Immune response elicited by the oral administration of an intermediate strain of IBDV in chickens

Comparative Pathogenicity of Malaysian variant and very virulent infectious bursal disease viruses in chickens

Variant infectious bursal disease virus (vaIBDV) has been identified in various countries with significant economic losses. Recently, the first identification of variant strain in Malaysia was reported. The pathogenicity of the Malaysian variant, UPM1432/2019 and very virulent infectious bursal disease virus (vvIBDV), UPM1056/2018 strains were comparatively evaluated in specific-pathogen-free (SPF) chickens based on gross and histopathological examinations and viral load. Four-week-old SPF chickens were randomly divided into 3 groups; Group 1 served as the control, while groups 2 and 3 birds were challenged with the vaIBDV and vvIBDV, respectively. Three birds from each group were weighed, euthanised and necropsied at 2-, 3-, 4-, 5-, 7- and 21-days post-challenge (dpc). Unlike UPM1056/2018 group, birds from UPM1432/2019 group did not show clinical signs or death. UPM1056/2018 strain caused 11% mortality rate in the infected chickens. The bursal body index (BBIX) for UPM1432/2019- and UPM1056/2018 groups was < 0.7 from 2 dpc and continued to decrease to 0.49 and 0.45, respectively at 21 dpc. UPM1432/2019 strain was more persistent in the bursa than UPM1056/2018 strain. Both strains induced similar pathological lesions in SPF chicks. These results indicate that the Malaysian vaIBDV severely damaged the immune organs of chickens and was more persistent in bursal tissue than vvIBDV. The study provides insight into the pathogenicity of the variant strain as further study may be required to evaluate the efficacy of the current available IBD vaccines in Malaysia against the strain.

Recombinant production of two xylanase-somatostatin fusion proteins retaining somatostatin immunogenicity and xylanase activity in Pichia pastoris

Somatostatin (SS) is one of the peptide hormones that regulate the endocrine system in animals. When SS is used to immunize animals, the correspondingly generated anti-SS antibody neutralizes the SS and, therefore, alleviates its growth inhibiting effects. This is of great value to the livestock industry; however, previously developed methods fail to obtain enough recombinant SS in an economical way. Herein, we describe the employment of a commonly used feed enzyme, i.e., xylanase, as a carrier protein for recombinant expression of SS in large quantity. The SS gene was fused to one of the two xylanase genes (XynCDBFV and BsXynC) and recombinantly expressed in Pichia pastoris. The purified xylanase-SS fusion proteins displayed excellent antigenicity and immunogenicity. In addition, they retained the enzymatic activities and thermostability of the xylanases, indicating that they can catalyze hydrolysis of xylan in plant cell wall of the animal feeds and stand the high temperature in feed pelleting. Thus, the xylanase-SS fusion proteins serve as an excellent candidate chimeric bifunctional vaccine-feed enzyme protein retaining both SS immunogenicity and xylanase activity. KEY POINTS: • Somatostatin is expressed in P. pastoris as fusion proteins with two xylanases. • The chimeric proteins retain both immunogenicity and xylanase activity. • The xylanase-SS proteins may serve as bifunctional proteins in livestock industry.

The Stronger Downregulation of in vitro and in vivo Innate Antiviral Responses by a Very Virulent Strain of Infectious Bursal Disease Virus (IBDV), Compared to a Classical Strain, Is Mediated, in Part, by the VP4 Protein

IBDV is economically important to the poultry industry. Very virulent (vv) strains cause higher mortality rates than other strains for reasons that remain poorly understood. In order to provide more information on IBDV disease outcome, groups of chickens (n = 18) were inoculated with the vv strain, UK661, or the classical strain, F52/70. Birds infected with UK661 had a lower survival rate (50%) compared to F52/70 (80%). There was no difference in peak viral replication in the bursa of Fabricius (BF), but the expression of chicken IFNα, IFNβ, MX1, and IL-8 was significantly lower in the BF of birds infected with UK661 compared to F52/70 (p < 0.05) as quantified by RTqPCR, and this trend was also observed in DT40 cells infected with UK661 or F52/70 (p < 0.05). The induction of expression of type I IFN in DF-1 cells stimulated with polyI:C (measured by an IFN-β luciferase reporter assay) was significantly reduced in cells expressing ectopic VP4 from UK661 (p < 0.05), but was higher in cells expressing ectopic VP4 from F52/70. Cells infected with a chimeric recombinant IBDV carrying the UK661-VP4 gene in the background of PBG98, an attenuated vaccine strain that induces high levels of innate responses (PBG98-VP4UK661) also showed a reduced level of IFNα and IL-8 compared to cells infected with a chimeric virus carrying the F52/70-VP4 gene (PBG98-VP4F52/70) (p < 0.01), and birds infected with PBG98-VP4UK661 also had a reduced expression of IFNα in the BF compared to birds infected with PBG98-VP4F52/70 (p < 0.05). Taken together, these data demonstrate that UK661 induced the expression of lower levels of anti-viral type I IFN and proinflammatory genes than the classical strain in vitro and in vivo and this was, in part, due to strain-dependent differences in the VP4 protein.

Differential expression of pro-inflammatory and anti-inflammatory genes of layer chicken bursa after experimental infection with infectious bursal disease virus

Infectious bursal disease (IBD) is one of the most prevalent infectious diseases caused by IBD virus (IBDV), which results in bursal necrosis and immunosuppression that cause severe damage to the immune system in chickens. Cytokines are important mediators and regulators of both types of host responses. In the present study, layer chickens were artificially challenged with IBDV, and the differential expression of inflammatory genes was explored by using quantitative real-time PCR, which offered basic data for further study of IBDV pathogenesis. Data showed that after IBDV infection, the virus load in the bursa of Fabricius (BF) peaked at 96 h and then gradually decreased. Compared with those of the negative-infected group, the mRNA expression levels of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6, IL-7, IL-8, tumor necrosis factor [TNF]-α, transforming growth factor [TGF]-β) and anti-inflammatory cytokine IL-10 in the infected group increased to varying degrees at 12 to 192 h, respectively. Furthermore, the IL-1β mRNA expression peaked at 48 h; the mRNA transcript levels of IL-6, IL-8, and IL-10 were the highest at 96 h; TNF-α mRNA expression peaked at 120 h; the IL-7 mRNA expression peaked at 144 h; and the TGF-β mRNA transcript level was the highest at 192 h. Taken together, these observations indicated that along with the change pattern of IBDV proliferation in BF, the mRNA expression of cytokines (IL-1β, IL-6, IL-7, IL-8, IL-10, TNF-α, TGF-β) obviously increased, and the kinetics of each of these cytokines was different. The kinetics of IL-6/IL-10 mRNA expression ratio was significantly positively correlated with that of the virus load. These results suggest that IBDV infection seriously interferes with the natural immune response mediated by inflammatory cytokines in chickens.

Virus-Induced Immunosuppression in Chickens

A healthy immune system is a cornerstone for poultry production. Any factor diminishing the immune responses will affect production parameters and increase cost. There are numerous factors, infectious and noninfectious, causing immunosuppression (IS) in chickens. This paper reviews the three viral diseases that most commonly induce IS or subclinical IS in chickens: Marek's disease virus (MDV), chicken infectious anemia virus (CIAV), and infectious bursal disease virus (IBDV), as well as the interactions among them. MDV-induced IS (MDV-IS) affects both humoral and cellular immune responses. It is very complex, poorly understood, and in many cases underdiagnosed. Vaccination protects against some but not all aspects of MDV-IS. CIAV induces apoptosis of the hemocytoblasts resulting in anemia, hemorrhages, and increased susceptibility to bacterial infections. It also causes apoptosis of thymocytes and dividing T lymphocytes, affecting T helper functions, which are essential for antibody production and cytotoxic T lymphocyte (CTL) functions. Control of CIAV is based on vaccination of breeders and maternal antibodies (MAbs). However, subclinical IS can occur after MAbs wane. IBDV infection affects the innate immune responses during virus replication and humoral immune responses as a consequence of the destruction of B-cell populations. Vaccines with various levels of attenuation are used to control IBDV. Interactions with MAbs and residual virulence of the vaccines need to be considered when designing vaccination plans. The interaction between IBDV, CIAV, and MDV is critical although underestimated in many cases. A proper control of IBDV is a must to have proper humoral immune responses needed to control CIAV. Equally, long-term control of MDV is not possible if chickens are coinfected with CIAV, as CIAV jeopardizes CTL functions critical for MDV control.