DHAV-1 Blocks the Signaling Pathway Upstream of Type I Interferon by Inhibiting the Interferon Regulatory Factor 7 Protein.

Duck hepatitis A virus (DHAV), which mainly infects 1- to 4-week-old ducklings, has a fatality rate of 95% and poses a huge economic threat to the duck industry. However, the mechanism by which DHAV-1 regulates the immune response of host cells is rarely reported. This study examined whether DHAV-1 contains a viral protein that can regulate the innate immunity of host cells and its specific regulatory mechanism, further exploring the mechanism by which DHAV-1 resists the host immune response. In the study, the dual-luciferase reporter gene system was used to screen the viral protein that regulates the host innate immunity and the target of this viral protein. The results indicate that the DHAV-1 3C protein inhibits the pathway upstream of interferon (IFN)-ß by targeting the interferon regulatory factor 7 (IRF7) protein. In addition, we found that the 3C protein inhibits the nuclear translocation of the IRF7 protein. Further experiments showed that the 3C protein interacts with the IRF7 protein through its N-terminus and that the 3C protein degrades the IRF7 protein in a caspase 3-dependent manner, thereby inhibiting the IFN-ß-mediated antiviral response to promote the replication of DHAV-1. The results of this study are expected to serve as a reference for elucidating the mechanisms of DHAV-1 infection and pathogenicity.

Development and evaluation of an indirect ELISA based on recombinant structural protein VP2 to detect antibodies against duck hepatitis A virus.

An indirect enzyme-linked immunosorbent assay (I-ELISA) based on the VP2 protein of duck hepatitis A virus type 3 (DHAV-3) was established in this study. The optimal dilutions of antigen, serum and goat anti-duck IgG conjugate were 1:1600 (2.23 µg/mL), 1:160 and 1:2000, respectively. The optimal blocking buffer was 1% skim milk. The cut-off value for the method was 0.25, and the analytical sensitivity of the method was 1:5120. The results of specific evaluation showed that except for DHAV-1, DHAV-3 antisera did not cross-react with any other common duck-sensitive pathogens, indicating that this method can be used to detect DHAV-3 and DHAV-1 antibodies. The coefficients of variation (CVs) were lower than 10 %. The coincidence rate between the VP2-DHAV-3-ELISA and the neutralization test was 93.3 %. In summary, the I-ELISA method based on VP2 protein has high sensitivity, specificity, and coincidence rate compared with the neutralization test and has advantages in serum monitoring. The I-ELISA method based on VP2 protein provides a simple and rapid method for the detection of anti-DHAV antibodies and the epidemiological monitoring of DHAV.

Regulation of Apoptosis by Enteroviruses.

Enterovirus infection can cause a variety of diseases and severely impair the health of humans, animals, poultry, and other organisms. To resist viral infection, host organisms clear infected cells and viruses via apoptosis. However, throughout their long-term competition with host cells, enteroviruses have evolved a series of mechanisms to regulate the balance of apoptosis in order to replicate and proliferate. In the early stage of infection, enteroviruses mainly inhibit apoptosis by regulating the PI3K/Akt pathway and the autophagy pathway and by impairing cell sensors, thereby delaying viral replication. In the late stage of infection, enteroviruses mainly regulate apoptotic pathways and the host translation process via various viral proteins, ultimately inducing apoptosis. This paper discusses the means by which these two phenomena are balanced in enteroviruses to produce virus-favoring conditions - in a temporal sequence or through competition with each other. This information is important for further elucidation of the relevant mechanisms of acute infection by enteroviruses and other members of the picornavirus family.

The VP3 protein of duck hepatitis A virus mediates host cell adsorption and apoptosis.

Duck hepatitis A virus (DHAV) causes an infectious disease that mainly affects 1- to 4-week-old ducklings, resulting in considerable loss to the duck industry. Although there have been many studies on DHAV in recent years, the effects on host infection and pathogenesis of DHAV-1 remain largely unknown. This study investigated the effects of the DHAV-1 structural protein VP3 on DHAV-1 virus adsorption and apoptosis to explore the role of VP3 in the viral life cycle. The effects of DHAV-1 VP3 and an antibody against the protein on virion adsorption was analyzed by qRT-PCR. The results showed that the virus copy number for the rabbit anti-VP3 IgG-treated group was significantly lower than that for the negative control group but higher than that for the rabbit anti-DHAV-1 IgG-treated group. This result indicates that VP3 mediates DHAV-1 virus adsorption but that it is not the only protein that involved in this process. In addition, a eukaryotic recombinant plasmid, pCAGGS/VP3, was transfected into duck embryo fibroblasts (DEFs), and the apoptotic rate was determined by DAPI staining, the TUNEL assay and flow cytometry. DAPI staining showed nucleus fragmentation and nuclear edge shifting. TUNEL assay results revealed yellow nuclei, and flow cytometry indicated a significant increase in the apoptotic rate. In addition, qRT-PCR revealed increased in the transcriptional levels of the apoptotic caspase-3, -8 and -9, with the largest increase for caspase-3, followed by caspase-9 and caspase-8. Enzyme activity analysis confirmed these results. Furthermore, the VP3 protein decreased the mitochondrial membrane potential, and the transcriptional levels of the proapoptotic factors Bak, Cyt c and Apaf-1 in the mitochondrial apoptotic pathway were significantly upregulated. These data suggest that expression of VP3 in DEFs induces apoptosis and may primarily activate caspase-3-induced apoptosis through mitochondrion-mediated intrinsic pathways. The findings provide scientific data to clarify DHAV-1 infection and pathogenesis.