Differential modulation of beta-defensin gene expression by Salmonella Enteritidis in intestinal epithelial cells from resistant and susceptible chicken inbred lines

Probiotics/prebiotics effect on chicken gut microbiota and immunity in relation to heat-stress and climate-change mitigation

Heat stress is a serious hazard that threatens world poultry production. The avian gut microbiome plays a critical role in improving nutrient utilization, competing with pathogens, stimulating an immune response, and reducing inflammatory reactions. Hence, the gut microbiome has a positive impact on the host's health which appears in the shape of improved body weight, feed conversion rate, and increased birds' productivity (meat or eggs). Accordingly, this review shed light on the chicken gut microbiome, its correlation with the immunity of chicken, and how this affects the general health condition of the bird as well as, the role of prebiotics and probiotics in improving the gut health and increasing birds' productivity, especially under climate change and heat stress condition. The review aims to focus on the significance of maintaining healthy chickens in order to increase the production of poultry meat to satisfy human needs. A robust microbiota and a well-functioning immune system synergistically contribute to the optimal health and productivity of chickens.

A novel avian intestinal epithelial cell line: its characterization and exploration as an in vitro infection culture model for Eimeria species

BACKGROUND

The gastrointestinal epithelium plays an important role in directing recognition by the immune system, and epithelial cells provide the host's front line of defense against microorganisms. However, it is difficult to cultivate avian intestinal epithelial cells in vitro for lengthy periods, and the lack of available cell lines limits the research on avian intestinal diseases and nutritional regulation. Chicken coccidiosis is a serious intestinal disease that causes significant economic losses in the poultry industry. In vitro, some cell line models are beneficial for the development of Eimeria species; however, only partial reproduction can be achieved. Therefore, we sought to develop a new model with both the natural host and epithelial cell phenotypes.

METHODS

In this study, we use the SV40 large T antigen (SV40T) gene to generate an immortalized cell line. Single-cell screening technology was used to sort positive cell clusters with epithelial characteristics for passage. Polymerase chain reaction (PCR) identification, immunofluorescence detection, and bulk RNA sequencing analysis and validation were used to check the expression of epithelial cell markers and characterize the avian intestinal epithelial cell line (AIEC). AIECs were infected with sporozoites, and their ability to support the in vitro endogenous development of Eimeria tenella was assessed.

RESULTS

This novel AIEC consistently expressed intestinal epithelial markers. Transcriptome assays revealed the upregulation of genes associated with proliferation and downregulation of genes associated with apoptosis. We sought to compare E. tenella infection between an existing fibroblast cell line (DF-1) and several passages of AIEC and found that the invasion efficiency was significantly increased relative to that of chicken fibroblast cell lines.

CONCLUSIONS

An AIEC will serve as a better in vitro research model, especially in the study of Eimeria species development and the mechanisms of parasite-host interactions. Using AIEC helps us understand the involvement of intestinal epithelial cells in the digestive tract and the immune defense of the chickens, which will contribute to the epithelial innate defense against microbial infection in the gastrointestinal tract.

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.

Novel chicken two-dimensional intestinal model comprising all key epithelial cell types and a mesenchymal sub-layer

The intestinal epithelium plays a variety of roles including providing an effective physical barrier and innate immune protection against infection. Two-dimensional models of the intestinal epithelium, 2D enteroids, are a valuable resource to investigate intestinal cell biology and innate immune functions and are suitable for high throughput studies of paracellular transport and epithelial integrity. We have developed a chicken 2D enteroid model that recapitulates all major differentiated cell lineages, including enterocytes, Paneth cells, Goblet cells, enteroendocrine cells and leukocytes, and self-organises into an epithelial and mesenchymal sub-layer. Functional studies demonstrated the 2D enteroids formed a tight cell layer with minimal paracellular flux and a robust epithelial integrity, which was maintained or rescued following damage. The 2D enteroids were also able to demonstrate appropriate innate immune responses following exposure to bacterial endotoxins, from Salmonella enterica serotype Typhimurium and Bacillus subtilis. Frozen 2D enteroids cells when thawed were comparable to freshly isolated cells. The chicken 2D enteroids provide a useful ex vivo model to study intestinal cell biology and innate immune function, and have potential uses in screening of nutritional supplements, pharmaceuticals, and bioactive compounds.

Immunomodulation of Antimicrobial Peptides Expression in the Gastrointestinal Tract by Probiotics in Response to Stimulation by Salmonella minnesota Lipopolysaccharides

The aim was to determine whether probiotics-feeding can affect the expression and localization of avian beta defensins (AvBDs) and proinflammatory cytokines in response to Salmonella minnesota lipopolysaccharide (LPS) in the gastrointestinal tract. One-day-old male Chunky broiler chicks were fed with or without 0.4% probiotics for 7 days (P-group and non-P-group, respectively). Then, they were orally challenged with no LPS (0-LPS), 1 µg LPS (1-LPS), or 100 µg LPS (100-LPS) (n = 5, each), in experiment 1, and with no LPS and 1 µg LPS (n = 6, each) in experiment 2. Five hours after LPS challenge, the proventriculi and ceca were collected. A total of seven and eight AvBDs were identified in proventriculus and cecum, respectively. The density of ir-AvBD12 in the surface epithelium of proventriculus increased in the P-group in response to 1-LPS and 100-LPS stimulation. In experiment 1, the expression of two AvBDs in the proventriculus and six AvBDs in the cecum of 1-LPS chicks was higher in P-group than in the non-P-group. Results of experiment 2 showed similar tendency to experiment 1. These results suggest that probiotics-feeding may enhance the immunodefense system mediated by AvBDs but not by cytokine, against infection by Gram-negative bacteria.

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.

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.

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.

Dose-dependent differential resistance of inbred chicken lines to avian pathogenic Escherichia coli challenge

Avian pathogenic E. coli (APEC) cause severe respiratory and systemic disease. To address the genetic and immunological basis of resistance, inbred chicken lines were used to establish a model of differential resistance to APEC, using strain O1 of serotype O1:K1:H7. Inbred lines 7₂, 15I and C.B12 and the outbred line Novogen Brown were inoculated via the airsac with a high dose (10⁷ colony-forming units, CFU) or low dose (10⁵ CFU) of APEC O1. Clinical signs, colibacillosis lesion score and bacterial colonization of tissues after high dose challenge were significantly higher in line 15I and C.B12 birds. The majority of the 15I and C.B12 birds succumbed to the infection by 14 h post-infection, whilst none of the line 7₂ and the Novogen Brown birds developed clinical signs. No difference was observed after low dose challenge. In a repeat study, inbred lines 7₂ and 15I were inoculated with low, intermediate or high doses of APEC O1 ranging from 10⁵ to 10⁷ CFU. The colonization of lung was highest in line 15I after high dose challenge and birds developed clinical signs; however, colonization of blood and spleen, clinical signs and lesion score were not different between lines. No difference was observed after intermediate or low dose challenge. Ex vivo, the phagocytic and bactericidal activity of lung leukocytes from line 7₂ and 15I birds did not differ. Our data suggest that although differential resistance of inbred lines 7₂, 15I and C.B12 to APEC O1 challenge is apparent, it is dependent on the infectious dose. Research Highlights Lines 15I and C.B12 are more susceptible than line 7₂ to a high dose of APEC O1. Differential resistance is dose-dependent in lines 15I and 7₂. Phagocytic and bactericidal activity is similar and dose independent.

Transcripts of antibacterial peptides in chicken erythrocytes infected with Marek's disease virus

BACKGROUND

Chicken erythrocytes are involved in immunity through binding of toll-like receptors (TLRs) with their ligands to activate downstream signaling and lead to cytokine production in erythrocytes. Some avian β-defensins (AvBDs) are constitutively expressed in tissues and some others can be induced by various bacteria and viruses. However, the expression of AvBDs in erythrocytes has not yet been studied extensively.

RESULTS

The transcripts of eight AvBDs (AvBD1 to AvBD7, and AvBD9) and liver-expressed antimicrobial peptide-2 (LEAP-2) were found in normal chicken erythrocytes. The expression levels of AvBD2, 4 and 7 were significantly increased (P < 0.01), whereas the levels of AvBD1, 6 and 9 were significantly decreased (P < 0.01) after Marek's disease virus (MDV) infection. The mRNA expression level of LEAP-2 was not significantly changed after MDV infection. Highest viral nucleic acid (VNA) of MDV in the feather tips among the tested time points was found at 14 days post-infection (d.p.i.). In addition, 35 MD5-related gene segments were detected in the erythrocytes at 14 d.p.i. by transcriptome sequencing.

CONCLUSIONS

These results suggest that the AvBDs in chicken erythrocytes may participate in MDV-induced host immune responses.

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.

Expression and regulation of avian beta-defensin 8 protein in immune tissues and cell lines of chickens

Objective

Defensins are a large family of antimicrobial peptides and components of the innate immune system that invoke an immediate immune response against harmful pathogens. Defensins are classified into alpha-, beta-, and theta-defensins. Avian species only possess beta-defensins (AvBDs), and approximately 14 AvBDs (AvBD1–AvBD14) have been identified in chickens to date. Although substantial information is available on the conservation and phylogenetics, limited information is available on the expression and regulation of AvBD8 in chicken immune tissues and cells.

Methods

We examined AvBD8 protein expression in immune tissues of White Leghorn chickens (WL) by immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (RT-qPCR). In addition, we examined AvBD8 expression in chicken T-, B-, macrophage-, and fibroblast-cell lines and its regulation in these cells after lipopolysaccharide (LPS) treatment by immunocytochemistry and RT-qPCR.

Results

Our results showed that chicken AvBD8 protein was strongly expressed in the WL intestine and in macrophages. AvBD8 gene expression was highly upregulated in macrophages treated with different LPS concentrations compared with that in T- and B-cell lines in a time-independent manner. Moreover, chicken AvBD8 strongly interacted with other AvBDs and with other antimicrobial peptides as determined by bioinformatics.

Conclusion

Our study provides the expression and regulation of chicken AvBD8 protein in immune tissues and cells, which play crucial role in the innate immunity.

The Unusual Resistance of Avian Defensin AvBD7 to Proteolytic Enzymes Preserves Its Antibacterial Activity

Defensins are frontline peptides of mucosal immunity in the animal kingdom, including birds. Their resistance to proteolysis and their ensuing ability to maintain antimicrobial potential remains questionable and was therefore investigated. We have shown by bottom-up mass spectrometry analysis of protein extracts that both avian beta-defensins AvBD2 and AvBD7 were ubiquitously distributed along the chicken gut. Cathepsin B was found by immunoblotting in jejunum, ileum, caecum, and caecal tonsils, while cathepsins K, L, and S were merely identified in caecal tonsils. Hydrolysis product of AvBD2 and AvBD7 incubated with a panel of proteases was analysed by RP-HPLC, mass spectrometry and antimicrobial assays. AvBD2 and AvBD7 were resistant to serine proteases and to cathepsins D and H. Conversely cysteine cathepsins B, K, L, and S degraded AvBD2 and abolished its antibacterial activity. Only cathepsin K cleaved AvBD7 and released Ile4-AvBD7, a N-terminal truncated natural peptidoform of AvBD7 that displayed antibacterial activity. Besides the 3-stranded antiparallel beta-sheet typical of beta-defensins, structural analysis of AvBD7 by two-dimensional NMR spectroscopy highlighted the restricted accessibility of the C-terminus embedded by the N-terminal region and gave a formal evidence of a salt bridge (Asp9-Arg12) that could account for proteolysis resistance. The differential susceptibility of avian defensins to proteolysis opens intriguing questions about a distinctive role in the mucosal immunity against pathogen invasion.

Evolution of the avian β-defensin and cathelicidin genes

Background

β-defensins and cathelicidins are two families of cationic antimicrobial peptides (AMPs) with a broad range of antimicrobial activities that are key components of the innate immune system. Due to their important roles in host defense against rapidly evolving pathogens, the two gene families provide an ideal system for studying adaptive gene evolution. In this study we performed phylogenetic and selection analyses on β-defensins and cathelicidins from 53 avian species representing 32 orders to examine the evolutionary dynamics of these peptides in birds.

Results and conclusions

Avian β-defensins are found in a gene cluster consisting of 13 subfamiles. Nine of these are conserved as one to one orthologs in all birds, while the others (AvBD1, AvBD3, AvBD7 and AvBD14) are more subject to gene duplication or pseudogenisation events in specific avian lineages. Avian cathelicidins are found in a gene cluster consisting of three subfamilies with species-specific duplications and gene loss. Evidence suggested that the propiece and mature peptide domains of avian cathelicidins are possibly co-evolving in such a way that the cationicity of the mature peptide is partially neutralised by the negative charge of the propiece prior to peptide secretion (further evidence obtained by repeating the analyses on primate cathelicidins). Negative selection (overall mean d_N < d_S) was detected in most of the gene domains examined, conserving certain amino acid residues that may be functionally crucial for the avian β-defensins and cathelicidins, while episodic positive selection was also involved in driving the diversification of specific codon sites of certain AMPs in avian evolutionary history. These findings have greatly improved our understanding of the molecular evolution of avian AMPs and will be useful to understand their role in the avian innate immune response. Additionally, the large dataset of β-defensin and cathelicidin peptides may also provide a valuable resource for translational research and development of novel antimicrobial agents in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0465-3) contains supplementary material, which is available to authorized users.

Intestinal microbiome of poultry and its interaction with host and diet

The gastrointestinal (GI) tract of poultry is densely populated with microorganisms which closely and intensively interact with the host and ingested feed. The gut microbiome benefits the host by providing nutrients from otherwise poorly utilized dietary substrates and modulating the development and function of the digestive and immune system. In return, the host provides a permissive habitat and nutrients for bacterial colonization and growth. Gut microbiome can be affected by diet, and different dietary interventions are used by poultry producers to enhance bird growth and reduce risk of enteric infection by pathogens. There also exist extensive interactions among members of the gut microbiome. A comprehensive understanding of these interactions will help develop new dietary or managerial interventions that can enhance bird growth, maximize host feed utilization, and protect birds from enteric diseases caused by pathogenic bacteria.

Avian host defense peptides

Host defense peptides (HDPs) are important effector molecules of the innate immune system of vertebrates. These antimicrobial peptides are also present in invertebrates, plants and fungi. HDPs display broad-spectrum antimicrobial activities and fulfill an important role in the first line of defense of many organisms. It is becoming increasingly clear that in the animal kingdom the functions of HDPs are not confined to direct antimicrobial actions. Research in mammals has indicated that HDPs have many immunomodulatory functions and are also involved in other physiological processes ranging from development to wound healing. During the past five years our knowledge about avian HDPs has increased considerably. This review addresses our current knowledge on the evolution, regulation and biological functions of HDPs of birds.

Host-Mycobacterium avium subsp. paratuberculosis interactome reveals a novel iron assimilation mechanism linked to nitric oxide stress during early infection

BACKGROUND

The initial interaction between host cell and pathogen sets the stage for the ensuing infection and ultimately determine the course of disease. However, there is limited knowledge of the transcripts utilized by host and pathogen and how they may impact one another during this critical step. The purpose of this study was to create a host-Mycobacterium avium subsp. paratuberculosis (MAP) interactome for early infection in an epithelium-macrophage co-culture system using RNA-seq.

RESULTS

Establishment of the host-MAP interactome revealed a novel iron assimilation system for carboxymycobactin. Iron assimilation is linked to nitric oxide synthase-2 production by the host and subsequent nitric oxide buildup. Iron limitation as well as nitric oxide is a prompt for MAP to enter into an iron sequestration program. This new iron sequestration program provides an explanation for mycobactin independence in some MAP strains grown in vitro as well as during infection within the host cell. Utilization of such a pathway is likely to aid MAP establishment and long-term survival within the host.

CONCLUSIONS

The host-MAP interactome identified a number of metabolic, DNA repair and virulence genes worthy for consideration as novel drug targets as well as future pathogenesis studies. Reported interactome data may also be utilized to conduct focused, hypothesis-driven research. Co-culture of uninfected bovine epithelial cells (MAC-T) and primary bovine macrophages creates a tolerant genotype as demonstrated by downregulation of inflammatory pathways. This co-culture system may serve as a model to investigate other bovine enteric pathogens.

Sequence polymorphism and expression variability of Crassostrea gigas immune related genes discriminate two oyster lines contrasted in term of resistance to summer mortalities

Summer mortalities of Crassostreagigas are a major concern in oyster aquaculture. They are the result of a complex interaction between the host, pathogens and environmental factors. Oyster genetics have been identified as an essential determinant of oyster susceptibility to summer mortalities. As the capability of oysters to circumvent diseases depends in part on their immune defenses, we aimed to analyze the gene expression and sequence polymorphism of 42 immune related genes in two oyster lines selected for their “High” (H) and “Low” (L) survival to summer mortalities. Results showed that the variability of gene expression and the sequence polymorphism acting on particular genes could enable the discrimination between H and L oyster lines. Besides, a higher sequence polymorphism was observed on the L line affecting 11 of the 42 analyzed genes. By analyzing gene expression, sequence polymorphism and gene copy number of two antimicrobial peptide families (Cg-Defs and Cg-Prp), and an antimicrobial protein (Cg-BPI) on individual oysters, we showed that gene expression and/or sequence polymorphism could also discriminate H and L oyster lines. Finally, we observed a positive correlation between the gene expression and the gene copy number of antimicrobials and that sequence polymorphism could be encoded in the genome. Overall, this study gives new insights in the relationship between oyster immunity and divergent phenotypes, and discusses the potential implication of antimicrobial diversity in oyster survival to summer mortalities.

Infection with Mycobacterium avium subsp. paratuberculosis results in rapid interleukin-1β release and macrophage transepithelial migration

Pathogen processing by the intestinal epithelium involves a dynamic innate immune response initiated by pathogen-epithelial cell cross talk. Interactions between epithelium and Mycobacterium avium subsp. paratuberculosis have not been intensively studied, and it is currently unknown how the bacterium-epithelial cell cross talk contributes to the course of infection. We hypothesized that M. avium subsp. paratuberculosis harnesses host responses to recruit macrophages to the site of infection to ensure its survival and dissemination. We investigated macrophage recruitment in response to M. avium subsp. paratuberculosis using a MAC-T bovine macrophage coculture system. We show that M. avium subsp. paratuberculosis infection led to phagosome acidification within bovine epithelial (MAC-T) cells as early as 10 min, which resulted in upregulation of interleukin-1β (IL-1β) at transcript and protein levels. Within 10 min of infection, macrophages were recruited to the apical side of MAC-T cells. Inhibition of phagosome acidification or IL-1β abrogated this response, while MCP-1/CCL-2 blocking had no effect. IL-1β processing was dependent upon Ca(2+) uptake from the extracellular medium and intracellular Ca(2+) oscillations, as determined by EGTA and BAPTA-AM [1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester)] treatments. Thus, M. avium subsp. paratuberculosis is an opportunist that takes advantage of extracellular Ca(2+)-dependent phagosome acidification and IL-1β processing in order to efficiently transverse the epithelium and enter its niche--the macrophage.

Hatching egg and newly hatched chick yolk sac total IgY content at 3 broiler breeder flock ages

During the first week of the posthatching period, before the immune system is mature enough to produce its own B lymphocytes, a chick's humoral immunity depends on maternal antibodies (IgY) received from the egg yolk. During incubation and after hatching, the yolk sac (YS) membrane transfers nutrients (including IgY) from the egg yolk to the developing embryo or newly hatched chick. The objective of this study was to determine the effects of breeder flock age on the total IgY content of egg yolks and chick YS from a commercial broiler breeder strain. Hatching eggs from the same broiler breeder flock were collected at 32, 40, and 55 wk of age. One group of eggs per flock age was used to determine the egg yolk total IgY content. Another group of eggs was incubated for 21.5 d, and upon hatching, the YS of newly hatched chicks were collected to determine the total IgY content. Egg and egg yolk weight increased with flock age, but YS weights did not reflect egg yolk weight. The total IgY content per gram of egg yolk increased with flock age; this fact plus the observed yolk weight increase with flock age notably increased the total IgY contained in yolks of eggs laid by 55-wk-old breeders. However, chicks hatching from 55-wk-old breeders had less IgY per gram of YS than chicks from 32- and 40-wk-old breeders. Whether there are differences in the rates of YS absorption between chicks of different breeder ages is unknown. This research provided total IgY values for broiler breeder egg yolk and chick YS of a commonly used meat-type chicken strain. Differences in egg yolk and YS total IgY contents due to flock age in this type of bird had not been previously reported. Research on the physiological consequences of YS absorption rates in chicks from different breeder ages is advised.

Initial insights into structure-activity relationships of avian defensins

Numerous β-defensins have been identified in birds, and the potential use of these peptides as alternatives to antibiotics has been proposed, in particular to fight antibiotic-resistant and zoonotic bacterial species. Little is known about the mechanism of antibacterial activity of avian β-defensins, and this study was carried out to obtain initial insights into the involvement of structural features or specific residues in the antimicrobial activity of chicken AvBD2. Chicken AvBD2 and its enantiomeric counterpart were chemically synthesized. Peptide elongation and oxidative folding were both optimized. The similar antimicrobial activity measured for both L- and D-proteins clearly indicates that there is no chiral partner. Therefore, the bacterial membrane is in all likelihood the primary target. Moreover, this work indicates that the three-dimensional fold is required for an optimal antimicrobial activity, in particular for gram-positive bacterial strains. The three-dimensional NMR structure of chicken AvBD2 defensin displays the structural three-stranded antiparallel β-sheet characteristic of β-defensins. The surface of the molecule does not display any amphipathic character. In light of this new structure and of the king penguin AvBD103b defensin structure, the consensus sequence of the avian β-defensin family was analyzed. Well conserved residues were highlighted, and the potential strategic role of the lysine 31 residue of AvBD2 was emphasized. The synthetic AvBD2-K31A variant displayed substantial N-terminal structural modifications and a dramatic decrease in activity. Taken together, these results demonstrate the structural as well as the functional role of the critical lysine 31 residue in antimicrobial activity.

Emergency and therapeutic vaccination--is stimulating innate immunity an option?

There is increasing evidence that activation of innate immunity, in animals and man, by live vaccines, sub-unit vaccines or synthetic or non-synthetic stimulants can induce a profound and rapidly induced resistance to pathogens, including infectious agents that are unrelated to the stimulating antigen or agent. We review the evidence for this phenomenon and present the proposition that this approach might be used to stimulate immunity during the life of the animal when susceptibility to infection is high and when normal vaccination procedures may be inappropriate.

Transcriptional profiling of cecal gene expression in probiotic- and Salmonella-challenged neonatal chicks

Probiotics are currently used to improve health and reduce enteric pathogens in poultry. However, the mechanisms by which they reduce or prevent disease are not known. Salmonella are intracellular pathogens that cause acute gastroenteritis in humans, and infections by nontyphoid species of Salmonella also can result in diarrhea, dehydration, and depression in poultry. Frequently, however, no clinical signs of infection are apparent in poultry flocks. In this study, day-of-hatch chicks were challenged with Salmonella enterica serovar Enteritidis (SE) and treated 1 h later with a poultry-derived, Lactobacillus-based probiotic culture (FloraMax-B11, Pacific Vet Group USA Inc., Fayetteville, AR). Cecae were collected 12 and 24 h posttreatment for Salmonella detection and RNA isolation for microarray analysis of gene expression. At both 12 and 24 h, SE was significantly reduced in chicks treated with the probiotic as compared with the birds challenged with only SE (P < 0.05). Microarray analysis revealed gene expression differences among all treatment groups. At 12 h, 170 genes were expressed at significantly different levels (P < 0.05), with a minimum difference in expression of 1.2-fold. At 24 h, the number of differentially regulated genes with a minimum 1.2-fold change was 201. Pathway analysis revealed that at both time points, genes associated with the nuclear factor kappa B complex, as well as genes involved in apoptosis, were significantly regulated. Based on this analysis, probiotic-induced differential regulation of the genes growth arrest-specific 2 (GAS2) and cysteine-rich, angiogenic inducer, 61 (CYR61) may result in increased apoptosis in the cecae of chicks. Because Salmonella is an intracellular pathogen, we suggest that increased apoptosis may be a mechanism by which the probiotic culture reduces Salmonella infection.

Expression of Toll-like receptors and avian β-defensins and their changes in response to bacterial components in chicken sperm

The aim of the present study was to examine whether chicken sperm express mRNA of Toll-like receptors (TLR) and avian β-defensins (avBD), and whether the expression of avBD in the sperm are regulated by the interaction of TLR-2 and TLR-4 with their corresponding ligands. Total RNA was extracted from fresh sperm and mRNA expression for TLR and avBD were examined by reverse-transcription PCR. Changes in the expression of avBD-5, avBD-9, avBD-10, and avBD-12 in the sperm after incubation with lipopolysaccharide (LPS; TLR-4 ligand) or lipopeptide (Pam3CSK4; TLR-2 ligand) were examined by real-time PCR. Among 8 types of TLR, PCR products of 7 types, namely, TLR-2 to TLR-5, TLR-7, TLR-15, and TLR-21, were identified in the sperm. The sperm also expressed cluster of differentiation 14 (CD14), which is required for the binding of LPS to TLR-4. Out of 14 avBD types reported in the chicken, a total of 9 types, namely, avBD-1, avBD-3, avBD-5, and avBD-7 to avBD-12 were expressed by the sperm, whereas avBD-5, avBD-9, avBD-10, and avBD-12 showed dense signals on the gel. Expression levels of avBD-5, avBD-9, avBD-10, and avBD-12 were significantly increased in the sperm stimulated with LPS, and that of avBD-5 was also enhanced by Pam3CSK4. These results suggest that avian sperm have the ability of the innate host defense to protect themselves from infection in the male and female genital tracts.

In vitro tests of natural allelic variation of innate immune genes (avian β-defensins) reveal functional differences in microbial inhibition

Allelic variation in immune genes might result from, and contribute to, host-pathogen evolution. Functional allelic variation in the innate immune system has received little attention. Here, we investigate whether naturally occurring allelic variation within the avian innate immune system (β-defensins) is associated with variation in antimicrobial activity. We tested differences in in vitro antimicrobial properties of the synthesized products of two alleles of avian β-defensin 7, both of which occur at high frequency in natural populations of the great tit (Parus major). Only one allele strongly inhibited the growth of the gram-positive bacterium Staphylococcus aureus, but both alleles strongly inhibited growth of the gram-negative bacterium Escherechia coli. Our data demonstrate functional allelic variation in natural defensin genes, and we discuss how differences in efficacy against microbial species might contribute to maintaining this variation.

Primary structure and antibacterial activity of chicken bone marrow-derived beta-defensins

Three biologically active beta-defensins were purified by chromatography from chicken bone marrow extract: avian beta-defensin 1 (AvBD1), AvBD2, and the newly isolated beta-defensin AvBD7. Mass spectrometry analyses showed that bone marrow-derived AvBD1, -2, and -7 peptides were present as mature peptides and revealed posttranslational modifications for AvBD1 and AvBD7 in comparison to their in silico-predicted amino acid sequences. Tandem mass spectrometry analysis using the nanoelectrospray-quadrupole time of flight method showed N-terminal glutaminyl cyclization of mature AvBD7 and C-terminal amidation of mature AvBD1 peptide, while posttranslational modifications were absent in bone marrow-derived mature AvBD2 peptide. Furthermore, mass spectrometry analysis performed on intact cells confirmed the presence of these three peptides in mature heterophils. In addition, the antibacterial activities of the three beta-defensins against a large panel of gram-positive and -negative bacteria were assessed. While the three defensins displayed similar antibacterial spectra of activity against gram-positive strains, AvBD1 and AvBD7 exhibited the strongest activity against gram-negative strains in comparison to AvBD2.