Modulatory roles of proinflammatory cytokines on the expression of cathelicidins in the lower regions of the oviduct of laying hens

Week-Old Chicks with High Bacteroides Abundance Have Increased Short-Chain Fatty Acids and Reduced Markers of Gut Inflammation

As important commensals in the chicken intestine, Bacteroides are essential complex carbohydrate degraders, and short-chain fatty acid (SCFA) producers that are highly adapted to the distal gut. Previous studies have shown large variation in Bacteroides abundance in young chickens. However, limited information is available regarding how this variation affects the gut microbiome and host immunity. To investigate how elevated or depleted Bacteroides levels affect gut microbial functional capacity and impact host response, we sampled 7-day-old broiler chickens from 14 commercial production flocks. Week-old broiler chickens were screened and birds with low Bacteroides (LB) and high Bacteroides (HB) abundance were identified via 16S rRNA gene amplicon sequencing and quantitative PCR (qPCR) assays. Cecal microbial functionality and SCFA concentration of chickens with distinct cecal Bacteroides abundance were profiled by shotgun metagenomic sequencing and gas chromatography, respectively. The intestinal immune responses of LB and HB chickens were assessed via reverse transcription qPCR. Results showed that the gut microbiota of the LB group had increased abundance of lactic acid bacteria pyruvate fermentation pathway, whereas complex polysaccharide degradation and SCFA production pathways were enriched in the HB group (P < 0.05), which was supported by increased SCFA concentrations in the ceca of HB chickens (P < 0.05). HB chickens also showed decreased expression of interleukin-1β and increased expression of interleukin-10 and tight-junction protein claudin-1 (P < 0.05). Overall, the results indicated that elevated Bacteroides may benefit the 7-day broiler gut and that further work should be done to confirm the causal role of Bacteroides in the observed positive outcomes. IMPORTANCE To date, limited information is available comparing distinct Bacteroides compositions in the chicken gut microbial communities, particularly in the context of microbial functional capacities and host responses. This study showed that possessing a microbiome with elevated Bacteroides in early life may confer beneficial effects to the chicken host, particularly in improving SCFA production and gut health. This study is among the first metagenomic studies focusing on the early life chicken gut microbiota structure, microbial functionality, and host immune responses. We believe that it will offer insights to future studies on broiler gut microbial population and their effects on host health.

Multi-Omics Analysis After Vaginal Administration of Bacteroides fragilis in Chickens

The reproductive tract of chickens is an important organ for egg formation. The vagina is in close contact with the external environment, which may lead to the invasion of a variety of pathogenic bacteria, affect the internal and external quality of eggs, and even increase mortality and cause economic loss. In recent years, probiotics as a substitute for antibiotics have brought economic benefits in livestock and poultry production. In the present study, we investigated the effects of vaginal administration of Bacteroides fragilis on the cloacal microbiota, vaginal transcriptome and metabolomics of chickens and evaluated the beneficial potential of B. fragilis. The results showed that B. fragilis treatment could affect the microbial composition of the cloaca. Transcriptome analysis found that the immune-related genes CCN3, HAS2, and RICTOR were upregulated, that the inflammatory genes EDNRB, TOX, and NKX2-3 were downregulated, and that DEGs were also enriched in the regulation of the inflammatory response, cellular metabolism, and synaptic response pathways. In addition, the differential metabolites were mainly related to steroid hormone biosynthesis, unsaturated fatty acid biosynthesis, and arachidonic acid metabolism, and we identified associations between specific differential metabolites and genes. Overall, this study provides a theoretical basis for the application of B. fragilis as a potential probiotic in livestock and poultry production.

Effects of Toll-like Receptor Ligands on the Expression of Proinflammatory Cytokines and Avian β-defensins in Cultured Chick Intestine

Few studies have focused on the regulation of cytokine and avian β-defensin (AvBDs) expression for promoting immune defense in the avian intestine. The aim of this study was to investigate the effects of different Toll-like receptor (TLR) ligands (bacterial patterns) on the expression of proinflammatory cytokines (IL-1β and IL-6) and AvBDs (AvBD1, AvBD4, and AvBD7) in the chick intestine. The ileum and cecum of 3-day-old chicks were collected and examined histologically to identity the cells present in the intestinal mucosa. Other tissues were cultured with or without the TLR2, TLR4, and TLR21 ligands—Pam3CSK4, LPS, and CpG-ODN—for 1 or 3 h. The gene expression profiles of proinflammatory cytokines and AvBDs were determined in these tissues using real-time polymerase chain reaction (PCR). The mucosa of the ileum and cecum contained leukocytes, luminal and crypt epithelial cells, and other enterocytes. Pam3CSK4 tended to downregulate the expression of IL-1β, AvBD1, and AvBD7 in the ileum but upregulated their expression in the cecum. LPS downregulated the expression of IL-1β and IL-6 in both the ileum and the cecum, whereas it upregulated the expression of AvBD1, AvBD4, and AvBD7 in the cecum. CpG-ODN upregulated the expression of IL-6 and AvBD7 in the ileum and IL-1β in the cecum, and downregulated the expression of IL-1β and AvBDs in the ileum. We suggested that the expression levels of proinflammatory cytokines and AvBDs in the chick intestine are affected by TLR2, TLR4, and TLR21 ligands. Thus, these innate immune factors may be modulated by the luminal microbe complex in the intestine.

Effect of antibiotic treatment on microbial composition and expression of antimicrobial peptides and cytokines in the chick cecum

The aim of this study was to confirm whether the expression of innate immune molecules in the chick cecum is altered in association with changes in the composition of the intestinal microbiome that are regulated by treatment with antibiotics. Broiler chicks were administered with antibiotics (penicillin and streptomycin) daily, and the composition of the microbiota, expression of innate immune molecules, and localization of antimicrobial peptides in the chick cecum were examined at day 7 and day 14 using real-time PCR and immunohistochemistry. The oral administration of antibiotics caused an increase in the relative frequency of the Enterobacteriaceae family and a decrease in some gram-negative (Barnesiellaceae) and gram-positive bacterial (Clostridiaceae and Erysipelotrichaceae) families. The gene expression levels of immune molecules, including 4 Toll-like receptors (TLR) (TLR 2, 4, 5, and 21), inflammation-related cytokines (IL-1β, TGFβ3, TGFβ4, and IL-8), and antimicrobial peptides (avian β-defensins and cathelicidins) showed a tendency to decrease with antibiotic treatment at day 7. However, expression levels of TLR21 and some cytokines (IL-1β, TGFβ3, and IL-8) were higher in the cecum or cecal tonsils of the antibiotic-treated group than in those of the control at day 14. The immunoreactive avian β-defensin 2 and cathelicidin 1 proteins were localized in the leukocyte-like cells in the lamina propria, and they were aggregated in the form of small islands. We conclude that the expression of innate immune molecules, including TLR, inflammation-related cytokines, and antimicrobial peptides, in the cecum are altered in association with changes in the density or composition of the luminal microbiota during the early phase of life in chicks.

Molecular characterization, mRNA gene expression, and antimicrobial activity of 2 new cathelicidin genes in goose

Cathelicidins represent a major group of host defense peptides (HDPs) that share a highly conserved cathelin-like domain. In birds, this gene family has been identified in many species. However, no information was available in the goose until now. In this study, we present the molecular characterization of 2 goose cathelicidin genes, namely goose CATH2 and goose CATH3, for the first time. The complete cDNA of goose CATH2 and goose CATH3 were 571 bp and 573 bp in length, respectively, and the deduced amino acid sequences exhibited high similarity with other avian cathelicidins. Furthermore, evolutionary analyses indicated that all known cathelicidins form 3 distinct clusters from reptiles, while the oldest cathelicidin member, which is known as CATHB1, is very likely absent in the goose genome. Meanwhile, highly expressed goose CATH2 and goose CATH3 were also observed in primary and secondary lymphoid tissues, same as the observations in other avian species. In addition, chemically synthesized mature peptides of the 2 cathelicidins exerted optimal antimicrobial abilities to a range of gram-negative and gram-positive bacteria. The discovery and characterization of goose cathelicidins complete the knowledge for goose HDPs and might contribute to understanding the evolution of avian cathelicidins as well as for the development of antibacterial agents.

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.

Effects of TLR Ligands on the Expression of Cytokines and Possible Role of NFκB in its Process in the Theca of Chicken Follicles

The aim of this study was to determine the effects of Toll-like receptor (TLR) ligands on the expression of cytokines in chicken follicular theca and to investigate whether nuclear factor-κB (NFκB) was involved in their expression. The follicular theca was collected from the largest follicle of laying hens. In experiment 1, the expression of TLRs in the theca interna and externa was confirmed using RT-PCR. The theca tissues were then incubated with or without Pam3CSK4 (TLR2 ligand), poly I:C (TLR3 ligand), LPS (TLR4 ligand), flagellin (TLR5 ligand), R837 (TLR7 ligand), and CpG-ODN (TLR21 ligand) for 3 h, after which cytokine expression (IL-1β, IL-6, TNFSF15, CXCLi2, IFN-α, and IFN-β) was analyzed by real-time PCR. In experiment 2, the theca tissues were incubated in a medium containing Pam3CSK4, poly I:C, LPS, or CpG-ODN with or without BAY 11-7085 (an inhibitor of NFκB) for 3 h. The results of experiment 1 revealed that all TLRs, namely TLR1 (type 1 and 2), TLR2 (type 1 and 2), 3–5, 7, 15, and 21, were expressed in the follicular theca, although the PCR products of TLR1 (type 2) and TLR21 were faint. Moreover, Pam3CSK4 and LPS upregulated the expression of all detected cytokines, except for IFN-α, whose expression was not upregulated by LPS. Poly I:C upregulated the expression of IL-6, CXCLi2, and IFN-β, while CpG-ODN upregulated IL-1β. Flagellin and R837 did not significantly affect cytokine expression. In experiment 2, the expression of IL-1β, IL-6, CXCLi2 and IFN-β in tissues incubated with LPS was downregulated by BAY 11-7085. These results suggest that the innate immune system, including pattern recognition by TLRs and cytokine synthesis, occur in the theca; whereas, functions for recognition of bacterial patterns is more developed than that of viral ones.

Innate antiviral immune response against infectious bronchitis virus and involvement of prostaglandin E2 in the uterine mucosa of laying hens

Infectious bronchitis virus (IBV) is an enveloped RNA virus that causes deformities in eggshells. The aim of this study was to investigate the innate immune response to IBV, and to determine whether prostaglandin (PG) E2, which is synthesized during inflammation, is involved in the innate immune response in the uterine mucosa. The effects of intra-oviductal inoculation with attenuated IBV (aIBV) on the expression of viral RNA recognition receptors and innate antiviral factors were examined by real-time PCR and immunohistochemistry, and on PGE2 levels by ELISA. Then, the effects of PGE2 on the expression of innate antiviral factors in cultured uterine mucosal cells were examined. The results showed that the expression of RNA virus pattern recognition receptors (TLR3, 7, and MDA5), antimicrobial peptides (avian β-defensins, including AvBD1, 2, 4-6 and cathelicidins, including CATH1 and 3), and interferons (IFNα, β, γ, λ) were upregulated, and the expression of cyclooxygenase 2 (PG synthase) and the level of PGE2 were increased in the uterine mucosa following aIBV inoculation. The number of AvBD2-positive cells in the mucosa also increased in response to aIBV. In cultured mucosal cells (mainly epithelial), the expression of AvBD4, 10-13 and IFNα, β, and λ was upregulated following incubation with 500 nM PGE2. These results suggest that the expression of viral RNA-recognition receptors, AvBDs, CATHs, and IFNs and PGE2 are induced by the IBV antigen, and that the expression of a different set of AvBDs is also induced by PGE2 in the cultured uterine mucosal cells. These antiviral factors may play a role in the protection of the uterine mucosa from IBV infection.