Cloning, characterization, and expression analysis of a CC chemokine gene from turbot (Scophthalmus maximus)

CC and CXC chemokines in turbot (Scophthalmus maximus L.): Identification, evolutionary analyses, and expression profiling after Aeromonas salmonicida infection

Chemokines are a superfamily of structurally related cytokines, which exert essential roles in guiding cell migration in development, homeostasis, and immunity. CC and CXC chemokines are the two major subfamilies in teleost species. In this study, a total of seventeen CC and CXC chemokines, with inclusion of twelve CC and five CXC chemokines, were systematically identified from the turbot genome, making turbot the teleost harboring the least number of CC and CXC chemokines among all teleost species ever reported. Phylogeny, synteny, and genomic organization analyses were performed to annotate these genes, and multiple chemokine genes were identified in the turbot genome, due to the tandem duplications (CCL19 and CCL20), the whole genome duplications (CCL20, CCL25, and CXCL12), and the teleost-specific members (CCL34-36, CCL44, and CXCL18). In addition, chemokines were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in liver, gill, and spleen. Moreover, most chemokines were significantly differentially expressed in gill and spleen after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that turbot chemokines interacted with a few immune-related genes such as interleukins, cathepsins, stats, and TLRs. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines in teleost.

CC chemokine 1 protein from Cromileptes altivelis (CaCC1) promotes antimicrobial immune defense

Chemokines are a family of small signaling proteins that are secreted by various cells. In addition to their roles in immune surveillance, localization of antigen, and lymphocyte trafficking for the maintenance of homeostasis, chemokines also function in induce immune cell migration under pathological conditions. In the present study, a novel CC chemokine gene (CaCC1) from humpback grouper (Cromileptes altivelis) was cloned and characterized. CaCC1 comprised a 435 bp open reading frame encoding 144 amino acid residues. The putative molecular weight of CaCC1 protein was 15 kDa CaCC1 contains four characteristic cysteines that are conserved in other known CC chemokines. CaCC1 also shares 11.64%-90.28% identity with other teleost and mammal CC chemokines. Phylogenetic analysis revealed that CaCC1 is most closely related to Epinephelus coioides EcCC1, both of which are in a fish-specific CC chemokine clade. CaCC1 was constitutively expressed in all examined C. altivelis tissues, with high expression levels in skin, heart, liver, and intestine. Vibrio harveyi stimulation up-regulated CaCC1 expression levels in liver, spleen, and head-kidney. Functional analyses revealed that the recombinant protein (rCaCC1) could induce the migration of head-kidney lymphocytes from C. altivelis. Moreover, rCaCC1 significantly enhanced phagocytosis in head-kidney macrophages from C. altivelis. In addition, rCaCC1 exhibited antimicrobial activities against Staphylococcus aureus, Edwardsiella tarda, and V. harveyi. In vivo, CaCC1 overexpression improved bacterial clearance in V. harveyi infected fish. Conversely, CaCC1 knockdown resulted in a significant decrease of bacterial clearance. These results demonstrate the important roles that CaCC1 plays in homeostasis and in inflammatory response to bacterial infection.

Full-length transcriptome sequencing and identification of immune-related genes in the critically endangered Hucho bleekeri

Hucho bleekeri is a glacial relict and critically endangered fish restricted to the Yangtze River drainage in China. The lack of basic genomic information and immune characteristics will hinder the way toward protecting this species. In the present study, we conducted the first transcriptome analysis of H. bleekeri using the combination of SMRT and Illumina sequencing technology. Transcriptome sequencing generated a total of 93,330 non-redundant full-length unigenes with a mean length of 3072 bp. A total of 92,472 (99.08%) unigenes were annotated in at least one of the Nr protein, Swiss-Prot, KEGG, KOG, GO, Nt and Pfam databases. KEGG analysis showed that a total of 7240 unigenes belonging to 28 immune pathways were annotated to the immune system category. Meanwhile, differentially expressed genes between mucosa-associated tissues (skin, gill and hindgut) and systemic-immune tissues (spleen, head kidney and liver) were obtained. Importantly, genes participating in diverse immune signalling pathways and their expression profiles in H. bleekeri were discussed. In addition, a large number of long non-coding RNAs (lncRNAs) and simple sequence repeats (SSRs) were obtained in the H. bleekeri transcriptome. The present study will provide basic genomic information for H. bleekeri and for further research on analysing the characteristics of both the innate and adaptive immune systems of this critically endangered species.

The effect of dietary cecropin AD on intestinal health, immune response and disease resistance of juvenile turbot (Scophthalmus maximus L.)

Cecropin AD (CAD) is a commercial cationic antimicrobial peptide that has been seldom studied in marine fish. This study investigated the effects of dietary CAD on intestinal health, immune response, disease resistance, and growth performance of turbot. A diet using fishmeal and plant protein as the main protein resources was used as the control (crude protein 53%, crude lipid 12%). CAD was supplemented into the control diet at the level of 250, 500, 750, and 1000 mg kg^-1 to formulate four experimental diets, C1, C2, C3, and C4, respectively. No significant difference was observed in fish growth performance, feed utilization efficiency and whole-body composition among all groups. Dietary CAD significantly increased the activity of lysozyme and complement component 3 level in both serum and distal intestine (DI), as well as the immunoglobulin M content in DI. The gene expression of immune cytokines such as IFN-γ, IL-1β, and chemokine SmCCL19, and the goblet cell number in DI were also significantly increased by dietary CAD supplementation. Compared with the control group, the microbiota analysis indicated group C4 showed significantly decreased α-diversity, obvious alternation in dominant bacteria composition at phylum level, different clustering, and significantly decreased relative abundance of Lactobacillus. Besides, the relative abundance of Bacteroides was significantly decreased in groups C1, C3, and C4. In addition, the lowest mortality of turbot challenged with Edwardsiella tarda was observed in fish fed diets C2 and C3. In conclusion, moderate levels of CAD in diet of turbot improved the intestinal immune response without disrupting the intestinal bacterial community, and enhanced the disease resistance. However, dietary CAD at 1000 mg kg^-1 greatly affected the intestinal bacterial composition and showed potentially inhibitory effects towards Lactobacillus.

Analysis of Manifestation of CC and CXC Chemokine Genes in Olive Flounders (Paralichthys olivaceus) Artificially Infected with VHSV during the Early Developmental Stage

Chemokines is a small protein that plays a major role in inflammatory reactions and viral infections as a chemotactic factor of cytokines involved in innate immunity. Most of the chemokines belong to the chemokine groups CC and CXC. To investigate the immune system of the olive flounder (Paralichthys olivaceus), an expression pattern specifically induced in the early developmental stages of analysis is examined using qRT-PCR. We also examined tissue-specific expression of both CC and CXC chemokine in healthy olive flounder samples. CC and CXC chemokine shows increased expression after immune-related organs are formed compared to expression during early development. CC chemokine was more highly expressed in the fin, but CXC chemokine showed higher expression in the gills, spleen, intestines, and stomach. Spatial and temporal expression analysis of CC and CXC chemokine were performed following viral hemorrhagic septicemia virus (VHSV) infection. CC chemokine showed high expression in the gills, which are respiratory organs, whereas CXC chemokine was more highly expressed in the kidneys, an immune-related organ. These results suggest that CC and CXC chemokine play an important role in the immune response of the olive flounder, and may be used as basic data for the immunological activity and gene analysis of it as well as other fish.

Basal polarization of the immune responses to Streptococcus agalactiae susceptible and resistant tilapia (Oreochromis niloticus)

One of the highest priority areas for improvement is the development of effective strategies for decreasing disease mortality levels in aquaculture production, a better understanding of the components of the fish immune system and their functions in the context of pathogen invasion is needed. Tilapia is the most common fish in South China, and Streptococcus agalactiae has become the most serious disease problem for tilapia industry in China. Here, we profiled gene expression differences between tilapia differing in their susceptibility to S. agalactiae both basally (before infection) and at three early timepoints post-infection (5 h, 50 h, and 7 d). Between group comparisons revealed 5756 unique genes differentially expressed greater than 2-fold at one or more timepoints. And the resistant fish showed much more strong ability in pathogen recognition, antigen presentation, immune activation, while the susceptible fish showed fast activation of apoptosis. Taken together, the immune profiles expand our knowledge for molecular mechanisms for disease resistance, as well as provide solid molecular resources for further identification of the candidate markers for disease-resistant selection and evaluation of disease prevention and treatment options for tilapia industry.

CK12a, a CCL19-like Chemokine That Orchestrates both Nasal and Systemic Antiviral Immune Responses in Rainbow Trout

Chemokines and chemokine receptors have rapidly diversified in teleost fish but their immune functions remain unclear. We report in this study that CCL19, a chemokine known to control lymphocyte migration and compartmentalization of lymphoid tissues in mammals, diversified in salmonids leading to the presence of six CCL19-like genes named CK10a, CK10b, CK12a, CK12b, CK13a, and CK13b. Salmonid CCL19-like genes all contain the DCCL-conserved motif but share low amino acid sequence identity. CK12 (but not CK10 or CK13) is constitutively expressed at high levels in all four trout MALT. Nasal vaccination with a live attenuated virus results in sustained upregulation of CK12 (but not CK10 or CK13) expression in trout nasopharynx-associated lymphoid tissue. Recombinant His-tagged trout CK12a (rCK12a) is not chemotactic in vitro but it increases the width of the nasal lamina propria when delivered intranasally. rCK12a delivered intranasally or i.p. stimulates the expression of CD8α, granulysin, and IFN-γ in mucosal and systemic compartments and increases nasal CD8α⁺ cell numbers. rCK12a is able to stimulate proliferation of head kidney leukocytes from Ag-experienced trout but not naive controls, yet it does not confer protection against viral challenge. These results show that local nasal production of CK12a contributes to antiviral immune protection both locally and systemically via stimulation of CD8 cellular immune responses and highlight a conserved role for CK12 in the orchestration of mucosal and systemic immune responses against viral pathogens in vertebrates.

Transcriptomic profiling revealed the signatures of intestinal barrier alteration and pathogen entry in turbot (Scophthalmus maximus) following Vibrio anguillarum challenge

The mucosal immune system serves as the frontline barriers of host defense against pathogen infection, especially for the fishes, which are living in the pathogen rich aquatic environment. The intestine constitutes the largest surface body area in constantly contact with the external pathogens, and plays a vital role in the immune defense against inflammation and pathogen infection. Previous studies have revealed that fish intestine might serves as the portal of entry for Vibrio anguillarum. To characterize the immune actors and their associated immune activities in turbot intestine barrier during bacterial infection, here we examined the gene expression profiles of turbot intestine at three time points following experimental infection with V. anguillarum utilizing RNA-seq technology. A total of 122 million reads were assembled into 183,101 contigs with an average length of 1151 bp and the N50 size of 2302 bp. Analysis of differential gene expression between control and infected samples at 1 h, 4 h, and 12 h revealed 2079 significantly expressed genes. Enrichment and pathway analysis of the differentially expressed genes showed the centrality of the pathogen attachment and recognition, antioxidant/apoptosis, mucus barrier modification and immune activation/inflammation in the pathogen entry and host immune responses. The present study reported the novel gene expression patterns in turbot mucosal immunity, which were overlooked in previous studies. Our results can help to understand the mechanisms of turbot host defense, and may also provide foundation to identify the biomarkers for future selection of disease-resistant broodstock and evaluation of disease prevention and treatment options.

Characterization and expression analysis of a peptidoglycan recognition protein gene, SmPGRP2 in mucosal tissues of turbot (Scophthalmus maximus L.) following bacterial challenge

Peptidoglycan recognition receptor proteins (PGRPs), a group of pattern recognition receptors (PRRs), can recognize peptidoglycan (PGN) of the bacteria cell wall and play an important role in host immune defense against pathogen infection. They are highly structurally conserved through evolution, but with different function in innate immunity between invertebrates and vertebrates. In teleost fish, several PGRPs have been characterized recently. They have both amidase activity and bactericidal activity and are involved in indirectly killing bacteria and regulating multiple signaling pathways. However, the knowledge of PGRPs in mucosal immunity of teleost fish is still limited. In this study, we identified a PGRPs gene (SmPGRP2) of turbot and investigated its expression patterns in mucosal tissues after challenge with Gram-positive bacteria Streptococcus iniae and Gram-negative bacteria Vibrio anguillarum. Phylogenetic analysis showed the strongest relationship of turbot PGRP to halibut, which was consistent with their phylogenetic relationships. In addition, SmPGRP2 was ubiquitously expressed in turbot tissues, and constitutive expression levels were higher in classical immune tissues (including liver, spleen, and head-kidney) than mucosal tissues (intestine, gill and skin). After bacterial challenge, the expression of SmPGRP2 was induced and showed a general trend of up-regulation in mucosal tissues, except in intestine following V. anguillarum infection. These different expression patterns varied depending on both pathogen and tissue type, suggesting its distinct roles in the host immune response to bacterial pathogen.

Chemokine receptor CXCR3 in turbot (Scophthalmus maximus): cloning, characterization and its responses to lipopolysaccharide

Chemokine (C-X-C motif) receptor 3, a member of the G protein-coupled receptors superfamily, regulates the responses of many immune responses. In this experiment, we cloned and characterized the cDNA of CXCR3 in Scophthalmus maximus (turbot). A 5'-UTR of 216-bp, a 259-bp 3'-UTR with a poly (A) tail and a 1089-bp CDS encoding 362 amino acids form the cDNA of CXCR3, which is 1564-bp long. Phylogenetic analyses indicated that turbot CXCR3 shared a high similarity with other CXCR3s and shared more similarity with CXCR5 than the other subfamilies of chemokines. The CXCR3 protein in turbot showed the highest similarity with the CXCR3b from rainbow trout (44.5%), which indicated that this CXCR3 gene/protein may be a CXCR3b isoform. Quantitative real-time PCR analysis showed that CXCR3 transcripts were constitutively expressed in all the tissues of the non-injected turbot used in this study, with the highest expression occurring in blood. Several immune-related tissues of fish, such as the spleen, head kidney, liver and blood, tissues, which were abundant of lymphocyte, were investigated in this study. CXCR3 gene was expressed at the highest level in blood than the other tested tissues. The injection experiment suggested that the CXCR3 expression level after LPS injection was significantly up-regulated in all immune-related tissues in turbot. These results improve our understanding of the functions of CXCR3 in the turbot immune response.

Molecular characterization and expression analysis of nine CC chemokines in half-smooth tongue sole, Cynoglossus semilaevis

Chemokines are a large, diverse group of small cytokines that can be classified into several families, including the CC chemokine family, which plays a pivotal role in host defense by inducing leukocyte chemotaxis under physiological and inflammatory conditions. Here we studied 9 CC chemokines from half-smooth tongue sole (Cynoglossus semilaevis). Phylogenetic analysis divided these chemokines into four groups. The tissue specific expression patterns of the 9 chemokines under normal physiological conditions varied much, with most chemokines highly expressed in immune organs, while some other chemokines showing high expression levels in non-immune organs. In addition, the 9 chemokines exhibited similar or distinctly different expression profiles in response to the challenge of virus and intracellular and extracellular bacterial pathogens. These results indicate that in tongue sole, CC chemokines may be involved in different immune responses as homeostatic or inflammatory chemokines.

Trancriptomic profiling revealed the signatures of acute immune response in tilapia (Oreochromis niloticus) following Streptococcus iniae challenge

Streptococcus iniae is the most significant bacterial disease of tilapia throughout the world, and commonly leads to tremendous economic losses. In contrast to other important fish species, our knowledge about the molecular mechanisms of tilapia in response to bacterial infection is still limited. Here, therefore, we utilized RNA-seq to first profiling of host responses in tilapia spleen following S. iniae infection at transcriptome level. A total of 223 million reads were obtained and assembled into 192,884 contigs with average length 844 bp. Gene expression analysis between control and infected samples at 5 h, 50 h, and 7 d revealed 1475 differentially expressed genes. In particular, the differentially expressed gene set was dramatically induced as early as 5 h, and rapidly declined to basal levels at 50 h. Enrichment and pathway analysis of the differentially expressed genes revealed the centrality of the pathogen attachment and recognition, cytoskeletal rearrangement and immune activation/inflammation in the pathogen entry and host inflammatory responses. Understanding of these responses can highlight mechanisms of tilapia host defense, and expand our knowledge of teleost immunology. Our findings will set a foundation of valuable biomarkers for future individual, strain, and family-level studies to evaluate immune effect of vaccine and individual response in host defense mechanisms to S. iniae infection, to select disease resistant families and strains.

CsCCL17, a CC chemokine of Cynoglossus semilaevis, induces leukocyte trafficking and promotes immune defense against viral infection

CC chemokines are the largest subfamily of chemokines, which are important components of the innate immune system. To date, sequences of several CC chemokines have been identified in half-smooth tongue sole (Cynoglossus semilaevis); however, the activities and functions of these putative chemokines remain unknown. Herein, we characterized a CC chemokine, CsCCL17, from tongue sole, and examined its activity. CsCCL17 contains a 303 bp open reading frame, which encodes a polypeptide of 100 amino acids with a molecular mass of 12 kDa CsCCL17 is phylogenetically related to the CCL17/22 group of CC chemokines and possesses the typical arrangement of four cysteines and an SCCR motif found in known CC chemokines. Under normal physiological conditions, CsCCL17 expression was detected in spleen, liver, heart, gill, head kidney, muscle, brain, and intestine. When the fish were infected by bacterial and viral pathogens, CsCCL17 expression was significantly up-regulated in a time-dependent manner. Chemotactic analysis showed that recombinant CsCCL17 (rCsCCL17) induced migration of peripheral blood leukocytes. A mutagenesis study showed that when the two cysteine residues in the SCCR motif were replaced by serine, no apparent chemotactic activity was observed in the mutant protein rCsCCL17M. rCsCCL17 enhanced the resistance of tongue sole against viral infection, but rCsCCL17M lacked this antiviral effect. Taken together, these findings indicate that CsCCL17 is a functional CC chemokine with the ability to recruit leukocytes and enhance host immune defense in a manner that requires the conserved SCCR motif.

Cloning and expression analysis of three novel CC chemokine genes from Japanese flounder (Paralichthys olivaceus)

Chemokines are small cytokines secreted by various cell types. They not only function in cell activation, differentiation and trafficking, but they also have influences on many biological processes. In this study, three novel CC chemokine genes Paol-SCYA105, 106 and 107 in Japanese flounder (Paralichthys olivaceus) were cloned and characterized. Paol-SCYA105 was mainly detected in gill, kidney and spleen, Paol-SCYA106 was detected in all tissues examined and Paol-SCYA107 was mainly detected in the spleen and kidney. Paol-SCYA105 and Paol-SCYA106 gene expressions peaked in kidney at day 3 after viral hemorrhagic septicemia virus infection and decreased at day 6, but Paol-SCYA106 still remained at a high level at day 6. Paol-SCYA107 gene expression was significantly up-regulated in kidney at day 6 after viral hemorrhagic septicemia virus infection. In response to infection by Gram-negative Edwardsiella tarda and Gram-positive Streptococcus iniae in kidney, only Paol-SCYA106 gene expression significantly increased. Together, these results indicate that these three novel CC chemokines are involved in the immune response against pathogen infections.

Characterization of a novel CC chemokine CCL4 in immune response induced by nitrite and its expression differences among three populations of Megalobrama amblycephala

A novel CC chemokine gene, chemokine CC motif ligand 4 (CCL4), was isolated from Megalobrama amblycephala. The full-length cDNA was 913 bp, encoding 94 amino acid residues. The deduced amino acid sequence possessed the typical arrangement of four cysteines as found in other known CC chemokines. The expression of M. amblycephala CCL4 during the early development showed the mRNA levels before hatching and at 62 h post fertilized (hpf) were significantly higher than other post-hatching stages (P < 0.05). Besides, it was widely expressed in all detected tissues with the highest transcription in liver, followed by intestine, spleen and gill, where a larger number of immune cells including lymphocytes and macrophages are present. Our findings had fully confirmed that CCL4 expression was strongly induced in vitro and quickly up-regulated after nitrite stress, then substantially altered in all tested tissues, supporting a potential pro-inflammatory function. We also indicated that inflammation effect might firstly happen in blood after nitrite stress. Furthermore, the tissue expression differences of CCL4 among three natural populations revealed that CCL4 mRNA in Yuni Lake population was obviously higher than the other two populations, Liangzi Lake population and Poyang Lake population, which will provide valuable insights into breeding strategies for selecting population with better immune property of M. amblycephala.

Immune gene discovery in the crucian carp Carassius auratus

The crucian carp Carassius auratus (Cyprinidae) is one of the important fish species in aquaculture. Although the crucian carp has several economic benefits, their immune system and gene information have not been investigated in depth as yet. Here, we performed the transcriptome analysis of C. auratus using the pyrosequencing method and selected several immune-related genes. Of unigenes obtained in this species, we identified a number of immune system-related genes (e.g. adhesive protein, antimicrobial protein, apoptosis- and cell cycle-related protein, cellular defense effector, immune regulator, pattern recognition protein, protease, protease inhibitor, reduction/oxidation-related protein, signal transduction-related protein and stress protein) that are potentially useful for studies on fish immunity. To be of public and practical use, we designed primer pairs of each gene from the crucian carp for real-time RT-PCR application and tested the amplicon identity of entire gene sets with the total RNA sample. For comparative analysis, we measured tissue-preferential transcript profiles of selected genes. This study will be helpful to extend our knowledge on the immune system of the crucian carp in comparative aspects and to develop the crucian carp as a potential model organism for aquatic quality monitoring in fish farming.

SmCCL19, a CC chemokine of turbot Scophthalmus maximus, induces leukocyte trafficking and promotes anti-viral and anti-bacterial defense

Chemokines are classified into several different subfamilies, of which CC chemokines constitute the largest subfamily in teleost. The prominent structural characteristic of CC chemokines is the presence of an Asp-Cys-Cys-Leu (DCCL) motif. To date, cDNA sequences of several CC chemokines have been identified in turbot (Scophthalmus maximus), however, the activity and function of these putative chemokines remain unknown. In this study, we examined the biological effect of the turbot CC chemokine SmCCL19, which has been previously reported as KC70 and shown to be regulated in expression by bacterial infection. To facilitate functional analysis, recombinant SmCCL19 (rSmCCL19) and a mutant form of SmCCL19, SmCCL19M, that bears serine substitutions at the two cysteine residues of the DCCL motif were purified from Escherichia coli. Chemotactic analysis showed that rSmCCL19 induced migration of head kidney leukocytes in a dose-dependent manner, whereas rSmCCL19M caused no apparent cellular migration. To examine the in vivo effect of rSmCCL19, turbot were administered with rSmCCL19 or rSmCCL19M before being inoculated with viral and bacterial pathogens. Subsequent tissue infection analysis showed that the viral and bacterial loads in rSmCCL19-adminsitered fish were significantly reduced, whereas the pathogen loads in rSmCCL19M-adminsitered fish were largely comparable to those in the control fish. Consistent with these observations, significant inductions of immune relevant genes were observed in rSmCCL19-adminsitered fish but not in rSmCCL19M-adminsitered fish. Taken together, these results indicate that SmCCL19 recruits leukocytes and augments host immune defense in a manner that depends on the conserved DCCL motif.

Identification and expression analysis of a CC chemokine from cobia (Rachycentron canadum)

Chemokines are small, secreted cytokine peptides known principally for their ability to induce migration and activation of leukocyte populations and regulate the immune response mechanisms. The cobia (Rachycentron canadum), a marine finfish species, has a great potential for net cage aquaculture in the South China Sea. We isolated and characterized a CC chemokine cDNA from cobia-designated RcCC2. Its cDNA is 783 bp in length and encodes a putative protein of 110 amino acids. Homology and phylogenetic analysis revealed that the RcCC2 gene, which contains four conserved cysteine residues, shares a high degree of similarity with other known CC chemokine sequences and is closest to the CCL19/21 clade. The mRNA of RcCC2 is expressed constitutively in all tested tissues, including gill, liver, muscle, spleen, kidney, head kidney, skin, brain, stomach, intestine and heart, but not blood, with the highest level of expression in gill and liver. The reverse transcription quantitative polymerase chain reaction was used to examine the expression of the RcCC2 gene in immune-related tissues, including head kidney, spleen and liver, following intraperitoneal injection of the viral mimic polyriboinosinic polyribocytidylic acid, formalin-killed Vibrio carchariae (bacterial vaccine) and phosphate-buffered saline as a control. RcCC2 gene expression was up-regulated differentially in head kidney, spleen and liver during 12 h after challenge. These results indicate that the RcCC2 gene is inducible and is involved in immune responses, suggesting RcCC2 has an important role in the early stage of viral and bacterial infections.

Molecular identification and expression analysis of the CC chemokine gene in rock bream (Oplegnathus fasciatus) and the biological activity of the recombinant protein

We identified the CC chemokine cDNA designated as RbCC1 (CC chemokine 1 in rock bream, Oplegnathus fasciatus), which was isolated using expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCC1 cDNA (850 bp) contained an open reading frame (ORF) of 366 bp encoding 122 amino acids. Results from our phylogenetic analysis demonstrated that the RbCC1 was closest relationship to the orange-spotted grouper and Mi-iyu croaker CC chemokines located within the fish CC chemokine group. RbCC1 was significantly expressed in the intestine, spleen, liver, and PBLs (peripheral blood leukocytes). Rock bream PBLs were stimulated with several mitogens, LPS and Con A/PMA which significantly induced the expression of RbCC1 mRNA in the PBLs. The RbCC1 mRNA expression in several tissues under conditions of bacterial and viral challenge was examined. The experimental challenge revealed that the kidney and spleen of fish infected with Streptococcus iniae showed the most significant increases in RbCC1 expression compared to the control. In the case of RSIV infection, the RbCC1 mRNA expression was markedly up-regulated in the liver. In this study, recombinant RbCC1 (approximately 53 kDa) was produced using an Escherichia coli expression system followed by purification. Subsequently, the addition of purified rRbCC1 was examined to investigate the impact on the proliferative and chemotactic activity on kidney leukocytes from rock bream. The results demonstrated that the rRbCC1 induces significant biological activity on kidney leukocyte proliferation and attraction at concentrations in the range of 10-300 μg/mL and suggests that rRbCC1 could be utilized as an immune-stimulant and/or molecular adjuvant to enhance the immune effects of vaccines.

Molecular cloning, characterization and expression analysis of a CC chemokine gene from miiuy croaker (Miichthys miiuy)

Chemokines are a family of structurally related chemotactic cytokines that regulate the migration of leukocytes, under both physiological and inflammatory conditions. A partial cDNA of CC chemokine gene designed as Mimi-CC3 was isolated from miiuy croaker (Miichthys miiuy) spleen cDNA library. Unknown 3' part of the cDNA was amplified by 3'-RACE. The complete cDNA of Mimi-CC3 contains an 89-nt 5'-UTR, a 303-nt open reading frame and a 441-nt 3'-UTR. Three exons and two introns were identified in Mimi-CC3. The deduced Mimi-CC3 protein sequences contain a 22 amino acids signal peptide and a 78 amino acids mature polypeptide, which possesses the typical arrangement of four cysteines as found in other known CC chemokines. It shares low amino acid sequence identities with most other fish and mammalian CC chemokines (less than 54.1 %), but shares very high identities with large yellow croaker CC chemokine (94.6 %). Phylogenetic analysis showed that Mimi-CC3 gene may have an orthologous relationship with mammalian/amphibian CCL25 gene. Tissue expression distributed analysis showed that Mimi-CC3 gene was constitutively expressed in all nine tissues examined, although at different levels. Upon stimulated with Vibrio anguillarum, the time-course analysis using a real-time PCR showed that Mimi-CC3 transcript in kidney and liver was obviously up-regulated and reached the peak levels, followed by a recovery. Mimi-CC3 expression in kidney was more strongly increased than in liver. However, down-regulation was observed in spleen. These results indicated that Mimi-CC3 plays important roles in miiuy croaker immune response as well as in homeostatic mechanisms.

Identification of a cobia (Rachycentron canadum) CC chemokine gene and its involvement in the inflammatory response

The chemokines regulate immune cell migration under inflammatory and physiological conditions. We investigated a CC chemokine gene (RcCC1) from cobia (Rachycentron canadum). The full-length RcCC1 cDNA is comprised 673 nucleotides and encodes a four-cysteine arrangement 99-amino-acid protein typical of known CC chemokines. The genomic DNA of RcCC1 consists of three exons and two introns. Phylogenetic analysis showed that RcCC1 was closest to the MIP group of CC chemokines. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed RcCC1 was constitutively expressed in all tissues examined, with relative strong expression in gill, blood, kidney, spleen, and head kidney. The RcCC1 transcripts in the head kidney, spleen, and liver were quickly up-regulated after stimulation with formalin-inactivated Vibrio carchariae (bacterial vaccine) or polyriboinosinic polyribocytidylic acid (poly I:C). These results indicate RcCC1 not only plays a role in homeostasis, but also may be involved in inflammatory responses to bacterial and viral infection.

Chemokines in teleost fish species

Chemokines are chemoattractant cytokines defined by the presence of four conserved cysteine residues which in mammals can be divided into four subfamilies depending on the arrangement of the first two conserved cysteines in their sequence: CXC (α), CC (β), C and CX(3)C classes. Evolutionarily, fish can be considered as an intermediate step between species which possess only innate immunity (invertebrates) and species with a fully developed acquired immune network such as mammals. Therefore, the functionality of their different immune cell types and molecules is sometimes also intermediate between innate and acquired responses. The first chemokine gene identified in a teleost was a rainbow trout (Oncorhynchus mykiss) chemokine designated as CK1 in 1998. Since then, many different chemokine genes have been identified in several fish species, but their role in homeostasis and immune response remains largely unknown. Extensive genomic duplication events and the fact that chemokines evolve more quickly than other immune genes, make it very difficult to establish true orthologues between fish and mammalian chemokines that would help us with the ascription of immune roles. In this review, we describe the current state of knowledge of chemokine biology in teleost fish, focusing mainly on which genes have been identified so far and highlighting the most important aspects of their expression regulation, due to the great lack of functional information available for them. As the number of chemokine genes begins to close down for some teleost species, there is an important need for functional assays that may elucidate the role of each of these molecules within the fish immune response.

An inflammatory CC chemokine of Cynoglossus semilaevis is involved in immune defense against bacterial infection

Chemokines are a family of small cytokines that regulate leukocyte migration. Based on the arrangement of the first two cysteine residues, chemokines are classified into four groups called CXC(α), CC(β), C, and CX(3)C. In this study, we identified a CC chemokine, CsCCK1, from half-smooth tongue sole (Cynoglossus semilaevis) and analyzed its biological activity. The deduced amino acid sequence of CsCCK1 contains 111 amino acid residues and is phylogenetically belonging to the CCL19/21/25 group of CC chemokines. CsCCK1 possesses a DCCL motif that is highly conserved among CC chemokines. Quantitative real time RT-PCR analysis showed that the expression of CsCCK1 was relatively abundant in immune organs under normal physiological conditions and was upregulated by experimental infection of a bacterial pathogen. Purified recombinant CsCCK1 (rCsCCK1) induced chemotaxis in peripheral blood leukocytes (PBL) of both tongue sole and turbot (Scophthalmus maximus) in a dose-dependent manner. Mutation of the CC residues in the DCCL motif by serine substitution completely abolished the biological activity of rCsCCK1. When rCsCCK1, but not the mutant protein, was added to the cell culture of PBL, it enhanced cellular resistance against intracellular bacterial infection. Taken together, these results indicate that CsCCK1 is a functional CC chemokine whose biological activity depends on the DCCL motif and that CsCCK1 plays a role in host immune defense against bacterial infection.