Real-time gene expression analysis in carp (Cyprinus carpio L.) skin: inflammatory responses caused by the ectoparasite Ichthyophthirius multifiliis

Immunological effects of DNA vaccination and interleukin utilization as an adjuvant in Astyanax lacustris immunized against Ichthyophthirius multifiliis

The increasing significance of the aquaculture sector and commercially valuable species underscores the need to develop alternatives for controlling diseases such as Ichthyophthirius multifiliis-induced ichthyophthiriasis. This ciliated protozoan parasite threatens nearly all freshwater fish species, causing substantial losses in the fishery industry. Despite this, effective large-scale treatments are lacking, emphasizing the necessity of adopting preventive strategies. While the pathogenesis of ichthyophthiriasis and its immune stimulation allows for vaccination strategies, precise adjustments are crucial to ensure the production of an effective vaccine compound. Therefore, this study aimed to evaluate the impact of immunizing Astyanax lacustris with a genetic vaccine containing IAG52A from I. multifiliis and the molecular adjuvant IL-8 from A. lacustris. Transcript analysis in immunized A. lacustris indicated mRNA production in fish muscles, demonstrating an expression of this mRNA. Fish were divided into five groups, receiving different vaccine formulations, and all groups received a booster dose 14 days after the initial immunization. Samples from vaccinated fish showed increased IL-1β mRNA expression in the spleen within 6 h post the second dose and after 14 days. In the head kidney, IL-1β mRNA expression showed no significant difference at 6 and 24 h but an increase was noted in fish injected with IAG and IAG + IL-8 after 14 days. IL-8 mRNA expression in the spleen and kidney did not significantly differ from the control group. Histological analysis revealed no variation in leukocyte concentration at 6 and 24 h post-vaccination; however, after 14 days, the groups injected with IAG and IAG + IL-8 exhibited a higher leukocyte density at the application sites than the control. The obtained data suggest that the used vaccine is transcribed, indicating its potential to stimulate innate immune response parameters through mRNA cytokine expression and leukocyte migration.

What can we learn about fish neutrophil and macrophage response to immune challenge from studies in zebrafish

Fish rely, to a high degree, on the innate immune system to protect them against the constant exposure to potential pathogenic invasion from the surrounding water during homeostasis and injury. Zebrafish larvae have emerged as an outstanding model organism for immunity. The cellular component of zebrafish innate immunity is similar to the mammalian innate immune system and has a high degree of sophistication due to the needs of living in an aquatic environment from early embryonic stages of life. Innate immune cells (leukocytes), including neutrophils and macrophages, have major roles in protecting zebrafish against pathogens, as well as being essential for proper wound healing and regeneration. Zebrafish larvae are visually transparent, with unprecedented in vivo microscopy opportunities that, in combination with transgenic immune reporter lines, have permitted visualisation of the functions of these cells when zebrafish are exposed to bacterial, viral and parasitic infections, as well as during injury and healing. Recent findings indicate that leukocytes are even more complex than previously anticipated and are essential for inflammation, infection control, and subsequent wound healing and regeneration.

Differentially expressed proteins and microbial communities of the skin regulate disease resistance to Chinese tongue sole (Cynoglossus semilaevis)

Vibriosis, caused by Vibrio, seriously affects the health of fish, shellfish, and shrimps, causing large economic losses. Teleosts are represent the first bony vertebrates with both innate and adaptive immune responses against pathogens. Aquatic animals encounter hydraulic pressure and more pathogens, compared to terrestrial animals. The skin is the first line of defense in fish, constituting the skin-associated lymphoid tissue (SALT), which belongs to the main mucosa-associated lymphoid tissues (MALT). However, little is known about the function of immunity related proteins in fish. Therefore, this study used iTRAQ (isobaric tags for relative and absolute quantitation) to compare the skin proteome between the resistant and susceptible families of Cynoglossus semilaevis. The protein integrin beta-2, the alpha-enolase isoform X1, subunit B of V-type proton ATPase, eukaryotic translation initiation factor 6, and ubiquitin-like protein ISG15, were highly expressed in the resistant family. The 16S sequencing of the skin tissues of the resistant and susceptible families showed significant differences in the microbial communities of the two families. The protein-microbial interaction identified ten proteins associated with skin microbes, including immunoglobulin heavy chain gene (IGH), B-cell lymphoma/leukemia 10 (BCL10) and pre-B-cell leukemia transcription factor 1 isoform X2 (PBX2). This study highlights the interaction between skin proteins and the microbial compositions of C. semilaevis and provides new insights into understanding aquaculture breeding research.

Effect of transporting Oreochromis niloticus in water with and without sodium chloride on skin morphology and some immunity-related genes expression

The aim of this study was to examine the effects of salt addition on the skin gene expression of Mucin, Antimicrobial peptides, cortisol, and glucose in Oreochromis niloticus after 5-hour transportation in water. Three groups were compared: Control, post-transport without salt (PT-S), and post-transport with 5 g salt-1(PT + S), with a stocking density of 28.6 gL-1, 20 fish for each experimental group. The results showed that the PT-S group had more significant changes in gene expression than the PT + S group, suggesting that salt alleviated the stress and immune responses of O. niloticus. The PT-S group had higher expression of mucin- 2(MUC + 2) (7.58 folds) and mucin-5AC (MUC5-AC) (6.29 folds) than the PT + S group (3.30 folds and 4.16 folds, respectively). The PT-S group also had lower expression of β-defensin-1 (Dβ1) (0.42 folds), β-defensin-2 (Dβ2) (0.29 folds), and Cath1 (0.16 folds) than the PT + S group (0.82 folds, 0.69 folds, and 0.75 folds, respectively). The skin morphology of the PT-S group revealed some white patches with no goblet cell openings, while the PT + S group had better preservation of skin features with some goblet cell openings and slight white patches. This study indicates that O. niloticus can benefit from sodium chloride during transportation, as it helps to reduce stress and inflammation, balance mineral levels, enhance health and immunity, and regulate mucous secretion.

Unraveling the host-parasite interaction: immune response in Oreochromis mossambicus to Cymothoa eremita (Isopoda, Cymothoidae) infection

The host immune response in Oreochromis mossambicus during natural infection with the isopod Cymothoa eremita was investigated. The naturally infected fishes were examined for enzyme profile, viz., respiratory burst activity (RBA), myeloperoxidase activity (MPO), and expression of immune-related genes, viz., toll-like receptor 22 (TLR 22), interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), complement component (C3), chemokine (CXCa), and β-actin in tissues of various organs (buccal cavity, gills and anterior kidney). Significant reduction (P < 0.05) in RBA and MPO was observed in the parasite-infected fishes when compared to the uninfected control fishes. In the buccal cavity, the expression of the immune-related genes was significantly (P < 0.05) upregulated, whereas all the genes except IL-1β were significantly (P < 0.05) upregulated in the anterior kidney. In the case of gill tissue, the expressed genes showed a varied type of regulation. The immunological responses in O. mossambicus during isopod infection have not been investigated in detail so far, and this is the first study unveiling such insights. Hence, this study will help to improve our molecular understanding of the host-immune response to parasitic isopod infection.

Repeated exposure affects susceptibility and responses of Atlantic salmon (Salmo salar) towards the ectoparasitic salmon lice (Lepeophtheirus salmonis)

Atlantic salmon (Salmo salar) is repeatedly exposed to and infected with ectoparasitic salmon lice (Lepeophtheirus salmonis) both in farms and in nature. However, this is not reflected in laboratory experiments where fish typically are infected only once. To investigate if a previous lice infection affects host response to subsequent infections, fish received 4 different experimental treatments; including 2 groups of fish that had previously been infected either with adult or infective salmon lice larvae (copepodids). Thereafter, fish in all treatment groups were infected with either a double or a single dose of copepodids originating from the same cohort. Fish were sampled when lice had developed into the chalimus, the pre-adult and the adult stage, respectively. Both the specific growth rate and cortisol levels (i.e. a proxy for stress) of the fish differed between treatments. Lice success (i.e. ability to infect and survive on the host) was higher in naïve than in previously infected fish (pre-adult stage). The expression of immune and wound healing transcripts in the skin also differed between treatments, and most noticeable was a higher upregulation early in the infection in the group previously infected with copepodids. However, later in the infection, the least upregulation was observed in this group, suggesting that previous exposure to salmon lice affects the response of Atlantic salmon towards subsequent lice infections.

Efficacy of dietary live or heat-killed Bacillus subtilis in goldfish (Carassius auratus) infected with Ichthyophthirius multifiliis

BACKGROUND

The beneficial effects of Bacillus subtilis on growth, immune response, and disease resistance against various diseases in different fish species have been proved. However, there are no data concerning this probiotic effect on skin mucosal immunity in fish infected with Ichthyophthirius multifiliis (Ich). Ich has a high mortality rate in both edible and ornamental fish and consequently is concerned with heavy economic losses.

OBJECTIVES

Thus, we assessed the efficacy of live and heat-killed B. subtilis on skin immunity and histopathology in goldfish (Carassius auratus) infected with Ich.

METHODS

Goldfish (144 fish, 2.38 g average weight) were stocked in nine glass tanks each in three replicates. Fish were fed 10⁹ CFU g^-1 live or heat-killed B. subtilis for 80 days.

RESULTS

Probiotic administration in both viable and non-viable forms could enhance the growth performance in goldfish. Probiotic therapy also reduced the density of the parasite and histopathological level on skin and gill tissues of the treated fish. Real-time polymerase chain reaction analysis showed a higher expression of lysozyme and tumour necrosis factor-α in the treated groups compared to the control group.

CONCLUSIONS

These data demonstrated the beneficial effect of B. subtilis as probiotic and paraprobiotic on growth performance and disease resistance to Ich infestation in goldfish.

Effect of transporting Oreochromis niloticus in water with and without sodium chloride on some skin immunity-related genes expression.. [DOI: 10.21203/rs.3.rs-2588120/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

This study conducted to investigate Mucin, Antimicrobial peptides, Cytokines, prolactin and growth hormones gene expression of skin of Oreochromis niloticus after transportation for 5-hour in water with and without salt. Three experimental groups (Control, post-transport without salt (PT-S) and post-transport with 5g salt/L (PT + S)) were investigated. Overall, they were dramatically changed in the PT-S group than PT + S group indicating that the addition of salt to transport water mitigated the stress effect on the O. niloticus physiology and immunity. MUC + 2 a greater up-regulation was recorded in the PT-S group (7.58 folds) comparing to 3.30 folds in the PT + S group and the MUC5-AC greater up-regulated in the PT-S group (6.29 folds) comparing to a 4.16 folds in the PT + S group. The antimicrobial peptides Dβ1, Dβ2 and Cath1 genes expression were all significantly down regulated in the PT-S and PT + S skin comparing with the control and this down regulation was more dramatic in the PT-S group recording 0.42, 029 and 0.16 folds matching with 0.82, 0.69 and 0.75 in the PT + S group respectively. Scanning microscopy of skin of PT-S group showed few scratched white patches among normal regions that may represent thickened surface with absence of opening of goblets cell, while the skin of PT + S group showed moderate preservation of surface skin features with some goblet cells opening and slight thickened white patches could be observed and goblet cells opening were not so clear like control.

The effect of different intensities of the ectoparasitic salmon lice (Lepeophtheirus salmonis) on Atlantic salmon (Salmo salar)

The effect of different intensities of the ectoparasitic salmon lice (Lepeophtheirus salmonis) on stress, growth and the expression of immune and wound healing transcripts in the skin of Atlantic salmon (Salmo salar) was investigated. Lice infection success and survival were similar at the chalimus and preadult stage in the low and high dose group, but infection success and survival were significantly lower in the high than in the low dose group at the adult stage. The expression of investigated transcripts was not correlated to lice intensities, but several of them were significantly differently expressed locally in the skin at the site of lice attachment in infected fish compared to controls. This included an up-regulation of pro-inflammatory markers at the site of lice attachment (e.g., interleukin 1-beta, interleukin 8 and the acute phase protein serum amyloid A), a reduction of markers of adaptive immunity (cluster of differentiation 8-alpha and immunoglobulin M) and decreased expression of the anti-inflammatory cytokine interleukin 10.

cMOS enhanced the mucosal immune function of skin and gill of goldfish (Carassius auratus Linnaeus) to improve the resistance to Ichthyophthirius multifiliis infection

of supporting mucosal immune barrier integrity and prevention of some pathogenic infections in aquatic species, are key areas of active study, often focusing on feed additives. The objectives of this study were to explore the effects of feeding cMOS (concentrated mannan oligosaccharide) on the gill and skin mucosal barriers of goldfish (Carassius auratus Linnaeus) and evaluate health status during Ichthyophthirius multifiliis infection. After feeding the cMOS-containing diet for 60 days, Hematoxylin and eosin (H&E) staining showed greater length of gill lamella and thicker dermal dense layer, while Alcian Blue and Periodic acid-Schiff (AB-PAS) staining showed higher numbers of mucin cells in cMOS fed fish. Chemical analysis showed that fish fed cMOS had greater enzyme activity of lysozyme (LZM) and alkaline phosphatase (AKP) in gill and skin tissues, while qRT-PCR revealed higher expression of Muc-2 and IL-1β, as well as lower expression of IL-10. After Ichthyophthirius multifiliis challenge, goldfish fed the cMOS diet had lower mortality and infection rates, as well as fewer visible white spots on the body surfaces. Histologically, the gill and skin of these fish presented less tissue damage and fewer parasites, and had a greater number of mucus cells. In addition, the expression of Muc-2 and IL-10 were notably higher while the expression of IL-1β was significantly lower in cMOS fed goldfish than control fed fish. In this study, cMOS fed goldfish had stronger immune barrier function of skin and gill mucous, and better survival following Ichthyophthirius multifiliis infection.

Expression of cytokine genes at tick attachment and control sites of Namaqua Afrikaner, Dorper and South African Mutton Merino sheep

Cytokines are immune response components important in innate immunity and inflammatory response. They are harnessed as part of local immunological responses by animals to combat local infections and/or infestations. This study investigated expression of four selected cytokine genes, namely, interleukin 1 beta (IL-1β), chemokine C-C ligand 2 (CCL2), chemokine C-C ligand 26 (CCL26) and interleukin 8 (IL-8), at tick attachment and control sites in a South African indigenous sheep breed the Namaqua Afrikaner (NA) and two commercial breeds, the Dorper and South African Mutton Merino (SAMM). The NA was previously shown to be more resistant to infestation by ticks than the two commercial breeds. NA ewes expressed IL-1β more at tick attachment sites compared to Dorpers. The NA breed was also more likely to upregulate the expression of the CCL2, CCL26 and IL-8 genes at tick attachment sites compared to control sites than the other breeds. The results of this study gave an indication that cytokines are involved in immune responses to tick challenge and laid a foundation for further studies under controlled challenge conditions.

Innate cell-mediated cytotoxicity of CD8+ T cells against the protozoan parasite Ichthyophthirius multifiliis in the ginbuna crucian carp, Carassius auratus langsdorfii

Cytotoxic T cells are known to have the ability to kill microbe-infected host cells, which makes them essential in the adaptive immunity processes of various vertebrates. In this study, we demonstrated innate cell-mediated cytotoxicity of CD8⁺ T cells against protozoan parasites found in the ginbuna crucian carp. When isolated effector cells such as CD8⁺, CD4⁺ (CD4-1⁺), or CD8^- CD4^- (double-negative, DN), from naïve ginbuna crucian carp were co-incubated with target parasites (Ichthyophthirius multifiliis), CD8⁺ cells from the kidney and gill showed the highest cytotoxic activity. On the other hand, DN cells, which include macrophages and CD4^- CD8^- lymphocytes, showed the lowest cytotoxic activity against I. multifiliis. Additionally, the cytotoxic activity of CD8⁺ cells was found to significantly decrease in the presence of a membrane separating the effector cells from I. multifiliis. Furthermore, the serine protease inhibitor 3,4-dichloroisocoumarin and perforin inhibitor concanamycin A significantly inhibited the cytotoxic activity of CD8⁺ cells. These results demonstrate that CD8⁺ T cells of ginbuna crucian carp can kill extracellular parasites in a contact-dependent manner via serine proteases and perforin. Therefore, we conclude that CD8⁺ T cells play an essential role in anti-parasite innate immunity of teleost fish.

Transcriptomic profiling revealed key signaling pathways for cold tolerance and acclimation of two carp species

Background

Closely related species of the carp family (Cyprinidae) have evolved distinctive abilities to survive under cold stress, but molecular mechanisms underlying the generation of cold resistance remain largely unknown. In this study, we compared transcriptomic profiles of two carp species to identify key factors and pathways for cold tolerance and acclimation.

Results

Larvae of Songpu mirror carp and Barbless carp that were pretreated at 18 °C for 24 h significantly improved their survival rates under lethal cold temperature at 8 °C or 10 °C, indicating that two carp species possess the ability of cold acclimation. However, Songpu mirror carp exhibited stronger abilities of cold tolerance and acclimation than Barbless carp. Transcriptomic profiles of Songpu mirror carp and Barbless carp larvae at 28 °C and 18 °C were compared during cold acclimation through RNA-seq. Differentially expressed genes that are closely associated with the differences in cold acclimation between two carp species were identified through bioinformatics and Venn’s diagram analysis. GO enrichment analysis of these genes indicated that cellular component assembly involved in morphogenesis, secondary alcohol metabolism and drug transport were the most up-regulated biological processes during cold acclimation of Songpu mirror carp. Conversely, positive regulation of macroautophagy, intracellular protein transport, and organonitrogen compound catabolism were the most down-regulated biological processes during cold acclimation of Barbless carp. KEGG enrichment analysis revealed that factors in the FoxO-related signaling pathways are mainly responsible for the development of differences in cold tolerance and acclimation between two carp species since altering the phosphorylation of key proteins in the FoxO-related signaling pathways with inhibitors or an activator significantly decreased the cold tolerance and acclimation of Songpu mirror carp. These data provided key clues for dissection of molecular mechanisms underlying the development of cold tolerance and acclimation in carps.

Conclusions

These findings indicate that larvae of two carp species possess different abilities of cold tolerance and can build cold acclimation under mild low temperature. Multiple biological processes and FoxO-related signaling pathways are closely associated with the development of differences in cold tolerance and acclimation between two carp species.

The nature and consequences of co-infections in tilapia: A review

Co-infections commonly arise when two or multiple different pathogens infect the same host, either as simultaneous or as secondary concurrent infection. This potentiates their pathogenic effects and leads to serious negative consequences on the exposed host. Numerous studies on the occurrence of the bacterial, parasitic, fungal and viral co-infections were conducted in various tilapia species. Co-infections have been associated with serious negative impacts on susceptible fish because they increase the fish susceptibility to diseases and the likelihood of outbreaks in the affected fish. Co-infections can alter the disease course and increase the severity of disease through synergistic and, more rarely, antagonistic interactions. In this review, reports on the synergistic co-infections and their impacts on the affected tilapia species are highlighted. Additionally, their pathogenic mechanisms are briefly discussed. Tilapia producers should be aware of the possible occurrence of co-infections and their effects on the affected tilapia species and in particular of the clinical signs and course of the disease. To date, there is still limited information regarding the pathogenicity mechanisms and pathogen interactions during these co-infections. This is generally due to low awareness regarding co-infections, and in many cases, a dominant pathogen is perceived to be of vital importance and hence becomes the target of treatment while the treatment of the co-infectious agents is neglected. This review article aimed at raising awareness regarding co-infections and helping researchers and fish health specialists pay greater attention to these natural cases, leading to increased research and more consistent diagnosis of co-infectious outbreaks in order to improve control strategies to protect tilapia when infected with multiple pathogens.

Comprehensive transcriptional changes in the liver of Kanglang white minnow (Anabarilius grahami) in response to the infection of parasite Ichthyophthirius multifiliis

Simple Summary

Kanglang white minnow (KWM, Anabarilius grahami), is a typical “3E” (Endangered, Endemic and Economic) fish species in Yunnan-Guizhou Plateau. As one of the traditional “Four Famous Fishes” in Yunnan province, it has become the major local aquaculture species with increasing demand after the success of artificial breeding. However, this economically important fish is highly susceptible to the infection of a parasite ciliate, Ichthyophthirius multifiliis (Ich), during the practical procedure of artificial breeding. To examine the host immune responses to Ich, we divided the experimental fishes into three groups (including control, early-infected stage, and late-infected stage) for transcriptome sequencing to analyze the differentially expressed genes (DEGs) and immune response mechanisms.

Abstract

The notorious parasite Ichthyophthirius multifiliis (Ich) has been recorded worldwide in fish species and causes white spot disease, posing major threats and resulting in severe losses to international fish production. Extensively effective strategies for treating Ich are not available yet, and genetic mechanisms of hosts in response to the parasite are still largely unknown. In this study, we selected Kanglang white minnow (KWM, Anabarilius grahami) to examine its liver transcriptional changes after Ich infection, as white spot disease is one bottleneck problem in exploring this economically important species. We divided the experimental fishes into three groups (control, early-infected, and late-infected) to examine differentially expressed genes (DEGs). A total of 831 DEGs were identified and classified into 128 significantly enriched GO (Gene Ontology) terms and 71 significantly enriched KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. Most of these terms or pathways were functionally enriched in immunity, inflammatory response, and apoptosis, such as nucleotide-binding oligomerization domain-like (NOD-like) receptor signaling, tumor necrosis factor (TNF) signaling, interleukin-17 (IL-17) signaling, and apoptosis pathways. We also identified 178 putative antimicrobial peptides (AMPs) and AMP precursors based on our previously reported genome assembly of KWM, and revealed that the expressional patterns varied according to different types. In summary, our work reported the first comprehensive transcriptional changes in KWM in response to the exogenous infection of Ich, which would lay a solid foundation for in-depth studies on disease defense or resistant strains selection in this valuable fish.

β-Glucan improves wound healing in silver catfish (Rhamdia quelen)

The immune modulating activity of β-glucan on aquatic species has been a matter of intense investigation. Here, we aimed to investigate the effect of β-glucan on wound healing of silver catfish, a Neotropical South American scale-free fish. Small sections of skin and muscle (3 mm in diameter) were removed and fish were bathed daily with β-glucan (0.1% and 0.5%) up to 28 days when cicatrization was complete. A group of fish similarly injured and non-exposed to β-glucan was used as control. Wound closure and healing was monitored visually and by histopathological analysis. In fish bathed with 0.5% β-glucan we found reduced blood cortisol levels at day one post-wounding and, by day 7 post wounding, the deposition of granulation tissue was higher compared to non-exposed fish. In addition, from day 7 forward, wound size was significantly lower in fish bathed with 0.5% β-glucan. Histopathological analysis of the wounded site indicated a thin layer of immature epidermal cells at day one post wounding. A discrete inflammation with mixed inflammatory cell infiltrate was observed on wounded muscle and was lower by day 7 post wounding on fish bathed with 0.5% β-glucan. By day 14 post wounding, the deposition of collagen fibers and the presence of fibroblast and new muscle fibers were higher in fish exposed to 0.5% β-glucan, and dermis restoration was complete. Thus, our results indicate that in silver catfish wound healing occurs rapidly and improves greatly by daily bathing with β-glucan.

Immune responses of fish to Ichthyophthirius multifiliis (Ich): A model for understanding immunity against protozoan parasites

The parasitic ciliate Ichthyophthirius multifiliis (Ich), which infects almost all freshwater fish species, provides an optimal model for the study of immunity against extracellular protozoa. Ich invades the epithelia of mucosal tissues, forms white spots covering the whole body, and induces high mortality, while survivor fish develop both innate and adaptive immunity against Ich attack in systemic and mucosal tissues. Besides the protective roles of the Toll-like receptor (TLR)-mediated innate immune response, the critical immune functions of novel IgT in the skin, gut, gill, and olfactory organ of teleosts have been demonstrated in recent years, and all this information contributes to the ontogeny of the mucosal immune response in vertebrates. Especially in rainbow trout, Ich-infected fish exhibited higher IgT concentrations and titers in the mucosa and increased IgT⁺ B-lymphocyte proliferation in mucosal tissues. IgM mainly functions in the adaptive immune response in the systemic tissues of rainbow trout, accompanied with increased IgM⁺ B-lymphocyte proliferation in the head kidney of Ich-infected trout. However, little is known about the interaction between these mucosal tissues and systemic immune organs and the interaction between the inductive immune organs and functional immune organs. Immobilization antigens (Iags), located on the parasite cell and ciliary membranes, have been characterized to be targeted by specific antibodies produced in the host. The crosslinking of antigens mediated by antibodies triggers either an escape response or the immobilization of Ich. With more knowledge about the Iags of Ich and the immunity of teleosts, a more targeted vaccine, even a DNA vaccine, can be developed for the immune control strategy of Ich. Due to the high frequency of clinical fish ichthyophthiriasis, the study of fish immune responses to Ich provides an optimal experimental model for understanding immunity against extracellular protozoa.

Bisphenol S-induced chronic inflammatory stress in liver via peroxisome proliferator-activated receptor γ using fish in vivo and in vitro models

Bisphenol S (BPS) has been widely used as a bisphenol alternative in recent few years. However, with mounting evidence suggesting that the presence of BPS in the environment also poses risks to ecosystems and human health, we decided to use the juvenile common carp (Cyprinus carpio) and its primary macrophages as in vivo and in vitro models to examine if BPS is a safe substitute of BPA. The present study evaluated the immune responses of chronic BPS exposure and their mechanisms of action associated with peroxisome proliferator-activated receptor (PPAR) signaling pathway. Potential oxidative stress and pro-inflammatory effects of BPS exposure were identified in fish liver after 60-day exposure, based on the increased reactive oxygen species (ROS) production, antioxidant capacity, NO production, lipid peroxidation, and induction of inflammatory cytokine expression, as well as acute phase protein levels of C-reactive protein, immunoglobulin M, lysozyme, and complement component 3. Moreover, pparγ, PPAR pathway-associated genes retinoid x receptor α (rxrα) and nuclear factor-κb (nfκb) presented a rough concentration-dependent alteration after BPS exposure. An acute BPS exposure to the isolated primary macrophages from juvenile common carp was performed to help elucidate gene expression patterns of pparγ, rxrα, and nfκb in a typical immune cell model, the results were consistent with what we found in vivo experiments for long-term BPS exposure. Furthermore, with coexposure to BPS and a PPARγ antagonist, the restriction of PPAR signaling pathway significantly inhibited the induction of ROS and the mRNA level of interleukin-1β, confirming the involvement of PPAR pathway in BPS-induced chronic inflammatory stress in liver.

Transcriptomic analysis of immunity in rainbow trout (Oncorhynchus mykiss) gills infected by Ichthyophthirius multifiliis

The parasite Ichthyophthirius multifiliis infecting skin, fins and gills of a wide range of freshwater fish species, including rainbow trout, is known to induce a protective immune response in the host. Although a number of studies have reported activation of several immune genes in infected fish host, the immune response picture is still considered incomplete. In order to address this issue, a comparative transcriptomic analysis was performed on infected versus uninfected rainbow trout gills and it showed that a total of 3352 (7.2%) out of 46,585 identified gene sequences were significantly regulated after parasite infection. Of differentially expressed gene sequences, 1796 genes were up-regulated and 1556 genes were down-regulated. These were classified into 61 Gene Ontology (GO) terms and mapped to 282 reference canonical pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Infection of I. multifiliis induced a clear differential expression of immune genes, related to both innate and adaptive immunity. A total of 268 (6.86%) regulated gene sequences were known to take part in 16 immune-related pathways. These involved pathways related to the innate immunity such as the Chemokine signaling pathway, Platelet activation, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, and Leukocyte transendothelial migration. Elevated transcription of genes encoding the TLR 8 gene and chemokines (CCL4, CCL19, CCL28, CXCL8, CXCL11, CXCL13, CXCL14) was recorded indicating their roles in recognition of I. multifiliis and subsequent induction of the inflammatory response, respectively. A number of upregulated genes in infected gills were associated with antigen processing/presentation and T and B cell receptor signaling (including B cell marker CD22 involved in B cell development). Overall the analysis supports the notion that I. multifiliis induces a massive and varied innate response upon which a range of adaptive immune responses are established which may contribute to the long lasting protection of immunized rainbow trout.

Association between adaptive immunity and neutrophil dynamics in zebrafish (Danio rerio) infected by a parasitic ciliate

The protective immune response in zebrafish (Danio rerio) against the parasitic ciliate Ichthyophthirius multifiliis, targeting host skin, fins and gills, comprises an accelerated and manifold elevated immunoglobulin gene expression as well as a significantly elevated number of neutrophils at infected sites. Experimental fish were subjected to a primary I. multifiliis infection followed by a series of secondary exposures before they were challenged by a high dosage of infective theronts. Immunized fish responded immediately with a protective response suggesting existence of immunological memory whereas fish exposed to the parasite for the first time obtained a marked infection. The primary response to infection was dominated by expression of genes encoding acute phase reactants and inflammatory cytokines as well as recruitment of neutrophils at infected locations. Immunized fish showed a significantly upregulated immunoglobulin gene expression following challenge, which indicates existence of a secondary response effected by antibodies. Both responses induced a significantly elevated expression of the Th2 signature cytokine Il13. The increased presence of neutrophils in immunized fish suggests that innate cell mediated immunity supplements or influence the protective response against the parasite.

Generation and functional evaluation of a DNA vaccine co-expressing Cyprinid herpesvirus-3 envelope protein and carp interleukin-1 beta

Cyprinid herpesvirus 3 (CyHV-3) infection in carp causes a fatal and highly contagious disease that results in huge economic losses in common and koi carp aquaculture worldwide. Thus the development of an effective vaccine to protect carp stocks against the CyHV3 virus is imperative. In this study, we immunized common carps with a DNA vaccine consisting of a plasmid that co-expresses the CyHV-3 envelope protein ORF25 and the carp IL-1β gene in order to evaluate the adjuvant potential of IL-1β. Our result shows that antibodies specific to ORF25 can be detected as early as one week after intramuscular injection of the DNA vaccine at low dosage. Moreover, the co-expression of IL-1β can enhance the potency of the vaccine, as demonstrated by a higher antibody level after the third immunizations. Importantly, the DNA vaccine reduced mortality in carps when they were immunized prior to a CyHV-3 challenge, as compared to negative control groups. However, despite being able to induce higher neutralizing antibody titres, the co-expression of IL-1β in the DNA vaccine did not significantly improve the overall survival of immunized fish following virus challenge. Furthermore, the DNA vaccine can protect carps from tissue damage and histopathological alteration caused by viral infection. These strongly suggests that the vaccine can efficiently elicit protective immunity against CyHV-3 infection. In conclusion, the DNA vaccine formulated with the pIRES-ORF25-IL-1β DNA construct can protect carp against CyHV-3 infection and has potential applicability in the aquaculture industry.

The in vivo action of chronic bisphenol F showing potential immune disturbance in juvenile common carp (Cyprinus carpio)

Bisphenol F (BPF) has been increasingly introduced into industrial applications as a replacement for bisphenol A (BPA), and has emerged as a ubiquitous environmental contaminant worldwide. Few studies have assessed the in vivo toxicities of BPF, particularly long-term exposure toxicities. In the present study, we examined whether long-term BPF exposure in vivo would evoke oxidative stress in the immune system of juvenile common carp. The results suggested that BPF exposure increased ROS content, oxidative stress indices, complement component 3, and immunoglobulin M contents, as well as the expression of inflammatory cytokine genes. Moreover, higher levels of nf-κb p65 gene expression were correlated with the induced ROS content and NF-κB pathway-associated genes, a strong indication that the mode of action of BPF is related to the NF-κB signaling pathway. We also provide evidence that the effects of BPF are comparable to those of BPA with regards to regulation of the immune response in teleosts, and therefore suggest that such chemical analogs should be thoroughly evaluated for their potential toxicity before they can be considered as "safer" replacements.

Molecular identification of Trichodina compacta Van As and Basson, 1989 (Ciliophora: Peritrichia) from cultured Oreochromis niloticus in Egypt and its impact on immune responses and tissue pathology

Trichodinids are peritrichous ciliated protozoa that affect both wild and cultured fishes. Several Trichodina species have low host specificity and are morphologically distinct, facilitating their identification based primarily on the presence of adhesive discs and the number of attached denticles. A trichodinid species named Trichodina compacta was first reported by Van As and Basson (1989) (Protozoa: Ciliophora: Peritrichia). However, in trichodinid infestations, morphological characteristics are insufficient for identifying the infesting species. Therefore, molecular and phylogenetic analyses are considered to be promising and useful tools for identifying the infesting species. This study aimed to achieve the molecular identification of a trichodinid infestation in Nile tilapia and to construct the phylogenetic relationships between the identified species and other peritrichous parasites. Moreover, we also aimed to study the pathological and immunological impacts of trichodinids on fry tissue to improve our understanding of the immune responses of teleost fish to trichodinae parasitic infestations and develop a better control method. Here, we used molecular techniques to identify the isolated trichodina species as T. compacta and demonstrated that Trichodina infestation in Nile tilapia is associated with remarkable immunogenic and inflammatory responses (increased il-1β expression and decreased il-8 and tgf-β expression). These findings improve our understanding of the responses of teleost fish to trichodinid parasite infestation and will be helpful for the development of novel control strategies that reverse the inflammatory and immunogenic alterations that occur in infested fish.

Serum adenosine deaminase and xanthine oxidase activities in silver catfish naturally infected with Ichthyophthirius multifiliis: The influence of these enzymes on inflammatory and oxidative status

Adenosine deaminase (ADA) activity, through adenosine (Ado) levels, as well as xanthine oxidase (XO) activity through uric acid levels exerts an essential role on immune and inflammatory responses during infectious diseases. Thus, the aim of this study was to evaluate the involvement of seric ADA and XO activities in the inflammatory and oxidative status of silver catfish naturally infected with Ichthyophthirius multifiliis. Seric ADA activity decreased, while Ado levels increased in infected animals compared to uninfected animals. Moreover, the seric XO activity increased in infected animals compared to uninfected animals, alongside the seric levels of uric acid, metabolites of nitric oxide (NOx) and reactive oxygen species (ROS). Based on this evidence, the downregulation of seric ADA activity exerts an anti-inflammatory profile, contributing to restricting the inflammatory process. The most important finding is that upregulation of seric XO activity leads to an excessive formation of uric acid, which contributes to oxidative and inflammatory processes. Moreover, uric acid induces the release of pro-inflammatory and pro-oxidative mediators, such NOx and ROS, which contribute directly to disease pathogenesis. In summary, the upregulation of XO activity may be considered a pathway involved in NOx and ROS production in silver catfish infected with I. multifiliis.

Toxic Effects of Bisphenol S Showing Immunomodulation in Fish Macrophages

Bisphenol S (BPS), a structural analogue of bisphenol A (BPA), has been increasingly used as a common replacement of BPA due to health concerns regarding the former. However, mounting evidence suggests that BPS has similar endocrine-disrupting effects as BPA, and likewise, its presence in the environment may pose considerable risks to ecosystems and human health. Using fish primary macrophages (fpMQs), we here evaluated the immunomodulatory effects of BPS and its mechanisms of action associated with estrogen receptors (ERs). Following BPS exposure at environmentally relevant concentrations from 0.1 to 1000 μg/L, we observed approximate concentration-dependent increases in nitric oxide and reactive oxygen species generation and total antioxidant capacity as well as the gene expression of inflammatory cytokines in fpMQs. BPS impaired phagocytic capability but enhanced fpMQ activation levels in response to lipopolysaccharide stimulation and promoted apoptosis, indicating an impact on cell functions. At a concentration of 100 μg/L, BPS and BPA showed comparable pro-inflammatory potential with both up-regulating the production of free radicals and cytokine expression; however, BPS had no significant potency with regards to inducing lipid peroxidation and apoptosis, different from BPA's effects. Moreover, BPS induced both erα and erβ2 expression in fpMQs, whereas BPA induced only erα expression. This study demonstrates that, similarly to BPA, exposure to low doses of BPS significantly disturbs the immune response of fpMQs in vitro and first reveals overlapping but different roles of ERs in response to BPS and BPA.

Histopathological effects, responses of oxidative stress, inflammation, apoptosis biomarkers and alteration of gene expressions related to apoptosis, oxidative stress, and reproductive system in chlorpyrifos-exposed common carp (Cyprinus carpio L.)

In this study, we aimed to identify the toxic effects of chlorpyrifos exposure on the tissues of common carp. For this purpose, we evaluated histopathological changes in the brain, gills, liver, kidney, testis, and ovaries after 21 days of chlorpyrifos exposure. Activation of 8-OHdG, cleaved caspase-3, and iNOS were assesed by immunofluorescence assay in chlorpyrifos-exposed brain and liver tissue. Additionally, we measured the expression levels of caspase-3, caspase-8, iNOS, MT1, CYP1A, and CYP3A genes in chlorpyrifos-exposed brain tissue, as well as the expression levels of FSH and LH genes in chlorpyrifos-exposed ovaries, using qRT-PCR. We observed severe histopathological lesions, including inflammation, degeneration, necrosis, and hemorrhage, in the evaluated tissues of common carp after both high and low levels of exposure to chlorpyrifos. We detected strong and diffuse signs of immunofluorescence reaction for 8-OHdG, iNOS, and cleaved caspase-3 in the chlorpyrifos-exposed brain and liver tissues. Furthermore, we found that chlorpyrifos exposure significantly upregulated the expressions of caspase-3, caspase-8, iNOS, and MT1, and also moderately upregulated CYP1A and CYP3A in the brain tissue of exposed carp. We also noted downregulation of FSH and LH gene expressions in chlorpyrifos-exposed ovary tissues. Based on our results, chlorpyrifos toxication caused crucial histopathological lesions in vital organs, induced oxidative stress, inflammation, and apoptosis in liver and brain tissues, and triggered reproductive sterility in common carp. Therefore, we can propose that chlorpyrifos toxication is highly dangerous to the health of common carp. Moreover, chlorpyrifos pollution in the water could threaten the common carp population. Use of chlorpyrifos should be restricted, and aquatic systems should be monitored for chlorpyrifos pollution.

Transcriptomic profiling of Tibetan highland fish (Gymnocypris przewalskii) in response to the infection of parasite ciliate Ichthyophthirius multifiliis

Gymnocypris przewalskii is a native cyprinid in the Lake Qinghai of the Qinghai-Tibetan Plateau. G. przewalskii is highly susceptible to the infection of a parasite, Ichthyophthirius multifiliis, in the artificial propagation and breeding. To better understand the host immune reaction to I. multifiliis infection, we characterize the gene expression profiles in the spleen of healthy and I. multifiliis infected G. przewalskii by RNA-seq. Totally, the transcriptomic analysis produces 463,031,110 high quality reads, which are assembled to 213,538 genes with N50 of 1918 bp and the average length of 1205 bp. Of assembled genes, 90.52% are annotated by public databases. The expression analysis shows 744 genes are significantly changed by the infection of I. multifiliis, which are validated by qRT-PCR with the correlation coefficient of 0.896. The differentially expressed genes are classified into 689 GO terms and 230 KEGG pathways, highlighting the promoted innate immunity in I. multifiliis infected G. przewalskii at 2 days post infection. Our results pinpoint that the up-regulated genes are enriched in TLR signaling pathway, inflammatory response and activation of immune cell migration. On the contrary, complement genes are down-regulated, indicating the evasion of host complement cascades by I. multifiliis. The repressed genes are also enriched in the pathways related to metabolism and endocrine, suggesting the metabolic disturbance in I. multifiliis treated G. przewalskii. In summary, the present study profiles the gene expression signature of G. przewalskii in the responses to I. multifiliis infection, and improves our understanding on molecular mechanisms of host-parasite interaction in G. przewalskii, which focuses the crucial function of TLRs, cytokines and complement components in the host defense against I. multifiliis.

Cypermethrin toxication leads to histopathological lesions and induces inflammation and apoptosis in common carp (Cyprinus carpio L.)

Cypermethrin (Cyp), a known neurotoxic pesticide, is widely used in agricultural applications. In the present study, the aim was to determine the histopathological effects of Cyp toxication and evaluate the activation of inducible nitric oxide synthetase (iNOS) and 8-hydroxy-2-deoxyguanosine (8-OHdG) using an immunofluorescence assay. Thereafter, we identified the expressions of caspase 3, capsase 8, iNOS, and metallothionein 1 (MT1) genes in common carp using quantitative reverse transcription polymerase chain reaction (qRT-PCR). High and low doses of Cyp were administered to experimental groups for 24, 48, 72, and 96 h. As a result, necrotic neurons in different stages and desquamation of ependymal cells due to necrosis were detected in the brain. Histopathological changes, including hyperplasia of lamellar cells, telangiectasia of lamellae and thickening due to cellular infiltration in gills, hemorrhage, diffuse hydropic degeneration, and focal necrosis in the liver were observed in the experimental groups. Immunopositive reactions of 8-OHdG were clearly observed in the nuclei and cytoplasm of neurons, and positive reactions for iNOS were detected in the cytoplasm of neurons and in the glial cells of the experimental groups. Furthermore, we found that caspase 3, capsase 8, iNOS, and MT1 genes were up-regulated in the brain when exposed to both high and low doses of Cyp. In conclusion, our findings revealed that Cyp toxication harms the organs of common carp, particularly the brain, and also gives rise to inflammation, DNA damage, and apoptosis. Therefore, the use of Cyp should be restricted to protect the health of aquatic animals.

Transcriptomic variation of locally-infected skin of Epinephelus coioides reveals the mucosal immune mechanism against Cryptocaryon irritans

Fish skin is the largest immunologically active mucosal organ, providing first-line defense against external pathogens. However, the skin-associated immune mechanisms of fish are still unclear. Cryptocaryon irritans is an obligate ectoparasitic ciliated protozoan that infects almost all marine fish, and is believed to be an excellent pathogen model to study fish mucosal immunity. In this study, a de novo transcriptome assembly of Epinephelus coioides skin post C. irritans tail-infection was performed for the first time using the Illumina HiSeq™ 2500 system. Comparative analyses of infected skin (group Isk) and uninfected skin (group Nsk) from the same challenged fish and control skin (group C) from uninfected control fish were conducted. As a result, a total of 91,082 unigenes with an average length of 2880 base pairs were obtained and among them, 38,704 and 48,617 unigenes were annotated based on homology with matches in the non-redundant and zebrafish database, respectively. Pairwise comparison resulted in 10,115 differentially-expressed genes (DEGs) in the Isk/C group comparison (4,983 up-regulated and 5,132 down-regulated), 2,275 DEGs in the Isk/Nsk group comparison (1,319 up-regulated and 956 down-regulated) and 4,566 DEGs in the Nsk/C group comparison (1,534 up-regulated and 3,032 down-regulated). Seven immune-related categories including 91 differentially-expressed immune genes (86 up-regulated and 5 down-regulated) were scrutinized. Both DEGs and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and immune-related gene expression analysis were used, and both analyses showed that the genes were more significantly altered in the locally-infected skin than in the uninfected skin of the same challenged fish. This suggests the skin's local immune response is important for host defense against this ectoparasite infection. Innate immune molecules, including hepcidin, C-type lectin, transferrin, transferrin receptor protein, serum amyloid A, cathepsin and complement components were significantly up-regulated (fold-change ranged from 3.3 to 12,944) in infected skin compared with control skin. The up-regulation of chemokines and chemokine receptors and activation of the leukocyte transendothelial migration pathway suggested that leucocytes intensively migrated to the local infected sites to mount a local immune defense. Toll-like receptors (TLRs) 1, 2, 5 and 5S were most significantly up-regulated in the infected skin, suggesting that these TLRs may be involved in parasite pathogen-associated molecular pattern (PAMPs) recognition. Up-regulation of the dendritic cell markers CD209 and CD83 and other antigen presentation pathway molecules provided evidence for skin local antigen presentation. Up-regulation of the T cell markers CD4 and CD48, B cell markers CD22 and CD81 and B cell receptor signaling kinase Lyn, showed the presence and population expansion of T/B cells at locally-infected sites, which suggested possible activation of a local specific immune response in the skin. Our results will facilitate in-depth understanding of local immune defense mechanisms in fish skin against ectoparasite infection.

Expression of immune genes in systemic and mucosal immune tissues of channel catfish vaccinated with live theronts of Ichthyophthirius multifiliis

Ichthyophthiriasis caused by Ichthyophthirius multifiliis (Ich) has a worldwide distribution and affects most freshwater fishes. Fish surviving natural infection and/or immunized with Ich develop strong innate and adaptive immune responses. However, there is a lack of the knowledge regarding immune gene expression patterns in systemic and mucosal immune tissues, and how immune genes interact and lead to innate and adaptive immune protection against Ich infection in fish. The objective of this study was to investigate the expression of innate and adaptive immune-related genes in systemic (liver, spleen) and mucosal (gill, intestine) tissues of channel catfish over time following vaccination with live Ich theronts. The vaccinated fish showed significantly higher antibody titers and survival (95%) than those of mock immunized fish. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 h (h4) to 2 days (d2) post-vaccination in systemic immune tissues. Immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) were more highly upregulated and remained upregulated for longer duration in systemic tissues than in mucosal tissues of the vaccinated fish. The cytokine genes IL-1βa and IFN-γ were rapidly upregulated in both systemic and mucosal tissues of vaccinated fish, with peak expression from h4 to d1 post-vaccination. Toll-like receptor genes TLR-1 and TLR-9 showed relatively stable upregulation in the gill of immunized fish following vaccination. Results of this study revealed the molecular immune responses in mucosal and systemic tissues of vaccinated fish and demonstrated that Ich vaccination resulted in innate and adaptive immune responses against Ich infection.

Immune reactivity in early life stages of sea-cage cultured Pacific bluefin tuna naturally infected with blood flukes from genus Cardicola (Trematoda: Aporocotylidae)

Pacific bluefin tuna (PBT), Thunnus orientalis, due to its high average price on the market is an economically valuable fish species. Infections by blood flukes from the genus Cardicola (Trematoda: Aporocotylidae) represent a growing concern for the cage culture of bluefin tuna in Japan, Australia and Southern Europe. The accumulation of numerous Cardicola eggs in the fish gills causes severe pathology that has been linked to mortality in PBT juveniles up to one year old. The only effective treatment used to mitigate the infection is the oral administration of the antihelminthic drug praziquantel (PZQ) to the affected fish. However, with the need to minimise therapeutic drug use in aquaculture it is hoped that immunoprophylaxis can provide a future alternative to protect the PBT juveniles against Cardicola infection. Currently, little is known of the host immune response to these parasites and of their infection dynamics. In this study, using real-time qPCR we aimed to quantitatively detect C. orientalis and C. opisthorchis DNA within the gills and heart of cultured PBT juveniles and to investigate the host immune response at the transcriptional level in the gills. The research focused mainly during early stages of infection soon after young PBT were transferred to culture cages (from 14 to 77 days post-transfer). An increase (up to 11-fold) of immune-related genes, namely IgM, MHC-I, TCR-β and IL-1β was observed in the PBT gills infected with Cardicola spp. (28-77 days post-transfer). Furthermore, IgM (19-fold increase) and MHC-I (11.5-fold increase) transcription was strongly up-regulated in gill samples of PBT infected with C. orientalis relative to uninfected fish but not in fish infected with C. opisthorchis. Cardicola-specific DNA was first detected in the host 14 days post-transfer (DPT) to sea-cages which was 55 days earlier than the first detection of parasite eggs and adults by microscopy. Oral administration of PZQ did not have an immediate effect on parasite DNA presence in the host and the DNA presence started to reduce after 24 days only in the host heart. The results provide evidence of an immune response in early age sea-cage cultured juveniles of PBT naturally infected with C. orientalis and C. opisthorchis. This response, whilst not protective against primary infection, provides evidence that immunisation at an early age may have potential as a health strategy.

Infection and immunity against Ichthyophthirius multifiliis in zebrafish (Danio rerio)

Ichthyophthirius multifiliis, causing white spot disease, is a serious pathogen in aquaculture as well as for the ornamental fish industry. In carp, channel catfish and rainbow trout the immune responses against the parasite have been partly elucidated and these species are able to acquire a high level of immunity against the disease. Zebrafish are however, known to be more resilient towards the disease than channel catfish but the pathology and the ability to obtain protection is unknown. In this study a primary infection in the gills of zebrafish was described and the subsequent acquirement of immunity was evaluated. The parasites in the gills induced hyperplasia, an increase of mucus cells, adhesion and shortening of the secondary lamellae, narrowing of water channels and proliferation. The parasite burden was significantly lower in survivor fish and where all naive fish died within 6 days following secondary infection (challenge) only one of the survivor fish died. This study demonstrates that zebrafish are susceptible to I. multifiliis and that gill pathology is similar to the situation observed in rainbow trout. Furthermore, zebrafish are able to acquire immunity against white spot disease and may therefore be a suitable model organism to study innate and protective immunology and host/parasite interactions during I. multifiliis infections.

The dynamics of neutrophils in zebrafish (Danio rerio) during infection with the parasite Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is a ciliated protozoan parasite infecting the skin and gills of freshwater fish. Neutrophils are attracted to the infection sites, as a part of the innate immune response. In this study a transgenic line of zebrafish (Tg(MPO:GFP)(i114)) with GFP-tagged neutrophils was infected with I. multifiliis and the neutrophil influx in the caudal fin was quantified. Twenty-four hours post infection (pi) the neutrophil count had gone up with an average of 3.4 fold. Forty-eight h pi the neutrophil count had dropped 12% and 72 h pi it had dropped to 21% compared to 24 h pi. At 72 h pi the neutrophil count was 2.7 times higher than prior to infection. A few dead parasites were observed, which were disintegrated and covered internally and externally with neutrophils. Live parasites, both surrounded by neutrophils and with no neutrophils in the near vicinity, were found during the infection. Neutrophils interacted directly with the parasites with pseudopod formation projecting towards the pathogen. These results indicate a strong innate immune response immediately following infection and/or a subsequent immune evasion by the parasite.

Molecular immune response of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

The parasite Ichthyophthirius multifiliis (Ich) has been reported in various freshwater fishes worldwide and results in severe losses to both food and aquarium fish production. The fish surviving natural infections or immunized with live theronts develop strong specific and non-specific immune responses. Little is known about how these immune genes are induced or how they interact and lead to specific immunity against Ichthyophthirius multifiliis in channel catfish Ictalurus punctatus. This study evaluated the differential expression of immune-related genes, including immunoglobulin, immune cell receptor, cytokine, complement factor and toll-like receptors in head kidney from channel catfish at different time points after immunization with live theronts of I. multifiliis. The immunized fish showed significantly higher anti-Ich antibody expressed as immobilization titer and ELISA titer than those of control fish. The vast majority of immunized fish (95%) survived theront challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hour (h4) to 2 days (d2) post immunization. Expression of immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) showed up-regulation from h4 to d6 post immunization, indicating that different immune cells were actively involved in cellular immune response. Cytokine gene expression (IL-1βa, IL-1βb, IFN-γ and TNF-α) increased rapidly at h4 post immunization and were at an up-regulated level until d2 compared to the bovine serum albumin control. Expression of complement factor and toll-like receptor genes exhibited a rapid increase from h4 to d2 post immunization. Results of this study demonstrated differential expression of genes involved in the specific or non-specific immune response post immunization and that the vaccination against Ich resulted in protection against infection by I. multifiliis.

Expression Profile Analysis of miR-221 and miR-222 in Different Tissues and Head Kidney Cells of Cynoglossus semilaevis, Following Pathogen Infection

Half-smooth tongue sole (Cynoglossus semilaevis) is an important marine commercial fish species in China, which suffers from widespread disease outbreaks. Recently, in this regard, our group identified immune-related microRNAs (miRNAs) of C. semilaevis following Vibrio anguillarum infection. Furthermore, miRNA microarray was utilized to characterize the immune roles of important miRNA candidates in response to bacterial infection. Therefore, in the present study, we characterized miR-221 and miR-222 and profiled their expression after challenge. Here, miR-221 and miR-222 precursors were predicted to have a typical hairpin structure. Both miRNAs were expressed in a broad range of tissues in C. semilaevis, while miR-221 and miR-222 were significantly differentially expressed in the immune tissues of C. semilaevis among three small RNA libraries [control group (CG), bacteria-challenged fish without obvious symptoms of infection (NOSG), and bacteria-challenged fish with obvious symptoms of infection (HOSG)]. In order to further characterize and understand the immune response of miR-221 and miR-222, therefore, we profiled miR-221 and miR-222 expression in selected immune tissues after challenge with V. anguillarum. Both miR-221 and miR-222 were upregulated in the liver and spleen, while different expression patterns were observed in the head kidney. In addition, in half-smooth tongue sole head kidney cell line after challenge with lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (poly I:C), peptidoglycan (PGN), and red-spotted grouper nervous necrosis virus (RGNNV), both miR-221 and miR-222 showed significant difference in expression response to pathogen. Meanwhile, the target gene of miR-221 and miR-222 was predicted, which indicated that tumor necrosis factor receptor-associated factor 6 (TRAF6) and interleukin-1 beta (IL-1β) were the target genes of miR-221 and miR-222, respectively. Collectively, these findings indicated that miR-221 and miR-222 have putative roles in innate immune response during C. semilaevis exposure to pathogens. Our findings could expand the knowledge of immune function of C. semilaevis miRNA and guide future studies on C. semilaevis immunity.

Transcriptomic analysis of koi (Cyprinus carpio) spleen tissue upon cyprinid herpesvirus 3 (CyHV3) infection using next generation sequencing

Cyprinid Herpesvirus 3 (CyHV-3) can infect and specifically cause a huge economic loss in both common carp (Cyprinus carpio) and its ornamental koi variety. The molecular mechanisms underlying CyHV-3 infection are not well understood. In this study, koi spleen tissues of both mock and CyHV-3 infection groups were collected, and high-throughput sequencing technology was used to analyze the differentially expressed genes (DEGs) at the transcriptome level. A total of 105,356,188 clean reads from two libraries were obtained. After the de novo assembly of the transcripts, 129,314 unigenes were generated. Of these unigenes, 70,655 unigenes were matched to the known proteins in the database, while 2190 unigenes were predicted by ESTScan software. Comparing the infection group to the mock group, a total of 23,029 significantly differentially expressed unigenes were identified, including 10,493 up-regulated DEGs and 12,536 down-regulated DEGs. GO (Gene Ontology) annotation and functional enrichment analysis indicated that all of the DEGs were annotated into GO terms in three main GO categories: biological process, cellular component and molecular function. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis of the DEGs showed that a total of 12,002 DEG unigenes were annotated into 256 pathways classified into 6 main categories. Additionally, 20 differentially expressed genes were validated by quantitative real-time PCR. As the first report of a transcriptome analysis of koi carp with CyHV-3 infection, the data presented here provide knowledge of the innate immune response against CyHV-3 in koi carp and useful data for further research of the molecular mechanism of CyHV-3 infection.

The in vitro immune modulatory effect of bisphenol A on fish macrophages via estrogen receptor α and nuclear factor-κB signaling

Bisphenol A (BPA) is a well-known environmental endocrine-disrupting chemical. Employing primary macrophages from head kidney of red common carp (Cyprinus carpio), the present study aimed to evaluate the immune modulatory effect of BPA and to explore its potential action mechanism associated with estrogen receptor (ER) and nuclear factor-κB (NF-κB) pathways. A dynamic response process was observed in macrophages upon various concentrations of BPA exposure, which significantly enhanced the antibacterial activity of macrophages at 0.1, 1, or 10 μg/L, but instead induced the apoptosis at 100, 1000, and 10,000 μg/L. A potential pro-inflammatory effect of BPA exposure was suggested, judging from the increased production of nitrite oxide and reactive oxygen species (ROS), the induction of interleukin-1β mRNA and protein, as well as NF-κB and other NF-κB-associated immune gene expression. Following BPA coexposure with the ER or NF-κB antagonist, the induction of ROS, ERα, and NF-κB-associated immune gene expression was significantly inhibited, implying interaction between those two pathways. This study thus indicated that low doses of BPA exposure alone could significantly disturb the immune response of fish primary macrophages in vitro, and for the first time revealed the synergistic action of ERα and NF-κB transcription factors in the BPA effect.

Skin immune response in the zebrafish, Danio rerio (Hamilton), to Aeromonas hydrophila infection: a transcriptional profiling approach

Skin plays an important role in innate immune responses to bacterial infection, but its molecular mechanism remains unclear in fish. The transcriptional profiling of the skin immune response to Aeromonas hydrophila infection of the zebrafish, Danio rerio (Hamilton), was performed by Affymetrix microarray analysis. The results showed that 538 genes were differentially expressed, of which 388 genes were up-regulated and 150 genes were down-regulated. The expression patterns for 106 representative genes were observed to be up-regulated in zebrafish skin at 24 and 36 h post-infection, and gene expression changes were clearly greater at 36 h. Gene Ontology classification indicated that 222 genes were significantly associated with the skin immunity, including complement activation, acute-phase response, stress response, chemotaxis and apoptosis. Further Kyoto Encyclopedia of Genes and Genomes analysis showed that the significant pathways included MAPK, p53, Wnt, TGF-β, Notch, ErbB, JAK-STAT, VEGF, mTOR and Calcium signalling in skin immune responses, and several genes (e.g. akt2l, frap1, nras, rac1, xiap) were found to be involved in signalling networks. Moreover, expression changes in nine selected genes were verified by real-time qPCR analysis. This is the first known report on transcriptome analysis in the skin of zebrafish against the pathogen A. hydrophila.

Sequence and expression analysis of rainbow trout CXCR2, CXCR3a and CXCR3b aids interpretation of lineage-specific conversion, loss and expansion of these receptors during vertebrate evolution

The chemokine receptors CXCR1-3 bind to 11 chemokines (CXCL1-11) that are clustered on the same chromosome in mammals but are largely missing in ray-finned fish. A second CXCR1/2, and a CXCR3a and CXCR3b gene have been cloned in rainbow trout. Analysis of CXCR1-R3 genes in lobe-finned fish, ray-finned fish and tetrapod genomes revealed that the teleostomian ancestor likely possessed loci containing both CXCR1 and CXCR2, and CXCR3a and CXCR3b. Based on this synteny analysis the first trout CXCR1/2 gene was renamed CXCR1, and the new gene CXCR2. The CXCR1/R2 locus was shown to have further expanded in ray-finned fish. In relation to CXCR3, mammals appear to have lost CXCR3b and birds both CXCR3a and CXCR3b during evolution. Trout CXCR1-R3 have distinct tissue expression patterns and are differentially modulated by PAMPs, proinflammatory cytokines and infections. They are highly expressed in macrophages and neutrophils, with CXCR1 and CXCR2 also expressed in B-cells.

Immunity to Ichthyophthirius infections in fish: a synopsis

Ichthyophthirius multifiliis is a ciliated protozoan parasite that infects freshwater fish. It has been the subject of both applied and basic research for over 100years, which can be attributed to its world-wide distribution and its significant economic impact on both food and aquarium fish production. I. multifiliis serves as a model for studies in fish on innate and acquired immunity, as well as on mucosal immunity. Although an obligate parasite, I. multifiliis is relatively easily passaged from infected to naïve fish in laboratory aquaria, and is easily observed and manipulated under laboratory conditions. It parasitizes the epithelia of the skin and gills, which facilitates in vivo experimentation and quantification of challenge. This review provides a description of both mucosal and systemic innate and adaptive immune responses to parasite infection, a synopsis of host-parasite immunobiology, vaccine research, and suggested areas for future research to address critical remaining questions. Studies in carp and rainbow trout have shown that extensive tissue damage occurs when the parasite invades the epithelia of the skin and gills and substantial focal and systemic inflammatory responses are elicited by the innate immune response. The adaptive immune response is initiated when phagocytic cells are activated by antigens released by the parasite. It is not known whether activated T and B cells proliferate locally in the skin and gills following infection or migrate to these sites from the spleen or anterior kidney. I. multifiliis infection elicits both mucosal and systemic antibody production. Fish that survive I. multifiliis infection acquire protective immunity. Memory B cells provide long-term humoral memory. This suggests that protective vaccines are theoretically possible, and substantial efforts have been made toward developing vaccines in various fish species. Exposure of fish to controlled surface infections or by intracoelomic injection of live theronts provides protection. Vaccination with purified immobilization antigens, which are GPI-anchored membrane proteins, also provides protection under laboratory conditions and immobilization antigens are currently the most promising candidates for subunit vaccines against I. multifiliis.

Interleukin gene expression is strongly modulated at the local level in a fish-parasite model

The goal of this work was to identify interleukin (IL)-related genes in the gilthead sea bream (GSB) (Sparus aurata L.) and how they are modulated by the parasite Enteromyxum leei, a myxozoan that causes severe enteritis with a strong inflammatory response. A Blast-X search of our transcriptomic GSB database (www.nutrigroup-iats.org/seabreamdb) identified 16 new sequences encompassing seven ILs (IL-7, IL-8, IL-10, IL-12β, IL-15, IL-18, and IL-34), the interleukin enhancer-binding factor 2 (ILF2), and eight IL receptors (IL-R); IL-R1, IL-6RA, IL-6RB, IL-8RA, IL-10RA, IL-10RB, IL-18R1, and IL-22R. Except for ILF2, their expression, plus that of IL-1β, IL-1R2, IL-6, and TNF-α (from public repositories), were analysed by 96-well PCR array of samples of blood, spleen, head kidney, and intestine of GSB that were anally intubated with E. leei (recipient group, RCPT). Only the expression profile of the intestine of RCPT fish showed significant difference as compared to samples from PBS-inoculated fish. At 17 days post intubation (dpi), the expression of key pro-inflammatory ILs, such as IL-8, IL-8R, IL-12β, and TNFα was significantly up-regulated, whereas at 64 dpi, anti-inflammatory IL expression (IL-6, IL-6RB, IL-7, IL-10, IL-10RA, and IL-15) was predominant. These results indicate a modification of the IL expression at late times post infection, probably to protect the fish intestine from the parasite and damage inflicted by an excessive inflammatory response. Furthermore, the response is mainly mediated at the local level as no significant changes were detected in blood, spleen and head kidney.

Expression of immune system-related genes during ontogeny in experimentally wounded common carp (Cyprinus carpio) larvae and juveniles

We investigated the effect of full-thickness incisional wounding on expression of genes related to the immune system in larvae and juveniles of common carp (Cyprinus carpio). The wounds were inflicted by needle puncture immediately below the anterior part of the dorsal fin on days 7, 14, 28 and 49 after fertilization. We followed the local gene expression 1, 3 and 7 days after wounding by removing head and viscera before extracting RNA from the remaining part of the fish, including the wound area. In addition, we visually followed wound healing. Overall the wounds had regenerated to a point where they were microscopically indistinguishable from normal tissue by day 3 post-wounding in all but the juvenile carp wounded on day 49 post-fertilization. In these juveniles the wounded area was still visible even 7 days post-wounding. On the transcriptional level a very limited response was observed in the investigated genes as a result of the wounding. HSP70 was downregulated 1 and 3 days post-wounding in the smallest larvae. However, HSP70 was differentially expressed at different time-points in a similar manner in wounded and mock-wounded groups, thus suggesting a stress effect of the handling, which may have overshadowed some transcriptional effects of the wounding. MMP-9, TGF-β1 and IgZ1 were slightly but significantly upregulated at few time-points, while no effect of wounding was detected on the expression of IgM, C3, IL-1β and IL-6 family member M17.

β-Glucan-supplemented diets increase poly(I:C)-induced gene expression of Mx, possibly via Tlr3-mediated recognition mechanism in common carp (Cyprinus carpio)

We have previously observed that in common carp (Cyprinus carpio), administration of β-glucan (MacroGard®) as feed additive leads to a lower expression of pro-inflammatory cytokines suggesting that this immunostimulant may be preventing an acute and potentially dangerous response to infection, particularly in the gut. However, in general, mechanisms to detect and eliminate pathogens must also be induced in order to achieve an efficient clearance of the infection. Protection against viral diseases acquired through β-glucan-supplemented feed has been extensively reported for several experimental models in fish but the underlining mechanisms are still unknown. Thus, in order to better characterize the antiviral action induced by β-glucans in fish, MacroGard® was administered daily to common carp in the form of supplemented commercial food pellets. Carp were fed for a period of 25 days prior to intra-peritoneal injection with polyinosinic:polycytidylic acid (poly(I:C)), a well-known double-stranded RNA mimic that triggers a type-I interferon (IFN) response. Subsequently, a set of immune related genes, including mx, were analysed by real-time PCR on liver, spleen, head kidney and mid gut tissues. Results obtained confirmed that treatment with β-glucan alone generally down-regulated the mRNA expression of selected cytokines when compared to untreated fish, while mx gene expression remained stable or was slightly up-regulated. Injection with poly(I:C) induced a similar down-regulated gene expression pattern for cytokines in samples from β-glucan fed fish. In contrast, poly(I:C) injection markedly increased mx gene expression in samples from β-glucan fed fish but hardly in samples from fish fed control feed. In an attempt to explain the high induction of mx, we studied Toll-like receptor 3 (TLR3) gene expression in these carp. TLR3 is a prototypical pattern recognition receptor considered important for the binding of viral double-stranded RNA and triggering of a type-I IFN response. Through genome data mining, two sequences for carp tlr3 were retrieved (tlr3.1 and tlr3.2) and characterized. Constitutive gene expression of both tlr3.1 and tlr3.2 was detected by real-time PCR in cDNA of all analysed carp organs. Strikingly, 25 days after β-glucan feeding, very high levels of tlr3.1 gene expression were observed in all analysed organs, with the exception of the liver. Our data suggest that β-glucan-mediated protection against viral diseases could be due to an increased Tlr3-mediated recognition of ligands, resulting in an increased antiviral activity of Mx.

MH II-DAB gene expression in grass carp Ctenopharyngodon idella (Valenciennes) after infection with the ciliate parasite, Ichthyophthirius multifiliis

The grass carp, Ctenopharyngodon idella (Valenciennes), is one of the most extensively aquacultured freshwater fish in China. However, because of the lack of effective control measures and the high-density culture environment, considerable economic losses are caused by infection of C. idella with the parasitic ciliate, Ichthyophthirius multifiliis. The major histocompatibility (MH) DAB gene belongs to antigen-presented genes in the class II genomic region, which is associated with parasite resistance. To understand the relationship of the DAB gene with I. multifiliis infection in grass carp, the expression profiles of MH II-DAB were studied in tissues using real-time quantitative polymerase chain reaction. The results showed that expression of the MH II-DAB gene was up-regulated in head kidney after I. multifiliis infection, and the expression peak appeared earlier in the study (case) group than in the control group. The obvious up-regulation peak of MH II-DAB gene was found at days 2 and 4 in skin; at 12 h to day 4 in spleen; at 12 h and days 1 and 6 in gill; and at day 10 in blood, whereas the MH II-DAB gene was down-regulated in liver and intestines after I. multifiliis infection. These results have implications for better understanding C. idella resistance to I. multifiliis infection.

Probiotics-pathogen interactions elicit differential regulation of cutaneous immune responses in epidermal cells of Atlantic cod Gadus morhua

Little is known on the cutaneous immune responses during probiotics-pathogen interactions in fish. Thus, this study employed Atlantic cod primary epidermal (EP) cell cultures as a model to understand this interaction. The probiotics-pathogen interactions in the EP cell cultures were elucidated using Vibrio anguillarum 2133 (VA) as the pathogen and two host-derived bacteria (GP21 and GP12) as the probiotics. There was a regional size difference on the EP cells; i.e., EP cells from the dorsal region were significantly larger than the EP cells at the ventral side. VA significantly decreased viability of EP cells. In the presence of probiotics, this inhibition was mitigated. The probiotics reduced VA-induced cellular apoptosis and the probiotics-pathogen interactions influenced cellular myeloperoxidase activity during the latter stage of co-incubation. The probiotics-pathogen interactions triggered differential regulation of immune-related genes and the effects of the interaction were dependent on the region where the cells were isolated and the length of the co-incubation period. In most cases, the presence of probiotics alone showed no significant change on the mRNA level of immune genes in the EP cells but triggered immunostimulatory activity when incubated with VA. This study showed that the virulence of VA in EP cells could be modulated by host-derived probiotics and the immunomodulatory characteristics of the two candidate probionts advanced their immune-related probiotic potential.