Comparison of respiratory burst activity of inflammatory neutrophils in ayu (Plecoglossus altivelis) and carp (Cyprinus carpio)

Transcriptomic Analysis of Fish Hosts Responses to Nervous Necrosis Virus

Nervous necrosis virus (NNV) has been responsible for mass mortalities in the aquaculture industry worldwide, with great economic and environmental impact. The present review aims to summarize the current knowledge of gene expression responses to nervous necrosis virus infection in different fish species based on transcriptomic analysis data. Four electronic databases, including PubMed, Web of Science, and SCOPUS were searched, and more than 500 publications on the subject were identified. Following the application of the appropriate testing, a total of 24 articles proved eligible for this review. NNV infection of different host species, in different developmental stages and tissues, presented in the eligible publications, are described in detail, revealing and highlighting genes and pathways that are most affected by the viral infection. Those transcriptome studies of NNV infected fish are oriented in elucidating the roles of genes/biomarkers for functions of special interest, depending on each study’s specific emphasis. This review presents a first attempt to provide an overview of universal host reaction mechanisms to viral infections, which will provide us with new perspectives to overcome NNV infection to build healthier and sustainable aquaculture systems.

Chemokine CXCb1 stimulates formation of NETs in trunk kidney neutrophils of common carp

Both in mammals and in fish, CXC chemokines activate leukocytes and regulate their migration both under normal physiological and inflammatory conditions. Moreover, in mammalian neutrophils CXC chemokines also stimulate the formation of neutrophil extracellular traps (NETs). Here, we investigated the effects of recombinant carp CXCL8s and CXCb1 on NET formation in neutrophils from the head (HK) and trunk (TK) kidney of carp. We found that neither recombinant CXCL8s nor CXCb1 stimulated DNA release in HK-derived neutrophils, while in TK-derived cells rcCXCb1 stimulated the release of NETs, composed of extracellular DNA co-localized with citrulline H3 histone and neutrophil elastase. Furthermore, CXCb1-induced NET release required NADPH oxidase activity, while it did not change upon treatment with CXCR inhibitors. In conclusion, we demonstrated, for the first time in fish, that CXCb1 chemokine induces formation of NETs in TK-derived neutrophils and this process is ROS-dependent. The difference between HK and TK-derived neutrophils is probably related to differences in the maturation state of these cells.

Maturation-associated changes in the non-specific immune response against Flavobacterium psychrophilum in Ayu Plecoglossus altivelis

In this study, we investigated maturation-associated changes in non-specific immune responses of ayu against Flavobacterium psychrophilum. The gonadosomatic index was minimum on 16 June, began to increase on 17 July, and reached the maximum value during August. The highest phagocytic rate (16.3%) was observed on 16 June, which decreased significantly to 5.6% on 26 August. The number of viable bacteria after the serum treatment was highest during August, suggesting that bactericidal activity of the serum decreased along with the sexual maturation. Gene expression levels of interleukin-8, and tumor necrosis factor-α in the spleen did not change significantly during this period, whereas the level of suppressor of cytokine signaling (SOCS)3 was significantly higher on 26 August than that on 16 July (p < 0.05). These results suggest that phagocytic activity of trunk kidney leukocytes and serum bactericidal activity against F. psychrophilum decreased with sexual maturation, and that SOCS3 may be related to the decrease in non-specific immune activity in ayu.

A simple and non-invasive method for analyzing local immune responses in vivo using fish fin

Immunocompetence is an important parameter that reflects disease resistance in fish. Very few methods to examine immunocompetence in vivo have been developed, even for mammals. In the present study, we present a unique method for analyzing local immune responses using fish fin. We first demonstrated the migration of granulocytes to the site of zymosan injection in fin in a dose-dependent manner and that this could be easily observed macroscopically due to the fin membrane transparency. We also demonstrated phagocytic activity of accumulated leukocytes after zymosan administration and that almost all phagocytes were granulocytes. In addition, we succeeded to detect respiratory burst activity of granulocytes in vivo without any in vitro treatment of cells, indicating that our present method is suitable for the analysis of granulocyte phagocytic function in vivo. The method provides a unique tool applicable for fishes that possess transparent fins and may lead to better understanding of the mechanisms of local immune responses in fish.

Stimulatory effects of heat-killed Enterococcus faecalis on cell-mediated immunity in fish

Intracellular bacterial and viral diseases are widespread in the aquaculture industry and cause serious economic losses. Development of effective vaccines and adjuvants that can induce cell-mediated immunity is urgently needed for prevention of these diseases. Here we report the immunostimulatory effects of probiotic bacteria ''E. faecalis'' in ginbuna crucian carp Carassius auratus langsdorfii. Intraperitoneal injection of heat-killed E. faecalis induced an increase in CD4-1⁺ lymphocytes, CD8α⁺ lymphocytes and macrophages in vivo. Expression of Th1 cytokine genes was enhanced by exposure to the bacteria in vitro. We identified the leukocyte subsets that expressed specific Th1 cytokine genes: granulocytes and macrophages produced IL12 and IFNγrel2, respectively, while lymphocytes produced IFNγs including IFNγ1 and IFNγ2. Finally, expression of Th1 cytokines was also enhanced by intraperitoneal injection of heat-killed E. faecalis in vivo, while expression of Th2 cytokine was unchanged. Together, these findings suggest that heat-killed E. faecalis can induce cell-mediated immunity in fish.

Neutrophil Development, Migration, and Function in Teleost Fish

It is now widely recognized that neutrophils are sophisticated cells that are critical to host defense and the maintenance of homeostasis. In addition, concepts such as neutrophil plasticity are helping to define the range of phenotypic profiles available to cells in this group and the physiological conditions that contribute to their differentiation. Herein, we discuss key features of the life of a teleost neutrophil including their development, migration to an inflammatory site, and contributions to pathogen killing and the control of acute inflammation. The potent anti-microbial mechanisms elicited by these cells in bony fish are a testament to their long-standing evolutionary contributions in host defense. In addition, recent insights into their active roles in the control of inflammation prior to induction of apoptosis highlight their importance to the maintenance of host integrity in these early vertebrates. Overall, our goal is to summarize recent progress in our understanding of this cell type in teleost fish, and to provide evolutionary context for the contributions of this hematopoietic lineage in host defense and an efficient return to homeostasis following injury or infection.

Expressed sequence tag analyses of three leukocyte subpopulations in ayu Plecoglossus altivelis altivelis, separated by monoclonal antibodies

Ayu Plecoglossus altivelis altivelis are one of the most economically important fish for freshwater aquaculture in Japan. We conducted expressed sequence tag analyses of three leukocyte subpopulations, thrombocytes, neutrophils, and B lymphocytes in ayu using a next generation sequencer. The sequencing and de novo assembly yielded 22,494, 22,733, and 16,505 contigs from the thrombocyte, neutrophil, and B lymphocyte cDNA libraries, respectively. Pathways involving endocytosis, phagosomes, and lysosomes, were found in all three cDNA libraries using pathway analysis. The thrombocyte cDNA library contained 2894 unique sequences, including CXC chemokine receptor 4 and MHC class II. Cytokine and cytokine receptor genes such as interleukin (IL)-1β, IL-8, IL-1 receptor (IL-1R), IL-8RA, and IL-8RB were found among the 3056 unique sequences of the neutrophil cDNA library. Typical B lymphocyte related genes such as B cell linker protein, immunoglobulin (Ig) M, IgD and transforming growth factor β were found in the 1590 unique sequences of the B lymphocyte cDNA library. In summary, a large number of immune-related genes were identified from the three leukocyte cDNA libraries. Our results represent a valuable sequence resource for understanding the immune system function in ayu.

Protective efficacies and immune responses induced by recombinant HCD, atpD and gdhA against bacterial cold-water disease in ayu (Plecoglossus altivelis)

Protective efficacies of three antigenic proteins (3-hydroxyacyl-CoA dehydrogenase (HCD), ATP synthase beta subunit (atpD), and glutamate dehydrogenase (gdhA)) against Flavobacterium psychrophilum were investigated in ayu (Plecoglossus altivelis). Recombinant proteins of HCD, atpD, and gdhA were expressed in Escherichia coli BL21 cells. Ayu were then vaccinated with inactivated cells via the intraperitoneal route. Compared with the empty BL21- and PBS-injected groups, the vaccinated group had a significantly longer survival time after challenge with F. psychrophilum. The antibody titers against each recombinant protein were significantly higher in serum from vaccinated fish, compared with serum from control fish. Results of indirect immunofluorescence assays using serum indicated that the HCD, atpD, and gdhA proteins are located on the surface of F. psychrophilum. These results suggest that these three surface proteins are protective antigens and are good candidates for development of vaccines against bacterial cold-water disease in ayu.

Antimicrobial mechanisms of fish leukocytes

Early activation and coordination of innate defenses are critical for effective responses against infiltrating pathogens. Rapid engagement of immune cells provides a critical first line of defense soon after pathogen infiltration. Activation leads to a well-orchestrated set of events that sees the induction and regulation of intracellular and extracellular antimicrobial defenses. An array of regulatory mediators, highly toxic soluble molecules, degradative enzymes and antimicrobial peptides provides maximal protection against a wide range of pathogens while limiting endogenous damage to host tissues. In this review we highlight recent advances in our understanding of innate cellular antimicrobial responses of teleost fish and discuss their implications to cell survival, immunomodulation and death. The evolutionary conservation of these responses is a testament to their effectiveness against pathogen infiltration and their commitment to effective maintenance of host homeostasis. Importantly, recent developments in teleost fish systems have identified novel host defense strategies that may be unique to this lower vertebrate group or may point to previously unknown innate mechanisms that also play a significant role in higher vertebrate host immunity.

Clonal growth of carp (Cyprinus carpio) T cells in vitro

Carp kidney leukocytes co-cultured with a supporting cell layer resulted in the rapid proliferation of various types of leukocytes including immature leukocytes. Expressions of marker genes for multiple blood cell lineages were observed in the primary culture. However, after several passages, the proliferating cells expressed only T cell and macrophage marker genes. Further RT-PCR analysis revealed that the proliferating cells expressed TCR constant regions (Cα, Cβ, Cγ, Cδ), CD3γ/δ and CD4 (CD4L-1), but did not express CD8α and CD8β. Additionally, in situ hybridization analysis showed that the majority of proliferating cells expressed Cα, Cβ, Cγ, Cδ and CD4. Moreover, 5'-RACE sequences of TCR variable regions (Vα, Vβ, Vγ, Vδ) revealed that the proliferating cells contained a polyclonal T cell repertoire, and most of the Vα and Vβ sequences were functional, but the Vγ and Vδ sequences were non-functional with frame shifts and stop codons. Taken together, these results indicate that the proliferating cells after serial passages predominantly contained CD4+ CD8- αβT cells that simultaneously co-expressed non-functional γδTCR. To obtain CD4+ αβT cell (helper T cell) clones, single cells were picked up from the bulk culture, seeded into each well of 96-well plates and cultured in the presence of supporting cells and conditioned media. T cell colonies formed from single cells after 2-3 weeks. These colony cells expressed Cα, Cβ, Cδ and CD4, and weakly expressed Cγ, but did not express CD8α, CD8β and CD4L-2. Taken together, these results indicate that these clonal T cells resemble a subpopulation of mammalian CD4+ helper T cells.

Immune response of Japanese flounder Paralichthys olivaceus to outer membrane protein of Edwardsiella tarda

The humoral and cellular immune responses of Japanese flounder, Paralichthys olivaceus, were investigated following intraperitioneal injection with outer membrane protein (OMP) of Edwardsiella tarda in Freund's incomplete adjuvant (FIA). The specific serum antibody titre against OMP of E. tarda were measured using ELISA for 14 weeks, and the total serum antibody concentrations were also determined according to the sandwich ELISA standard model constructed using purified IgM. Both of the specific and total antibodies had an increase and reached their peaks 4 weeks after immunization. Simultaneously, the percentages of sIg + lymphocytes in blood, spleen, pronephros and mesonephros were detected by flow cytometry. It was shown that the percentages of sIg + lymphocytes in all lymphoid organs reached their peak levels 4 weeks after immunization, and then decreased gradually. To investigate the protection against infection, three challenges were performed in the same way at day 14, 30 and 100 after immunization, fish challenged at day 30 showed a higher relative percentage survival (RPS) of 71 compared to the 14-day group (30) and 100-day group (53), which indicated a positive correlation between the survival and the levels of the antibody.

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.

Habitat-specific adaptation of immune responses of stickleback (Gasterosteus aculeatus) lake and river ecotypes

Freshwater populations of three-spined sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of stickleback ecotypes. Here, naive laboratory-bred sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River sticklebacks in the lake had higher parasite loads than lake sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river sticklebacks exposed to lake when compared with river conditions. Although river sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake sticklebacks in their native habitat. River sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.

The innate immune response of finfish--a review of current knowledge

The decline in the fisheries of traditional marine species has been an incentive for the diversification of today's aquaculture sector into the intensive rearing of many finfish species. The increasing interest in commercial farming of different finfish species is expected to result in similar environmental and husbandry-related problems as have been experienced in the development of the salmonid farming industry. An understanding of the biology of the fish species being cultured, in particular the immune response is important for improved husbandry and health management of the species. The innate immune system of fish has generated increasing interest in recent years and is now thought to be of key importance in primary defence and in driving adaptive immunity. This review focuses on key components (cellular and humoral) of the innate immune responses of different fish species of commercial importance.

Interrogation of living cells using alternating current scanning electrochemical microscopy (AC-SECM)

In this paper we present the application of alternating current scanning electrochemical microscopy (AC-SECM) to the study of living cells. Commercial AFM instrumentation was modified to allow for performing robust AC-SECM measurements. Constant height AC imaging of the Cos-7 cells, performed directly in cell culture medium without the addition of a redox mediator, provided topographical information of the cell. Stationary tip measurements on the AC current were carried out to investigate the cellular activity of a single cell. The dependence of AC current magnitude on tip-to-sample separation distance was used to monitor real time changes in cell height of individual Cos-7 cells. Furthermore, AC-SECM was employed to observe changes in metabolic cellular activity stimulated by ethanol and phorbol-1,2-myristate-acetate-3. The effect of changing cellular activity on constant height AC-SECM imaging was also studied.

mRNA expression patterns of the BPI/LBP molecule in the Atlantic cod (Gadus morhua L.)

Bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) are important components of the mammalian innate defence system against Gram-negative infections. cDNA encoding a protein related to mammalian BPI and LBP have been cloned from several teleosts including the Atlantic cod (Gadus morhua L.). Using real-time PCR an increase in cod BPI/LBP expression in whole blood and peritoneal cells was demonstrated one, two and four days after intraperitoneal injection of inactivated Vibrio anguillarum. Although constitutively produced in the head kidney, a moderate rise of BPI/LBP mRNA production was seen on day two in this organ. After seven days the BPI/LBP mRNA levels at the three locations examined were almost back to normal. In situ hybridisation demonstrated a leucocytic localisation and morphology of the BPI/LBP expressing cells in various tissues. A combination of in situ hybridisation and peroxidase staining of head kidney leucocytes showed that the BPI/LBP producing cells are peroxidase positive and possible neutrophil like cells. The results suggest that the cod BPI/LBP is important in the first-line defence against bacterial infections and has a function more related to the mammalian BPI molecule than the LBP counterpart.