TRIM25 inhibits infectious bursal disease virus replication by targeting VP3 for ubiquitination and degradation.

Infectious bursal disease virus (IBDV), a double-stranded RNA virus, causes immunosuppression and high mortality in 3-6-week-old chickens. Innate immune defense is a physical barrier to restrict viral replication. After viral infection, the host shows crucial defense responses, such as stimulation of antiviral effectors to restrict viral replication. Here, we conducted RNA-seq in avian cells infected by IBDV and identified TRIM25 as a host restriction factor. Specifically, TRIM25 deficiency dramatically increased viral yields, whereas overexpression of TRIM25 significantly inhibited IBDV replication. Immunoprecipitation assays indicated that TRIM25 only interacted with VP3 among all viral proteins, mediating its K27-linked polyubiquitination and subsequent proteasomal degradation. Moreover, the Lys854 residue of VP3 was identified as the key target site for the ubiquitination catalyzed by TRIM25. The ubiquitination site destroyed enhanced the replication ability of IBDV in vitro and in vivo. These findings demonstrated that TRIM25 inhibited IBDV replication by specifically ubiquitinating and degrading the structural protein VP3.

Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens.

Immunosuppression can increase the susceptibility of chickens to other disease-causing pathogens and interfere with the efficacy of vaccination against those pathogens. Chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) are common causes of immunosuppression in chickens. Immunosuppression was induced by experimental infection with either CAV or IBDV to assess the effect of immunosuppression on the efficacy of vaccination with Mycoplasma gallisepticum strain ts-304 against infection with virulent M. gallisepticum, a common bacterial pathogen of chickens worldwide. Birds were experimentally infected with either CAV or IBDV at 1 week of age, before vaccination and challenge with M. gallisepticum to examine the effect of immunosuppression at the time of vaccination, or at 6 weeks of age, after vaccination against M. gallisepticum but before challenge with virulent M. gallisepticum, to investigate the effect of immunosuppression at the time of challenge. All birds were vaccinated with a single dose of the ts-304 vaccine at 3 weeks of age and experimentally challenged with the virulent M. gallisepticum strain Ap3AS at 8 weeks of age. In immunosuppressed chickens there was a reduction in protection offered by the ts-304 vaccine at two weeks after challenge, as measured by tracheal mucosal thicknesses, serum antibody levels against M. gallisepticum, air sac lesion scores and virulent M. gallisepticum load in the trachea. Immunosuppressed birds with detectable serum antibodies against M. gallisepticum were less likely to have tracheal lesions. This study has shown that immunosuppression caused by infection with CAV or IBDV can interfere with vaccination against mycoplasmosis in chickens.

Characterizations of glucose-rich polysaccharides from Amomum longiligulare T.L. Wu fruits and their effects on immunogenicities of infectious bursal disease virus VP2 protein.

The aim of this study is to explore the characterization of Amomum longiligulare T.L. Wu fruits polysaccharide (ALP) and their immune enhancement effects. Two homogeneous polysaccharides (ALP1 and ALP2) were isolated from the fruits. The structural characterization results showed that ALP1 (26.10 kDa) and ALP2 (64.10 kDa) were both mainly composed of glucose. Furthermore, ALP1 was consisted of (1,2)-α-D-Glcp, (1,2,3)-α-D-Glcp and T-α-D-Glcp, while ALP2 was consisted of T-α-D-Glcp, (1,3)-α-D-Glcp and (1,3,6)-α-D-Glcp. Afterwards, the immune enhancement effects of two polysaccharides were evaluated by determining their effects on immunogenicities of infectious bursal disease virus (IBDV) VP2 protein. Chickens were immunized with IBDV VP2 protein accompanied with ALP1/ALP2. And the results indicated both ALP1 and ALP2 promoted the weights and bursa of fabricius indexes of chickens. In addition, both two polysaccharides increased specific IBDV antibody levels, while ALP1 possessed higher immune enhancement ability and was expected to be an adjuvant for IBDV VP2 protein.

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-1ß genes in the immortalized chicken embryo fibroblast cell line DF-1. Inhibition of caspase-1 by Belnacasan (VX-765) suppressed the transcription of IL-1ß, 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.

Comparative bursal cytokine gene expression and apoptosis in vaccinated chickens following virulent infectious bursal disease virus challenge.

The bursal cytokine gene expression and apoptosis were compared in vaccinated chickens with either live or immune-complex infectious bursal disease virus (IBDV) vaccines with or without virulent IBDV challenge. The cytokine gene expressions were evaluated at 5 and 12 day-post-challenge (DPC). The apoptotic marker Caspase-3 was determined by IHC on collected bursae, thymus, spleen, and kidneys at 12 DPC. A significantly decreased bursal cytokine levels were observed in the all-vaccinated birds except for IL-6 in the classic IBD vaccines at 5DPC. A significant upregulation of the IL-2 was observed in the live IBD vaccinated birds. No significant differences in the bursa and thymus Caspase-3 positive cells. However, splenic and renal apoptosis was significantly higher in the live IBD vaccine groups. Results indicate that both vaccine types reduce the IBDV-induced bursal proinflammatory cytokines and apoptosis. However, classic IBD vaccines failed to clear the challenge virus or reduce splenic and renal apoptosis.

Monitoring serologic response to single in ovo vaccination with an immune complex vaccine against infectious bursal disease in broilers.

The infectious bursal disease (IBD) virus is one of the most resistant and prevalent virus worldwide in the poultry industry, being vaccination the main tool to control the disease. For this reason, consistent and uniform immunization of broiler flocks against IBD is necessary to avoid the disease spreading. The aim of this study was to apply and assess an epidemiologic mapping tool focused on the immunization by in ovo single broiler vaccination using an immune complex IBD vaccine. With this regard, 7,576 serum samples were collected from 603 broiler flocks raised in 354 Spanish farms. To do so, blood samples were randomly collected from birds with ages between 35 to 51 d, and the serum was analyzed by ELISA. The results obtained from this study suggested a high uniform immunization against IBDV and a protective immunization between 35 and 51 d of age, with mean titer values ranging between 6,331 and 7,426. In addition, seroprevalence titer data of this large-scale monitoring study fitted a polynomial equation with a R2 value of 0.77, helping to explain and predict the humoral response to IBD vaccination. This seroprevalence map was applied to broiler production and was based on business intelligence tool that incorporates newly developed mapping tool to cover the need of having real-time information of humoral response to IBD vaccination and could be an effective tool for veterinary services to control and prevent IBD.

A unified genotypic classification of infectious bursal disease virus based on both genome segments.

Infectious bursal disease virus (IBDV) of chickens is a birnavirus with a bi-segmented double-stranded RNA genome, the segments designated as A and B. We performed phylogenetic analysis using a 366-bp fragment of segment A (nt 785-1150) and a 508-bp fragment of segment B (nt 328-835) of IBDV. A total of 463 segment A and 434 segment B sequences from GenBank, including the sequences of eight recent Bangladeshi isolates, were used in the analysis. The analysis revealed eight genogroups of segment A under serotype 1, designated as A1 (classical), A2 (US antigenic variant), A3 (very virulent), A4 (dIBDV), A5 (atypical Mexican), A6 (atypical Italian), A7 (early Australian) and A8 (Australian variant), and a single genogroup under serotype 2, designated as A0. On the other hand, segment B could be categorized into five genogroups irrespective of serotype, these being B1 (classical-like), B2 (very virulent-like), B3 (early Australian-like), B4 (Polish & Tanzanian) and B5 (Nigerian). Segment B of serotype 2 strains clustered within genogroup B1. With the bi-segmented genome of IBDV, these differences would allow for a total of 45 possible assortments. Based on the combinations of segment A and segment B genogroups observed in 463 IBDV strains, a total of 15 genotypes could be recognized. Recent Bangladeshi IBDV strains, isolated in 2016, appeared to be segment reassortants having segment A of genogroup A3 (very virulent) and segment B of genogroup B3 (early Australian-like). An extended system of nomenclature of IBDV strains is proposed.

Safety and Efficacy Profile of Live, Intermediate Plus Vaccine Against Infectious Bursal Disease Based on Strain G6.

Infectious bursal disease (IBD) is an acute, highly contagious, immunosuppressive disease of young chickens that causes considerable economic loss in the poultry industry worldwide. Vaccination with live attenuated vaccines is still the most important method used for the control and prevention of IBD in chickens. Here we present the results of in vitro characterization, as well as efficacy and safety testing of a live, intermediate plus vaccine against IBD based on strain G6. Strain characterization confirmed that G6 strain is an intermediate plus strain, showing a high degree of homology with the existing vaccine strains of the same virulence. Safety studies showed that chickens can be vaccinated from 10 days of age. Onset and duration of immunity in specific pathogen free and maternally derived antibodies (MDA) chickens was proven to be 14 and 35 days after vaccination, respectively. When immunizing MDA-positive chickens, vaccine is capable of breakthrough at a titer of ≤500 ELISA units. The field trial conducted on commercial broilers showed a 95% protection against vvIBDV challenge. Stability of the freeze-dried vaccine after reconstitution was confirmed over a period of 3 h. Overall, IBD G6 vaccine has shown good safety and efficacy profile in accordance with European Pharmacopoeia requirements.

Characterization of antigenic variant infectious bursal disease virus strains identified in South Korea.

Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases of young chickens, causing considerable economic losses to the poultry industry. More than 30 years ago, an antigenic variant (av) pathotype of the IBD virus (IBDV) was reported to originate in, and subsequently spread among, poultry farms in the USA. Recently, a novel avIBDV lineage was identified in China and was shown to exhibit clear differences in its pathogenicity as well as molecular characteristics compared with the previously isolated variant strains. In this study, we conducted a passive surveillance of chicken carcasses submitted to our research division from June-December 2019, and detected the IBDV strains by reverse transcription PCR. Five avIBDV strains were isolated, and their pathogenicity was determined by necropsy and molecular analysis. Additionally, a coinfection field case involving an avIBDV strain and a very virulent IBDV (vvIBDV) strain was identified. Multiple sequence alignment and phylogenetic analysis of partial viral protein 1 (VP1) and hypervariable region (hv) VP2 genes revealed that those strains originated from two different avIBDV lineages. The co-occurrence of two sub-groups of avIBDVs in South Korea confirms for the first time the evolution of antigenic variant IBDV strains, and highlights the urgency for the development of new strategies for IBDV intervention in South Korea.RESEARCH HIGHLIGHTS Five avIBDV strains were identified in South Korea by passive surveillance test in 2019.A coinfection between two IBDV strains from different genogroups was reported in a field case.By phylogenetic analysis, Korean avIBDVs belonged to two distinct lineages of antigenic variant genogroup.

Efficacy of a turkey herpesvirus double construct vaccine (HVT-ND-IBD) against challenge with different strains of Newcastle disease, infectious bursal disease and Marek's disease viruses.

A double construct vaccine of turkey herpesvirus (HVT) was prepared that contains the fusion (F) gene from Newcastle disease virus (NDV) and the viral protein 2 (VP2) gene from infectious bursal disease virus (IBDV). Safety of the vaccine (HVT-ND-IBD) was confirmed and efficacy was evaluated after subcutaneous (SC) vaccination at 1 day of age or the in ovo route of vaccination. Challenges were performed with velogenic NDV strains (Texas GB and Herts Weybridge 33/56), with different strains of IBDV (classical strain STC; very virulent strain CS89 and variant E strain) and with Marek's disease virus (MDV) strain RB1B. Vaccination with HVT-ND-IBD induced a high level of protection against these challenges. Vaccination with HVT is often combined with Rispens CVI988 vaccine and live ND vaccines for higher and earlier, MD and ND protection, respectively. HVT-ND-IBD vaccination in combination with these vaccines showed MD protection as early as 4 days post vaccination and ND protection as early as 2 weeks post vaccination. The long protection as seen with HVT vaccination was confirmed by demonstrating protection against NDV up to 60 weeks. Finally, to evaluate the performance of the vaccine in commercial birds with maternally-derived antibodies, two field trials were performed, using in ovo vaccination in broilers and SC vaccination in combination with Rispens CVI988 vaccine in layer-type birds. The efficacy was confirmed for all components by challenges. These results demonstrate that HVT-ND-IBD is a safe and highly efficacious vaccine for simultaneous control of ND, IBD and MD. RESEARCH HIGHLIGHTS A double construct HVT vaccine with the NDV F and the IBDV VP2 genes was prepared. The vaccine protects against three important diseases: MDV, NDV and IBDV. In ovo and sub-cutaneous vaccination was evaluated in the field in commercial chickens.

Recombinant Lactococcus Expressing a Novel Variant of Infectious Bursal Disease Virus VP2 Protein Can Induce Unique Specific Neutralizing Antibodies in Chickens and Provide Complete Protection.

Recent reports of infectious bursal disease virus (IBDV) infections in China, Japan, and North America have indicated the presence of variant, and the current conventional IBDV vaccine cannot completely protect against variant IBDV. In this study, we constructed recombinant Lactococcus lactis (r-L. lactis) expressing a novel variant of IBDV VP2 (avVP2) protein along with the Salmonella resistance to complement killing (RCK) protein, and Western blotting analysis confirmed that r-L. lactis successfully expressed avVP2-RCK fusion protein. We immunized chickens with this vaccine and subsequently challenged them with the very virulent IBDV (vvIBDV) and a novel variant wild IBDV (avIBDV) to evaluate the immune effect of the vaccine. The results show that the r-L. lactis-avVP2-RCK-immunized group exhibited a 100% protection rate when challenged with avIBDV and 100% survival rate to vvIBDV. Furthermore, this immunization resulted in the production of unique neutralizing antibodies that cannot be detected by conventional ELISA. These results indicate that r-L. lactis-avVP2-RCK is a promising candidate vaccine against IBDV infections, which can produce unique neutralizing antibodies that cannot be produced by other vaccines and protect against IBDV infection, especially against the variant strain.

[Co-expression, purification and bioassay of three avian viral antigens].

To achieve uniform soluble expression of multiple proteins in the same Escherichia coli strain, and simplify the process steps of antigen production in genetic engineering subunit multivalent vaccine, we co-expressed three avian virus proteins including the fowl adenovirus serotype 4 (FAdV-4) Fiber-2 protein, infectious bursal disease virus (IBDV) VP2 protein and egg-drop syndrome virus (EDSV) Fiber protein in E. coli BL21(DE3) cells after optimization of gene codon, promoter, and tandem expression order. The purified proteins were analyzed by Western blotting and agar gel precipitation (AGP). The content of the three proteins were well-proportioned after co-expression and the purity of the purified proteins were more than 80%. Western blotting analysis and AGP experiment results show that all the three co-expression proteins had immunoreactivity and antigenicity. It is the first time to achieve the three different avian virus antigens co-expression and co-purification, which simplified the process of antigen production and laid a foundation for the development of genetic engineering subunit multivalent vaccine.

Novel variant infectious bursal disease virus suppresses Newcastle disease vaccination in broiler and layer chickens.

Newcastle disease (ND) is one of the most important avian diseases that seriously threaten the poultry industry worldwide. Sometimes vaccination might not effectively reduce ND occurrence in some poultry farms for unclear reasons. Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases, and the novel variant IBD virus (IBDV) is threatening chicken farms in China. This study evaluated the influence of the novel variant IBDV (SHG19 strain) on immunization of ND vaccine (LaSota strain) in broiler and layer chickens. In commercial broilers, the hemagglutination inhibition antibody titers against LaSota strain were decreased by the prior infection of the novel variant IBDV. Pathological examination revealed that the novel variant IBDV severely damaged the key immune organs of the bursa and spleen, and the B lymphocytes in the bursa were severely destroyed, which was the primary reason involved in the immunosuppression on ND vaccination. Moreover, the novel variant IBDV dramatically reduced the BW of infected broilers by about 16% compared to that of control, which indicated huge economic losses. Furthermore, this study confirmed the immunosuppression induced by the novel variant IBDV in specific pathogen-free layer chickens. In this study, it was discovered that the novel variant IBDV could interfere with ND vaccination in both broilers and layers, which was one important factor involved in immune failure in poultry farms. This study therefore suggests the urgency to control the novel variant IBDV infection for healthy breeding.

A reassortment vaccine candidate of the novel variant infectious bursal disease virus.

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), is the most important immunosuppressive disease threatening the poultry industry worldwide. Recently, the novel variant IBDV has been emerging in large-scale in Asia including China and is becoming a new threat to the healthy development of the poultry industry, but no ideal vaccine is available. Therefore, it is necessary and urgent to develop a new vaccine against the novel variant IBDV. In this study, based on the skeleton of an attenuated vaccine strain Gt, a reassortment virus strain rGtVarVP2 was constructed for the first time, which could express the main protective antigen VP2 of the novel variant IBDV and replicate well in cell culture. Subsequently, the safety and effectiveness of rGtVarVP2 were further evaluated using animal experiments. The rGtVarVP2 is nonpathogenic to specific-pathogen-free (SPF) chicken. The immunization of rGtVarVP2 could induce the specific neutralizing antibodies against the novel variant IBDV. The challenge protection tests further confirmed the effectiveness of the IBDV reassortment virus rGtVarVP2. No atrophy and obvious lesions were observed in the immunization group while the bursae of non-immunization control group were severely destroyed after challenge, which showed that rGtVarVP2 could provide complete protection against the novel variant IBDV. These data indicate that the vaccine candidate (rGtVarVP2 strain) is safe and effective, which is of great significance for comprehensive control of IBD and healthy breeding.

Comparative study on dynamic and immunopathology of four intermediate-plus infectious bursal disease (IBD) vaccines in commercial broiler chickens.

INTRODUCTION: The selection of the right IBD control strategy is primarily based on the choice of the appropriate vaccine strain. High maternal IBD-specific antibodies (Abs) compete with the efficacy IBD vaccine, which necessitates the application of intermediate-plus vaccine strain. METHODS: A comparative experimental study was designed for evaluation of four different commercially available intermediate-plus IBD vaccines in commercial broilers before complete weaning of IBD-specific maternal Abs. RESULTS: As determined by IBD- specific quantitative real-time polymerase chain reaction, three tested vaccine strains (228E, Winterfield H2512, and Winterfield 2512) were able to establish in the bursal tissues as early as six hours (hrs) post-vaccination (PV). Both the 228E and the Winterfield H2512 strains vaccinated groups had the highest viral load and replication rate in the bursal tissues at 24, 36, 48 and 72 hrs PV. Earlier seroconversion, 7-14 days PV, was observed in the case of Winterfield H2512, 228E, and Winterfield 2512 vaccinated birds compared to the Lukert vaccinated birds. The 228E strain was more virulent and induces the highest lesion score with severe degrees of lymphocyte depletion and necrosis which persisted up to 28 days PV. CONCLUSION: Overall, the different intermediate-plus IBD strains possess variable early kinetics in the bursal tissues and eliciting antibody (Ab) responses differently withdifferent degrees of bursal lesions. The assessment of the intrabursal vaccine load together with humoral immunity and bursal damage lesion score are fundamental parameters in the evaluation of the intermediate-plus IBD vaccines.

Reverse genetics approaches for live-attenuated vaccine development of infectious bursal disease virus.

Infectious bursal disease (IBD), which is caused by infectious bursal disease virus (IBDV) infection, leads to severe immunosuppression in young chickens and results in significant economic losses in the poultry industry. To date, vaccination with live-attenuated vaccine (LAV) is a convenient method to provide effective protection against IBDV infection. Classical attenuated viruses are usually obtained by either passaging virus in cultured cells or natural isolation. However, these empiric attenuation methods, which are time-consuming and not guaranteed, are not reliable for emergent antigenic variant and very virulent IBDV strains. The reverse genetics (RG) system opens a new avenue for the development of IBDV LAV. In this review, we summarize the current knowledge on the biological characteristics of IBDV structure and genome organization, as well as the established RG systems. We also describe the details for the strategies used to develop IBDV LAV based on the RG systems.

Alteration of immunological parameters in infectious bronchitis vaccinated-specific pathogen-free broilers after the use of different infectious bursal disease vaccines.

The vaccines currently available to control infectious bursal disease (IBD) include live-attenuated and inactivated vaccines, immune-complex vaccines, and vaccines consisting of viral constructs of herpesvirus of turkeys genetically engineered to express VP2 surface protein. To evaluate the impact of vaccines on the chicken immune system, 2 animal trials were performed in specific pathogen-free broiler chickens. In trial 1, birds were either vaccinated when they are one-day old with a dual recombinant herpes virus of turkey construct vaccine, expressing VP2 protein of (IBDV) and F protein of Newcastle disease virus, or an immune-complex IBDV vaccine or birds were not vaccinated. At 14, 28, and 35 D, the bursa of Fabricius was collected for bursa:body weight (B:BW) ratio calculation. In trial 2, birds were vaccinated when they were 1-day old according to the same protocol as trial 1, but at day 14, all groups also received a live infectious bronchitis (IB) vaccine. At 0, 7, 14, 21, and 28 days after IB vaccination, birds were tested by ELISA for IB serology and, soon after the last blood sampling, they were euthanized for collection of Harderian glands, trachea, and spleen and testing by flow cytometry for characterization of mononuclear cells. The immune-complex vaccine groups showed significantly lower B:BW ratio, lower IBV antibody titers, and higher mean percentage of CD8+ T cells in the spleen, trachea, and Harderian glands than those in the other experimental groups. The results of the in vivo trials coupled with a depth analysis of the repertoire of parameters involved in the immune response to IBD and IB vaccinations show one vaccine may influence the immune response of other vaccines included in the vaccination program.

Development of a recombinant VP2 vaccine for the prevention of novel variant strains of infectious bursal disease virus.

Since 2017, novel variant strains of infectious bursal disease virus (nvIBDV) have been detected in China, while the current vaccines on the market against very virulent IBDV have limited protection against this subtype virus. In this context, a strain of the virus has been isolated, and sequencing alignment and bird regression experiments showed that the virus was IBDV, belonging to the nvIBDV subtype (and named IBDV FJ-1812). Furthermore, the Escherichia coli expression system was used to successfully express soluble nvIBDV rVP2, which is specifically recognized by an anti-IBDV standard serum and anti-nvIBDV positive serum, and could be assembled into 14 - 17 nm virus-like particles. Based on the purified nvIBDV rVP2, we developed an IBDV FJ-1812 VP2 VLP vaccine at a laboratory scale to evaluate protection by this vaccine; in addition, we also prepared an IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV and evaluated its cross-protection against nvIBDV. Results of bird experiments showed that the nvIBDV rVP2 vaccine could induce high titres of specific antibodies, completely protect the bursa of Fabricius from viral infection, and provide 100% immune protection to SPF and Ross 308 broiler chickens. Furthermore, the IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV could provide 60% protection for SPF chickens and 80% protection for Ross 308 broiler chickens. This report provides important technical supports for the prevention and control of nvIBDV in the future.

Assessment of the role of intracloacal inoculation of live infectious bursal disease vaccine in breaking through maternally derived antibodies.

Infectious bursal disease (IBD) remains a potential worldwide threat to the poultry industry despite several vaccination approaches. Because maternally derived antibodies (MDA) constitute a critical problem for IBD vaccination, we examined the efficiency of the intracloacal vaccination approach in breaking through MDA. Experiment 1 determined the ability of the vaccinal strain to multiply in the bursa of Fabricius (BF) in chicks with a high level of MDA. Using real-time polymerase chain reaction, we quantified the strain in the bursae of vaccinated and non-vaccinated chicks. Experiment 2 was performed on three groups of chicks with high levels of MDA: group 1, non-vaccinated non-challenged; group 2, non-vaccinated challenged; and group 3, vaccinated challenged. Seroconversion to IBDV was measured using enzyme-linked immunosorbent assay. Groups 2 and 3 were challenged by vvIBDV at 25 days of age. Experiment 3 studied the effect of early IBD vaccinal strain multiplication on the immune response of vaccinated and non-vaccinated chicks to other vaccines. In experiment 1, the vaccinal strain showed progressive multiplication and reached the detectable titre in BF at 12 h post-vaccination despite high MDA titre. Experiment 2 showed that chicks in group 3 had significant seroconversion against IBDV. After challenge, group 3 showed significant improvements in several measured parameters compared with group 2. Moreover, results of experiment 3 proved that early multiplication of the vaccinal strain in the BF has no significant effect on the immune system or immune response to other vaccines. These results proved the promising success of this IBD vaccination approach.RESEARCH HIGHLIGHTS IBD vaccinal strain succeeded in multiplying in BF after intracloacal inoculation.Vaccinated chicks showed significant seroconversion of IBDV antibody titres.Vaccinated chicks showed a significant protection level against vvIBDV.Early IBD vaccination did not affect the immune response to other vaccines.

T cell subset profile and inflammatory cytokine properties in the gut-associated lymphoid tissues of chickens during infectious bursal disease virus (IBDV) infection.

While infectious bursal disease virus (IBDV) mainly targets immature B cells and causes T cell infiltration in the bursa of Fabricius (BF) of chickens, the effect of IBDV infection on the properties of T cells and relevant cytokine production in avian gut-associated lymphoid tissues (GALTs) remains unknown. Here, we show that while the CD8+ T cell subset is not affected, IBDV infection decreases the percentage of CD4+ T cells in the cecal tonsil (CT), but not in esophagus tonsil, pylorus tonsil, and Meckel's diverticulum of GALTs, in contrast to BF and spleen, in which the proportion of CD4+ cells increases upon IBDV infection. Further, IBDV infection upregulates IFN-γ, IL-10, and the T cell checkpoint receptor LAG-3 mRNA expression in BF. In contrast, in CTs, IBDV infection significantly increases the production of IFN-ß and CTLA-4 mRNA, while no significant effect is seen in the case of IFN-γ, IL-10 and LAG-3. Together, our data reveal differential modulation of T cell subsets and proinflammatory cytokine production in different lymphoid tissues during the course of IBDV infection.