Molecular characterization of three novel perforins in common carp (Cyprinus carpio L.) and their expression patterns during larvae ontogeny and in response to immune challenges

Oral administration of a new copper (I) complex with coumarin as ligand: modulation of the immune response and the composition of the intestinal microbiota in Onchorhynchus mykiss

[Cu(NN1)2]ClO4 is a copper (I) complex, where NN1 is an imine ligand 6-((quinolin-2-ylmethylene) amino)-2H-chromen-2-one obtained by derivatization of natural compound coumarin, developed for the treatment of infectious diseases that affect salmonids. In previous research, we showed that the Cu(I) coordination complex possesses antibacterial activity against Flavobacterium psychrophilum, providing protection against this pathogen in rainbow trout during challenge assays (with an RPS of 50%). In the present study, the effects of administering [Cu(NN1)2]ClO4 to Oncorhynchus mykiss over a 60-days period were evaluated with regard to systemic immune response and its potential to alter intestinal microbiota composition. In O. mykiss, an immunostimulatory effect was evident at days 30 and 45 after administration, resulting in an increment of transcript levels of IFN-γ, IL-12, TNF-α, lysozyme and perforin. To determine whether these immunomodulatory effects correlated with changes in the intestinal microbiota, we analyzed the metagenome diversity by V4 16S rRNA sequencing. In O. mykiss, both [Cu(NN1)2]ClO4 and commercial antibiotic florfenicol had comparable effects at the phylum level, resulting in a predominance of proteobacteria and firmicutes. Nonetheless, at the genus level, florfenicol and [Cu(NN1)2]ClO4 complex exhibited distinct effects on the intestinal microbiota of O. mykiss. In conclusion, our findings demonstrate that [Cu(NN1)2]ClO4 is capable of stimulating the immune system at a systemic level, while inducing alterations in the composition of the intestinal microbiota in O. mykiss.

[Cu(NN1)2]ClO4, a Copper (I) Complex as an Antimicrobial Agent for the Treatment of Piscirickettsiosis in Atlantic Salmon

Piscirickettsia salmonis is the pathogen that most affects the salmon industry in Chile. Large quantities of antibiotics have been used to control it. In search of alternatives, we have developed [Cu(NN1)2]ClO4 where NN1 = 6-((quinolin-2-ylmethylene)amino)-2H-chromen-2-one. The antibacterial capacity of [Cu(NN1)2]ClO4 was determined. Subsequently, the effect of the administration of [Cu(NN1)2]ClO4 on the growth of S. salar, modulation of the immune system and the intestinal microbiota was studied. Finally, the ability to protect against a challenge with P. salmonis was evaluated. The results obtained showed that the compound has an MIC between 15 and 33.9 μg/mL in four isolates. On the other hand, the compound did not affect the growth of the fish; however, an increase in the transcript levels of IFN-γ, IL-12, IL-1β, CD4, lysozyme and perforin was observed in fish treated with 40 μg/g of fish. Furthermore, modulation of the intestinal microbiota was observed, increasing the genera of beneficial bacteria such as Lactobacillus and Bacillus as well as potential pathogens such as Vibrio and Piscirickettsia. Finally, the treatment increased survival in fish challenged with P. salmonis by more than 60%. These results demonstrate that the compound is capable of protecting fish against P. salmonis, probably by modulating the immune system and the composition of the intestinal microbiota.

The early ontogenetic development of immune cells and organs in teleosts

Fully developed teleosts possess a highly developed immune system comprising both innate and adaptive elements, but when hatching from the egg, the yolksac larva is still at an ontogenetically incomplete stage with regard to physiological, including immunological, functions. The immune system in these young fish stages is far less developed when compared to the youngs appearing from reptile and avian eggs and from most mammals at parturition. In those vertebrate groups the early ontogenetic development of the fetus is highly protected. The lack of a fully developed immune system in yolksac larvae of fish is critical, because this stage encounters a potentially hostile and infectious aquatic environment. The strong selective pressure on the immune system of the yolksac larva and the youngest fry stages explains the existence of a multi-facetted innate system, which is protecting the young fish stages against viral, bacterial and parasitic infections. The sequential development of immune cells and organs depends on host species and its environmental setting. However, a strong armament comprising innate cells (neutrophilic granulocytes, macrophages) and molecules (receptors, lectins, complement, AMPs and constitutively expressed immunoglobulins) protect the earliest stages. The adaptive immune elements, including T-cells and B-cells, occur gradually in headkidney, spleen, thymus, tonsils, bursa equivalent (if present) and mucosa associated lymphoid cells. A functional protective response following immunization occur later.

Immune response of DNA vaccinated-gilthead seabream (Sparus aurata) against LCDV-Sa infection: relevance of the inflammatory process

Lymphocystis disease is one of the main viral pathologies affecting cultured gilthead seabream (Sparus aurata) in the Mediterranean region. Recently, we have developed a DNA vaccine based on the major capsid protein (MCP) of the Lymphocystis disease virus 3 (LCDV-Sa). The immune response triggered by either LCDV-Sa infection or vaccination have been previously studied and seem to be highly related to the modulation of the inflammatory and the IFN response. However, a comprehensive evaluation of immune-related gene expression in vaccinated fish after viral infection to identify immunogenes involved in vaccine-induced protection have not been carried out to date. The present study aimed to fulfill this objective by analyzing samples of head-kidney, spleen, intestine, and caudal fin from fish using an OpenArray® platform containing targets related to the immune response of gilthead seabream. The results obtained showed an increase of deregulated genes in the hematopoietic organs between vaccinated and non-vaccinated fish. However, in the intestine and fin, the results showed the opposite trend. The global effect of fish vaccination was a significant decrease (p<0.05) of viral replication in groups of fish previously vaccinated, and the expression of the following immune genes related to viral recognition (tlr9), humoral and cellular response (rag1 and cd48), inflammation (csf1r, elam, il1β, and il6), antiviral response (isg15, mx1, mx2, mx3), cell-mediated cytotoxicity (nccrp1), and apoptosis (prf1). The exclusive modulation of the immune response provoked by the vaccination seems to control the progression of the infection in the experimentally challenged gilthead seabream.

Regulation of Il-2 on the expression of granzyme B- and perforin-like genes and its functional implication in grass carp peripheral blood neutrophils

Granzyme (Gzm) B and perforin, both as cytotoxic proteins, can collaborate to induce the death of target cells as well as the microbes. They were originally discovered in cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells and confer the cytotoxic activities of these cells. In the present study, the coding sequences of a granzyme b-like (gcgzmbl) and a perforin-like (gcprfl) genes were cloned from grass carp (Ctenopharyngodon idellus) and their specific antibodies were subsequently prepared and validated. The mRNA and protein expression of these two cytotoxic proteins in grass carp peripheral blood neutrophils was demonstrated by quantitative PCR (qPCR) and immunofluorescence staining, respectively. In the same cell model, expression of gcGzmbl and gcPrfl was stimulated by grass carp interleukin (Il)-2 in a dose- and time-dependent manners and Erk, NF-κB and Stat5 pathways were found to be involved in the regulation of Il-2 on the genes' expression. Additionally, glycolysis was proved to play a role in the stimulation of Il-2 on gcGzmbl and gcPrfl expression in peripheral blood neutrophils. As combating the invading microorganisms is one of the main functions of neutrophils, the roles of gcGzmbl and gcPrfl in the anti-bacterial activities of grass carp peripheral blood neutrophils were explored. Results showed that immunoneutralization of gcGzmbl or gcPrfl significantly attenuated the antimicrobial abilities of the neutrophils enhanced by Il-2. These findings shed a light on the expression, regulation and functions of granzyme B- and perforin-like proteins in fish peripheral blood neutrophils and enrich the understanding of Il-2 function in fish innate immunity.

The dynamic immune responses of Mandarin fish (Siniperca chuatsi) to ISKNV in early infection based on full-length transcriptome analysis and weighted gene co-expression network analysis

Mandarin fish (Siniperca chuatsi) been seriously harmed by infectious spleen and kidney necrosis virus (ISKNV) in recent years, but the early immune response mechanism of infection is still unknown. Here, we performed RNA sequencing on the spleens of mandarin fish infected with ISKNV at 0, 12, 24, 48, and 72 h post-infection (hpi) using short-read Illumina RNA sequencing and long-read Pacific Biosciences isoform sequencing to generate a full-length transcriptome. The immune responses of mandarin fish infected with ISKNV at the molecular level were characterized by RNA-seq analysis and weighted gene co-expression network analysis (WGCNA). A total of 26,528 full-length transcript sequences were obtained. There were 2,729 (1,680 up-regulated and 1,112 down-regulated), 1,874 (1,136 up-regulated and 738 down-regulated), 2,032 (1,158 up-regulated and 847 down-regulated), and 4,176 (2,233 up-regulated and 1,943 down-regulated) differentially expressed genes (DEGs) in mandarin fish at 12, 24, 48, and 72 hpi, compared with uninfected fish, respectively. A total of four modules of co-expressed DEGs identified by WGCNA were significantly positively correlated to the four time points after infection, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the immune-related DEGs in all these modules were mainly enriched in Phagosome, Endocytosis, Herpes simplex infection, and Cytokine-cytokine receptor interaction pathways. Further analysis showed that oher signaling pathways, including CAMs, NOD-like receptor and ER protein processing, Intestinal immune network for IgA production, TLR pathway, and Apoptosis significantly enriched in four modules corresponding to 12, 24, 48, and 72 hpi respectively, had specifically participated in the immune response. Hub genes identified based on the high-degree nodes in the WGCN, including CAM3, IL-8, CCL21, STING, SNX1, PFR and TBK1, and some DEGs such as MHCI, MHCII, TfR, STING, TNF α, TBK1, IRF1, and NF-kB, BCR, IgA and Bcl-XL had involved in dynamic molecular response of mandarin fish to ISKNV infection. In sum, this study provides a set of full-length transcriptome of the spleen tissue of mandarin fish for the first time and revealed a group of immune genes and pathways involved in different temporal responses to ISKNV infection, which has implications for resource conservation and aiding the development of strategies to prevent virus early infection for mandarin fish.

Identification and functional analysis of the perforin-1 like gene in disease resistance in half smooth tongue sole (Cynoglossus semilaevis)

The pore-forming protein perforin is one of the effectors of cell-mediated killing via the granule exocytosis pathway. In this study, a genome-wide association study was conducted in Vibrio harveyi disease-resistant and disease-susceptible families of half smooth tongue sole (Cynoglossus semilaevis) to determine the genes accounting for host resistance, and a perforin homologue was identified, designated perforin-1 like (CsPRF1l). The full-length cDNA of CsPRF1l is 1835 bp, and encodes 514 amino acids. The CsPRF1l gene consists of 10 exons and 9 introns, spanning approximately 7 kb. The amino acid sequence of CsPRF1l shows 60.35, 54.03, 41.92, and 34.17% identities to Morone saxatilis PRF1l, Oryzias melastigma PRF1l, Danio rerio PRF1.5 and Homo sapiens PRF, respectively. Sequence analysis revealed the presence of membrane attack complex/perforin (MACPF) and C2 domains in CsPRF1l. Quantitative real-time PCR showed that CsPRF1l presented a higher intestinal expression level in disease-resistant families than in susceptible families. Tissue expression pattern analysis showed that CsPRF1l is present in most of the tested tissues and highly expressed in the intestine, brain, stomach and gills. After challenge with V. harveyi, CsPRF1l mRNA was markedly upregulated in the liver, spleen, kidney, intestine, gills and skin. In addition, the recombinant CsPRF1l protein exhibited obvious antimicrobial activity against V. harveyi in vitro and in a zebrafish model. Collectively, these data indicate that CsPRF1l modulates host immune defense against V. harveyi invasion and provide clues about the efficacy of rCsPRF1l in fish that will give rise to useful therapeutic applications for V. harveyi infection in C. semilaevis.

Summary and comparison of the perforin in teleosts and mammals: A review

Perforin, a pore-forming glycoprotein, has been demonstrated to play key roles in clearing virus-infected cells and tumour cells due to its ability of forming 'pores' on the cell membranes. Additionally, perforin is also found to be associated with human diseases such as tumours, virus infections, immune rejection and some autoimmune diseases. Until now, plenty of perforin genes have been identified in vertebrates, especially the mammals and teleost fish. Conversely, vertebrate homologue of perforin gene was not identified in the invertebrates. Although recently there have been several reviews focusing on perforin and granzymes in mammals, no one highlighted the current advances of perforin in the other vertebrates. Here, in addition to mammalian perforin, the structure, evolution, tissue distribution and function of perforin in bony fish are summarized, respectively, which will allow us to gain more insights into the perforin in lower animals and the evolution of this important pore-forming protein across vertebrates.

Molecular characterization of a new IgZ3 subclass in common carp (Cyprinus carpio) and comparative expression analysis of IgH transcripts during larvae development

Background

Immunoglobulins (Igs) distributed among systemic immune tissues and mucosal immune tissues play important roles in protecting teleosts from infections in the pathogen-rich aquatic environment. Teleost IgZ/IgT subclasses with different tissue expression patterns may have different immune functions.

Results

In the present study, a novel secreted IgZ heavy chain gene was cloned and characterized in common carp (Cyprinus carpio). This gene exhibited a different tissue-specific expression profile than the reported genes IgZ1 and IgZ2. The obtained IgZ-like subclass gene designated CcIgZ3, had a complete open reading frame contained 1650 bp encoding a protein of 549 amino acid residues. Phylogenetic analysis revealed that CcIgZ3 was grouped with carp IgZ2 and was in the same branch as IgZ/IgT genes of other teleosts. Basal expression detection of the immunoglobulin heavy chain (IgH) in healthy adult common carp showed that CcIgZ3 transcripts were widely expressed in systemic immune tissues and mucosal-associated lymphoid tissues. CcIgZ3 was expressed at the highest levels in the head kidneys, gills, and gonads, followed by the spleen, hindgut, oral epithelium, liver, brain, muscle, foregut, and blood; it was expressed at a very low level in the skin. The transcript expression of CcIgZ3 in leukocytes isolated from peripheral blood cells was significantly higher than that in leukocytes isolated from the spleen. Different groups of common carp were infected with Aeromonas hydrophila via intraperitoneal injection or immersion. RT-qPCR analysis demonstrated that significant differences in CcIgZ3 mRNA levels existed between the immersion and injection groups in all the examined tissues, including the head kidney, spleen, liver, and hindgut; in particular, the CcIgZ3 mRNA level in the hindgut was higher in the immersion group than in the injection group. The different routes of A. hydrophila exposure in common carp had milder effects on the IgM response than on the CcIgZ3 response. Further study of the relative expression of the IgH gene during the development of common carp showed that the tissue-specific expression profile of CcIgZ3 was very different from those of other genes. RT-qPCR analysis demonstrated that the CcIgZ3 mRNA level increased gradually in common carp during the early larval development stage from 1 day post fertilization (dpf) to 31 dpf with a dynamic tendency similar to those of IgZ1 and IgZ2, and IgM was the dominant Ig with obviously elevated abundance. Analyses of the tissue-specific expression of IgHs in common carp at 65 dpf showed that CcIgZ3 was expressed at mucosal sites, including both the hindgut and gill; in contrast, IgZ1 was preferentially expressed in the hindgut, and IgZ2 was preferentially expressed in the gill. In addition to RT-qPCR analysis, in situ hybridization was performed to detect CcIgZ3-expressing cells and IgM-expressing cells. The results showed that CcIgZ3 and IgM transcripts were detectable in the spleens, gills, and hindguts of common carp at 65 dpf.

Conclusions

These results reveal that CcIgZ3 gene transcripts are expressed in common carp during developmental stage not only in systemic tissues but also in mucosal tissues. CcIgZ3 expression can be induced in immune tissues by A. hydrophila challenge via immersion and intraperitoneal injection with significantly different expression profiles, which indicates that CcIgZ3 is involved in the antimicrobial immune response and might play an important role in gut mucosal immunity.

Teleost cytotoxic T cells

Cell-mediated cytotoxicity is one of the major mechanisms by which vertebrates control intracellular pathogens. Two cell types are the main players in this immune response, natural killer (NK) cells and cytotoxic T lymphocytes (CTL). While NK cells recognize altered target cells in a relatively unspecific manner CTLs use their T cell receptor to identify pathogen-specific peptides that are presented by major histocompatibility (MHC) class I molecules on the surface of infected cells. However, several other signals are needed to regulate cell-mediated cytotoxicity involving a complex network of cytokine- and ligand-receptor interactions. Since the first description of MHC class I molecules in teleosts during the early 90s of the last century a remarkable amount of information on teleost immune responses has been published. The corresponding studies describe teleost cells and molecules that are involved in CTL responses of higher vertebrates. These studies are backed by functional investigations on the killing activity of CTLs in a few teleost species. The present knowledge on teleost CTLs still leaves considerable room for further investigations on the mechanisms by which CTLs act. Nevertheless the information on teleost CTLs and their regulation might already be useful for the control of fish diseases by designing efficient vaccines against such diseases where CTL responses are known to be decisive for the elimination of the corresponding pathogen. This review summarizes the present knowledge on CTL regulation and functions in teleosts. In a special chapter, the role of CTLs in vaccination is discussed.

Molecular characterization and functional analysis of interferon regulatory factor 9 (irf9) in common carp Cyprinus carpio: a pivotal molecule in the Ifn response against pathogens

In the present study, interferon (IFN) regulatory factor (IRF) 9 gene (irf9) was identified and characterized in common carp Cyprinus carpio. The predicted protein sequence of Irf9 contains a DNA binding domain (DBD) that possess five tryptophans, an IRF association domain (IAD) and two nuclear localisation signals (NLS). Alignment of Irf9 of C. carpio with the corresponding Irf9 proteins of other species showed that the DBD is more highly conserved than the IAD. The putative Irf9 protein sequence of C. carpio shares higher identities with teleosts (53.8-82.3%) and lower identities with mammals (30.2-31.0%). Phylogenetic studies of the putative amino-acid sequence of IRF9 based on the neighbour-joining method showed that Irf9 of C. carpio has the closest relationship with the grass carp Ctenopharyngodon idella. Tissue distribution analysis showed that irf9 transcripts were detectable in all examined tissues with the highest expression in the skin and the lowest expression in the head kidney. Poly I:C and Aeromonas hydrophila stimulation up-regulated irf9 expression in the spleen, head kidney, foregut and hindgut at different time intervals. In addition, irf9 was induced by Poly I:C and lipopolysaccharides (LPS) in vitro. These results indicate that Irf9 participates in antiviral and antibacterial immunity. Transfection of irf9 up-regulated the expression of cytokines, including type I IFN, protein kinase R (PKR), interferon-stimulated gene (ISG)15 and tumour necrosis factor (TNF)α in epithelioma papulosum cyprini cells (EPC) upon poly I:C and LPS stimulation. A dual-luciferase reporter assay revealed that Irf9 has no effect on NF-κB activation. The present study on Irf9 provides new insights into the IFN system of C. carpio and a valuable experimental platform for future studies on the immune system of fish.

Nanomaterials-based Electrochemical Immunosensors

With the development of nanomaterials and sensor technology, nanomaterials-based electrochemical immunosensors have been widely employed in various fields. Nanomaterials for electrode modification are emerging one after another in order to improve the performance of electrochemical immunosensors. When compared with traditional detection methods, electrochemical immunosensors have the advantages of simplicity, real-time analysis, high sensitivity, miniaturization, rapid detection time, and low cost. Here, we summarize recent developments in electrochemical immunosensors based on nanomaterials, including carbon nanomaterials, metal nanomaterials, and quantum dots. Additionally, we discuss research challenges and future prospects for this field of study.