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

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.

Transcriptome analysis and immune gene expression of channel catfish (Ictalurus punctatus) fed diets with inclusion of frass from black soldier fly larvae

The larval waste, exoskeleton shedding, and leftover feed components of the black soldier fly and its larvae make up the by-product known as frass. In this study, we subjected channel catfish (Ictalurus punctatus) to a 10-week feeding trial to assess how different dietary amounts of frass inclusion would affect both systemic and mucosal tissue gene expression, especially in regard to growth and immune-related genes. Fish were divided in quadruplicate aquaria, and five experimental diets comprising 0, 50, 100, 200, and 300 g of frass per kilogram of feed were fed twice daily. At the end of the trial, liver, head kidney, gill, and intestine samples were collected for gene expression analyses. First, liver and intestine samples from fish fed with a no frass inclusion diet (control), low-frass (50 g/kg) inclusion diet, or a high-frass (300 g/kg) inclusion diet were subjected to Illumina RNA sequencing to determine global differential gene expression among diet groups. Differentially expressed genes (DEGs) included the upregulation of growth-related genes such as glucose-6-phosphatase and myostatin, as well as innate immune receptors and effector molecules such as toll-like receptor 5, apolipoprotein A1, C-type lectin, and lysozyme. Based on the initial screenings of low/high frass using RNA sequencing, a more thorough evaluation of immune gene expression of all tissues sampled, and all levels of frass inclusion, was further conducted. Using targeted quantitative PCR panels for both innate and adaptive immune genes from channel catfish, differential expression of genes was identified, which included innate receptors (TLR1, TLR5, TLR9, and TLR20A), proinflammatory cytokines (IL-1β type a, IL-1β type b, IL-17, IFN-γ, and TNFα), chemokines (CFC3 and CFD), and hepcidin in both systemic (liver and head kidney) and mucosal (gill and intestine) tissues. Overall, frass from black soldier fly larvae inclusion in formulated diets was found to alter global gene expression and activate innate and adaptive immunity in channel catfish, which has the potential to support disease resistance in this species in addition to demonstrated growth benefits.

Characterization of digenetic trematodes infecting African catfish (Clarias gariepinus) based on integrated morphological, molecular, histopathological, and immunological examination

Parasitic infection may cause massive losses in Clarias gariepinus fries and fingerlings. Therefore, this study aimed to characterize the digenetic trematodes species (two adults' flukes and one metacercariae) infecting African catfish Clarias gariepinus, as well as their histopathological impacts on infected fish. The intestinal flukes were identified as Orientocreadium batrachoides and Masenia bangweulensis based on their morphological and molecular characteristics. Sequencing of their 28S (LSU rRNA) and 18S rRNA (SSU rRNA) genes confirmed that these trematodes belong to the families Orientocreadiidae and Cephalogonimidae, respectively. The metacercariae trematode infecting skin and muscles were only morphologically identified as Cyanodiplostomum sp. The gene expression levels of MHC II increased in naturally infected fish either with O. batrachoides or Cyanodiplostomum sp. alone, compared with uninfected catfish. In addition, lysozyme levels in individual fish serum increased in catfish infected either with O. batrachoides or Cyanodiplostomum sp. alone. Histopathological examination of the skin revealed embedded parasitic cysts that displaced tissue in the dermis. Surrounding tissues were infiltrated with melanomacrophages and displayed dermal edema. Histopathological analysis showed O. batrachoides or M. bangweulensis between the gastric folds of the stomach of infected catfish, causing infiltration of mononuclear inflammatory cells in the lamina propria.

Dose effects of a DNA vaccine encoding immobilization antigen on immune response of channel catfish against Ichthyophthirius multifiliis

Channel catfish (Ictalurus punctatus) vaccinated with pcDNA3.1-IAg52b plasmid DNA vaccine encoding immobilization antigen genes of Ichthyophthirius multifiliis (Ich) produced anti-Ich antibodies and were partially protected (20% survival) in a previous study. Here we evaluated whether a higher dose or two doses of pcDNA3.1-IAg52b vaccine could provide better protection for catfish against Ich. Fish were distributed into 6 groups and vaccinated using following schemes: 1.10 μg pcDNA3.1-IAg52b fish^-1, 2.20 μg pcDNA3.1-IAg52b fish^-1, 3. two doses of 10 μg pcDNA3.1-IAg52b fish^-1 with 7 days between doses, 4.20 μg pcDNA3.1 fish^-1 (mock-vaccinated control), 5.15,000 live theronts fish^-1 (positive control), and 6. non-vaccinated and non-challenge control. Parasite infection levels, serum anti-Ich antibody levels, fish mortality and immune-related gene expression were determined during the trial. Fish vaccinated with a single dose of 20 μg pcDNA3.1-IAg52b fish^-1 or two doses of 10 μg fish^-1 had higher anti-Ich antibody levels than fish receiving a single dose of 10 μg fish^-1. Survival was significantly higher in fish receiving 20 μg vaccine fish^-1 (35.6%) or 2 doses of 10 μg fish^-1 (48.9%) than fish injected with a single dose of 10 μg fish^-1 (15.6%) or mock-vaccinated control (0%). Fish vaccinated at the dose 20 μg fish^-1 had higher expression of vaccine DNA in muscle than fish vaccinated with 10 μg fish^-1. Fish vaccinated with the DNA vaccine showed higher up-regulation than mock-vaccinated control in the expression of IgM, CD4, MHC I and TcR-α genes during most of time points after vaccination. Further studies are needed to improve efficacy of DNA vaccines by using multiple antigens in the DNA vaccines.

Transcriptome analysis in the skin of Carassius auratus challenged with Aeromonas hydrophila

Skin plays an important role in the innate immune responses of fish, particularly towards bacterial infection. To understand the molecular mechanism of mucosal immunity of fish during bacterial challenge, a de novo transcriptome assembly of crucian carp Carassius auratus skin upon Aeromonas hydrophila infection was performed, the latter with Illumina Hiseq 2000 platform. A total of 118111 unigenes were generated and of these, 9693 and 8580 genes were differentially expressed at 6 and 12 h post-infection, respectively. The validity of the transcriptome results of eleven representative genes was verified by quantitative real-time PCR (qRT-PCR) analysis. A comparison with the transcriptome profiling of zebrafish skin to A. hydrophila with regards to the mucosal immune responses revealed similarities in the complement system, chemokines, heat shock proteins and the acute-phase response. GO and KEGG enrichment pathway analyses displayed the significant immune responses included TLR, MAPK, JAK-STAT, phagosome and three infection-related pathways (ie., Salmonella, Vibrio cholerae and pathogenic Escherichia coli) in skin. To our knowledge, this study is the first to describe the transcriptome analysis of C. auratus skin during A. hydrophila infection. The outcome of this study contributed to the understanding of the mucosal defense mechanisms in cyprinid species.

Immune response of channel catfish (Ictalurus punctatus) against Ichthyophthirius multifiliis post vaccination using DNA vaccines encoding immobilization antigens

The channel catfish (Ictalurus punctatus) immune response against Ichthyophthirius multifiliis (Ich) after vaccination using plasmid DNA vaccines pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, encoding Ich immobilization antigen genes was studied. Parasite infection level, serum anti-Ich antibodies level, fish mortality after theront challenge, and immune-related gene expression were measured. After in vitro transfection of walking catfish gill cells (G1b) with both pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, antigens IAG52A and IAG52B were detected. During the vaccination trial, 76-fold increase in the Iag52b gene expression was observed in the vaccinated fish group h4 post vaccination. Administration of DNA vaccines by IM injection induced significant gene up-regulation in the head kidney, including immunoglobulin M (IgM), cluster of differentiation 4 (CD4), major histocompatibility I (MHC I), and T cell receptor α (TcR-α) from h4 to d5 post immunization. Fish vaccinated with DNA vaccines or theronts showed increased gene expression of the cytokine interferon (IFN-γ), complement component 3 (C3), and toll-like receptor-1 (TLR-1). Anti-Ich antibodies were detected in fish received pcDNA3.1-IAg52a, pcDNA3.1-IAg52b and the combination of both vaccines d10 post vaccination. Fish vaccinated with pcDNA3.1-IAg52b showed mild parasite infection level, partial survival (20%) and longer mean day to death (MDD) after theront challenge. By contrast, a heavy parasite load, 0% survival and short MDD were observed in the sham vaccinated control fish that received pcDNA3.1 (plasmid without genes encoding Ich immobilization antigen). Further research is needed to improve DNA vaccines for Ich that can induce strong protective immunity in fish. Suggested studies include improved transfection efficiency, use of appropriate adjuvants and including additional parasite antigen genes in the plasmid.

Differential immune gene response in gills, skin, and spleen of rainbow trout Oncorhynchus mykiss infected by Ichthyophthirius multifiliis

Infection of rainbow trout with the parasitic ciliate Ichthyopthirius multifiliis induces differential responses in gills, skin and spleen. A controlled experimental infection was performed and expression of immune-relevant genes in skin, gills, and spleen were recorded by qPCR at day 1 and 8 after parasite exposure. Infection induced a marked reaction involving regulation of innate and adaptive immune genes in rainbow trout at day 8 post-infection. The expression level of a total of 22 out of 24 investigated genes was significantly higher in gills compared to skin reflecting the more sensitive and delicate structure of gills. Especially pro-inflammatory cytokines IL-6, IL-17 C1, regulatory cytokines IL-4/13A, IL-10, TGFβ, complement factor C5, chemokines CK10, CK12, acute phase proteins (precerebellin, hepcidin) and immunoglobulins (IgM, IgT) displayed differential expression levels. The spleen, a central immune organ with no trace of the parasite, showed elevated expression of IgM, IgT, complement factor C5 and chemokine CK10 (compared to skin and gills directly exposed to the parasite), indicating an interaction between the infected surface sites and central immune organs. This communication could be mediated by chemokines CK10 and CK12 and cytokine IL-4/13A and may at least partly explain the establishment of a systemic response in rainbow trout against the parasite.

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.

Effect of miconazole nitrate on immunological response and its preventive efficacy in Labeo rohita fingerlings against oomycetes Saprolegnia parasitica

This study evaluated the effect of sublethal doses of antifungal drug miconazole nitrate (MCZ) on immunological responses and its role as a prophylactic drug against S. parasitica in Labeo rohita fingerlings. Fish were fed with sublethal doses of MCZ, that is, T1-6.30 mgMCZ kgBW^-1 , T2-12.61 mgMCZ kgBW^-1 and T3-25.22 mgMCZ kgBW^-1 , and sampling was done at different time intervals for 240 hr. Immunological parameters viz. lysozyme activity, oxygen radical production and plasma antiprotease activity showed significant enhancement (p < 0.05) in fish fed with T2 and T3 doses. Expression of immune-relevant genes such as TLR-22 and β2-M showed significantly higher expression at 6 hr and 24 hr of sampling in both liver and head kidney. However, these genes showed a downregulation after 120 hr of sampling in both the tissues. Preventive efficacy study showed that single dose of MCZ provides protection against oomycetes up to the fourth day of infection. Significantly higher mortality was observed in control diet-fed fish as compared to fish fed with MCZ medicated diet. Thus, it can be concluded that the MCZ can act as a potent antifungal agent for preventing oomycetes infection as well as to enhance the immune response.

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.

Expression of immune genes in skin of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

The objective of this study was to evaluate differential expression of innate and adaptive immune genes, including immunoglobulin, immune cell receptor, cytokine, inflammatory protein, toll-like receptors (TLR) and recombination-activating gene (RAG) in skin from channel catfish, Ictalurus punctatus after immunization with live theronts of Ichthyophthirius multifiliis (Ich) by intraperitoneal injection. The immunized catfish showed significantly higher survival rate (95%) than those of mock-immunized control fish (0% survival) after the theront challenge. The gene expression of innate immune system, such as cytokines (IL-1β type a, IL-1β type b, IFN-γ, TGF1-β and TNF-α) and inflammatory proteins (NF-kB and iNOS 2), showed significant upregulation at day 1 (D1) post-immunization. Expression of TLR genes exhibited a rapid increase from hour 4 (h4) to D10 post-immunization. Genes of the adaptive response, such as the cell receptor MHC I, CD8⁺ , CD4⁺ and TCR-α, showed upregulation at D1, D6 and D10. The TCR-β expression increased rapidly at h4 and remained upregulated until D10. Immunoglobulin IgM upregulation was detected from h4 until D2 while IgD expression was increased from D1 until D10. Rapid upregulation of innate and adaptive immune genes in skin of catfish following live theront vaccination was demonstrated in this study ultimately resulting in significant protection against Ich 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.

Live recombinant Lactococcus lactis vaccine expressing immobilization antigen (i-Ag) for protection against Ichthyophthirius multifiliis in goldfish

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. Lactobacillus strains have a number of properties that make them attractive candidates as delivery vehicles for the presentation to the mucosa of compounds with pharmaceutical interest, in particular vaccines. Here, the present study was conducted to evaluate a live recombinant Lactococcus lactis vaccine expressing immobilization antigen (IAG-52X) in protection against I. multifiliis. A 1266 bp gene fragment containing a potential antigenic epitope of the 48 kDa immobilization antigen of I. multifiliis was assembled from six synthetic ohgonucleotides and cloned into pSIP409 and electrotransformed into Lactobacillus plantarum NC8. The recombinant vaccine candidate was then orally fed into goldfish. The expression of immune-related genes: complement component 3 (C3), MHC I, IgM gene in blood from goldfish at different time points after immunization were evaluated. Immunized fish were than challenged with a lethal dose of infectious I. multifiliis. The cumulative mortality and relative percentage survival (RPS) were also determined. Our results showed that the antibody level in the blood and skin of the immunized fish was statistically significant (P < 0.05) in relation to the control groups. Goldfish orally immunized with NC8-pSIP409- IAG-52X had high serum antibody titers that ranged from 32 to 256 after 28d post immunization, while fish fed with NC8-pSIP409 or PBS had no detectable immobilizing antibody response. Expression of IgM, C3, MHC I genes in the group immunized with IAG-52X were significantly (P < 0.05) up regulated as compared with control group, indicating that different immune cells were actively involved in cellular immune response. The results showed that the average survival rate of fish orally immunized with 10⁸ and 10⁶NC8-pSIP409-IAG-52X was 60% and 50% respectively. Therefore, NC8-pSIP409-IAG-52X could become a promising oral vaccine candidate against I. multifiliis.