Heterophils are associated with resistance to systemicSalmonella enteritidisinfections in genetically distinct chicken lines

Adapted tissue assay for the assessment of ileal granulocyte degranulation following in ovo inoculation with select bacteria or coccidial challenge in chickens

A previously described heterophil degranulation assay was adapted for use with ileal mucosal tissue via quantification of β-D-glucuronidase and assay end product 4-methylumbelliferone (4-MU). Three initial experiments evaluated the effect of in ovo inoculations of Citrobacter freundii (CF) or mixed lactic acid bacteria (LAB) on ileal granulocyte degranulation. Inoculations were administered on embryonic d18, body weights (BW) were recorded on day of hatch (DOH) and d10 to calculate body weight gain (BWG), and ileal mucosal scrapings were collected on DOH or d10 for the 4-MU assay. In all experiments, treatments were statistically analyzed relative to control groups. Treatments minimally affected BWG in all in ovo experiments (p > 0.05) relative to respective control groups. Similarly, ileal degranulation in in ovo treatments did not statistically differ (p > 0.05). Based on BWG, in ovo treatments may have induced low-level inflammation unable to elicit detectable changes via the 4-MU assay. Four subsequent experiments were conducted to evaluate effects of Eimeria maxima (EM) on ileal degranulation. Treatments included non-inoculated controls and low, medium, or high EM infection. Across all four experiments, final BW or BWG over the inoculation period were suppressed (p < 0.05) in EM groups relative to respective controls with the exception of EM-low (p = 0.094) and EM-medium (p = 0.096) in one trial. Ileal mucosal scrapings for the 4-MU assay were collected on day of peak lesions. Resulting values were reduced (p < 0.05) for EM treated birds in three experiments with the exception of EM-medium (p = 0.247). No differences were observed in one experiment (p = 0.351), which may have been attributed to a variation in strain of infecting Eimeria. Although refinement for low level inflammation is warranted, results indicate successful adaptation of the 4-MU assay for use with intestinal tissue during significant gastrointestinal inflammation.

Addition of a protected complex of biofactors and antioxidants to breeder hen diets confers transgenerational protection against Salmonella enterica serovar Enteritidis in progeny chicks

Addition of vitamins and antioxidants has been long associated with increased immunity and are commonly used in the poultry industry; however, less is known regarding their use in broiler breeder hens. The objective of this study was to determine if feeding a complex of protected biofactors and antioxidants composed of vitamins and fermentation extracts to broiler breeder hens conferred resistance against Salmonella enterica serovar Enteritidis (S. Enteritidis) in the progeny chicks. Three-day-old chicks from control- and supplement-fed hens were challenged with S. Enteritidis and necropsied 4- and 11-days postchallenge (dpc) to determine if there were differences in invasion and colonization. Serum and jejunum were evaluated for various cytokine and chemokine production. Fewer (P = 0.002) chicks from supplement-fed hens had detectable S. Enteritidis in the ceca (32.6%) compared to chicks from control-fed hens (64%). By 11 dpc, significantly (P < 0.001) fewer chicks from supplement-fed hens were positive for S. Enteritidis (liver [36%]; ceca [16%]) compared to chicks from the control hens (liver [76%]; ceca [76%]). The recoverable S. Enteritidis in the cecal content was also lower (P = 0.01) at 11 dpc. In additional to the differences in invasion and colonization, cytokine and chemokine production were distinct between the 2 groups of chicks. Chicks from supplement-fed hens had increased production of IL-16, IL-6, MIP-3α, and RANTES in the jejunum while IL-16 and MIP-1β were higher in the serum of chicks from the control-fed hens. By 11 dpc, production of IFN-γ was decreased in the jejunum of chicks from supplement-fed hens. Collectively, these data demonstrate adding a protected complex of biofactors and antioxidants to the diet of broiler breeder hens offers a measure of transgenerational protection to the progeny against S. Enteritidis infection and reduces colonization that is mediated, in part, by a robust and distinct cytokine and chemokine response locally at the intestine and systemically in the blood.

High Affinity Iron Acquisition Systems Facilitate but Are Not Essential for Colonization of Chickens by Salmonella Enteritidis

The roles of TonB mediated Fe³⁺ (ferric iron) uptake via enterobactin (involving biosynthesis genes entABCDEF) and Fe²⁺ (ferrous iron) uptake through the FeoABC transporter are poorly defined in the context of chicken-Salmonella interactions. Both uptake systems are believed to be the major contributors of iron supply in the Salmonella life cycle. Current evidence suggests that these iron uptake systems play a major role in pathogenesis in mammals and as such, they represent promising antibacterial targets with therapeutic potential. We investigated the role of these iron uptake mechanisms regarding the ability of Salmonella Enteritidis (SEn) strains to colonize in a chicken infection model. Further we constructed a bioluminescent reporter to sense iron limitation during gastrointestinal colonization of Salmonella in chicken via ex vivo imaging. Our data indicated that there is some redundancy between the ferric and ferrous iron uptake mechanisms regarding iron acquisition during SEn pathogenesis in chicken. We believe that this redundancy of iron acquisition in the host reservoir may be the consequence of adaptation to unique avian environments, and thus warrants further investigation. To our knowledge, this the first report providing direct evidence that both enterobactin synthesis and FeoABC mediated iron uptake contribute to the virulence of SEn in chickens.

A Novel Approach against Salmonella: A Review of Polymeric Nanoparticle Vaccines for Broilers and Layers

This work discusses the present-day limitations of current commercial Salmonella vaccines for broilers and layers and explores a novel approach towards poultry vaccination using biodegradable nanoparticle vaccines against Salmonella. With the increasing global population and poultry production and consumption, Salmonella is a potential health risk for humans. The oral administration of killed or inactivated vaccines would provide a better alternative to the currently commercially available Salmonella vaccines for poultry. However, there are currently no commercial oral killed-vaccines against Salmonella for use in broilers or layers. There is a need for novel and effective interventions in the poultry industry. Polymeric nanoparticles could give way to an effective mass-administered mucosal vaccination method for Salmonella. The scope of this work is limited to polymeric nanoparticles against Salmonella for use in broilers and layers. This review is based on the information available at the time of the investigation.

Comprehensive Analyses of circRNA Expression Profiles and Function Prediction in Chicken Cecums After Eimeria tenella Infection

Coccidiosis is an important intestinal parasitic disease that causes great economic losses to the global poultry production industry. Circular RNAs (circRNAs) are long non-coding RNAs that play important roles in various infectious diseases and inflammatory responses. However, the expression profiles and functions of circRNAs during Eimeria tenella (E. tenella) infection remain unclear. In this study, high-throughput sequencing was carried out to detect circRNAs in chicken cecal tissues from the control (JC), resistant (JR), and susceptible (JS) groups on day 4.5 postinfection (pi), respectively. A total of 104 circRNAs were differentially expressed, including 47 circRNAs between the JS and JC groups, 38 between the JR and JS groups, and 19 between the JR and JC groups. Functional analyses indicated that these differentially expressed circRNAs were involved in pathways related to E. tenella infection; the adaptive immune response was enriched in the JS vs JC group, the NF-kappa B signaling and natural killer cell-mediated cytotoxicity pathways were enriched in the JS vs JC and JR vs JC groups, while the B cell receptor signaling pathway was enriched in only the JR vs JC group. Moreover, the coexpression network of differentially expressed circRNAs and mRNAs suggested that circRNA2202 and circRNA0759 associated with DTX1 in the JS vs JC group, circRNA4338 associated with VPREB3 and CXCL13L3 in the JR vs JC group, and circRNA2612 associated with IL8L1 and F2RL2 in the JR vs JS group were involved in the immune response upon E. tenella infection. In conclusion, our results provide valuable information on the circRNAs involved in the progression of chicken E. tenella infection and advance our understanding of the circRNA regulatory mechanisms of host resistance and susceptibility to E. tenella infection in chickens.

A microencapsulated feed additive containing organic acids, thymol, and vanillin increases in vitro functional activity of peripheral blood leukocytes from broiler chicks

During the first week after hatch, young chicks are vulnerable to pathogens as the immune system is not fully developed. The objectives of this study were to determine if supplementing the starter diet with a microencapsulated feed additive containing citric and sorbic acids, thymol, and vanillin affects in vitro functional activity of peripheral blood leukocytes (PBLs). Day-old chicks (n = 800) were assigned to either a control diet (0 g/metric ton [MT]) or a diet supplemented with 500 g/MT of the microencapsulated additive. At 4 D of age, peripheral blood was collected (100 birds per treatment), and heterophils and monocytes isolated (n = 4). Heterophils were assayed for the ability to undergo degranulation and production of an oxidative burst response while nitric oxide production was measured in monocytes. Select cytokine and chemokine mRNA expression levels were also determined. Statistical analysis was performed using Student t test comparing the supplemented diet to the control (P ≤ 0.05). Heterophils isolated from chicks fed the microencapsulated citric and sorbic acids, thymol, and vanillin had higher (P ≤ 0.05) levels of degranulation and oxidative burst responses than those isolated from chicks on the control diet. Heterophils from the supplemented chicks also had greater (P ≤ 0.05) expression of IL10, IL1β, and CXCL8 mRNA than those from control-fed chicks. Similarly, nitric oxide production was significantly (P ≤ 0.05) higher in monocytes isolated from birds fed the supplement. The cytokine and chemokine profile in monocytes from the supplement-fed chicks showed a significant (P ≤ 0.05) drop in IL10 mRNA expression while IL1β, IL4, and CXCL8 were unchanged. In conclusion, 4 D of supplementation with a microencapsulated blend made up of citric and sorbic acids, thymol, and vanillin enhanced the in vitro PBL functions of degranulation, oxidative burst, and nitric oxide production compared with the control diet. Collectively, the data suggest feeding broiler chicks a diet supplemented with a microencapsulated blend of citric and sorbic acids, thymol, and vanillin may prime key immune cells making them more functionally efficient and acts as an immune-modulator to boost the inefficient and undeveloped immune system of young chicks.

Modulation of the Immune Response to Improve Health and Reduce Foodborne Pathogens in Poultry

Salmonella and Campylobacter are the two leading causes of bacterial-induced foodborne illness in the US. Food production animals including cattle, swine, and chickens are transmission sources for both pathogens. The number of Salmonella outbreaks attributed to poultry has decreased. However, the same cannot be said for Campylobacter where 50⁻70% of human cases result from poultry products. The poultry industry selects heavily on performance traits which adversely affects immune competence. Despite increasing demand for poultry, regulations and public outcry resulted in the ban of antibiotic growth promoters, pressuring the industry to find alternatives to manage flock health. One approach is to incorporate a program that naturally enhances/modulates the bird's immune response. Immunomodulation of the immune system can be achieved using a targeted dietary supplementation and/or feed additive to alter immune function. Science-based modulation of the immune system targets ways to reduce inflammation, boost a weakened response, manage gut health, and provide an alternative approach to prevent disease and control foodborne pathogens when conventional methods are not efficacious or not available. The role of immunomodulation is just one aspect of an integrated, coordinated approach to produce healthy birds that are also safe and wholesome products for consumers.

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.

Evaluation of genetic resistance to Salmonella Pullorum in three chicken lines

Resistance to diseases varies considerably among populations of the same species and can be ascribed to both genetic and environmental factors. Salmonella Pullorum (SP) is responsible for significant losses in the poultry industry, especially in developing countries. To better understand SP resistance in chicken populations with different genetic backgrounds, we orally challenged 3 chicken lines with SP-a highly selected commercial breed (Rhode Island Red, RIR), a local Chinese chicken (Beijing You, BY), and a synthetic layer line (dwarf, DW)-at 4 d of age. Two traits related to SP resistance, survival, and bacterial carriage in the spleen were evaluated after infection. Survival rates were recorded up to 40 d of age when all chickens still alive were killed to verify the presence of SP in the spleen to determine carrier state. Mortalities for RIR, BY, and DW chicks were 25.1%, 8.3%, and 22.7%, respectively, and the corresponding carrier-states in the spleens were 17.9%, 0.6%, and 15.8%. Survival and carrier-state heritabilities were estimated using an animal threshold model. Survival heritability was 0.197, 0.091, and 0.167 in RIR, BY, and DW populations, respectively, and the heritabilities of carrier state for DW and RIR were 0.32 and 0.16, respectively. This is the first time that the heritability of the SP carrier state has been evaluated in chickens. Our study provides experimental evidence that chickens with various genetic background exhibited significantly different SP-resistant activities and heritabilities. These results may be useful for selecting lines with better disease resistance.

Differential Levels of Cecal Colonization by Salmonella Enteritidis in Chickens Triggers Distinct Immune Kinome Profiles

Salmonella enterica serovar Enteritidis are facultative intracellular bacteria that cause disease in numerous species. Salmonella-related infections originating from poultry and/or poultry products are a major cause of human foodborne illness with S. Enteritidis the leading cause worldwide. Despite the importance of Salmonella to human health and chickens being a reservoir, little is known of the response to infection within the chicken gastrointestinal tract. Using chicken-specific kinome immune peptide arrays we compared a detailed kinomic analysis of the chicken jejunal immune response in a single line of birds with high and low Salmonella loads. Four-day-old chicks were challenged with S. Enteritidis (10⁵ cfu) and cecal content and a section of jejunum collected at three times: early [4-7 days post-infection (dpi)], middle (10-17 dpi), and late (24-37 dpi). Salmonella colonization was enumerated and birds with the highest (n = 4) and lowest (n = 4) loads at each time were selected for kinomic analyses. Key biological processes associated with lower loads of Salmonella clustered around immune responses, including cell surface receptor signaling pathway, positive regulation of cellular processes, defense response, innate immune response, regulation of immune response, immune system process, and regulation of signaling. Further evaluation showed specific pathways including chemokine, Jak-Stat, mitogen activated protein kinase, and T cell receptor signaling pathways were also associated with increased resistance. Collectively, these findings demonstrate that it is possible to identify key mechanisms and pathways that are associated with increased resistance against S. Enteritidis cecal colonization in chickens. Therefore, providing a foundation for future studies to identify specific proteins within these pathways that are associated with resistance, which could provide breeders additional biomarkers to identify birds naturally more resistant to this important foodborne pathogen.

In vitro and in vivo generation of heterophil extracellular traps after Salmonella exposure

The release of extracellular traps (ETs) by granulocytes is a unique strategy to stop the dissemination of microbial pathogens. This study was undertaken to elucidate the potential of avian granulocytes (heterophils) to form ETs that can arrest and kill Salmonella organisms. After in vitro exposure of isolated heterophils and in vivo infection of day-old chicks with Salmonella enterica subsp. enterica serovars Infantis (SI) or Enteritidis (SE), the generation of ETs as well as the trapping and survivability of Salmonella organisms in the ET meshwork were determined by means of microscopy and spectrophotometry. In vitro, heterophils were able to form ETs within 15min after SE and SI inoculation. At 120min and with a multiplicity of infection of 1 and 5, SI induced significantly more ETs and DNA release than SE. Both SE and SI were found to be associated with the ET structures. Live-dead staining showed most of the microorganisms within the extracellular scaffold alive. In vivo, heterophils were detected in cecal lumen of SE-, but not SI-infected chicks. In cecum of the SE-exposed chicks, ET formations were scarcely detected whereas intact heterophils with phagocytosed bacteria were frequently found. The results evidence the capability of heterophils to generate ETs after SE and SI exposure in vitro. However, an infection of chicks with Salmonella did not significantly induce the formation of ET structures in cecum. Thus, the process to form ETs (ETosis) seems not to be of special relevance for Salmonella defense within the cecal lumen of young chicks.

Application of imaging flow cytometry for characterization of acute inflammation in non-classical animal model systems

Phagocytes display marked heterogeneity in their capacity to induce and control acute inflammation. This has a significant impact on the effectiveness of antimicrobial immune responses at different tissue sites as well as their predisposition for inflammation-associated pathology. Imaging flow cytometry provides novel opportunities for characterization of these phagocyte populations through high spatial resolution, statistical robustness, and a broad range of quantitative morphometric cell analysis tools. This study highlights an integrative approach that brings together new tools in imaging flow cytometry with conventional methodologies for characterization of phagocyte responses during acute inflammation. We focus on a comparative avian in vivo challenge model to showcase the added depth gained through these novel quantitative multiparametric approaches even in the absence of antibody-based cellular markers. Our characterization of acute inflammation in this model shows significant conservation of phagocytic capacity among avian phagocytes compared to other animal models. However, it also highlights evolutionary divergence with regards to phagocyte inflammation control mechanisms based on the internalization of apoptotic cells.

Potential immunomodulatory effects of non-dialyzable materials of cranberry extract in poultry production

Studies on effects of cranberry products in animals, especially in chickens, are very scarce or even lacking. This study investigated the immunomodulatory effect of high molecular weight non-dialyzable materials (NDMs) of cranberry extract. The in vitro antioxidant and anti-inflammatory activities were investigated. The ability of NDMs (0, 1, 2, or 4 mg/mL) to enhance phagocytic activities was also evaluated using chicken heterophils (CHEs) against Staphylococcus aureus Furthermore, a broiler model was used to determine the effect of NDMs on the humoral immune response. Seven-d-old chicks were vaccinated with the infectious bursal disease virus (IBDV) vaccine S-706, and treated orally with 0, 2, 4, or 8 mg/mL/bird NDMs for five consecutive days. Serum immunoglobulin level (Ig), and antibody concentration against IBDV, infectious bronchitis virus (IBV), Newcastle disease virus (NDV), and avian reovirus (ARV) were measured weekly by enzyme-linked immunosorbent assay (ELISA). NDMs showed >five-fold higher antioxidant activity (oxygen radical absorbance capacity = 222.7 mg trolox/g) than the commercial raw cranberry juice from which it derived (oxygen radical absorbance capacity = 39.6 mg trolox/g). Likewise, NDMs demonstrated anti-inflammatory activities comparable to Naproxen but better than those of Ibuprofen. The susceptibility of S. aureus to phagocytosis by CHEs increased significantly (P < 0.05) at 4 mg/mL NDMs in the medium. While no intracellular bacteria were counted in CHEs after phagocytosis in the presence of 2 and 4 mg/mL NDMs, 1 mg/mL NDMs demonstrated a significant (P < 0.05) intracellular killing activity in CHEs against S. aureus compared to the untreated CHEs. Results from the in vivo studies indicated that birds receiving 2 and 4 mg/mL/bird NDMs had a higher serum IgM level (P < 0.05), and their antibody titers against IBDV tended to increase with NDMs administration (P = 0.06) on d 35. These results suggest that NDMs enhances bacterial susceptibility to immuno-defense mechanisms, and may be useful as immunomodulators against infections.

The genomic architecture of resistance to Campylobacter jejuni intestinal colonisation in chickens

BACKGROUND

Campylobacter is the leading cause of foodborne diarrhoeal illness in humans and is mostly acquired from consumption or handling of contaminated poultry meat. In the absence of effective licensed vaccines and inhibitors, selection for chickens with increased resistance to Campylobacter could potentially reduce its subsequent entry into the food chain. Campylobacter intestinal colonisation levels are influenced by the host genetics of the chicken. In the present study, two chicken populations were used to investigate the genetic architecture of avian resistance to colonisation: (i) a back-cross of two White Leghorn derived inbred lines [(61 x N) x N] known to differ in resistance to Campylobacter colonisation and (ii) a 9(th) generation advanced intercross (61 x N) line.

RESULTS

The level of colonisation with Campylobacter jejuni following experimental infection was found to be a quantitative trait. A back-cross experiment using 1,243 fully informative single nucleotide polymorphism (SNP) markers revealed quantitative trait loci (QTL) on chromosomes 7, 11 and 14. In the advanced intercross line study, the location of the QTL on chromosome 14 was confirmed and refined and two new QTLs were identified located on chromosomes 4 and 16. Pathway and re-sequencing data analysis of the genes located in the QTL candidate regions identified potential pathways, networks and candidate resistance genes. Finally, gene expression analyses were performed for some of the candidate resistance genes to support the results.

CONCLUSION

Campylobacter resistance in chickens is a complex trait, possibly involving the Major Histocompatibility Complex, innate and adaptive immune responses, cadherins and other factors. Two of the QTLs for Campylobacter resistance are co-located with Salmonella resistance loci, indicating that it may be possible to breed simultaneously for enhanced resistance to both zoonoses.

Differential ex vivo responses of primary leukocytes from turkey pedigree lines to Salmonella Heidelberg

Escalating product recalls as a consequence of Salmonella-contaminated poultry products have resulted in detrimental economic impacts in the poultry industry. One potential long-term alternative method to Salmonella prevention is genetic selection to improve innate resistance. This study evaluated the ex vivo effects of Salmonella Heidelberg (SH) on phagocytic and bactericidal leukocyte function in turkeys from six pedigree lines (A-F). Day-of-hatch poults (n = 48) were placed and raised in cages (2 birds/gender/genetic line/cage) to 35 d when heterophils and peripheral blood mononuclear cells (PBMCs) were extracted from males and females of each line. Cells were used in phagocytic and bactericidal assays to determine the ex vivo effects of SH on turkey leukocyte activity. Data were analyzed using the Fit Model platform in JMP Pro 10.0 (SAS Institute Inc.) with differences considered significant at P ≤ 0.05 and data reported as LS Means with SEM. Although genetic line had no significant effect on phagocytosis of SH by heterophils and PBMCs, cumulatively, female cells exhibited higher phagocytosis potential than those from males. The main effect of gender was significant on bactericidal activity of PBMCs when incubated at a 1:10 and 1:100 PBMC to SH ratio. Genetic line also had a significant effect on bactericidal activity of PBMCs with cells from line F exhibiting the best activity. These results suggest that gender had a marked cumulative effect on phagocytosis of SH by heterophils and PBMCs while both genetic line and gender had a prominent effect on bacterial killing of SH by turkey PBMCs. Once able to determine genetic markers associated with these immune responses to Salmonella, genetic selection for increased resistance may become feasible in turkeys.

Heterophil Phagocytic Activity Stimulated by Lactobacillus salivarius L61 and L55 Supplementation in Broilers with Salmonella Infection

Newborn chicks are susceptible to Salmonella enterica serovar Enteritidis (SE). The objective of this study was to evaluate the effect of Lactobacillus probiotic isolated from chicken feces on heterophil phagocytosis in broiler chicks. A total of 150 newborn broiler chicks were divided into 5 groups (30 chicks per group) as follows: group 1 (normal control), given feed and water only, group 2 (positive control) given feed, water and SE infection, group 3 (L61 treated) given feed, water, SE infection followed by Lactobacillus salivarius L61 treatment, group 4 (L55 treated) given feed, water, SE infection followed by L. salivarius L55 treatment, and group 5 given feed, water, SE infection followed by L. salivarius L61 + L55 combination treatment. After SE infection, L. salivarius treatment lasted for 7 days. The results showed that L. salivarius L61 and L. salivarius L55 treatment, either alone or combination of both, increased the survival rate after SE infection, and upregulated heterophil phagocytosis and phagocytic index (PI). Conversely, chick groups treated with Lactobacillus showed lower SE recovery rate from cecal tonsils than that of the positive control group. The PI values of the chicken group with SE infection, followed by the combination of L. salivarius L61 and L. salivarius L55 were the highest as compared to either positive control or normal control group. Two Lactobacillus strains supplementation group showed significantly (p<0.05) higher PI value at 48 h than 24 h after treatment.

Splenic gene expression profiling in White Leghorn layer inoculated with the Salmonella enterica serovar Enteritidis

Salmonella enterica serovar Enteritidis (SE) is a foodborne pathogen that can threaten human health through contaminated poultry products. Live poultry, chicken eggs and meat are primary sources of human salmonellosis. To understand the genetic resistance of egg-type chickens in response to SE inoculation, global gene expression in the spleen of 20-week-old White Leghorn was measured using the Agilent 4 × 44 K chicken microarray at 7 and 14 days following SE inoculation (dpi). Results showed that there were 1363 genes significantly differentially expressed between inoculated and non-inoculated groups at 7 dpi (I7/N7), of which 682 were up-regulated and 681 were down-regulated genes. By contrast, 688 differentially expressed genes were observed at 14 dpi (I14/N14), of which 371 were up-regulated genes and 317 were down-regulated genes. There were 33 and 28 immune-related genes significantly differentially expressed in the comparisons of I7/N7 and I14/N14 respectively. Functional annotation revealed that several Gene Ontology (GO) terms related to immunity were significantly enriched between the inoculated and non-inoculated groups at 14 dpi but not at 7 dpi, despite a similar number of immune-related genes identified between I7/N7 and I14/N14. The immune response to SE inoculation changes with different time points following SE inoculation. The complicated interaction between the immune system and metabolism contributes to the immune responses to SE inoculation of egg-type chickens at 14 dpi at the onset of lay. GC, TNFSF8, CD86, CD274, BLB1 and BLB2 play important roles in response to SE inoculation. The results from this study will deepen the current understanding of the genetic response of the egg-type chicken to SE inoculation at the onset of egg laying.

Early life microbial colonization of the gut and intestinal development differ between genetically divergent broiler lines

Background

Host genetic makeup plays a role in early gut microbial colonization and immune programming. Interactions between gut microbiota and host cells of the mucosal layer are of paramount importance for a proper development of host defence mechanisms. For different livestock species, it has already been shown that particular genotypes have increased susceptibilities towards disease causing pathogens.

The objective of this study was to investigate the impact of genotypic variation on both early microbial colonization of the gut and functional development of intestinal tissue. From two genetically diverse chicken lines intestinal content samples were taken for microbiota analyses and intestinal tissue samples were extracted for gene expression analyses, both at three subsequent time-points (days 0, 4, and 16).

Results

The microbiota composition was significantly different between lines on each time point. In contrast, no significant differences were observed regarding changes in the microbiota diversity between the two lines throughout this study. We also observed trends in the microbiota data at genus level when comparing lines X and Y. We observed that approximately 2000 genes showed different temporal gene expression patterns when comparing line X to line Y. Immunological related differences seem to be only present at day 0, because at day 4 and 16 similar gene expression is observed for these two lines. However, for genes involved in cell cycle related processes the data show higher expression over the whole course of time in line Y in comparison to line X.

Conclusions

These data suggest the genetic background influences colonization of gut microbiota after hatch in combination with the functional development of intestinal mucosal tissue, including the programming of the immune system. The results indicate that genetically different chicken lines have different coping mechanisms in early life to cope with the outside world.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1646-6) contains supplementary material, which is available to authorized users.

Genome-wide SNP analysis identifies major QTL for Salmonella colonization in the chicken

Salmonella-infected poultry products are a major source of human Salmonella infection. The prophylactic use of antimicrobials in poultry production was recently banned in the EU, increasing the need for alternative methods to control Salmonella infections in poultry flocks. Genetic selection of chickens more resistant to Salmonella colonization provides an attractive means of sustainably controlling the pathogen in commercial poultry flocks and its subsequent entry into the food chain. Analysis of different inbred chickens has shown that individual lines are consistently either susceptible or resistant to the many serovars of Salmonella that have been tested. In this study, two inbred chicken lines with differential susceptibility to Salmonella colonization (61 ((R)) and N((S)) ) were used in a backcross experimental design. Unlike previous studies that used a candidate gene approach or low-density genome-wide screens, we have exploited a high-density marker set of 1255 SNPs covering the whole genome to identify quantitative trait loci (QTL). Analysis of log-transformed caecal bacterial levels between the parental lines revealed a significant difference at 1, 2, 3 and 4 days post-infection (P < 0.05). Analysis of the genotypes of the backcross (F1  × N) population (n = 288) revealed four QTL on chromosomes 2, 3, 12 and 25 for the two traits examined in this study: log-transformed bacterial counts in the caeca and presence of a hardened caseous caecal core. These included one genome-wide significant QTL on chromosome 2 at 20 Mb and three additional QTL, on chromosomes 3, 12 and 25 at 96, 15 and 1 Mb, respectively, which were significant at the chromosome-wide level (P < 0.05). The results generated in this study will inform future breeding strategies to control these pathogens in commercial poultry flocks.

Critical Role of Glycogen Synthase Kinase-3β in Regulating the Avian Heterophil Response to Salmonella enterica Serovar Enteritidis

A microarray-assisted gene expression screen of chicken heterophils revealed glycogen synthase kinase-3β (GSK-3β), a multifunctional Ser/Thr kinase, to be consistently upregulated 30–180 min following stimulation with Salmonella enterica serovar Enteritidis (S. Enteritidis). The present study was designed to delineate the role of GSK-3β in regulating the innate function of chicken heterophils in response to S. Enteritidis exposure. Using a specific GSK-3β ELISA assay, 30 min after infection with S. Enteritidis, heterophils had a significant decrease (p ≤ 0.05) in total GSK-3β, but a significant increase (p ≤ 0.05) in phosphorylated GSK-3β (Ser9). By 60 min post-infection, there was no difference in the amount of phosphorylated GSK-3β (Ser9) in either the uninfected and infected heterophils. S. Enteritidis interaction with heterophils alters GSK-3β activity by stimulating phosphorylation at Ser9 and that peaks by 30 min post-infection. Further, inhibition of GSK3β with lithium chloride resulted in a significant decrease (p ≤ 0.05) in NF-κB activation and expression of IL-6, but induces a significant increase (p ≤ 0.05) in the expression of the anti-inflammatory cytokine, IL-10. Using a phospho-specific antibody array confirmed the phosphorylation of GSK-3β (Ser9) as well as the phosphorylation of the downstream cytokine-activated intracellular signaling pathway involved in stimulating immune responses, IκB, the IκB subunit IKK-β, and the NF-κB subunits p105, p65, and c-Rel. Our data revealed that the phosphorylation of GSK-3β (Ser9) is responsible for inducing and controlling an innate response to the bacteria. Our findings suggest that the repression of GSK-3 activity is beneficial to the host cell and may act as a target for treatment in controlling intestinal colonization in chickens. Further experiments will define the in vivo modulation of GSK-3 as a potential alternative to antibiotics in salmonella and other intestinal bacterial infections.

The consequence of low mannose-binding lectin plasma concentration in relation to susceptibility to Salmonella Infantis in chickens

Mannose-binding lectin (MBL) is a key protein in innate immunity. MBL binds to carbohydrates on the surface of pathogens, where it initiates complement activation via the lectin-dependent pathway or facilitates opsonophagocytosis. In vitro studies have shown that human MBL is able to bind to Salmonella, but knowledge in relation to chicken MBL and Salmonella is lacking. In order to study this relation day-old chickens from two selected lines L10H and L10L, differing in MBL serum concentration, were either orally infected with S. Infantis (S.123443) or kept as non-infected controls. The differences between healthy L10H and L10L chicken sublines were more profound than differences caused by the S. Infantis infection. The average daily body weight was higher for L10H than for L10L, regardless of infection, indicating beneficial effects of MBL selection on growth. Salmonella was detected in cloacal swabs and the number of Salmonella positive chickens during the experiment was significantly higher in L10L than L10H, indicating that MBL may affect the magnitude of Salmonella colonisation in day-old chickens. MBL expression was determined in ceca tissue by real-time RT-PCR. L10H chickens showed a significantly higher relative expression than L10L at days 1 and 41 pi, regardless of infection. Finally, flow cytometric analysis of whole blood from infected chickens showed that L10H had a significantly higher count of all assessed leucocyte subsets on day 5 pi, and also a higher count of monocytes on day 12 pi than L10L. No difference was observed between infected and non-infected L10L chicken.

Selection for pro-inflammatory mediators yields chickens with increased resistance against Salmonella enterica serovar Enteritidis

Salmonella is a leading cause of foodborne illness and can be transmitted through consumption of contaminated poultry; therefore, increasing a flock's natural resistance to Salmonella could improve food safety. Previously, we characterized the heterophil-mediated innate immune response of 2 parental broiler lines and F1 reciprocal crosses and showed that increased heterophil function and expression of pro-inflammatory mediators corresponds with increased resistance against diverse pathogens. A preliminary selection trial showed that individual sires had varying inherent levels of pro-inflammatory mediators and selection based on a high or low phenotype was passed onto progeny. Based on these results, we hypothesized selection of broilers for higher levels of the pro-inflammatory mediators IL-6, CXCLi2, and CCLi2 would produce progeny with increased resistance against Salmonella Enteritidis. Peripheral blood leukocytes were isolated from 75 commercial broiler sires, screened, and 10 naturally high and low expressing sires were selected and mated to randomly selected dams to produce the first generation of "high" and "low" progeny. The mRNA expression of CXCLi2 and CCLi2 were significantly (P ≤ 0.02) higher in the high progeny and were more resistant to liver and spleen organ invasion by Salmonella Enteritidis compared with low progeny. Production of the second generation yielded progeny that had differences (P ≤ 0.03) in all 3 mediators and further improved resistance against Salmonella Enteritidis. Feed conversion ratio and percent breast meat yield were calculated and were equal, whereas the high birds weighed slightly, but significantly, less than the low birds. These data clearly demonstrate that selection based on a higher phenotype of key pro-inflammatory mediators is a novel means to produce broilers that are naturally more resistant to Salmonella, one of the most important foodborne pathogens affecting the poultry industry.

The avian heterophil

Heterophils play an indispensable role in the immune defense of the avian host. To accomplish this defense, heterophils use sophisticated mechanisms to both detect and destroy pathogenic microbes. Detection of pathogens through the toll-like receptors (TLR), FC and complement receptors, and other pathogen recognition receptors has been recently described for the avian heterophil. Upon detection of pathogens, the avian heterophil, through a network of intracellular signaling pathways and the release and response to cytokines and chemokines, responds using a repertoire of microbial killing mechanisms including production of an oxidative burst, cellular degranulation, and production of extracellular matrices of DNA and histones (HETs). In this review, the authors describe the recent advances in our understanding of the avian heterophil, its functions, receptors and signaling, identified antimicrobial products, cytokine and chemokine production, and some of the effects of genetic selection on heterophils and their functional characteristics.

Characterization of responses initiated by different Toll-like receptor 2 ligands in chicken spleen cells

Toll-like receptors (TLRs) are pattern recognition receptors that mediate host responses to pathogens by promoting cellular activation and the production of cytokines. Ligands for TLRs are conserved structural motifs of pathogens termed pathogen-associated molecular patterns. In the case of TLR2, these ligands include peptidoglycan, lipomannan and lipopeptides. In mammals, it has been shown that different TLR2 ligands induce distinct cytokine responses. However, whether a similar phenomenon occurs in chickens remains to be determined. To this end, chicken splenocytes were stimulated with three different TLR2 ligands: Pam3CSK4, FSL-1 and lipomannan, and the relative gene expression of several cytokines was quantified at 2, 6 and 18h post-stimulation. The results suggest that Pam3 and FSL-1 modulate the kinetics of the pro-inflammatory cytokine response differently, as Pam3 induced a robust interleukin (IL)-1β response, while FSL-1 induced an early and prolonged up-regulation of IL-8. Furthermore, it appears that all three TLR2 ligands induce a mixed T-helper (TH) 1 and 2-like response, as characterized by the up-regulation of IFN-γ, IL-12, IL-4 and IL-13. In conclusion, we have demonstrated that different TLR2 ligands may induce different cytokine responses in chicken splenocytes. Future studies may be aimed at examining the immunomodulating effects of these ligands in vivo.

Gene Expression Analysis of Toll-Like Receptor Pathways in Heterophils from Genetic Chicken Lines that Differ in Their Susceptibility to Salmonella enteritidis

Previously conducted studies using two chicken lines (A and B) show that line A birds have increased resistance to a number of bacterial and protozoan challenges and that heterophils isolated from line A birds are functionally more responsive. Furthermore, when stimulated with Toll-like receptor (TLR) agonists, heterophils from line A expressed a totally different cytokine and chemokine mRNA expression pattern than heterophils from line B. A large-scale gene expression profile using an Agilent 44K microarray on heterophils isolated from line A and line B also revealed significantly differential expression in many immune-related genes following Salmonella enteritidis (SE) stimulation, which included genes involved in the TLR pathway. Therefore, we hypothesize the differences between the lines result from distinctive TLR pathway signaling cascades that mediate heterophil function and, thus, innate immune responsiveness to SE. Using quantitative RT-PCR on mRNA from heterophils isolated from control and SE-stimulated heterophils of each line, we profiled the expression of all chicken homologous genes identified in a reference TLR pathway. Several differentially expressed genes found were involved in the TLR-induced My88-dependent pathway, showing higher gene expression in line A than line B heterophils following SE stimulation. These genes included the TLR genes TLR4, TLR15, TLR21, MD-2, the adaptor proteins Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP), Tumor necrosis factor-receptor associated factor 3 (TRAF3), the IκB kinases transforming growth factor-β-activating kinase 1 (TAK1), IKKε and IKKα, the transcription factors NFkB2 and interferon regulatory factor 7, phosphatidylinositol-3 kinase (PI-3K), and the mitogen-activated protein kinase p38. These results indicate that higher expression of TLR signaling activation of both MyD88-dependent and TRIF-dependent pathways are more beneficial to avian heterophil-mediated innate immunity and a complicated regulation of downstream adaptors is involved in stronger induction of a TLR-mediated innate response in the resistant line A. These findings identify new targets for genetic selection of chickens to increase resistance to bacterial infections.

Systemic response to Campylobacter jejuni infection by profiling gene transcription in the spleens of two genetic lines of chickens

Campylobacter jejuni (C. jejuni) is a leading cause of human bacterial enteritis worldwide with poultry products being a major source of C. jejuni contamination. The chicken is the natural reservoir of C. jejuni where bacteria colonize the digestive tract of poultry, but rarely cause symptoms of disease. To understand the systemic molecular response mechanisms to C. jejuni infection in chickens, total splenic RNA was isolated and applied to a whole genome chicken microarray for comparison between infected (I) and non-infected (N) chickens within and between genetic lines A and B. There were more total splenic host genes responding to the infection in resistant line A than in susceptible line B. Specifically, genes for lymphocyte activation, differentiation and humoral response, and Ig light and heavy chain were upregulated in the resistant line. In the susceptible line, genes for regulation of erythrocyte differentiation, hemopoiesis, and RNA biosynthetic process were all downregulated. An interaction analysis between genetic lines and treatment demonstrated distinct defense mechanisms between lines: the resistant line promoted apoptosis and cytochrome c release from mitochondria, whereas the susceptible line responded with a downregulation of both functions. This was the first time that such systemic defensive mechanisms against C. jejuni infection have been reported. The results of this study revealed novel molecular mechanisms of the systemic host responses to C. jejuni infection in chickens that warrant further investigation.

Advances in avian immunology--prospects for disease control: a review

In order to develop novel solutions to avian disease problems, including novel vaccines and/or vaccine adjuvants, and the identification of disease resistance genes which can feed into conventional breeding programmes, it is necessary to gain a more thorough understanding of the avian immune response and how pathogens can subvert that response. Birds occupy the same habitats as mammals, have similar ranges of longevity and body mass, and face similar pathogen challenges, yet birds have a different repertoire of organs, cells, molecules and genes of the immune system compared to mammals. This review summarises the current state of knowledge of the chicken's immune response, highlighting differences in the bird compared to mammals, and discusses how the availability of the chicken genome sequence and the associated postgenomics technologies are contributing to theses studies and also to the development of novel intervention strategies againts avian and zoonotic disease.

Gene expression profiling of the local cecal response of genetic chicken lines that differ in their susceptibility to Campylobacter jejuni colonization

Campylobacter jejuni (C. jejuni) is one of the most common causes of human bacterial enteritis worldwide primarily due to contaminated poultry products. Previously, we found a significant difference in C. jejuni colonization in the ceca between two genetically distinct broiler lines (Line A (resistant) has less colony than line B (susceptible) on day 7 post inoculation). We hypothesize that different mechanisms between these two genetic lines may affect their ability to resist C. jejuni colonization in chickens. The molecular mechanisms of the local host response to C. jejuni colonization in chickens have not been well understood. In the present study, to profile the cecal gene expression in the response to C. jejuni colonization and to compare differences between two lines at the molecular level, RNA of ceca from two genetic lines of chickens (A and B) were applied to a chicken whole genome microarray for a pair-comparison between inoculated (I) and non-inoculated (N) chickens within each line and between lines. Our results demonstrated that metabolism process and insulin receptor signaling pathways are key contributors to the different response to C. jejuni colonization between lines A and B. With C. jejuni inoculation, lymphocyte activation and lymphoid organ development functions are important for line A host defenses, while cell differentiation, communication and signaling pathways are important for line B. Interestingly, circadian rhythm appears play a critical role in host response of the more resistant A line to C. jejuni colonization. A dramatic differential host response was observed between these two lines of chickens. The more susceptible line B chickens responded to C. jejuni inoculation with a dramatic up-regulation in lipid, glucose, and amino acid metabolism, which is undoubtedly for use in the response to the colonization with little or no change in immune host defenses. However, in more resistant line A birds the host defense responses were characterized by an up-regulation lymphocyte activation, probably by regulatory T cells and an increased expression of the NLR recognition receptor NALP1. To our knowledge, this is the first time each of these responses has been observed in the avian response to an intestinal bacterial pathogen.

Genetic control of resistance to salmonellosis and to Salmonella carrier-state in fowl: a review

Salmonellosis is a frequent disease in poultry stocks, caused by several serotypes of the bacterial species Salmonella enterica and sometimes transmitted to humans through the consumption of contaminated meat or eggs. Symptom-free carriers of the bacteria contribute greatly to the propagation of the disease in poultry stocks. So far, several candidate genes and quantitative trait loci (QTL) for resistance to carrier state or to acute disease have been identified using artificial infection of S. enterica serovar Enteritidis or S. enterica serovar Typhimurium strains in diverse genetic backgrounds, with several different infection procedures and phenotypic assessment protocols. This diversity in experimental conditions has led to a complex sum of results, but allows a more complete description of the disease. Comparisons among studies show that genes controlling resistance to Salmonella differ according to the chicken line studied, the trait assessed and the chicken's age. The loci identified are located on 25 of the 38 chicken autosomal chromosomes. Some of these loci are clustered in several genomic regions, indicating the possibility of a common genetic control for different models. In particular, the genomic regions carrying the candidate genes TLR4 and SLC11A1, the Major Histocompatibility Complex (MHC) and the QTL SAL1 are interesting for more in-depth studies. This article reviews the main Salmonella infection models and chicken lines studied under a historical perspective and then the candidate genes and QTL identified so far.

Selection of broilers with improved innate immune responsiveness to reduce on-farm infection by foodborne pathogens

Economic pressure on the modern poultry industry has directed the selection process towards fast-growing broilers that have a reduced feed conversion ratio. Selection based heavily on growth characteristics could adversely affect immune competence leaving chickens more susceptible to disease. Since the innate immune response directs the acquired immune response, efforts to select poultry with an efficient innate immune response would be beneficial. Our laboratories have been evaluating the innate immune system of two parental broiler lines to assess their capacity to protect against multiple infections. We have shown increased in vitro heterophil function corresponds with increased in vivo resistance to Gram-positive and Gram-negative bacterial infections. Additionally, there are increased mRNA expression levels of pro-inflammatory cytokines/chemokines in heterophils isolated from resistant lines compared to susceptible lines. Collectively, all data indicate there are measurable differences in innate responsiveness under genetic control. Recently, a small-scale selection trial was begun. We identified sires within a broiler population with higher and/or lower-than-average pro-inflammatory cytokine/chemokine mRNA expression levels and subsequently utilized small numbers of high-expressing and low-expressing sires to produce progeny with increased or decreased, respectively, pro-inflammatory cytokine/chemokine profiles. This novel approach should allow us to improve breeding stock by improving the overall immunological responsiveness. This will produce a line of chickens with an effective pro-inflammatory innate immune response that should improve resistance against diverse pathogens, improve responses to vaccines, and increase livability. Ongoing work from this project is providing fundamental information for the development of poultry lines that will be inherently resistant to colonization by pathogenic and food-poisoning microorganisms. Utilization of pathogen-resistant birds by the poultry production industry would significantly enhance the microbiological safety of poultry products reaching the consumer.

Gene expression profiling in chicken heterophils with Salmonella enteritidis stimulation using a chicken 44 K Agilent microarray

Background

Salmonella enterica serovar Enteritidis (SE) is one of the most common food-borne pathogens that cause human salmonellosis and usually results from the consumption of contaminated poultry products. The mechanism of SE resistance in chickens remains largely unknown. Previously, heterophils isolated from broilers with different genetic backgrounds (SE-resistant [line A] and -susceptible [line B]) have been shown to be important in defending against SE infections. To dissect the interplay between heterophils and SE infection, we utilized large-scale gene expression profiling.

Results

The results showed more differentially expressed genes were found between different lines than between infection (SE-treated) and non-infection (control) samples within line. However, the numbers of expressed immune-related genes between these two comparisons were dramatically different. More genes related to immune function were down-regulated in line B than line A. The analysis of the immune-related genes indicated that SE infection induced a stronger, up-regulated gene expression of line heterophils A than line B, and these genes include several components in the Toll-like receptor (TLR) signaling pathway, and genes involved in T-helper cell activation.

Conclusion

We found: (1) A divergent expression pattern of immune-related genes between lines of different genetic backgrounds. The higher expression of immune-related genes might be more beneficial to enhance host immunity in the resistant line; (2) a similar TLR regulatory network might exist in both lines, where a possible MyD88-independent pathway may participate in the regulation of host innate immunity; (3) the genes exclusively differentially expressed in line A or line B with SE infection provided strong candidates for further investigating SE resistance and susceptibility. These findings have laid the foundation for future studies of TLR pathway regulation and cellular modulation of SE infection in chickens.

The feathering gene is linked to degranulation and oxidative burst not cytokine/chemokine mRNA expression levels orSalmonella enteritidisorgan invasion in broilers

In the past, we showed differences in heterophil function between parental broilers (A [fast feathering] > B [slow feathering]) and their F1 reciprocal crosses (D [fast feathering] > C [slow feathering]). In the present study, we evaluated the linkage of the feathering gene to heterophil function, pro-inflammatory cytokine/chemokine mRNA expression levels, and resistance to Salmonella enteritidis organ invasion. Heterophils were isolated from 2-day-old chickens (C and D) separated into males and females - slow males and females (SM and SF), and fast males and females (FM and FF). Heterophil functions of degranulation and oxidative burst were measured. Heterophils from FF chickens (183+/-8.9) released more (P < 0.05) beta-d-glucuronidase (microM) than heterophils from SF chickens (149+/-3.7); FF heterophils (4.6 x 10(4)) generated a significantly (P < 0.05) greater oxidative burst (mean relative fluorescent units) compared with SF heterophils (4.2 x 10(4)). Interleukin-6, CXCLi2, and interferon-alpha mRNA expression levels were quantitated by real-time quantitative reverse transcriptase-polymerase chain reaction. No differences were observed between SM and FM or between SF and FF heterophils. Finally, 1-day-old chickens were administered S. enteritidis and liver/spleen organ invasion was quantitated. No differences were observed between the number of S. enteritidis-positive FF and SF chickens, but FM were significantly (P < 0.05) more resistant to S. enteritidis organ invasion than SM chickens. The data indicate degranulation and oxidative burst were linked with the feathering gene; however, interleukin-6, CXCLi2, and interferon-alpha mRNA expression levels were not. Furthermore, susceptibility to in vitro S. enteritidis organ invasion was not linked to the feathering gene.

In vivo priming heterophil innate immune functions and increasing resistance to Salmonella enteritidis infection in neonatal chickens by immune stimulatory CpG oligodeoxynucleotides

Oligodeoxynucleotides (ODN) containing CpG dinucleotides (CpG-ODN) mimic bacterial DNA and stimulate the innate immune system of vertebrates. Here, we investigated the effects of intraperitoneal (ip) administered CpG-ODN on the innate immune functions of chicken heterophils. Our results demonstrated CpG-ODN-dependent priming of chicken heterophil degranulation and oxidative burst. Heterophils from chickens treated with CpG-ODN exhibited significantly higher (p<0.05) degranulation activity compared to PBS and control ODN (ODN containing no CpG motif) treated groups when stimulated with opsonized Salmonella enterica serovar enteritidis. Similarly, oxidative burst activity, which generates bactericidal reactive oxygen species, was significantly higher (p<0.05) in heterophils from the CpG-ODN treated group than from PBS and control ODN groups when stimulated with formalin-killed S. enteritidis. The priming effects of CpG-ODN on heterophil immune functions continued at least 4 days post-treatment. In the infection study, newly hatched chickens were treated with CpG-ODN, control ODN or PBS for 24h then challenged with oral inoculation of S. enteritidis. A significant reduction (p<0.05) in colonization by S. enteritidis was observed in chickens treated with CpG-ODN. Our study provides evidence that immunostimulatory CpG-ODN potentiates the innate immune responses of heterophils and enhances resistance to infectious pathogens in neonatal chickens.

Evolution and Function of Leukocyte RNase A Ribonucleases of the Avian Species, Gallus gallus

In this study, we explore the evolution and function of two closely related RNase A ribonucleases from the chicken, Gallus gallus. Separated by approximately 10 kb on chromosome 6, the coding sequences of RNases A-1 and A-2 are diverging under positive selection pressure (dN > dS) but remain similar to one another (81% amino acid identity) and to the mammalian angiogenins. Immunoreactive RNases A-1 and A-2 (both approximately 16 kDa) were detected in peripheral blood granulocytes and bone marrow. Recombinant proteins are ribonucleolytically active (kcat = 2.6 and 0.056 s(-1), respectively), and surprisingly, both interact with human placental ribonuclease inhibitor. RNase A-2, the more cationic (pI 11.0), is both angiogenic and bactericidal; RNase A-1 (pI 10.2) has neither activity. We demonstrated via point mutation of the catalytic His110 that ablation of ribonuclease activity has no impact on the bactericidal activity of RNase A-2. We determined that the divergent domains II (amino acids 71-76) and III (amino acids 89-104) of RNase A-2 are both important for bactericidal activity. Furthermore, we demonstrated that these cationic domains can function as independent bactericidal peptides without the tertiary structure imposed by the RNase A backbone. These results suggest that ribonucleolytic activity may not be a crucial constraint limiting the ongoing evolution of this gene family and that the ribonuclease backbone may be merely serving as a scaffold to support the evolution of novel, nonribonucleolytic proteins.

Toll-like receptor agonists stimulate differential functional activation and cytokine and chemokine gene expression in heterophils isolated from chickens with differential innate responses

Heterophils isolated from distinct broilers (lines A and B) differ in function and cytokine gene expression profiles. Nothing is known about Toll-like receptor (TLR) expression nor functional activation and cytokine/chemokine gene expression of line A and B heterophils when stimulated with TLR agonists. We found that line A and B heterophils express the same range of TLRs. All the bacterial TLR agonists, peptidoglycan, the synthetic lipoprotein Pam3CSK4, ultra-pure lipopolysaccharide, and flagellin all induced significantly greater functional activation of heterophils from line A compared to B. Only stimulation with the guanosine analog, loxoribine, (LOX) induced a significantly greater functional response in B over A. Additionally, all heterophils from line A stimulated with the bacterial TLR agonists had dramatic upregulation of pro-inflammatory cytokine and chemokine mRNA expression, whereas heterophils from line B had little or no upregulation of these genes. However, stimulation of all heterophils from line B with the bacterial TLR agonists and LOX induced a significant upregulation of IFN-alpha, with little transcription of this cytokine gene in line A heterophils. These findings suggest that the difference in heterophil functional efficiency between these parent lines is due to recognition of pathogens and activation of signaling pathways that induce innate cytokine and chemokine responses.