Immune gene expression in the spleen of chickens experimentally infected with Ascaridia galli

Hepatic transcriptomic analysis reveals differential regulation of metabolic and immune pathways in three strains of chickens with distinct growth rates exposed to mixed parasite infections

During parasite infections, the liver may prioritise immune-related pathways over its metabolic functions. Intestinal infections caused by Ascaridia galli and Heterakis gallinarum impair feed intake, nutrient absorption, and weight gain. Histomonas meleagridis, vectored by H. gallinarum, can also damage liver tissues, potentially impairing liver functions. This study examined the hepatic gene expression in three strains of chickens: Ross-308 (R), Lohmann Brown Plus (LB), and Lohmann Dual (LD), 2 weeks after an experimental infection (n = 18) with both A. galli and H. gallinarum or kept as uninfected control (n = 12). Furthermore, H. gallinarum infection led to a co-infection with H. meleagridis. The mixed infections reduced feed intake and the average daily weight gain (P < 0.001). The infections also increased the plasma concentrations of alpha (1)-acid glycoprotein and the antibody titre against H. meleagridis (P = 0.049), with no strain differences (P > 0.05). For host molecular response, 1887 genes were differentially expressed in LD, while 275 and 25 genes were differentially expressed in R and LB, respectively. The up-regulated genes in R and LD were mostly related to inflammatory and adaptive immune responses, while down-regulated genes in LD were involved in metabolic pathways, including gluconeogenesis. Despite performance differences among the strains, worm burdens were similar, but hepatic molecular responses differed significantly. Moreover, there was an indication of a shift in hepatic functions towards immune-related pathways. We, therefore, conclude that the liver shifts its functions from metabolic to immune-related activities in chickens when challenged with mixed parasite species.

1H-NMR based-metabolomics reveals alterations in the metabolite profiles of chickens infected with ascarids and concurrent histomonosis infection

BACKGROUND

Gut infections of chickens caused by Ascaridia galli and Heterakis gallinarum are associated with impaired host performance, particularly in high-performing genotypes. Heterakis gallinarum is also a vector of Histomonas meleagridis that is often co-involved with ascarid infections. Here, we provide a first insight into the alteration of the chicken plasma and liver metabolome as a result of gastrointestinal nematode infections with concomitant histomonosis. 1H nuclear magnetic resonance (1H-NMR) based-metabolomics coupled with a bioinformatics analysis was applied to explore the variation in the metabolite profiles of the liver (N = 105) and plasma samples from chickens (N = 108) experimentally infected with A. galli and H. gallinarum (+H. meleagridis). This was compared with uninfected chickens at different weeks post-infection (wpi 2, 4, 6, 10, 14, 18) representing different developmental stages of the worms.

RESULTS

A total of 31 and 54 metabolites were quantified in plasma and aqueous liver extracts, respectively. Statistical analysis showed no significant differences (P > 0.05) in any of the 54 identified liver metabolites between infected and uninfected hens. In contrast, 20 plasma metabolites including, amino acids, sugars, and organic acids showed significantly elevated concentrations in the infected hens (P < 0.05). Alterations of plasma metabolites occurred particularly in wpi 2, 6 and 10, covering the pre-patent period of worm infections. Plasma metabolites with the highest variation at these time points included glutamate, succinate, trimethylamine-N-oxide, myo-inositol, and acetate. Differential pathway analysis suggested that infection induced changes in (1) phenylalanine, tyrosine, and tryptophan metabolism, (2) alanine, aspartate and glutamate metabolism; and 3) arginine and proline metabolism (Pathway impact > 0.1 with FDR adjusted P-value < 0.05).

CONCLUSION

In conclusion, 1H-NMR based-metabolomics revealed significant alterations in the plasma metabolome of high performing chickens infected with gut pathogens-A. galli and H. gallinarum. The alterations suggested upregulation of key metabolic pathways mainly during the patency of infections. This approach extends our understanding of host interactions with gastrointestinal nematodes at the metabolic level.

Synergistic pathogenicity of avian orthoreovirus and Staphylococcus aureus on SPF chickens

Avian arthritis is a relatively common disease in the poultry industry, the cause of which is complex. Bacterial arthritis is often caused by infection of Staphylococcus aureus (S. aureus), whereas viral arthritis is caused by avian orthoreovirus (ARV). To investigate the infection of S. aureus and ARV in cases of avian arthritis, a total of 77 samples characterized by arthritis were collected and detection. The results showed that 68.83% of the samples were positive for ARV, and 66.23% were positive for S. aureus. Among them, the ARV mono-infection rate was 22.08%, the S. aureus mono-infection rate was 19.48%, and ARV and S. aureus co-infection rate was 45.45%, indicating that ARV and S. aureus co-infection is common in arthritis cases. To further investigate the synergistic pathogenicity of ARV and S. aureus, ARV and S. aureus were used to mono-infect, co-infect, and (or) sequential infect SPF chickens and the clinical indications, pathologic changes, ARV load, S. aureus bacterial distribution, and cytokine level of the challenged chickens were evaluated. Decreased weight gain, increased mortality, and difficulties in standing were observed in all dual-infected groups and the singular-infected group. There were significantly more severe macroscopic and microscopic hock lesions, and larger amounts of a wider range of tissue distribution of ARV antigens and S. aureus bacterial distribution in the dual-infected groups compared to the single-infected and control groups. Cytokine detection showed a significant change in IFN-γ, IL-1β, and IL-6 levels in the infected groups, especially in the ARV-S. aureus co-infection, and (or) sequential infection groups, compared with the control group. Hence, ARV and S. aureus synergistically increased mortality in infected chickens, potentiated the severity of arthritis, and increased the amount of ARV RNA in tendons.

Ascaridia galli infection in chicken: Pathobiology and immunological orchestra

BACKGROUND

Ascaridia galli is the largest gut-dwelling helminth of chickens, which confers adverse effects on meat and egg production; thus, on the animal protein supply and the economy. Both adult and immature parasites affect gut health, but larval stages play a major role in pathology.

AIMS

Here, we present immunology and pathology of A. galli in chickens.

MATERIALS AND METHODS

Literatures were surveyed through online platforms such as PubMed, Google Scholar and Researchgate.

RESULTS

The larvae cause excessive mucus production, damage to the intestinal gland, hemorrhage, anemia, diarrhea, and malnutrition. The adult worms can cause death by intestinal obstruction and intussusception. Although both cellular and humoral immunity are involved in fighting against ascariasis, the role of naturally acquired immunity is poorly defined. In cellular immunity, Th-2 cytokines (IL-4, IL-5, IL-9, and IL-13), goblet cells (mucin), gut-associated lymphoid tissues, CD8α+ intraepithelial cells, TCRγδ + T cells, and TGF-β4 form a protective band. Type 2 immunity provides protection by forming a network of endogenous damage-associated molecular patterns, chitin, and parasitic antigens. Among antibodies, IgY is the most prominent in chickens and provides temporary humoral protection. During parasitic infection, infiltration of various immune cells is evident, especially in the intestinal epithelium, lamina propria, and crypts of the duodenum and jejunum. In chickens older than 12 weeks, gradual reduction of worm burden is more successful than the younger birds. Female chickens exert a short-lived but higher level of protection by passing IgY to chicks in the form of egg yolk antibodies. In laying conditions, immunity differs between breeds. This review provides an overview of the silent but inevitable pathological changes induced by A. galli and the interaction of host immunity with the parasite.

Campylobacter jejuni infection induces dynamic expression of avian host defense peptides in vitro and in vivo

Campylobacter jejuni is considered as the leading cause of worldwide foodborne bacterial gastroenteritis. Chicken is the main reservoir of C. jejuni. Avian innate immune responses to C. jejuni remain poorly defined. Chicken host defense peptides (HDPs) are the major components of avian innate immune system. This study aimed to characterize the chicken HDPs responses to C. jejuni in vitro and in vivo. In the HD11 macrophage cell line, the HDPs, including AvBD1-2, CATH1-3, AvBD7, AvBD4, and AvBD6, were relatively higher expressed in untreated cells, whereas the expressions were suppressed after C. jejuni infection. In contrast, C. jejuni infection significantly increased the expression of the lower expressed HDPs, such as AvBD3, AvBD5, AvBD8-14, and CATHB1, in untreated cells. In the chicken challenge experiment, the immune tissues of spleens and cecal tonsils were collected from C. jejuni-infected and uninfected chickens at 1, 3 and 15 day post inoculation (DPI). In spleens of C. jejuni-infected chickens, only AvBD14 expression was elevated at 1 DPI. The majority of avian HDPs were significantly up-regulated at 3 DPI and dramatically decreased to the levels of uninfected controls at 15 DPI. In chicken cecal tonsils, only AvBD9 and AvBD14 were significantly up-regulated at 1 DPI with C. jejuni infection. Collectively, C. jejuni infection induced dynamic expression of chicken HDPs in both macrophage HD11 and immune tissues of chickens. Suppression of chicken HDPs expression may be an evasion strategy of C. jejuni for persistent colonization in chicken intestine by circumventing the chicken immune system.

Prevalence and magnitude of gastrointestinal helminth infections in cage-free laying chickens in Australia

Helminth infections have been re-emerging with the growing popularity of free-range and floor-based chicken production systems. The aim of this study was to determine the prevalence and worm burdens of intestinal helminth infection in cage-free laying chickens in Australia. In an online survey about worm prevalence, a high proportion of respondents reported the detection of Ascaridia galli (77%), followed by tapeworms (69%) and caecal worms (Heterakis gallinarum) (62%), whereas fewer respondents (23%) reported the presence of hair worms (Capillaria spp.) in their flocks. Total worm recovery from 407 laying hens on four farms found that 92.1% of hens harboured one or more helminth parasite with a prevalence of 73 to 100% across farms. Mixed infections were common with 79% of hens harbouring two or more helminth species. The prevalence of nematode species H. gallinarum, A. galli and Capillaria spp. was 87, 82 and 35% respectively. Five cestode species were found with a low individual chicken prevalence (Raillietina tetragona 4.7%, Raillietina echinobothrida 3.2%, Raillietina cesticillus 5.2%, Choanotaenia infundibulum 4.4%, and Hymenolepis cantaniana 4.4%). The hens harboured an average of 71 worms with H. gallinarum having the highest mean burden (45.5 worms/hen) followed by A. galli (22.0 worms/hen), Capillaria spp. (2.7 worms/hen) and cestodes (0.8 worms/hen). The sex ratio (female:male worms) was 1.38:1 for A. galli, and 1.77:1 for H. gallinarum. There was a strong positive correlation between A. galli female worm count and excreta egg count (EECs) (r_s = 0.94, P < 0.0001) and also between total nematode worm count and EEC (r_s = 0.82, P < 0.0001) in individual hens. When investigating intestinal excreta (n = 10) and caecal excreta (n = 10) of 16 chicken flocks the prevalence of infection with ascarid worms in intestinal and caecal excreta was 71 and 78% respectively and 27% prevalence of Capillaria spp. in intestinal excreta with mean EECs of 407, 404, and 18 eggs/g of excreta (EPG), respectively. These results suggest that most chickens kept in free-range or floor production systems are infected with one or more helminth parasite species. Heavy worm infections would likely affect the production performance and welfare of birds with adverse economic impact. Strategic or tactical anthelmintic treatment with effective anthelmintic could reduce this impact.

Development of specific monoclonal antibodies for the detection of natural chicken tumor necrosis factor-alpha

Tumor necrosis factor alpha (TNF-α) is an important proinflammatory cytokine and the only known cytokine that can directly kill tumor cells. Unlike mammalian counterparts, chicken TNF-α (chTNF-α) gene has not been identified until very recently due to its high GC content (∼70%) and long GC fragments. The biological functions of this newly-identified cytokine and its detection methods remain to be further investigated. In this study, the extracellular domain of chTNF-α was cloned into prokaryotic vector after codon optimization and recombinant chTNF-α protein was expressed. Subsequently, using recombinant chTNF-ɑ as immunogen, rabbit polyclonal antibody (pAb) and eight clones of mouse anti-chTNF-ɑ monoclonal antibodies (mAbs) were produced, respectively. Both the pAb and mAbs specifically recognized recombinant chTNF-ɑ expressed in E.coli and transfected COS-7 cells. Further mapping the antigenic region showed that all the mAbs recognized a region of amino acid residues 195-285 of chTNF-ɑ. Furthermore, an antigen-capture enzyme-linked immunosorbent assay for the detection of chTNF-ɑ was established using one mAb and the pAb. This assay showed no cross-reactivity with irrelevant Trx-fused antigens and could detect natural chTNF-ɑ expressed by mitogen-activated chicken splenocytes in a dose-dependent manner, with a detection limit of 1 ng/mL. Collectively, our results indicated that the mAbs and pAb against chTNF-α are specific and could be used for the study of the biological functions of chTNF-ɑ and the detection of chTNF-ɑ.

Infection by a helminth parasite is associated with changes in DNA methylation in the house sparrow

Parasites can exert strong selective pressures on their hosts and influence the evolution of host immunity. While several studies have examined the genetic basis for parasite resistance, the role of epigenetics in the immune response to parasites is less understood. Yet, epigenetic modifications, such as changes in DNA methylation, may allow species to respond rapidly to parasite prevalence or virulence. To test the role of DNA methylation in relation to parasite infection, we examined genome-wide DNA methylation before and during infection by a parasitic nematode, Syngamus trachea, in a natural population of house sparrows (Passer domesticus) using reduced representation bisulfite sequencing (RRBS). We found that DNA methylation levels were slightly lower in infected house sparrows, and we identified candidate genes relating to the initial immune response, activation of innate and adaptive immunity, and mucus membrane functional integrity that were differentially methylated between infected and control birds. Subsequently, we used methylation-sensitive high-resolution melting (MS-HRM) analyses to verify the relationship between methylation proportion and S. trachea infection status at two candidate genes in a larger sample dataset. We found that methylation level at NR1D1, but not CLDN22, remained related to infection status and that juvenile recruitment probability was positively related to methylation level at NR1D1. This underscores the importance of performing follow-up studies on candidate genes. Our findings demonstrate that plasticity in the immune response to parasites can be epigenetically mediated and highlight the potential for epigenetic studies in natural populations to provide further mechanistic insight into host-parasite interactions.

Infection with Ascaridia galli Does Not Significantly Alter Intestinal Microbiota and Is Cleared After Changes in the Expression of Cytokines

Because of the trend of cage-free egg production, infections with the nematode Ascaridia galli are receiving increased attention. The aim of this study was to establish a timeline for the influence of A. galli on the expression of key cytokines related to a parasitic immune response, and on the composition of the jejunal microbiota. Twenty-eight male layer-type birds were challenged at 24, 25, and 26 days of age. An additional 28 birds were kept as uninfected controls. Starting on Day 31, three birds of each group were euthanized every week until 8 wk postinfection (PI). The number of larvae isolated from the intestinal wall decreased over time, until no larvae were seen at 7 and 8 wk PI. At 5 wk PI, there was a numerical upregulation of all cytokines (TGF-β, IFN-γ, IL-4, IL-8, IL-10, IL-13) in the infected group, but this change was only statistically significant for IL-13. At this time point, larvae were expected to have developed into adults that would have shed eggs in the feces. However, no adult worms were seen and there was no egg shedding. For the microbiota analysis, there were significant differences in the alpha diversity (Faith's phylogenetic diversity) between challenge and control groups, and the beta diversity analysis showed slight differences between samples, suggesting that the age of the birds was the main reason for the separation of groups. These findings suggest that the upregulation of all cytokines evaluated in Week 5 might be the reason for resolution of the infection. Possible explanations are that a high infection dose and the fact that birds were fed with a more nutritionally dense feed might have contributed to the birds' immune system clearing the infection before the worms were able to reach maturity.

Identification of The Main Intestinal Helminths of Local Breed Chickens (Gallus Gallus Domesticus Linnaeus, 1758) Reared in Traditional Mode in The Oran Region

In order to gain a better etiological and epidemiological knowledge of the parasitic diseases of local breed chickens reared in extensive (traditional) mode, a study was carried out in the Oran region during the periods from February 2020 to April 2020. Ten chickens were examined by the helminthologic autopsy method to identify parasitic helminths in the digestive tract. Four species of helminths have been identified: two species of nematodes: Ascaridia galli and Heterakis gallinarum and two species of cestodes: Raillietina cesticillus and Raillietina tetragona. Six chickens were carriers of the parasites, for an overall level of infestation of 60 % with an average infestation of 7 parasites per chicken. The rate of parasitism and infestation varied from species to species, Heterakis gallinarum being the most dominant species. The estimate of the infestation rate by each group shows a predominance of nematodes with 62 parasites (88.5 %) compared to cestodes (8 parasites) with a significantly higher difference (P <0.05). The results obtained show that chickens of the local Gallus gallus domesticus breed in the Oran region are heavily infested by parasites including Heterakis gallinarum, the predominant species.

Global and regional prevalence of helminth infection in chickens over time: a systematic review and meta-analysis

Gastrointestinal helminth parasites are a concern for the poultry industry worldwide as they can affect the health, welfare, and production performance. A systematic review of the prevalence over time in different countries may improve our understanding of gastrointestinal helminthiasis in chickens and subsequently lead to improved poultry health. The aim of this systematic review and meta-analysis was to provide an overview of the published information regarding the epidemiology and the diagnostic approaches of chicken helminth infection. Six databases were searched for studies, and a total of 2,985 articles published between 1942 and 2019 were identified and subsequently screened for eligibility using title or abstract and full text assessment, resulting in 191 publications to be used in the study. Postmortem diagnostics (73.8%) and the flotation technique (28.8%) were commonly used to detect helminth infections with a pooled prevalence of 79.4% ranging from 4 to 100%. More than 30 helminth species in chicken populations were identified including Ascaridia galli (35.9%), Heterakis gallinarum (28.5%), Capillaria spp. (5.90%), and Raillietina spp. (19.0%) being the most prevalent. The reported prevalence of helminth infection decreased over time in developing countries while it increased in the developed world. Chicken kept in backyard and free-range systems had a markedly higher pooled prevalence of helminth infection (82.6 and 84.8%, respectively) than those housed in cage production systems (63.6%). This may indicate the need for more rigorous control and prevention measures in free-range and backyard production systems using regular deworming coupled with access to early and accurate diagnosis allowing for early intervention.

Interactions between starch source and gelatinisation degree on performance and small intestinal digestion in broiler chickens

1. A 2 × 2 factorial arrangement was used to test the hypothesis that, in pelleted diets, legume starch is digested less rapidly and to a lesser extent than cereal starch, and that increased gelatinisation through extrusion would eliminate the differences between the starch sources. In addition, the trial examined whether a lower ratio of starch to nitrogen disappearance rate (SNDR) could improve feed conversion ratio (FCR).2. At 17 d of age, male broilers were randomly distributed among four dietary treatments, consisting of either wheat or faba bean starch-rich fraction (FBS) as the sole starch source and pelleting or extrusion as processing methods. Each treatment had 10 replicate pens containing five birds each.3. Extrusion resulted in a more extensive starch gelatinisation compared to pelleting, as expected.4. No difference in weight gain at 29 d of age was observed between birds fed starch sources. However, birds fed wheat tended (P = 0.080) to have better FCR than those fed FBS, while the effect of processing methods was insignificant. Thus, there was no interaction between starch source and processing method on FCR.5. In pelleted diets, FBS had lower and slower starch digestibility compared to wheat in all intestinal segments (P < 0.05). The interaction between starch source and processing method in all intestinal segments (P < 0.001) demonstrated that FBS responded more to gelatinisation through extrusion than did wheat. Thus, differences in starch digestibility between the wheat and FBS were eliminated with extrusion.6. Feeding extruded diets significantly increased the upper jejunal expression of GLUT1, GLUT2 and SGLT1 compared to pelleted diets, which suggested that glucose absorption was less likely to be a limiting factor for starch utilisation.7. Pelleting resulted in a lower ratio (P < 0.001) of SNDR compared to extrusion (on average 1.4-fold) but did not improve FCR.

Molecular phylogenetic and in silico analysis of glyceraldeyde-3-phosphate dehydrogenase (GAPDH) gene from northern bobwhite quail (Colinus virginianus)

Many recent studies have been focused on prevalence and impact of two helminth parasites, eyeworm Oxyspirura petrowi and caecal worm Aulonocephalus pennula, in the northern bobwhite quail (Colinus virginianus). However, few studies have attempted to examine the effect of these parasites on the bobwhite immune system. This is likely due to the lack of proper reference genes for relative gene expression studies. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is a glycolytic enzyme that is often utilized as a reference gene, and in this preliminary study, we evaluated the similarity of bobwhite GAPDH to GAPDH in other avian species to evaluate its potential as a reference gene in bobwhite. GAPDH was identified in the bobwhite full genome sequence and multiple sets of PCR primers were designed to generate overlapping PCR products. These products were then sequenced and then aligned to generate the sequence for the full-length open reading frame (ORF) of bobwhite GAPDH. Utilizing this sequence, phylogenetic analyses and comparative analysis of the exon-intron pattern were conducted that revealed high similarity of GAPDH encoding sequences among bobwhite and other Galliformes. Additionally, This ORF sequence was also used to predict the encoded protein and its three-dimensional structure which like the phylogenetic analyses reveal that bobwhite GAPDH is similar to GAPDH in other Galliformes. Finally, GAPDH qPCR primers were designed, standardized, and tested with bobwhite both uninfected and infected with O. petrowi, and this preliminary test showed no statistical difference in expression of GAPDH between the two groups. These analyses are the first to investigate GAPDH in bobwhite. These efforts in phylogeny, sequence analysis, and protein structure suggest that there is > 97% conservation of GADPH among Galliformes. Furthermore, the results of these in silico tests and the preliminary qPCR indicate that GAPDH is a prospective candidate for use in gene expression analyses in bobwhite.

Hepatic transcriptome study of Taenia asiatica infection in suckling pigs

Taenia asiatica is a crucial Taenia that is prevalent in East and Southeast Asia. Domestic pigs and wild boars are essential intermediate hosts for Taenia. Cysticercus larvae are mainly parasitic in the liver of domestic pigs. The Taenia asiatica was collected from Liangmu Township, Duyun City, Guizhou Province. Twelve Yorkshire Suckling pigs of 20 days of age were randomly divided into an experimental and control group of 6 pigs each. RNA sequencing (RNA-seq) technology was used to detect the expression differences of the mRNA transcriptomes in the liver of the experimental and control group at different infection times. Differential genes were analyzed by bioinformatics and verified by Real Time-PCR(RT-PCR). On the 15th and 75th days after infection, 152 and 558 differentially expressed genes were detected in the liver of the experimental group, respectively, accounting for 0.85% and 3.12% of all identified transcribed RNA genes, respectively. Through GO and KEGG related bioinformatics analysis, it was found that these differentially expressed genes are involved in the immune response, material metabolism, fibrosis, and tissue proliferation and repair of suckling pig liver, and related to MHC antigen processing and presentation, cytochrome P450, transforming growth factor-beta (TGF-β) signaling pathway and so on. Cysticercus asiatica parasites cause significant differential gene expression in the liver of suckling pigs. Specific differentially expressed genes are involved in biological processes such as liver metabolism, immune response, and tissue repair or regeneration in suckling pigs. The immune evasion is related to the immuno-suppressive response of the intermediate host.

Highly multiplexed quantitative PCR-based platform for evaluation of chicken immune responses

To address the need for sensitive high-throughput assays to analyse avian innate and adaptive immune responses, we developed and validated a highly multiplexed qPCR 96.96 Fluidigm Dynamic Array to analyse the transcription of chicken immune-related genes. This microfluidic system permits the simultaneous analysis of expression of 96 transcripts in 96 samples in 6 nanolitre reactions and the 9,216 reactions are ready for interpretation immediately. A panel of 89 genes was selected from an RNA-seq analysis of the transcriptional response of chicken macrophages, dendritic cells and heterophils to agonists of innate immunity and from published transcriptome data. Assays were confirmed to be highly specific by amplicon sequencing and melting curve analysis and the reverse transcription and preamplification steps were optimised. The array was applied to RNA of various tissues from a commercial line of broiler chickens housed at two different levels of biosecurity. Gut-associated lymphoid tissues, bursa, spleen and peripheral blood leukocytes were isolated and transcript levels for immune-related genes were defined. The results identified blood cells as a potentially reliable indicator of immune responses among all the tissues tested with the highest number of genes significantly differentially transcribed between birds housed under varying biosecurity levels. Conventional qPCR analysis of three differentially transcribed genes confirmed the results from the multiplex qPCR array. A highly multiplexed qPCR-based platform for evaluation of chicken immune responses has been optimised and validated using samples from commercial chickens. Apart from applications in selective breeding programmes, the array could be used to analyse the complex interplay between the avian immune system and pathogens by including pathogen-specific probes, to screen vaccine responses, and as a predictive tool for immune robustness.

Avian coronavirus infection induces mannose-binding lectin production in dendritic cell precursors of chicken lymphoid organs

The aim of this immunocytochemical study was to compare mannose-binding lectin (MBL) production induced by avian coronavirus in the spleen and caecal tonsil (CT). One-day-old specific-pathogen-free (SPF) chickens were experimentally infected with six QX field isolates and the H120 vaccine strain. In the negative control birds, the spleen was MBL negative, while the CT showed scattered MBL-positive cells in close proximity and within the surface epithelium and germinal centre (GC)-like cell clusters. MBL was detectable in the ellipsoid-associated cells (EACs) and cell clusters in the periarterial lymphoid sheath (PALS) by 7 days post infection (dpi). In both organs, the MBL-positive cells occupy antigen-exposed areas, indicating that GC formation depends on resident precursors of dendritic cells. The majority of MBL-positive EACs express the CD83 antigen, providing evidence that coronavirus infection facilitated the maturation of dendritic cell precursors. Surprisingly, co-localisation of MBL and CD83 was not detectable in the CT. In the spleen (associated with circulation), the EACs producing MBL and expressing CD83 are a common precursor of both follicular (FDC) and interdigitating dendritic cells (IDC). In the CT (gut-associated lymphoid tissue, GALT) the precursors of FDC and IDC are MBL-producing cells and CD83-positive cells, respectively. In the CT the two separate precursors of lymphoid dendritic cells provide some 'autonomy' for the GALT.

Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

Fast growing broilers are less able to cope with fitness related challenges. As the allocation of metabolic resources may be traded off between performance and defence functions in parasitized hosts, we hypothesized that fast growing broilers are more sensitive to mixed nematode infections compared with slower growing genotypes under the same environmental conditions. Therefore, we compared male birds of genotypes selected for either meat production (Ross-308, R) or egg production (Lohmann Brown Plus, LB) or for both purposes (Lohmann Dual, LD), to assess their resistance and tolerance to mixed nematode infections with Ascaridia galli and Heterakis gallinarum. While infections reduced feed intake in all three genotypes, feed conversion efficiency was not affected. Infections impaired growth performance only in R birds, indicating lower tolerance in the fast growing genotype compared with slower growing LB and LD genotypes. Impaired tolerance in R birds was associated with a relative nutrient scarcity due to an infection-induced lower feed intake. Resistance to experimentally induced infections depended on host genotype as well as on the worm species involved. Overall, the A. galli burden was higher in R than LB, whereas the burden of LD was not different from that of R and LB. In contrast, the H. gallinarum burden of first generation worms was similar in the three genotypes. Susceptibility to re-infection with H. gallinarum was higher in LB than in LD, whereas very low levels of re-infection were observed in R birds. Our data collectively suggest that resistance and tolerance to mixed nematode infections are sensitive to growth rate in chickens. These differences amongst genotypes may partly be associated with a mismatch between the actual nutrient supply and genotype-specific nutrient requirements.

A mono-component microbial protease improves performance, net energy, and digestibility of amino acids and starch, and upregulates jejunal expression of genes responsible for peptide transport in broilers fed corn/wheat-based diets supplemented with xylanase and phytase

A total of 90 male Ross 308 broiler chicks were used in a digestibility and performance bioassay to explore the effect of reduction in dietary protein and digestible amino acids and inclusion of an exogenous mono-component protease on amino acid digestibility, net energy, jejunal gene expression, and bird performance. Four dietary treatments were created by the supplementation, or not, of 2 control diets with a mono-component exogenous protease. The control diets were corn/wheat/soybean meal-based and were formulated to be either nutritionally adequate or reduced in protein and amino acids (around 3%). The 2 control diets were supplemented with xylanase and phytase (2000 FYT). Treatments were therefore arranged as a 2 × 2 factorial design. The reduction in diet nutrient density had no significant effect on various experimental outcomes (including bird performance, amino acid digestibility, and net energy [NE]) that were measured with the exception of a reduction in the expression of aminopeptidase N and glucose transporter 2. However, the addition of exogenous protease resulted in an increase in weight gain and a reduction in feed conversion ratio (around 4%; P < 0.05) and an increase in the digestibility of several amino acids (P < 0.05) and starch (P = 0.06). Protease addition also resulted in an increase in both apparent metabolizable energy (AME) (+73 kcal/kg; P < 0.05) and NE (+107 kcal/kg; P < 0.05). The addition of exogenous protease to the diet also increased the jejunal expression of genes responsible for peptide transport (PepT2; P < 0.01) and starch digestion (sucrase isomaltase; P = 0.06). These results confirm the efficacy of exogenous protease in broiler diets that contain both xylanase and phytase and suggest substantial beneficial effects that extend beyond protein and amino acid nutrition. The effect of exogenous protease on energy partitioning, starch digestibility and the efficiency of nitrogen cycling is an area for further study.

The Long Pentraxin PTX3 Is of Major Importance Among Acute Phase Proteins in Chickens

The expression level of acute phase proteins (APPs) mirrors the health status of an individual. In human medicine, C-reactive protein (CRP), and other members of the pentraxin family are of significant relevance for assessing disease severity and prognosis. In chickens, however, which represent the most common livestock species around the world, no such marker has yet gained general acceptance. The aim of this study was therefore, to characterize chicken pentraxin 3 (chPTX3) and to evaluate its applicability as a general marker for inflammatory conditions. The mammalian and chicken PTX3 proteins were predicted to be similar in sequence, domain organization and polymeric structure. Nevertheless, some characteristics like certain sequence sections, which have varied during the evolution of mammals, and species-specific glycosylation patterns, suggest distinct biological functions. ChPTX3 is constitutively expressed in various tissues but, interestingly, could not be found in splenic tissue samples without stimulation. However, upon treatment with lipopolysaccharide (LPS), PTX3 expression in chicken spleens increased to 95-fold within hours. A search for PTX3 reads in various publicly available RNA-seq data sets of chicken spleen and bursa of Fabricius also showed that PTX3 expression increases within days after experimental infection with viral and bacterial pathogens. An experimental infection with avian pathogenic E.coli and qPCR analysis of spleen samples further established a challenge dose-dependent significant up-regulation of chPTX3 in subclinically infected birds of up to over 150-fold as compared to untreated controls. Our results indicate the potential of chPTX3 as an APP marker to monitor inflammatory conditions in poultry flocks.

Co-expulsion of Ascaridia galli and Heterakis gallinarum by chickens

Worm expulsion is known to occur in mammalian hosts exposed to mono-species helminth infections, whilst this phenomenon is poorly described in avian hosts. Mono-species infections, however, are rather rare under natural circumstances. Therefore, we quantified the extent and duration of worm expulsion by chickens experimentally infected with both Ascaridia galli and Heterakis gallinarum, and investigated the accompanying humoral and cell-mediated host immune responses in association with population dynamics of the worms. Results demonstrated the strong co-expulsion of the two ascarid species in three phases. The expulsion patterns were characterized by non-linear alterations separated by species-specific time thresholds. Ascaridia galli burden decreased at a daily expulsion rate (e) of 4.3 worms up to a threshold of 30.5 days p.i., followed by a much lower second expulsion rate (e = 0.46), which resulted in almost, but not entirely, complete expulsion. Heterakis gallinarum was able to induce reinfection within the experimental period (9 weeks). First generation H. gallinarum worms were expelled at a daily rate of e = 0.8 worms until 36.4 days p.i., and thereafter almost no expulsion occurred. Data on both humoral and tissue-specific cellular immune responses collectively indicated that antibody production in chickens with multispecies ascarid infections is triggered by Th2 polarisation. Local Th2 immune responses and mucin-regulating genes are associated with the regulation of worm expulsion. In conclusion, the chicken host is able to eliminate the vast majority of both A. galli and H. gallinarum in three distinct phases. Worm expulsion was strongly associated with the developmental stages of the worms, where the elimination of juvenile stages was specifically targeted. A very small percentage of worms was nevertheless able to survive, reach maturity and induce reinfection if given sufficient time to complete their life cycle. Both humoral and local immune responses were associated with worm expulsion.

Characterization of Spleen Transcriptome and Immunity Against Avian Colibacillosis After Immunization With Recombinant Attenuated Salmonella Vaccine Strains

Avian pathogenic Escherichia coli (APEC) causes extraintestinal infections in poultry. Vaccines targeting APEC in chickens have been partially successful, but many lack heterologous protection. Recombinant attenuated Salmonella vaccine (RASV) strains can induce broad immunity against Salmonella and be modified to deliver E. coli antigens. Along with vaccine characteristics, understanding the host response is crucial for developing improved vaccines. The objectives of this study were to evaluate host responses to vaccination with an RASV producing E. coli common pilus (ECP) and assess protection against APEC infection in chickens. Four-day-old White Leghorn chickens were unvaccinated or orally vaccinated and boosted 2 weeks later with RASV χ8025(pYA3337), RASV χ8025(pYA4428) carrying ecp operon genes, or a combination of χ8025(pYA3337) and χ8025(pYA4428) (Combo). To assess host responses, serum IgY and intestinal IgA antibody titers were measured, and spleen samples (n = 4/group) were collected from unvaccinated and Combo vaccinated 4-week-old chickens for RNA-seq. Vaccine protection potential against Salmonella and APEC was evaluated in vitro using bacterial inhibition assays. Five-week-old chickens were challenged via air sac with either an APEC O2 or O78 strain. E. coli was enumerated from internal organs, and gross colibacillosis lesions were scored at necropsy. RASV immunized chickens elicited anti-E. coli antibodies. The spleen transcriptome revealed that 93% (89/96) of differentially expressed genes (DEG) were more highly expressed in Combo vaccinated compared to unvaccinated chickens, with signal as the most significantly impacted category. RNA-seq analysis also revealed altered cellular and metabolic processes, response to stimulus after vaccination, and immune system processes. Six DEG including genes linked to transcription regulation, actin cytoskeleton, and signaling were highly positively correlated with antibody levels. Samples from RASV immunized chickens showed protection potential against Salmonella strains using in vitro assays, but a variable response was found for APEC strains. After APEC challenges, significant differences were not detected for bacterial loads or gross lesions scores, but χ8025(pYA3337) immunized and χ8025(pYA4428) immunized chickens had significantly fewer number of APEC-O2-positive samples than unvaccinated chickens. This study shows that RASVs can prime the immune system for APEC infection, and is a first step toward developing improved therapeutics for APEC infections in chickens.

Effect of the nematophagous fungus Pochonia chlamydosporia on soil content of ascarid eggs and infection levels in exposed hens

BACKGROUND

The nematophagous fungus Pochonia chlamydosporia can degrade ascarid (e.g. Ascaridia galli) eggs in agar and soil in vitro. However, it has not been investigated how this translates to reduced infection levels in naturally exposed chickens. We thus tested the infectivity of soil artificially contaminated with A. galli (and a few Heterakis gallinarum) eggs and treated with P. chlamydosporia. Sterilised and non-sterilised soils were used to examine any influence of natural soil biota.

METHODS

Unembryonated eggs were mixed with sterilised (S)/non-sterilised (N) soil, either treated with the fungus (F) or left as untreated controls (C) and incubated (22 °C, 35 days) to allow eggs to embryonate and fungus to grow. Egg number in soil was estimated on days 0 and 35 post-incubation. Hens were exposed to the soil (SC/SF/NC/NF) four times over 12 days by mixing soil into the feed. On day 42 post-first-exposure (p.f.e.), the hens were euthanized and parasites were recovered. Serum A. galli IgY level and ascarid eggs per gram of faeces (EPG) were examined on days -1 and 36 (IgY) or 40 p.f.e. (EPG).

RESULTS

Egg recovery in SF soil was substantially lower than in SC soil, but recovery was not significantly different between NF and NC soils. SF hens had a mean worm count of 76 whereas the other groups had means of 355-453. Early mature/mature A. galli were recovered from SF hens whereas hens in the other groups harboured mainly immature A. galli. Heterakis gallinarum counts were low overall, especially in SF. The SF post-exposure IgY response was significantly lower while EPG was significantly higher compared to the other groups.

CONCLUSIONS

Pochonia chlamydosporia was very effective in reducing ascarid egg numbers in sterilised soil and thus worm burdens in the exposed hens. However, reduced exposure of hens shifted A. galli populations toward a higher proportion of mature worms and resulted in a higher faecal egg excretion within the study period. This highlights a fundamental problem in ascarid control: if not all eggs in the farm environment are inactivated, the resulting low level infections may result in higher contamination levels with associated negative long-term consequences.

Pattern recognition receptor genes expression profiling in indigenous chickens of India and White Leghorn

Pattern recognition receptors (PRR) such as Toll-like receptors, NOD-like receptors, RIG-I helicase receptors, and C-type lectin receptors play a critical role in innate immunity as a first line of defense against invading pathogens through recognition of pathogen and/or damage-associated molecular patterns. Genetic makeup of birds is known to play a role in resistance or susceptibility to various infectious diseases. Therefore, the present study was carried out to elucidate the differential expression of PRR and some of the cytokine genes in peripheral blood mononuclear cells of indigenous chicken breeds such as Ghagus and Nicobari and an exotic chicken breed, White Leghorn (WLH). The stability of expression of reference genes in peripheral blood mononuclear cells of 3 breeds was first determined using NormFinder and BestKeeper programs. NormFinder determined B2M and G6PDH reference genes as the best combination with stability value of 0.38. Out of total 14 genes studied, expression of ten genes was found to be significantly different among 3 breeds after normalization with these reference genes. Ghagus breed showed higher level of expression of TLR1LB, TLR7, NOD1, NOD5, B-Lec, IFNβ, IL1β, and IL8 genes when compared to Nicobari breed. Further, Ghagus showed higher expression of TLR1LB, MDA5, LGP2, B-Lec, IL1β, and IL8 genes as compared to WLH breed. Higher expression of LGP2 and MDA5 genes was observed in Nicobari compared to the WLH breed while higher expression of TLR7, NOD1, NOD5, and IFNβ genes was observed in WLH as compared to Nicobari breed. No difference was observed in the expression of TLR1LA, TLR3, B-NK, and IFNα genes among 3 breeds. Study revealed significant breed effect in expression profile of PRR and some of the cytokine genes and Ghagus breed seems to have better expression profile of these genes linked to the innate immunity when compared to the WLH and Nicobar breeds.

Detection of Ascaridia galli infection in free-range laying hens

Reliable methods for detection of A. galli infection using excreta egg count (EEC) and ELISA assays to determine A. galli specific IgY levels in serum and yolk samples were compared from hens infected naturally and artificially. Artificially infected hens were used to generate samples for analysis of preferred detection methods and to generate contaminated ranges for use in the naturally acquired infection study in which Lohmann Brown hens (n = 200) at 16 weeks of age were randomly assigned to four treatments with five replicate pens. Hens of negative control (NC) ranged on a decontaminated area, hens of low infection, medium infection and positive control (PC) ranged on the areas previously contaminated by hens artificially infected with 250, 1000 and 2500 A. galli eggs/hen, respectively. Additionally, hens of PC were orally infected with 1000 A. galli eggs/hen. Anti A. galli antibody levels in hen serum (SIgY) and yolk (YIgY) were measured before range access, and 2, 7 and 12 weeks after access to the contaminated ranges. In a natural infection study, eggs were detected in the excreta of all hens 4 weeks after range access, with the exception of NC in which no eggs were detected. EEC increased to reach maximum value (2204 ± 307 eggs/g) after 11 weeks of range access and then declined at 12 weeks (905 ± 307eggs/g) (p < 0.01). While SIgY OD values were not different in hens between any groups before range access, after 2 weeks, both SIgY and YIgY gradually increased in hens of PC (1.17 ± 0.03 and 0.88 ± 0.04) and medium infection (1.07 ± 0.03 and 0.96 ± 0.04) compared to low infection (0.38 ± 0.03 and 0.29 ± 0.04) (p < 0.01) and NC. After 12 weeks, SIgY were similar in hens of PC, medium and low groups whereas YIgY was higher in hens of low infection group (p < 0.01). Sensitivity of the serum and egg yolk antibody levels assay to detect A. galli infection was 100% and 96%, respectively, whereas the pooled EEC method yielded a sensitivity of 93%. The results of this study suggest that hens naturally infected with A. galli produce both SIgY and YIgY at different levels depending on the infection intensity and duration of exposure which allows the diagnosis of prior infection or early diagnosis of current infection. Use of the practical and non-invasive method of yolk sample analysis for detecting IgY can be just as informative as using serum samples to detect A. galli infection.

Characterization of Chicken Tumor Necrosis Factor-α, a Long Missed Cytokine in Birds

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine playing critical roles in host defense and acute and chronic inflammation. It has been described in fish, amphibians, and mammals but was considered to be absent in the avian genomes. Here, we report on the identification and functional characterization of the avian ortholog. The chicken TNF-α (chTNF-α) is encoded by a highly GC-rich gene, whose product shares with its mammalian counterpart 45% homology in the extracellular part displaying the characteristic TNF homology domain. Orthologs of chTNF-α were identified in the genomes of 12 additional avian species including Palaeognathae and Neognathae, and the synteny of the closely adjacent loci with mammalian TNF-α orthologs was demonstrated in the crow (Corvus cornix) genome. In addition to chTNF-α, we obtained full sequences for homologs of TNF-α receptors 1 and 2 (TNFR1, TNFR2). chTNF-α mRNA is strongly induced by lipopolysaccharide (LPS) stimulation of monocyte derived, splenic and bone marrow macrophages, and significantly upregulated in splenic tissue in response to i.v. LPS treatment. Activation of T-lymphocytes by TCR crosslinking induces chTNF-α expression in CD4⁺ but not in CD8⁺ cells. To gain insights into its biological activity, we generated recombinant chTNF-α in eukaryotic and prokaryotic expression systems. Both, the full-length cytokine and the extracellular domain rapidly induced an NFκB-luciferase reporter in stably transfected CEC-32 reporter cells. Collectively, these data provide strong evidence for the existence of a fully functional TNF-α/TNF-α receptor system in birds thus filling a gap in our understanding of the evolution of cytokine systems.

Time- and dose-dependent development of humoral immune responses to Ascaridia galli in experimentally and naturally infected chickens

Factors affecting the development of Ascaridia galli-specific humoral responses and their protective roles are largely unknown. We investigated the effects of time and infection dose on A. galli-specific IgY antibody levels following experimental infection. The acquisition and development of new infections and reinfections were also monitored by using tracer birds. Relationships between the retrospective IgY and the final worm burden of the birds were investigated to determine whether humoral immune responses generated during infection provide protection to the host animal. Young chickens were infected (+) with either 100 or 1000 embryonated eggs of A. galli (100+: n = 45; 1000+: n = 45) or kept as uninfected controls (CON: n = 10). Uninfected birds were also added to each infection group as tracer (T) birds (T100+; n = 5 and T1000+; n = 5). Faecal egg counts and IgY antibody concentrations in plasma and egg yolk were determined at selected intervals. Final worm burdens were quantified at 28 weeks post infection (wpi). The plasma antibody (PAB) and egg yolk antibody (EAB) levels of experimentally infected birds were compared to those of control and tracer birds throughout the study period, and PAB levels were found to depend initially on the infection dose but thereafter mainly on reinfections. Starting at wpi 2, 1000+ had consistently higher PAB levels than CON did (P < 0.05). With exceptions at wpi 0, 2 and 12, PAB levels were also higher (P < 0.05) or tended to be higher (P < 0.10) in 100+ than in CON. An earlier and higher increase was observed in the PAB levels of T1000+ than in those of T100+, implying that (re-)infection occurrence depended on the infection dose. Although 1000+ showed higher (P < 0.05) EAB levels than CON did at both wpi 14 and 18, EAB levels were higher in 100+ than in CON only at wpi 28 (P < 0.05). The total worm burdens in the initial experimentally infected birds were similar (P = 0.257); they were also highly comparable between experimentally and naturally infected birds, indicating that final worm burden was mainly determined by the naturally occurring infections resulting from continuous exposure. When all available information on the retrospective plasma and egg yolk IgY levels was collectively evaluated to estimate the larval or total worm burdens of the experimentally infected birds, both PAB and EAB levels at particular wpi were significantly associated with worm burden, especially with larval count. In conclusion, our data support the hypothesis that the number of larvae, rather than the number of mature worms, affects the antibody levels in both plasma and egg yolk. Despite the increased levels of A. galli-specific antibodies in plasma and egg yolk throughout the study period, only a weak indication was found that antibodies might be directly associated with protection.

Reference gene selection for the shell gland of laying hens in response to time-points of eggshell formation and nicarbazin

Ten reference genes were investigated for normalization of gene expression data in the shell gland of laying hens. Analyses performed with geNorm revealed that hypoxanthine phosphoribosyltransferase 1 (HPRT1) and hydroxymethylbilane synthase (HMBS) were the two most stable reference genes in response to post-oviposition time alone (POT) or with nicarbazin treatment (POT+N) of laying hens. NormFinder analyses showed that the two most stable reference genes in response to POT and POT+N were 18S ribosomal RNA (18S rRNA), ribosomal protein L4 (RPL4) and HMBS, RPL4, respectively. BestKeeper analyses showed that 18S rRNA, RPL4 and HPRT1, HMBS were the two most stable reference genes for POT, and POT+N, respectively. Of the ten reference genes, all except B2M showed geNorm M <0.5, suggesting that they were stably expressed in the shell gland tissue. Consensus from these three programs suggested HPRT1 and HMBS could be used as the two most stable reference genes in the present study. Expression analyses of four candidate target genes with the two most and the two least stable genes showed that a combination of stable reference genes leads to more discriminable quantification of expression levels of target genes, while the least stable genes failed to do so. Therefore, HMBS and HPRT1 are recommended as the two most stable reference genes for the normalization of gene expression data at different stages of eggshell formation in brown-egg laying hens. Available statistical programs for reference gene ranking should include more robust analysis capability to analyse the gene expression data generated from factorial design experiments.

Widespread extrahepatic expression of acute-phase proteins in healthy chicken (Gallus gallus) tissues

Acute phase proteins (APP) are plasma proteins that can modify their expression in response to inflammation caused by tissue injury, infections, immunological disorders or stress. Although APP are produced mainly in liver, extrahepatic production has also been described. As a prerequisite to get insight the expression of APP in chicken during diseases, this study investigated the presence of five APP, including alpha1-acid glycoprotein (AGP), Serum Amyloid A (SAA), PIT54, C-Reactive protein (CRP) and Ovotransferrin (OVT) in twenty tissues collected from healthy chicken (Gallus gallus) by quantitative Real Time PCR and immunohistochemistry. As expected, APP gene abundance was higher in liver compared with other tissues. The mRNA coding for CRP, OVT and SAA was detected in all analyzed tissues with a higher expression in gastrointestinal tract, respiratory and lymphatic samples. SAA expression was particularly high in cecal tonsil, lung, spleen and Meckel's diverticulum, whereas OVT in lung, bursa of Fabricius and pancreas. AGP and PIT54 mRNA expression were detected in all tissues but at negligible levels. Immunohistochemical expression of AGP and OVT was variably detected in different organs, being identified in endothelium of every tissue. Positive cells were present in the epithelium of the mucosal layer of gastrointestinal tract and kidney. Lung and central nervous system stained for both proteins. No positive staining was detected in lymphoid tissues and muscle. These results suggest that most tissues can express different amount of APP even in healthy conditions and are therefore capable to mount a local acute phase reaction.