Extrahepatic synthesis of complement components in the rainbow trout (Oncorhynchus mykiss)

RNA-Sequencing Analysis of the Spleen and Gill of Takifugu rubripes in Response to Vibrio harveyi Infection

Takifugu rubripes is commonly subjected to the disease-causing bacterium, Vibrio harveyi. However, the mechanism involved in the immune response of T. rubripes to V. harveyi infection is unclear. We conducted a transcriptomic analysis of the spleen and gill from T. rubripes infected with V. harveyi. We obtained 60,981,357 and 60,760,550 clean reads from the control and infected spleens, and 57,407,586 and 57,536,651 clean reads from the control and infected gills, respectively. We also identified 1,560 and 1,213 differentially expressed genes in the spleen and gill, respectively. Gene ontology analysis revealed that the most enriched biological process in both the spleen and gill was "immune response". The most enriched Kyoto Encyclopedia of Genes and Genomes immune response-related pathways were the NOD-like receptor signaling pathway in the spleen and cytokine-cytokine receptor interaction in the gill. We found 10 candidate immune-related genes in the spleen and gill. These putative immune pathways and candidate genes will provide insight into the immune response mechanisms of T. rubripes against V. harveyi.

Transcriptome Analysis in the Head Kidney of Rainbow Trout (Oncorhynchus mykiss) Immunized with a Combined Vaccine of Formalin-Inactivated Aeromonas salmonicida and Vibrio anguillarum

This study aimed to identify the molecular mechanisms regulated by a combined vaccine against Aeromonas salmonicida and Vibrio anguillarum (O1 serotype). These bacteria cause furunculosis and vibriosis, respectively, and are associated with a high mortality in rainbow trout in Korea. The vaccine upregulated gene expression of TCRα, T-bet, sIgM, and mIgM, markers of an activated adaptive immune response. On days 1, 3, and 5, transcriptome analysis revealed 862 (430 up- and 432 downregulated), 492 (204 up- and 288 downregulated), and 741 (270 up- and 471 downregulated) differentially expressed genes (DEGs), respectively. Gene ontology (GO) enrichment analysis identified 377 (108 MF, 132 CC, 137 BP), 302 (60 MF, 180 CC, 62 BP), and 314 (115 MF, 129 CC, 70 BP) GOs at days 1, 3, and 5, respectively. Kyoto Encyclopedia of Genetic and Genomic enrichment analysis identified eight immune system-related pathways like cytokine-cytokine receptor interaction, NF-kappaB signaling pathway, TNF signaling pathway, NOD-like receptor signaling pathway, cytosolic DNA sensing pathway, cell adhesion molecule, complement and coagulation cascade, and antigen processing and presentation. In the analysis of the protein–protein interaction of immune-related DEGs, a total of 59, 21, and 21 interactional relationships were identified at days 1, 3, and 5, respectively, with TNF having the highest centrality at all three time points.

Impact of chronic exposure of rainbow trout, Oncorhynchus mykiss, to low doses of glyphosate or glyphosate-based herbicides

Glyphosate is an herbicidal active substance (AS) entering in the composition of a large diversity of pesticide products (glyphosate-based herbicides; GBH) used in modern intensive agriculture. This compound has a favorable environmental safety profile but was suspected to induce deleterious effects in aquatic organisms, with a potential effect of some associated co-formulants. This study aimed to assess the impact of direct and chronic exposure to glyphosate on the health status of rainbow trout, Oncorhynchus mykiss. A total of 36 genitors were exposed daily for 10 months to a dose of glyphosate representative of environmental concentrations (around 1 μg L-1) using the AS alone or two GBHs formulations (i.e. Roundup Innovert® and Viaglif Jardin®) and findings were compared to an unexposed control group (n=12). The effects of chemical exposure on the reproductive capacities, hemato-immunologic functions, energetic metabolism, oxidative stress and specific biomarkers of exposure were analyzed over a period of 4 months covering spawning. A limited mortality between 15% and 30% specific to the spawning occurred under all conditions. No differences were observed in reproduction parameters i.e. mean weights, relative fertility and fecundity. Red blood cell count, hematocrit index, mean corpuscular volume and white blood cell counts were similar for all the sampling dates. Significant changes were observed two months before spawning with a 70% decrease of the proportion of macrophages in trout exposed to Viaglif only and a reduction of 35% of the phagocytic activity in fish exposed to the two GBHs. Trends towards lower levels of expression of tumor necrosis factor-α (between 38% and 66%) were detected one month after the spawning for all contaminated conditions but without being statistically significant. Biomarkers of exposure, i.e. acetylcholine esterase and carbonic anhydrase activities, were not impacted and none of the chemical contaminants disturbed the oxidative stress or metabolism parameters measured. These results suggest that a 10 months exposure of rainbow trout to a concentration of 1 μg L-1 of glyphosate administered using the pure active substance or two GBHs did not significantly modify their global health including during the spawning period. The immunological disturbances observed will need to be further explored because they could have a major impact in response to infectious stress.

Identification, characterization, and immunological analysis of complement component 4 from grass carp (Ctenopharyngodon idella)

Complement component 4 (C4) has critical immunological functions in vertebrates. In the current study, a C4 homolog (gcC4) was identified in grass carp (Ctenopharyngodon idella). The full-length 5458 bp gcC4 cDNA contained a 5148 bp open reading frame (ORF) encoding a protein of 1715 amino acids with a signal peptide and eight conservative domains. The gcC4 protein has a high level of identity with other fish C4 counterparts and is phylogenetically clustered with cyprinid fish C4. The gcC4 transcript shows wide tissue distribution and is inducible by Aeromonas hydrophila in vivo and in vitro. Furthermore, its expression also fluctuates upon lipopolysaccharide or flagellin stimulation in vitro. During infection, the gcC4 protein level decreases or increases to varying degrees, and the intrahepatic C4 expression location changes. With gcC4 overexpression, interleukin 1 beta, tumor necrosis factor alpha, and interferon transcripts are all upregulated by A. hydrophila infection. Meanwhile, overexpression of gcC4 reduces bacterial invasion or proliferation. Moreover, gcC4 may activate the NF-κB signaling pathway. These findings demonstrate the vital role of gcC4 in the innate immunity of grass carp.

Quantification of Defensive Proteins in Skin Mucus of Atlantic salmon Using Minimally Invasive Sampling and High-Sensitivity ELISA

Simple Summary

The external surfaces of fish, including the skin, are covered by mucus. Mucus is an important and multifunctional matrix of substantial complexity. The mucus is viscous and sticky, and adheres to the underlying epithelium, making the sampling of mucus challenging. To help define more standardized protocols for mucus sampling, we here compare three different sampling methods. The methods include scraping of mucus, wiping of mucus, and absorption of the liquid part of mucus. We compare the resulting damage to the fish skin and compare the content of two specific immune proteins in the three sample types. Using histological examination, we show that absorption leads to very limited damage to the skin epithelium while scraping causes substantial damage. Using Enzyme-Linked Immunosorbent Assay (ELISA) methods, we show that the mucus sample types contain similar amounts of antigen specific immunoglobulin M (IgM) and complement component 5 (C5), respectively. The levels of the IgM but not the C5 were moderately correlated between mucus and blood from the same fish, suggesting the importance of fish skin mucus for analyzing antigen-specific IgM after vaccination procedures. We conclude that absorption is an easily performed and minimally invasive sampling method that produces mucus samples with comparable contents of IgM and C5.

Abstract

Protocols used to collect fish skin mucus may inadvertently compromise the sampled fish or the resulting sample. Here, we used three methods (wiping, scraping, and absorption) to collect skin mucus from Atlantic salmon and compared their invasiveness on fish skin epithelium. We found that the absorption method was the least invasive. We also compared the abundance of antigen-specific immunoglobulin M subtype A antibodies (IgM-A Ab) and complement component 5 (C5) in mucus samples collected from vaccinated fish by the three methods. An enzyme-cascade-amplification strategy colorimetric immune assay was optimized and used to analyze IgM-A, and ELISA was used to analyze C5. The abundance of antigen-specific IgM-A in skin mucus was comparable between the three methods, but C5 was significantly lower in absorbed mucus in comparison to in the wiped or scraped mucus samples. Absorbed skin mucus samples collected from various body regions of salmon, levels of C5 were comparable, while specific IgM-A amounts varied between the regions. By comparing three mucus-absorbing materials (medical wipe, gauze, and cotton) for their ability to absorb and release IgM-A and C5, medical wipes proved to be ideal for IgM-A analysis, whereas gauze was the best for C5 analysis.

Overexpression of T-bet, GATA-3 and TGF-ß Induces IFN-γ, IL-4/13A, and IL-17A Expression in Atlantic Salmon

The overexpression of GATA-3, T-bet and TGF-ß may theoretically induce IL-4/A, IFN-γ and IL-17A expression, respectively. Whether this also applies to fish is not yet known. The plasmid vectors encoding reporter gene (RFP)-tagged T-bet, GATA-3 and TGF-ß were used as overexpression tools, transfected into cells or injected intramuscularly to monitor the expression of IFN-γ, IL-4/13A and IL-17A. In addition, the fish were either experimentally challenged with Vibrio anguillarum (VA group) or Piscirickettsia salmonis (PS group). The reporter gene (RFP) inserted upstream of the GATA-3, T-bet and TGF-ß genes, was observed in muscle cell nuclei and in inflammatory cells after intramuscular (i.m.) injection. PS group: following the injection of GATA-3 and T-bet-encoding plasmids, the expression of GATA-3 and T-bet was high at the injection site. The spleen expression of IFN-γ, following the injection of a T-bet-encoding plasmid, was significantly higher on day 2. VA group: The T-bet and GATA-3-overexpressing fish expressed high T-bet and GATA-3 mRNA levels in the muscles and on day 4 post-challenge. The expression of TGF-ß in the muscles of fish injected with TGF-ß-encoding plasmids was significantly higher on days 7 (8 days pre-challenge) and 19 (4 days after challenge). The protective effects of the overexpression of T-bet, GATA-3 and TGF-ß on both bacterial infections were negligible.

Do the toll-like receptors and complement systems play equally important roles in freshwater adapted Dolly Varden char (Salvelinus malma)?

Unlike the normal anadromous lifestyle, Chinese native Dolly Varden char (Salvelinus malma) is locked in land and lives in fresh water lifetime. To explore the effect of freshwater adaption on its immune system, we constructed a pooled cDNA library of hepatopancreas and spleen of Chinese freshwater Dolly Varden char (S. malma). A total of 27,829 unigenes were generated from 31,233 high-quality transcripts and 17,670 complete open reading frames (ORF) were identified. Totally 25,809 unigenes were successfully annotated and it classified more native than adaptive immunity-associated genes, and more genes involved in toll-like receptor signal pathway than those in complement and coagulation cascades (51 vs 3), implying the relative more important role of toll-like receptors than the complement system under bacterial injection for the freshwater Dolly Varden char. These huge different numbers of TLR and complement system identified in freshwater Dolly Varden char probably caused by distinct evolution pressure patterns between fish TLR and complement system, representative by TLR3 and TLR5 as well as C4 and C6, respectively, which were under purifying and positively selecting pressure, respectively. Further seawater adaptation experiment and the comparison study with our library will no doubt be helpful to elucidate the effect of freshwater adaption of Chinese native Dolly Varden char on its immune system.

Changes in natural haemolytic complement activity induced by stress in gilthead seabream (Sparus aurata L.)

In aquaculture, animals can be continually exposed to environmental stress factors that put their health and even survival at risk. Two experiments were performed to evaluate the impact of different stress conditions (acute crowding and anaesthetic) on the natural haemolytic complement activity in serum and skin mucus of gilthead seabream (Sparus aurata L.). In the first experiment, fish were subjected to 10 kg m^-3 (low density, control group) and 50 kg m^-3 (high density, crowding group) during 2, 24 and 48 h. In the second experiment, fish were unexposed (control) or exposed to 40 ppm of MS-222 or 5 ppm or 10 ppm of clove oil for 1 h. In fish maintained in acute crowding conditions only an increase of the haemolytic complement activity was observed in the skin mucus after 24 h of exposure. However, a similar statistically significant increase was observed in serum and skin mucus of fish exposed for 1 h to the lowest concentration of clove oil (5 ppm) tested. The results point to a new and alternative way to assess stress in farmed fish by using skin mucus instead of blood serum and confirm that the measurement of natural haemolytic complement activity serves as an indicator of stress in fish.

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.

A teleost complement factor Ba possesses antimicrobial activity and inhibits bacterial infection in fish

Complement factor B (Bf) is a component of the complement system. Following activation of the alternative pathway of the complement system, factor B is cleaved into Ba and Bb fragments. In fish, the Bf of rainbow trout is known to act as a C3 convertase, but the function of the Ba fragment is essentially unknown. In this study, we examined the expression patterns of tongue sole Cynoglossus semilaevis Bf (named CsBf) and the biological activity of the Ba fragment of CsBf (named CsBa). CsBf possesses the conserved domains of Bf and shares 39.9%-56.4% sequence identities with other fish Bf. CsBf expression was high in liver, muscle, and heart, and low in intestine, blood, and kidney. Bacterial infection significantly induced CsBf expression in kidney, spleen, and liver in a time-dependent manner. Recombinant CsBa (rCsBa) exhibited apparent binding capacities to bacteria and tongue sole peripheral blood leukocytes, and binding of rCsBa to bacteria inhibited bacterial growth. When overexpressed in tongue sole, CsBa significantly reduced bacterial dissemination in fish tissues. Together these results indicate for the first time that a fish Ba possesses antibacterial effect as well as immune cell-binding capacity, and thus probably plays a role in host immune defense against bacterial infection.

Assessment of immune status of yellowfin seabream (Acanthopagrus latus) during short term exposure to phenanthrene

The aim of the present investigation was to assess the immune status in yellowfin seabream (Acanthopagrus latus) exposed to different concentrations of phenanthrene (Phe) for 14days. In addition, the Phe accumulation in the fish muscle was measured during the experiment. Fish were injected with different concentrations (0, 2, 20 and 40mg/kg) of Phe and samples were taken from tissue and blood of fish 1, 4, 7 and 14days after injection. Exposure of fish to Phe caused a significant decrease in white blood cells, C3 and C4 levels, lysosomal membrane stability, lysozyme activity after 4days and antibacterial activity after 7days of the experiment. In contrast, cortisol level significantly increased after 4days. The concentration of Phe in fish muscle increased rapidly after 4days. The main tissue changes observed in the head kidney including increase in melanomacrophage centers (MMCs), empty spaces between cells and hemorrhage. The degree of tissue changes ranged from normal to moderate in Phe-treated fish. The size and number of MMCs in treated fish were significantly higher than control. In conclusion, Phe toxicity in yellowfin seabream can induce increased cortisol level, tissue changes and immune suppression.

Comprehensive and comparative transcription analyses of the complement pathway in rainbow trout

The complement system is one of the most ancient and most essential innate immune cascades throughout the animal kingdom. Survival of aquatic animals, such as rainbow trout, depends on this early inducible, efficient immune cascade. Despite increasing research on genes coding for complement components in bony fish, some complement-related genes are still unknown in salmonid fish. In the present study, we characterize the genes encoding complement factor D (CFD), CD93 molecule (CD93), and C-type lectin domain family 4, member M (CLEC4M) from rainbow trout (Oncorhynchus mykiss). Subsequently, we performed comprehensive and comparative expression analyses of 36 complement genes including CFD, CD93, and CLEC4M and further putative complement-associated genes to obtain general information about the functional gene interaction within the complement pathway in fish. These quantification analyses were conducted in liver, spleen and gills of healthy fish of two rainbow trout strains, selected for survival (strain BORN) and growth (Import strain), respectively. The present expression study clearly confirms for rainbow trout that liver represents the primary site of complement expression. Spleen and gills also express most complement genes, although the mean transcript levels were generally lower than in liver. The transcription data suggest a contribution of spleen and gills to complement activity. The comparison of the two rainbow trout strains revealed a generally similar complement gene expression. However, a significantly lower expression of numerous genes especially in spleen seems characteristic for the BORN strain. This suggests a strain-specific complement pathway regulation under the selected rearing conditions.

Effects of Cortisol Administered through Slow-Release Implants on Innate Immune Responses in Rainbow Trout (Oncorhynchus mykiss)

Cortisol is a key hormone in the fish stress response with a well-known ability to regulate several physiological functions, including energy metabolism and the immune system. However, data concerning cortisol effects on fish innate immune system using a more controlled increase in cortisol levels isolated from any other stress related signaling is scarce. The present study describes the effect of doses of cortisol corresponding to acute and chronic levels on the complement and lysozyme activity in plasma of the rainbow trout (Oncorhynchus mykiss). We also evaluated the effects of these cortisol levels (from intraperitoneally implanted hydrocortisone) on the mRNA levels quantified by RT-qPCR of selected key immune-related genes in the liver, head kidney, and spleen. For that purpose, 60 specimens of rainbow trout were divided in to two groups: a control group injected with a coconut oil implant and another group injected with the same implant and cortisol (50 μg cortisol/g body weight). Our results demonstrate the role of cortisol as a modulator of the innate immune response without the direct contribution of other stress axes. Our results also show a relationship between the complement and lysozyme activity in plasma and mRNA levels in liver, supporting the important role of this organ in producing these immune system proteins after a rise of cortisol in the fish plasma.

Molecular cloning, characterization and expression of the complement component Bf/C2 gene in grass carp

The complement system is an integral part of the host immune system and plays an immunoregulatory role at the interface between the innate and acquired immune responses. Factor B (Bf) serves as the catalytic subunit of complement C3 convertase in the alternative pathway (AP), while in the classical pathway (CP), this function is subjected to C2. In this study, we cloned and characterized the two Bf/C2 genes of grass carp, gcBf/C2A and gcBf/C2B. The gcBf/C2A and gcBf/C2B cDNA sequences are 2259 and 3004 bp in length, and the open reading frames (ORFs) of gcBf/C2A and gcBf/C2B were found to encode peptides of 752 and 837 amino acids, respectively. The genes share 30.7% amino acid identity with each other and 32.4-38.3% and 31.4-33% with the Bf and C2 genes in humans and mice. GcBf/C2A and gcBf/C2B were expressed in a wide range of grass carp tissues, with the highest level of expression of both genes detected in the liver. After a challenge with Aeromonas hydrophila, gcBf/C2A was significantly upregulated, especially at 4 h after infection, and the significantly higher expression of gcBf/C2B (27.3-fold) was found in the head kidney at 24 h post-challenge. The expression of gcBf/C2A was quickly upregulated at 1 day post-hatching and peaked at 5 days post-hatching. The maximum expression of gcBf/C2B was found at 1 day post-hatching. In conclusion, our data enables a better understanding of the physiological function of the Bf/C2 complement genes in vertebrates.

The complement system in teleost fish: progress of post-homolog-hunting researches

Studies on the complement system of bony fish are now finishing a stage of homologue-hunting identification of the components, unveiling existence of almost all the orthologues of mammalian complement components in teleost. Genomic and transcriptomic data for several teleost species have contributed much for the homologue-hunting research progress. Only an exception is identification of orthologues of mammalian complement regulatory proteins and complement receptors. It is of particular interest that teleost complement components often exist as multiple isoforms with possible functional divergence. This review summarizes research progress of teleost complement system following the molecular identification and sequence analysis of the components. The findings of extensive expression analyses of the complement components with special emphasis of their prominent extrahepatic expression, acute-phase response to immunostimulation and various microbial infections, and ontogenic development including maternal transfer are discussed to infer teleost-specific functions of the complement system. Importance of the protein level characterization of the complement components is also emphasized, especially for understanding of the isotypic diversity of the components, a unique feature of teleost complement system.

Cloning and molecular characterization of two complement Bf/C2 genes in large yellow croaker (Pseudosciaena crocea)

Complement components factor B and C2 are two crucial proteases in the alternative pathway (AP) and classical pathway (CP). Two Bf/C2 cDNAs, LycBf/C2A and LycBf/C2B were isolated from the large yellow croaker (Pseudosciaena crocea) by suppression subtractive hybridization (SSH) and rapid amplification of cDNA ends (RACE). Through sequence alignment and computer 3D modeling analysis, we found that both of the deduced proteins contain three complement control protein (CCP) modules, a von Willebrand factor A (vWFA) domain, and one serine protease (SP) domain. Both structural analysis and phylogenetic analyses suggested that LycBf/C2A is more like human factor B than human C2 while LycBf/C2B is more human C2-like. After that, RT-PCR assay showed that LycBf/C2A and LycBf/C2B were mostly expressed in liver, albeit detectable in other tissues. Finally, after being infected with attenuated live Vibrio anguillarum strain, the expression level of LycBf/C2A and LycBf/C2B were found remarkably up-regulated in liver, spleen and kidney, indicating that the two complement factors play a pivotal role in the immune response to bacterial challenge in large yellow croaker.

Effects of serum on phagocytic activity and proteomic analysis of tilapia (Oreochromis mossambicus) serum after acute osmotic stress

The objective of the study was to analyze the effect of serum from freshwater (FW) exposed tilapia or from 25 ppt seawater (SW) exposed tilapia on the ability to mediate the phagocytic activity of tilapia phagocytes. To analyze the phagocytic activity, head kidney (HK) and spleen leukocytes were tested in 300 or 500 mOsm medium using three different treatment groups (a) control, (b) addition of 25% serum from freshwater (FW) exposed tilapia, and (c) addition of 25% of serum from 25 ppt seawater (SW) exposed tilapia. HK leukocytes cultured in 300 and 500 mOsm media for 4 h showed an increase of phagocytic ability in the control group as compared to the addition of serum from either FW or SW exposed tilapia. HK leukocytes exposed to 500 mOsm medium showed a higher phagocytic ability than those leukocytes exposed to 300 mOsm medium in each corresponding group. Concurrently, spleen leukocytes in the control group showed a higher phagocytic ability than those leukocytes with the addition of serum from FW or SW exposed tilapia. As compared to spleen leukocytes cultured in 300 mOsm medium, leukocytes cultured in 500 mOsm medium showed an increase of phagocytic ability within their respective group. To further investigate the observed phenomenon, 2D-gel electrophoresis was performed for analyzing the differentially expressed proteins in serum that was thought to influence the phagocytic ability. Up-regulated serum proteins in SW exposed tilapia contained complement C3 protein, NADH dehydrogenase (Ubiquinone) Fe-S protein 3, Mg(2+)-dependent neutral sphingomyelinase, Semaphorins, and Caspase 3. Taken together these results suggest that addition of serum decreased the phagocytic activity in HK and spleen leukocytes in vitro, furthermore, induced proteins semaphorin, complement C3, Mg(2+)-dependent neutral sphingomyelinase, and Caspase 3 are up-regulated in the serum, which might have decreased the phagocytic activity upon exposure to hyperosmotic solutions.

Comparative analysis of the acute response of the trout, O. mykiss, head kidney to in vivo challenge with virulent and attenuated infectious hematopoietic necrosis virus and LPS-induced inflammation

BACKGROUND

The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray.

RESULTS

The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed.

CONCLUSION

In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

The C3 subtypes are differentially regulated after immunostimulation in rainbow trout, but head kidney macrophages do not contribute to C3 transcription

The complement system plays key roles in innate and adaptive immunity through mediating phagocytosis, chemotaxis and cell lysis. Complement component C3 is a central component in the complement cascade and belongs to the acute-phase proteins whose synthesis increase immediately upon inflammatory stimuli. The liver is the main producer of C3 and it is a well-known fact that the mammalian monocyte-macrophage lineage is a major contributor to extrahepatic C3. Immunomodulators, such as LPS and beta-glucan, can stimulate complement, lysozyme, natural killer cells and antibody responses in fish, thus enhancing the resistance to bacterial pathogens and parasitic infections. The aim of this study was to assess the effects of LPS and beta-glucan on the expression of interleukins (IL-1beta1, IL-1beta2 and IL-6) and the modulated expression of C3 subtypes (C3-1, C3-3 and C3-4) in the rainbow trout (Oncorhynchus mykiss) using real-time RT-PCR. From in vitro studies, we demonstrated that head kidney macrophages from rainbow trout and Atlantic salmon showed no basal transcription of C3. After immunostimulation, the cells responded by increased levels of ILs, but transcription of C3 was not induced. In contrast to the in vitro findings, the rainbow trout complement C3 subtypes were differentially regulated 48 h after in vivo stimulation with LPS and beta-glucan. These results support the previous findings of absence of C3 in macrophages of the spotted wolffish (Anarhichas minor) and is the first functional study showing differential regulation of the C3 subtypes in any vertebrate.