New reports on iron related proteins: Molecular characterization of two ferroportin genes in common carp (Cyprinus carpio L.) and its expression pattern

Iron uptake, transport, and storage require the involvement of several proteins, including ferroportin (fpn), the sole known iron efflux transporter. Due to its critical function fpn has been studied, particularly in humans. Here, we characterized the ferroportin gene in common carp (Cyprinus carpio L.) and performed RNA-seq analysis to evaluate its constitutive transcription levels across different tissues. Our results indicate that C. carpio possesses two functional fpns with distinct expression patterns, highlighting the potential for functional divergence and expression differentiation among fpns in this species.

2D-DIGE proteomic analysis of blood plasma reveals changes in immune- and stress-associated proteins following hormonal stimulation of carp males

In carp aquaculture, hormonal manipulation with an analog of GnRH (Ovopel) and carp pituitary extract (CPE), which act at different levels of the hypothalamic-pituitary-gonadal axis, is a routine practice to enhance sperm production. Our recent studies revealed that hormonal stimulation of male carp was associated with changes in the seminal plasma proteome, including blood origin proteins. Here, we explored whether Ovopel and CPE could affect the blood proteome of male carp. Both preparations induced increases in semen volume, total number of sperm, and testosterone level. However, hormonal stimulation did not affect the plasma cortisol and glucose levels. A comparative proteomic analysis of carp blood plasma between the control (PBS) and the hormonally treated males revealed significant changes (>1.2 <-1.2-fold change, P < 0.05) in the abundance of 30 spots (14 up- and 16 downregulated) and 44 spots (28 up- and 16 downregulated) upon CPE and Ovopel treatment, respectively. The most significantly affected pathways were acute phase response signaling, the coagulation system, LXR/RXR and FXR/RXR activation; however, there were different sets of proteins in Ovopel- and CPE-treated males. The majority of differentially abundant proteins were involved in the regulation of the immune defense response, the response to stress, and complement activation. Moreover hormonal stimulation with CPE markedly increased the bactericidal activity of blood and both preparations caused profound changes in gene expression in hematopoietic organs. This work is important in understanding the biological processes behind the protein-based response to hormonal stimulation of sperm production in fish.

Re-evaluation of common carp (Cyprinus carpio L.) housekeeping genes for gene expression studies - considering duplicated genes

Quantitative real-time PCR is one of the most widely used techniques for measuring changes in the expression of target transcripts due to its sensitivity, specificity, and cost-effectiveness. However, the essential step that determines appropriate and correct data interpretation is the selection of proper endogenous control genes. Identifying useful reference genes with stable expression is critical for accurate normalization and precise results. Functional divergence of duplicated genes in tetraploid species, like common carp, can complicate the choice for a proper reference gene. In the present study, we determined the expression stability of duplicated genes of 40s, b2m, ef1α, gapdh, g6pd, and odc1 in different tissues of common carp (Cyprinus carpio L.). Gene expression analysis comprised healthy control fish, fish under bacterial and parasitic infections, and across the early stage of common carp development. Obtained data were compared with the actb gene, which is used widely as a reference in RT-qPCR analysis. The application of the three different algorithms - geNorm, NormFinder, BestKeeper, allowed comparative evaluation of the expression stability of the tested genes. Subsequently, the RefFinder, a web-based tool, was used to rank the examined housekeeping genes comprehensively. We demonstrate variable transcription stability levels in the examined mRNAs as well as differences in expression between paralog gene copies. The 40s, b2m, ef1α and actb genes showed the most stable expression across all physiological conditions and tissues. The gapdh, odc1, and g6pd gene variants demonstrated lower stability. Differences in expression patterns between duplicated genes underline the possibility of functional divergence between them. This aspect should be considered in polyploid species before selecting the reference gene(s). Our study also points on the importance of choice for a reference gene (paralog) when expressing newly identified genes and the spatial expression profile is performed. SUBJECTS: Aquaculture, Molecular Biology, Fish Science.

Differences in growth of Trypanoplasma borreli in carp serum is dependent on transferrin genotype

Kinetoplastid parasites require transferrin (Tf), being the main source of iron, for growth and multiplication. This group of parasites developed a unique receptor-mediated system for acquiring host Tf which bears no structural homology with the host transferrin receptor. Trypanoplasma borreli, a blood parasite of common carp, probably uses a similar mechanism to sequester iron from host transferrin. In this study, we demonstrate a critical role of Tf for parasite growth. For in vitro studies we isolated and purified Tf from carp homozygous for the D or G allele of Tf. We obtained Tf-depleted serum using specific antibodies to carp Tf and studied gene expression in vivo during T. borreli infection with Real Time-quantitative PCR. We demonstrate that T. borreli cannot survive in medium supplemented with Tf-depleted serum while reconstitution with Tf restores normal growth. The critical role of Tf for parasite survival was shown in incomplete medium (medium without serum): addition of purified Tf significantly increased parasite survival. We also demonstrate that Tf polymorphism has a significant impact on T. borreli multiplication. Cultured parasites die more quickly in an environment containing D-typed Tf, as compared to medium with G-typed Tf. Gene expression during T. borreli infection in carp did not show an acute phase response. We could, however, observe an increased transcription of Tf in the head kidney, which may be associated with an immunological function of the Tf protein.

The many faces of transferrin: Does genotype modulate immune response?

In this study, the expression of pro-inflammatory and iron metabolism genes were analysed under Trypanoplasma borreli (T. borreli) challenge in common carp. Three transferrin (Tf) genotypic groups: two homozygous - DD, GG, and heterozygous DG were intraperitoneally infected with a dose of 2.16 × 10⁵/100 μL parasites. Organ and blood samples were collected at weekly intervals. During the infection period, mortality and parasitaemia were assessed along with measurements of blood iron concentrations and antibody levels. Expression of Tf, Fer, IRP1 and 2, TfR 1a and 1b, Hep, TNF α1 and α2, and IL-1 β was measured in the peak of parasitaemia and the week preceding the peak. Study revealed, that changes in iron blood level induced by parasite were not correlated with the activities of iron homeostasis genes. Neither iron content nor the specific antibody response correlated with survival. We demonstrate that challenged carp, display three distinct, Tf genotype dependent activity patterns of iron homeostasis genes expression. The expected, "classical" way of up-regulation represented homozygous DD individuals. In contrast, GG individuals demonstrated downward trend, while gene expressions of heterozygous DG carp could be defined as an intermediate. We speculate, whether this phenomenon is related to the transferrin molecule itself or to Tf-genotypes being markers of other factors, that influence the iron homeostasis genes activities. We discussed the role of alarmins in triggering the immune response. Distinct genes activating patterns of homozygous genotypes DD and GG had no consequences in terms of mortality rates caused by T.borreli. The highest mortality was observed in the heterozygous group DG. In conclusion, this study suggest that transferrin variant, but not iron blood concentration, has a significant impact on carp immune response to blood parasite infection. This research sheds a new light on the inflammation process and interaction between a host and invaders.

Immune response of juvenile common carp (Cyprinus carpio L.) exposed to a mixture of sewage chemicals

Pharmaceuticals and household chemicals are important components of municipal sewage. Many of them are biologically active, disrupting not only hormonal regulation of aquatic animals but also, indirectly, disturbing their immunological protection. In the environment, chemicals rarely act as individual substances, but as elements of mixtures. Therefore, the aim of this study was to check whether the acute laboratory exposure of common carp juveniles to a mixture of ibuprofen, sodium dodecyl sulphate (SDS), dimethyl sulfoxide (DMSO) and 17 α-ethynylestradiol in increasing concentrations, modifies the levels of innate immunity (lysozyme, C-reactive protein) as well as general stress (metallothioneins, heat shock proteins HSP70) markers in brain, liver, gills, spleen and mucus. The levels of the markers were measured by an immunodetection technique. Not only do the pharmaceuticals and household chemicals impair immunological reactions of young carp in various tissues but also do that in a concentration-dependent manner in the liver, gills, spleen and mucus. This has a very important implication, since it may result in higher sensitivity of young fish to pathogens due to energy allocation to defence processes. The comparisons of the pattern of stress reactions in the studied organ samples indicated that mucus appeared to be a good, non-invasive material for monitoring of environmental state and fish conditions.

Hormonal stimulation of carp is accompanied by changes in seminal plasma proteins associated with the immune and stress responses

Hormonal stimulation in common carp is a routine practice to enhance sperm production and control gamete maturation. This study aimed to compare the proteome of carp seminal plasma between control and Ovopel-induced males using two-dimensional differential in-gel electrophoresis. Ovopel induction increased sperm volume, total sperm count, seminal plasma osmolality, and pH and decreased seminal plasma protein concentration. In total, 36 spots were identified (23 up- and 13 downregulated), corresponding to 23 proteins differentially abundant in seminal plasma after Ovopel induction (p < .05; fold change 1.2). The majority of proteins were associated with the immune and stress responses including the transport protein (hephaestin), antiproteases (fetuin, α2-macroglobulin, TIMP2), complement components (C3, complement factor B/C2A), regulator of the coagulation cascade (plasminogen), modulators of the innate immune response, such as intelectin, ApoA and ApoE, and the cathepsin/cystatin system, and stress response (enolase1). In addition, hormonal stimulation seems to be related to the proteins involved in lipid metabolism, signal transduction, and tissue remodeling. Our results suggest that hormonal stimulation is not just concomitant with the hydration of testis but also induces the synthesis and secretion of seminal plasma proteins involved in sperm maturation and protection against stress induced by administration of the exogenous hormone. SIGNIFICANCE: It is well known that hormonal stimulation of male fish induces the final maturation of spermatozoa. However, molecular and biochemical basis underlying hormone-induced changes in semen is unknown at present. This study for the first time reveals, using proteomic approach, that hormonal stimulation in addition to hydration of testis is accompanied by significant changes in seminal plasma proteins related mainly to immune and stress response, lipid metabolism, signal transduction and tissue remodeling. These changes are associated with gene expression and synthesis and secretion of seminal plasma proteins by reproductive tissues. Overall, our results provide a framework for understanding the molecular mechanism responsible for hormonal stimulation in the reproductive tract of fish males.

Acyclovir inhibits Cyprinid herpesvirus 3 multiplication in vitro

Cyprinid herpesvirus 3 (CyHV-3), also known as koi herpesvirus (KHV), is an aetiological agent of a virulent and lethal disease in common and koi carp. In this study, we examined in vitro the anti-CyHV-3 activity of acyclovir (ACV), nucleoside analogue commonly used against human herpesviruses, as well as acyclovir monophospate (ACV-MP). The cytotoxicity of the ACV and the ACV-MP for two common carp cell lines, CCB (Common carp brain) and KF1 (Koi carp fin 1), was determined by means of MTT and crystal violet assays. In subsequent studies, the concentration of 66.67 μM was applied. The ACV and the ACV-MP (66.67 μM) inhibited a cytopathic effect (CPE) induced by the CyHV-3 virus in the CCB (ACV by 66%, ACV-MP by 58%) and the KF1 (ACV by 25%, ACV-MP by 37%). The viral load measured by the means of TaqMan qPCR was reduced in a range of 67%-93% depending on the analogue, the cell line and the time of incubation. The expression of viral genes (ORF149, ORF3, ORF134 and ORF78) in CCB cells infected with the CyHV-3 was strongly downregulated within the range of 78%-91%. In summary, both the ACV and the ACV-MP can inhibit CyHV-3 replication in vitro.

A full-body transcriptome and proteome resource for the European common carp

Background

The common carp (Cyprinus carpio) is the oldest, most domesticated and one of the most cultured fish species for food consumption. Besides its economic importance, the common carp is also highly suitable for comparative physiological and disease studies in combination with the animal model zebrafish (Danio rerio). They are genetically closely related but offer complementary benefits for fundamental research, with the large body mass of common carp presenting possibilities for obtaining sufficient cell material for advanced transcriptome and proteome studies.

Results

Here we have used 19 different tissues from an F1 hybrid strain of the common carp to perform transcriptome analyses using RNA-Seq. For a subset of the tissues we also have performed deep proteomic studies. As a reference, we updated the European common carp genome assembly using low coverage Pacific Biosciences sequencing to permit high-quality gene annotation. These annotated gene lists were linked to zebrafish homologs, enabling direct comparisons with published datasets. Using clustering, we have identified sets of genes that are potential selective markers for various types of tissues. In addition, we provide a script for a schematic anatomical viewer for visualizing organ-specific expression data.

Conclusions

The identified transcriptome and proteome data for carp tissues represent a useful resource for further translational studies of tissue-specific markers for this economically important fish species that can lead to new markers for organ development. The similarity to zebrafish expression patterns confirms the value of common carp as a resource for studying tissue-specific expression in cyprinid fish. The availability of the annotated gene set of common carp will enable further research with both applied and fundamental purposes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3038-y) contains supplementary material, which is available to authorized users.

Stress-induced adaptation of neutrophilic granulocyte activity in K and R3 carp lines

Both in mammals and fish, stress induces remarkable changes in the immune response. We focused on stress-induced changes in the activity of neutrophilic granulocytes in the R3 and K lines of common carp, which showed differential stress responses. Our study clearly demonstrates that a prolonged restraint stress differentially affects the activity of K and R3 carp neutrophils. In the K line, stress decreased the respiratory burst, while in the R3 line it reduced the release of extracellular DNA. Surprisingly, the stress-induced changes in ROS production and NET formation did not correlate with changes in gene expression of the inflammatory mediators and GR receptors. In neutrophilic granulocytes from K carp, gene expression of the stress-sensitive cortisol GR1 receptor was significantly higher than in neutrophils from R3 fish, which will make these cells more sensitive to high levels of cortisol. Moreover, upon stress, neutrophilic granulocytes of K carp up-regulated gene expression of the anti-inflammatory cytokine IL-10 while this was not observed in neutrophilic granulocytes of R3 carp. Therefore, we can hypothesize that, in contrast to R3 neutrophils, the more cortisol sensitive neutrophils from K carp respond to stress with up-regulation of IL-10 and consequently reduction of ROS production. Most probably the ROS-independent NET formation in K carp is not regulated by this anti-inflammatory cytokine. These data may indicate a predominantly ROS-independent formation of NETs by carp neutrophilic granulocytes. Moreover, they underline the important role of IL-10 in stress-induced immunoregulation.

Activity of the hypothalamus-pituitary-interrenal axis (HPI axis) and immune response in carp lines with different susceptibility to disease

The stress response transmitted by the HPA axis is one of the best examples of neuroendocrine-immune interactions that are critical for survival. Analogous to the situation in mammals, the stress response in fish is characterized by the activation of the hypothalamo-pituitary-interrenal axis (HPI). Effects of cortisol on the fish immune system comply with findings in mammals and suggest that the differences in sensitivity to stress will influence the immune response and as a consequence of survival. Therefore, we studied the stress response and its immunity-related effects in four different carp lines (R3, R3xR8, K and R2) that display a differential pathogen susceptibility. Previous studies indicate that R3xR8 and R3 carp are susceptible to bacterial and parasite infection, while R2 and K are relatively resistant to infection. Interestingly, the most striking effect of stress on leukocyte composition and activity was observed in the pathogen-resistant K carp, even though no robust changes in gene expression of stress-involved factors were observed. In contrast, R3 carp showed no spectacular stress-induced changes in their immunological parameters with concurrent significant activation of the HPI axis. Upon stress, the R3 carp showed up-regulation of crf, pomc and gr2 gene expression in the hypothalamus. Furthermore in R3 carp, at all levels of the HPI axis, stress induced the highest up-regulation of il-1β gene expression. Although we are aware of the complexity of the interactions between stress and pathogen susceptibility and of the risk of interpretation based on correlations, it is noteworthy that the fish more susceptible to infection also exhibited the highest response to stress.

Differential effects of alloherpesvirus CyHV-3 and rhabdovirus SVCV on apoptosis in fish cells

Whilst Herpesviridae, which infect higher vertebrates, actively influence host immune responses to ensure viral replication, it is mostly unknown if Alloherpesviridae, which infect lower vertebrates, possess similar abilities. An important antiviral response is clearance of infected cells via apoptosis, which in mammals influences the outcome of infection. Here, we utilise common carp infected with CyHV-3 to determine the effect on the expression of genes encoding apoptosis-related proteins (p53, Caspase 9, Apaf-1, IAP, iNOS) in the pronephros, spleen and gills. The influence of CyHV-3 on CCB cells was also studied and compared to SVCV (a rhabdovirus) which induces apoptosis in carp cell lines. Although CyHV-3 induced iNOS expression in vivo, significant induction of the genetic apoptosis pathway was only seen in the pronephros. In vitro CyHV-3 did not induce apoptosis or apoptosis-related expression whilst SVCV did stimulate apoptosis. This suggests that CyHV-3 possesses mechanisms similar to herpesviruses of higher vertebrates to inhibit the antiviral apoptotic process.

Interaction between type I interferon and Cyprinid herpesvirus 3 in two genetic lines of common carp Cyprinus carpio

Cyprinid herpesvirus 3 (CyHV-3) infection in common carp Cyprinus carpio L. and its ornamental koi varieties can induce the severe systemic disease known as koi herpesvirus disease. This disease is characterised by a rapid replication and spreading of the virus through multiple organs and results in a fast onset of mortality (starting on Day 6 post infection) in up to 100% of infected fish. During the first phase of viral infections, type I interferons (IFNs) have generally been proven to be essential in inducing an innate immune response; however, very little is known about the type I IFN response to herpesviruses in fish. The aim of this work was to study the type I IFN responses during CyHV-3 infection in 2 genetically divergent lines of common carp which presented differing survival rates. Our results show that CyHV-3 induced a systemic type I IFN response in carp, and the magnitude of type I IFN expression is correlated with the virus load found in skin and head kidney. In this in vivo experimental setup, the level of type I IFN response cannot be linked with higher survival of carp during CyHV-3 infection.

C-reactive protein and complement as acute phase reactants in common carp Cyprinus carpio during CyHV-3 infection

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a highly virulent and lethal disease of common carp Cyprinus carpio and its ornamental koi varieties. However, specific knowledge about immune mechanisms behind the infection process is very limited. We aimed to evaluate the effect of the CyHV-3 infection on the profile of 2 major components of the common carp immune acute phase response: the C-reactive protein (CRP) and the complement system. Common carp were infected with CyHV-3 by bath immersion. Fish were sampled before the infection and at 6, 12, 24, 72, 120 and 336 h post-infection for serum and head kidney, liver, gill and spleen tissues. CRP levels and complement activity were determined from the serum, whereas CRP- and complement-related genes (crp1, crp2, c1rs, bf/c2, c3, masp2) expression profiles were analysed in the tissues by quantitative PCR. Both CRP levels and complement activity increased significantly up to 10- and 3-fold, respectively, in the serum of infected fish during the challenge. Analysis revealed distinct organ- and time-dependent expression profile patterns for all selected genes. These results suggest that CRP and complement behave as acute phase reactants to CyHV-3 infection in common carp with an organ- and time-dependent response.

Biology and host response to Cyprinid herpesvirus 3 infection in common carp

Viruses from the family Alloherpesviridae form an aquatic clade of herpesviruses infecting fish and amphibia. Diseases caused by these herpesviruses are of increasing importance because of the high morbidity and mortality associated with the infection, and the difficulties in diagnosing latently infected carriers. Cyprinid herpesvirus 3 (CyHV-3) induces a severe disease and mortality in common carp and thus greatly affects carp aquaculture and trade. This review summarises advancements in the understanding of the infection process and the current knowledge on immune responses of carp to CyHV-3. A focus is laid on host genetics and immunity responsible for resistance/survival from the disease and on the viral mechanisms accountable for evasion of carp immune responses. As current knowledge of immune responses to CyHV-3 is still limited, perspectives for future studies are outlined. Analysing CyHV-3 fish-host interactions will be useful and thought-provoking for a basic understanding of fish immune responses.

Isolation, characterisation and cDNA sequencing of a new form of parvalbumin from carp semen

Parvalbumins (Pv) are calcium-binding proteins present mainly in the muscle and nervous system where they act as a Ca2+ buffer. Our previous work demonstrated the presence of Pv-I in carp semen and indicated the presence of a second Pv (Pv-II). The purpose of the present work was to identify, purify and determine the full-length cDNA sequence of Pv-II from carp testis. Pv-II from seminal plasma was purified by ion-exchange chromatography (IEC) and preparative electrophoresis, while the Pv-II from spermatozoa was purified by IEC, gel filtration and preparative electrophoresis. The purified Pv-II was submitted to an analysis of molecular mass, isoelectric point (pI), amino-acid sequence and oligomerisation ability. The amino-acid sequence was used to construct primers and obtain the full-length cDNA sequence of seminal-specific Pv-II from carp testis. Analysis of the cDNA sequence indicated that carp-testis Pv-II was distinct from carp-muscle parvalbumins. Pv-II was distinct from Pv-I regarding sequence, molecular mass and pI. Both parvalbumins had the ability to form oligomers or to bind to other proteins. Carp seminal plasma had a protective effect against parvalbumin oligomerisation. Pv-II underwent post-translational modification such as n-acetylation and cysteinylation. The present study is the first to report the full-length cDNA sequence of parvalbumin from carp testis.

Dietary β-glucan stimulate complement and C-reactive protein acute phase responses in common carp (Cyprinus carpio) during an Aeromonas salmonicida infection

The effect of β-glucans as feed additive on the profile of C-reactive protein (CRP) and complement acute phase responses was studied in common carp Cyprinus carpio after exposition to a bacterial infection with Aeromonas salmonicida. Carp were orally administered with β-glucan (MacroGard®) for 14 days with a daily β-glucan intake of 6 mg per kg body weight. Fish were then intraperitoneally injected with either PBS or 1 × 10⁸ bacteria per fish and sampled at time 0, 6, 12, 24, 48, 72, 96 and 120 h post-injection (p.i.) for serum and head kidney, liver and mid-gut tissues. CRP levels and complement activity were determined in the serum samples whilst the gene expression profiles of CRP and complement related genes (crp1, crp2, c1r/s, bf/c2, c3 and masp2) were analysed in the tissues by quantitative PCR. Results obtained showed that oral administration of β-glucan for 14 days significantly increased serum CRP levels up to 2 fold and serum alternative complement activity (ACP) up to 35 fold. The bacterial infection on its own (i.e. not combined with a β-glucan feeding) did have significant effects on complement response whilst CRP was not detectably induced during the carp acute phase reaction. However, the combination of the infection and the β-glucan feeding did show significant effects on both CRP and complement profiles with higher serum CRP levels and serum ACP activity in the β-glucan fed fish than in the control fed fish. In addition, a distinct organ and time dependent expression profile pattern was detected for all the selected genes: a peak of gene expression first occurred in the head kidney tissue (6 h p.i. or 12 h p.i.), then an up-regulation in the liver several hours later (24 h p.i.) and finally up- or down-regulations in the mid-gut at 24 h p.i. and 72 h p.i. In conclusion, the results of this study suggest that MacroGard® stimulated CRP and complement responses to A. salmonicida infection in common carp.

Cyprinid herpesvirus 3 infection disrupts the skin barrier of common carp (Cyprinus carpio L.)

Cyprinid herpesvirus-3 (CyHV-3) is recognised as a pathogen which causes mass mortality in populations of carp, Cyprinus carpio. One of the characteristic symptoms of the disease associated with CyHV-3 infection is the occurrence of skin lesions, sloughing off the epithelium and a lack of mucus. Furthermore, fish then seem to be more susceptible to secondary infections by bacterial, parasitic or fungal pathogens which may cause further mortality within the population. The observed pathological alterations lead to the assumption that the carp skin barrier is strongly challenged during CyHV-3 associated disease. Therefore we examined mRNA expression of genes encoding inflammatory mediators, type I interferons, and the following skin defence molecules: antimicrobial peptides, claudins, and mucin. In addition, we monitored changes in the bacterial flora of the skin during disease conditions. Our results show that CyHV-3 associated disease in the skin of common carp leads to a reduction in mRNA expression of genes encoding several important components of the mucosal barrier, in particular mucin 5B, beta defensin 1 and 2, and the tight junction proteins claudin 23 and 30. This caused changes in the bacterial flora and the development of secondary bacterial infection among some individual fish. To our knowledge this is the first report showing that under disease conditions associated with virus infection, the mucosal barrier of fish skin is disrupted resulting in a higher susceptibility to secondary infections. The reported clinical signs of CyHV-3 skin infection can now be explained by our results at the molecular level, although the mechanism of a probable virus induced immunomodulation has to be investigated further.

Interferon type I responses to virus infections in carp cells: In vitro studies on Cyprinid herpesvirus 3 and Rhabdovirus carpio infections

Interferons (IFNs) are secreted mediators that play a fundamental role in the innate immune response against viruses among all vertebrate classes. Common carp is a host for two highly contagious viruses: spring viraemia of carp virus (Rhabdovirus carpio, SVCV) and the Cyprinid herpesvirus 3 (CyHV-3), which belong to Rhabdoviridae and Alloherpesviridae families, respectively. Both viruses are responsible for significant losses in carp aquaculture. In this paper we studied the mRNA expression profiles of genes encoding for proteins promoting various functions during the interferon pathway, from pattern recognition receptors to antiviral genes, during in vitro viral infection. Furthermore, we investigated the impact of the interferon pathway (stimulated with poly I:C) on CyHV-3 replication and the speed of virus spreading in cell culture. The results showed that two carp viruses, CyHV-3 and SVCV induced fundamentally different type I IFN responses in CCB cells. SVCV induced a high response in all studied genes, whereas CyHV-3 seems to induce no response in CCB cells, but it induces a response in head kidney leukocytes. The lack of an IFN type I response to CyHV-3 could be an indicator of anti-IFN actions of the virus, however the nature of this mechanism has to be evaluated in future studies. Our results also suggest that an activation of type I IFN in CyHV-3 infected cells can limit the spread of the virus in cell culture. This would open the opportunity to treat the disease associated with CyHV-3 by an application of poly I:C in certain cases.

Reduced inflammatory response to Aeromonas salmonicida infection in common carp (Cyprinus carpio L.) fed with β-glucan supplements

The objective of the present study was to determine the action of β-glucans as feed additives on the gene expression profile of some inflammatory-related cytokines from common carp (Cyprinus carpio L.) during the early stages of a non-lethal bacterial infection with Aeromonas salmonicida. β-glucan (MacroGard(®)), was administered daily to carp (6 mg per kg body weight) in the form of supplemented commercial food pellets for 14 days prior to infection. Control and treated fish were then intraperitoneally injected with PBS or 4×10(8) bacteria per fish and were sampled at time 0 and 6h, 12h, 1 day, 3 days and 5 days post-injection. Head kidney and gut were collected and the gene expression patterns for tnfα1, tnfα2, il1β, il6 and il10 were analyzed by quantitative PCR. Results obtained showed that treatment with β-glucans generally down-regulated the expression of all measured genes when compared to their corresponding controls. After injection, highest changes in the gene expression levels were obtained at 6h; particularly, in head kidney there was higher up-regulation of tnfa1 and tnfa2 in infected fish fed β-glucans in comparison to control feed; however, in gut there was a significant down-regulation of tnfα1, tnfα2, il1β and il6 in infected fish fed β-glucans. Analysis of carp specific antibodies against A. salmonicida 30 days after injection revealed their levels were reduced in the infected β-glucan group. In conclusion, a diet supplemented with β-glucan (MacroGard(®)) reduced the gene expression levels of some inflammation-related cytokines in common carp. Such a response appears to be dependent of organ studied and therefore the immunostimulant may be preventing an acute and potential dangerous response in gut, whilst enhancing the inflammatory response in head kidney when exposed to A. salmonicida.

Gene expression analysis of common carp (Cyprinus carpio L.) lines during Cyprinid herpesvirus 3 infection yields insights into differential immune responses

Cyprinid herpesvirus 3 (CyHV-3), also known as koi herpesvirus (KHV), is the etiological agent of a virulent and lethal disease in common and koi carp. This study aimed to determine the genetic basis underlying the common carp immune response to the CyHV-3 virus. Two common carp lines (R3 and K) were infected with CyHV-3 by immersion. The R3 line presented a 20% higher survival rate compared to the K line and significantly lower viral loads as measured at day 3 post infection (p.i.). Microarray analysis using a common carp slides containing a number of 10,822 60-mer probes, revealed that 581 genes in line K (330 up-regulated, 251 down-regulated) and 107 genes in line R3 (77 up-regulated, 30 down-regulated), showed at least a 2-fold difference in expression at day 3 p.i. compared to day 0. Genes which showed at least a 4-fold difference in expression in both lines were selected as potential markers of a CyHV-3 infection in common carp. Additionally, 76 genes showed at least 2-fold differentially expression between K and R3 lines at day 3 p.i. Significantly higher expression of several immune-related genes including number of those which are involve in pathogen recognition, complement activation, MHC class I-restricted antigen presentation and development of adaptive mucosal immunity was noted in more resistant R3 line. Further real-time PCR based analysis provided evidence for higher activation of CD8(+) T cells in R3 line. This study uncovered wide array of immune-related genes involved into antiviral response of common carp toward CyHV-3. It is also demonstrated that the outcome of this severe disease in large extent could be controlled by genetic factors of the host.

Isolation and characterization of transferrin from common carp (Cyprinus carpio L) seminal plasma

Transferrin (Tf) in fish is recognized as a component of non-specific humoral defense mechanisms against bacteria. It is a major protein of common carp seminal plasma but its structure and localization in carp testis is unknown. In this study we developed a simple and efficient three-step purification procedure consisting of affinity chromatography (Con A-Sepharose), hydrophobic interaction chromatography (Phenyl Sepharose) and gel filtration (Superdex 200). The molecular mass of Tf has been determined to be 73.6 kDa and isoelectric point 5.1. The peculiar characteristics of carp transferrin were the lack of carbohydrate component and binding of iron ions by only one functional iron-binding site. Western blot analysis revealed a strong similarity of carp seminal plasma Tf to carp blood Tf and Tf from seminal plasma of other cyprinids but a lower similarity to salmonid and percid fishes. Tf was localized to the blood vessels of the carp testis which strongly suggest that most Tf of carp seminal plasma originates from blood. In conclusion, seminal plasma Tf has a unique structure and is similar or identical to blood Tf.

Resistance of common carp (Cyprinus carpio L.) to Cyprinid herpesvirus-3 is influenced by major histocompatibility (MH) class II B gene polymorphism

The role of MH class II B (Cyca-DAB1-like) genes in resistance of common carp (Cyprinus carpio L.) to Cyprinid herpesvirus-3 (CyHV-3), also known as koi herpesvirus (KHV) was analysed. The material consisted of 934 fish from six carp crosses. Fish were challenged with CyHV-3 at an age of 7 and 10 months. During challenge experiments the peak of mortality caused by CyHV-3 was observed at days 8-12 p.i. and the overall cumulative mortality reached 79.9%. Among six Cyca-DAB1-like genotypes, revealed by PCR-RF-SSCP analysis, one genotype (E) was found associated with higher resistance to CyHV-3. Three other genotypes (B, H and J) could be linked to higher susceptibility to CyHV-3. Analysis of the alleles that compose the Cyca-DAB1-like genotypes linked one particular allele (Cyca-DAB1*05) to significantly increased, and two alleles (Cyca-DAB1*02 and Cyca-DAB1*06) to significantly decreased resistance to CyHV-3. Our data indicate that MH class II B genes could be used as potential genetic markers in breeding of common carp for resistance to this virus.

Allelic discrimination, three-dimensional analysis and gene expression of multiple transferrin alleles of common carp (Cyprinus carpio L.)

We cloned and sequenced four different transferrin (Tf) alleles (C, D, F and G) of European common carp (Cyprinus carpio carpio L.) and studied allelic diversity with respect to differences in sequence, constitutive transcription and three-dimensional structure. Most of the disulfide bonds were conserved between human and carp Tf, and modeling confirmed the overall conservation of the three-dimensional structure of carp Tf. While the iron-binding sites in the C-lobe of carp Tf were completely conserved, in the N-lobe the majority of iron-coordinating residues were not conserved. This may have a serious impact on the ability of carp Tf to bind iron with both the C- and N-lobe. In contrast to human Tf, we could not detect potential N-glycosylation sites in carp Tf, which does not seem to be a glycoprotein. Comparison of the cDNA of the four Tf alleles of carp indicated 21 polymorphic sites of which 13 resulted in non-synonymous changes. Allelic diversity did not seem to influence the overall conservation of carp Tf. Neither the iron binding sites nor the receptor binding of carp Tf seemed influenced by allelic diversity. Possibly, interaction with pathogen-associated receptors for Tf could be influenced by allelic diversity. Basal gene expression of Tf alleles D and G was especially high in carp liver. Although we could detect a higher transcription level of allele D than of Tf allele G in head kidney, thymus and spleen, the differences seem minor with respect to the very high transcription level in liver. Preliminary results with Tf-typed serum suggest a difference in the ability of Tf alleles D and G to modulate LPS-induced NO production in carp macrophages.

The induction of nitric oxide response of carp macrophages by transferrin is influenced by the allelic diversity of the molecule

The central role of transferrin (Tf) as an iron transporting protein has been extended by observations that modified versions of Tf also participate in the regulation of innate immunity. We report on the isolation of two carp Tf proteins (alleles D and G) to purity using rivanol precipitation and ion-exchange chromatography, and describe the activation of head kidney-derived carp macrophages by cleaved Tf. We demonstrate the superiority of the D-type over the G-type Tf in inducing nitric oxide (NO) and confirm previous observations that full-length Tf cannot induce NO in fish macrophages. We believe that cleaved Tf fragments should be considered to be "alarmins". We discuss the possibility that parasites such as Trypanoplasma borreli cleave Tf and use Tf fragments to their advantage by modulating the NO induction in carp macrophages.

Classical crosses of common carp (Cyprinus carpio L.) show co-segregation of antibody response with major histocompatibility class II B genes

In cyprinids, two paralogous groups of major histocompatibility (MH) class II B genes, DAB1 and DAB3, have been reported but have not been studied in detail. In our study on MH association with immune responsiveness in common carp (Cyprinus carpio L.) we have taken a long-term approach using divergent selection for antibody production. We report the co-segregation of Cyca-DAB1-like and Cyca-DAB3-like genes with antibody response, in backcrosses to high- and low-responsive parental carp lines. We show that the presence of Cyca-DAB1-like, but not Cyca-DAB3-like genes, preferentially leads to a high DNP-specific antibody response in carp. Background genes other than Cyca-DAB genes also influenced the level of antibody response. Our data support the hypothesis of a genetic control by Cyca-DAB genes on the antibody response measured. We could not detect an association of the Cyca-DAB genes with disease resistance to the parasite Trypanoplasma borreli. Sequence information, constitutive transcription levels and our co-segregation data indicate that both paralogous Cyca-DAB1-like and Cyca-DAB3-like groups represent functional MH class II B genes. Previously defined differences in allelic diversity between Cyca-DAB1-like genes, especially, identify Cyca-DAB1 as the most interesting DAB gene for further study in common carp.

Application of PCR-RF-SSCP to study major histocompatibility class II B polymorphism in common carp (Cyprinus carpio L.)

A variety of methods have been applied for the characterization of major histocompatibility (MH) polymorphism in fish. We optimized a technique designated polymerase chain reaction-restriction fragments-single strand conformation polymorphism (PCR-RF-SSCP) for screening a large number of individuals for the Cyca-DAB1 and Cyca-DAB2 genes polymorphism in common carp. The advantages of this technique are simplicity, high sensitivity and low costs. PCR-RF-SSCP analysis revealed different genotypes consisting of unique combinations of the Cyca-DAB1 and Cyca-DAB2 sequences with the number of SSCP bands clearly correlating with the degree of heterozygosity of the Cyca-DAB1 and Cyca-DAB2 genes. We found four alleles for Cyca-DAB1 (*02-*05) gene but only one allele for Cyca-DAB2 (*02) and noted that the Cyca-DAB2 gene was either homozygous or absent. PCR-RF-SSCP analysis of n=79 carp individuals challenged with Aeromonas hydrophila indicated that individuals bearing no Cyca-DAB2 gene showed higher cumulative mortality and lower bacterial agglutination titers during the experiment. We suggest that our PCR-RF-SSCP method can be used to study correlations of different MH class II B genotypes/alleles with resistance of common carp to specific pathogens.

Serum CRP-like protein profile in common carp Cyprinus carpio challenged with Aeromonas hydrophila and Escherichia coli lipopolysaccharide

The potential of C-reactive protein (CRP)-like proteins to be used as a biomarker of health status in cultured carp obtained from various European fish lines has been assessed. Varying CRP-like protein levels in the serum of carp were monitored using an indirect competitive enzyme-linked immunosorbent assay. CRP-like protein basal levels in normal fish varied between carp lines, ranging on average from 2.9+/-0.15 to 12.57+/-1.19 microg ml(-1). Serum levels of CRP-like protein in carp were observed to increase several fold in fish infected with the pathogen Aeromonas hydrophila. However, carp injected with Escherichia coli lipopolysaccharide (LPS) serotype 0111:B4 did not exhibit an increase in CRP-like proteins levels.

Differential transcription of multiple forms of alpha-2-macroglobulin in carp (Cyprinus carpio) infected with parasites

Alpha-2-macroglobulin (a2M) is a non-specific protease inhibitor involved in host defense mechanisms, inhibiting both endogenous and exogenous proteases. It is unique among the plasma anti-proteases with respect to the diversity of proteases that it can inactivate. Carp a2M consists of an alpha and beta chain of which the first includes the bioactive regions. Previously, three a2M alpha chain sequences were reported for East-Asian common carp. We studied a2M alpha chain variability in European common carp and report the cloning of a fourth a2M alpha chain with distinct sequence diversity in the bait region. The role of a2M in the immune response to parasites was studied in the liver of carp infected with Trypanoplasma borreli or with Ichthyophthirius multifiliis. Quantitative gene transcription analysis showed a differential regulation of the four isoforms, most clearly seen in infections with I. multifiliis. A2M3 was the only a2M isoform with a highly upregulated transcription during infection, suggesting that this particular isoform is of foremost biological importance.

Genetic differences in natural antibody levels in common carp (Cyprinus carpio L.)

In mammals, natural antibodies (Nabs) are mostly of the IgM isotype and can bind to a particular antigen or pathogen even if the host has never been exposed. Despite their early detection and abundance, the exact role and genetic control of Nabs remain unclear. We have used an indirect ELISA with three different antigens (keyhole limpet haemocyanin, chicken ovalbumin and bovine serum albumin) to demonstrate the ubiquitous presence of Nabs in common carp. Serum levels of Nabs increased with age, i.e. 10-month-old fish showed higher levels than 4-month-old fish. Also, fish grown in earth ponds showed higher levels of Nabs than fish grown in a clean environment of UV-treated water. Furthermore, we show that Nabs are present in different levels in the serum of carp lines with a different genetic background, suggestive of a genetic control. These genetic differences were independent of antigen, age and environment. Genetic differences in levels of Nabs could not unequivocally be related to differences in survival under farmed conditions. The possibilities for using levels of Nabs as marker criterion for selection for genetic disease resistance are discussed.