Bursal transcriptome of chickens protected by DNA vaccination versus those challenged with infectious bursal disease virus

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.

Tissue distribution and developmental changes of interferon regulatory factors in chickens and effects of infectious bursal disease virus infection

Interferon regulatory factors (IRFs) are a family of transcription factors that play a role in a variety of biological processes including immune regulation of interferon and expression of inflammatory cytokines. However, the data on IRFs are rather limited in chickens. In the present study, qRT-PCR was used to study the tissue distribution of IRFs in chickens at D15 (the 15th day of raising) and developmental changes of all chIRFs (Chicken interferon regulatory factors) in BF from E15 (the 15th day of incubation) to D15. The effects of IBDV infection with chickens on the transcriptional level of chIRFs were also investigated. The results showed: (1) chIRF1 mRNA was expressed much more abundantly in intestinal tract, chIRF2, chIRF6, chIRF7, chIRF8 and chIRF10 distributed mainly in liver or/and kidney. The expression of chIRF5 was mainly in spleen and chIRF4 distributed uniquely abundantly in BF. (2) The mRNA expression levels of chIRF5, chIRF7, chIRF8 and chIRF10 was low before hatching of chicken and at D1 and increased significantly from D5 till to the experiment end and the fold change of chIRF5 at D10 and chIRF7 at D5 reached 41.0-fold and 15.7-fold compared to that of E15, respectively (P < 0.05). ChIRF4 mRNA level was always high during the whole experiment except for E15 and it was 11.9-fold at the highest time point than that of E15 (the lowest time point). (3) When chicken was infected with IBDV, the expression levels of chIRF2, chIRF7 and chIRF10 mRNA had the tendency of increasing first and then decreasing but they peaked at 1dpi, 2 dpi, and 3dpi, respectively. The expression of chIRF5 mRNA was suppressed obviously during the whole experiment stage in IBDV-infected chicken. And chIRF4 expression was up-regulated transitorily at 1dpi and then was suppressed on a very low level till to the experiment end. Conclusion: The chIRFs were constitutively expressed in different tissues examined and has tissue-specific expression. Of them, chIRF2, chIRF4, chIRF5, chIRF7, chIRF8 and chIRF10 were related closely with the development or immune response of BF, and when chicken was infected with IBDV, some of them were activated, earlier or later on, some of them were suppressed. These findings would help to sieve out a few antiviral chIRF candidate gene to improve the host's innate immune and provide a foundation of the further exploiting a new vaccine adjuvant.

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.

Systematic Identification of Host Immune Key Factors Influencing Viral Infection in PBL of ALV-J Infected SPF Chicken

Although research related to avian leukosis virus subgroup J (ALV-J) has lasted for more than a century, the systematic identification of host immune key factors against ALV-J infection has not been reported. In this study, we establish an infection model in which four-week-old SPF chickens are infected with ALV-J strain CHN06, after which the host immune response is detected. We found that the expression of two antiviral interferon-stimulated genes (ISGs) (Mx1 and IFIT5) were increased in ALV-J infected peripheral blood lymphocytes (PBL). A significant CD8⁺ T cell response induced by ALV-J appeared as early as seven days post-infection (DPI), and humoral immunity starting from 21 DPI differed greatly in the time scale of induction level. Meanwhile, the ALV-J viremia was significantly decreased before antibody production at 14 DPI, and eliminated at 21 DPI under a very low antibody level. The up-regulated CD8⁺ T cell in the thymus (14DPI) and PBL (7 DPI and 21 DPI) was detected, indicating that the thymus may provide the output of CD8⁺ T cell to PBL, which was related to virus clearance. Besides, up-regulated chemokine CXCLi1 at 7 DPI in PBL was observed, which may be related to the migration of the CD8⁺ T cell from the thymus to PBL. More importantly, the CD8 ^high+ T cell response of the CD8αβ phenotype may produce granzyme K, NK lysin, or IFN-γ for clearing viruses. These findings provide novel insights and direction for developing effective ALV-J vaccines.

Selenium Deficiency Affects Immune Function by Influencing Selenoprotein and Cytokine Expression in Chicken Spleen

Se is an important bioelement essential for a healthy immune system. Dietary Se influences both innate and adaptive immune responses. However, the effects of Se deficiency in chicken spleen are still unknown; thus, we designed an experiment to study the role of Se in chicken spleen. A total of 180 one-day-old sea blue white laying hens were randomly allocated into two groups (a control group and a Se-deficient group). The control group was fed a diet supplemented with sodium selenite with a final Se content of 0.15 mg/kg, and the Se-deficient group was fed a Se-deficient diet with a Se content of 0.033 mg/kg. Twenty selenoproteins and ten cytokines were investigated in detail. The expression levels of selenoproteins in spleen were determined via real-time qPCR at 15, 35, and 55 days, and cytokine levels were determined using ELISA at 15, 35, and 55 days. Protein-protein interaction predictions and principal component analysis were performed. We found that the selenoprotein mRNA levels were significantly lower (P < 0.05) in the Se-deficient group compared with the control group. The expression levels of IL-2, IL-1β, IL-6, IFN-α, and IL-17 were significantly lower (P < 0.05), and the levels of IL-8, IL-10, IFN-γ, IFN-β, and TNF-α were significantly higher (P < 0.05) in the Se-deficient group. These selenoproteins were positively correlated with component 1 and component 2 of the PCA, but the relationship between cytokines and principal components in spleens was very complex. The investigation showed that Se deficiency caused a reduction in selenoprotein gene expression and further affected certain cytokines levels. Our results provide some compensatory data about selenoproteins and cytokines in spleens of Se-deficient chickens and provide clues for further research on the relationship between selenoproteins and cytokines.

Early immune responses and profiling of cell-mediated immunity-associated gene expression in response to rHVT-IBD vaccination

Infectious bursal disease (IBD) remains a major threat to the poultry industry. Recombinant herpesvirus of turkey (rHVT)-IBD vaccines have been successfully used to induce a protective immune response against IBD. However, the capacity for rHVT-IBD vaccines to induce early protection without detectable antibodies, and the underlying mechanisms mediating specific cell-mediated responses in the early stages following vaccination, have been poorly investigated. Therefore, in this study, specific pathogen-free (SPF) chickens were vaccinated with rHVT-IBD and T-cell subsets were analyzed. Both splenic and circulating CD8⁺ cell populations increased at 7 days postvaccination (dpv). Next, the expression of adaptive immunity-related genes was analyzed in the spleen and lung of rHVT-IBD-vaccinated chickens. Upregulation of CD8 expression was observed at 7 dpv. Interestingly, a parallel increase in the transcription of granzymes A and K was also detected from 7 dpv. To our knowledge, the latter result is the first to be reported, and it suggests that cytotoxic activity of CD8⁺ T lymphocytes is activated. In contrast, expression of the innate genes examined remained largely unchanged following vaccination. To further investigate the IBD virus (IBDV)-specific responses triggered by rHVT-IBD vaccination, vaccinated chickens were inoculated with an attenuated IBDV strain with the aim of restimulating induced immune responses in vivo. The expression profiles of various genes associated with adaptive immune responses were subsequently analyzed in lung, spleen, and bursa of Fabricius samples. Significant upregulation of CD4, CD8, perforin, and IFNγ expression were observed in the bursa samples 7 days postinoculation (dpi). In the lung, transcript levels of CD8, granzymes and perforin were also significantly higher in the rHVT-IBD-vaccinated chickens at 7 dpi, thereby suggesting that specific cellular immune responses were activated. Overall, these results support the hypothesis that stimulation of specific CD8⁺ cell-mediated immunity contributes to the response against IBDV in rHVT-IBD-vaccinated chickens.

Lipopolysaccharide induces acute bursal atrophy in broiler chicks by activating TLR4-MAPK-NF-κB/AP-1 signaling

We investigated the mechanisms that induce atrophy of the chicken bursa of Fabricius (BF) upon lipopolysaccharide (LPS) treatment in young chicks. LPS treatment resulted in ∼36% decrease in bursal weight within 36 h (P < 0.01). Histological analysis showed infiltration of eosinophilic heterophils and nucleated oval shaped RBCs in or near blood vessels of the BF from LPS-treated chicks. Scanning electron micrographs showed severe erosion and breaks in the mucosal membrane at 12 h and complete exuviation of bursal mucosal epithelial cells at 36 h. We observed decreased cell proliferation (low PCNA positivity) and increased apoptosis (high TUNEL and ssDNA positivity) in the BF 12-72 h after LPS treatment. RNA-seq analysis of the BF transcriptome showed 736 differentially expressed genes with most expression changes (637/736) 12 h after LPS treatment. KEGG pathway analysis identified TLR4-MAPK-NF-κB/AP-1 as the key signaling pathway affected in response to LPS stimulation. These findings indicate LPS activates the TLR4-MAPK-NF-κB/AP-1 signaling pathway that mediates acute atrophy of the chicken bursa of Fabricius by inducing inflammation and apoptosis.

Expression of perforin, granzyme A and Fas ligand mRNA in caecal tissues upon Eimeria tenella infection of naïve and immune chickens

Cytotoxic cells of the immune system may kill infected or transformed host cells via the perforin/granzyme or the Fas ligand (FasL) pathways. The purpose of this study was to determine mRNA expression of perforin, granzyme A and FasL in Eimeria tenella-infected tissues at primary infection and infection of immune chickens as an indirect measure of cytotoxic cell activity. Chickens were rendered immune by repeated E. tenella infections, which were manifested as an absence of clinical signs or pathological lesions and significantly reduced oocyst production upon challenge infection. During primary E. tenella infection, perforin, granzyme A and FasL mRNA expression in caecal tissue was significantly increased at 10 days after infection, compared to uninfected birds. In contrast, at infection of immune birds, perforin and granzyme A mRNA expression in caecal tissue was significantly increased during the early stages of E. tenella challenge infection, days 1-4, which coincided with a substantial reduction of parasite replication in these birds. These results indicate the activation of cytotoxic pathways in immune birds and support a role for cytotoxic T cells in the protection against Eimeria infections.

Infectious bursal disease virus in poultry: current status and future prospects

Infectious bursal disease virus (IBDV) affects immature B lymphocytes of the bursa of Fabricius and may cause significant immunosuppression. It continues to be a leading cause of economic losses in the poultry industry. IBDV, having a segmented double-stranded RNA genome, is prone to genetic variation. Therefore, IBDV isolates with different genotypic and phenotypic diversity exist. Understanding these features of the virus and the mechanisms of protective immunity elicited thereof is necessary for developing vaccines with improved efficacy. In this review, we highlighted the pattern of virus evolution and new developments in prophylactic strategies, mainly the development of new generation vaccines, which will continue to be of interest for research as well as field application in the future.

Selenoproteins and heat shock proteins play important roles in immunosuppression in the bursa of Fabricius of chickens with selenium deficiency

Selenium (Se) is necessary for the immune system in chicken and mediates its physiological functions through selenoproteins. Heat shock proteins (Hsps) are indispensable for maintaining normal cell function and for directing the immune response. The aim of the present study was to investigate the effects of Se deficiency on the messenger ribonucleic acid (mRNA) expression levels of selenoproteins and Hsps as well as immune functions in the chicken bursa of Fabricius. Two groups of chickens, namely the control and Se-deficient (L group) groups, were reared for 55 days. The chickens were offered a basal diet, which contained 0.15 mg Se/kg in the diet fed to the control group and 0.033 mg Se/kg in the diet fed to the L group. We performed real-time quantitative polymerase chain reaction to detect the mRNA expression levels of selenoproteins and Hsps on days 15, 25, 35, 45 and 55. Western blotting was used to determine the protein expression levels of Hsps on days 35, 45 and 55, and immune functions were assessed through an enzyme-linked immunosorbent assay on days 15, 35, and 55. The data showed that the mRNA expression levels of selenoproteins, such as Txnrd1, Txnrd2, Txnrd3, Dio1, Dio2, Dio3, GPx1, GPx2, GPx3 GPx4, Sepp1, Selo, Sel-15, Sepx1, Sels, Seli, Selu, Selh, and SPS2, were significantly lower (P < 0.05) in the L group compared with the control group. Additionally, the mRNA and protein expression levels of Hsps (Hsp27, Hsp40, Hsp60, Hsp70, and Hsp90) were also significantly higher (P < 0.05) in the L group. The expression levels of IL-2, IL-6, IL-8, IL-10, IL-17, IL-1β, IFN-α, IFN-β, and IFN-γ were significantly lower (P < 0.05) and TNF-α was significantly higher (P < 0.05) in the L group compared with the control group. Our results show that immunosuppression was accompanied by a downregulation of mRNA expression levels of selenoproteins and an upregulation of the Hsp mRNA expression levels. Thus, Se deficiency causes defects in the chicken bursa of Fabricius, and selenoproteins and Hsps play important roles in immunosuppression in the bursa of Fabricius of chickens with Se deficiency.