Identification, expression profiles and antiviral activities of a type I IFN from gibel carp Carassius auratus gibelio

IRF9 inhibits CyHV-3 replication by regulating the PI3K-AKT signalling pathway in common carp (Cyprinus carpio) epithelial cells

Interferon regulatory factor 9 (IRF9) is an important transcriptional regulator involved in innate and adaptive immunity. Cyprinid herpesvirus-3 (CyHV-3) is a virus causing widespread death and great economic loss in farmed common carp (Cyprinus carpio). However, the effect of IRF9 on CyHV-3 infection in common carp has not been reported. In this study, during CyHV-3 infection, IRF9 overexpression in common carp fin epithelial (CCF) cells significantly reduced the expression of viral factor thymidine kinase (TK) and open reading frame 72 (ORF72), and knockdown of IRF9 produced the opposite results (p < 0.05). In CCF cells. The IRF9 protein was expression in the nucleus and was rapidly induced in CCF cells by CyHV-3 infection. In addition, several genes associated with virus infection, including type I interferon (IFNI), IFN-stimulated gene 15 (ISG15), myxovirus resistance 1 (Mx1) and Viperin were induced in CCF cells overexpressing IRF9 upon CyHV-3 infection. IRF9 overexpression induced by CyHV-3 infection significantly increased the gene expression of Mx1 and phosphoinositide 3-kinase (PI3K) and the protein expression of protein kinase B (AKT) (p < 0.01). Interestingly, IRF9 did not significantly affect Mx1 gene expression when AKT protein levels remained unchanged during CyHV-3 infection of CCF cells. Furthermore, a significant resistance-related locus was found in the IRF9 sequence in "Longke-11" mirror carp (M11) and Yellow River carp (p < 0.05). These results indicated that IRF9 inhibited viral replication by upregulating the expression of Mx1 via the PI3K-AKT signalling pathway during CyHV-3 infection in CCF cells and provide some basis for the study of the antiviral molecular mechanisms of common carp.

Transcriptome analysis identifies LGP2 as an MDA5-mediated signaling activator following spring viremia of carp virus infection in common carp (Cyprinus carpio L.)

The common carp (Cyprinus carpio L.) is an important farmed species worldwide. Mucosal-associated lymphoid tissues play an essential role in the fight against pathogen infection. Spring viremia of carp virus (SVCV) poses a serious threat to the common carp aquaculture industry. Understanding the molecular mechanisms driving mucosal immune responses to SVCV infection is critical. In this study, the mucosal tissues (gills, foregut and hindgut) were collected from normal and infected fishes for transcriptome analysis. A total of 932,378,600 clean reads were obtained, of which approximately 80% were successfully mapped to the common carp genome. 577, 1,054 and 1,014 differential expressed genes (DEGs) were identified in the gills, foregut and hindgut, respectively. A quantitative polymerase chain reaction assay indicated that the DEGs expression in the foregut following SVCV infection was consistent with the transcriptome results. Among them, two key genes of the retinoic acid-inducible gene I (RIG-I)-like receptor family, melanoma-differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2) (i.e., CcMDA5 and CcLGP2), underwent further analysis. Overexpression of CcMDA5 or CcLGP2 increased phosphorylation of TANK-binding kinase 1 and interferon regulatory factor 3 and the expression of interferon-1 (ifn-1), myxovirus resistance (mx), viperin and interferon-stimulated gene 15 (isg15), and inhibited SVCV replication in epithelioma papulosum cyprini cells. Furthermore, CcLGP2 significantly upregulated the CcMDA5-induced ifn-1 mRNA expression and the activation of the ifn-1 promoter. Finally, confocal microscopy and coimmunoprecipitation experiments revealed that CcLGP2 colocalizes and interacts with CcMDA5 via the C-terminal regulatory domain. This study provides essential gene resources for understanding the fish immune response to SVCV infection and sheds light on the potential role of fish LGP2 in the MDA5 regulation.

Type I interferons in ray-finned fish (Actinopterygii)

Interferons (IFNs) are proteins of vital importance in the body's immune response. They are formed in different types of cells and have been found in fish, amphibians, reptiles and mammals. Two types of IFN have been found in ray-finned fish (Superclass: Osteichthyes, Class: Actinopterygii) so far, i.e. IFN type I (IFN I) and IFN type II (IFN II), while the presence of IFN type III (IFN III), which is found in phylogenetically older cartilaginous fishes, was not confirmed in this taxonomic group of vertebrates. Currently, type I IFN in Actinopterygii is divided into three groups, I, II and III, within which there are subgroups. These cytokines in these animals show primarily antiviral activity through the use of a signalling pathway JAK-STAT (Janus kinases - Signal transducer and activator of transcription) and the ability to induce ISG (IFN-stimulated genes) expression, which contain ISRE complexes (IFN-stimulated response elements). On the other hand, in Perciformes and Cyprinidae, it was found that type I/I interferons also participate in the antimicrobial response, inter alia, by inducing the expression of the inducible nitric oxide synthase (iNOS) and influencing the production of reactive oxygen species (ROS) in cells carrying out the phagocytosis process.

Development of monoclonal antibodies against serum immunoglobulins from gibel carp (Carassius auratus gibelio) and their applications in serodiagnosis of inapparent infection and evaluation of vaccination strategies

The disease outbreak caused by viral infection and bacterial pathogens has hampered the sustainable development of the gibel carp (Carassius auratus gibelio) industry, lack of monoclonal antibodies against serum immunoglobulin (Ig) of gibel carp has impeded the development of nonfatal immunoassays in detection of pathogen infection and understanding of fish immune response post vaccination. In the present study, serum Ig of gibel carp was purified by a combination of salting-out and DEAE Sepharose Column chromatography. The purified Ig had an apparent molecular weight of 74 kDa and 24 kDa in SDS-PAGE. Three monoclonal antibodies (MAbs) against Ig, designed as 2F4-1G10, 3H3-1E8 and 7H11-1C8, were developed with purified Ig preparations, which were selected on the basis of the indirect enzyme-linked immunosorbent assay (ELISA). Western blotting showed that MAbs 2F4-1G10 and 7H11-1C8 reacted with the heavy chain of IgM, while MAb 3H3-1E8 showed a reaction with the light chain. MAb 7H11-1C8 could react with surface Ig-positive (sIg+) lymphocytes under indirect immunofluorescence assay. Fluorescence-activated cell sorter analysis revealed that the percentage of sIg + lymphocytes were 32.68% in peripheral blood and 12.13% in pronephros. MAb 7H11-1C8 was proven to be effective in detecting the Cyprinid Herpesvirus 2-specific serum Ig, and determining the levels of Aeromonas hydrophila specific Ig in serum and immune organs under different vaccination strategies.

Cyprinid Herpesvirus 2 miR-C12 Attenuates Virus-Mediated Apoptosis and Promotes Virus Propagation by Targeting Caspase 8

DNA viruses, most notably members of the herpesvirus family, generally encode miRNAs to mediate both virus and host genes expression. We previously demonstrated that Cyprinid herpesvirus 2 (CyHV-2) encodes 17 miRNAs that are involved in innate immune signaling pathways. In this study, the function of CyHV-2-encoded miRNA was further investigated in GiCF cells. We found that miR-C4 promoted CyHV-2-induced apoptosis, while miR-C12 decreased CyHV-2-induced apoptosis. miR-C12 targeted to 3' UTR sequence of caspase 8 and suppressed the expression of caspase 8. Besides, the silencing of caspase 8 by specific siRNA led to the attenuation of CyHV-2-induced apoptosis. Furthermore, caspase 8 was downregulated in cells transfected with miR-C12 during CyHV-2 infection. Overexpression of miR-C12 significantly suppressed CyHV-2-induced apoptosis, while silencing of miR-C12 promoted CyHV-2-induced apoptosis. Finally, inhibition of miR-C12 resulted in suppression of CyHV-2 propagation, overexpression of miR-C12, and CASP8-siRNA-1 facilitated CyHV-2 propagation. Taken together, our results demonstrated that CyHV-2-encoded miR-C12 to suppress virus-induced apoptosis and promoted virus replication by targeting caspase 8.