Comparative analysis of two types of CXCL8 from Japanese flounder (Paralichthys olivaceus)

PoIL8-L, a teleost interleukin-8 like, enhances leukocyte cellular vitality and host defense against bacterial infections in Japanese flounder (Paralichthys olivaceus)

Interleukin-8 (IL-8), a CXC chemokine, exerts pivotal effect on cell migration, inflammatory response, and immune regulation. In this study, we examined the immunological characteristics of an IL-8 like homologue (PoIL8-L) in Japanese flounder (Paralichthys olivaceus). PoIL8-L contains a conserved chemokine CXC domain and 105 amino acid residues. PoIL8-L expression in tissues was constitutive, and significantly regulated by V. havieri or E. tarda infection. In vitro, rPoIL8-L could bind to eight tested bacteria, exhibited bacteriostatic and bactericidal effects against certain bacteria, and could bind to the targeted bacterial Ⅳ pilin protein rPilA of E. tarda. Furthermore, rPoIL8-L could attach to peripheral blood leukocytes, and enhance their immune genes expression, respiratory burst, chemotaxis, proliferation, acid phosphatase activity, and phagocytic activity. Additionally, rPoIL8-L induce neutrophils to extrude neutrophil extracellular traps. In vivo, rPoIL8-L could promote host resistance to E. tarda infection. In summary, these findings provide fresh perspectives on the immunological antibacterial properties of IL-8 in teleost.

IL8 of Takifugu rubripes is a chemokine that interacts with peripheral blood leukocytes and promotes antibacterial defense

Interleukin 8 (IL8) is a CXC chemokine that plays a crucial role on promoting inflammatory response and immune regulation. In teleost, IL8 can induce the migration and activation of immune cells. However, the biological functions of IL8 are still unknown in Takifugu rubripes. In this study, we examined the biological characteristics of TrIL8 in T. rubripes. TrIL8 is composed of 98 residues and contained a chemokine CXC domain. We found that the TrIL8 expression was detected in diverse organs and significantly increased by Vibrio harveyi or Edwardsiella tarda challenge. The recombinant TrIL8 (rTrIL8) exhibited significantly the binding capacities to 8 tested bacteria. In addition, rTrIL8 could bind to peripheral blood leukocytes (PBL), and increased the expression of immune gene, resistance to bacterial infection, respiratory burst, acid phosphatase activity, chemotactic activity, and phagocytic activity of PBL. In the presence of rTrIL8, T. rubripes was enhanced the resistance to V. harveyi infection. These results indicated that TrIL8 is a chemokine and involved in the activation of immune cells against bacterial infection in teleost.

Molecular characterization and expression patterns of CXCL8 gene from blunt snout bream (Megalobrama amblycephala) and its chemotactic effects on macrophages and neutrophils

CXCL8 is a typical CXC-type chemokine, which mediates the migration of immune cells from blood vessels to the site of inflammation or injury to clear pathogenic microorganisms and repair damaged tissues. In this study, Megalobrama amblycephala CXCL8 (MaCXCL8) gene was identified and characterized. Sequence analysis showed that the deduced MaCXCL8 protein possessed the typical structure of CXCL8 from other species, with the characteristic CXC cysteine residues in the N-terminal and accompanied by a DLR motif (Asp-Leu-Arg motif). Phylogenetic analysis revealed that MaCXCL8 was homologous to that of Ctenopharyngodon idella and other cyprinid fishes. MaCXCL8 gene was expressed in all detected healthy tissues, with the highest expression levels in the spleen, and its expression was significantly up-regulated upon the challenge of Aeromonas hydrophila and Lipopolysaccharide (LPS) both in juvenile M. amblycephala tissues and primary macrophages. The immunohistochemical assay showed that MaCXCL8 was mainly distributed in the nucleus and cytoplasm, and its expression levels increased observably with the prolongation of bacterial infection. In addition, recombinant MaCXCL8 protein exhibited significant chemotactic effects on neutrophils and macrophages. In conclusion, MaCXCL8 is involved in the immune response of M. amblycephala, and these findings will be helpful to understand the biological roles of MaCXCL8 and provide a theoretical basis for the prevention and control of fish bacterial diseases.

Blood transcriptome analysis revealed the immune changes and immunological adaptation of wildness training giant pandas

The giant panda (Ailuropoda melanoleuca) is a global flagship species for biodiversity conservation. As the time for captive giant pandas to be released into the wild matures, wildness training is provided to allow adaptation to their natural environment. It is assumed that changes in the immune system would be integral in this adaptation from captive to wild, where many more pathogens would be encountered in their natural habitats. Therefore, this study aims to determine the expression changes of immune-related genes and their potential as immunoassay markers for adaptation monitoring in wildness training giant pandas, and then to understand the adaptation strategy of wildness training giant pandas to the wild environment, thereby improving the success rate of panda reintroduction. We obtained 300 differentially expressed genes (DEGs) by RNA-seq, with 239 up-regulated and 61 down-regulated DEGs in wildness training giant pandas compared to captive pandas. Functional enrichment analysis indicated that up-regulated DEGs were enriched in several immune-related terms and pathways. There were 21 immune-related DEGs, in which most of them were up-regulated in wildness training giant pandas, including several critical innate and cellular immune genes. IL1R2 was the most significantly up-regulated gene and is a signature of homeostasis within the immune system. In the protein-protein interaction (PPI) analysis, CXCL8, CXCL10, and CCL5 were identified as the hub immune genes. Our results suggested that wildness training giant pandas have stronger innate and cellular immunity than captive giant pandas, and we proposed that a gene set of CXCL8, CXCL10, CCL5, CD3D, NFKBIA, TBX21, IL12RB2, and IL1R2 may serve as potential immunoassay markers to monitor and assess the immune status of wildness training giant pandas. Our study offers the first insight into immune alterations of wildness training giant pandas, paving the way for monitoring and evaluating the immune status of giant pandas when reintroducing them into the wild.

Two ACTH analogs exert differential effects on monocytes/macrophages function regulation in ayu (Plecoglossus altivelis)

Adrenocorticotropic hormone (ACTH), a bioactive peptide of the family of melanocortins, is generated from pro-opiomelanocortin (POMC). So far, the research on the specific functions of ACTH in the immune system of teleosts is limited. We determined two complementary DNA (cDNA) sequences of POMC in ayu (Plecoglossus altivelis), termed PaPOMC-A and PaPOMC-B. PaPOMCs transcripts occurred in all examined tissues, and their expression in immune tissues changed following experimental infection with Vibrio anguillarum. PaACTH-B, but not PaACTH-A, suppressed the phagocytosis of monocytes/macrophages (MO/MФ). Two isoforms of PaACTH increased the bactericidal capacity of MO/MФ. PaACTH-A increased anti-inflammatory cytokine expression, while PaACTH-B decreased pro-inflammatory cytokine expression in MO/MФ. Compared with PaACTH-B treatment, the PaACTH-A treatment improved survival rate and reduced the bacterial load in V. anguillarum-infected ayu through interleukin (IL)-10. Our results indicate that the two PaACTH isoforms exert different effects in the host defense against bacterial infection.

Molecular characterization and expression analysis of Japanese flounder (Paralichthys olivaceus) chemokine receptor CXCR2 in comparison with CXCR1

Chemokines are categorized into five families; one of the families is the CXC chemokines, which are critical in the pro-inflammatory process. CXC chemokines transmit signals and mediate a cell's biological activities by binding to cell surface receptors known as chemokine receptors (CXCRs). In this study, the CXCR2 from Japanese flounder (Paralichthys olivaceus) (JfCXCR2) was identified and characterized at the molecular level. The JfCXCR2 gene has a 1077 bp open reading frame that encodes a protein of 359 amino acid residues with seven transmembrane domains. Phylogenetic analysis of JfCXCR2 revealed that it belonged to the fish CXCR2 subfamily. Furthermore, JfCXCR2 was compared with the previously identified Japanese flounder CXCR1 (JfCXCR1). The expression analysis of uninfected Japanese flounder showed that JfCXCR1 and JfCXCR2 were expressed in all the tissues and organs tested but mainly in immune-related organs, including the kidney and spleen. Infection by Streptococcus iniae significantly increased the level of JfCXCR1 and JfCXCR2 mRNA in the kidney at days 1 and 3 post-infection. On the other hand, VHSV (viral hemorrhagic septicemia virus) and Edwardsiella tarda infection significantly increased JfCXCR2 mRNA levels in the kidney at days 3 and 6 post-infection, respectively. Conversely, JfCXCR1 expression was not significantly changed by either E. tarda or VHSV infection. Additionally, the peripheral blood leukocytes (PBLs) stimulated by recombinant proteins rCXCL8_L1a and rCXCL8_L1b were found to have significantly increased levels of JfCXCR1 and JfCXCR2 mRNA. Interestingly, even higher levels of JfCXCR1 and JfCXCR2 expression were observed in PBLs stimulated with rCXCL8_L1a and rCXCL8_L1b than in PBLs stimulated with either recombinant protein. These data suggest that bacterial infections may activate JfCXCR1. By contrast, JfCXCR2 may be activated by both bacterial and viral infection to mediate the immune response. These data can contribute to further understanding the functions of CXCR1 and CXCR2 in the fish immune system.

The efficacy of lactic acid bacteria usage in turbot Scophthalmus maximus on intestinal microbiota and expression of the immune related genes

To understand the efficacy of lactic acid bacteria (LAB) as probiotics on the growth, immune response and intestinal microbiota of turbot Scophthalmus maximus, in this study, the Leuconostoc mesenteroides HY2 strain screened from wide caught fish was bath administrated for juvenile turbot with no bacteria administrated as control. The mRNA levels of toll-like receptors 3 (TLR3), interleukin 8 (IL-8) and interferon induced with helicase C domain 1 (IFIH1) in different organs (i.e. intestine, liver, spleen, kidney, brain and skin) were analyzed using RT-PCR technology. The intestinal microbiota was analyzed by 16S rRNA sequencing, in which principal co-ordinates analysis (PCoA) as well as cluster analysis was performed. The results showed that the specific growth rate of turbot in the LAB treatment was significantly higher than those of the control group (P < 0.05). The expression levels of TLR3, IL-8 and IFIH1 were significantly up-regulated in the organs of LAB treatment, except that IL-8 was slightly down-regulated in kidney. A total of 42 phyla in intestinal microbiota were identified. The composition of intestinal microbiota showed significant differences between LAB treatment and the control group. Shannon index in the LAB treatment was significantly increased while Simpson index significantly declined. The PCoA and cluster analysis exhibited significant differences in the composition and abundance between the two groups. Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria acted as biomarkers which may have effects to promote absorption and/or trigger the immune function. In conclusion, the administration of HY2 strain was capable of improving growth performance of turbot by enhancing immune response and optimizing structure and diversity of intestinal microbiota.

Interleukin-8 (IL-8) Expression in the Olive Flounder (Paralichthys olivaceus) against Viral Hemorrhagic Septicemia Virus (VHSV) Challenge

Interleukin-8 (IL-8) is an inflammatory cytokine that plays an important role in the inflammatory response through the activation of neutrophil cells. The expression of IL-8 was investigated in early developmental stages of the olive flounder and in tissues of 8-month-old individuals. The expression of IL-8 increased after the initiation of the immune system rather than at the early stage of development, and high expression was observed in the gills and spleen, the organs associated with immunity and metabolism. In addition, IL-8 expression after infection by viral hemorrhagic septicemia virus significantly increased in the fin, gill, muscles, and spleen. These results suggest that IL-8 is closely related to inflammation and immune regulation in the immune response of the olive flounder and may be used as a basis for studies on the immune systems of other fish.

Unraveling the evolutionary origin of ELR motif using fish CXC chemokine CXCL8

Chemokines are chemotactic proteins involved in host defense through the migration of immune-regulatory cells to the site of infection. Interleukin-8 (CXCL8/IL8) is the most studied "ELR-CXC chemokine/neutrophil activating chemokine (NAC) that regulate neutrophil trafficking during infections and inflammation by binding to its cognate G-protein coupled receptors CXCR1/CXCR2. The "ELR" motif of NAC chemokines is essential for the CXCR1/CXCR2 receptor activation. In order to understand the evolutionary origin of "ELR" motif in the CXC chemokines, a thorough evolutionary study of CXCL8 gene from various fishes and primates was performed. Phylogenetic analysis revealed that the CXCL8 gene can be classified into four distinct lineages (CXCL8-L1a, CXCL8-L1b, CXCL8-L2, and CXCL8-L3), where CXCL8-L1a is the fastest evolving lineage and CXCL8-L3 is the slowest. Selection analysis suggested that The "ELR/DLR" motif containing branches (gadoid and coelacanth) are positively selected. The probable evolutionary trend of "ELR" motif suggested that this motif in ancestor CXCL8 is evolved from the GGR of Lamprey (Agnatha), followed by duplication giving rise to two main motifs in CXCL8 "NXH" in L3 lineage and "ELR/DLR" in L1a/L1b lineages. Although, structural analysis suggested that the overall topology of the CXCL8 proteins is similar, differences do exist at the individual structural elements among the members of different lineages. Functional distance analysis suggested that the CXCL8-L3 lineage is more distant compared to the CXCL8-L1a and L1b lineages from the inferred ancestor. Functional divergence analysis between different lineages suggested that most of the selected residues are important for receptor or glycosaminoglycan binding. Such a functional diversification can be attributed to the novel set of functions adopted by CXCL8 in various species.

Molecular characterization and biological functioning of interleukin-8 in Siberian sturgeon (Acipenser baeri)

Interleukin-8, otherwise known as CXCL8, is a CXC chemokine that plays a pivotal regulatory role in immune and inflammation responses of animals. Here, we identified an interleukin-8 homologue from Siberian sturgeon (Acipenser baeri), named AbIL-8, which belongs to the lineage 1 group of teleost fish IL-8s. The cDNA of Abil-8 is 1130 bp in length, containing a 5'- untranslated region (UTR) of 50 bp, a 3'- UTR of 783 bp, and an open reading frame (ORF) of 297 bp that encodes a protein consisting of 98 amino acids. The deduced AbIL-8 contained five cysteines, four of which are highly conserved, and an ELR motif typical of known mammalian CXC chemokines was also found preceding the CXC motif. Our phylogenetic analysis showed that AbIL-8 clustered with the CXCL8_L1 sequences from other teleosts, being clearly distinct from those of either birds or mammals. Abil-8 mRNA was constitutively expressed in all tested tissues and significantly up-regulated in the liver and spleen tissues by the bacteria Aernomas hydrophila. The in vitro experiment using primary spleen cells stimulated with heat-killed Aernomas hydrophila or lipopolysaccharide (LPS) revealed a similar expression pattern to that found in vivo, whereas stimulation on spleen cells with β-glucan or polyI:C elicited negligible changes in levels of Abil-8 mRNA. Purified recombinant AbIL-8 not only exhibited chemotactic activity for lymphocytes and monocytes in peripheral blood leukocytes (PBLs) and, to a lesser extent, spleen cells, but also stimulated the proliferation of spleen cells at 10 ng/mLor above. Furthermore, intraperitoneal injection of rAbIL-8 also up-regulated the expression of immuno-related genes (IL-6, IgM and MHCIIβ) at 24 h. Collectively, these results enhance our understanding of how IL-8 functions in the regulation of the immune responses in sturgeon.

Full-length and a smaller globular fragment of adiponectin have opposite roles in regulating monocyte/macrophage functions in ayu, Plecoglossus altivelis

Adiponectin (ADP), a regulator of the innate immune system, plays a role in the progression of inflammation and metabolic disorders in mammals. However, the role of ADP in fish is poorly understood. Here, we cloned the cDNA sequence of a ADP homolog (PaADP) gene from ayu. Multiple sequence alignment revealed that PaADP presented typical characteristics of ADPs. Phylogenetic tree analysis showed that PaADP was most closely related to that of rainbow trout. In healthy ayu, the transcripts of PaADP were detected in most of the tested tissues and cells, with the highest level in the adipose tissue. Upon V. anguillarum infection, the mRNA expression of PaADP was significantly up-regulated in the tissues and cells except adipose tissue. Subsequently, the full-length mature PaADP (fPaADP) and the globular domain fragment (gPaADP) were prokaryotically expressed in bacteria and purified, and anti-PaADP antibodies were produced. Western blot analysis revealed that three fragments including fPaADP and gPaADP were existed in ayu serum. The recombinant fPaADP (rfPaADP) had an anti-inflammatory effect on ayu MO/MФ by upregulating anti-inflammatory cytokine expressions, downregulating pro-inflammatory cytokine expressions, inhibiting the phagocytosis and subsequent bacterial killing. In contrast, the recombinant gPaADP (rgPaADP) presented a pro-inflammatory effect on ayu MO/MФ by upregulating pro-inflammatory cytokine expression, downregulating anti-inflammatory cytokine expressions, enhancing the phagocytosis and subsequent bacterial killing. These results suggested that fPaADP and gPaADP have opposite roles in the regulation of MO/MФ functions in ayu.

Molecular characterization and functional activity of CXCL8_L3 in large yellow croaker Larimichthys crocea

CXCL8, also called interleukin-8, is a typical CXC chemokine that plays a key role in promoting inflammation. Phylogenetically, fish CXCL8 chemokines can be divided into three subgroups, CXCL8_L1, CXCL8_L2, and CXCL8_L3, of which CXCL8_L3 is a new subgroup. The CXCL8_L3 gene sequences have been reported in many fish species, but their function remains unknown. Here, a CXCL8_L3 (LycCXCL8_L3) gene was cloned from large yellow croaker Larimichthys crocea. Its open reading frame (ORF) was 309 nucleotides long, encoding a peptide of 102 amino acids. The deduced LycCXCL8_L3 protein contains an 18-aa signal peptide and an 84-aa mature polypeptide, which has four conserved cysteine residues (C30, C32, C57, and C73) as found in other known CXCL8 chemokines. Phylogenetic analysis showed LycCXCL8_L3 formed a major clade with CXCL8_L3 sequences from other fish species. The LycCXCL8_L3 transcript was constitutively expressed in all examined tissues and significantly up-regulated in the spleen and head kidney tissues by inactivated trivalent bacterial vaccine. The LycCXCL8_L3 transcript was also detected in peripheral blood leukocytes (PBLs), primary head kidney macrophages (PKM), and large yellow croaker head kidney cell line (LYCK), with the highest levels in PKM. Recombinant LycCXCL8_L3 (rLycCXCL8_L3) protein could not only chemotactically attract lymphocytes and eosinophils in PBLs, but also enhance the respiratory burst activity of PKM. These results indicate that LycCXCL8_L3 may play an important role in the inflammatory response of large yellow croaker. To our knowledge, this is the first report on functional study of the CXCL8_L3 in fish.

Molecular identification and functional analysis of KLF2 in Plecoglossus altivelis (ayu): It's regulatory role in monocyte/macrophage activation

Monocytes/macrophages (MO/MФ) play an important role in the response to infection in Plecoglossus altivelis (ayu). However, the role of transcription factors in the function of ayu MO/MФ is poorly understood. Here, we cloned the cDNA sequence of the Kruppel-like factor 2 (PaKLF2) gene from ayu. Phylogenetic analysis indicated that PaKLF2 was closest to that of Atlantic salmon (Salmo salar). Real time quantitative PCR (RT-qPCR) revealed that the PaKLF2 mRNA level was highest in the peripheral blood mononuclear cells among all tested tissues. The mRNA expression of PaKLF2 was upregulated in the head kidney, liver, spleen, and brain after Listonella anguillarum infection. Subsequently, PaKLF2 was expressed and purified to prepare anti-PaKLF2 antibodies. After L. anguillarum challenge, the PaKLF2 mRNA and protein levels were significantly upregulated in ayu MO/MФ. Moreover, PaKLF2 knockdown in MO/MФ resulted in the enhancement of cytokine production as well as phagocytotic and bactericidal capability. Therefore, PaKLF2 may modulate the immune response in ayu by suppressing the function of MO/MФ.

The extent to which immunity, apoptosis and detoxification gene expression interact with 17 alpha-methyltestosterone

Innate immunity is the first line of defence against invasion by foreign pathogens. One widely used synthetic androgen for the production of all-male fish, particularly commercially valuable Nile tilapia, Oreochromis niloticus, is 17 alpha-methyltestosterone (MT). The present study investigates the effect of MT on innate immunity, cellular apoptosis and detoxification and the mortality rate, during and after the feeding of fry with 0-, 40-and 60-mg MT/kg. Expression analysis was completed on interleukin 1 beta (il1β), interleukin 8 (il8), tumour necrosis factor alpha (tnfα), CXC2- and CC-chemokines, interferon (ifn), myxovirus resistance (mx), toll-like receptor 7 (tlr7), immunoglobulin M heavy chain (IgM heavy chain), vitellogenin (vtg), cellular apoptosis susceptibility (cas) and glutathione S-transferase α1 (gstα1). Expression analysis revealed that MT had a significant impact on these genes, and this impact varied from induction to repression during and after the treatment. Linear regression analysis showed a significant association between the majority of the tested gene transcript levels and mortality rates on the 7^th and 21^st days of hormonal treatment and 2 weeks following hormonal cessation. The results are thoroughly discussed in this article. This is the first report concerning the hazardous effect of MT on a series of genes involved in immunity, apoptosis and detoxification in the Nile tilapia fry.

Molecular cloning, structure and expressional profiles of two novel single-exon genes (PoCCR6A and PoCCR6B) in the Japanese flounder (Paralichthys olivaceus)

CCR6 is an important binding receptor of CCL20 and beta-defensins, and has multiple functions in the innate and acquired immune responses. In this study, we cloned the PoCCR6A and PoCCR6B genes of the Japanese flounder and studied the gene structure and expression patterns of these two genes in bacterial infection. The full-length PoCCR6A cDNA is 1415 bp and the open reading frame (ORF) is 1113 bp, encoding a 370-amino-acid peptide. The full-length PoCCR6B cDNA is 2193 bp and the ORF is 1029 bp, encoding a 363-amino-acid peptide. The structures of PoCCR6A and PoCCR6B indicate that they are single-exon genes. The predicted proteins encoded by PoCCR6A and PoCCR6B have the typical G-protein-coupled receptor (GPCR) family signature of seven transmembrane domains and several conserved structural features. A tissue distribution analysis showed that PoCCR6A is predominately expressed in the intestine, gill, and blood, and PoCCR6B in the gill, spleen, and liver. The expression patterns of the two chemokine receptors were analyzed during bacterial infection. In spleen and kidney, the expression of PoCCR6A was significantly upregulated at 24 h after infection, whereas the expression of PoCCR6B was steady at these time points. While in intestine, both of them were upregulated at 6 h-12 h after infection, and in gill the expression levels of them were upregulated at 24 h. The patterns of expression suggested that PoCCR6A and PoCCR6B play an important role in the immune response of the Japanese flounder, especially in the mucosal tissues.