Local cellular immune response plays a key role in protecting chickens against hepatitis-hydropericardium syndrome (HHS) by vaccination with a recombinant fowl adenovirus (FAdV) chimeric fiber protein

Virulence of fowl adenovirus (FAdV) serotype 4 strains impacts cell proliferation and immune response of primary chicken-embryo intestinal epithelial cells

Fowl adenovirus serotype 4 (FAdV-4) causes hepatitis-hydropericardium syndrome (HHS) in chickens, leading to substantial economic losses. Following oral uptake, the virus infects intestinal epithelial cells (IEC) to overcome the first entrance barrier. The initial cellular interactions and intestinal immune responses are not well understood. This study uses a primary IEC culture model to investigate infection dynamics of virulent (AG234) and non-pathogenic (KR5) FAdV-4 strains and cellular defence mechanisms. Cell growth and viral propagation were assessed at 4, 12, 24, and 48 hours post-infection (hpi) using immunofluorescence and automated image analysis. The innate immune response was assessed by the mRNA expression of the Toll-like receptors (TLR1B, TLR2B, TLR3, TLR4, and TLR21) and the cytokines (IL-1β, IL-6, IL-10, IL-13, and IFN-γ). KR5 did not significantly reduce IEC growth; notable proliferation between 4 and 48 hpi was observed. Although IEC growth was initially similar, AG234 decreased cell numbers at 48 hpi. Compared to KR5, the abundance of AG234-infected cells was already higher at 4 hpi. Nevertheless, at 48 hpi, the number of IEC infected with the virulent strain was less than KR5, albeit without significance. The AG234 infection primarily activated the immune response at 48 hpi, characterised by a significant mRNA up-regulation of TLR3, TLR21, IL-1β and INF-γ compared to the negative control. KR5 induced a substantially higher expression of IL-13 mRNA compared to the control at 48 hpi. The results show that FAdV virulence significantly affects cell growth, viral augmentation, and the immune response. The chicken IEC culture system presented in this study effectively propagates FAdVs to examine the initial stage of intestinal infection.

Vaccination strategies to protect chickens from fowl adenovirus (FAdV)-induced diseases: A comprehensive review

In recent years, fowl adenovirus (FAdV)-induced diseases became a global problem with considerable impact on chicken health and welfare. This has prompted numerous studies to focus on experimental immunization strategies using whole virus formulations (live or killed vaccines), some of them modified as recombinantly constructed vector vaccines. In addition, FAdV capsid proteins were frequently reported as immunizing antigens (subunit vaccines), with fiber proteins being amongst the most successful candidates. To date, there is no standardized protocol to assess vaccine efficacy in experimental FAdV protection studies, with the consequence that the experimental settings present several degrees of variations even when sharing similar premises. Differences in formulation preparations, route of inoculation, antigen dose, vaccination scheme, choice of challenge strain, or type and age of the birds are capable to greatly influence the magnitude of the immune response and the consequent protective efficacy, altogether addressing remaining challenges. Beyond the antigen composition of a vaccine, the epidemiology of FAdVs with the potential of vertical transmission of virus and/or antibodies from breeders to progenies has a substantial impact on protection strategies. The goal of this review is to outline a broad overview of the findings made thus far regarding immunization strategies against diseases associated to FAdV infections, considering the literature published since the appearance of hepatitis-hydropericardium syndrome (HHS) in the late Eighties, in order to emphasize the current knowledge on FAdV vaccines and highlight fields of future research and intervention.

Protective Efficacy of an Inactivated Recombinant Serotype 4 Fowl Adenovirus Against Duck Adenovirus 3 in Muscovy Duck

BACKGROUND

Duck adenovirus 3 (DAdV-3) is an emerging pathogen that has caused severe economic losses to the duck industry in China. Recently, the infection of ducks with serotype 4 fowl adenovirus (FAdV-4) has also been reported in China. Therefore, an efficient bivalent vaccine to control the diseases caused by DAdV-3 and FAdV-4 is extremely urgent. In our previous study, a recombinant FAdV-4 expressing Fiber-2 of DAdV-3 was generated and designated as rFAdV-4-Fiber-2/DAdV-3.

METHODS

Here, the recombinant virus rFAdV-4-Fiber-2/DAdV-3 was inactivated to serve as a bivalent vaccine, and its immunogenicity and protective efficacy against DAdV-3 were evaluated in Muscovy ducks.

RESULTS

The subcutaneous injection of rFAdV-4-Fiber-2/DAdV-3 could efficiently induce antibodies against Fiber-2 of DAdV-3 and neutralize antibodies against FAdV-4. After challenges with DAdV-3, in comparison with the non-immunized ducks, the immunized ducks did not show any bodyweight loss, gross lesions, or histopathologic change. Moreover, viral loads in livers and kidneys from immunized ducks were undetectable, whereas those in non-immunized ducks with challenge were significantly high.

CONCLUSIONS

All these data demonstrate that the inactivated recombinant virus rFAdV-4-Fiber-2/DAdV-3 has the potential to be an efficient vaccine candidate against both FAdV-4 and DAdV-3, although efficacy for FAdV-4 needs to be confirmed experimentally.

Fowl adenovirus 8a isolated from chickens with runting and stunting syndrome induces inclusion body hepatitis and hepatitis-hydropericardium syndrome in chicken embryos

Background and Aim

Fowl adenovirus (FAdV) is the etiological agent of inclusion body hepatitis (IBH) and hepatitis-hydropericardium syndrome (HHS) in poultry. It is also detected in chickens with runting and stunting syndrome (RSS). FAdV has been detected worldwide, and genotypes 8a, 8b, and 11 have been identified in chickens with enteric problems in Brazil. Nevertheless, none of them have been isolated; therefore, these viruses propagate; thus, the viral behavior and pathogenicity are unknown in Brazil. This study aimed to isolate FAdV from the enteric content of chickens affected by RSS.

Materials and Methods

Enteric content samples from chickens affected with RSS and a positive polymerase chain reaction (PCR) test for FAdV were inoculated into specific pathogen-free chicken embryonated eggs (CEEs) through the yolk and chorioallantoic membrane routes on 8 and 10 days of age, respectively and the eggs were incubated for five days for viral isolation.

Results

The embryos exhibited dwarfism, beak atrophy, and pale claws. In addition, some embryos displayed edema and gelatin-like characteristics. The liver exhibited hepatomegaly and multiple necrotic foci, resembling the appearance of nutmeg. In addition, the kidneys appeared enlarged and pale. After 8 days of incubation, the hearts of the inoculated embryos showed hydropericardium. Microscopic evaluation revealed the presence of hepatitis, which was characterized by the presence of intranuclear inclusion bodies and cellular necrosis. Viral FAdV particles were observed in kidney cells using electron microscopy. Viral DNA was detected in the embryos in all three passages, and viral gene copies were also measured in some organs, with high FAdV gene copies detected in the spleen and bursa beyond the liver.

Conclusion

The molecular characterization of FAdV revealed that the isolated strain belonged to genotype 8a of FAdV. Here, FAdV-8a from chickens infected with RSSs produced IBH/HHS in CEE, and FAdV-8a detected in RSS outbreaks, in addition to producing IBH/HHS in chicken embryos, could be a possible viral agent that causes IBH/HHS in chickens.

Humoral, cellular immunity and efficacy of bioreactor propagated and inactivated Fowl adenovirus 8b adjuvanted with Montanide 71VG in broiler chickens

Objectives

The study aimed to inactivate the FAdV isolate (UPM11142P5B1) produced in a bioreactor and assess the humoral and cellular immunity, efficacy, and virus shedding in broiler chickens.

Materials and Methods

The isolate was grown in a bioreactor, inactivated using binary ethyleneimine, adjuvanted with Montanide 71VG, and injected into day-old broiler chickens either with or without booster groups. The following parameters were measured: T lymphocyte profile in the liver, spleen, and thymus; FAdV antibody titer; clinical symptoms; gross and histological alterations in the liver, spleen, and thymus; virus copy number in the liver and cloacal shedding.

Results

Compared to the unchallenged control group, booster (BG), and non-booster (NBG), the challenged control group (CCG) had a larger liver: body weight (BW) ratio, milder clinical signs, gross lesions, and histological alterations. They also had a lower BW. At 7, 21, 35, and 42 days post-inoculation (dpi), the NBG and BG exhibited higher antibody levels than the UCG. At 35 dpi, challenged BG and NBG produced more antibodies than CCG. In BG and NBG, T cells were stimulated in the spleen, thymus, and liver. At 35 and 42 dpi, the challenged BG and NBG showed significantly decreased viral copy numbers in the liver and shedding, respectively, along with increased lymphocyte counts.

Conclusion

The inactivated UPM11142P5B1 with Montanide 71VG could be a vaccine against FAdV 8b infections in chickens.

Research Note: Overview of fowl adenovirus serotype 4: structure, pathogenicity, and progress in vaccine development

Fowl adenovirus serotype 4 (FAdV) is highly pathogenic and lethal to chickens, especially broilers, which has emerged as one of the most important economic losses for the poultry industry in the past few years. Although inactivated vaccines have been widely used to control FAdV diseases, with the passage of time and the advancement of technology, live attenuated vaccines and subunit vaccines have also been developed, which are more attractive and effective vaccine candidates. This is an overview of avian adenoviruses, especially FAdV, which is related to the structure, pathogenicity of adenoviruses in birds, development and strategies used to make and use vaccines using different methods. As well as during this study it was determined that various vaccines against the new FAdV-4 genotype have been developed and many advances have been made in control disease However, many studies conducted in this field need extensive investigation.

Protective immune response induced by Leghorn male hepatoma cell-adapted fowl adenovirus-4

Fowl adenovirus-4 (FAdV-4) is a highly contagious virus that causes acute and lethal hepatitis. It leads to substantial economic losses in the poultry industry. Among the structural proteins of FAdV-4, hexon and fiber2 are associated with immunopathogenesis. A frameshift mutation was generated in the fiber2 protein by seral passages in the Leghorn male hepatoma (LMH) cell line. Immunization using the attenuated virus (80 times passaged) before the virulent FAdV-4 challenge protected hosts from the infection and cleared the invading virus. In immunized animals, activated CD4+ and CD8+ T cell populations were larger during the FAdV-4 challenge. The change in the B cell population was similar. Myeloid cells were highly increased during FAdV-4 infection after the immunization, but the immunization inhibited the expansion in both liver and spleen. The functional gene expression for immune modulation was strongly associated with immune cell changes in the liver, however, this association was not strong in the spleen. The present findings imply that genetic modification by cellular adaptation regulates immune cell phenotype and function in the target organ. In addition, we suggest the attenuated virus as a protective strategy against the novel FAdV-4 strains.

The Immunological Basis for Vaccination

Vaccination is crucial for health protection of poultry and therefore important to maintaining high production standards. Proper vaccination requires knowledge of the key players of the well-orchestrated immune system of birds, their interdependence and delicate regulation, and, subsequently, possible modes of stimulation through vaccine antigens and adjuvants. The knowledge about the innate and acquired immune systems of birds has increased significantly during the recent years but open questions remain and have to be elucidated further. Despite similarities between avian and mammalian species in their composition of immune cells and modes of activation, important differences exist, including differences in the innate, but also humoral and cell-mediated immunity with respect to, for example, signaling transduction pathways, antigen presentation, and cell repertoires. For a successful vaccination strategy in birds it always has to be considered that genotype and age of the birds at the time point of immunization as well as their microbiota composition may have an impact and may drive the immune reactions into different directions. Recent achievements in the understanding of the concept of trained immunity will contribute to the advancement of current vaccine types helping to improve protection beyond the specificity of an antigen-driven immune response. The fast developments in new omics technologies will provide insights into protective B- and T-cell epitopes involved in cross-protection, which subsequently will lead to the improvement of vaccine efficacy in poultry.

Short chain fatty acids facilitate protective immunity by macrophages and T cells during acute fowl adenovirus-4 infection

Short chain fatty acids (SCFAs) are major gut metabolites that are involved in the regulation of dysfunction in immune responses, such as autoimmunity and cytokine storm. Numerous studies have reported a protective action of SCFAs against infectious diseases. This study investigated whether SCFAs have protective effect for immunity during fowl adenovirus-4 (FAdV-4) infection. We examined whether SCFA mixture (acetate, propionate, and butyrate) administration could protect against intramuscular challenge of a virulent viral strain. SCFA treatment promoted MHCII-expressing monocytes, the active form of T cells, and effector molecules in both peripheral and lymphoid tissues. It also boosted the production of immune molecules involved in pathogen elimination by intraepithelial lymphocytes and changed the intestinal microbial composition. We suggest that gut metabolites influence the gut microbial environment, and these changes stimulate macrophages and T cells to fight against the intramuscular challenge of FAdV-4.