Advances in Fish Cytokine Biology Give Clues to the Evolution of a Complex Network

Temperature effects on teleost immunity in the light of climate change

Temperature is an important environmental modulator of teleost immune activity. Susceptibility of teleosts to temperature variation depends on the species-specific adaptive temperature range, and the activity of the teleost immune system is generally temperature-dependent. Similar to many physiological and metabolic traits of ectotherms, temperature modulates the activity of immune traits. At low temperatures, acquired immunity of many teleost species is down-modulated, and their immuno-competence mainly depends on innate immunity. At intermediate temperatures, both innate and acquired immunity are fully active and provide optimal protection, including long-lasting immunological memory. When temperatures increase and reach the upper permissive range, teleost immunity is compromised. Moreover, temperature shifts may have negative effects on teleost immune functions, in particular if shifts occur rapidly with high amplitudes. On the contrary, short-term temperature increase may help teleost immunity to fight against pathogens transiently. A major challenge to teleosts therefore is to maintain immuno-competence throughout the temperature range they are exposed to. Climate change coincides with rising temperatures, and more frequent and more extreme temperature shifts. Both are likely to influence the immuno-competence of teleosts. Nonetheless, teleosts exist in habitats that differ substantially in temperature, ranging from below zero in the Arctic's to above 40°C in warm springs, illustrating their enormous potential to adapt to different temperature regimes. The present review seeks to discuss how changes in temperature variation, induced by climate change, might influence teleost immunity.

Review of inflammation in fish and value of the zebrafish model

Inflammation is a crucial step in the development of chronic diseases in humans. Understanding the inflammation environment and its intrinsic mechanisms when it is produced by harmful stimuli may be a key element in the development of human disease diagnosis. In recent decades, zebrafish (Danio rerio) have been widely used in research, due to their exceptional characteristics, as a model of various human diseases. Interestingly, the mediators released during the inflammatory response of both the immune system and nervous system, after its integration in the hypothalamus, could also facilitate the detection of injury through the register of behavioural changes in the fish. Although there are many studies that give well-defined information separately on such elements as the recruitment of cells, the release of pro- and anti-inflammatory mediators or the type of neurotransmitters released against different triggers, to the best of our knowledge there are no reviews that put all this knowledge together. In the present review, the main available information on inflammation in zebrafish is presented in order to facilitate knowledge about this important process of innate immunity, as well as the stress responses and behavioural changes derived from it.

Immune Responses of Asian Seabass Lates calcarifer to Dietary Glycyrrhiza uralensis

To understand the impacts of dietary Glycyrrhiza uralensis on the immune responses of Lates calcarifer, the expression of immune-related genes including crp, c-3, c-4, mtor, mlst-8, eif4e, hsp-70, hsp-90, il-8il-8, il-10, tgfβ1, tnf, ifn-γ1, and mxf in L. calcarifer juveniles was evaluated in this study. Fish were fed experimental diets with G. uralensis levels of 0%, 1%, 3%, and 5% for 56 days. The results showed that dietary G. uralensis could improve the growth and survival of L. calcarifer and regulate the immune-related genes' expression in L. calcarifer. Dietary G. uralensis significantly upregulated the expression level of crp, mtor, hsp-90, c-3, and c-4 genes in the liver of L. calcarifer, while hsp-70 gene expression was nearly downregulated. It did not upregulate the expression of elf4e and mlst-8 in the 1% and 3% inclusion groups, but it was the exact opposite in the 5% inclusion group. G. uralensis significantly affected the expression of il-8, il-10, tnf, ifn-γ1, mxf, and tgfβ1 in the head kidney of L. calcarifer. G. uralensis upregulated the expression of tnf and tgfβ1 consistently, but ifn-γ1 was at a low expression level. The expression of il-8 and il-10 was upregulated in the 1% group, while it was downregulated in the 5% group. The results from the present study indicate that dietary G. uralensis appeared to improve the immune function of L. calcarifer, and the optimum inclusion level should be between 1-3%.

Establishment and characterization of two head kidney macrophage cell lines from large yellow croaker (Larimichthys crocea)

Two continuous macrophage cell lines (LCM07 and LCM10) were established for the first time from the head kidney of the marine fish large yellow croaker (Larimichthys crocea). To date, both cell lines have been subcultured for more than 100 passages in 12 months. Notably, the LCM07 and LCM10 cells have distinct morphology and immune function. LCM07 cells showed strong contact inhibition in crowded conditions, while this was not observed in the LCM10 cells because they could grow in an overlapping manner. Correspondingly, LCM10 cells were slenderer than LCM07 cells. LCM07 cells had stronger phagocytic ability than LCM10 cells, while LCM10 cells had stronger respiratory burst activity after incubation with lipopolysaccharide (LPS) and phorbol ester (PMA). LCM07 cells had stronger Escherichia coli killing ability than LCM10 cells. The mRNA of macrophage markers, namely that of CD11b, CD114, CD68, CD86, CD209, and CD163, were all expressed in primary macrophages as well as the two cell lines. The mRNA expression levels of selected inflammatory cytokines, namely interleukin (IL)-1β, IL-8, and tumor necrosis factor (TNF)α, were all upregulated after incubation with LPS. LPS also regulated key components of the mitogen-activated protein kinase (MAPK) signaling pathway, i.e., p38, ERK (extracellular signal-regulated kinase), and JNK (Jun N-terminal kinase) and their phosphorylated forms. Arachidonic acid (ARA) downregulated the LPS-induced upregulation of IL-1β, IL-8, and TNFα, revealing that LCM07 and LCM10 cells are useful for studying nutritional immunity. In conclusion, two distinct macrophage cell lines have been established for the first time from the head kidney of marine fish, which could be useful for studying immunity and nutritional immunity.

High-throughput proteomic profiling of the fish liver following bacterial infection

Background

High-throughput proteomics was used to determine the role of the fish liver in defense responses to bacterial infection. This was done using a rainbow trout (Oncorhynchus mykiss) model following infection with Aeromonas salmonicida, the causative agent of furunculosis. The vertebrate liver has multifaceted functions in innate immunity, metabolism, and growth; we hypothesize this tissue serves a dual role in supporting host defense in parallel to metabolic adjustments that promote effective immune function. While past studies have reported mRNA responses to A. salmonicida in salmonids, the impact of bacterial infection on the liver proteome remains uncharacterized in fish.

Results

Rainbow trout were injected with A. salmonicida or PBS (control) and liver extracted 48 h later for analysis on a hybrid quadrupole-Orbitrap mass spectrometer. A label-free method was used for protein abundance profiling, which revealed a strong innate immune response along with evidence to support parallel rewiring of metabolic and growth systems. 3076 proteins were initially identified against all proteins (n = 71,293 RefSeq proteins) annotated in a single high-quality rainbow trout reference genome, of which 2433 were maintained for analysis post-quality filtering. Among the 2433 proteins, 109 showed significant differential abundance following A. salmonicida challenge, including many upregulated complement system and acute phase response proteins, in addition to molecules with putative functions that may support metabolic re-adjustments. We also identified novel expansions in the complement system due to gene and whole genome duplication events in salmonid evolutionary history, including eight C3 proteins showing differential changes in abundance.

Conclusions

This study provides the first high-throughput proteomic examination of the fish liver in response to bacterial challenge, revealing novel markers for the host defense response, and evidence of metabolic remodeling in conjunction with activation of innate immunity.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5092-0) contains supplementary material, which is available to authorized users.

Dispersible MoS2 micro-sheets induced a proinflammatory response and apoptosis in the gills and liver of adult zebrafish

High concentrations of CS-MoS₂ micro-sheets caused lamellar fusions and localized lesions in gill and liver, respectively. Moreover, they also disturbed the expression levels of genes related with antioxidant enzymes, proinflammatory response and apoptosis.

Interleukin 1β and interleukin 1 receptor antagonist gene polymorphisms and cervical cancer: a meta-analysis

OBJECTIVES

Previous studies investigating the association between interleukin 1β (IL-1β) and its receptor antagonist (IL-1RN) polymorphism and cervical cancer risk have reported controversial results. Thus, we examined these associations by performing meta-analyses.

METHODS AND MATERIALS

Fourteen studies testing the association between IL-1β and/or IL-1RN gene polymorphisms and cervical cancer were examined: 5 studies of IL-1β-511C/T, 3 studies of IL-1β-31T/C, and 6 studies of IL-1RN. Overall and ethnicity-specific summary odds ratios (ORs) and corresponding 95% confidence intervals (CIs) for cervical cancer associated with these polymorphisms were estimated using fixed- and random-effects models. Heterogeneity and publication bias were evaluated.

RESULTS

Meta-analysis of all 6 studies showed variant genotypes of IL-1RN to be associated with an elevated cervical cancer risk (RN2/RN2 vs RN1/RN1: OR, 2.64; 95% CI, 1.29-5.40; recessive: OR, 2.15; 95% CI, 1.06-4.38; dominant: OR, 1.60; 95% CI, 1.07-2.38). Combined analysis indicated that IL-1β-511C/T polymorphism was also associated with increased risk of cervical cancer (TT vs CC: OR, 1.56; 95% CI, 1.22-1.99; CT vs CC: OR, 1.61; 95% CI, 1.31-1.99; dominant: OR, 1.60; 95% CI, 1.31-1.95). No significant association of IL-1β-31T/C and cervical cancer risk was detected. There was no evidence of publication bias.

CONCLUSIONS

This meta-analysis suggested that the IL-1RN and IL-1β-511C/T polymorphisms may contribute to genetic susceptibility of cervical cancer. More studies are needed to further evaluate the role of the IL-1β-31T/C polymorphism in the etiology of cancer.

17β-Estradiol induces changes in cytokine levels in head kidney and blood of juvenile sea bass (Dicentrarchus labrax, L., 1758)

The cytokine network is involved in the immune system communication. As estrogens influence the cytokine expression in mammals, this study investigated the impact of exogenous estrogenic pollutants on selected cytokines in Dicentrarchus labrax. The gene expression of Interleukin 6, Tumour Necrosis Factor α, Transforming Growth Factor β1 and Interleukin 1β was assessed and accomplished with protein measurements in the blood for the last two. Impacts through 17β-estradiol mainly occurred at the beginning of organ regionalisation, thus falling together with a developmentally induced increase of Interleukin 1β and Tumour Necrosis Factor α gene expression in 102 dph fish. 17β-estradiol depressed this modification after 35 days of exposure and the cytokine gene expression tended to be generally down-regulated independently of the 17β-estradiol concentrations after 56 days of exposure. This impact was confirmed at the protein level, showing that 17β-estradiol affects the fine control of the cytokine network in sea bass.

Environmental associations with gene transcription in Babine Lake rainbow trout: evidence for local adaptation

The molecular genetic mechanisms facilitating local adaptation in salmonids continue to be poorly characterized. Gene transcription is a highly regulated step in the expression of a phenotype and it has been shown to respond to selection and thus may be one mechanism that facilitates the development of local adaptation. Advances in molecular genetic tools and an increased understanding of the functional roles of specific genes allow us to test hypotheses concerning the role of variable environments in shaping transcription at known-function candidate loci. To address these hypotheses, wild rainbow trout were collected in their first summer and subjected to metabolic and immune challenges. We assayed gene transcription at candidate loci that play a role in the molecular genetic response to these stresses, and correlated transcription with temperature data from the streams and the abundance and diversity of bacteria as characterized by massively parallel pyrosequencing. Patterns of transcriptional regulation from resting to induced levels varied among populations for both treatments. Co-inertia analysis demonstrated significant associations between resting levels of metabolic gene transcription and thermal regime (R (2) = 0.19, P = 0.013) as well as in response to challenge (R (2) = 0.39, P = 0.001) and resting state and challenged levels of cytokine gene transcription with relative abundances of bacteria (resting: R (2) = 0.25, P = 0.009, challenged: R (2) = 0.65, P = 0.001). These results show that variable environments, even within a small geographic range (<250 km), can drive divergent selection among populations for transcription of genes related to surviving stress.

Impact of thiamine deficiency on T-cell dependent and T-cell independent antibody production in lake trout

Lake trout Salvelinus namaycush on thiamine-replete and thiamine-depleted diets were evaluated for the effects of thiamine status on in vivo responses to the T-dependent antigen trinitophenol (TNP)-keyhole limpet hemocyanin (TNP-KLH), the T-independent antigen trinitrophenol-lipolysaccaharide (TNP-LPS), or Dulbecco's phosphate-buffered saline (DPBS; negative control fish). Plasma antibody concentrations were evaluated for possible differences in total anti-TNP activity as well as differences in response kinetics. Associations between anti-TNP activity and muscle and liver thiamine concentrations as well as ratios of muscle-to-liver thiamine to anti-TNP activity were also examined. Thiamine-depleted lake trout that were injected with TNP-LPS exhibited significantly more anti-TNP activity than thiamine-replete fish. The depleted fish injected with TNP-LPS also exhibited significantly different response kinetics relative to thiamine-replete lake trout. No differences in activity or kinetics were observed between the thiamine-replete and -depleted fish injected with TNP-KLH or in the DPBS negative controls. Anti-TNP activity in thiamine-depleted lake trout injected with TNP-KLH was positively associated with muscle thiamine pyrophosphate (thiamine diphosphate; TPP) concentration. A negative association was observed between the ratio of muscle-to-liver TPP and T-independent responses. No significant associations between anti-TNP activity and tissue thiamine concentration were observed in the thiamine-replete fish. We demonstrated that thiamine deficiency leads to alterations in both T-dependent and T-independent immune responses in lake trout.

Characterization and expression analysis of Th-POK from the Japanese pufferfish, Takifugu rubripes

In fish, T cell lineage commitment has not been studied, although there are reports related to CD4 and CD8 positive cells. This study describes the cloning and analysis of a master regulator involved in this process, the Th-POK gene in Japanese pufferfish, Takifugu rubripes. The Fugu Th-POK cDNA was composed of 1901 bp, with a 75 bp 5'-UTR, a 131 bp 3'-UTR, and a 1692 bp open reading frame which translates into a peptide of 564 amino acid residues. The deduced Fugu Th-POK protein contained a BTB/POZ domain, Krüppel motif (H/C linker) and Krüppel-like zinc finger DNA binding domain with C2H2 structure. The homology analysis of Fugu Th-POK (ZBTB7B) with other known ZBTB7 members (ZBTB7A, 7C) showed low identity, and the phylogenetic tree analysis showed the Fugu Th-POK clustered with the mammalian Th-POK, away from other ZBTB7 members. The analysis of transcriptional control region of Th-POK gene suggested that the 5'-flanking region and intron 1 include numerous canonical binding motifs for transcription factors regulating T cell development. The genomic organization of the Fugu Th-POK gene was composed of three exons and two introns, and its structure was identical to that of its human counterpart. Comparison of the Fugu and human genomes showed that high levels of conserved synteny existed around the Th-POK gene. The high expression of the Fugu Th-POK gene in unstimulated tissues was seen in head kidney, muscle, skin and gills. Moreover, the expression of the Fugu Th-POK gene in thymic cells was increased by LPS, polyI:C and PHA stimulation.

Establishment of a multiplex RT-PCR assay for the rapid detection of fish cytokines

To monitor the expression of cytokine genes in Japanese pufferfish, a novel platform for quantitative multiplexed analysis was developed. This custom-designed multiplex RT-PCR assay was used to analyze the expression profiles of 19 cytokine genes, including pro-inflammatory (IL-1β, IL-6, IL-17A/F3, IL-18, TNF-α, TNF-N), anti-inflammatory (IL-4/13A, IL-4/13B, IL-10), T-cell proliferation/differentiation (IL-2, IL-15, IL-21, TGF-β1), B-cell activation/differentiation (IL-7, IL-6, IL-4/13A, IL-4/13B), NK cell stimulation (IL-12p35 and IL-12p40), induction of anti-viral activity (I-IFN-1 and IFN-γ), and monocyte/macrophage progenitor cell proliferation (M-CSF1b) cytokines in head kidney cells under immune stimulatory conditions. The expression profiles were dissimilar in the unstimulated control and immune-stimulated cells. Moreover, increased expression profile was observed due to different stimulations for IL-1β, IL-6, IL-10, IL-12p35, IL-12p40, IL-21, TNF-α, TNF-N, I-IFN-1 and IFN-γ genes. These results suggest that cytokine genes could be used as biomarkers to know the immune status of fish. The constructed multiplex RT-PCR assay will enhance understanding on immune regulation by cytokines in fish.

Teleost IgSF immunoregulatory receptors

In all animals innate immunity is the first line of immune defense from invading pathogens. The prototypical innate cellular responses such as phagocytosis, degranulation, and cellular cytotoxicity are elicited by leukocytes in a diverse range of animals including fish, amphibians, birds and mammals reinforcing the importance of such primordial defense mechanisms. In mammals, these responses are intricately controlled and coordinated at the cellular level by distinct subsets of immunoregulatory receptors. Many of these surface proteins belong to the immunoglobulin superfamily and in mammals elaborate immunoregulatory receptor networks play a major role in the control of infectious diseases. Recent examination of teleost immunity has begun to further illustrate the complexities of these receptor networks in lower vertebrates. However, little is known about the mechanisms that control how immunoregulatory receptors influence cellular decision making in ectothermic vertebrates. This review focuses on several families of recently discovered immunoglobulin superfamily members in fish that share structural, phylogenetic and in some cases functional relationships with mammalian immunoregulatory receptors. Further characterization of these teleost innate immune receptor families will provide detailed information regarding the conservation and importance of innate immune defense strategies throughout vertebrate evolution.

T cell diversity and TcR repertoires in teleost fish

In vertebrates, the diverse and extended range of antigenic motifs is matched to large populations of lymphocytes. The concept of immune repertoire was proposed to describe this diversity of lymphocyte receptors--IG and TR--required for the recognition specificity. Immune repertoires have become useful tools to describe lymphocyte and receptor populations during the immune system development and in pathological situations. In teleosts, the presence of conventional T cells was first proposed to explain graft rejection and optimized specific antibody production. The discovery of TR genes definitely established the reality of conventional T cells in fish. The development of genomic and EST databases recently led to the description of several key T cell markers including CD4, CD8, CD3, CD28, CTLA4, as well as important cytokines, suggesting the existence of different T helper (Th) subtypes, similar to the mammalian Th1, Th2 and Th17. Over the last decade, repertoire studies have demonstrated that both public and private responses occur in fish as they do in mammals, and in vitro specific cytotoxicity assays have been established. While such typical features of T cells are similar in both fish and mammals, the structure of particular repertoires such as the one of gut intra-epithelial lymphocytes seems to be very different. Future studies will further reveal the particular characteristics of teleost T cell repertoires and adaptive responses.

Effects of the polycyclic ketone tonalide (AHTN) on some cell viability parameters and transcription of P450 and immunoregulatory genes in rainbow trout RTG-2 cells

To assess the potential effects of environmental pollutants belonging to the musk fragrances group in the physiology of aquatic animal species, in this work we treated rainbow trout RTG-2 cells with the polycyclic ketone tonalide (AHTN) at dilutions ranging from 3.5 to 500 ng/ml. The following parameters were monitored: intracellular ATP concentration (energy production), mitochondrial membrane potential (early apoptosis marker), cell viability (vital staining with DFP), quantitative expression of genes coding for the cytochrome P450 detoxifying enzymes CYP1A1 and CYP3A27, and of genes coding for the immunoregulatory peptides IL-1β, IL-8, TNFα, Cox-2 and TGF-β. Obtained results showed that incubation with tonalide induced in RTG-2 cells no effects on cell viability, a slight increase of mitochondrial membrane potential activity, and a significant increase in intracellular ATP concentration. However, dramatic effects were observed in transcription levels of some tested genes, with upregulation levels of 300 and 600 times measured for TGF-β and TNFα, respectively and of 150 times for the CYP3A27 gene. Our results show for the first time the potent effects exerted by tonalide on immunoregulatory genes of RTG-2 cells and also indicate that the measured sensitivity of RTG-2 towards tonalide was in the same range of that currently available using chemical methods. A possible use of the panel of genes we employed as a tool for the monitoring of musk fragrances in biological samples is discussed.

Starvation alters the liver transcriptome of the innate immune response in Atlantic salmon (Salmo salar)

BACKGROUND

The immune response is an energy demanding process, which has effects in many physiological pathways in the body including protein and lipid metabolism. During an inflammatory response the liver is required to produce high levels of acute phase response proteins that attempt to neutralise an invading pathogen. Although this has been extensively studied in both mammals and fish, little is known about how high and low energy reserves modulate the response to an infection in fish which are ectothermic vertebrates. Food withdrawal in fish causes a decrease in metabolic rate so as to preserve protein and lipid energy reserves, which occurs naturally during the life cycle of many salmonids. Here we investigated how the feeding or fasting of Atlantic salmon affected the transcriptional response in the liver to an acute bacterial infection.

RESULTS

Total liver RNA was extracted from four different groups of salmon. Two groups were fed or starved for 28 days. One of each of the fed or starved groups was then exposed to an acute bacterial infection. Twenty four hours later (day 29) the livers were isolated from all fish for RNA extraction. The transcriptional changes were examined by micro array analysis using a 17 K Atlantic salmon cDNA microarray. The expression profiling results showed major changes in gene transcription in each of the groups. Enrichment for particular biological pathways was examined by analysis of gene ontology. Those fish that were starved decreased immune gene transcription and reduced production of plasma protein genes, and upon infection there was a further decrease in genes encoding plasma proteins but a large increase in acute phase response proteins. The latter was greater in magnitude than in the fish that had been fed prior to infection. The expression of several genes that were found altered during microarray analysis was confirmed by real time PCR.

CONCLUSIONS

We demonstrate that both starvation and infection have profound effects on transcription in the liver of salmon. There was a significant effect on the transcriptional response to infection depending on the prior feeding regime of the fish. It is likely that the energy demands on protein synthesis for acute phase response proteins are relatively high in the starved fish which have reduced energy reserves. This has implications for dietary control of fish if an immune response is anticipated.

Establishment of an IFN-gamma specific reporter cell line in fish

An interferon (IFN)-gamma responsive stable cell line RTG-3F7 has been developed for rainbow trout by modifying the RTG-2 cell line through transfection with a plasmid construct (pGL4.14[luc2/hygro]-PrTAP2) containing a promoter element from the IFN-gamma responsive gene TAP2 linked to a luciferase reporter gene and a hygromycin resistance gene. Following transfection single clones were selected in 96 well plates using hygromycin B, and those showing specific activation after rIFN-gamma stimulation were maintained. Five clones that showed the highest reporter activity to rIFN-gamma were incubated with different stimuli to examine specificity. No significant induction of luciferase was observed following exposure to recombinant type I IFN, LPS, PHA or poly I:C. The cell line was responsive to rIFN-gamma at concentrations between 150 pg and 20 ng ml(-1). Supernatants of primary cultures of head kidney leucocytes stimulated with PHA, known to induce IFN-gamma gene expression, were also used to assess the reporter activity of the stable cell line. A dose-dependent induction of the promoter activity was observed with these supernatants indicating the presence of IFN-gamma. These results indicate that the stable cell line RTG-3F7 is an excellent tool for monitoring the presence of trout IFN-gamma in biological samples, and in addition, enables the study of intracellular signalling pathways of IFNs, their receptor interactions, and other closely related signalling networks.

Identification and characterization of the transcription factors involved in T-cell development, t-bet, stat6 and foxp3, within the zebrafish, Danio rerio

The discovery of cytokines expressed by T-helper 1 (Th1), Th2, Th17 and T-regulatory (T(reg)) cells has prompted speculation that these types of responses may exist in fish, arising early in vertebrate evolution. In this investigation, we cloned three zebrafish transcription factors, T-box expressed in T cells (t-bet), signal transducer and activator of transcription 6 (stat6) and fork-head box p3 (foxp3), in which two transcripts are present, that are important in the development of a number of these cell types. They were found within the zebrafish genome, using a synteny approach in the case of t-bet and foxp3. Multiple alignments of zebrafish t-bet, stat6 and foxp3 amino acids with known vertebrate homologues revealed regions of high conservation, subsequently identified to be protein domains important in the functioning of these transcription factors. The gene organizations of zebrafish t-bet and foxp3 were identical to those of the human genes, with the second foxp3 transcript lacking exons 5, 6, 7 and 8. Zebrafish stat6 (21 exons and 20 introns) was slightly different from the human gene, which contained 22 exons and 21 introns. Immunostimulation of zebrafish head kidney and spleen cells with phytohaemagglutinin, lipopolysaccharide or Poly I:C, showed a correlation between the expression of t-bet, stat6 and foxp3 with other genes involved in Th and T(reg) responses using quantitative PCR. These transcription factors, together with many of the cytokines that are expressed by different T-cell subtypes, will aid future investigations into the Th and T(reg) cell types that exist in teleosts.

Local and systemic gene expression responses of Atlantic salmon (Salmo salar L.) to infection with the salmon louse (Lepeophtheirus salmonis)

Background

The salmon louse (SL) is an ectoparasitic caligid crustacean infecting salmonid fishes in the marine environment. SL represents one of the major challenges for farming of salmonids, and veterinary intervention is necessary to combat infection. This study addressed gene expression responses of Atlantic salmon infected with SL, which may account for its high susceptibility.

Results

The effects of SL infection on gene expression in Atlantic salmon were studied throughout the infection period from copepodids at 3 days post infection (dpi) to adult lice (33 dpi). Gene expression was analyzed at three developmental stages in damaged and intact skin, spleen, head kidney and liver, using real-time qPCR and a salmonid cDNA microarray (SFA2). Rapid detection of parasites was indicated by the up-regulation of immunoglobulins in the spleen and head kidney and IL-1 receptor type 1, CD4, beta-2-microglobulin, IL-12β, CD8α and arginase 1 in the intact skin of infected fish. Most immune responses decreased at 22 dpi, however, a second activation was observed at 33 dpi. The observed pattern of gene expression in damaged skin suggested the development of inflammation with signs of Th2-like responses. Involvement of T cells in responses to SL was witnessed with up-regulation of CD4, CD8α and programmed death ligand 1. Signs of hyporesponsive immune cells were seen. Cellular stress was prevalent in damaged skin as seen by highly significant up-regulation of heat shock proteins, other chaperones and mitochondrial proteins. Induction of the major components of extracellular matrix, TGF-β and IL-10 was observed only at the adult stage of SL. Taken together with up-regulation of matrix metalloproteinases (MMP), this classifies the wounds afflicted by SL as chronic. Overall, the gene expression changes suggest a combination of chronic stress, impaired healing and immunomodulation. Steady increase of MMP expression in all tissues except liver was a remarkable feature of SL infected fish.

Conclusion

SL infection in Atlantic salmon is associated with a rapid induction of mixed inflammatory responses, followed by a period of hyporesponsiveness and delayed healing of injuries. Persistent infection may lead to compromised host immunity and tissue self-destruction.

Will advances in fish immunology change vaccination strategies?

This review will discuss some of the recent advances in discovering immune genes in fish, in terms of their relevance to vaccine design and development. Particular emphasis will be placed on the many cytokine and costimulatory molecules now known, with examples drawn from the mammalian literature as to their potential value for fish vaccinology. A new area of vaccine research will also be touched upon, where efficacious responses are elicited by inhibiting the natural negative regulators of immune responses, such as Treg cell products and SOCS proteins.

Characterization and expression of the transcription factor PU.1 during LPS-induced inflammation in the rainbow trout (Oncorhynchus mykiss)

The transcription factor PU.1 plays a key role in hematopoietic lineage development and therefore in determining immune cell fate. A full length cDNA transcript of 1237 nucleotides encoding a highly conserved putative protein of 293 amino acids was identified by EST analysis in lipopolysaccharide (LPS) activated trout macrophages. Phylogenetic analyses highlight the significant level of structural conservation of the PU.1 transcription factor reinforcing the importance of this molecule in animal immunity. In trout, the PU.1 mRNA shows a tissue-specific expression pattern and is induced in vivo by LPS in muscle, liver, intestine and brain. Furthermore PU.1 is highly expressed in trout macrophages in primary culture. In situ expression analysis in the head kidney describes a large number of PU.1+ve cells distributed through the tissue in both LPS-treated and control animals. Cellular proliferation examined by BrdU immunohistochemistry (IHC) shows that LPS regulates hematopoietic processes in adult fish by stimulating cellular proliferation 3 days after treatment. These studies provide initial insights into hematopoietic/cellular processes in the head kidney of rainbow trout after in vivo LPS challenge.

Cell-mediated immune responses in rainbow trout after DNA immunization against the viral hemorrhagic septicemia virus

To identify viral proteins that induce cell-mediated cytotoxicity (CMC) against viral hemorrhagic septicemia virus (VHSV)-infected cells, rainbow trout were immunized with DNA vectors encoding the glycoprotein G or the nucleocapsid protein N of VHSV. The G protein was a more potent trigger of cytotoxic cells than the N protein. Peripheral blood leukocytes (PBL) isolated from trout immunized against the G protein killed both VHSV-infected MHC class I matched (RTG-2) and VHSV-infected xenogeneic (EPC) target cells, suggesting the involvement of both cytotoxic T lymphocytes (CTL) and NK cells, respectively. In contrast, PBL from trout that were immunized against the N protein only killed VHSV-infected RTG-2 cells, indicating that this protein only elicits a CTL response. Further, a significant killing capacity of these PBL was only observed during summer months. PBL from fish that were immunized against the VHSV G protein significantly killed VHSV-infected but not infectious hematopoietic necrosis virus (IHNV)-infected targets indicating antigen specificity. Thus, this is the first report on cytotoxic immune responses after DNA vaccination in fish. Furthermore, cells isolated from the inflamed site of DNA injection were stained and transferred to isogeneic DNA-vaccinated recipients. Most of the stained donor leukocytes accumulated at the recipients' DNA injection site showing, for the first time, leukocyte homing in fish. Transferred donor leukocytes mainly migrated to the homologous vaccine injection site rather than to injection sites of heterologous vaccines, suggesting the antigen specificity of homing. By demonstrating CMC responses to distinct viral proteins and homing in rainbow trout, these results substantially contribute to the understanding of the teleost immune system.

Characterisation and expression analysis of the interleukin genes, IL-1beta, IL-8 and IL-10, in Atlantic cod (Gadus morhua L.)

The mammalian interleukins IL-1beta and IL-8 are important pro-inflammatory cytokines often used as markers of an activated inflammatory response, while IL-10 is regarded as an anti-inflammatory cytokine and plays a crucial role in the regulation of inflammation. Few cytokines from gadoid fish have been described, and herein the sequence and expression of these interleukin genes are studied in Atlantic cod (Gadus morhua L.). IL-1beta, IL-8 and IL-10 from cod show similarities in gene organisation and predicted protein sequences, compared to counterpart genes in other teleosts. Gene expression was studied using quantitative real time PCR in response to several treatments both in vitro and in vivo. In adherent head kidney cells, infectious pancreatic necrosis virus (IPNV) and lipopolysaccharide (LPS) significantly stimulated gene expression of IL-1beta. The expression of IL-1beta was not increased after treatment with a viral imitator (poly I:C), and neither IL-8 nor IL-10 responded to any of these agents in vitro. However, in vivo administrated poly I:C and formalin-killed Vibrio anguillarum (In-V.ang) induced interleukin expression, varying in intensity between different organs. IL-1beta and IL-10 gene expression profiles showed an opposite induction pattern in the in vivo experiments. Injection of In-V.ang highly induced IL-1beta expression, while a low induction was evident for IL-10, whereas the opposite was observed after injection of poly I:C. This pattern was particularly marked in spleen, where also IL-8 followed the expression pattern of IL-1beta. The opposite expression profiles indicate a suppressive role for IL-10 on the transcription of IL-1beta, and to a lesser extent on IL-8 transcription. Along with the identification of important promoter regulatory motives, these results provide tools for studying inflammatory responses in cod.

Proteome analysis of the Atlantic salmon (Salmo salar) cell line SHK-1 following recombinant IFN-γ stimulation

Type II IFN exists as a single molecule (IFN-gamma) in contrast to type I IFN, of which there are a number of different forms. IFN-gamma is involved both directly and indirectly in antiviral activity, stimulation of bactericidal activity, antigen presentation and activation of macrophages. Recently IFN-gamma was cloned from a salmonid fish, the rainbow trout and a functional recombinant protein produced exhibited IFN-gamma activity. This recombinant IFN-gamma was used to stimulate an Atlantic salmon cell line, SHK-1, to monitor the changes in protein expression by proteomic analysis 24 h after stimulation compared to unstimulated control cells. An SHK-1 cell proteome map was developed and proteins altered in abundance by the IFN-gamma stimulation were identified. Under the analytical conditions used, 22 proteins were found to be altered in abundance, 15 increased and 7 decreased. Several proteins were excised from the gel and identified, following trypsin digestion and MALDI-MS/MS/LC-MS and database interrogation. Transcriptional analysis of five mRNAs encoding proteins increased in abundance by IFN-gamma in the proteome analysis was determined by real-time PCR. We assessed the correlation between gene expression and change in abundance of proteins for these genes.

Growth hormone and fish immune system

This paper reviews the immunomodulatory effects, extra-pituitary expression and paracrine action of growth hormone (GH), and a possible role of GH/insulin-like growth factor-I (IGF-I) axis in the immune system of teleost fish. In some euryhaline fish, the activation of immune functions observed during seawater acclimation appears to be associated with the osmoregulatory action of GH. Administration of GH enhances many aspects of immune functions including non-specific defences; cytotoxic, phagocytic, haemolytic and lysozyme activities. GH also activates immunoglobulin production as a specific defense and increases ceruloplasmin levels as an acute-phase protein. The GH gene is also expressed in many extra-pituitary tissues of fish, especially in lymphoid organs and cells. Several endocrine factors appear to act on immune function through modification of GH secretion from fish leucocytes. Exposure of phagocytic leucocytes of tilapia to IGF-I in vitro stimulated proliferation and superoxide production associated with phagocytosis. Exposure to GH had no significant effect on IGF-I secretion from tilapia leucocytes, despite of the fact that they secreted significant amounts of IGF-I. GH and IGF-I appear to act in a paracrine manner in the regulation of the teleostean immune system. Further studies are necessary to characterize the interactions of GH with other endocrine and paracrine factors.