Regulation pattern of fish irf4 (the gene encoding IFN regulatory factor 4) by STAT6, c-Rel and IRF4

Characterisation, evolution and expression analysis of the interferon regulatory factor (IRF) family from olive flounder (Paralichthys olivaceus) in response to Edwardsiella tarda infection and temperature stress

Interferon regulatory factor (IRF) family involves in the transcriptional regulation of type I Interferons (IFNs) and IFN-stimulated genes (ISGs) and plays a critical role in cytokine signaling and immune response. However, systematic identification of the IRF gene family in teleost has been rarely reported. In this study, twelve IRF members, named PoIRF1, PoIRF2, PoIRF3, PoIRF4a, PoIRF4b, PoIRF5, PoIRF6, PoIRF7, PoIRF8, PoIRF9, PoIRF10 and PoIRF11, were identified from genome-wide data of olive flounder (Paralichthys olivaceus). Phylogenetic analysis indicated that PoIRFs could be classified into four clades, including IRF1 subfamily (PoIRF1, PoIRF11), IRF3 subfamily (PoIRF3, PoIRF7), IRF4 subfamily (PoIRF4a, PoIRF8, PoIRF9, PoIRF10) and IRF5 subfamily (PoIRF5, PoIRF6). They were evolutionarily related to their counterparts in other fish. Gene structure and motif analysis showed that PoIRFs protein sequences were highly conserved. Under normal physiological conditions, all PoIRFs were generally expressed in multiple developmental stages and healthy tissues. After E. tarda attack and temperature stress, twelve PoIRFs showed significant and different changes in mRNA levels. The expression of PoIRF1, PoIRF3, PoIRF4a, PoIRF5, PoIRF7, PoIRF8, PoIRF9, PoIRF10 and PoIRF11 could be markedly induced by E. tarda, indicating that they played a key role in the process of antibacterial immunity. Besides, temperature stress could significantly stimulate the expression of PoIRF3, PoIRF5, PoIRF6 and PoIRF7, indicating that they could transmit signals rapidly when the temperature changes. In conclusion, this study reported the molecular properties and expression analysis of PoIRFs, and explored their role in immune response, which laid a favorable foundation for further studies on the evolution and functional characteristics of the IRF family in teleost fish.

Three IRF4 paralogs act as negative regulators of type Ⅰ IFN responses in yellow catfish (Pelteobagrus fulvidraco)

IRF4 is a master member of the interferon regulatory factor (IRF) family playing vital regulatory roles in immune system development and function. Tetrapods have a single-copy IRF4 gene, while teleosts harbor duplicated IRF4 genes. This work describes three IRF4 paralogs from yellow catfish (Pelteobagrus fulvidraco), designated PfIRF4A, PfIRF4B and PfIRF4B-like. These genes all contain a typical IRF structural architecture. Phylogenic and synteny analyses indicate that they should arise from the teleost-specific whole-genome duplication. PfIRF4 genes are abundantly expressed in the immune-related tissues and upregulated by PolyI:C, LPS, and Edwardsiella ictaluri. Ectopic expression of these genes inhibits the activation of fish type Ⅰ IFN promoters and downregulates the transcription levels of IFN-responsive genes, thus allowing the efficient replication of a fish rhabdovirus, spring viremia of carp virus (SVCV). PfIRF4s possess a repressive effect on MyD88-mediated activation of IFN and NF-κB. Some differences are observed between each individual paralog. PfIRF4B is the main form expressed across the tissues and the most up-regulated one after pathogen induction. It exerts a stronger inhibitory effect on IFN antiviral response than the other two paralogs. PfIRF4A and PfIRF4B-like are primarily present in the nucleus, while PfIRF4B displays colocalization and direct associations with MyD88 in the cytoplasm. Overall, the data demonstrate that three PfIRF4 paralogs show shared and individual functional properties in the negative regulation of type Ⅰ IFN response.

Modulation of fish immune response by interferon regulatory factor 4 in redlip mullet (Liza haematocheilus): Delineation through expression profiling, antiviral assay, and macrophage polarization analysis

Interferon regulatory factor 4 (IRF4) is a crucial member of IRF family, which acts as an imperative transcription factor in the development and maturation of multiple lineages of blood cells and also plays a pivotal role in host defense against microbial infections. In the present study, we aimed to investigate the detailed structural and functional aspects of a redlip mullet IRF4 homolog (LhIRF4). The LhIRF4 open reading frame consists of 1347 base pairs encoding 449 amino acids, with the DNA-binding domain sharing significant homology with that of other vertebrate IRF4 homologs. The highest transcription levels of LhIRF4 were observed in the mullet intestine and spleen under normal physiological conditions. Furthermore, a time-dependent upregulation of LhIRF4 transcription was observed in the spleen and head kidney tissues upon pathogenic challenges. When overexpressed in mullet cells, LhIRF4 was localized to the nucleus and significantly stimulated the transcription of several host antiviral genes. Moreover, the overexpression of LhIRF4 strongly inhibited the replication of viral hemorrhagic septicemia virus (VHSV) in vitro. The function of LhIRF4 in regulation of macrophage M2 polarization has also been evidently demonstrated in RAW 264.7 cells. Taken together, our findings indicate the profound role of LhIRF4 in modulating immune responses against microbial infections in redlip mullet.

Promoter Binding and Nuclear Retention Features of Zebrafish IRF Family Members in IFN Response

Interferon regulatory factors (IRFs) constitute a family of transcription factors that synchronize interferon (IFN) antiviral response through translocating to nucleus and binding to the promoters of IFN and IFN-stimulated genes (ISGs). Fish contain 11 IRF members; however, whether or how fish IRF family genes function in IFN response remains limited. Herein, we determine the regulatory roles of 11 zebrafish IRF family members in IFN response relevant to their subcellular localization and promoter binding. Zebrafish IRF family members display three patterns of constitutive localization, only in nucleus (IRF1/2/9/11), only in cytoplasm (IRF3/5/7), and largely in nucleus with small amounts in cytoplasm (IRF4b/6/8/10). DNA pull-down assays confirm that all zebrafish IRF proteins are capable to bind fish IFN promoters, albeit to various degrees, thus regulating IFN gene transcription as activators (IRF1/3/5/6/7/8/9/11) or repressors (IRF2/4b/10). Further characterization of distinct IFN gene activation reveals that IRF1/3/5/6/7/8/9/11 efficiently stimulate zebrafish IFNφ1 expression, and IRF1/7/11 are responsible for zebrafish IFNφ3 expression. Two conserved basic residues within the helix α3 of DNA binding domains (DBDs) contribute to constitutive or inducible nuclear import for all zebrafish IRF family members and DNA binding for most members, thereby enabling them to function as transcription factors. Our results reveal a conserved and general mechanism that specifies zebrafish IRF family proteins to nuclear import and DNA binding, thereby regulating fish IFN response.

Genomic selection signatures in farmed Colossoma macropomum from tropical and subtropical regions in South America

Tambaqui or cachama (Colossoma macropomum) is one of the most important neotropical freshwater fish used for aquaculture in South America, and its production is concentrated at low latitudes (close to the Equator, 0°), where the water temperature is warm. Therefore, understanding how selection shapes genetic variations and structure in farmed populations is of paramount importance in evolutionary biology. High‐throughput sequencing to generate genome‐wide data for fish species allows for elucidating the genomic basis of adaptation to local or farmed conditions and uncovering genes that control the phenotypes of interest. The present study aimed to detect genomic selection signatures and analyze the genetic variability in farmed populations of tambaqui in South America using single‐nucleotide polymorphism (SNP) markers obtained with double‐digest restriction site‐associated DNA sequencing. Initially, 199 samples of tambaqui farmed populations from different locations (located in Brazil, Colombia, and Peru), a wild population (Amazon River, Brazil), and the base population of a breeding program (Aquaculture Center, CAUNESP, Jaboticabal, SP, Brazil) were genotyped. Observed and expected heterozygosity was 0.231–0.350 and 0.288–0.360, respectively. Significant genetic differentiation was observed using global FST analyses of SNP loci (FST = 0.064, p < 0.050). Farmed populations from Colombia and Peru that differentiated from the Brazilian populations formed distinct groups. Several regions, particularly those harboring the genes of significance to aquaculture, were identified to be under positive selection, suggesting local adaptation to stress under different farming conditions and management practices. Studies aimed at improving the knowledge of genomics of tambaqui farmed populations are essential for aquaculture to gain deeper insights into the evolutionary history of these fish and provide resources for the establishment of breeding programs.

Grass carp Mre11A activates IFN 1 response by targeting STING to defend against GCRV infection

Mre11A is considered as a cytosolic DNA receptor in mammals. However, it is rarely known about Mre11A in other vertebrates. Recently, a mammalian ortholog of Mre11A has been identified in grass carp (Ctenopharyngodon idellus) in our lab. Phylogenetic-tree analysis provided evidence for a close genetic relationship between C.idellus Mre11A and Carassius auratus Mre11A. The tissue expression profile of CiMre11A was detected, with a relatively higher level of expression in kidney, intestines, liver and spleen than that in other tissues after grass carp reovirus (GCRV) infection. Similarly, CiMre11A was also up-regulated in CIK cells after treatment with GCRV. Q-PCR and dual-luciferase assays indicated that the transcription levels of IFN1 and ISG15 were inhibited by CiMre11A knockdown, but were gradually augmented after CIK cells were transfected with increasing amounts of CiMre11A. Subcellular localization assays showed that a part of CiMre11A was translocated from the nucleus to the cytoplasm. Co-immunoprecipitation and co-localization assays demonstrated that CiMre11A interacts with CiSTING in response to GCRV infection. In CIK cells, the expressions of both IFN1 and ISG15 were acutely up-regulated by CiMre11A overexpression, as well as by co-overexpression of CiMre11A and CiSTING. CiMre11A and CiSTING induced the phosphorylation and cytoplasmic-to-nuclear translocation of IRF7 in CIK cells. The multiplication of GCRV in CIK cells was inhibited by the overexpression of CiMre11A and CiSTING.

Molecular characterization of the interferon regulatory factor (IRF) family and functional analysis of IRF11 in the large yellow croaker (Larimichthys crocea)

Interferon regulatory factors (IRFs) are a family of transcription factors involved in regulating interferon (IFN) responses and immune cell development. A total of 11 IRFs have been identified in teleost fish. Here, a complete repertoire of 11 IRFs (LcIRFs) in the large yellow croaker (Larimichthys crocea) was characterized with the addition of five newly identified members, LcIRF2, LcIRF5, LcIRF6, LcIRF10, and LcIRF11. These five LcIRFs possess a DNA-binding domain (DBD) at the N-terminal that contains five to six conserved tryptophan residues and an IRF-association domain (IAD) or IAD2 at the C-terminal that is responsible for interaction with other IRFs or co-modulators. Phylogenetic analysis showed that the 11 LcIRFs were divided into four clades including the IRF1 subfamily, IRF3 subfamily, IRF4 subfamily, and IRF5 subfamily. These are evolutionarily related to their respective counterparts in other fish species. The 11 LcIRFs were constitutively expressed in all examined tissues, although at different expression levels. Upon polyinosinic: polycytidylic acid (poly (I:C)) stimulation, the expression of all 11 LcIRFs was significantly induced in the head kidney and reached the highest levels at 6 h post-stimulation (except LcIRF4). LcIRF1, LcIRF3, LcIRF7, LcIRF8, and LcIRF10 were more strongly induced by poly (I:C) than the other LcIRFs. Significant induction of all LcIRFs was observed in the spleen, with LcIRF2, LcIRF5, LcIRF6, LcIRF7, LcIRF9, and LcIRF11 reaching their highest levels at 48 h LcIRF3 and LcIRF11 showed a stronger response to poly (I:C) in the spleen than the other LcIRFs. In addition, LcIRF1, LcIRF3, LcIRF7, LcIRF9, LcIRF10, and LcIRF11 were significantly induced by Vibro alginolyticus in both the spleen and the head kidney, with LcIRF1 strongly induced. Thus, LcIRFs exhibited differential inducible expression patterns in response to different stimuli in different tissues, suggesting that LcIRFs have different functions in the regulation of immune responses. Furthermore, overexpression of LcIRF11 activated the promoters of LcIFNc, LcIFNd, and LcIFNh, and differentially induced the expression levels of LcIFNs and IFN-stimulated genes (ISGs). Overexpression of LcIRF11 in epithelioma papulosum cyprinid (EPC) cells inhibited the replication of viral genes after infection of spring viremia of carp virus (SVCV). These data suggested that LcIRF11 may function as a positive regulator in regulating the cellular antiviral response through induction of type I IFN expression. Taken together, the present study reported molecular characterization and expression analysis of 11 IRFs in the large yellow croaker, and investigated the role of LcIRF11 in the antiviral response, which laid a good foundation for further study on the evolution and functional characterization of fish IRFs.

Zebrafish as a Model for Fish Diseases in Aquaculture

The use of zebrafish as a model for human conditions is widely recognized. Within the last couple of decades, the zebrafish has furthermore increasingly been utilized as a model for diseases in aquacultured fish species. The unique tools available in zebrafish present advantages compared to other animal models and unprecedented in vivo imaging and the use of transgenic zebrafish lines have contributed with novel knowledge to this field. In this review, investigations conducted in zebrafish on economically important diseases in aquacultured fish species are included. Studies are summarized on bacterial, viral and parasitic diseases and described in relation to prophylactic approaches, immunology and infection biology. Considerable attention has been assigned to innate and adaptive immunological responses. Finally, advantages and drawbacks of using the zebrafish as a model for aquacultured fish species are discussed.

Construction of irf4a Transgenic Zebrafish Using Tol2 System and Its Potential Application

Purpose:

Interferon regulatory factor 4 (IRF4) is identified as a transcriptional factor and plays an important role in the immune response in mammals; however, there are few reports about the function of zebrafish IRF4.

Methods:

We first amplified the coding sequence of irf4a from the testis of zebrafish. Besides, the fragments of irf4a, P2A, EGFP, and Tol2 vector were added for homologous recombination. By sequencing, we can get the Tol2-ef1α-irf4a-EGFP recombinant plasmid and it was microinjected into zebrafish embryos. Fluorescence observation was proceeded at days 3 post fertilization; F0 generations expressing green fluorescence in multiple tissues throughout the body were screened as the founder and raised them to sexual maturity. After mating with WT zebrafish to generate F1 offspring, polymerase chain reaction was used to identify whether irf4a was integrated into the zebrafish genome.

Conclusion:

We obtained the systematic overexpressed irf4a transgenic zebrafish with green fluorescence labeled in spine, eyes, heart, brain, and other tissues. The transgenic zebrafish will be used as a tool for the role of IRF4a in the immune response to the inflammation preconditioning in the future study.

Expression, subcellular localization, and potential antiviral function of three interferon regulatory factors in the big-belly seahorse (Hippocampus abdominalis)

Interferon regulatory factors (IRFs) are among the most important transcription mediators and have multiple biological functions, such as antiviral and antimicrobial defense, cell differentiation, immune modulation, and apoptosis. Three IRF family members (HaIRF4-like, HaIRF6, and HaIRF8) of the big belly seahorse (Hippocampus abdominalis) were molecularly and functionally characterized at the sequence and transcriptional level. The coding sequences of HaIRF4-like, HaIRF6, and HaIRF8 were 1214, 1485, and 1266 bp in length, encoding proteins of size 46.21, 55.32, and 47.56 kDa, respectively. Potential viral transcription and replication was detected against VHSV infection using qPCR in HaIRFs-transfected FHM cells. IRFs significantly reduced viral gene expression at 24 h and 48 h post infection and the expression of interferon-stimulated genes (ISGs) was modulated at transcriptional level upon HaIRF overexpression in FHM cells. Subcellular HaIRF localization was observed using GFP-tagged expression vectors in FHM cells. HaIRF4-like and HaIRF8 were localized to the nucleus, whereas HaIRF6 was observed in the cytoplasm. All three IRFs were ubiquitously expressed in all analyzed tissues of the big belly seahorse. The mRNA expression of IRF4-like, IRF6, and IRF8 increased significantly post injection in the blood and gills following LPS, poly (I:C), and Streptococcus iniae challenge. These findings demonstrate that seahorse IRFs are involved in host defense mechanisms against immune stimulants and HaIRFs induce interferon and ISGs which trigger antiviral activity against viral infections in the host.

Activated grass carp STAT6 up-regulates the transcriptional level and expression of CCL20 and Bcl-xl

In mammals, signal transducer and activator of transcription 6 (STAT6) is a broad-spectrum transcriptional regulator involved in cellular immune responses and apoptosis by regulating the immune-related genes and various functional genes. The structure, expression and tyrosine-based phosphorylation of STAT6 are conserved from fish to mammal. However, except the sporadic reports from zebra fish, the function of fish STAT6 has not been well reported. Here, we cloned and characterized the full length cDNA sequence of grass carp (Ctenopharyngodon idella) STAT6 (CiSTAT6). Meanwhile, the activation mechanism and the potential function of CiSTAT6 were studied. The full length cDNA of CiSTAT6 is 2747 bp with an ORF of 2313 bp encoding a polypeptide of 770 amino acids. Phylogenetic tree analysis revealed that CiSTAT6 shares the maximum homology with Cyprinus carpio STAT6. CiSTAT6 was significantly up-regulated and interacted with each other to form the homodimer after treatment with poly I:C. The transfected CiSTAT6 in fish cell lines can activate the promoter activities of CCL20 and Bcl-xl and increase their mRNA levels. In addition, we also found that CiSTAT6 can increase cell viability and inhibit cell apoptosis. Taken together, grass carp STAT6 plays an important part in innate immunity and anti-apoptosis.

STING positively regulates human ORMDL3 expression through TBK1-IRF3-STAT6 complex mediation

Orosomucoid 1-like protein 3 (ORMDL3) is an asthma candidate gene associated with virus-triggered recurrent wheeze. Stimulator of interferon gene (STING) controls TLR-independent cytosolic responses to viruses. However, the association of STING with ORMDL3 is unclear. Here, we have shown that ORMDL3 expression shows a linear correlation with STING in recurrent wheeze patients. In elucidating the molecular mechanisms of the ORMDL3-STING relationship, we found that STING promoted the transcriptional activity of ORMDL3, which was significantly associated with increased levels of interferon regulatory factor 3 (IRF3) and signal transducer and activator of transcription 6 (STAT6). Further study showed that via activation of TANK binding kinase 1 (TBK1), STING enhanced the phosphorylation and binding of IRF3 and STAT6, which upregulated ORMDL3 by binding to the promoter. Our results showed that STING positively regulated ORMDL3 through the TBK1-IRF3-STAT6 complex.

Identification of DEAD-Box RNA Helicase DDX41 as a Trafficking Protein That Involves in Multiple Innate Immune Signaling Pathways in a Zebrafish Model

DDX41 is an important sensor for host recognition of DNA viruses and initiation of nuclear factor-κB (NF-κB) and IFN signaling pathways in mammals. However, its occurrence and functions in other vertebrates remain poorly defined. Here, a DDX41 ortholog [Danio rerio DDX41 (DrDDX41)] with various conserved structural features to its mammalian counterparts was identified from a zebrafish model. This DrDDX41 was found to be a trafficking protein distributed in the nucleus of resting cells but transported into the cytoplasm under DNA stimulation. Two nuclear localization signal motifs were localized beside the coiled-coil domain, whereas one nuclear export signal motif existed in the DEADc domain. DrDDX41 acts as an initiator for the activation of NF-κB and IFN signaling pathways in a Danio rerio STING (DrSTING)-dependent manner through its DEADc domain, which is a typical performance of mammalian DDX41. These observations suggested the conservation of DDX41 proteins throughout the vertebrate evolution, making zebrafish an alternative model in understanding DDX41-mediated immunology. With this model system, we found that DrDDX41 contributes to DrSTING–Danio rerio STAT6 (DrSTAT6)-mediated chemokine (Danio rerio CCL20) production through its DEADc domain. To the best of our knowledge, this work is the first report showing that DDX41 is an upstream initiator in this newly identified signaling pathway. The DrDDX41-mediated signaling pathways play important roles in innate antibacterial immunity because knockdown of either DrDDX41 or DrSTING/DrSTAT6 significantly reduced the survival of zebrafish under Aeromonas hydrophilia or Edwardsiella tarda infection. Our findings would enrich the current knowledge of DDX41-mediated immunology and the evolutionary history of the DDX41 family.

TH9 cell differentiation, transcriptional control and function in inflammation, autoimmune diseases and cancer

Naïve CD4⁺T cells differentiate into various T cell subsets depending on the specific cytokine environment. T_H9 cells are less well-characterized than other T cell subsets, and factors that control their development and function have only recently been identified. It is now clear that T_H9 cells play critical roles in immune-mediated diseases, including allergic airway, autoimmune and inflammatory bowel diseases, and cancer. Thus, the promotion or suppression of T_H9 cell differentiation, transcriptional control and function may provide novel treatments for clinical inflammation, autoimmune diseases and tumors.

Establishment of a cell line with high transfection efficiency from zebrafish Danio rerio embryos and its susceptibility to fish viruses

A cell line ZBE3 isolated from a continuous cell culture derived from zebrafish Danio rerio blastomeres by clonal growth was characterized. ZBE3 cells had been subcultured for >120 passages since the initial primary culture of the blastomeres. The ZBE3 cells grow stably at temperature from 20 to 32° C with an optimum temperature of 28° C in ESM2 or ESM4 medium with 15% foetal bovine serum (FBS). The optimum FBS concentration for ZBE3 cell growth ranged from 15 to 20%. Cytogenetical analysis indicated that the modal chromosome number of ZBE3 cells was 50, the same as the diploid chromosome number of D. rerio. Significant cytopathic effect was observed in ZBE3 cells after infection with redspotted grouper nervous necrosis virus, Singapore grouper iridovirus and grass carp reovirus, and the viral replication in the cells was confirmed by real-time quantitative PCR and transmission electron microscopy, indicating the susceptibility of ZBE3 cells to the three fish viruses. After transfected with pEGFP-N3 plasmid, ZBE3 cells showed a transfection efficiency of about 40% which was indicated by the percentage of cells expressing green fluorescence protein. The stable growth, susceptibility to fish viruses as well as high transfection efficiency make ZBE3 cells be a useful tool in transgenic manipulation, fish virus-host cell interaction and immune response in fish.

Expression pattern analysis of IRF4 and its related genes revealed the functional differentiation of IRF4 paralogues in teleost

In mammals, interferon regulatory factor 4 (IRF4) plays an important role in the process of development and differentiation of B cells, T cells and dendritic cells. It can regulate immune pathway through IRF5, MyD88, IL21, PGC1α, and NOD2. In the present study, we investigated the expression pattern of IRF4 paralogues and these related genes for the first time in teleosts. The results showed that these genes were all expressed predominantly in known immune tissues while IRF5 was also relatively highly expressed in muscle. IRF4b, IL21, MyD88, IRF5 and NOD2 showed maternal expression in the oocyte and the higher expression of IRF4a, Mx and PGC1α before hatching might be involved in the embryonic innate defense system. Zebrafish embryonic fibroblast (ZF4) cells were infected with GCRV and SVCV. During GCRV infection, the expression of Mx was significantly up-regulated from 3 h to 24 h, reaching the highest level at 12 h (101.5-fold over the controls, P < 0.001). And the expression of IRF4a was significantly up-regulated from 3 h to 48 h, reaching the highest level at 12 h (13.75-fold over the controls, P < 0.001). While the expression of IRF4b was only slightly up-regulated at 12 h and 24 h (3.39-fold, 1.93-fold) above control levels, respectively. Whereas the expression of Mx was significantly up-regulated during SVCV infection from 1 h to 48 h, reaching the highest level at 24 h (11.49-fold over the controls, P < 0.001). IRF4a transcripts were significantly up-regulated from 6 h to 24 h, reaching the highest level at 24 h (41-fold over the controls, P < 0.01). IRF4b only showed a slightly up-regulation by SVCV at 24 h (3.2-fold over the controls, P < 0.01). IRF4a and IRF4b displayed a distinct tissue expression pattern, embryonic stages expression and inducible expression in vivo and in vitro, suggesting that IRF4 paralogues might play different roles in immune system.

Investigating the potential immune role of fish NCAMs: Molecular cloning and expression analysis in mandarin fish

The immune role of NCAMs has been revealed in mammals, yet there is no such report in fish. Hence, we analyzed the molecular characterizations and immune-associated expression patterns of NCAMs in mandarin fish. Three NCAM members, named mfNCAM1a, mfNCAM1b and mfNCAM2, were identified. Among the cDNA sequences of mfNCAMs, AU-rich elements in the 3' UTRs of mfNCAM1b and mfNCAM2 as well as VASE sequences in the fourth Ig-like domain-encoding regions of mfNCAM1a and mfNCAM1b were discovered. Moreover, the syntenic analysis suggested that the duplication of NCAM1 is fish-specific. At mRNA and protein levels, the expression analyses revealed that mfNCAMs existed in both systemic and mucosal immune tissues, and located within lymphoid cells. Upon stimulated either by LPS or poly I:C, the expression level of mfNCAM1a was significantly up-regulated in head kidney, spleen, liver, and gut, whereas mfNCAM1b only in head kidney and liver, and mfNCAM2 only in liver. Additionally, the cells coexpressed mfNCAM1 and mfNCCRP-1 might imply the equivalents to mammalian NK cells. Our finding firstly demonstrates the member-specific immune-related tissue expression pattern and immune activity for fish NCAMs. Current data indicate that mfNCAM2 has little immune activity, while the immune activity of mfNCAM1a exists in more tissues than mfNCAM1b, and mfNCAM1a may tend to respond more actively to viral while mfNCAM1b to bacterial stimulants. Additionally, NCAM1b should be a fish-specific member with unique immune function, judging from its different expression pattern, immune activity as well as phylogenetic relationship to mfNCAM1a.