Kinetics of chicken embryonic thymocyte development in ovo and in organ culture

Temporal dynamics of innate and adaptive immune responses in broiler birds to oral delivered chitosan nanoparticle-based Salmonella subunit antigens

Salmonella enterica serovar Enteritidis (S. Enteritidis, SE) infection of poultry causes a significant risk to public health through contamination of meat and eggs. Current Salmonella vaccines have failed to provide strong mucosal immunity in the intestines to reduce Salmonella shedding and food contamination. Considering the short lifespan of broilers, an easy-to-deliver, safe and effective Salmonella vaccine is urgently needed. Our goal in this study was to demonstrate the ability of chitosan nanoparticle (CNP) vaccine delivery platform in activating immune response to Salmonella antigens in broilers inoculated orally. In an initial study, soluble whole antigen of SE entrapped in CNP was inoculated but the specific immune responses were poor. Therefore, the CNP entrapped immunogenic outer membrane proteins (OMP) and flagellin (FLA) of SE and surface conjugated with FLA [CNP-(OMP + FLA)] was developed. In broilers inoculated orally with CNP-(OMP + FLA) formulation once or twice, we monitored the temporal expression of innate immune molecules and antigen specific lymphocyte proliferation. In the cecal tonsils of CNP-(OMP + FLA) inoculated birds, we observed enhanced expression of mRNA coding Toll-like receptors (TLRs)- 1, 4, 5, and 7, especially at dpv 21. In addition, both OMP and FLA specific lymphocytes proliferation at dpv 7 and 21 by CNP-(OMP + FLA) were enhanced in the spleen. In conclusion, CNP-(OMP + FLA) formulation augmented both innate and lymphocyte responses in orally inoculated broilers. Further studies are needed to determine the candidate subunit CNP vaccine's efficacy in a challenge trial.

Avaliação microbiológica, histológica e imunológica de frangos de corte desafiados com Salmonella Enteritidis e Minnesota e tratados com ácidos orgânicos

Dois experimentos foram desenvolvidos para avaliar a eficiência de ácidos orgânicos frente a Salmonella enterica enterica sorovar Enteritidis (SE) e Minnesota (SM) em frangos. No primeiro experimento foram avaliados 3 tratamentos: T1 - ração adicionada de ácido orgânico, T2 - ração adicionada de ácido orgânico e ácido orgânico na água de bebida, T3 - grupo controle. Todos os animais foram inoculados com SE, via oral. A utilização de ácidos orgânicos na ração (T1) e na ração e na água (T2) diminuíram a excreção de Salmonella no papo e no ceco 7 dias pós inoculação com SE e houve redução de células CD3+ no jejuno dos frangos. No segundo experimento foram avaliados 4 tratamentos sendo T1 - controle, T2 - controle inoculado via oral com Salmonella Minnesota (SM), T3 - animais inoculados via oral com SM e ácidos orgânicos na ração e T4 - animais inoculados via oral com SM e ácidos orgânicos na ração e na água de bebida. Ácidos orgânicos a ração (T3) e na ração e na água (T4) reduziram a excreção de SM em papo de frangos de corte desafiados, 7 dias após inoculação. O uso de ácidos orgânicos na ração e na ração e na água foram mais eficientes em reduzir SE do que SM.

Identification of microRNA in the developing chick immune organs

MicroRNAs (miRNAs) are small (approximately 19-24 nt) noncoding RNAs that participate in posttranscriptionally regulating gene expression. MicroRNAs display very dynamic expression patterns with many being expressed in a temporal as well as a spatial manner. Immune genes have been shown to have a higher propensity for miRNA target sites compared to the rest of the genome, thus suggesting that miRNA are key regulators of the immune system. To better understand the involvement of miRNA in the immune system, a comprehensive profile of miRNA expression in the immune organs will be necessary. As a first step toward building such a profile, we pyrosequenced four small RNA libraries derived from the spleen and the bursa of Fabricius of embryonic chicks at days 15 and 20 of development. A total of 90,322 sequence reads were obtained, among which 44,387 reads represented known chicken miRNAs, 3,503 reads were not found in the Gallus gallus database but were homologs of miRBase miRNAs from other species, and 2,023 reads represented potentially novel chicken miRNAs that have not previously been identified. Many miRNAs identified in our work have been shown to be involved in regulating immune genes in other vertebrate species. For example, the miRNAs miR-221 and miR-222, which are known regulators of lymphocyte differentiation, were identified in our studies and appeared to be differentially expressed among the libraries. Overall, our results show that many of the identified miRNAs display dynamic expression patterns, suggesting that these miRNAs play diverse roles in the immune system.

Increased glucose availability activates chicken thymocyte metabolism and survival

Glucose metabolism in mammalian thymocytes is coupled to their development and selection in the thymus. In chickens, thymocytes develop in a low glucose concentration in ovo and a high glucose concentration posthatch. To determine the effect of glucose concentration on thymocyte glucose metabolism, embryonic thymic lobes were cultured in media containing varying glucose concentrations and thymocytes were isolated for analysis. Glucose transporter-1 (Glut-1) and Glut-3 mRNA abundance was at least 2-fold higher in thymocytes incubated with 10 and 20 mmol/L glucose than in those incubated with 0 mmol/L glucose (P < 0.05) and glucose uptake was greatest in thymocytes incubated with 20 mmol/L glucose (P < 0.05). Thymocytes incubated with 0 and 20 mmol/L glucose had 185% greater hexokinase activity than in those incubated with 10 mmol/L glucose (P < 0.05). Consequently, thymocyte glucose utilization was dependent upon glucose availability. Increased glucose utilization resulted in a higher mitochondrial membrane potential in thymocytes incubated with 15 mmol/L glucose than in those incubated with 5 mmol/L glucose (P < 0.05), indicating enhanced thymocyte energy status in response to high glucose concentrations. Additionally, thymocyte viability was lower in thymocytes incubated with 5 mmol/L glucose than in those incubated with 10 and 15 mmol/L glucose (P < 0.05) and rates of thymocyte apoptosis were higher in thymocytes incubated with 5 mmol/L glucose than in those incubated with 15 mmol/L glucose (P < 0.05). Glucose availability induced metabolic changes in thymocytes that altered their energy status and survival. Consequently, these data indicate that glucose availability may influence the development of naïve T cells in the chicken thymus.

Functional analysis of neuropeptides in avian thymocyte development

The function of lymphoid organs and immune cells is often modulated by peptides and hormones produced by the neuroendocrine and immune systems. We have previously reported the intrathymic expression of neuropeptides in the thymus of different species and that neuropeptides can influence murine thymocyte development in vitro. To further explore the evolutionary nature of neuroendocrine interactions in the thymus, we identified the expression of calcitonin-gene-related peptide, neuropeptide Y, somatostatin (SOM), substance P and vasointestinal polypeptide, as well as their receptors on chicken thymic epithelial cells (TEC) and thymocytes by immunofluorescence and reverse transcription polymerase chain reaction (RT-PCR). All the studied neuropeptides and their receptors were found to be expressed in both TEC and thymocytes, suggesting that intrathymic neuroendocrine interactions may take place within the avian thymus. In order to elucidate whether such interactions play a role in avian thymocyte development, neuropeptides and their antagonists were added to embryonic thymus organ cultures and found to influence chicken thymopoiesis. In particular, an antagonist of SOM increased the proportion of double-positive thymocytes, while SOM itself appeared to inhibit the early stages of thymocyte development. Taken together, these data provide further evidence to suggest that neuropeptides play a conserved role in vertebrate thymocyte development.

Energy metabolism in developing chicken lymphocytes is altered during the embryonic to posthatch transition

Adequate energy status in lymphocytes is vital for their development. The ability of developing chicken lymphocytes to acquire and metabolize energy substrates was determined during embryonic days (e) and neonatal days (d) of life when primary-energy substrate metabolism is altered at the whole-animal level. In 3 experiments, bursacytes and thymocytes were isolated on e17, e20, d1, d3, d7, or d14 to analyze markers associated with glucose, glutamine, and lipid metabolism. Bursacyte glucose transporter-3 (Glut-3) mRNA abundance increased from d1 to d14 and hexokinase-1 (HK-1) mRNA abundance was maximum on e20 (P<0.05). Thymocyte Glut-1, Glut-3, and HK-1 mRNA abundance increased from e17 to d14 (P<0.05). HK enzyme activity increased from e20 to d3 in bursacytes and d3 to d7 in thymocytes (P<0.05). Glucose uptake by bursacytes and thymocytes was greater on d14 compared to d1 and d7 (P<0.05). Bursacyte and thymocyte sodium coupled neutral amino acid transporter-2 and glutaminase (GA) mRNA abundance increased from e20 to d7 (P<0.05). GA enzyme activity increased from e20 to d7 in bursacytes (P<0.05) and did not change in thymocytes. Carnitine palmitoyl transferase enzyme activity did not change over time in either cell type. These studies suggest that developing B and T lymphocytes adapt their metabolism during the first 2 wk after hatch. Developing lymphocytes increase glucose metabolism with no change in fatty acid metabolism and bursacytes, but not thymocytes, increase glutamine metabolism. Understanding the factors that regulate lymphocyte development in neonatal chicks may help promote their adaptive immune responses to pathogens in early life.

ChT1, an Ig Superfamily Molecule Required for T Cell Differentiation

The thymus is colonized by circulating progenitor cells that differentiate into mature T cells under the influence of the thymic microenvironment. We report here the cloning and function of the avian thymocyte Ag ChT1, a member of the Ig superfamily with one V-like and one C2-like domain. ChT1-positive embryonic bone marrow cells coexpressing c-kit give rise to mature T cells upon intrathymic cell transfer. ChT1-specific Ab inhibits T cell differentiation in embryonic thymic organ cultures and in thymocyte precursor cocultures on stromal cells. Thus, we provide clear evidence that ChT1 is a novel Ag on early T cell progenitors that plays an important role in the early stages of T cell development.

CD4, CD8 and TCR defined T-cell subsets in thymus and spleen of 2- and 7-week old commercial broiler chickens

To better understand immune development and function in meat-type chickens (broilers), the proportions of T-cells expressing CD4, CD8, and T-cell receptors (TCR) in the thymus and spleen were determined by three-color fluorescence and flow cytometry in 2- and 7-week old broilers raised in commercial growing conditions. Broiler thymocytes consisted of single-(CD4+CD8- and CD4-CD8+) and double-(CD4+CD8+) positive subpopulations. Within these CD4+ and/or CD8+ thymocyte populations, all types of TCR (y delta, V beta 1 alpha beta, and V beta 2 alpha beta) could be identified. In the thymus, percentages of CD4+CD8- cells increased, CD4-CD8+ cells remained unchanged, and CD4+CD8+ cells decreased between 2 and 7 weeks of age. In the spleen, in addition to single-positive lymphocytes, double-positive populations were identified, expressing either y delta or alpha beta TCR. The percentage of CD4+CD8- splenocytes decreased, and the percentages of both CD4-CD8+ and CD4+CD8+ splenocytes increased between 2 and 7 weeks of age. Age-associated shifts in TCR usage (the proportion of cells expressing a certain type of TCR) were observed in the single-positive, but not in the double-positive, T-cell populations of both thymus and spleen. This multiparameter cell population analysis in broilers demonstrates thymic and splenic T-cell subsets similar to those previously described in layers. Differences in the proportions among T-cell subsets between 2- and 7-week old broilers likely reflect a more competent immune system in the older birds.

Intraembryonic haemopoietic cells and early T cell development

T cell precursors in the chick embryo have been localized into the intraembryonic mesenchyme (IEM) and into the para-aortic region before the first wave of the thymic colonization on embryonic day (ED) 6,5-8. The cell surface markers of avian prethymic stem cells are not known. It is also not known whether these precursor cells are already committed to the T cell lineage before their thymic colonization. In 7-day-old chick embryos Ov+ cells were found in the para-aortic region. Also the endothelial cells of the embryonic dorsal aorta were positively stained. Ov antigen might represent a very primitive marker for precursor cells having the potentiality to differentiate both to haemopoietic and endothelial cells. Scattered CD45+ cells were observed in the same para-aortic area as in many haemopoietic areas in the loose embryonic mesenchymal tissues. CD8 alpha (MoAb 3-298) expressing haemopoietic cells were detected before thymic colonization on ED6. In flow cytometric analysis of IEM precursors Ov, CD45 and CD8 alpha expressing cells seemed to form distinct subsets suggesting heterogeneity of these haemopoietic cells.

T cell development in the chicken

This review summarizes our current view of gamma delta and alpha beta T cell development in the chicken. In it we emphasize the functional interplay between the gamma delta and alpha beta T cell subpopulations.