Two type II IFN members, IFN-γ and IFN-γ related (rel), regulate differentially IRF1 and IRF11 in zebrafish

IRF11 synergizes with STAT1 and STAT2 to promote type I IFN production

Interferon regulatory factor 11 (IRF11), a fish specific member of IRF family, is a transcription factor known for its positive role in teleost antiviral defense by regulating IFN expression. Despite its recognized function, the precise mechanism of IRF11 in type I IFNs production remains largely unknown. In this study, we identified IRF11 in Japanese eel, Anguilla japonica, (AjIRF11) and determined its involvement in the later phase of fish IFN production. Our results demonstrate that IRF11-induced IFN production operates through ISRE binding. Mutations in each ISRE site within the promoter of AjIFN2 or AjIFN4 abolished IRF11-mediated activation of IFN promoters. In addition, the overexpression of AjIRF11 does not significantly impact the activation of AjIFN promoters induced by RLR-related signaling pathway proteins. Furthermore, IRF11-knockdown in ZFLs (zebrafish liver cells) has no effect on the RLRs-induced expression of zebrafish IFN-φ1 and IFN-φ3, indicating that IRF11 is not involved in the RLR-mediated IFN production. However, AjIRF11 can form transcription complexes with AjSTAT1 or AjSTAT2, or form homo- or heterodimers with AjIRF1 to stimulate the transcription of type I IFNs. Overall, it is shown in this study that IRF11 can act synergistically with STAT1 and/or STAT2 for the induction of IFN.

Two IFNa3s mediate the regulation of IRF9 in the process of infection with Streptococcus iniae in yellowfin seabream, Acanthopagrus latus (Hottuyn, 1782)

IRF9 can play an antibacterial role by regulating the type I interferon (IFN) pathway. Streptococcus iniae can cause many deaths of yellowfin seabream, Acanthopagrus latus in pond farming. Nevertheless, the regulatory mechanism of type I IFN signalling by A. latus IRF9 (AlIRF9) against S. iniae remains elucidated. In our study, AlIRF9 has a total cDNA length of 3200 bp and contains a 1311 bp ORF encoding a presumed 436 amino acids (aa). The genomic DNA sequence of AlIRF9 has nine exons and eight introns, and AlIRF9 was expressed in various tissues, containing the stomach, spleen, brain, skin, and liver, among which the highest expression was in the spleen. Moreover, AlIRF9 transcriptions in the spleen, liver, kidney, and brain were increased by S. iniae infection. By overexpression of AlIRF9, AlIRF9 is shown as a whole-cell distribution, mainly concentrated in the nucleus. Moreover, the promoter fragments of -415 to +192 bp and -311 to +196 bp were regarded as core sequences from two AlIFNa3s. The point mutation analyses verified that AlIFNa3 and AlIFNa3-like transcriptions are dependent on both M3 sites with AlIRF9. In addition, AlIRF9 could greatly reduce two AlIFNa3s and interferon signalling factors expressions. These results showed that in A. latus, both AlIFNa3 and AlIFNa3-like can mediate the regulation of AlIRF9 in the process of infection with S. iniae.

Bmp4 in Zebrafish Enhances Antiviral Innate Immunity through p38 MAPK (Mitogen-Activated Protein Kinases) Pathway

Bone morphogenetic proteins (BMPs) are a group of structurally and functionally related signaling molecules that comprise a subfamily, belonging to the TGF-β superfamily. Most BMPs play roles in the regulation of embryonic development, stem cell differentiation, tumor growth and some cardiovascular and cerebrovascular diseases. Although evidence is emerging for the antiviral immunity of a few BMPs, more BMPs are needed to determine whether this function is universal. Here, we identified the zebrafish bmp4 ortholog, whose expression is up-regulated through challenge with grass carp reovirus (GCRV) or its mimic poly(I:C). The overexpression of bmp4 in epithelioma papulosum cyprini (EPC) cells significantly decreased the viral titer of GCRV-infected cells. Moreover, compared to wild-type zebrafish, viral load and mortality were significantly increased in both larvae and adults of bmp4-/- mutant zebrafish infected with GCRV virus. We further demonstrated that Bmp4 promotes the phosphorylation of Tbk1 and Irf3 through the p38 MAPK pathway, thereby inducing the production of type I IFNs in response to virus infection. These data suggest that Bmp4 plays an important role in the host defense against virus infection. Our study expands the understanding of BMP protein functions and opens up new targets for the control of viral infection.

Novel Dimeric Architecture of an IFN-γ-Related Cytokine Provides Insights into Subfunctionalization of Type II IFNs in Teleost Fish

Gene duplication leads to subfunctionalization of paralogs. In mammals, IFN-γ is the sole member of the type II IFN family and binds to a receptor complex consisting of IFN-γR1 and IFN-γR2. In teleost fish, IFN-γ and its receptors have been duplicated due to the teleost-specific whole-genome duplication event. In this study, the functions of an IFN-γ-related (IFN-γrel) cytokine were found to be partially retained relative to IFN-γ in grass carp (Ctenopharyngodon idella [CiIFN-γrel]). CiIFN-γrel upregulated the expression of proinflammatory genes but had lost the ability to activate genes involved in Th1 response. The results suggest that CiIFN-γrel could have been subfunctionalized from CiIFN-γ. Moreover, CiIFN-γrel induced STAT1 phosphorylation via interaction with duplicated homologs of IFN-γR1 (cytokine receptor family B [CRFB] 17 and CRFB13). Strikingly, CiIFN-γrel did not bind to the IFN-γR2 homolog (CRFB6). To gain insight into the subfunctionalization, the crystal structure of CiIFN-γrel was solved at 2.26 Å, revealing that it forms a homodimer that is connected by two pairs of disulfide bonds. Due to the spatial positions of helix A, loop AB, and helix B, CiIFN-γrel displays a unique topology that requires elements from two identical monomers to form a unit that is similar to IFN-γ. Further, mutagenesis analyses identified key residues interacting with CiIFN-γrel receptors and those required for the biological functions. Our study can help understand the subfunctionalization of duplicated IFN-γ paralogs in fish.

Transcriptome analysis of grass carp (Ctenopharyngodon idella) and Holland's spinibarbel (Spinibarbus hollandi) infected with Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is a protozoan ciliate that causes white spot disease (also known as ichthyophthiriasis) in freshwater fish. Holland's spinibarbel (Spinibarbus hollandi) was less susceptible to white spot disease than grass carp (Ctenopharyngodon Idella). In this study, grass carp and Holland's spinibarbel are infected by I. multifiliis and the amount of infection is 10,000 theronts per fish. All grass carp died within 12 days after infection, and the survival rate of Holland's spinibarbel was more than 80%. In order to study the difference in sensitivity of these two fish species to I. multifiliis, transcriptome analysis was conducted using gill, skin, liver, spleen and head kidney of Holland's spinibarbel and grass carp at 48 h post-infection with I. multifiliis. A total of 489,296,696 clean reads were obtained by sequencing. A total of 105 significantly up-regulated immune-related genes were obtained by Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis in grass carp. Cluster of differentiation 40 (CD40), cluster of differentiation 80 (CD 80), tumor necrosis factor-alpha (TNF-α), toll-like receptor 4 (TLR-4), interleukin 1 beta (IL-1β) and other inflammatory-related genes in grass carp were enriched in the cytokine-cytokine receptor interaction pathway and toll-like receptor pathway. In Holland's spinibarbel, a total of 46 significantly up-regulated immune-related genes were obtained by GO classification and KEGG pathway enrichment analysis. Immune-related genes, such as Immunoglobin heavy chain (IgH), cathepsin S (CTSS), complement C1q A chain (C1qA), complement component 3 (C3) and complement component (C9) were enriched in phagosome pathway, lysosome pathway and complement and coagulation concatenation pathway. C3 was significantly up-regulated in gill and head kidney. Fluorescence in situ hybridization (FISH) showed that the C3 gene was highly expressed in gill tissue of Holland's spinibarbel infected with I. multifiliis. A small amount of C3 gene was expressed in the gill arch of grass carp after infected with I. multifiliis. In conclusion, the severe inflammatory response in vivo after infecting grass carp with I. multifiliis might be the main cause of the death of grass carp. The extrahepatic expression of the gene of Holland's spinibarbel might play an important role in the immune defense against I. multifiliis.

Functional analysis and regulation mechanism of interferon gamma in macrophages of large yellow croaker (Larimichthys crocea)

Interferon gamma (IFN-γ) is a widely expressed cytokine that has potent antiviral and immunomodulatory effects. The expression and bioactivity of IFN-γ have been reported in several fish species. However, the molecular mechanism mediated by IFN-γ in fish macrophages has not been completely elucidated. This study used the macrophage cell line to investigate the functional activities and regulation mechanism of large yellow croaker IFN-γ (LcIFN-γ). Herein, the mRNA expression of Lcifn-γ was significantly upregulated in macrophages after LPS and poly(I:C) treatment. Recombinant LcIFN-γ protein (rLcIFN-γ) significantly enhanced the phagocytic ability and respiratory burst activity of macrophages. Meanwhile, rLcIFN-γ induced M1 phenotype polarization of macrophages with the upregulated expressions of pro-inflammatory gene. Moreover, rLcIFN-γ upregulated the IFN-stimulated genes (ISGs) expression and activated JAK (Janus tyrosine kinases)-STAT (signal transducer and activator of transcription) signaling pathway by causing the phosphorylation of JAK1 and STAT1^Tyr701. Furthermore, the promoter activity of IFN-regulatory factor 1 (IRF1) was significantly upregulated by the phosphorylated transcription factor STAT1 through binding to its promoter region. In addition to the classical JAK-STAT pathway, rLcIFN-γ also activated multiple distinct signaling cascades such as mitogen-activated protein kinase (MAPK) and protein kinase B (AKT) pathways. Overall, this study indicated the powerful effects of LcIFN-γ on macrophage activation of large yellow croaker and its molecular mechanism.

Bmp8a is an essential positive regulator of antiviral immunity in zebrafish

Bone morphogenetic protein (BMP) is a kind of classical multi-functional growth factor that plays a vital role in the formation and maintenance of bone, cartilage, muscle, blood vessels, and the regulation of adipogenesis and thermogenesis. However, understanding of the role of BMPs in antiviral immunity is still limited. Here we demonstrate that Bmp8a is a newly-identified positive regulator for antiviral immune responses. The bmp8a^−/− zebrafish, when infected with viruses, show reduced antiviral immunity and increased viral load and mortality. We also show for the first time that Bmp8a interacts with Alk6a, which promotes the phosphorylation of Tbk1 and Irf3 through p38 MAPK pathway, and induces the production of type I interferons (IFNs) in response to viral infection. Our study uncovers a previously unrecognized role of Bmp8a in regulation of antiviral immune responses and provides a target for controlling viral infection.

Zhang, Liu and colleagues identify the role of Bmp8a in antiviral immunity in zebrafish and provide mechanistic insight into its function. Bmp8a could serve as a future target for investigative studies of antiviral immune responses.

IRF11 regulates positively type I IFN transcription and antiviral response in mandarin fish, Siniperca chuatsi

In vertebrates, a total of eleven interferon (IFN) regulatory factors (IRFs), IRF1 to IRF11 are reported, with the conserved presence of IRF1 to IRF9 in all classes of vertebrates. However, IRF10 has been reported only in fish and birds, and IRF11 seems to be a fish specific IRF member. In this study, IRF11 in mandarin fish Siniperca chuatsi was found upregulated following virus infection, and IRF11 was localized constitutively in nucleus as revealed through immunofluorescence test. The overexpression and/or luciferase reporter assays showed that IRF11 can induce transcriptionally the ISRE activity, and the expression of type I IFNs, IFNc and IFNh, as well as the IFN-stimulated gene, Mx, thus inhibiting the Siniperca chuatsi rhabdovirus (SCRV) replication as indicated in the reduced expression of virus protein genes. It is thus suggested that IRF11 in mandarin fish and probably in other teleost fish can exert its antiviral effect through the upregulation of type I IFNs and ISGs.

Molecular insight, expression profile and subcellular localization of two STAT family members, STAT1a and STAT2, from Japanese eel, Anguilla japonica

Signal transducer and activator of transcription 1 (STAT1) and STAT2 are critical components of type I and type II IFNs signaling. To date, seven STAT family proteins have been identified from mammals. However, the information on STAT genes in teleost fish is still limited. In the present study, two STAT family genes (STAT1a and STAT2) were identified from Japanese eel, Anguilla japonica and designated as AjSTAT1a and AjSTAT2. The open reading frames of AjSTAT1a and AjSTAT2 are 2244 bp and 2421 bp, encoding for polypeptides of 747 aa and 806 aa, respectively. Both AjSTAT1a and AjSTAT2 contain the conserved domains of STAT proteins. Phylogenetic analysis was performed based on the STATs protein sequences, and showed that AjSTAT1a and AjSTAT2 shared the closest relationship with Oncorhynchus mykiss. Quantitative real-time PCR analysis revealed that AjSTAT1a and AjSTAT2 were expressed in most examined tissues, with the highest expression both in blood. Significantly up-regulated transcripts of AjSTAT1a and AjSTAT2 were detected in response to poly I:C stimulation, and Edwardsiella tarda induced increase in the expression of AjSTAT1a and AjSTAT2 genes. Subcellular localization analysis showed that in both IFNγ-stimulated and unstimulated EPC cells AjSTAT1a and AjSTAT2 were mainly distributed in the cytoplasm, but few AjSTAT1a was distributed in the nucleus. All these results suggested that AjSTAT1a and AjSTAT2 may be critical for regulating the host innate immune defense against pathogens invasion.

Identification and characterization of IRF9 from black carp Mylopharyngodon piceus

Interferon regulatory factor 9 (IRF9) plays a crucial role in JAK-STAT signaling in human and mammal. However, the relationship between IRF9 and STAT1 in teleost fish remains largely unknown. The previous study has elucidated that two STAT1 isoforms (bcSTAT1a and bcSTAT1b) of black carp (Mylopharyngodon piceus) play an important role during the innate immune activation initiated by grass carp reovirus (GCRV). In this paper, black carp IRF9 (bcIRF9) has been identified and characterized. bcIRF9 was distributed majorly in the nucleus and the linker domain (LD) of bcIRF9 was vital for its nuclear localization. bcIRF9 showed ISRE-inducing activity in reporter assay and presented antiviral activity against GCRV in plaque assay, in which both DNA binding domain (DBD) and LD of bcIRF9 were essential for its antiviral signaling. bcIRF9 was identified to interact with both bcSTAT1a and bcSTAT1b in the co-immunoprecipitation assay. It was interesting that bcIRF9-mediated antiviral signaling was up-regulated by bcSTAT1a; however, down-regulated by bcSTAT1b. Thus, our data support the conclusion that bcIRF9 plays an important role in the innate immune defense against GCRV, in which two STAT1 proteins function differently.

Chitosan reduces the protective effects of IFN-γ2 on grass carp (Ctenopharyngodon idella) against Flavobacterium columnare infection due to excessive inflammation

IFN-γ is an immunomodulatory factor that has been extensively studied in phenotypes of mammalian macrophages and multifarious inflammatory responses. Usually these studies relied on the classical synergistic activation of IFN-γ with LPS (LipoPolySaccharides). However, non-mammalian vertebrates, and in particular fish, are not very susceptible to LPS, and easily acquire tolerance upon repeated exposure. Therefore, for studies in fish, it is necessary to replace the classical IFN-γ+LPS immune system activation method, and find other pathogen-associated molecular patterns (PAMPs) capable of stimulating the fish immune system. Here we used an important farmed fish species, Ctenopharyngodon idella, to study the effects of CiIFN-γ2 (C. idella IFN-γ2) and chitosan (CS) on its immune responses in vivo and vitro. Our results showed that the combination of CS and CiIFN-γ2 significantly enhanced the activation of macrophages, with an activation intensity even stronger than in CiIFN-γ2 and CiIFN-γ2+LPS groups. In vivo, injection of CiIFN-γ2 could improve the survival rate of C. idella infected with Flavobacterium columnare, while a combined injection of CiIFN-γ2+CS only improved protection in the early stages after the challenge. Notably, both injections reduced the bacterial load of viscera and improved the levels of several plasma parameters (TP, T-SOD, LA, and NO). However, a dramatic up-regulation of inflammatory factors, severe inflammatory damage in the intestines and hepatopancreas, and increased mortality in late stages of infection were observed in the CiIFN-γ2+CS group. Our findings provide new insights into the macrophage activation phenotypes and inflammatory responses in fish. They also demonstrate that CiIFN-γ2 could be used as a potential immunopotentiator, but not in combination with CS. This suggests that selection of immunological adjuvants should be carefully tested experimentally.

Receptor complex and signalling pathway of the two type II IFNs, IFN-γ and IFN-γrel in mandarin fish or the so-called Chinese perch Siniperca chuatsi

IFN-γ, as the sole member of mammalian type II IFN, is a multifunctional cytokine which exerts its effects through two distinct IFN-γ receptors, IFNGR1 and IFNGR2. However, in teleost fish, another IFN-γ homologous gene, namely IFN-γ related gene (IFN-γrel), has been identified. Although IFN-γ and IFN-γrel genes have been described in some fish species, many important aspects remain poorly understood in relation with their signalling and function. In the present study, IFN-γ and IFN-γrel, as well as their receptors, cytokine receptor family B (CRFB) 17, CRFB13, two of which are homologous to IFNGR1 in mammals, and CRFB6, homolomous to IFNGR2, have been characterized in mandarin fish, Siniperca chuatsi. It was revealed that the two type IFN members exhibit antiviral activity, and IFN-γ transduces downstream signalling through CRFB13 and CRFB6, while IFN-γrel interacts with CRFB17 to activate downstream signalling. Moreover, IFN-γ and IFN-γrel have been shown to exert antiviral biological activity in a STAT1-dependent manner. Intracellular domain analysis of CRFB17 and CRFB13 demonstrated that the Y386 tyrosine residue of CRFB13 is required for the activation of the IFN-γ-mediated biologic response, and the Y324 and Y370 residues in CRFB17 are required to activate IFN-γrel signalling.

Insights into teleost interferon-gamma biology: An update

Interferon-gamma (IFN-ϒ) is probably one of the most relevant cytokines orchestrating the immune response in vertebrates. Although the activities mediated by this molecule are well known in mammals, several aspects of the IFN-ϒ system in teleosts remain a riddle to scientists. Numerous studies support a potentially similar role of the fish IFN-ϒ signalling pathway in some well-described immunological processes induced by this cytokine in mammals. Nevertheless, the existence in some teleost species of duplicated ifng genes and an additional gene derived from ifng known as interferon-γ-related (ifngrel), among other things, raises new interesting questions about the mode of action of these various molecules in fish. Moreover, certain IFN-ϒ-mediated activities recently observed in mammals are still fully unknown in fish. Another attractive but mainly unexplored curious property of IFN-ϒ in vertebrates is its potential dual role depending on the type of pathogen. In addition, some aspects mediated by this molecule could favour the resolution of a bacterial infection but be harmful in the context of a viral disease, and vice versa. This review collects old and new aspects of IFN-ϒ research in teleosts and discusses new questions and pathways of investigation based on recent discoveries in mammals.

Transcriptome analysis provides insights into molecular immune mechanisms of rabbitfish, Siganus oramin against Cryptocaryon irritans infection

The rabbitfish Siganus oramin is resistant to the ciliate parasite Cryptocaryon irritans. L-amino acid oxidase (LAAO) protein from rabbitfish can kill C. irritans in vitro, however, other immune defence mechanisms against C. irritans remains unknown. Here, we generated transcriptomes of rabbitfish skin at 12 h post infection (PI) by C. irritans. The transcriptomes contained 238, 504, 124 clean reads were obtained and then assembled into 258,869 unigenes with an average length of 621 bp and an N50 of 833 bp. Among them, we obtained 418 differentially expressed genes (DEGs) in the skin of rabbitfish under C. irritans infection and control conditions, including 336 significantly up-regulated genes and 82 significantly down-regulated genes. Seven immune-related categories with 32 differentially expressed immune genes were obtained using Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. DEGs included innate immune molecules, such as LAAO, antimicrobial peptide, lysozyme g, as well as complement components, chemokines and chemokine receptors, NOD-like receptor/Toll-like receptor signaling pathway molecules, antigen processing and T/B cell activation and proliferation molecules. We further validated the expression results of nine immune-related DEGs using quantitative real-time PCR. This study provides new insights into the early immune response of a host that is resistant to C. irritans.

STAT1a and STAT1b of black carp play important roles in the innate immune defense against GCRV

Signal transducer and activator of transcription 1 (STAT1) plays an important role in the Janus kinase (JAK)-STAT signaling of human and mammals; however, the mechanism of STAT1 in innate immune activation of teleost fishes remains largely unknown. In this study, two STAT1 homologues (bcSTAT1a and bcSTAT1b) of black carp (Mylopharyngodon piceus) have been cloned and characterized. Both bcSTAT1a and bcSTAT1b transcription in host cells was obviously increased in response to the stimulation of poly (I:C), lipopolysaccharide (LPS), grass carp reovirus (GCRV) and interferon (IFN); however, the increase rate of bcSTAT1b transcription post stimulation was obviously higher than that of bcSTAT1a. bcSTAT1a and bcSTAT1b were distributed in both cytoplasm and nucleus in the immunofluorescence staining assay. Self-association of bcSTAT1a and bcSTAT1b, and the interaction between bcSTAT1a and bcSTAT1b have been detected through co-immunoprecipitation (co-IP) assay; and the data of native polyacrylamide gel electrophoresis (PAGE) implied that bcSTAT1a and bcSTAT1b might form homodimer and heterodimer in vivo like their mammalian counterparts. Both bcSTAT1a and bcSTAT1b presented IFN-inducing ability in report assay, and both bcSTAT1a and bcSTAT1b showed antiviral activities against GCRV in EPC cells. Our data support the conclusion that both bcSTAT1a and bcSTAT1b play important roles in host antiviral innate immune activation initiated by GCRV.

Granulomatous inflammation in ginbuna crucian carp Carassius auratus langsdorfii against Mycobacterium gordonae

In this study, we investigated the immune responses against Mycobacterium gordonae in ginbuna crucian carp. Cumulative mortality of ginbuna injected with 2.0 × 10⁷ CFU of M. gordonae was 50% at 170 days post-infection. CD4-1, CD8α, T-bet and IFNγ2 gene expression levels were significantly upregulated in ginbuna injected with 1.9 × 10⁸ CFU of M. gordonae at 21 and 28 days post-infection. The CD4-2 level did not change during the experiment. Granulomatous responses consisted of central macrophage accumulation and surrounding lymphocytes, and Ziehl-Neelsen-positive bacteria were observed in the trunk kidney of the challenged fish. Immunohistochemistry using anti-ginbuna IFNγs and anti-ginbuna CD4-1 polyclonal antibody revealed that the marginal lymphocytes were positive for CD4-1, and the IFNγ-producing cells surrounded the mycobacterial cell-laden phagocytes. These results suggest that CD4-1⁺ cells and IFNγ2 play important roles in the granulomatous inflammation against Mycobacterial infections in teleosts.

Interferons type II and their receptors R1 and R2 in fish species: Evolution, structure, and function

Interferon gamma (IFN-γ) is one of the key players in the immune system of vertebrates. The evolution and properties of IFN-γ and its receptors in fish species are of special interest as they point to the origin of innate immunity in vertebrates. We studied the phylogeny, biophysical and structural properties of IFN-γ and its receptors. Our phylogeny analysis suggests the existence of two groups of IFN-γ related proteins, one specific for Acanthomorpha, the other for Cypriniformes, Characiformes and Siluriformes. The analysis further shows an ancient duplication of the gene for IFN-γ receptor 1 (IFN- γR1) and the parallel existence of the duplicated genes in all current teleost fish species. In contrast, only one gene can be found for receptor 2, IFN- γR2. The specificity of the interaction between IFN- γ and both types of IFN- γR1 was determined by microscale thermophoresis measurements of the equilibrium dissociation constants for the proteins from three fish species. The measured preference of IFN- γ for one of the two forms of receptor 1agrees with the bioinformatic analysis of the coevolution between IFN- γ and receptor 1. To elucidate structural relationships between IFN-γ of fish and other vertebrate species, we determined the crystal structure of IFN-γ from olive flounder (Paralichthys olivaceus, PoliIFN-γ) at crystallographic resolution of 2.3 Å and the low-resolution structures of Takifugu rubripes, Oreochromis niloticus, and Larimichthys crocea IFN-γ by small angle X-ray diffraction. The overall PoliIFN-γ fold is the same as the fold of the other known IFN- γ structures but there are some significant structural differences, namely the additional C-terminal helix G and a different angle between helices C and D in PoliIFN-γ.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

Composition and transcription of all interferon regulatory factors (IRFs), IRF1‒11 in a perciform fish, the mandarin fish, Siniperca chuatsi

Interferon regulatory factors (IRFs) are a family of mediators in various biological processes including immune modulation of interferon (IFN) and proinflammatory cytokine expression. However, the data on the complete composition of IRFs is rather limited in teleost fish. In the present study, all IRF members, i.e. IRF1‒11 with two IRF4, IRF4a and IRF4b have been characterised in an aquaculture species of fish, the mandarin fish, Siniperca chuatsi, in addition to the previous report of IRF1, IRF2, IRF3 and IRF7 from the fish. These IRFs are constitutively expressed in various organs/tissues of the fish, and their expression can be induced following the stimulation of polyinosinic:polycytidylic acid (poly(I:C)) and the infection of infectious spleen and kidney necrosis virus (ISKNV), a viral pathogen of mandarin fish in aquaculture. The ISKNV infection induced the significant increase in the expression of some IRF genes, i.e. IRF2, IRF4a, IRF7, IRF9, IRF10 at 24 or 36 h post-infection (hpi) in spleen and head-kidney, and the significant increase of some other IRF genes, e.g. IRF1, IRF3, IRF4b, IRF5, IRF6, IRF8 at later stage of infection from 72, or 96, or even 120 hpi, which may imply the inhibitory effect of ISKNV on fish immune response. It is considered that the present study provides the first detailed analysis on all IRF members in an aquaculture species of fish, and can be served as the base for further investigation on the role of IRFs in teleost fish.

Antitumor and Immunoregulatory Activities of Seleno-β-Lactoglobulin on S180 Tumor-Bearing Mice

Degeneration of immune organs like thymus and spleen has been discovered in tumor-bearing mice; which increases the difficulties on oncotherapy. More effective drugs which target the protection of immune organs are expected to be researched. In this study; we aim to analyze the antitumor and immunoregulatory activities of seleno-β-lactoglobulin (Se-β-lg) on S180 tumor-bearing mice. Results indicated that Se-β-lg exhibited a remarkable inhibitory effect on S180 solid tumors with the inhibition rate of 48.38%; and protected the thymuses and spleens of S180-bearing mice. In addition, Se-β-lg could also balance the proportions of CD4⁺ and CD8⁺ T cells in spleens; thymuses and peripheral bloods; and improve Levels of IL-2; IFN-γ; TNF-α in mice serums. β-lg showed weaker bioactivities while SeO₂ showed stronger toxicity on mice. Therefore our results demonstrated that Se-β-lg possessed stronger antitumor and immunoregulatory activities with lower side effects and had the potential to be a novel immunopotentiator and antitumor agent.