Neutrophils and B-cells in Atlantic cod (Gadus morhua L.)

Climate change can impair bacterial pathogen defences in sablefish via hypoxia-mediated effects on adaptive immunity

Low-oxygen levels (hypoxia) in aquatic habitats are becoming more common because of global warming and eutrophication. However, the effects on the health/disease status of fishes, the world's largest group of vertebrates, are unclear. Therefore, we assessed how long-term hypoxia affected the immune function of sablefish, an ecologically and economically important North Pacific species, including the response to a formalin-killed Aeromonas salmonicida bacterin. Sablefish were held at normoxia or hypoxia (100% or 40% air saturated seawater, respectively) for 6-16 weeks, while we measured a diverse array of immunological traits. Given that the sablefish is a non-model organism, this involved the development of a species-specific methodological toolbox comprised of qPCR primers for 16 key immune genes, assays for blood antibacterial defences, the assessment of blood immunoglobulin (IgM) levels with ELISA, and flow cytometry and confocal microscopy techniques. We show that innate immune parameters were typically elevated in response to the bacterial antigens, but were not substantially affected by hypoxia. In contrast, hypoxia completely prevented the ∼1.5-fold increase in blood IgM level that was observed under normoxic conditions following bacterin exposure, implying a serious impairment of adaptive immunity. Since the sablefish is naturally hypoxia tolerant, our results demonstrate that climate change-related deoxygenation may be a serious threat to the immune competency of fishes.

Evolutionarily conserved mechanisms regulating stress-induced neutrophil redistribution in fish

Introduction

Stress may pose a serious challenge to immune homeostasis. Stress however also may prepare the immune system for challenges such as wounding or infection, which are likely to happen during a fight or flight stress response.

Methods

In common carp (Cyprinus carpio L.) we studied the stress-induced redistribution of neutrophils into circulation, and the expression of genes encoding CXC chemokines known to be involved in the regulation of neutrophil retention (CXCL12) and redistribution (CXCL8), and their receptors (CXCR4 and CXCR1-2, respectively) in blood leukocytes and in the fish hematopoietic organ - the head kidney. The potential involvement of CXC receptors and stress hormone receptors in stress-induced neutrophil redistribution was determined by an in vivo study with selective CXCR inhibitors and antagonists of the receptors involved in stress regulation: glucocorticoid/mineralocorticoid receptors (GRs/MRs), adrenergic receptors (ADRs) and the melanocortin 2 receptor (MC2R).

Results

The stress-induced increase of blood neutrophils was accompanied by a neutrophil decrease in the hematopoietic organs. This increase was cortisol-induced and GR-dependent. Moreover, stress upregulated the expression of genes encoding CXCL12 and CXCL8 chemokines, their receptors, and the receptor for granulocytes colony-stimulation factor (GCSFR) and matrix metalloproteinase 9 (MMP9). Blocking of the CXCR4 and CXCR1 and 2 receptors with selective inhibitors inhibited the stress-induced neutrophil redistribution and affected the expression of genes encoding CXC chemokines and CXCRs as well as GCSFR and MMP9.

Discussion

Our data demonstrate that acute stress leads to the mobilization of the immune system, characterized by neutrophilia. CXC chemokines and CXC receptors are involved in this stress-induced redistribution of neutrophils from the hematopoietic tissue into the peripheral blood. This phenomenon is directly regulated by interactions between cortisol and the GR/MR. Considering the pivotal importance of neutrophilic granulocytes in the first line of defense, this knowledge is important for aquaculture, but will also contribute to the mechanisms involved in the stress-induced perturbation in neutrophil redistribution as often observed in clinical practice.

Development of a monoclonal antibody specific to burbot (Lota lota) IgM and optimization of an ELISA to measure anti-Aeromonas sp. antibody titers following pathogen challenge

Burbot (Lota lota) are an ideal candidate for cool or cold-water aquaculture and are gaining interest because of their high economic value, low temperature requirements, and fast growth rate. Limited information exists on the innate and adaptive immune systems of this species. This is partly due to the lack of species-specific tools to determine antibody responses following disease or vaccination or to characterize the immune response in general. An anti-IgM monoclonal antibody (mAb 27C) was developed and characterized via enzyme-linked immunosorbent assay (ELISA) and Western blot for species specificity, affinity to the heavy chain of burbot IgM, and cross-reactivity to other reagents used in the analysis. The 27C monoclonal antibody was further utilized to develop an ELISA protocol to measure the specific antibody response of burbot following exposure to two pathogenic strains of Aeromonas sp. (A141 and IR004). This ELISA confirmed that vaccinated burbot that survived the challenge with either strain developed statistically higher titers of anti-Aeromonas antibodies specific for the relative strain when compared to fish that were not vaccinated or challenged. Western blot analysis further demonstrated that burbot surviving challenge had serum IgM that recognized distinct antigens specific to the strain they were challenged with, A141 bound to antigens in the 50-250Kda range and IR004 bound to a distinct 150Kda antigen. Western blots further indicated that each strain shared antigenic regions regardless of experimental Aeromonas strain exposure. Finally, immunofluorescent staining confirmed that mAb 27C binds to membrane-bound IgM (presumably B cells) on burbot head kidney cells. Taken together, results from this study demonstrate that mAb 27C specifically recognized burbot IgM and will be an important tool to further characterize the adaptive and cellular immune responses of this fish species.

Evaluation of Ammonia Nitrogen Exposure in Immune Defenses Present on Spleen and Head-Kidney of Wuchang Bream (Megalobrama amblycephala)

Ammonia is one of the most important environmental factors in aquatic ecosystems. However, there are limited studies on the effects of chronic or long-term ammonia stress and its potential molecular mechanism in fish. This study aimed to investigate the immune response and molecular mechanisms in the spleen and head-kidney of fish following chronic ammonia exposure. Megalobrama amblycephala (9.98 ± 0.48 g) were exposed to different concentrations of total ammonia nitrogen (0-30 mg/L) for 30 days. Ammonia exposure caused significant increases in cortisol levels and decreases in lysozyme and complement 3/4 concentrations in the serum, indicating inhibitory effects of ammonia stress on innate immune responses. Ammonia exposure also induced concentration-dependent increases in ammonia concentrations in tissue, pathological damage and indexes of spleen and head-kidney. Additionally, the contents of immunoglobulin M (IgM), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) as well as mRNA levels of toll-like receptors (TLRs)/Myeloid differentiation factor 88 (MyD88)-independent signaling molecules in the spleen and head-kidney were significantly downregulated after ammonia exposure. Our findings suggested that chronic ammonia exposure caused the suppression of innate and adaptive immune responses through downregulating TLR/MyD88-independent signaling. Adverse influences of chronic ammonia stress were more severe in the spleen than in the head-kidney.

The Antibacterial Activity of Erythrocytes From Goose (Anser domesticus) Can Be Associated With Phagocytosis and Respiratory Burst Generation

In the lumen of blood vessels, there are large numbers of erythrocytes, which are approximately 95% of the total blood cells. Although the function of erythrocytes is to transport oxygen in the organism, recent studies have shown that mammalian and teleost erythrocytes are involved in the immune response against bacterial infections. However, the immune mechanisms used by avian erythrocytes are not yet clear. Here, we demonstrated that erythrocytes from goose have the ability to phagocytose as well as conduct antimicrobial activity. Firstly, we revealed the phagocytosis or adhesion activity of goose erythrocytes for latex beads 0.1-1.0 μm in diameter by fluorescence microscopy, and scanning and transmission electron microscopy. The low cytometry results also proved that goose erythrocytes had a wide range of phagocytic or adhesion activity for different bacteria. Followed, the low cytometry analysis data further explored that the goose erythrocytes contain the ability to produce reactive oxygen species (ROS) and inducible nitric oxide synthase (iNOS) in response to bacterial stimulation, and also up-regulated the expression of NOX family includes NOX1 and NOX5. Finally, we also found that goose erythrocytes showed a powerful antibacterial activity against all the three bacteria, meanwhile the stimulation of three kinds of bacteria up-regulated the expression of inflammatory factors, and increased the production of antioxidant enzymes to protect the cells from oxidative damage. Herein, our results demonstrate that goose Erythrocytes possess a certain phagocytic capacity and antioxidant system, and that the antimicrobial activity of erythrocytes can occurred through the production of unique respiratory burst against foreign pathogenic bacteria, which provides new clues to the interaction between bacteria and avian erythrocytes.

Molecular characterization and immune regulatory, antioxidant, and antiapoptotic activities of thioredoxin domain-containing protein 17 (TXNDC17) in yellowtail clownfish (Amphiprion clarkii)

Thioredoxin domain-containing protein 17 (TXNDC17) is an important, highly conserved oxidoreductase protein, ubiquitously expressed in all living organisms. It is a small (~14 kDa) protein mostly co-expressed with thioredoxin 1 (TRx1). In the present study, we obtained the TXNDC17 gene sequence from a previously constructed yellowtail clownfish (Amphiprion clarkii) (AcTXNDC17) database and studied its phylogeny as well as the protein's molecular characteristics, antioxidant, and antiapoptotic effects. The full length of the AcTXNDC17 cDNA sequence was 862 bp with a 372 bp region encoding a 123 amino acid (aa) protein. The predicted molecular mass and isoelectric point of AcTXNDC17 were 14.2 kDa and 5.75, respectively. AcTXNDC17 contained a TRX-related protein 14 domain and a highly conserved N-terminal Cys⁴³-Pro⁴⁴-Asp⁴⁵-Cys⁴⁶ motif. qPCR analysis revealed that AcTXNDC17 transcripts were ubiquitously and differently expressed in all the examined tissues. AcTXNDC17 expression in the spleen tissue was significantly upregulated in a time-dependent manner upon stimulation with lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), and Vibrio harveyi. Besides, LPS-induced intrinsic apoptotic pathway (TNF-α, caspase-8, Bid, cytochrome C, caspase-9, and caspase-3) gene expression was significantly lower in AcTXNDC17-overexpressing RAW264.7 cells, as were NF-κB activation and nitric oxide (NO) production. Furthermore, the viability of H₂O₂-stimulated macrophages was significantly improved under AcTXNDC17 overexpression. Collectively, our findings indicate that AcTXNDC17 is involved in the innate immune response of the yellowtail clownfish.

Dietary phytic acid weakened the antimicrobial activity and aggravated the inflammatory status of head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella)

The present study aimed to explore the effects of phytic acid (PA) on the antimicrobial activity and inflammatory response in three immune organs (head kidney, spleen and skin) of on-growing grass carp (Ctenopharyngodon idella). To achieve this goal, we first conducted a 60-day growth trial by feeding fish with graded levels of PA (0, 0.8, 1.6, 2.4, 3.2 and 4.0%). Then, the fish were challenged with Aeromonas hydrophila for 6 days. Compared with the control group, the following results were obtained regarding supplementation with certain levels of PA in the diet. (1) There was an increase in skin haemorrhage and lesion morbidity in fish. (2) There was a decrease in activities or contents of immune factors, including lysozyme (LZ), complement 3 (C3), C4 and immunoglobulin M (IgM), and there was downregulation of gene expression levels of hepcidin, liver-expressed antimicrobial peptide 2A (LEAP-2A), LEAP-2B, and β-defensin-1 in immune organs. (3) There was upregulation in the gene expression of the following pro-inflammatory cytokines: tumour necrosis factor α (TNF-α), interleukin 1β (IL-1β) (except in the spleen), interferon γ2 (IFN-γ2), IL-6 (except in the spleen), IL-8, IL-12p40, IL-15 and IL-17D. These changes were partly related to the nuclear factor kappa B (NF-κB) signalling pathway, but downregulation of mRNA levels of anti-inflammatory cytokines (transforming growth factor β1 (TGF-β1), TGF-β2, IL-413/A, IL-413/B, IL-10 (except in the skin) and IL-11) occurred in a manner partially related to the target of rapamycin (TOR) signalling pathway. Finally, based on the broken-line analysis of skin haemorrhage and lesion morbidity and IgM content in the head kidney, the maximum tolerance levels of PA for on-growing grass carp (120.56-452.00 g) were estimated to be 1.79 and 1.31% of the diet, respectively.

Effects of gold nanoparticles in gilthead seabream-A proteomic approach

Despite the widespread use of nanoparticles (NPs), there are still major gaps of knowledge regarding the impact of nanomaterials in the environment and aquatic animals. The present work aimed to study the effects of 7 and 40 nm gold nanoparticles (AuNPs) - citrate and polyvinylpyrrolidone (PVP) coated - on the liver proteome of the estuarine/marine fish gilthead seabream (Sparus aurata). After 96 h, exposure to AuNP elicited alterations on the abundance of 26 proteins, when compared to the control group. AuNPs differentially affected several metabolic pathways in S. aurata liver cells. Among the affected proteins were those related to cytoskeleton and cell structure, gluconeogenesis, amino acids metabolism and several processes related to protein activity (protein synthesis, catabolism, folding and transport). The increased abundance of proteins associated with energy metabolism (ATP synthase subunit beta), stress response (94 kDa glucose-regulated protein) and cytoskeleton structure (actins and tubulins) may represent the first signs of cellular oxidative stress induced by AuNPs. Although higher gold accumulation was found in the liver of S. aurata exposed to 7 nm PVP-AuNPs, the 7 nm cAuNPs were more bioactive, inducing more effects in liver proteome. Gold accumulated more in the spleen than in the other assessed tissues of S. aurata exposed to AuNPs, highlighting its potential role on the elimination of these NPs.

Chilean aquaculture and the new challenges: Pathogens, immune response, vaccination and fish diversification

In Chile, the salmon and trout farmed fishing industries have rapidly grown during the last years, becoming one of the most important economic sources for the country. However, infectious diseases caused by bacteria, virus, mycoses and parasites, result in losses of up to 700 million dollars per year for the Chilean aquaculture production with the consequent increase of antibiotic and antiparasitic usage. After 30 years of its first appearance, the main salmon health problem is still the salmonid rickettsial septicaemia (SRS), which together with other disease outbreaks, reveal that vaccines do not provide acceptable levels of long-lasting immune protection in the field. On the other hand, due to the large dependence of the industry on salmonids production, the Chilean government promoted the Aquaculture diversification program by 2009, which includes new species such as Merluccius australis, Cilus gilberti and Genypterus chilensis, however, specific research regarding the immune system and vaccine development are issues that still need to be addressed and must be considered as important as the farm production technologies for new fish species. Based on the experience acquired from the salmonid fish farming, should be mandatory an effort to study the immune system of the new species to develop knowledge for vaccination approaches, aiming to protect these aquaculture species before diseases outbreaks may occur. This review focuses on the current status of the Chilean aquaculture industry, the challenges related to emerging and re-emerging microbial pathogens on salmonid fish farming, and the resulting needs in the development of immune protection by rational designed vaccines. We also discussed about what we have learn from 25 years of salmonid researches and what can be applied to the new Chilean farmed species on immunology and vaccinology.

Interactions of head-kidney leucocytes from giant grouper, Epinephelus lanceolatus, with pathogenic Streptococcus agalactiae strains from marine and terrestrial origins

Streptococcus agalactiae (Group B Streptococcus, GBS) is emerging as a genetically diverse species infecting farmed and wild fish, including commercially and culturally important groupers. To better understand how S. agalactiae are pathogenic in fish, we investigated interactions between isolates from fish and terrestrial hosts and the cellular immune system of Queensland grouper Epinephelus lanceolatus using flow cytometry. Adherent head-kidney leucocytes (HKL) from Queensland grouper displayed two main cell populations with distinct forward and side scatter by flow cytometry. The population of smaller and less complex cells (P1) was composed of monocytes, lymphocytes and thrombocytes, while the population of primarily larger and more complex cells (P2) comprised predominantly of macrophages and neutrophils. The cells in P2 had higher phagocytic index and capacity when incubated with fluorescent latex beads. HKL were activated by phorbol myristate acetate (PMA) but were unresponsive to lipopolysaccharide (LPS) and peptidoglycan (PTG), suggesting the absence of specific receptors on the surface of these cells for these ligands or a requirement for intermediates. In in vitro phagocytosis assays, all fish isolates of GBS activated a respiratory burst in P2 indicated by significant production of intracellular reactive oxygen species (ROS). Similarly, dog and cat isolates of different serotype and sequence type also induced ROS production in grouper HKL. However, human, crocodile and bovine isolates of GBS did not elicit significant ROS in HKL although they coincided with the highest phagocytic index. This suggests that these strains are capable of quenching ROS production. Terrestrial isolates significantly increased mortality of Queensland grouper leucocytes in vitro, aligned with a more diverse repertoire of cellular toxins in these strains. Opsonisation of a marine strain and terrestrial strain of GBS with antiserum raised against the marine strain resulted in an increase in ROS production by HKL in both cases although there was low antigenic cross reactivity between the two strains by flow cytometry, reflecting their diverse serotypes (Ib vs III). However, pre-incubation of either strain with normal serum from grouper also increased ROS production of HKL suggesting other opsonins may be involved. Based on these results it appears that piscine and terrestrial GBS isolates have contrasting strategies when interacting with the cellular immune system of Queensland grouper; the former seemingly evading phagocytosis, whilst the latter are readily phagocytosed but counteract ROS production.

Macropinocytosis-dependent endocytosis of Japanese flounder IgM+ B cells and its regulation by CD22

B cells in fish are proven to be endocytic and have a great contribution to innate immunity like phagocytosis. In this study, the endocytic capacity and the corresponding internalization pathways of IgM⁺ B cells in Japanese flounder (Paralichthys olivaceus) were investigated. The results showed that IgM⁺ B cells in peripheral blood leukocytes (PBL) and splenic leukocytes (SL) exhibited different abilities to ingest 0.5 μm and 1 μm latex beads through macropinocytosis-dependent endocytic pathway. Japanese flounder CD22 (PoCD22) co-stimulatory signals were identified to be essential for the innate immune responses in B cells. Most of IgM⁺ B cells and some IgM^- cells were demonstrated to be PoCD22 positive. When PoCD22 was blocked by antibody, the endocytic activities and reactive oxygen species (ROS) activities of SL IgM⁺ B cells were significantly increased, while the endocytic and ROS activities of PBL IgM⁺ B cells were significant decreased. These results collectively suggest that Japanese flounder IgM⁺ B cells are able to employ macropinocytosis-dependent endocytic pathway, which is under the regulation of CD22.

Cytochemical characterization of peripheral blood cell populations of two Cyprinidae, Carassius auratus and Ctenopharyngodon idellus

Fish are the most diverse species of all vertebrate groups, and their blood cells have shown variable characteristics in terms of morphology. Cytochemical staining for enzyme activity in blood leukocytes will help assess the immune function of fish. We characterize blood cells from crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idellus) by using a Diff-Quick stain as well as different cytochemical methods. Blood specimens obtained from crucian carp and grass carp were evaluated after cytochemical staining for acid phosphatase (ACP), alkaline phosphatase (ALP), naphthol AS chloroacetate esterase (AS-DNCE), naphthyl acetate esterase (NAE), α-naphthyl butyrate esterase (NBE), peroxidase (MPO) and periodic acid-Schiff's reaction (PAS) using commercial kits. Blood cell types were evaluated based on their morphological characteristics and the presence or absence of specific chromogen. The expression pattern of enzymes was similar between the two Cyprinidae and was also broadly consistent with other fish species. However, there were some interesting differences detected between crucian carp and grass carp, including naphthol AS chloroacetate esterase activity in monocytes, peroxidase activity and location in thrombocytes. The ACP, ALP and MPO expressions of different leukocytes of the two Cyprinidae were evaluated by Image Pro Plus and were analysed for statistical significant differences. This investigation provides basic haematology and enzyme activity analyses for crucian carp and grass carp and serves as an approach to evaluating the immune response of fish.

Low or excess levels of dietary cholesterol impaired immunity and aggravated inflammation response in young grass carp (Ctenopharyngodon idella)

The present study explored the effect of cholesterol on the immunity and inflammation response in the immune organs (head kidney, spleen and skin) of young grass carp (Ctenopharyngodon idella) fed graded levels of dietary cholesterol (0.041-1.526%) for 60 days and then infected with Aeromonas hydrophila for 14 days. The results showed that low levels of cholesterol (1) depressed the innate immune components [lysozyme (LZ), acid phosphatase (ACP), complements and antimicrobial peptides] and adaptive immune component [immunoglobulin M (IgM)], (2) up-regulated the mRNA levels of pro-inflammatory cytokines [interleukin 1β (IL-1β), IL-6, IL-8, IL-12p35, IL-12p40, IL-15, IL-17D, tumor necrosis factor α (TNF-α) and interferon γ2 (IFN-γ2)], partly due to the activated nuclear factor kappa B (NF-κB) signalling, and (3) down-regulated the mRNA levels of anti-inflammatory cytokines [IL-4/13B, IL-10, IL-11, transforming growth factor (TGF)-β1 and TGF-β2], partly due to the suppression of target of rapamycin (TOR) signalling in the immune organs of young grass carp. Interestingly, dietary cholesterol had no influences on the IκB kinase α (IKKα) and IL-4/13A mRNA levels in the head kidney, spleen and skin, the IL-1β and IL-12p40 mRNA levels in the spleen and skin, or the β-defensin-1 mRNA level in the skin of young grass carp. Additionally, low levels of cholesterol increased the skin haemorrhage and lesion morbidity. In summary, low levels of cholesterol impaired immunity by depressing the innate and adaptive immune components, and low levels of cholesterol aggravated the inflammation response via up-regulating the expression of pro-inflammatory cytokines as well as down-regulating the expression of anti-inflammatory cytokines partly through the modulation of NF-κB and TOR signalling in the immune organs of fish. Similar to the low level of cholesterol, the excess level of dietary cholesterol impaired immunity and aggravated inflammation response in the immune organs of fish. Finally, based on the percent weight gain (PWG), the ability against skin haemorrhage and lesions as well as the LZ activity in the head kidney and the ACP activity in the spleen, the optimal dietary cholesterol levels for young grass carp were estimated as 0.721, 0.826, 0.802 and 0.772% diet, respectively.

Molecular cloning, characterization and expression profiling of galectin-9 gene from Labeo rohita (Hamilton, 1822)

Galectin-9 is a b-galactoside-binding tandem repeat galectin that regulates many cellular functions, ranging from cell adhesion to pathogen recognition. In spite of extensive study of mammalian galectin importance in immune system, little is known about that of fish. To study the normal expression and immune response of Labeo rohita to pathogens, a tandem-repeat galectin-9 from Labeo rohita was identified and named LrGal-9. Its full-length cDNA was 1534 bp encoded 291 amino acids (35.12 KDa), shared the highest 81% identity with the galectin-9 of Danio rerio. LrGal-9 identified in this study lacked signal peptide and a transmembrane domain like galectin-9 members reported in other fishes. Quantitative PCR showed that LrGal-9 was lowly expressed in gill, muscle, heart, highly expressed in tested immune tissues (intestine, kidney, liver, spleen) in normal body. After Aeromonas hydrophila challenge, LrGal-9 was remarkably increased in all tested immune tissues in a time-dependent manner. These results suggest that LrGal-9 plays a role in innate immunity in Labeo rohita.

Internalization of large particles by turbot (Scophthalmus maximus) IgM+ B cells mainly depends on macropinocytosis

Increasing evidence has demonstrated support for the endocytic capacities of teleost B cells. In the present study, the ability of turbot IgM⁺ B cells to ingest microspheres of different sizes and the corresponding internalization pathways were investigated. The results showed that IgM⁺ B cells exhibited relatively high endocytic capacities for 0.5 μm and 1 μm latex beads, and that different mechanisms were employed for IgM⁺ and IgM^- cells to uptake 0.5 μm and 1 μm beads. For 0.5 μm beads, IgM⁺ B cells apparently employed macropinocytosis-dependent endocytic pathway, whereas IgM^- cells utilized a different process involving both clathrin- and caveolae-mediated pathways. For the uptake of 1 μm beads, IgM⁺ cells relied mainly on macropinocytosis and partially on caveolae-mediated pathway, while IgM^- cells utilized the routes similar to that of internalizing 0.5 μm beads. Consistently, the internalized microspheres were co-localized with high-molecular-mass dextran in IgM⁺ phagocytic cells. In addition to latex beads, IgM⁺ B cells could also ingest inactivated bacteria predominately through macropinocytosis and caveolae-mediated endocytosis. These results collectively indicated that macropinocytosis is principally responsible for particle uptake by turbot IgM⁺ B cells.

Experimental Challenge of Atlantic Cod (Gadus morhua) with a Brucella pinnipedialis Strain from Hooded Seal (Cystophora cristata)

Pathology has not been observed in true seals infected with Brucella pinnipedialis. A lack of intracellular survival and multiplication of B. pinnipedialis in hooded seal (Cystophora cristata) macrophages in vitro indicates a lack of chronic infection in hooded seals. Both epidemiology and bacteriological patterns in the hooded seal point to a transient infection of environmental origin, possibly through the food chain. To analyse the potential role of fish in the transmission of B. pinnipedialis, Atlantic cod (Gadus morhua) were injected intraperitoneally with 7.5 x 10⁷ bacteria of a hooded seal field isolate. Samples of blood, liver, spleen, muscle, heart, head kidney, female gonads and feces were collected on days 1, 7, 14 and 28 post infection to assess the bacterial load, and to determine the expression of immune genes and the specific antibody response. Challenged fish showed an extended period of bacteremia through day 14 and viable bacteria were observed in all organs sampled, except muscle, until day 28. Neither gross lesions nor mortality were recorded. Anti-Brucella antibodies were detected from day 14 onwards and the expression of hepcidin, cathelicidin, interleukin (IL)-1β, IL-10, and interferon (IFN)-γ genes were significantly increased in spleen at day 1 and 28. Primary mononuclear cells isolated from head kidneys of Atlantic cod were exposed to B. pinnipedialis reference (NCTC 12890) and hooded seal (17a-1) strain. Both bacterial strains invaded mononuclear cells and survived intracellularly without any major reduction in bacterial counts for at least 48 hours. Our study shows that the B. pinnipedialis strain isolated from hooded seal survives in Atlantic cod, and suggests that Atlantic cod could play a role in the transmission of B. pinnipedialis to hooded seals in the wild.

Phagocytosis in Teleosts. Implications of the New Cells Involved

Phagocytosis is the process by which cells engulf some solid particles to form internal vesicles known as phagosomes. Phagocytosis is in fact a specific form of endocytosis involving the vesicular interiorization of particles. Phagocytosis is essentially a defensive reaction against infection and invasion of the body by foreign substances and, in the immune system, phagocytosis is a major mechanism used to remove pathogens and/or cell debris. For these reasons, phagocytosis in vertebrates has been recognized as a critical component of the innate and adaptive immune responses to pathogens. Furthermore, more recent studies have revealed that phagocytosis is also crucial for tissue homeostasis and remodeling. Professional phagocytes in teleosts are monocyte/macrophages, granulocytes and dendritic cells. Nevertheless, in recent years phagocytic properties have also been attributed to teleost lymphocytes and thrombocytes. The possible implications of such cells on this important biological process, new factors affecting phagocytosis, evasion of phagocytosis or new forms of phagocytosis will be considered and discussed.

Functional characterization of IgM+ B cells and adaptive immunity in lumpfish (Cyclopterus lumpus L.)

The innate immune responses in lumpfish (Cyclopterus lumpus L.) have been shown to be functional, but little is currently known about the B cells, immunoglobulins or adaptive immune responses in this species. We have used anti-IgM antiserum to isolate B cells and compared them morphologically and functionally with other cell types. The fraction of IgM(+) cells among isolated peripheral blood leukocytes (PBL), head kidney leukocytes (HKL) and spleen leukocytes (SL) was in the range of 40%, 12% and 34%, respectively. The IgM(+) B cells had high phagocytic ability and were the predominant phagocytes in blood with higher capacity than IgM(+) B cells in HKL. Interestingly, among PBL, the most potent phagocytes were, in addition to monocytes, some small agranular uncharacterized IgM(-) cells. The IgM(+) B cells were positive for acid phosphatases (AcP), but negative for myeloperoxidase (MPO). Neutrophils were positive for MPO, while monocytes/macrophages and dendritic-like cells stained negatively. Monocytes/macrophages and the small, agranular IgM(-) cells stained most strongly positive for AcP corresponding to their high phagocytic capacity. Further, the ability to produce specific antibodies upon immunization verified adaptive immunity in the species. The high proportion of phagocytic IgM(+) B cells and their phagocytic ability indicate a significant role of phagocytic B cells in lumpfish innate immunity. The present analyses also give strong indications that vaccination and immunostimulation of farmed lumpfish can be used to prevent disease and mortality caused by pathogenic organisms.

Effect of dietary glutamine on growth performance, non-specific immunity, expression of cytokine genes, phosphorylation of target of rapamycin (TOR), and anti-oxidative system in spleen and head kidney of Jian carp (Cyprinus carpio var. Jian)

This study was designed to investigate the effects of dietary glutamine on the growth performance, cytokines, target of rapamycin (TOR), and antioxidant-related parameters in the spleen and head kidney of juvenile Jian carp (Cyprinus carpio var. Jian). Fish were fed the basal (control) and glutamine-supplemented (12.0 g glutamine kg(-1) diet) diets for 6 weeks. Results indicated that the dietary glutamine supplementation improved the growth performance, spleen protein content, serum complement 3 content, and lysozyme activity in fish. In the spleen, glutamine down-regulated the expression of the interleukin 1 and interleukin 10 genes, and increased the level of phosphorylation of TOR protein. In the head kidney, glutamine down-regulated the tumor necrosis factor α and interleukin 10 gene expressions, phosphorylated and total TOR protein levels, while up-regulated the transforming growth factor β2 gene expression. Furthermore, the protein carbonyl content was decreased in the spleen of fish fed glutamine-supplemented diet; conversely, the anti-hydroxyl radical capacity and glutathione content in the spleen were increased by glutamine. However, diet supplemented with glutamine did not affect the lipid peroxidation, anti-superoxide anion capacity, and antioxidant enzyme activities in the spleen. Moreover, all of these antioxidant parameters in the head kidney were not affected by glutamine. Results from the present experiment showed the importance of dietary supplementation of glutamine in benefaction of the growth performance and several components of the innate immune system, and the deferential role in cytokine gene expression, TOR kinase activity, and antioxidant status between the spleen and head kidney of juvenile Jian carp.

Flow cytometry analyses of phagocytic and respiratory burst activities and cytochemical characterization of leucocytes isolated from wrasse (Labrus bergylta A.)

We have isolated leucocytes from peripheral blood (PBL), head kidney (HKL) and spleen (SL) of wrasse (Labrus bergylta A.) and studied the innate immune responses phagocytosis and respiratory burst using flow cytometry. Further, we have characterized the phenotypic properties of the leucocytes by cytochemical staining. We could differentiate between several subsets of leucocytes; lymphocytes, monocytes/macrophages, neutrophils, eosinophils, basophils and small leucocytes that might be precursor or immature cells. One striking observation was the eosinophils which were present among HKL, PBL and SL. The neutrophils had rounded, bean shaped or bi-lobed nuclei and resembled neutrophils in Atlantic cod (Gadus morhua L.) and lumpsucker (Cyclopterus lumpus L.), but were different from the polymorphonucleated neutrophils in Atlantic salmon (Salmo salar L.) and humans. Basophils were observed, but they were rare. Phagocytosis and respiratory burst activities were detected among different cell types. Highest phagocytic activity was observed among monocytes/macrophages and small leucocytes. Several different subtypes had ability to perform an oxygen-dependent degradation of microbes, measured as respiratory burst activity. Knowledge of the basic properties of wrasse's leucocytes and innate immunology can benefit further studies on its adaptive immune responses.

Antibiotic uptake by cultured Atlantic cod leucocytes and effect on intracellular Francisella noatunensis subsp. noatunensis replication

The granuloma disease caused by Francisella noatunensis subsp. noatunensis in farmed Atlantic cod has not been successfully treated by use of antibacterials, even when antibacterial resistance testing indicates a sufficient effect. The reason for this treatment failure may be the intracellular existence of the bacteria within immune cells, mainly macrophages. To investigate the effect of antibacterials on intracellular Francisella replication, we established a protocol for the detection of drugs within Atlantic cod immune cells using high-performance liquid chromatography (HPLC). When the uptake and intracellular concentrations of oxolinic acid and flumequine were analysed in isolated adherent head kidney leucocytes (HKLs) by HPLC, we found that uptake was rapid and the intracellular concentrations reflected the extracellular exposure concentrations. To investigate the effect of the antibacterial compounds on intracellular bacterial replication, adherent HKLs experimentally infected with the bacteria were analysed using flow cytometry and intracellular labelling of bacteria by specific antibodies. We found that flumequine did not inhibit intracellular bacterial replication. Unexpectedly, the results indicated that the intracellularly effiacy of the drug was reduced. The HPLC method used proved to be highly applicable for accurate determination of intracellular drug concentrations. When combined with sensitive and specific flow cytometry analyses for identification and measurement of intracellular bacterial replication, we suggest that this approach can be very valuable for the design of antibacterial treatments of intracellular pathogens.

Immuno-histochemical determination of humoral immune markers within bacterial induced granuloma formation in Atlantic cod (Gadus morhua L.)

In this study the involvement of several humoral immune parameters of Atlantic cod (Gadus morhua L.) were studied in granuloma formed as a result of infection by Aeromonas salmonicida ssp. achomogenes. The results showed a clear association of immune parameters within the granuloma, in particular the localization of complement component C3, and including evidence for the presence of IgM, APoLP-A1 (Apolipoprotein), CRP-PI and CRP-PII (pentraxin).

Phagocytosis and respiratory burst activity in lumpsucker (Cyclopterus lumpus L.) leucocytes analysed by flow cytometry

In the present study, we have isolated leucocytes from peripheral blood, head kidney and spleen from lumpsucker (Cyclopterus lumpus L.), and performed functional studies like phagocytosis and respiratory burst, as well as morphological and cytochemical analyses. Different leucocytes were identified, such as lymphocytes, monocytes/macrophages and polymorphonuclear cells with bean shaped or bilobed nuclei. In addition, cells with similar morphology as described for dendritic cells in trout were abundant among the isolated leucocytes. Flow cytometry was successfully used for measuring phagocytosis and respiratory burst activity. The phagocytic capacity and ability were very high, and cells with different morphology in all three leucocyte preparations phagocytised beads rapidly. Due to lack of available cell markers, the identity of the phagocytic cells could not be determined. The potent non-specific phagocytosis was in accordance with a high number of cells positive for myeloperoxidase, an enzyme involved in oxygen-dependent killing mechanism present in phagocytic cells. Further, high respiratory burst activity was present in the leucocytes samples, verifying a potent oxygen- dependent degradation. At present, the specific antibody immune response could not be measured, as immunoglobulin or B-cells have not yet been isolated. Therefore, analyses of the specific immune response in this fish species await further clarification. The present study presents the first analyses of lumpsucker immunity and also the first within the order Scopaeniformes.

TGF-β1 exerts opposing effects on grass carp leukocytes: implication in teleost immunity, receptor signaling and potential self-regulatory mechanisms

In fish immunity, the regulatory role of transforming growth factor-β1 (TGF-β1) has not been fully characterized. Here we examined the immunoregulatory effects of TGF-β1 in grass carp peripheral blood leukocytes (PBL) and head kidney leukocytes (HKL). It is interesting that TGF-β1 consistently stimulated the cell viability and the mRNA levels of pro-inflammatory cytokines (Tnfα and Ifnγ) and T/B cell markers [Cd4-like (Cd4l), Cd8α, Cd8β and Igμ] in PBL, which contrasted with its inhibitory tone in HKL. Further studies showed that grass carp TGF-β1 type I receptor, activin receptor-like kinase 5 (ALK5), was indispensable for the immunoregulatory effects of TGF-β1 in PBL and HKL. Notably, TGF-β1 persistently attenuated ALK5 expression, whereas immunoneutralization of endogenous grass carp TGF-β1 could increase ALK5 mRNA and protein levels. It is consistent with the observation that TGF-β1 decreased the number of ALK5(+) leukocytes in PBL and HKL, revealing a negative regulation of TGF-β1 signaling at the receptor level. Moreover, transient treatment with TGF-β1 for 24 h was sufficient to induce similar cellular responses compared with the continuous treatment. This indicated a possible mechanism by which TGF-β1 triggered the down-regulation of ALK5 mRNA and protein, leading to the desensitization of grass carp leukocytes toward TGF-β1. Accordingly, our data revealed a dual role of TGF-β1 in teleost immunity in which it can serve as a positive or negative control device and provided additional mechanistic insights as to how TGF-β1 controls its signaling in vertebrate leukocytes.

A sequential study of incomplete Freund's adjuvant-induced peritonitis in Atlantic cod

Development of diagnostic and prophylactic methodologies is dependent on knowledge of the host's defence system and reaction to different vaccine adjuvants. Here we present a sequential morphological study of peritonitis and inflammatory cell processing of incomplete Freund's adjuvant (IFA) in intraperitoneally injected Atlantic cod. The peritoneal tissue responses were characterised using necropsy, histology and electron microscopy. An extensive inflammatory response as characterised by leukocyte morphology and contents of enzymes, presence of apoptotic cells and IFN-γ-expressing cells was observed. Three days post injection, IFA droplets were surrounded by different types of inflammatory cells and two different patterns could be discerned. The first was characterised by flattened and concentrically arranged interdigitating cells connected by desmosomes and with macrophage-like cells (MLCs) predominant in the periphery. The second type possessed four stratified layers with an inner layer containing many apoptotic MLCs; a second layer containing flattened and shrunken cells and outer layers comprising moderately flattened cells and an outermost layer of mononuclear cells expressing IFN-γ. Oil was detected both inside and outside MLCs. The two types of processes, of which the second was clearly stratified, were similar to those observed in other teleosts, indicating a variety of reaction modes or alternatively sequential process development. The numerous dead MLCs contributed to inflammation.

Presence and interaction of inflammatory cells in the spleen of Atlantic cod, Gadus morhua L., infected with Francisella noatunensis

Serious infectious diseases, accompanied by macrophage-dominated chronic inflammation, are common in farmed Atlantic cod. To increase knowledge relating to morphological aspects of such inflammatory responses, cod were challenged with Francisella noatunensis, an important bacterial pathogen of this fish species. Tissue and cell dynamics in the spleen were examined sequentially over 60 days. Small clusters of mainly macrophage-like cells (MLCs) staining for non-specific esterase and acid phosphatase developed with time. These foci were transiently infiltrated by pleomorphic proliferating cells of unknown nature and by granulocyte-like cells (GCLCs) staining for peroxidase and lysozyme. The latter cell type, which appeared to be resident in the red pulp of control fish, migrated into the inflammatory foci of infected fish. Cells expressing genes encoding IFN-γ and IL-8 increased in number during the study period. Bacteria were detected only in the MLCs and their number increased despite the extensive inflammation. Our results demonstrate an intimate spatial relationship in inflammatory foci between at least three cell types. The presence of GCLCs, together with MLCs, suggests pyogranulomatous inflammation as a more appropriate descriptive term than granulomatous inflammation.

Flow cytometry assays of respiratory burst in Atlantic salmon (Salmo salar L.) and in Atlantic cod (Gadus morhua L.) leucocytes

The oxidation of dihydrorhodamine 123 (DHR) to the fluorescent rhodamine 123 (RHO) was detected using flow cytometry. This assay for detection of respiratory burst activity was established in peripheral blood leucocytes (PBL) and head kidney leucocytes (HKL) of Atlantic salmon and Atlantic cod. The leucocytes were stimulated by phorbol 12-myristate 13-acetate (PMA). For cod cells 10 times lower concentration of PMA had to be used compared to salmon cells, as higher concentrations were toxic and resulted in considerable cell death. The cells found to be RHO-positive were monocytes/macrophages and neutrophils based on the scatter dot plots, but for salmon also some small cells were found to have high fluorescence intensity both in the flow cytometry analyses and by fluorescence microscopy of cytospin preparations. The nature of these cells is not known. For cod leucocytes, such cells were not obvious. The instrument settings are a bit more demanding for cod, as cod cells die more easily compared to salmon cells. In both assays the limit between negative and positive cells has to be carefully considered. The presented flow cytometry protocols for measurements of respiratory burst in salmon and cod leucocytes can be applied in various studies where respiratory burst functions are involved, such as to verify if it is activated or suppressed in connection with infections and immunostimulation.

The genome sequence of Atlantic cod reveals a unique immune system

Atlantic cod (Gadus morhua) is a large, cold-adapted teleost that sustains long-standing commercial fisheries and incipient aquaculture. Here we present the genome sequence of Atlantic cod, showing evidence for complex thermal adaptations in its haemoglobin gene cluster and an unusual immune architecture compared to other sequenced vertebrates. The genome assembly was obtained exclusively by 454 sequencing of shotgun and paired-end libraries, and automated annotation identified 22,154 genes. The major histocompatibility complex (MHC) II is a conserved feature of the adaptive immune system of jawed vertebrates, but we show that Atlantic cod has lost the genes for MHC II, CD4 and invariant chain (Ii) that are essential for the function of this pathway. Nevertheless, Atlantic cod is not exceptionally susceptible to disease under natural conditions. We find a highly expanded number of MHC I genes and a unique composition of its Toll-like receptor (TLR) families. This indicates how the Atlantic cod immune system has evolved compensatory mechanisms in both adaptive and innate immunity in the absence of MHC II. These observations affect fundamental assumptions about the evolution of the adaptive immune system and its components in vertebrates.

The immune response of juvenile Atlantic cod (Gadus morhua L.) to chronic exposure to produced water

Produced water (PW) is the main discharge from the offshore oil industry and contains oil-derived compounds such as poly-aromatic hydrocarbons, phenols, alkylphenols, and heavy metals. Studies suggest that PW discharges may affect the biota over larger areas from the oil drilling sites at sea than originally predicted. We investigated the effects of chronic exposure to PW on some aspects of juvenile Atlantic cod immunity, stress response and growth by intermittently exposing fish to 0, 100 or 200 ppm of PW for 22 weeks. No significant effects of PW were observed on growth, hepatosomatic index, condition factor or plasma cortisol. The respiratory burst (RB) of circulating leukocytes was significantly elevated in the 100 ppm group only, while the RB of head-kidney leukocytes was significantly decreased in both the 100 and 200 ppm groups. Significant up-regulation of the mRNA expression of beta-2-microglobulin, immunoglobulin-M light chain and interleukins-1beta and -8 was observed in the 200 ppm group, while the down-regulation of interferon stimulated gene 15 was obvious for both the 100 and 200 ppm groups. The results suggest that chronic exposure to environmentally relevant concentrations of PW causes modulations of the immune system of juvenile Atlantic cod with most immune parameters being stimulated, potentially resulting in an energetic cost that may be detrimental to the fish.

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.

A highly phagocytic cell line TO from Atlantic salmon is CD83 positive and M-CSFR negative, indicating a dendritic-like cell type

Leucocyte cell lines are valuable tools for immunological studies. In this study the TO cell line, originating from Atlantic salmon head kidney leucocytes, is described with respect to enzyme cytochemistry, functional studies, reactivity with leucocyte specific antibodies and immune gene expression. Pronounced characteristics of the TO cell line are the rapid adherence to the plastic growth surface, high phagocytic capacity and bactericidal functions. No respiratory burst activity, and little or no NO production were detected under the experimental conditions tested, and thus the TO cells appear to have other effective killing mechanisms. The cells are reactive with a leucocyte specific monoclonal antibody (MAb), but does not bind a neutrophil specific MAb or stain for myeloperoxidase. Real-time RT-PCR showed the expression in TO cells of several immune genes, some of which were significantly regulated following LPS stimulation. The expression of CD83 might indicate a dendritic cell (DC) origin of the TO cells, as this marker is considered a hallmark for DC. Expression of TCR-alpha or the macrophage marker M-CSFR was not detected. Based on the present analyses the TO cells display a mixture of known characteristics for macrophages and DCs. At the same time the TO cells lack some central functions of phagocytic/myeloid cells. As the TO cells are developed to a long-term culture one cannot exclude that some functions might have been lost in this process. Nevertheless, the features of the TO cells indicate their potential as a model system for immunological studies of salmon phagocytic cells.

Cell markers and determinants in fish immunology

Despite the impressive increase in the cloning and expression of genes encoding fish immunoregulatory molecules, the knowledge on "in vivo" and "in vitro" functional immunology of the corresponding peptide products is still at an initial stage. This is partly due to the lacking of specific markers for immunoregulatory peptides, that represent an indispensible tool to dissect immune reactions and to trace the fate of cellular events downstream of the activation. In this review we summarise the available information on functional immune activities of some teleost species and discuss the obtained data in an evolutionary and applied context.

Flow cytometry applications for exotic animals

This article describes applications of flow cytometry in hematology. It includes a basic description of how flow cytometers work and their use in enumerating cell populations based on phenotypic markers and measurement of cell functions. Challenges presented by limitations of reagents for exotic animals are described in addition to sources of cross-reactive antibodies.