The Evaluation of Cellular Immunity to Avian Viral Diseases: Methods, Applications, and Challenges

Insights into microstructure and expression of markers of proliferation, apoptosis and T cells in the spleen of cattle egret (Bubulcus ibis)

The spleen is the largest secondary lymphoid organ with significant roles in pathogen clearance. It is involved in several avian diseases. The cattle egret is a wild insectivorous bird of agricultural and socioeconomic importance. Data related to microstructural features of cattle egret spleen are lacking. The present study investigated the gross anatomical, histological and immunohistochemical characteristics of the cattle egret spleen. Proliferation (PCNA and PHH3), apoptosis (cleaved caspase 3, C.CASP3) and T-cell (CD3 and CD8) markers were assessed. Grossly, the spleen appeared brownish red, oval-shaped and located at the oesophago-proventricular junction. Histologically, the spleen was surrounded by a thin capsule sending a number of trabeculae which contained branches of the splenic vessels. The white pulp consisted of the periarteriolar lymphoid sheath and periellipsoidal lymphatic sheath (PELS). The red pulp was formed of sinusoids and cords. The penicillar capillaries, which represent the terminal segments of the splenic arterial tree were highly branched, wrapped by prominent ellipsoids and directly connected to the splenic sinusoids, suggesting a closed type of circulation. Immunohistochemically, proliferating cell nuclear antigen (PCNA)-expressing cells were distributed with high counts throughout the splenic parenchyma, being highest within the splenic cords and PELS. Both PHH3- and C.CASP3-expressing cells revealed a similar pattern to that of PCNA, although with fewer counts. Large numbers of T cells were observed throughout the splenic parenchyma, mainly within the cords, as revealed by CD3 and CD8 immunoreaction. The present study provides a clear insight into the precise structure of the spleen in cattle egrets and thus improves our understanding about birds' immunity.

Delineation of chicken immune markers in the era of omics and multicolor flow cytometry

Multiparameter flow cytometry is a routine method in immunological studies incorporated in biomedical, veterinary, agricultural, and wildlife research and routinely used in veterinary clinical laboratories. Its use in the diagnostics of poultry diseases is still limited, but due to the continuous expansion of reagents and cost reductions, this may change in the near future. Although the structure and function of the avian immune system show commonalities with mammals, at the molecular level, there is often low homology across species. The cross-reactivity of mammalian immunological reagents is therefore low, but nevertheless, the list of reagents to study chicken immune cells is increasing. Recent improvement in multicolor antibody panels for chicken cells has resulted in more detailed analysis by flow cytometry and has allowed the discovery of novel leukocyte cell subpopulations. In this article, we present an overview of the reagents and guidance needed to perform multicolor flow cytometry using chicken samples and common pitfalls to avoid.

Evaluation of Adjuvant Effect of Cytosine-Guanosine-Oligodeoxynucleotide in Meat-Type Chickens Coadministered In Ovo with Herpesvirus of Turkey Vaccine

Herpesvirus of turkey (HVT) increases activation of T cells in 1-day-old chickens when administered in ovo. This study evaluated whether adding cytosine-guanosine oligodeoxynucleotides (CpG ODNs) to the HVT vaccine could enhance the adjuvant effect of HVT. We used a CpG ODN dose of 10 μg per egg. The experimental groups were (1) diluent-only control (sham), (2) HVT, (3) HVT+CpG ODN, (4) HVT+non-CpG ODN, (5) CpG ODN, and (6) non-CpG ODN control. Cellular response evaluation included measuring the frequencies of macrophages (KUL01+MHC-II+), gamma delta T cells (γδTCR+MHC-II+), CD4+, and CD8+ T cell subsets, including double-positive (DP) cells. In addition, CD4+ and CD8+ T cell activation was evaluated by measuring the cellular expression of major histocompatibility complex class II (MHC-II), CD44 or CD28 costimulatory molecules. An adjuvant effect was considered when HVT+CpG ODN, but not HVT+non CpG ODN, or CpG ODN, or non-CpG ODN, induced significantly increased effects on any of the immune parameters examined when compared with HVT. The findings showed that (1) HVT vaccination induced significantly higher frequencies of γδ+MHC-II+ and CD4+CD28+ T cells when compared with sham chickens. Frequencies of DP and CD4+CD28+ T cells in HVT-administered birds were significantly higher than those observed in the non-CpG ODN group. (2) Groups receiving HVT+CpG ODN or CpG ODN alone were found to have significantly increased frequencies of activated CD4+ and CD8+ T cells, when compared with HVT. Our results show that CpG ODN administration in ovo with or without HVT significantly increased frequencies of activated CD4+ and CD8+ T cells.

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.

How to Break through the Bottlenecks of in Ovo Vaccination in Poultry Farming

Poultry farming is one of the pillar industries of global animal husbandry. In order to guarantee production, poultry are frequently vaccinated from the moment they are hatched. Even so, the initial immunity of chicks is still very poor as they are in the "window period" of immune protection. In ovo vaccination pushes the initial immunization time forward to the incubation period, thereby providing earlier immune protection for chicks. In ovo vaccination is currently a research hotspot of poultry disease prevention and control, which is in line with the intensification of poultry production. However, the vaccines currently available for in ovo vaccination are limited and cannot meet the needs of industrial development, so how to efficiently activate the adaptive immune response of chicken embryos becomes the key to restrict product development and technological progress of in ovo vaccination. Its breakthrough, to a large extent, depends on systematic illustration of the mechanism underlying the adaptive immune response post immunization. Clarification of this issue will provide us with theoretical support and potential solutions for the development of novel vaccines for in ovo vaccination, the augmentation of efficacy of current vaccines and the optimization of immune programs.

In Ovo Vaccination with Recombinant Herpes Virus of the Turkey-Laryngotracheitis Vaccine Adjuvanted with CpG-Oligonucleotide Provides Protection against a Viral Challenge in Broiler Chickens

Infectious laryngotracheitis (ILT) is an economically important disease in chickens. We previously showed that an in ovo adjuvantation of recombinant herpesvirus of the turkey-Laryngotracheitis (rHVT-LT) vaccine with CpG-oligonucleotides (ODN) can boost vaccine-induced responses in one-day-old broiler chickens. Here, we evaluated the protective efficacy of in ovo administered rHVT-LT + CpG-ODN vaccination against a wild-type ILT virus (ILTV) challenge at 28 days of age and assessed splenic immune gene expression as well as cellular responses. A chicken-embryo-origin (CEO)-ILT vaccine administered in water at 14 days of age was also used as a comparative control for the protection assessment. The results showed that the rHVT-LT + CpG-ODN or the CEO vaccinations provided significant protection against the ILTV challenge and that the level of protection induced by both the vaccines was statistically similar. The protected birds had a significantly upregulated expression of interferon (IFN)γ or interleukin (IL)-12 cytokine genes. Furthermore, the chickens vaccinated with the rHVT-LT + CpG-ODN or CEO vaccine had a significantly higher frequency of γδ T cells and activated CD4+ or CD8+ T cells, compared to the unvaccinated-ILTV challenge control. Collectively, our findings suggest that CpG-ODN can be used as an effective adjuvant for rHVT-LT in ovo vaccination to induce protective immunity against ILT in broiler chickens.

Effect of CpG-Oligonucleotide in Enhancing Recombinant Herpes Virus of Turkey-Laryngotracheitis Vaccine-Induced Immune Responses in One-Day-Old Broiler Chickens

Infectious laryngotracheitis (ILT) is an economically important disease of chickens. While the recombinant vaccines can reduce clinical disease severity, the associated drawbacks are poor immunogenicity and delayed onset of immunity. Here, we used CpG-oligonucleotides (ODN) as an in ovo adjuvant in boosting recombinant herpesvirus of turkey-laryngotracheitis (rHVT-LT) vaccine-induced responses in one-day-old broiler chickens. Two CpG-ODN doses (5 and 10 μg/egg) with no adverse effect on the vaccine-virus replication or chick hatchability were selected for immune-response evaluation. Results showed that while CpG-ODN adjuvantation induced an increased transcription of splenic IFNγ and IL-1β, and lung IFNγ genes, the IL-1β gene expression in the lung was significantly downregulated compared to the control. Additionally, the transcription of toll-like receptor (TLR)21 in the spleen and lung and inducible nitric oxide synthase (iNOS) in the spleen of all vaccinated groups was significantly reduced. Furthermore, splenic cellular immunophenotyping showed that the CpG-ODN-10μg adjuvanted vaccination induced a significantly higher number of macrophages, TCRγδ+, and CD4+ T cells as well as a higher frequency of activated T cells (CD4+CD44+) when compared to the control. Collectively, the findings suggested that CpG-ODN can boost rHVT-LT-induced immune responses in day-old chicks, which may help in anti-ILT defense during their later stages of life.

Phenotypic characterization of Eimeria tenella-specific chicken T-cells responding to in vitro parasite antigen re-stimulation

Introduction. Coccidiosis, caused by protozoan parasites of genus Eimeria, is a disease with large impact on poultry production worldwide. It is well known that Eimeria immunity is dependent on Th1-type responses.Gap Statement. In vitro assessment of Eimeria-specific T-cell activity would therefore be a valuable research tool but has so far proven difficult to establish.Aim. The present study aimed to evaluate in vitro induced blast transformation and CD25 expression in defined chicken T-cell populations as a measure of Eimeria immunity.Methodology. Three E. tenella infection experiments were performed and PBMC and/or spleen cells were collected between 6 and 16 days after infection of chickens. Cells were stimulated in vitro with E. tenella antigens and T-cell activation was assessed by immunofluorescence labelling and flow cytometry.Results. The results consistently showed statistically significant E. tenella specific activation of TCRα/β+T cells within a 'window' from 8 to 14 days after infection for both spleen cells and PBMC. Responding T-cells were identified as CD4+CD8-, CD4+CD8αα+ and CD4-CD8αβ+ where the CD4+CD8αα+ cells generally showed the highest responses. All three of these TCRα/βT-cell subsets showed significant E. tenella induced blast transformation and/or CD25 expression albeit not always in concert on the same days after infection indicating complex kinetics of T-cell responses. In general, responses were higher for spleen cells compared to PBMC for all responding T-cell populations.Conclusions. This methodology shows promise to study Eimeria-specific T-cells, e.g. to evaluate vaccine responses. Results indicated that a Th1-type response was induced and suggested a role for CD4+CD8αα+ cells in Eimeria immunity.