Development of Peyer's patch and cecal tonsil in gut-associated lymphoid tissues in the chicken embryo

Distribution and spatiotemporal development of organised lymphoid tissues in the chicken intestinal tract

Chickens exhibit a distinct immune architecture characterised by the absence of draining lymph nodes and the presence of a well-developed mucosa-associated lymphoid tissue. The structure and spatiotemporal development of chicken lymphoid tissues in the intestine are poorly documented. The macroscopically indistinct structure of chicken Peyer's patches has impeded studies into their development. The generation of CSF1R-eGFP reporter transgenic chickens enables visualisation of the development, organisation and extent of chicken lymphoid tissues by unique macroscopic views. CSF1R-eGFP reporter transgenic chickens were used to investigate the distribution and spatiotemporal development of PP and caecal tonsils in embryonic day 18 to 8-week-old chickens. Peyer's patch anlagen are present at ED18 with a similar frequency and distribution pattern observed in 2- and 8-week-old chickens. These findings can support in ovo and post-hatch mucosal vaccination strategies and the development of vaccine delivery systems targeted to the specialized epithelium overlying the Peyer's patches.

Physiological effects of in ovo delivery of bioactive substances in broiler chickens

The poultry industry has improved genetics, nutrition, and management practices, resulting in fast-growing chickens; however, disturbances during embryonic development may affect the entire production cycle and cause irreversible losses to broiler chicken producers. The most crucial time in the chicks' development appears to be the perinatal period, which encompasses the last few days of pre-hatch and the first few days of post-hatch. During this critical period, intestinal development occurs rapidly, and the chicks undergo a metabolic and physiological shift from the utilization of egg nutrients to exogenous feed. However, the nutrient reserve of the egg yolk may not be enough to sustain the late stage of embryonic development and provide energy for the hatching process. In addition, modern hatchery practices cause a delay in access to feed immediately post-hatch, and this can potentially affect the intestinal microbiome, health, development, and growth of the chickens. Development of the in ovo technology allowing for the delivery of bioactive substances into chicken embryos during their development represents a way to accommodate the perinatal period, late embryo development, and post-hatch growth. Many bioactive substances have been delivered through the in ovo technology, including carbohydrates, amino acids, hormones, prebiotics, probiotics and synbiotics, antibodies, immunostimulants, minerals, and microorganisms with a variety of physiological effects. In this review, we focused on the physiological effects of the in ovo delivery of these substances, including their effects on embryo development, gastrointestinal tract function and health, nutrient digestion, immune system development and function, bone development, overall growth performance, muscle development and meat quality, gastrointestinal tract microbiota development, heat stress response, pathogens exclusion, and birds metabolism, as well as transcriptome and proteome. We believe that this method is widely underestimated and underused by the poultry industry.

Transcriptome profiling reveals morphogenesis-related candidate genes and pathways in the chick embryonic small intestine

1. A better understanding of intestinal development is essential for the intestinal health of poultry. Intestinal villification starts on embryo day E15 and is generally completed before hatching (E21). The development of lymphoid organs in the intestine starts during embryogenesis. However, transcriptional information on the processing of intestinal morphogenesis and immune development during chick embryogenesis is limited.2. In this work, RNA-sequencing was performed using 12 biological replicates to investigate Hy-Line brown chick embryonic small intestinal transcription at E15 and E21. Differentially expressed genes (DEGs) between E15 and E21 were identified. GO and KEGG enrichment analyses, based on the DEGs, were performed to identify key GO terms in the biological process category and key KEGG pathways. PPI networks were constructed based on the DEGs in the key pathways to screen hub genes. The embryonic small intestinal morphology and IgA distribution were observed by histological processing. The serum levels of IgA and lysozyme were measured by ELISA.3. A total of 76.38 Gb of high-quality RNA-sequencing data were generated and uploaded. A total of 2,676 DEGs, between E15 and E21, were identified. Structural development and villification of the small intestine at E15 tended to proceed via the expression of nervous system development-related genes. A combination of the histological and serological results with the transcriptome data indicated that the identified genes and pathways may be strong candidates for intestinal morphogenesis-regulation.4. The small intestine appears to have developed a relatively complete morphology and transport, metabolism, digestion and immunity functions by E21. This work provided a transcriptome profile of the chick embryonic small intestine and provided insights into the intestinal development and health of poultry.

Review: β-glucans as Effective Antibiotic Alternatives in Poultry

The occurrence of microbial challenges in commercial poultry farming causes significant economic losses. Antibiotics have been used to control diseases involving bacterial infection in poultry. As the incidence of antibiotic resistance turns out to be a serious problem, there is increased pressure on producers to reduce antibiotic use. With the reduced availability of antibiotics, poultry producers are looking for feed additives to stimulate the immune system of the chicken to resist microbial infection. Some β-glucans have been shown to improve gut health, to increase the flow of new immunocytes, increase macrophage function, stimulate phagocytosis, affect intestinal morphology, enhance goblet cell number and mucin-2 production, induce the increased expression of intestinal tight-junctions, and function as effective anti-inflammatory immunomodulators in poultry. As a result, β-glucans may provide a new tool for producers trying to reduce or eliminate the use of antibiotics in fowl diets. The specific activity of each β-glucan subtype still needs to be investigated. Upon knowledge, optimal β-glucan mixtures may be implemented in order to obtain optimal growth performance, exert anti-inflammatory and immunomodulatory activity, and optimized intestinal morphology and histology responses in poultry. This review provides an extensive overview of the current use of β glucans as additives and putative use as antibiotic alternative in poultry.

Effects of age on immune function in broiler chickens

BACKGROUND

There are many diseases in poultry, many of which are caused by poor immune function. It is not clear how cytokines and various immune cell functions change with age in modern broilers. The purpose of this study was to explore the patterns of development of the immunity of the broiler chickens in cage.

RESULTS

The results showed that there were 3 development patterns of immunity in the broiler chickens. The first pattern was Down-Up. Cytokines and some immune indicators first decreased and then increased, and the lowest levels of immunity basically occurred from d 6 to 13. The second pattern was Up-Down, and from d 30 to 34, the highest levels of non-specific cellular immunity components, such as the peripheral blood mononuclear macrophage ratio, specific cellular immunity components, such as the peripheral blood helper T (Th) cell ratio and T cell and B cell proliferation activity, and mucosal immunity components, such as the ileal CD4, TGF-β1 and IgA mRNA levels, were observed. The third pattern was Up-Up, and the levels of the non-specific cellular immunity components, such as the serum nitric oxide (NO), C3 and C4 levels, the specific cellular immunity components, such as the spleen index, peripheral blood IL-2, IFN-γ/IL-4, cytotoxic T (Tc) cell ratio, and splenic NF-κB mRNA levels, the humoral immunity components, such as the serum IgG level, the mucosal immunity components, such as the ileal MHC-II, CD3d, TCRβ subunit, TCRζ subunit, IFN-γ, pIgR mRNA and ileal mucosa sIgA levels, were continuing to increase from d 1 to 34.

CONCLUSIONS

It could be concluded that the immune system and its function have not developed well in the broiler chickens d 6 to 13 and that the immune system does not mature until d 30 to 34 in the broiler chickens in cages. It is necessary to enhance the immune function of the broiler chickens through nutritional measures from d 1 to 30.

Molecular Drivers of Lymphocyte Organization in Vertebrate Mucosal Surfaces: Revisiting the TNF Superfamily Hypothesis

The adaptive immune system of all jawed vertebrates relies on the presence of B and T cell lymphocytes that aggregate in specific body sites to form primary and secondary lymphoid structures. Secondary lymphoid organs include organized MALT (O-MALT) such as the tonsils and Peyer patches. O-MALT became progressively organized during vertebrate evolution, and the TNF superfamily of genes has been identified as essential for the formation and maintenance of O-MALT and other secondary and tertiary lymphoid structures in mammals. Yet, the molecular drivers of O-MALT structures found in ectotherms and birds remain essentially unknown. In this study, we provide evidence that TNFSFs, such as lymphotoxins, are likely not a universal mechanism to maintain O-MALT structures in adulthood of teleost fish, sarcopterygian fish, or birds. Although a role for TNFSF2 (TNF-α) cannot be ruled out, transcriptomics suggest that maintenance of O-MALT in nonmammalian vertebrates relies on expression of diverse genes with shared biological functions in neuronal signaling. Importantly, we identify that expression of many genes with olfactory function is a unique feature of mammalian Peyer patches but not the O-MALT of birds or ectotherms. These results provide a new view of O-MALT evolution in vertebrates and indicate that different genes with shared biological functions may have driven the formation of these lymphoid structures by a process of convergent evolution.

Dynamics of Structural Barriers and Innate Immune Components during Incubation of the Avian Egg: Critical Interplay between Autonomous Embryonic Development and Maternal Anticipation

The integrated innate immune features of the calcareous egg and its contents are a critical underpinning of the remarkable evolutionary success of the Aves clade. Beginning at the time of laying, the initial protective structures of the egg, i.e., the biomineralized eggshell, egg-white antimicrobial peptides, and vitelline membrane, are rapidly and dramatically altered during embryonic development. The embryo-generated extra-embryonic tissues (chorioallantoic/amniotic membranes, yolk sac, and associated chambers) are all critical to counteract degradation of primary egg defenses during development. With a focus on the chick embryo (Gallus gallus domesticus), this review describes the progressive transformation of egg innate immunity by embryo-generated structures and mechanisms over the 21-day course of egg incubation, and also discusses the critical interplay between autonomous development and maternal anticipation.

The several elements of intestinal innate immune system at the beginning of the life of broiler chicks

Functional capacity of digestive system and intestinal adaptive immunity are immature at hatching of broiler chicks. Therefore, intestinal innate immunity after hatching is vital to young chicks. The purpose of this study was to investigate expression and tissue distributions of several elements of the innate immune system (i.e., TLR2, TLR4, CD83, and MHC class II expressing cells) in the intestine of one-day-old chicks. For this purpose, ileum and cecum were examined the under different conditions, which included the control and 1, 3, 6, 12, or 24 h after injection of lipopolysaccharide (LPS) and phosphate buffered saline. The findings indicated that regardless of the antigenic stimulation, Toll-like receptor (TLR) 2 and TLR4 expressing cells were present in the intestinal tissues of one-day-old chicks. We noticed that the intestinal segments have different TLR expression levels after LPS stimulation. Dendritic cells were identified, and they left the intestinal tissue after LPS treatment. MHC class II molecules were diffusely present in both the ileum and cecum. This study demonstrates that the intestinal tissue of one-day-old chicks has remarkable defensive material, including histological properties and several elements of the innate immune system. Microsc. Res. Tech. 79:604-614, 2016. © 2016 Wiley Periodicals, Inc.

Early life experiences affect the adaptive capacity of rearing hens during infectious challenges

This study aimed to investigate whether pre- and early postnatal experiences of rearing hens contribute to the ability to cope with infectious challenges at an older age. In a 2 × 2 factorial arrangement, 352 Lohmann Brown chicks were exposed to either suboptimal or optimized incubation plus hatch conditions, and to cage or enriched rearing from week 0 to 7 of age. After week 7 all rearing conditions were similar until the end of the experiment. The development of adaptive capacity to infectious challenges was investigated by introducing an Eimeria and Infectious Bronchitis (IB) infection on day 53 and day 92, respectively. BW gain and feed intake during the infections, duodenal lesions and amount of positive stained CD4+ T cells, CD8+ T cells and macrophages at day 4 and day 7 after Eimeria infection, as well as the IB antibody titer throughout the experimental period were determined. The results showed a significant interaction between incubation plus hatch and rearing environment. Optimized incubation plus hatch conditions followed by an enriched rearing environment resulted in the least weight loss (P < 0.05) and the highest feed intake (P < 0.01) from day 3 to day 7 after the Eimeria infection (day 56 to 60 of age), compared with all other treatments. In addition, the optimized × enriched chicks had the highest BW gain from day 7 to day 14 after IB infection (day 99 to 106 of age), compared with chicks housed in a cage environment (P < 0.01). Besides the interaction, optimized incubation plus hatch alone resulted in reduced macrophage numbers in the duodenal tissue at day 4 after Eimeria infection, compared with suboptimal incubation plus hatch, whereas the enriched rearing environment stimulated the recovery of intestinal damage caused by Eimeria (P < 0.05) and reduced the production of specific antibodies after IB infection (P < 0.05), compared with the cage environment. In conclusion, this study shows that early life experiences can indeed affect the capacity of rearing hens to cope with an Eimeria and IB infection at an older age, in which performance of chicks is best maintained after optimized incubation plus hatch followed by enriched rearing. This suggests that the development of adaptive capacity to infectious challenges can be influenced with management during a short period in pre- or early postnatal life, but that effects last for a considerable time after cessation of the specific management.

Cellular assessment of crop lymphoid tissue from specific-pathogen-free white leghorn chickens after Salmonella enteritidis challenge

The crop may be an important site along the upper alimentary tract in which a humoral immune response against Salmonella Enteritidis (SE) is elicited locally. The mucosal immune response within the crop (ingluvies) of specific-pathogen-free (SPF) white leghorn (WL) chickens against SE was investigated. Three trials were conducted using SPF WL pullets at age 5-6 wk. Trial 1 consisted of 77 birds evaluated for 10 wk post-SE infection (pi), trial 2 was composed of 72 birds monitored through 8 wk pi, and trial 3 was made up of 30 birds assessed for 5 wk pi. Birds were challenged per os with 10(8) colony-forming units/ml SE phage type 13. Crop lavage samples, crop tissues, ceca, and/or liver-spleen were collected preinfection and then at weekly intervals post-SE infection. Bacteriologic examination of cecal contents and/or liver-spleen occurred weekly to monitor progression of SE infection. Crop lavages were analyzed for SE-lipopolysaccharide (LPS)-specific immunoglobulin A (IgA) by enzyme-linked immunosorbent assay to assess humoral immune response. General histologic staining (hematoxylin and eosin [H&E] and methyl green-pyronin [MGP]) and immunohistochemical (IHC) staining (monoclonal antibodies CD45 and Bu-1) were applied to serial sections of crop to evaluate lymphoid tissue via light microscopy, to grade isolated lymphoid follicles (ILFs) by using score 0 (minimal, < 50 microm in diameter) to score 5 (sizable, > 200 microm in diameter) scale, and to characterize the cellular population of ILFs. Results revealed that cecum samples and liver-spleen samples were 100% SE culture positive at 1 wk pi, and then the percentage of SE positives progressively declined over time. Markedly increased crop SE-LPS-specific IgA antibodies were detected in crop samples by 2-3 wk pi, and the humoral response remained elevated above week 0 baseline for the duration of each trial. Crop ILFs of score 3 to 5 were observed in H&E-stained tissues, with an increased proportion of ILFs in post-SE-infected crops vs. uninfected. MGP staining showed plasma cells scattered within and at the periphery of ILFs. IHC staining revealed CD45 (pan-leukocyte) and Bu-1 (B-lymphocyte)-positive cells within crop ILFs. The chicken crop seems to be an organ in which lymphoid tissue may arise in response to enteric SE infection, and a site in which a humoral response may be generated against the SE pathogen.

Factors affecting intestinal health in poultry

The gastrointestinal (GI) tract has the most extensive exposed surface in the body and is constantly exposed to a wide variety of potentially harmful substances. The GI tract acts as a selective barrier between the tissues of the bird and its luminal environment. This barrier is composed of physical, chemical, immunological, and microbiological components. A wide range of factors associated with diet and infectious disease agents can negatively affect the delicate balance among the components of the chicken gut and, as a result, affect health status and production performance of birds in commercial poultry operations. Phasing out of antibiotic growth promoters from poultry diets in Europe and recent moves toward reduction or removal of these compounds in other parts of the world including North America will likely change the microbial profile of the GI tract environment in commercial poultry. This paper reviews the GI tract from developmental, immunological, and microbial standpoints and then discusses factors that can affect health status of this system. Necrotic enteritis and coccidiosis and their interactions, and possible consequences of antibiotic growth promoter removal from poultry diets with respect to these diseases, are discussed in more detail.

Upregulation of Oxidative Burst and Degranulation in Chicken Heterophils Stimulated with Probiotic Bacteria

The immune system of neonatal chicks is functionally immature during the first week of life. Researchers have previously demonstrated that the avian humoral response can be increased with probiotics. Although the humoral response provides the chick with an effective mechanism to combat pathogens, sufficient antibody titers are not attained until 7 to 10 d postinfection. However, the innate immune system (i.e., heterophils) can respond much more quickly to pathogens. The objective of this study was to determine whether probiotic bacteria can also upregulate heterophil function. Heterophils were isolated from the peripheral blood of neonatal chickens by using a discontinuous density gradient. Oxidative burst and degranulation are bactericidal mechanisms used by heterophils to kill pathogens and were used in this study as indicators of heterophil function. We found that each of the 10 "generally recognized as safe" probiotic isolates (designated G1 to G11) tested in vitro were capable of increasing (P < 0.05) heterophil oxidative burst and degranulation when compared with unstimulated controls. Bacillus subtilis (G3), Lactococcus lactis lactis (G6), and Lactobacillus acidophilus (G8) isolates were determined to elicit the greatest heterophil response in vitro and were subsequently fed to chicks. Phosphate-buffered saline or 1 of these 3 probiotic isolates (approximately 2.5 x 10(8) cfu/chick; 50 chicks/treatment) resuspended in PBS was administered by oral gavage on the day of hatch. Heterophils were isolated from chicks from each of these 4 treatment groups 24 h posttreatment. Significant increases in heterophil degranulation and oxidative burst were observed with the G3-, G6-, and G8-treated chicks when compared with heterophils isolated from birds with no probiotic treatment. These data suggest that probiotic bacteria can significantly improve heterophil oxidative burst and degranulation in broilers. To our knowledge, this is the first study demonstrating a relationship between probiotics and avian heterophil function.

Enhanced Gross Visualization of Chicken Peyer's Patch: Novel Staining Technique Applied to Fresh Tissue Specimens

The ileal Peyer's patches (Pp), secondary gut-associated lymphoid tissue of the mucosal immune system, may serve as an important site for monitoring inflammatory and immunologic responses of the host against enteric pathogens. Chicken Pp are often difficult to observe grossly, and a simple technique to enhance visualization of the Pp is lacking. Therefore, we designed a novel staining method that is quick, easy, and accurate to aid in gross identification and recovery of the chicken Pp from fresh tissue specimens. Lower alimentary tracts were harvested from White Leghorn hens and commercial broilers. The ileocecocolic region was excised intact, flushed with deionized water to remove ingesta, and a dilute eosin-Y solution was infused. After 1 min, the eosin-Y was gently extruded. Modified-crystal violet (mCV) was then injected into the gastrointestinal segment, where on the lymphoid tissue area became apparent at the serosal surface. The distal ileal Pp was visible as a pale whitish pink ovoid-focalized area with surrounding gut tissue stained light purple. The exact Pp site could be delineated at the serosal and mucosal surface by gross assessment. Light microscopy evaluation of hematoxylin and eosin-stained tissue slides prepared from the excised Pp site revealed lymphoid tissue aggregations with multiple follicular units indicative of Pp. The novel eosin-Y + mCV staining technique promotes rapid identification and accurate recovery of chicken Pp lymphoid tissue from fresh tissue specimens.

Impaired immune responses in broiler hatchling hindgut following delayed access to feed

One of the key stimulators of intestinal development in the chick is physical exposure to feed, while feed withholding delays the onset of gut development. A delay of 24-72 h in onset of feeding is quite common in the poultry industry due to variation in hatching time and hatchery treatments. As intestinal development occurs in concert with the development of the gut associated lymphoid tissue (GALT), we investigated the effects of short term feed withholding on development of GALT in broiler hatchlings. GALT activity was determined by antibody production (systemic and locally in the gut), distribution of B and T lymphocytes in the gut, expression of lymphocyte specific genes, and distribution of B and T lymphocytes in the cloacal bursa. Our findings show that while development of GALT in the foregut (duodenum, jejunum, ileum) was only slightly and temporarily impeded by feed withholding, GALT activity in the hindgut and the gut-related cloacal bursa was significantly delayed during the first 2 weeks of life: Systemic and intestinal antibody responses following rectal immunization to antigen were lower, colonization of the hindgut (cecum and colon) by T and B lymphocytes was delayed, as well as the expression of chIL-2 mRNA in hindgut T lymphocytes. We also found that the increase of B and T population size in the cloacal bursa was delayed with time. Full recovery occurred from 2 weeks of age. The 2-week vulnerable period should be seriously considered in circumstances where hatchlings are in transit for extended periods from hatcheries to farms.