, all vaccine formulations with poly(I:C) provided a significant protection against VHSV; possibly through an early induction of an anti-viral state. Our results suggest that chitosan-poly(I:C) NPs are a promising adjuvant candidate for future vaccine formulations.

Mannose receptor mediated phagocytosis of bacteria in macrophages of blunt snout bream (Megalobrama amblycephala) in a Ca(2+)-dependent manner

Mannose receptor (MR) is an important pattern-recognition receptor in macrophages and plays a critical role in immune responses. It is has been reported that mammalian macrophages are able to engulf a wide range of microorganisms mediated by Ca(2+)-dependent MR binding to terminal mannose residues which are frequently found on the pathogen surfaces. However, little is known about the MR-mediated phagocytosis in macrophages of fish. In this report, the distributions of MR in the macrophage and head kidney tissue from blunt snout bream were examined using MaMR specific antibody generated in our lab. Mannan and MaMR specific antibody inhibition experiments results collectively showed that MR was involved in the GFP-expressed E. coli engulfed in the macrophages, resulting in respiratory burst, nitric oxide production as well as inflammatory cytokines secretion, and the MaMR-mediated phagocytosis was Ca(2+)-dependent. These results will shed a new light on the immune functions of teleost MRs.

Depleted uranium disturbs immune parameters in zebrafish, Danio rerio: an ex vivo/in vivo experiment

In this study, we investigated the effects of depleted uranium (DU), the byproduct of nuclear enrichment of uranium, on several parameters related to defence system in the zebrafish, Danio rerio, using flow cytometry. Several immune cellular parameters were followed on kidney leucocytes: cell proportion, cell mortality, phagocytosis activity and associated oxidative burst and lysosomal membrane integrity (LMI). Effects of DU were tested ex vivo after 17 h of contact between DU and freshly isolated leucocytes from 0 to 500 µg DU/L. Moreover, adult zebrafish were exposed in vivo during 3 days at 20 and 250 µg DU/L. Oxidative burst results showed that DU increased reactive oxygen species (ROS) basal level and therefore reduced ROS stimulation index in both ex vivo and in vivo experiments. ROS PMA-stimulated level was also increased at 250 µg DU/L in vivo only. Furthermore, a decrease of LMI was detected after in vivo experiments. Cell mortality was also decreased at 20 µg DU/L in ex vivo experiment. However, phagocytosis activity was not modified in both ex vivo and in vivo experiments. A reduction of immune-related parameters was demonstrated in zebrafish exposed to DU. DU could therefore decrease the ability of fish to stimulate its own immune system which could, in turn, enhance the susceptibility of fish to infection. These results encourage the development and the use of innate immune analysis by flow cytometry in order to understand the effects of DU and more generally radionuclides on fish immune system and response to infectious diseases.

Rag1-/- mutant zebrafish demonstrate specific protection following bacterial re-exposure

Background

Recombination activation gene 1 deficient (rag1^−/−) mutant zebrafish have a reduced lymphocyte-like cell population that lacks functional B and T lymphocytes of the acquired immune system, but includes Natural Killer (NK)-like cells and Non-specific cytotoxic cells (NCC) of the innate immune system. The innate immune system is thought to lack the adaptive characteristics of an acquired immune system that provide enhanced protection to a second exposure of the same pathogen. It has been shown that NK cells have the ability to mediate adaptive immunity to chemical haptens and cytomegalovirus in murine models. In this study we evaluated the ability of rag1^−/− mutant zebrafish to mount a protective response to the facultative intracellular fish bacterium Edwardsiella ictaluri.

Methodology/Principal Findings

Following secondary challenge with a lethal dose of homologous bacteria 4 and 8 weeks after a primary vaccination, rag1^−/− mutant zebrafish demonstrated protective immunity. Heterologous bacterial exposures did not provide protection. Adoptive leukocyte transfers from previously exposed mutants conferred protective immunity to naïve mutants when exposed to homologous bacteria.

Conclusions/Significance

Our findings show that a component of the innate immune system mounted a response that provided significantly increased survival when rag1^−/− mutant zebrafish were re-exposed to the same bacteria. Further, adoptive cell transfers demonstrated that kidney interstitial leukocytes from previously exposed rag1^−/− mutant zebrafish transferred this protective immunity. This is the first report of any rag1^−/− mutant vertebrate mounting a protective secondary immune response to a bacterial pathogen, and demonstrates that a type of zebrafish innate immune cell can mediate adaptive immunity in the absence of T and B cells.

A privileged intraphagocyte niche is responsible for disseminated infection of Staphylococcus aureus in a zebrafish model

The innate immune system is the primary defence against the versatile pathogen, Staphylococcus aureus. How this organism is able to avoid immune killing and cause infections is poorly understood. Using an established larval zebrafish infection model, we have shown that overwhelming infection is due to subversion of phagocytes by staphylococci, allowing bacteria to evade killing and found foci of disease. Larval zebrafish coinfected with two S. aureus strains carrying different fluorescent reporter gene fusions (but otherwise isogenic) had bacterial lesions, at the time of host death, containing predominantly one strain. Quantitative data using two marked strains revealed that the strain ratios, during overwhelming infection, were often skewed towards the extremes, with one strain predominating. Infection with passaged bacterial clones revealed the phenomenon not to bedue to adventitious mutations acquired by the pathogen. After infection of the host, all bacteria are internalized by phagocytes and the skewing of population ratios is absolutely dependent on the presence of phagocytes. Mathematical modelling of pathogen population dynamics revealed the data patterns are consistent with the hypothesis that a small number of infected phagocytes serve as an intracellular reservoir for S. aureus, which upon release leads to disseminated infection. Strategies to specifically alter neutrophil/macrophage numbers were used to map the potential subpopulation of phagocytes acting as a pathogen reservoir, revealing neutrophils as the likely ‘niche’. Subsequently in a murine sepsis model, S. aureus abscesses in kidneys were also found to be predominantly clonal, therefore likely founded by an individual cell, suggesting a potential mechanism analogous to the zebrafish model with few protected niches. These findings add credence to the argument that S. aureus control regimes should recognize both the intracellular as well as extracellular facets of the S. aureus life cycle.

Prokaryotic expression, purification, and refolding of leukocyte cell-derived chemotaxin 2 and its effect on gene expression of head kidney-derived macrophages of a teleost fish, ayu (Plecoglossus altivelis)

Leukocyte cell-derived chemotaxin 2 (LECT2) is reported to be an immunorelevant protein in ayu (Plecoglossus altivelis). In this study, ayu LECT2 mature peptide (aLECT2m) was expressed as insoluble inclusion bodies in Escherichia coli. The denatured recombinant aLECT2m (raLECT2m) was refolded by a size-exclusion chromatography refolding process achieved by using arginine-containing mobile phase and a decreasing urea gradient. The in vitro chemotactic activity assay showed that the refolded raLECT2m had the bioactivity. By using suppression subtractive hybridization (SSH) method, we further identified up-regulated genes in ayu macrophages treated with refolded raLECT2m. These genes were tightly involved in endocytosis, hydrolysis, transcriptional regulation, signal transduction, and so on. Moreover, real-time quantitative PCR (RT-qPCR) results confirmed that selected 10 genes expression was significantly up-regulated in refolded raLECT2m-treated ayu macrophages. This study provides a basis for further studies of the mechanism of cytokine LECT2 in fish immune responses.

Phenotype, virulence and immunogenicity of Edwardsiella ictaluri cyclic adenosine 3',5'-monophosphate receptor protein (Crp) mutants in catfish host

Edwardsiella ictaluri is an Enterobacteriaceae that causes lethal enteric septicemia in catfish. Being a mucosal facultative intracellular pathogen, this bacterium is an excellent candidate to develop immersion-oral live attenuated vaccines for the catfish aquaculture industry. Deletion of the cyclic 3',5'-adenosine monophosphate (cAMP) receptor protein (crp) gene in several Enterobacteriaceae has been utilized in live attenuated vaccines for mammals and birds. Here we characterize the crp gene and report the effect of a crp deletion in E. ictaluri. The E. ictaluri crp gene and encoded protein are similar to other Enterobacteriaceae family members, complementing Salmonella enterica Δcrp mutants in a cAMP-dependent fashion. The E. ictaluri Δcrp-10 in-frame deletion mutant demonstrated growth defects, loss of maltose utilization, and lack of flagella synthesis. We found that the E. ictaluri Δcrp-10 mutant was attenuated, colonized lymphoid tissues, and conferred immune protection against E. ictaluri infection to zebrafish (Danio rerio) and catfish (Ictalurus punctatus). Evaluation of the IgM titers indicated that bath immunization with the E. ictaluri Δcrp-10 mutant triggered systemic and skin immune responses in catfish. We propose that deletion of the crp gene in E. ictaluri is an effective strategy to develop immersion live attenuated antibiotic-sensitive vaccines for the catfish aquaculture industry.

Phospholipase C-dependent Ca2+-sensing pathways leading to endocytosis and inhibition of the plasma membrane vacuolar H+-ATPase in osteoclasts

In osteoclasts, elevation of extracellular Ca2+ is an endogenous signal that inhibits bone resorption. We recently found that an elevation of extracellular Ca2+ decreased proton extrusion through the plasma membrane vacuolar H+-ATPase (V-ATPase) rapidly. In this study we investigated mechanisms underlying this early Ca2+-sensing response, particularly in reference to the activity of the plasma membrane V-ATPase and to membrane retrieval. Whole cell clamp recordings allowed us to measure the V-ATPase currents and the cell capacitance ( Cm) simultaneously. Cm is a measure of cell surface. Extracellular Ca2+ (2.5–40 mM) decreased Cm and the V-ATPase current simultaneously. The decreased Cm, together with the enhanced uptake of a lipophilic dye (FM1–43), indicated that Ca2+ facilitated endocytosis. The endocytosis was blocked by dynamin inhibitors (dynasore and dynamin-inhibitory peptide), by small interfering RNA (siRNA) targeting for dynanmin-2 and also by bafilomycin A1, a blocker of V-ATPases. The extracellular Ca2+-induced endocytosis and inhibition of the V-ATPase current were diminished by a phospholipase C inhibitor (U73122) and siRNA targeting for phospholipase C γ2 subunit. Holding the cytosolic Ca2+ at either high (0.5–5 μM) or low levels or inhibiting calmodulin by an inhibitor (W7) or an antibody (anti-CaM) decreased the stimulated endocytosis and the inhibition of the V-ATPase current. These data suggest that extracellular Ca2+ facilitated dynamin- and V-ATPase-dependent endocytosis in association with an inhibition of the plasma membrane V-ATPase. Phospholipase C, cytosolic Ca2+, and calmodulin were involved in the signaling pathways. Membrane retrieval and the plasma membrane V-ATPase activity may cooperate during the early phase of Ca2+-sensing response in osteoclasts.

Identification of phagocytic cells, NK-like cytotoxic cell activity and the production of cellular exudates in the coelomic cavity of adult zebrafish

Coelomic cavity (CC) cells of mature zebrafish harvested by lavage with media or trypsin-EDTA contained 0.80-1.20 x 10(5) and 2.0-3.5 x 10(5) cells, respectively. Media lavage was composed of granulocytes (60-80%), lymphocytes (10-20%), and NCC (4-10%). Granulocytes had large electron dense cytoplasmic paracrystalline granules and a segmented nucleus; they expressed plastin-1, myeloid specific peroxidase and MCSF mRNA; and they were NCAMP-1(+). Lymphocytes had B- and T-cell specific mRNA and were NCAMP-1(-) and NCCRP-1(-). NCC were 3 microm, NCAMP-1(+) and NCCRP-1(+) and did not express B- and T-cell specific mRNA. Additionally, trypsin lavage contained monocytes (marginated chromatin, low nuclear:cytoplasm ratio, sparse cytosolic granules) and macrophages (non-segmented nuclei, no margination of chromatin, abundant electron dense granules). E. coli injected into the CC were phagocytosed in a dose and time dependent fashion by granulocytes, monocytes and macrophages. NCC lysed mammalian target cells and NCAMP-1 expressing hybridoma cells in redirected lysis assays.