Localization and developmental expression of two chicken host defense peptides: cathelicidin-2 and avian β-defensin 9

During the breeding season, lymphocytes assemble into ellipse-shaped clusters in the uropygial gland of the jungle crow Corvus macrorhynchos

BACKGROUND

Recent studies indicate that the uropygial gland produces intraspecific chemosensory cues. The jungle crow Corvus macrorhynchos, which is a type of passerine, exhibits extreme morphological variation in the gonadal gland during the breeding season. Because the uropygial gland of the jungle crow sometimes exhibits morphological changes during the breeding season, we attempted to clarify the morphological changes in the uropygial gland of the jungle crow according to development and season.

METHODS

Captured birds were divided into three age groups according to the color of their upper palate: <1 year, 1-2 years, and >2 years old. Paraffin sections of the uropygial gland were stained with hematoxylin and eosin, Elastica van Gieson, Giemsa, and a proliferating cell nuclear antigen antibody.

RESULTS

Sexual dimorphism was not seen in the morphology of the uropygial gland in the jungle crow. However, changes due to growth and season were identified. During the breeding season in birds>2 years old, lymphocytes formed ellipse-shaped clusters around the glandular cavity. These clusters were invaded by collagen fibers from spherical cells.

CONCLUSIONS

Collagen fibers, which develop from spherical cells, seem to be related to lymphoid cluster migration. Ellipse-shaped lymphoid clusters may play a crucial role in reproductive behavior during the breeding season.

Effects of on-farm hatching versus hatchery hatching on growth performance, gut development, and intestinal health and function in broiler chickens

An alternative hatching system known as hatch on-farm (HOF) provides early access to feed compared to hatch in hatchery (HH) system. Early feeding may promote favorable gut development, potentially improving intestinal health and broiler performance. Previous studies have assessed the effects of HOF on chick quality, welfare and performance, its impacts on gut health remain inconclusive. A total of 560 Ross 308 male chicks were reared until d 38, hatched either in a hatchery (n = 280) or on-farm (n = 280), with 14 replicates per system and 20 birds per pen. Production parameters were periodically monitored. Digestive and immune organ characteristics, intestinal permeability and histomorphology were assessed on d 7, 14, and 38. High-throughput qPCR analyzed 79 ileal genes regarding barrier integrity, immune function, nutrient transporters, gut hormones, metabolism, and oxidation. HOF chicks had higher d1 body weights than HH chicks (P < 001), but this advantage disappeared within first week, with no subsequent performance differences. HOF chickens demonstrated increased duodenal villus width on d 7 and 14, and increased ileal crypt depth and submucosal thickness on d 7 (P < 0.05). Relative bursal weight was higher on d 14 (P = 0.018) and tended to be higher on d 38 in HOF chickens (P = 0.094). Intestinal permeability remained unaffected (P > 0.05), while HH chicks showed upregulation of gut barrier genes such as MUC5ac on d 7 and CLDN2 and MUC2 on d 14 (P < 0.05). HH chicks also showed upregulation of nutrient transports including VDR on d 7 and SLC30A1 and SLC5A9 on d 38, and decreased expression of the appetite-suppressing hormone CCK on d 7 (P < 0.05). HOF chicks upregulated immune-related genes, including IL-8 on d 7, IL-6, IFN-γ, AVBD9 on d 14, and NOS2 on d 38 (P < 0.05), and the oxidation gene HIF1A on d 38 (P = 0.039). In conclusion, although the HOF showed only transient growth advantages, it enhanced mucosal morphology and modulated immunity, indicating improved intestinal health.

Immunomodulatory properties of chicken cathelicidin-2 investigated on an ileal explant culture

As the threat posed by antimicrobial resistance grows more crucial, the development of compounds that can replace antibiotics becomes increasingly vital. Chicken cathelicidin-2 (Cath-2) belongs to the group of Host Defense Peptides (HDPs), which could provide a feasible solution for the treatment of gastrointestinal infections in poultry. It is a small peptide produced by the heterophil granulocytes of chickens as part of the innate immune response, and its immunomodulatory activity has already been demonstrated in several cell types. In this study, the effects of Cath-2 on the intestinal immune response were examined using ileal explant cultures isolated from chicken. Regarding our results, Cath-2 displayed a potent anti-inflammatory effect as it alleviated the LTA-caused elevation of interleukin (IL)-6 and IL-2 concentrations, and that of the IFN-γ/IL-10 ratio, furthermore, it increased the concentration of IL-10, alleviating the LTA-evoked decreased level of the anti-inflammatory cytokine. Moreover, when applied alone, it elevated the concentrations of IL-6, CXCLi2, and IL-2, providing evidence of its complex immunomodulatory mechanisms. In summary, Cath-2 was able to modulate the immune response of the intestinal wall not only by reducing pro-inflammatory cytokine release, but also through immune stimulation, demonstrating that it has the ability to improve innate immunity via a complex mechanism that may make it a suitable candidate for the control of intestinal infections.

Identification of a microbial sub-community from the feral chicken gut that reduces Salmonella colonization and improves gut health in a gnotobiotic chicken model

A complex microbial community in the gut may prevent the colonization of enteric pathogens such as Salmonella. Some individual or a combination of species in the gut may confer colonization resistance against Salmonella. To gain a better understanding of the colonization resistance against Salmonella enterica, we isolated a library of 1,300 bacterial strains from feral chicken gut microbiota which represented a total of 51 species. Using a co-culture assay, we screened the representative species from this library and identified 30 species that inhibited Salmonella enterica subspecies enterica serovar Typhimurium in vitro. To improve the Salmonella inhibition capacity, from a pool of fast-growing species, we formulated 66 bacterial blends, each of which composed of 10 species. Bacterial blends were more efficient in inhibiting Salmonella as compared to individual species. The blend that showed maximum inhibition (Mix10) also inhibited other serotypes of Salmonella frequently found in poultry. The in vivo effect of Mix10 was examined in a gnotobiotic and conventional chicken model. The Mix10 consortium significantly reduced Salmonella load at day 2 post-infection in gnotobiotic chicken model and decreased intestinal tissue damage and inflammation in both models. Cell-free supernatant of Mix10 did not show Salmonella inhibition, indicating that Mix10 inhibits Salmonella through either nutritional competition, competitive exclusion, or through reinforcement of host immunity. Out of 10 species, 3 species in Mix10 did not colonize, while 3 species constituted more than 70% of the community. Two of these species were previously uncultured bacteria. Our approach could be used as a high-throughput screening system to identify additional bacterial sub-communities that confer colonization resistance against enteric pathogens and its effect on the host.IMPORTANCESalmonella colonization in chicken and human infections originating from Salmonella-contaminated poultry is a significant problem. Poultry has been identified as the most common food linked to enteric pathogen outbreaks in the United States. Since multi-drug-resistant Salmonella often colonize chicken and cause human infections, methods to control Salmonella colonization in poultry are needed. The method we describe here could form the basis of developing gut microbiota-derived bacterial blends as a microbial ecosystem therapeutic against Salmonella.

Differential Salmonella Typhimurium intracellular replication and host cell responses in caecal and ileal organoids derived from chicken

Chicken infection with Salmonella Typhimurium is an important source of foodborne human diseases. Salmonella colonizes the avian intestinal tract and more particularly the caecum, without causing symptoms. This thus poses a challenge for the prevention of foodborne transmission. Until now, studies on the interaction of Salmonella with the avian gut intestine have been limited by the absence of in vitro intestinal culture models. Here, we established intestinal crypt-derived chicken organoids to better decipher the impact of Salmonella intracellular replication on avian intestinal epithelium. Using a 3D organoid model, we observed a significantly higher replication rate of the intracellular bacteria in caecal organoids than in ileal organoids. Our model thus recreates intracellular environment, allowing Salmonella replication of avian epithelium according to the intestinal segment. Moreover, an inhibition of the cellular proliferation was observed in infected ileal and caecal organoids compared to uninfected organoids. This appears with a higher effect in ileal organoids, as well as a higher cytokine and signaling molecule response in infected ileal organoids at 3 h post-infection (hpi) than in caecal organoids that could explain the lower replication rate of Salmonella observed later at 24 hpi. To conclude, this study demonstrates that the 3D organoid is a model allowing to decipher the intracellular impact of Salmonella on the intestinal epithelium cell response and illustrates the importance of the gut segment used to purify stem cells and derive organoids to specifically study epithelial cell -Salmonella interaction.

Evolutionary diversification of defensins and cathelicidins in birds and primates

Divergent evolution for more than 310 million years has resulted in an avian immune system that is complex and more compact than that of primates, sharing much of its structure and functions. Not surprisingly, well conserved ancient host defense molecules, such as defensins and cathelicidins, have diversified over time. In this review, we describe how evolution influenced the host defense peptides repertoire, its distribution, and the relationship between structure and biological functions. Marked features of primate and avian HDPs are linked to species-specific characteristics, biological requirements, and environmental challenge.

Host Defense Peptides in Nutrition and Diseases: A Contributor of Immunology Modulation

Host defense peptides (HDPs) are primary components of the innate immune system with diverse biological functions, such as antibacterial ability and immunomodulatory function. HDPs are produced and released by immune and epithelial cells against microbial invasion, which are widely distributed in humans, animals, plants, and microbes. Notably, there are great differences in endogenous HDP distribution and expression in humans and animals. Moreover, HDP expression could be regulated by exogenous substances, such as nutrients, and different physiological statuses in health and disease. In this review, we systematically assessed the regulation of expression and mechanism of endogenous HDPs from nutrition and disease perspectives, providing a basis to identify the specificity and regularity of HDP expression. Furthermore, the regulation mechanism of HDP expression was summarized systematically, and the differences in the regulation between nutrients and diseases were explored. From this review, we provide novel ideas targeted the immune regulation of HDPs for protecting host health in nutrition and practical and effective new ideas using the immune regulation theory for further research on protecting host health from pathogenic infection and excessive immunity diseases under the global challenge of the antibiotic-abuse-induced series of problems, including food security and microbial resistance.

In ovo Feeding as a Tool for Improving Performance and Gut Health of Poultry: A Review

Early growth and development of the gastrointestinal tract are of critical importance to enhance nutrients' utilization and optimize the growth of poultry. In the current production system, chicks do not have access to feed for about 48-72 h during transportation between hatchery and production farms. This lag time affects early nutrient intake, natural exposure to the microbiome, and the initiation of beneficial stimulation of the immune system of chicks. In ovo feeding can provide early nutrients and additives to embryos, stimulate gut microflora, and mitigate the adverse effects of starvation during pre-and post-hatch periods. Depending on the interests, the compounds are delivered to the embryo either around day 12 or 17 to 18 of incubation and via air sac or amnion. In ovo applications of bioactive compounds like vaccines, nutrients, antibiotics, prebiotics, probiotics, synbiotics, creatine, follistatin, L-carnitine, CpG oligodeoxynucleotide, growth hormone, polyclonal antimyostatin antibody, peptide YY, and insulin-like growth factor-1 have been studied. These compounds affect hatchability, body weight at hatch, physiological functions, immune responses, gut morphology, gut microbiome, production performance, and overall health of birds. However, the route, dose, method, and time of in ovo injection and host factors can cause variation, and thereby inconsistencies in results. Studies using this method have manifested the benefits of injection of different single bioactive compounds. But for excelling in poultry production, researchers should precisely know the proper route and time of injection, optimum dose, and effective combination of different compounds. This review paper will provide an insight into current practices and available findings related to in ovo feeding on performance and health parameters of poultry, along with challenges and future perspectives of this technique.

Antimicrobial peptides as an alternative to relieve antimicrobial growth promoters in poultry

1. This review describes different classes of antimicrobial peptides (AMP) found in the gastrointestinal (GI) tract of avian species, and their antimicrobial and immunomodulatory activities. The potential benefits of synthetic AMP in poultry production are examined, in the context of the use of AMP as alternatives to antimicrobial growth promoters (AGP).2. Since the mid-1950s, antibiotic growth promoters (AGP) have been used in feed at low prophylactic doses to modulate the homoeostasis of intestinal microbiota, decreasing the risk of intestinal dysbacteriosis and the growth of pathogens within the avian gut. Over the last three decades, AGP have faced major regulatory restrictions due to concerns of generating antimicrobial resistance (AMR). It is now well documented that the rate of infectious disease outbreaks is higher in flocks that are not fed prophylactic antibiotics, resulting in a compensatory increase in antimicrobial use for therapeutic purposes.3. Endogenous natural AMP production is associated with the presence of microbiota and their interaction with the intestinal epithelial and lamina propria lymphoid cells. Their antimicrobial activity shapes the beneficial microbiota population and controls intestinal pathogens such Clostridium and Salmonella spp., and stimulates the development and maturation of the local immune system.4. Similar to AGP, AMP can establish a well-balanced gut beneficial microbiota for adequate immune-competence, animal health and high growth performance parameters such as feed intake, daily weight, feed conversion and accumulated mortality.5. Antimicrobial proteins and peptides constitute an essential part of the innate immune system of all organisms and protect the host from invading pathogenic bacteria, viruses, fungi, and parasites by interacting with the negatively charged pathogen membranes.

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.

Effects of Probiotics Lactobacillus reuteri and Clostridium butyricum on the Expression of Toll-like Receptors, Pro- and Anti-inflammatory Cytokines, and Antimicrobial Peptides in Broiler Chick Intestine

The aim of this study was to determine the effects of live probiotics Lactobacillus reuteri (LR) and Clostridium butyricum (CB) on the expression of genes of innate immune system in broiler chick ileum and cecum. Chicks were administered 500 µl water with or without LR or CB, daily from day 1 to 6 after hatching. The ileum and cecum were collected on day 7 for analysis of gene expression of Toll-like receptors (TLRs), pro- and anti-inflammatory cytokines, and antimicrobial peptides (AMPs) using real-time PCR. The expression of TLR2-1 was upregulated by CB in the ileum and that of TLR5 was upregulated by both LR and CB. Expression of IL-1β and TGFβ2 in the ileum and of TGFβ3 and TGFβ4 in the cecum was upregulated by both LR and CB. The gene expressions of avian β-defensin (AvBD) 1 and cathelicidin (CATH) 3 were upregulated by CB and that of AvBD4 was upregulated by LR in the cecum. However, the expression of CATH2 in the ileum was downregulated by LR. These results suggest that probiotic LR and CB treatments affect a part of the innate defense system in the ileum and cecum by modulating the expression of innate immune molecules including TLRs, pro- and anti-inflammatory cytokines, and AMPs.

Development of innate immunity in chicken embryos and newly hatched chicks: a disease control perspective

Newly hatched chickens are confronted by a wide array of pathogenic microbes because their adaptive immune defences have limited capabilities to control these pathogens. In such circumstances, and within this age group, innate responses provide a degree of protection. Moreover, as the adaptive immune system is relatively naïve to foreign antigens, synergy with innate defences is critical. This review presents knowledge on the ontogeny of innate immunity in chickens pre-hatch and early post-hatch and provides insights into possible interventions to modulate innate responses early in the life of the bird. As in other vertebrate species, the chicken innate immune system which include cellular mediators, cytokine and chemokine repertoires and molecules involved in antigen detection, develop early in life. Comparison of innate immune systems in newly hatched chickens and mature birds has revealed differences in magnitude and quality, but responses in younger chickens can be boosted using innate immune system modulators. Functional expression of pattern recognition receptors and several defence molecules by innate immune system cells of embryos and newly hatched chicks suggests that innate responses can be modulated at this stage of development to combat pathogens. Improved understanding of innate immune system ontogeny and functionality in chickens is critical for the implementation of sound and safe interventions to provide long-term protection against pathogens. Next-generation tools for studying genetic and epigenetic regulation of genes, functional metagenomics and gene knockouts can be used in the future to explore and dissect the contributions of signalling pathways of innate immunity and to devise more efficacious disease control strategies.

Analysis of the Progeny of Sibling Matings Reveals Regulatory Variation Impacting the Transcriptome of Immune Cells in Commercial Chickens

There is increasing recognition that the underlying genetic variation contributing to complex traits influences transcriptional regulation and can be detected at a population level as expression quantitative trait loci. At the level of an individual, allelic variation in transcriptional regulation of individual genes can be detected by measuring allele-specific expression in RNAseq data. We reasoned that extreme variants in gene expression could be identified by analysis of inbred progeny with shared grandparents. Commercial chickens have been intensively selected for production traits. Selection is associated with large blocks of linkage disequilibrium with considerable potential for co-selection of closely linked "hitch-hiker alleles" affecting traits unrelated to the feature being selected, such as immune function, with potential impact on the productivity and welfare of the animals. To test this hypothesis that there is extreme allelic variation in immune-associated genes we sequenced a founder population of commercial broiler and layer birds. These birds clearly segregated genetically based upon breed type. Each genome contained numerous candidate null mutations, protein-coding variants predicted to be deleterious and extensive non-coding polymorphism. We mated selected broiler-layer pairs then generated cohorts of F2 birds by sibling mating of the F1 generation. Despite the predicted prevalence of deleterious coding variation in the genomic sequence of the founders, clear detrimental impacts of inbreeding on survival and post-hatch development were detected in only one F2 sibship of 15. There was no effect on circulating leukocyte populations in hatchlings. In selected F2 sibships we performed RNAseq analysis of the spleen and isolated bone marrow-derived macrophages (with and without lipopolysaccharide stimulation). The results confirm the predicted emergence of very large differences in expression of individual genes and sets of genes. Network analysis of the results identified clusters of co-expressed genes that vary between individuals and suggested the existence of trans-acting variation in the expression in macrophages of the interferon response factor family that distinguishes the parental broiler and layer birds and influences the global response to lipopolysaccharide. This study shows that the impact of inbreeding on immune cell gene expression can be substantial at the transcriptional level, and potentially opens a route to accelerate selection using specific alleles known to be associated with desirable expression levels.

Cellular Composition and Differentiation Signaling in Chicken Small Intestinal Epithelium

The small intestine plays an important role for animals to digest and absorb nutrients. The epithelial lining of the intestine develops from the embryonic endoderm of the embryo. The mature intestinal epithelium is composed of different types of functional epithelial cells that are derived from stem cells, which are located in the crypts. Chickens have been widely used as an animal model for researching vertebrate embryonic development. However, little is known about the molecular basis of development and differentiation within the chicken small intestinal epithelium. This review introduces processes of development and growth in the chicken gut, and compares the cellular characteristics and signaling pathways between chicken and mammals, including Notch and Wnt signaling that control the differentiation in the small intestinal epithelium. There is evidence that the chicken intestinal epithelium has a distinct cellular architecture and proliferation zone compared to mammals. The establishment of an in vitro cell culture model for chickens will provide a novel tool to explore molecular regulation of the chicken intestinal development and differentiation.

The Komodo dragon (Varanus komodoensis) genome and identification of innate immunity genes and clusters

Background

We report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons. They appear to be unaffected, suggesting that dragons have robust defenses against infection. While little information is available regarding the molecular biology of reptile immunity, it is believed that innate immunity, which employs antimicrobial host-defense peptides including defensins and cathelicidins, plays a more prominent role in reptile immunity than it does in mammals. .

Results

High molecular weight genomic DNA was extracted from Komodo dragon blood cells. Subsequent sequencing and assembly of the genome from the collected DNA yielded a genome size of 1.6 Gb with 45x coverage, and the identification of 17,213 predicted genes. Through further analyses of the genome, we identified genes and gene-clusters corresponding to antimicrobial host-defense peptide genes. Multiple β-defensin-related gene clusters were identified, as well as a cluster of potential Komodo dragon ovodefensin genes located in close proximity to a cluster of Komodo dragon β-defensin genes. In addition to these defensins, multiple cathelicidin-like genes were also identified in the genome. Overall, 66 β-defensin genes, six ovodefensin genes and three cathelicidin genes were identified in the Komodo dragon genome.

Conclusions

Genes with important roles in host-defense and innate immunity were identified in this newly sequenced Komodo dragon genome, suggesting that these organisms have a robust innate immune system. Specifically, multiple Komodo antimicrobial peptide genes were identified. Importantly, many of the antimicrobial peptide genes were found in gene clusters. We found that these innate immunity genes are conserved among reptiles, and the organization is similar to that seen in other avian and reptilian species. Having the genome of this important squamate will allow researchers to learn more about reptilian gene families and will be a valuable resource for researchers studying the evolution and biology of the endangered Komodo dragon.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6029-y) contains supplementary material, which is available to authorized users.

Expression of avian β-defensin mRNA in the chicken yolk sac

The chicken yolk sac (YS) plays an important role in nutrient absorption and immune function for the developing embryo. The avian β-defensins (AvBD) are cationic peptides that are important members of the innate immune system. The objective of this study was to profile AvBD mRNA expression patterns and distribution of cells expressing AvBD mRNA in the chicken YS. Expression of AvBD1, 2, 7, and 10 mRNA was low at embryonic day 7 (e7), increased to e9 through e13 and then declined to e19. Using in situ hybridization, AvBD10 mRNA was found to be expressed in endodermal epithelial cells, while AvBD1, 2, and 7 mRNA were expressed in heterophils. The developmental expression pattern and distribution of AvBD mRNA in the YS reveals the importance of these genes to protection of the developing chick embryo.

Cathelicidins PMAP-36, LL-37 and CATH-2 are similar peptides with different modes of action

Host defense peptides (HDPs) play a pivotal role in innate immunity and have, in addition to antimicrobial activity, also important immunomodulatory functions. Bacteria are less likely to develop resistance against HDPs because these peptides target and kill bacteria in multiple ways, as well as modulate the immune system. Therefore, HDPs, and derivatives thereof, are promising alternatives to traditional antibiotics. Hardly anything is known about the immunomodulatory functions of porcine cathelicidin PMAP-36. In this study, we aimed to determine both antibacterial and immunomodulatory activities of PMAP-36 comparing the properties of PMAP-36 analogs with two well-studied peptides, human LL-37 and chicken CATH-2. Transmission electron microscopy revealed different killing mechanisms of E. coli for PMAP-36, CATH-2 and LL-37. LL-37 binds LPS very weakly in contrast to PMAP-36, but it inhibits LPS activation of macrophages the strongest. The first 11 amino acids of the N-terminal side of PMAP-36 are dispensable for E. coli killing, LPS-neutralization and binding. Deletion of four additional amino acids resulted in a strong decrease in activity. The activity of full length PMAP-36 was not affected by monomerization, whereas the shorter analogs require dimerization for proper immunomodulatory activity but not for their antibacterial activity.

Synthetic CpG-ODN rapidly enriches immune compartments in neonatal chicks to induce protective immunity against bacterial infections

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) induce innate immunity against bacterial infections. Despite recent advances, how CpG-ODN alone protects against bacterial infections remained elusive. Here, we report for the first time, to our knowledge, that CpG-ODN orchestrates anti-microbial protective immunity by inducing a rapid enrichment of various immune compartments in chickens. In this study, eighteen-day-old embryonated eggs were injected with either 50 µg of CpG-ODN or saline (~n = 90 per group). In the first experiment, four days after CpG-ODN treatment, chicks were challenged subcutaneously with a virulent strain of Escherichia coli (E. coli) and mortality was monitored for 8 days. We found significant protection, and reduced clinical scores in CpG-ODN treated chicks. To gain insights into mechanisms of protection induced by CpG-ODN, first we investigated cytokine expression kinetics elicited by CpG-ODN. The spleen and lung were collected from embryos or chicks (n = 3-4 per group) at 10 time points post-CpG-ODN inoculation. Multiplex gene analysis (interleukin (IL)-1, IL-4, IL-6, IL-10, IL-18, interferon (IFN)-γ, IFN-α, and lipopolysaccharide induced tumor necrosis factor (LITAF), revealed a significantly higher expression of pro-inflammatory cytokines following CpG-ODN treatment compared to the saline controls. In our study, LITAF stands out in the cytokine profiles of spleen and lungs, underscoring its role in CpG-ODN-induced protection. The third experiment was designed to examine the effects of CpG-ODN on immune cell populations in spleen, lungs, and thymus. Flow cytometry analysis was conducted at 24, 48 and 72 hrs (thymus only collected at 72 hr) after CpG-ODN administration to examine the changes in CD4⁺ and CD8⁺ T-cell subsets, monocyte/macrophage cell populations and their expression of maturation markers (CD40 and CD86). Flow cytometry data indicated a significant enrichment of macrophages, CD4⁺ and CD8⁺ T-cell subsets in both spleen and lungs of CpG-ODN treated embryos and chicks. Macrophages in spleen and lungs showed an upregulation of CD40 but not CD86, whereas thymocytes revealed significantly high CD4 and CD8 expression. Overall, the present study has demonstrated that CpG-ODN provides protection in neonatal chicks against E. coli infection not only by eliciting cytokine responses and stimulating immune cells but also through enriching immunological niches in spleen and lungs.

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.

Visualisation and characterisation of mononuclear phagocytes in the chicken respiratory tract using CSF1R-transgenic chickens

The respiratory tract is a key organ for many avian pathogens as well as a major route for vaccination in the poultry industry. To improve immune responses after vaccination of chickens through increased uptake of vaccines and targeting to antigen presenting cells, a better understanding of the avian respiratory immune system is required. Transgenic MacReporter birds were used expressing a reporter gene (eGFP or mApple) under the control of the CSF1R promoter and enhancer in cells of the mononuclear phagocyte (MNP) lineage to visualize the ontogeny of the lymphoid tissue, macrophages and dendritic cells, in the trachea, lung and air sac of birds from embryonic day 18-63 weeks of age. Small aggregates of CSF1R-transgene+ cells start to form at the openings of the secondary bronchi at 1 week of age, indicative of the early development of the organised bronchus-associated lymphoid tissue. Immunohistochemical staining revealed subpopulations of MNPs in the lung, based on expression of CSF1R-transgene, CD11, TIM4, LAMP1, and MHC II. Specialised epithelial cells or M cells covering the bronchus-associated lymphoid tissue expressed CSF1R-transgene and type II pneumocytes expressed LAMP1 suggesting that these epithelial cells are phagocytic and transcytose antigen. Highly organised lymphoid tissue was seen in trachea from 4 weeks onwards. Throughout the air sacs at all ages, CSF1R-transgene+ cells were scattered and at later stages, CSF1R-transgene+ cells lined capillaries. These results will serve as a base for further functional characterization of macrophages and dendritic cells and their role in respiratory diseases and vaccine responses.

The potential for immunoglobulins and host defense peptides (HDPs) to reduce the use of antibiotics in animal production

Innate defense mechanisms are aimed at quickly containing and removing infectious microorganisms and involve local stromal and immune cell activation, neutrophil recruitment and activation and the induction of host defense peptides (defensins and cathelicidins), acute phase proteins and complement activation. As an alternative to antibiotics, innate immune mechanisms are highly relevant as they offer rapid general ways to, at least partially, protect against infections and enable the build-up of a sufficient adaptive immune response. This review describes two classes of promising alternatives to antibiotics based on components of the innate host defense. First we describe immunoglobulins applied to mimic the way in which they work in the newborn as locally acting broadly active defense molecules enforcing innate immunity barriers. Secondly, the potential of host defense peptides with different modes of action, used directly, induced in situ or used as vaccine adjuvants is described.

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.

Gene expression of AvBD6-10 in broiler chickens is independent of AvBD6, 9, and 10 peptide potency

The Avian β-defensin (AvBD) gene cluster contains fourteen genes; within this, two groups (AvBD6/7 and AvBD8 -10) encode charged peptides of >+5 (AvBD6/7), indicative of potent microbial killing activities, and ≤+4 (AvBD8-10), suggestive of reduced antimicrobial activities. Chicken broiler gut tissues are constantly exposed to microbes in the form of commensal bacteria. This study examined whether tissue expression patterns of AvBD6-10 reflected microbial exposure and the encoded peptides a functional antimicrobial hierarchy. Gut AvBD6-10 gene expression was observed in hatch to day 21 birds, although the AvBD8-10 profiles were eclipsed by those detected in the liver and kidney tissues. In vitro challenges of chicken CHCC-OU2 cells using the gut commensal Lactobacillus johnsonii (10⁴ CFU) did not significantly affect AvBD8-10 gene expression patterns, although upregulation (P < 0.05) of IL-Iβ gene expression was observed. Similarly, in response to Bacteriodes doreii, IL-Iβ and IL-6 gene upregulation were detected (P < 0.05), but AvBD10 gene expression remained unaffected. These data suggested that AvBD8-10 gene expression was not induced by commensal gut bacteria. Bacterial time-kill assays employing recombinant (r)AvBD6, 9 and 10 peptides (0.5μM - 12μM), indicated an antimicrobial hierarchy, linked to charge, of AvBD6 > AvBD9 > AvBD10 against Escherichia coli, but AvBD10 > AvBD9 > AvBD6 using Enterococcus faecalis. rAvBD10, selected due to its reduced cationic charge was, using CHCC-OU2 cells, investigated for cell proliferation and wound healing properties, but none were observed. These data suggest that in healthy broiler chicken tissues AvBD6/7 and AvBD8-10 gene expression profiles are independent of the in vitro antimicrobial hierarchies of the encoded AvBD6, 9 and 10 peptides.

Changes in the Expression of Avian β-defensins (AvBDs) and Proinflammatory Cytokines and Localization of AvBD2 in the Intestine of Broiler Embryos and Chicks during Growth

The aim of this study was to determine the changes in the expression of avian β-defensins (AvBDs) and proinflammatory cytokines and localization of AvBD2 in the intestine of broiler embryos and chicks during growth. The ileum and cecum of embryonic day 19 (ED19) and of day-old (D0) and 7-day-old (D7) chicks were collected. Gene expression levels of 10 AvBDs (AvBD1-8, 10, and 12) and proinflammatory cytokines (IL-1β, -6, and -8) were analyzed using real-time PCR, and the localization of AvBD2 was examined by immunohistochemistry. Gene expression levels of AvBD1, 2, 6, and 7 in the ileum and of AvBD1 and 4 in the cecum were higher on ED19 than on D7. The expression of AvBD10 in the ileum was higher on D0 than on ED19, whereas the expression levels of AvBD8 and 10 in the cecum were higher on D0 than on ED19, and that of AvBD10 decreased on D7. The expression levels of IL-1β, -6, and -8 in the ileum were higher on D7 than on ED19. The expression levels of IL-1β, -6, and -8 in the cecum were higher on D0 than on ED19, and that of IL-1β and -6 declined on D7. AvBD2-positive cells were localized in the lamina propria beneath epithelial cells of villi and crypts. The number of positive cells in the cecum mucosa was greater on D0 than on ED19 and D7. In conclusion, we suggest that AvBDs are expressed in the ileum and cecum of embryos and chicks at high levels before or just after hatching and decrease by D7. The expression of proinflammatory cytokines in the ileum increases with growth until D7, but is the highest in the cecum around hatching. These AvBDs and proinflammatory cytokines may play roles in host defense in the intestinal mucosa of embryos and neonatal chicks.