Mechanisms of Heat Stress on Neuroendocrine and Organ Damage and Nutritional Measures of Prevention and Treatment in Poultry

Heat stress (HS) due to high temperatures has adverse effects on poultry, including decreased feed intake, lower feed efficiency, decreased body weight, and higher mortality. There are complex mechanisms behind heat stress in poultry involving the neuroendocrine system, organ damage, and other physiological systems. HS activates endocrine glands, such as the pituitary, adrenal, thyroid, and gonadal, by the action of the hypothalamus and sympathetic nerves, ultimately causing changes in hormone levels: HS leads to increased corticosterone levels, changes in triiodothyronine and thyroxine levels, decreased gonadotropin levels, reduced ovarian function, and the promotion of catecholamine release, which ultimately affects the normal productive performance of poultry. Meanwhile, heat stress also causes damage to the liver, lungs, intestines, and various immune organs, severely impairing organ function in poultry. Nutrient additives to feed are important measures of prevention and treatment, including natural plants and extracts, probiotics, amino acids, and other nutrients, which are effective in alleviating heat stress in poultry. Future studies need to explore the specific mechanisms through which heat stress impacts the neuroendocrine system in poultry and the interrelationships between the axes and organ damage so as to provide an effective theoretical basis for the development of preventive and treatment measures.

Effects of different stocking densities on the development of reproductive and immune functions in young breeder pigeons during the rearing period

1. Stocking density (SD) is closely related to animal performance. This experiment was designed to evaluate the development of reproductive and immune functions of young pigeons under different SDs.2. A total of 288 (half male and half female) 40-day-old pigeons (body weight 400 ± 15 g) were allocated into four groups: High stocking density (HSD; 0.308 m3/bird), standard stocking density (SD; 0.616 m3/bird), and low stocking density (LSD; 1.232 m3/bird) and a caged (control; 0.04125 m3/bird). Every group had six replicates of the same sex.3. The results showed that caged male pigeons had the highest testis index, testosterone content, and gene expression of the androgen receptor gene. LSD treatment induced the highest concentrations of oestradiol, progesterone and mRNA levels of reproductive hormone receptor genes in female pigeons. In male pigeons, the spleen index (organ weight calculated as a percentage of total body weight) showed a peak level (0.09 ± 0.020) in the LSD group, and the thymus index peaked (0.23 ± 0.039) in SD group. However, the index for ovary, spleen, thymus and bursa of Fabricius in female pigeons showed no significant changes among different groups.4. The IL-1β, IL-8, IFN-γ, TGF-β and toll-like receptor 2 (TLR-2) mRNA levels reached their maximum values in both male and female pigeon spleens in the LSD group.5. Young male pigeons housed in cages showed increased testicular development while low stocking density increased the development of reproductive function in young female pigeons. A larger activity space could help enhance the immune function of both male and female pigeons.

Research Note: Isolation and immunomodulatory activity of bursal peptide, a novel peptide from avian immune system developments

The bursa of Fabricius (BF) is pivotal for B lymphocyte ontogenesis. In the present investigation, a novel bursal peptide, designated BP7, was extracted from BF and was found to stimulate colony-forming unit pre-B (CFU pre-B) formation at various concentrations (1 μg/mL, P < 0.05; 5 μg/mL, P < 0.05; 25 μg/mL, P < 0.05). Moreover, BP7 modulated B cell differentiation pathways. The immunoregulatory potential of BP7 was further assessed in avian and murine models subjected to immunization with inactivated avian influenza virus (AIV, H9N2 subtype). BP7 significantly augmented AIV-specific antibody levels (Prime immunization: 5 mg/kg, P < 0.05; Boost immunization: 0.4, 1, and 5 mg/kg, P < 0.05) and cytokine secretion in the avian model (IL-4 and IFN-γ: 0.4, 1, and 5 mg/kg, P < 0.05). Similarly, in the murine model, AIV-specific antibody levels (Prime and Boost immunization: 0.4, 1, and 5 mg/kg, P < 0.05) and cytokine production (IL-4 and IFN-γ: 0.4, 1, and 5 mg/kg, P < 0.05) were notably enhanced. This study offers novel insights into the mechanisms underlying B cell maturation and holds implications for future immunopharmacological interventions.

Effect of fecal microbiota transplantation on early intestinal immune function and histomorphology of immune organs in chicks

The intestinal microbiota drives the maturation of the immune system, which is essential for maintaining lifetime homeostasis. Whether fecal microbiota transplantation can promote the development of the immune system in chicks? On days 1, 3, and 5, the post-hatch Hy-line Brown chicks were treated with fecal suspension from breeding hens. Intestinal length, blood biochemical indicators, the morphology of immune organs, and intestinal immunity-related indicators were focused on days 7 and 14. Short-chain fatty acids were determined by gas chromatography. We discovered that fecal microbial transplantation significantly increased the area of the follicles and medulla from the bursa of Fabricius, as well as the area of the medulla, cortex, and both ratios from the thymus on 14 d, the concentration of butyric acid in feces, the levels of immunologically active substances (transforming growth factor-β, interleukin 10, forkhead box protein P3, G-Protein Coupled Receptor 43, immunoglobulin A, etc.) in serum or the intestine, and the number of goblet cells. Correlation analysis indicated that short-chain fatty acids, as metabolites of the gut microbiota, were correlated with intestinal immunity. In short, fecal microbiota transplantation regulated early intestinal immunity, which provided the possibility for the processing and utilization of gut microbiota as germplasm resources.

IMPACT STATEMENT

Modern management of eggs causes the normal vertical transmission of microbiota from hens to be significantly reduced. The risk of environmental threats to newborn chicks is raised. The microbial community helps to mature the immune system of chicks and protect them from pathogen invasion. We still have doubts about whether transplanting the microbiota can regulate gut immunity. Using the gut microbiota of hens as an excellent resource to improve the immunity of chicks may provide new ideas for the development of the poultry industry.

Effects and Mechanisms of Cage versus Floor Rearing System on Goose Growth Performance and Immune Status

Currently, FRS and CRS are the two predominant dryland rearing systems in the goose industry. However, the effects of these two systems on goose growth performance and health, as well as the underlying mechanisms, have not been fully clarified. Thus, this study aimed to compare growth performance and immune status, as well as investigate the genome-wide transcriptomic profiles of spleen in geese, between CRS and FRS at 270 d of age. Phenotypically, the body weight and body size traits were higher in geese under FRS, while the weight and organ index of spleen were higher in geese under CRS (p < 0.05). Noticeably, the bursa of Fabricius of geese under FRS was degenerated, while that under CRS was retained. At the serum level, the immune globulin-G (IgG) and interleukin-6 (IL-6) levels were higher in geese under CRS (p < 0.05). At the transcriptomic level, we identified 251 differentially expressed genes (DEGs) in the spleen between CRS and FRS, which were mainly enriched in scavenger receptor activity, inflammatory response, immune response, neuroactive ligand-receptor interaction, phenylalanine metabolism, ECM receptor interaction, calcium signaling pathway, phenylalanine, tyrosine, and tryptophan biosynthesis, regulation of actin cytoskeleton, and MAPK signaling pathways. Furthermore, through protein-protein interaction (PPI) network analysis, ten candidate genes were identified, namely, VEGFA, FGF2, NGF, GPC1, NKX2-5, FGFR1, FGF1, MEIS1, CD36, and PAH. Further analysis demonstrated that geese in CRS could improve their immune ability through the "phenylalanine metabolism" pathway. Our results revealed that the FRS improved growth performance, whereas the CRS improved goose immune function by increasing levels of IL-6 and IgG in serum. Moreover, the phenylalanine metabolism pathway could exert positive effects on immune function of geese under CRS. These results can provide reliable references for understanding how floor and cage rearing systems affect goose growth performance and immune capacity.

Transcriptome analysis revealed the roles of long non-coding RNA and mRNA in the bursa of Fabricius during pigeon (Columba livia) development

The bursa of Fabricius (BF) is the critical humoral immune organ to birds, playing an essential role in B lymphocyte differentiation. However, unlike other poultries, surgical removal of pigeon BF did not limit humoral immune responsiveness. To investigate the expression profiles and the potential role of mRNA and long non-coding RNA (LncRNA) in squab BFs, transcriptome analysis was performed by RNA-Sequencing (RNA-Seq) over three developmental stages (1-day, 13 and 26 days old). We identified 13,072 mRNAs and 19,129 lncRNAs, of which 2,752 mRNAs and 1,515 lncRNAs were differential expressed (DE) in pigeon BFs over three developmental stages. Cluster analysis presented different expression patterns in DE mRNAs and lncRNAs. Functional enrichment analysis revealed that DE lncRNAs and mRNAs with distinct expression patterns might play crucial roles in the immune system process and tissue morphogenesis. In particular, some DE genes and lncRNAs with higher expression levels in 13D or 26D are related to lymphocyte activation and differentiation, adaptive immune response, positive regulation of immune response, leukocyte migration, etc. Protein-protein interaction (PPI) network and Molecular Complex Detection (MCODE) analysis sreened six significant modules containing 37 genes from immune-related DE gene cluster, which is closely linked in B cell activation, lymphocyte differentiation, B cell receptor signaling pathway, etc. Our study characterizes mRNA and lncRNA transcriptomic variability in pigeon BFs over different developmental stages and enhances understanding of the mechanisms underlying physiological functions of pigeon BF.

Effect of Intermittent and Mild Cold Stimulation on the Immune Function of Bursa in Broilers

Cold stress causes growth performance to decrease and increases production costs. Cold adaptation can enhance immune function and alleviate the negative impact caused by the stress condition. The study investigated the effect of intermittent and mild cold stimulation on the immune function of the bursa of Fabricius in broilers. A total of 400 healthy one-day-old broilers were divided into the control group (CC) and cold stimulation (CS) groups. The CC group was raised at a conventional raising temperature of broilers, while the CS groups were raised at 3°C below the temperature of the CC for three-, four-, five-, or six-hour periods at one-day intervals from 15 to 35 days of age (D35), denoted CS3, CS4, CS5, and CS6, respectively. Subsequently, they were raised at 20°C from 36 to 49 days of age (D49). The expression levels of TLRs, cytokines, and AvBDs were determined to access the immune function of bursa in broilers. After 21-day IMCS (at D36), the expression levels of TLR1, TLR15 and TLR21, interleukin (IL)-8, and interferon (IFN)-γ, as well as AvBD8 in CS groups, were lower than those in CC (p < 0.05). The expression levels of TLR3, TLR4 and TLR7, were decreased in the CS3, CS5, and CS6 groups (p < 0.05), but there were no significant differences in both the CC and CS4 groups (p > 0.05). When the IMCS ended for 14 days (at D49), the expression levels of TLR2, TLR3, TLR5, TLR7, TLR15, and TLR21, and IL-8, as well as AvBD2, AvBD4 and AvBD7 in CS groups, were lower than those in CC (p < 0.05). In addition to CS4, the expression levels of TLR1, IFN-γ, and AvBD8 in CS3, CS5, and CS6 were still lower than those in CC (p < 0.05). We concluded that the intermittent and mild cold stimulation could regulate immunoreaction by modulating the production of TLRs, cytokines, and AvBDs in the bursa, which could help broilers adapt to low ambient temperature and maintain homeostasis.

Transcriptomic analysis of early B-cell development in the chicken embryo

The chicken bursa of Fabricius is a primary lymphoid tissue important for B-cell development. Our long-term goal is to understand the role of bursal microenvironment in an early B-cell differentiation event initiating repertoire development through immunoglobulin gene conversion in the chick embryo. We hypothesize that early bursal B-cell differentiation is guided by signals through cytokine receptors. Our theory is based on previous evidence for expression of the receptor tyrosine kinase superfamily members and interleukin receptors in unseparated populations of bursal B-cells and bursal tissue. Knowledge of the expressed genes that are responsible for B-cell differentiation is a prerequisite for understanding the bursal microenvironment's function. This project uses transcriptomic analysis to evaluate gene expression across early B-cell development. RNA-seq was performed with total RNA isolated from bursal B-cells at embryonic day (ED) 16 and ED 19 (n = 3). Approximately 90 million high-quality clean reads were obtained from the cDNA libraries. The analysis revealed differentially expressed genes involved in the Jak-STAT pathway, Wnt signaling pathway, MAPK signaling pathway, metabolic pathways including tyrosine metabolism, Toll-like receptor signaling pathway, and cell-adhesion molecules. The genes predicted to encode surface receptors, signal transduction proteins, and transcription factors identified in this study represent gene candidates for controlling B-cell development in response to differentiation factors in the bursal microenvironment.

The immunomodulatory functions and molecular mechanism of a new bursal heptapeptide (BP7) in immune responses and immature B cells

The bursa of Fabricius (BF) is the acknowledged central humoural immune organ unique to birds and plays a vital role in B lymphocyte development. In addition, the unique molecular immune features of bursal-derived biological peptides involved in B cell development are rarely reported. In this paper, a novel bursal heptapeptide (BP7) with the sequence GGCDGAA was isolated from the BF and was shown to enhance the monoclonal antibody production of a hybridoma. A mouse immunization experiment showed that mice immunized with an AIV antigen and BP7 produced strong antibody responses and cell-mediated immune responses. Additionally, BP7 stimulated increased mRNA levels of sIgM in immature mouse WEHI-231 B cells. Gene microarray results confirmed that BP7 regulated 2465 differentially expressed genes in BP7-treated WEHI-231 cells and induced 13 signalling pathways and various immune-related functional processes. Furthermore, we found that BP7 stimulated WEHI-231 cell autophagy and AMPK-ULK1 phosphorylation and regulated Bcl-2 protein expression. Finally, chicken immunization showed that BP7 enhanced the potential antibody and cytokine responses to the AIV antigen. These results suggested that BP7 might be an active biological factor that functions as a potential immunopotentiator, which provided some novel insights into the molecular mechanisms of the effects of bursal peptides on immune functions and B cell differentiation.

Changes in bursal B cells in chicken during embryonic development and early life after hatching

The bursa of Fabricius, the primary lymphoid organ for B cell development found only in birds, offers novel approaches to study B cell differentiation at various developmental stages. Here, we explored the changes and mechanism involved in the developmental stages of bursal B cells. The bursal B cells rapidly increased in the late embryonic stage and around hatching, which coincided with changes in specific cell surface markers. Moreover, the cells in the bursa were divided by size into small (low forward- and side-scatter) or large (high forward- and side-scatter) via flow cytometry. It is intriguing that the proportion of small and large B cells was reversed during this period. Because little is known about this phenomenon, we hypothesized that size-based B cell population could be used as an indicator to distinguish their status and stage during B cell development in chicken. The results demonstrated that large B cells are actively proliferating cells than small B cells. Additionally, large B cells showed higher mRNA expression of both proliferation- and differentiation-associated genes compared to small B cells. Taken together, these data show that large bursal B cells are the main source of proliferation and differentiation during B cell development in chickens.

Combination of novel and public RNA-seq datasets to generate an mRNA expression atlas for the domestic chicken

Background

The domestic chicken (Gallus gallus) is widely used as a model in developmental biology and is also an important livestock species. We describe a novel approach to data integration to generate an mRNA expression atlas for the chicken spanning major tissue types and developmental stages, using a diverse range of publicly-archived RNA-seq datasets and new data derived from immune cells and tissues.

Results

Randomly down-sampling RNA-seq datasets to a common depth and quantifying expression against a reference transcriptome using the mRNA quantitation tool Kallisto ensured that disparate datasets explored comparable transcriptomic space. The network analysis tool Graphia was used to extract clusters of co-expressed genes from the resulting expression atlas, many of which were tissue or cell-type restricted, contained transcription factors that have previously been implicated in their regulation, or were otherwise associated with biological processes, such as the cell cycle. The atlas provides a resource for the functional annotation of genes that currently have only a locus ID. We cross-referenced the RNA-seq atlas to a publicly available embryonic Cap Analysis of Gene Expression (CAGE) dataset to infer the developmental time course of organ systems, and to identify a signature of the expansion of tissue macrophage populations during development.

Conclusion

Expression profiles obtained from public RNA-seq datasets – despite being generated by different laboratories using different methodologies – can be made comparable to each other. This meta-analytic approach to RNA-seq can be extended with new datasets from novel tissues, and is applicable to any species.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4972-7) contains supplementary material, which is available to authorized users.

Transcriptome analyses of differential gene expression in the bursa of Fabricius between Silky Fowl and White Leghorn

Hyperpigmentation in Silky Fowl (SF) results in aberrant immune cell development. However, how melanocytes regulate B-cell proliferation in the bursa of Fabricius (BF) is unclear. To resolve this conundrum, we collected BFs from three-week-old SF and White Leghorn (WL) female chickens for RNA sequencing. The BF development was relatively weaker in SF than in WL. The transcriptome analyses identified 4848 differentially expressed genes, 326 long noncoding RNAs (lncRNAs), and 67 microRNAs in the BF of SF. The genes associated with melanogenesis was significantly higher, but that of the genes associated with the cytokine-cytokine receptor interactions and JAK-STAT signalling pathway was significantly lower in SF than in WL. Crucial biological processes, such as the receptor activity, cell communication, and cellular responses to stimuli, were clustered in SF. The predicted target lncRNAs genes were mainly associated with cell proliferation pathways such as JAK-STAT, WNT, MAPK, and Notch signalling pathways. Except for the above pathways, the target microRNA genes were related to the metabolism, melanogenesis, autophagy, and NOD-like and Toll-like receptor signalling pathways. The lncRNAs and microRNAs were predicted to regulate the JAK2, STAT3, and IL-15 genes. Thus, B-cell development in the BF of SF might be regulated and affected by noncoding RNAs.

Influence of the structural development of bursa on the susceptibility of chickens to infectious bursal disease virus

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is an acute, highly contagious immunosuppressive avian disease. Although age-dependent changes in susceptibility of chickens to IBDV have been established, the relationship between age-dependent structural changes in bursa of Fabricius and susceptibility of chickens to IBDV is still unclear. In the present study, we examined the bursa anatomical structure and pathological changes in specific-pathogen-free (SPF) white leghorn chickens 0 to 8 weeks post hatch (w.p.h.) and IBDV BC6/85-infected SPF chickens 2 to 6 w.p.h. respectively, by histology, histopathology, immunohistochemistry, and transmission electron microscopy. Almost all IBDV-exposed chickens (2 to 6 w.p.h.) were infected, with the severest bursal inflammation and complication in chickens at 3 w.p.h. Furthermore, the bursae of healthy chickens at 3 to 6 w.p.h. had decreased laminin immunoreactivities, lots of splits, and irregular shapes in basement membrane (BM) of cortico-medullary epithelium (CME), irregularly arranged CME, and large numbers of immunoglobulin M-bearing (IgM+) B lymphocytes in the medulla. The decreased barrier function of corticomedullary border and large amount of IgM+ B lymphocytes provide a chance for IBDV to easily contact and infect target cells at 3 to 6 w.p.h. By contrast, regular BM, neatly arranged CME, and few IgM+ B lymphocytes in healthy chickens younger than 2 w.p.h., as well as reduced IgM+ B lymphocytes and high immunoglobulin A (IgA) content in healthy chickens older than 8 w.p.h., were observed, suggesting that the integrity of corticomedullary border barrier, a small amount of target cells and high IgA content of the bursa could be the reasons for these chickens being less susceptible to IBDV. Although studies have shown how IBDV affects bursa, we focus first on the age-dependent changes of CME, BM of CME and IgA content, and our findings are the first to elucidate the structural development of bursa in relation to IBDV susceptibility from a morphological perspective.