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

Biophysiology of in ovo administered bioactive substances to improve gastrointestinal tract development, mucosal immunity, and microbiota in broiler chicks

Early embryonic exogenous feeding of bioactive substances is a topic of interest in poultry production, potentially improving gastrointestinal tract (GIT) development, stimulating immunization, and maximizing the protection capability of newly hatched chicks. However, the biophysiological actions and effects of in ovo administered bioactive substances are inconsistent or not fully understood. Thus, this paper summarizes the functional effects of bioactive substances and their interaction merits to augment GIT development, the immune system, and microbial homeostasis in newly hatched chicks. Prebiotics, probiotics, and synbiotics are potential bioactive substances that have been administered in embryonic eggs. Their biological effects are enhanced by a variety of mechanisms, including the production of antimicrobial peptides and antibiotic responses, regulation of T lymphocyte numbers and immune-related genes in either up- or downregulation fashion, and enhancement of macrophage phagocytic capacity. These actions occur directly through the interaction with immune cell receptors, stimulation of endocytosis, and phagocytosis. The underlying mechanisms of bioactive substance activity are multifaceted, enhancing GIT development, and improving both the innate and adaptive immune systems. Thus summarizing these modes of action of prebiotics, probiotics and synbiotics can result in more informed decisions and also provides baseline for further research.

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.

Oxidative stress mediated immunosuppression caused by ammonia gas via antioxidant/oxidant imbalance in broilers

1. Ammonia is one of major air pollutants in intensive poultry houses, where it causes immunosuppression in broilers. Although previous studies have focused on a particular organ, data on multiple organs have not been reported.2. In the following work, broilers were exposed to environmental ammonia (0, 10, 20, and 40 mg/m³ from 1-21 d old; and 0, 15, 30, and 60 mg/m³ from 22-42 d old).3. Ammonia exposure reduced bird spleen index at 42 d and thymus index at 14, 28, 35 and 42 d, meaning that ammonia caused immunosuppression in birds. Moreover, high ammonia exposure down-regulated the expression of toll-like receptor 4 (TLR4) in lung tissue at 21 d, as well as TLR4 in lung and tracheal mucosa at 42 d when analysed using qRT-PCR. It increased SIgA in saliva at 42 d when analysed by ELISA. Ammonia increased interleukin-6 (IL-6), IL-1β, interferon-α (IFN-α), and IFN-γ in serum at 28 d from the ELISA assay, which indicated that all of these factors took part in ammonia-immunosuppression in birds.4. Three antioxidants (CAT, SOD, T-AOC) decreased, and one oxidant MDA increased after ammonia exposure in the liver and blood, which indicated that ammonia caused oxidative stress via the imbalance of antioxidants/oxidants in birds.5. Correlation analysis showed that TLR4 and TLR15 in the tracheal mucosa were significantly positively related to IFN-γ and negatively related to IL-6. TLR2 in the lung was significantly positively related to IL-1β, and TLR2 in bird tracheal mucosa was negatively related to IL-6 in serum.6. The results suggested that oxidative stress mediated immunosuppression caused by ammonia gas via antioxidant/oxidant imbalance in broilers.

Delay of Feed Post-Hatch Causes Changes in Expression of Immune-Related Genes and Their Correlation with Components of Gut Microbiota, but Does Not Affect Protein Expression

Simple Summary

Newly hatched chicks do not have access to feed until between 48 and 72 h post-hatch based on standard practices in the poultry industry. How these practices affect the chicken’s immune system in not well understood. In this study, we investigated the effect of a delay in access to feed for 48 h in newly hatched chicks on the expression of various immune-related genes in the ileum and analyzed the correlation between these genes and the components of the ileal microbiota. The results suggest that several immune-related genes were affected by delayed access to feed and the age of the birds; however, these changes were transient, occurring mostly within 48 h of the return of birds to feed. In the correlation analysis between gene expression and components of the ileal microbiota, an increased number of significant correlations between immune-related genes and the genera Clostridium, Enterococcus, and the species Clostridium perfringens suggests a perturbation of the immune response and ileal microbiota in response to lack of feed immediately post-hatch. These results point out the complexity of the interplay between microbiota and the immune response and will help further explain the negative effects of delay in access to feed on production parameters in chickens.

Abstract

Because the delay of feed post-hatch (PH) has been associated with negative growth parameters, the aim of the current study was to determine the effect of delayed access to feed in broiler chicks on the expression of immune-related genes and select proteins. In addition, an analysis of the correlation between gene expression and components of the gut microbiota was carried out. Ross 708 eggs were incubated and hatched, and hatchlings were divided into FED and NONFED groups. The NONFED birds did not have access to feed until 48 h PH, while FED birds were given feed immediately PH. The ileum from both groups (n = 6 per group) was sampled at embryonic day 19 (e19) and day 0 (wet chicks), and 4, 24, 48, 72, 96, 144, 192, 240, 288, and 336 h PH. Quantitative PCR (qPCR) was carried out to measure the expression of avian interleukin (IL)-1β, IL-4, IL-6, IL-8, IL-18, transforming growth factor (TGF-β), toll-like receptor (TLR)2, TLR4, interferon (IFN)-β, IFN-γ, and avian β-defensins (AvBD) I, 2, 3, 5, 6, 7, 8, 9, and 10. Protein expression of IL-10, IL-1β, IL-8, and IL-18 were measured using ELISAs. A correlation analysis was carried out to determine whether any significant association existed between immune gene expression and components of the ileal luminal and mucosal microbiota. Expression of several immune-related genes (TGF-β, TLR4, IFN-γ, IL-1β, IL-4, IL-6, and AvBDs 8 and 9) were significantly affected by the interaction between feed status and age. The effects were transient and occurred between 48 and 96 h PH. The rest of the genes and four proteins were significantly affected by age, with a decrease in expression noted over time. Correlation analysis indicated that stronger correlations exist among gene expression and microbiota in NONFED birds. The data presented here indicates that delay in feed PH can affect genes encoding components of the immune system. Additionally, the correlation analysis between immune gene expression and microbiota components indicates that a delay in feed has a significant effect on the interaction between the immune system and the microbiota.

Non-Antibiotics Strategies to Control Salmonella Infection in Poultry

Salmonella spp. is a facultative intracellular pathogen causing localized or systemic infections, involving economic and public health significance, and remains the leading pathogen of food safety concern worldwide, with poultry being the primary transmission vector. Antibiotics have been the main strategy for Salmonella control for many years, which has allowed producers to improve the growth and health of food-producing animals. However, the utilization of antibiotics has been reconsidered since bacterial pathogens have established and shared a variety of antibiotic resistance mechanisms that can quickly increase within microbial communities. The use of alternatives to antibiotics has been recommended and successfully applied in many countries, leading to the core aim of this review, focused on (1) describing the importance of Salmonella infection in poultry and the effects associated with the use of antibiotics for disease control; (2) discussing the use of feeding-based (prebiotics, probiotics, bacterial subproducts, phytobiotics) and non-feeding-based (bacteriophages, in ovo injection, vaccines) strategies in poultry production for Salmonella control; and (3) exploring the use of complementary strategies, highlighting those based on -omics tools, to assess the effects of using the available antibiotic-free alternatives and their role in lowering dependency on the existing antimicrobial substances to manage bacterial infections in poultry effectively.

TLR2 and TLR4 molecules and antigen-presenting cell compositions in cecal tonsils of broiler chicks (Gallus gallus domesticus) in the first two weeks of the post-hatch period

Chickens do not have lymph nodes. Gut-associated lymphoid tissue is the major immunological organization for the digestive system. Cecal tonsils are an important part of this organization. This study is a descriptive and experimental study that was conducted to determine the histological development of the cecal tonsils and the distribution of Toll-like receptor (TLR) 2, TLR4 and antigen-presenting cells during the first 2 weeks of the chick's life. The tissue sections were stained using Crossmon's triple technique, Gordon and Sweet's silver impregnation, and streptavidin-biotin-peroxidase complex methods. The classical tonsil framework with fossa and tonsillar units were observed in 4 days cecal tissue. The web of reticular fibres forming the stroma of the tissue had the impression that the lymphoid cells filling in time. The development of cecal tonsil was completed histologically on the day 10 and following day 14 samples. Regardless of the antigenic stimulation, TLR2, TLR4 and CD83, major histocompatibility complex (MHC) class II molecules are present in proximal cecal tissue. However, CD83-positive dendritic cells in the germinal centre were first distinguished on day 7. Furthermore, the high antigen presentation capacity of the cecum with an intense MHC class II molecule expression was determined. Histological and immunohistochemical findings in this study revealed that both innate and adaptive cecal defence mechanisms were in the learning period during the first 2 weeks. The learning period of innate immunity may require more detailed research. However, the results obtained in this study will be taken into consideration in the vaccination programmes in chicks.

Bacillus subtilis-Based Probiotic Improves Skeletal Health and Immunity in Broiler Chickens Exposed to Heat Stress

Simple Summary

High ambient temperature is a major environmental stressor affecting the physiological and behavioral status of animals, increasing stress susceptibility and immunosuppression, and consequently increasing intestinal permeability (leaky gut) and related neuroinflammation. Probiotics, as well as prebiotics and synbiotics, have been used to prevent or decrease stress-associated detrimental effects on physiological and behavioral homeostasis in humans and various animals. The current data indicate that a dietary probiotic supplement, Bacillus subtilis, reduces heat stress-induced abnormal behaviors and negative effects on skeletal health in broilers through a variety of cellular responses, regulating the functioning of the microbiota–gut–brain axis and/or microbiota-modulated immunity during bone remodeling under thermoneutral and heat-stressed conditions.

Abstract

The elevation of ambient temperature beyond the thermoneutral zone leads to heat stress, which is a growing health and welfare issue for homeothermic animals aiming to maintain relatively constant reproducibility and survivability. Particularly, global warming over the past decades has resulted in more hot days with more intense, frequent, and long-lasting heat waves, resulting in a global surge in animals suffering from heat stress. Heat stress causes pathophysiological changes in animals, increasing stress sensitivity and immunosuppression, consequently leading to increased intestinal permeability (leaky gut) and related neuroinflammation. Probiotics, as well as prebiotics and synbiotics, have been used to prevent or reduce stress-induced negative effects on physiological and behavioral homeostasis in humans and various animals. The current data indicate dietary supplementation with a Bacillus subtilis-based probiotic has similar functions in poultry. This review highlights the recent findings on the effects of the probiotic Bacillus subtilis on skeletal health of broiler chickens exposed to heat stress. It provides insights to aid in the development of practical strategies for improving health and performance in poultry.

Riemerella anatipestifer infection affects intestinal barrier structure and immune reactions in the duck caecum

Riemerella anatipestifer (RA) infection causes high mortality and poor feed conversion, leading to great economic losses to the duck industry. This study investigated the effects of RA on the intestinal morphology and immune response of ducks. Histological examination showed that RA infection caused intestinal injury, including significantly reduced mucosal thickness on days 2, 3 and 5, significantly reduced villus height on days 1, 2, 3 and 5 (P < 0.05) and significantly reduced villus height to crypt depth ratios on days 2, 3, 5 and 9 of RA infection (P < 0.05). The expression of intestinal mucosal layer construction-associated genes and tight junction genes was significantly altered on at least one time point (day 1, 2, 3, 5, 9 or 14) after RA infection. Quantitative real-time polymerase chain reaction revealed that RA infection affected intestinal mucosal immune function. The genes encoding TLR4 (toll like receptor-4), TRAF6 (TNF receptor-associated factor 6), MYD88 (myeloid differentiation factor 88), IFN-γ (interferon-γ), IL (interleukin)-4 and IL-8 were significantly upregulated on day 2 of RA infection. Taken together, these results indicate that RA infection negatively affects intestinal barrier function in ducks due to impaired mucosal and villus-crypt structure and alters the mRNA expression of mucous layer construction-, intestinal tight junction-, and intestinal mucosal immunity-related genes.

Histological and immunohistochemical studies of the proximal caecum and caecal tonsils of quail (Coturnix coturnix japonica)

The proximal caecum in quails consists of lymphoid and non-lymphoid structures. The caecal tonsils in the proximal part of the caecum are units of gut-associated lymphoid tissue in poultry. This study aimed to examine the histological characteristics of the proximal caecum, as well as compositions of dendritic cells (DCs) and antigen-presenting cells (APCs) in the caecal tonsil of quails. Tissue sections were stained with Crossman's triple, periodic acid-Schiff, Gordon and Sweet's silver, Congo red and methyl green-pyronin dyes, as well as immunohistochemically by the streptavidin-biotin-peroxidase complex method. Caecal lymphoid tissue was located in the lamina propria and submucosa. Germinative centres were observed within the lymphoid tissue. Reticular fibres were mainly distributed in the border area of the germinal centre with only a few fibres scattered in the centre. Plasma cells were observed in the subepithelial region and germinal centres. Eosinophil granulocytes were prevalent in the lymphoid tissue. Additionally, CD83-immunoreactive DCs and MHC class II immunoreactive APCs were present in the subepithelial area and diffuse lymphoid tissue. While DCs were seen in the germinal centres of tonsillar units, APCs were rarely present in the germinal centres, but they were noticed around the germinal centres. In conclusion, the histological structure of the proximal caecum in quails and the distributions of some immunological cells in the caecal tonsils were revealed. Therefore, the defensive role of the caecal tonsils in the digestive system may be better understood, and comparative studies may be carried out.

Distribution of TLR4 and MHC class II molecules of the spleen in broiler chicks treated with and without LPS in the first 2 weeks of the post-hatch period

1. The purpose of this study was to investigate the distribution of Toll-like receptor-4 (TLR4) and major histocompatibility complex (MHC) class II molecules of the spleen in chicks treated with lipopolysaccharide (LPS) during the first 2 weeks of their life. 2. A total of 225 Ross-308 commercial broiler chicks were used. Within the 2-week experimental period, chicks were divided into 5 main groups according to the days of decapitation which were 1, 4, 7, 10 and 14 d after hatch. Each main group had 45 chicks. The main groups were further divided into three subgroups (15 chicks each), which included control chicks (no injection), and phosphate-buffered saline (PBS) and LPS-injected chicks. Spleen samples were collected 1-, 3-, 6-, 12- and 24-h after the PBS or LPS administrations. Tissue sections were stained using streptavidin-biotin-peroxidase complex staining method. 3. From 1 d of age, TLR4 positivity was found in the spleen in diffuse granular form. The cells showing intense TLR4 positivity were observed in periellipsoidal lymphoid tissue in 4-d-old chicks. The same cells were determined in the germinal centre of the spleen in 7-d-old chicks. LPS stimulation led to an increase in the intensity of TLR4 positivity in 14-d-old chicks. 4. From 1 d of age, MHC class II positivity was found in both white pulp and red pulp. This was higher in 14-d-old chicks injected with LPS than in the controls and the chicks injected with PBS. 5. The findings indicate that, from 1 d of age in chicks, the spleen has both non-specific defence elements and the molecules having the information to induce adaptive immunity. In addition, at the end of the 2-week experimental period, it was determined that the spleen had the capacity to recognise antigens.

Innate immune functions of avian intestinal epithelial cells: Response to bacterial stimuli and localization of responding cells in the developing avian digestive tract

Intestinal epithelial cells are multi-tasked cells that participate in digestion and absorption as well as in protection of the digestive tract. While information on the physiology and immune functions of intestinal epithelial cells in mammals is abundant, little is known of their immune function in birds and other species. Our main objectives were to study the development of anti-bacterial innate immune functions in the rapidly developing gut of the pre- and post-hatch chick and to determine the functional diversity of epithelial cells. After establishing primary intestinal epithelial cell cultures, we demonstrated their capacity to uptake and process bacteria. The response to bacterial products, LPS and LTA, induced expression of pro-inflammatory cytokine genes (IL-6, IL-18) as well as the expression of the acute phase proteins avidin, lysozyme and the secretory component derived from the polymeric immunoglobulin receptor. These proteins were then localized in gut sections, and the goblet cell was shown to store avidin, lysozyme as well as secretory component. Lysozyme staining was also located in a novel rod-shaped intestinal cell, situated at different loci along the villus, thus deviating from the classical Paneth cell in the mammal, that is restricted to crypts. Thus, in the chicken, the intestinal epithelium, and particularly goblet cells, are committed to innate immune protection. The unique role of the goblet cell in chicken intestinal immunity, as well as the unique distribution of lysozyme-positive cells highlight alternative solutions of gut protection in the bird.