Macrophage Migration Inhibitory Factor Triggers Inflammatory Responses During Very Virulent Infectious Bursal Disease Virus Infection

RNA-seq reveals role of cell-cycle regulating genes in the pathogenicity of a field very virulent infectious bursal disease virus

Infectious bursal disease virus (IBDV) infection causes highly contagious and immunosuppressive disease in poultry. The thymus, serving as the primary organ for T cell maturation and differentiation, plays an important role in the pathogenicity of IBDV in the infected chickens. However, there are no reports on the molecular pathogenesis of IBDV in the thymus currently. The aim of the study was to elucidate the molecular mechanisms underlying the pathogenicity of a field very virulent (vv) IBDV strain NN1172 in the thymus of SPF chickens using integrative transcriptomic and proteomic analyses. Our results showed that a total of 4,972 Differentially expressed genes (DEGs) in the thymus of NN1172-infected chickens by transcriptomic analysis, with 2,796 up-regulated and 2,176 down-regulated. Meanwhile, the proteomic analysis identified 726 differentially expressed proteins (DEPs) in the infected thymus, with 289 up-regulated and 437 down-regulated. Overall, a total of 359 genes exhibited differentially expression at both mRNA and protein levels, with 134 consistently up-regulated and 198 genes consistently down-regulated, as confirmed through a comparison of the RNA-seq and the proteomic datasets. The gene ontology (GO) analysis unveiled the involvement of both DEGs and DEPs in diverse categories encompassing cellular components, biological processes, and molecular functions in the pathological changes in IBDV-infected thymus. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the host mainly displayed severely disruption of cell survival/repair, proliferation and metabolism pathway, meanwhile, the infection triggers antiviral immune activation with a potential emphasis on the MDA5 pathway. Network inference analysis identified seven core hub genes, which include CDK1, TYMS, MCM5, KIF11, CCNB2, MAD2L1, and MCM4. These genes are all associated with cell-cycle regulating pathway and are likely key mediators in the pathogenesis induced by NN1172 infection in the thymus. This study discovered dominant pathways and genes which enhanced our understanding of the molecular mechanisms underlying IBDV pathogenesis in the thymus.

Enterococcus faecium C171: Modulating the Immune Response to Acute Lethal Viral Challenge

Commensal bacteria modulate acute immune responses to infection in hosts. In this study, Enterococcus faecium C171 was screened and isolated. This strain has similar basic characteristics to the reference probiotic, including strong anti-inflammatory and anti-infective effects. E. faecium C171 inhibits the production of pro-Caspase-1 and significantly reduces the production of interleukin-1β (IL-1β) in vitro. These reactions were confirmed using the Transwell system. Live E. faecium C171 mainly exerted an inhibitory effect on acute inflammation, whereas the anti-infective and immune-activating effects were primarily mediated by the E. faecium C171-produced bacterial extracellular vesicles (Efm-C171-BEVs). Furthermore, in the specific pathogen-free (SPF) chicken model, oral administration of E. faecium C171 increased the relative abundance of beneficial microbiota (Enterococcus and Lactobacillus), particularly Enterococcus, the most important functional bacteria of the gut microbiota. E. faecium C171 significantly inhibited the acute inflammatory response induced by a highly virulent infectious disease, and reduced mortality in SPF chickens by 75%. In addition, E. faecium C171 induced high levels of CD3+, CD4-, and CD8- immunoregulatory cells and CD8+ killer T cells, and significantly improved the proliferative activity of T cells in peripheral blood mononuclear cells, and the secretion of interferon-γ. These findings indicate that E. faecium C171 and Efm-C171-BEVs are promising candidates for adjuvant treatment of acute inflammatory diseases and acute viral infections.

An Infectious Bursal Disease Virus (IBDV) Reverse Genetics Rescue System and Neutralization Assay in Chicken B Cells

Infectious bursal disease virus (IBDV) is a major threat to the productivity of the poultry industry due to morbidity, mortality, and immunosuppression that exacerbates secondary infections and reduces the efficacy of vaccination programs. Field strains of IBDV have a preferred tropism for chicken B cells, the majority of which reside in the bursa of Fabricius (BF). IBDV adaptation to adherent cell culture is associated with mutations altering amino acids in the hypervariable region (HVR) of the capsid protein, which affects immunogenicity and virulence. Until recently, this has limited both the application of reverse genetics systems for engineering molecular clones, and the use of in vitro neutralization assays, to cell-culture-adapted strains of IBDV. Here, we describe the rescue of molecular clones of IBDV containing the HVR from diverse field strains, along with a neutralization assay to quantify antibody responses against the rescued viruses, both using chicken B cells. These methods are readily adaptable to any laboratory with molecular biology expertise and negate the need to obtain wild-type strains. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: A chicken B-cell rescue system for IBDV Basic Protocol 2: A chicken B-cell neutralization assay for IBDV.

Host Combats IBDV Infection at Both Protein and RNA Levels

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by infectious bursal disease virus (IBDV). In recent years, with the emergence of IBDV variants and recombinant strains, IBDV still threatens the poultry industry worldwide. It seems that the battle between host and IBDV will never end. Thus, it is urgent to develop a more comprehensive and effective strategy for the control of this disease. A better understanding of the mechanisms underlying virus-host interactions would be of help in the development of novel vaccines. Recently, much progress has been made in the understanding of the host response against IBDV infection. If the battle between host and IBDV at the protein level is considered the front line, at the RNA level, it can be taken as a hidden line. The host combats IBDV infection at both the front and hidden lines. Therefore, this review focuses on our current understanding of the host response to IBDV infection at both the protein and RNA levels.

Evaluating the Breadth of Neutralizing Antibody Responses Elicited by Infectious Bursal Disease Virus Genogroup A1 Strains Using a Novel Chicken B-Cell Rescue System and Neutralization Assay

Eight infectious bursal disease virus (IBDV) genogroups have been identified based on the sequence of the capsid hypervariable region (HVR) (A1 to A8). Given reported vaccine failures, there is a need to evaluate the ability of vaccines to neutralize the different genogroups. To address this, we used a reverse genetics system and the chicken B-cell line DT40 to rescue a panel of chimeric IBDVs and perform neutralization assays. Chimeric viruses had the backbone of a lab-adapted strain (PBG98) and the HVRs from diverse field strains as follows: classical F52-70 (A1), U.S. variant Del-E (A2), Chinese variant SHG19 (A2), very virulent UK661 (A3), M04/09 distinct (A4), Italian ITA-04 (A6), and Australian variant Vic-01/94 (A8). Rescued viruses showed no substitutions at amino acid positions 253, 284, or 330, previously found to be associated with cell-culture adaptation. Sera from chickens inoculated with wild-type (wt) (F52-70) or vaccine (228E) A1 strains had the highest mean virus neutralization (VN) titers against the A1 virus (log₂ 15.4 and 12.7) and the lowest against A2 viruses (log₂ 7.4 to 7.9; P = 0.0001 to 0.0274), consistent with A1 viruses being most antigenically distant from A2 strains, which correlated with the extent of differences in the predicted HVR structure. VN titers against the other genogroups ranged from log₂ 9.3 to 13.3, and A1 strains were likely more closely antigenically related to genogroups A3 and A4 than A6 and A8. Our data are consistent with field observations and validate the new method, which can be used to screen future vaccine candidates for breadth of neutralizing antibodies and evaluate the antigenic relatedness of different genogroups. IMPORTANCE There is a need to evaluate the ability of vaccines to neutralize diverse IBDV genogroups and to better understand the relationship between HVR sequence, structure, and antigenicity. Here, we used a chicken B-cell line to rescue a panel of chimeric IBDVs with the HVR from seven diverse IBDV field strains and to conduct neutralization assays and protein modeling. We evaluated the ability of sera from vaccinated or infected birds to neutralize the different genogroups. Our novel chicken B-cell rescue system and neutralization assay can be used to screen IBDV vaccine candidates, platforms, and regimens for the breadth of neutralizing antibody responses elicited, evaluate the antigenic relatedness of diverse IBDV strains, and when coupled with structural modeling, elucidate immunodominant and conserved epitopes to strategically design novel IBDV vaccines in the future.

Protective effects of the NLRP3 inflammasome against infectious bursal disease virus replication in DF-1 cells

Inflammatory responses are an important part of the innate immune response during viral infection. Various inflammasome complexes have been identified. The pyrin domain-containing 3 (NLRP3) inflammasome plays a critical role in detecting some RNA viruses, such as influenza virus. However, the effect of the NLRP3 inflammasome on infectious bursal disease virus (IBDV) replication is still unclear. Here, we report that IBDV-infection induces the transcription of NLRP3 inflammasome and IL-1β genes in the immortalized chicken embryo fibroblast cell line DF-1. Inhibition of caspase-1 by Belnacasan (VX-765) suppressed the transcription of IL-1β, reduced cell lysis, and significantly promoted IBDV replication in DF-1 cells. Furthermore, knockdown of NLRP3 by small interfering RNA promoted IBDV replication in the host cells. Thus, IBDV can induce NLRP3 inflammasome activation in DF-1 cells through a mechanism requiring viral replication, revealing a new antiviral mechanism employed by the host.

Comparison of two attenuated infectious bursal disease vaccine strains focused on safety and antibody response in commercial broilers

Background and Aim:

Infectious bursal disease (IBD) or Gumboro disease is one of the most detrimental diseases in the poultry industry worldwide. Previous scientific studies have shown that live IBD vaccination might induce transient immunosuppression, leading to suboptimal vaccine responses, and therefore lack of protection against other infectious diseases; therefore, selecting an IBD vaccine in commercial farms is a concern. This study aims to compare two commercially attenuated IBD vaccines (intermediate and intermediate-plus strains) in terms of safety and antibody response to IBD and Newcastle disease viruses (NDV) in commercial broilers.

Materials and Methods:

Overall, 216 Cobb broiler chickens were divided into three groups based on the IBD vaccine strain administered: V217 strain (Group 1), M.B. strain (Group 2), and an unvaccinated group (Group 3). Groups 1 and 2 were orally vaccinated with Hitchner B1 NDV vaccine strain 7 days after IBD vaccination. Blood samples were collected at IBD vaccination day (15 days of age) and at 7, 14, 21, and 28 days post-IBD vaccination. The immunosuppressive effects of the IBD vaccination were determined by NDV antibody response, the bursa:body weight (B:BW) ratio, and the histopathological lesion scores of the bursa of Fabricius. Phylogenetic analysis was also performed.

Results:

Phylogenetic analysis revealed that the M.B. strain belonged to a very virulent IBD strain, whereas the V217 strain belonged to a classical IBD virus strain. NDV antibody titers of the two vaccinated groups increased after ND vaccination, reaching their maximum at 14 days post-ND vaccination and decreasing thereafter. The V217 group presented the highest NDV humoral response from 7 days post-vaccination (dpv) to the end of the study. The mean NDV antibody titer of the V217 group was significantly (p<0.05) higher than that of the M.B. group at 14 dpv. In addition, the V217 strain-induced lower bursal lesions post-IBD vaccination and a higher B: BW ratio at 7 and 21 dpv compared to the M.B. group. The higher B: BW ratio, lower bursal lesions, and higher ND antibody response present in the V217 group indicate that the V217 strain induces lower immunosuppressive effects compared to the M.B. strain.

Conclusion:

The results of this study indicate that IBD vaccine selection merits consideration, as avoiding the immunosuppressive effects induced by live IBD vaccination and the consequent impact on response to other vaccines is important.

Very virulent infectious bursal disease virus-induced immune injury is involved in inflammation, apoptosis, and inflammatory cytokines imbalance in the bursa of fabricius

Infectious bursal disease virus (IBDV) can cause a highly contagious disease in young chickens, resulting in bursal necrosis that causes severe damage to the immune system. The effects of various IBDV strains on the bursa of Fabricius (BF) have been extensively studied; however, few studies have investigated the effects of IBDV strain LJ-5, a newly discovered very virulent IBDV (vvIBDV), infection on young chicken BF. In this study, three-week-old specific pathogen-free (SPF) chickens were infected with vvIBDV for one to five days. LJ-5 decreased the bursa index, B lymphocyte viability and immunoglobulin (Ig) levels, including IgM and IgA in the bursa and IgY in the sera. Histopathological analysis revealed necrosis and depletion of the lymphoid cells and complete loss of bursal architecture in the BF, and transmission electron microscopy revealed mitochondrial vacuoles, cristae breaks, and nuclear damage in vvIBDV-infected bursa tissue. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive nuclei significantly increased following IBDV infection. Cytokine levels increased in the bursa after IBDV infection, promoting inflammation and causing an inflammatory imbalance. Apoptotic gene expression confirmed that vvIBDV infection promotes the apoptosis of bursal cells. These results suggest that vvIBDV infection attenuate immune responses by reducing B lymphocyte activity of secretion Ig in the bursa or sera and triggers inflammation, apoptosis, and an imbalance of inflammatory cytokines in the BF, resulting in immune injury in SPF chickens, which offered basic data for further study of vvIBDV pathogenesis.

Ex vivo rescue of recombinant very virulent IBDV using a RNA polymerase II driven system and primary chicken bursal cells

Infectious Bursal Disease Virus (IBDV), a member of the Birnaviridae family, causes an immunosuppressive disease in young chickens. Although several reverse genetics systems are available for IBDV, the isolation of most field-derived strains, such as very virulent IBDV (vvIBDV) and their subsequent rescue, has remained challenging due to the lack of replication of those viruses in vitro. Such rescue required either the inoculation of animals, embryonated eggs, or the introduction of mutations in the capsid protein (VP2) hypervariable region (HVR) to adapt the virus to cell culture, the latter option concomitantly altering its virulence in vivo. We describe an improved ex vivo IBDV rescue system based on the transfection of an avian cell line with RNA polymerase II-based expression vectors, combined with replication on primary chicken bursal cells, the main cell type targeted in vivo of IBDV. We validated this system by rescuing to high titers two recombinant IBDV strains: a cell-culture adapted attenuated strain and a vvIBDV. Sequencing of VP2 HVR confirmed the absence of unwanted mutations that may alter the biological properties of the recombinant viruses. Therefore, this approach is efficient, economical, time-saving, reduces animal suffering and can be used to rescue other non-cell culture adapted IBDV strains.