Genetic and phenotypic correlations between antibody responses to Escherichia coli, infectious bursa disease virus (IBDV), and Newcastle disease virus (NDV), in broiler lines selected on antibody response to Escherichia coli

Modern broiler chickens exhibit a differential gastrointestinal immune and metabolic response to repeated CpG injection relative to a 1950s heritage broiler breed

The Athens Canadian Random Bred (ACRB) heritage broiler breed, which has not been selectively bred since the 1950s, is a point of comparison to the modern-day broiler and could highlight potential genetic-derived differences in immune responses. To observe the modern and heritage birds' immune responses in action, the innate immune ligand CpG oligonucleotides were administered at multiple time points through the birds' lives from the day after hatch to day 35 post-hatch. This study allowed for the observation of changes in metabolic and immune signaling in response to repeated injections of a known Toll-like receptor (TLR) ligand, CpG. Jejunum and cecal tonsil samples at multiple time points during grow out were collected and used for kinome array analysis to measure kinase activity in immunometabolic signaling pathways in the gut tissue. In addition cytokine gene expression was measured in these tissues. The modern birds' response to the treatment was more innate and showed evidence of metabolic energy shift. The heritage birds' response to the treatment was adaptive, with metabolic changes indicative of a well-regulated response. Overall, the results from this study suggest that modern broiler chickens do not adequately balance resources between growth and immune responses during an immune challenge, and this deficit is most evident around the 2-week post-hatch time point. This is a critical time for these birds, as their muscle deposition continues to accelerate, and they are vulnerable to disease challenges. Ideally, future work can clarify the reason for this response discrepancy in the modern broiler and therapeutic interventions to rescue this phenotype could be elucidated.

Genetic resistance to avian pathogenic Escherichia coli (APEC): current status and opportunities

Infections with avian pathogenic Escherichia coli (APEC) can be extremely detrimental to poultry health and production. Investigating host genetic variation could identify the biological mechanisms that control resistance to this pathogen and allow selection for improved resistance in experimental and commercial poultry populations. In this review, the current knowledge of how host genetics contributes to APEC resistance and future opportunities that would benefit the understanding or application of genetic resistance are discussed. Phenotypes, such as antibody responses, lesion scores, and mortality, revealed that genetic background impacts APEC resistance and interacts with other factors including the environment and challenge conditions. Experiments have used divergent selection for APEC-specific antibody levels to facilitate genetic studies, estimated heritabilities in relevant traits, detected quantitative trait loci using microsatellites, and made associations with sequence variation in the major histocompatibility complex, which collectively suggest that improving APEC resistance through selection is feasible, although genetic control is partial, complex, and highly polygenic. Additionally, functional genomics techniques have identified antimicrobial responses, toll-like receptor and cytokine signalling, and the cell cycle as central pathways in the host response to APEC challenge. Opportunities for future research are discussed, including the expansion of existing lines of research and the application of new technologies that are relevant to the study of host genetics and APEC. This review closes with prospective strategies for improvement of host genetic resistance to APEC.

An association between genetic variation in the roundabout, axon guidance receptor, homolog 2 gene and immunity traits in chickens

The roundabout, axon guidance receptor, homolog 2 (ROBO2) gene is one member of the roundabout (ROBO) family, which belongs to the immunoglobulin superfamily. The ROBO molecules are known to function in axon guidance and cell migration and are involved in SLIT/ROBO signaling. In this study, we obtained the full-length cDNA sequence of the chicken ROBO2 gene. Sequence analysis indicated that 3 SNP (1418G > A, 1421C > A and 2462T > C) exist in exons 5 and 12 of the ROBO2 gene. Genotyping results revealed that the allele frequency of SNP 1421C > A was similar in all tested breeds, but the allele frequencies of the other 2 SNP were different between White Leghorn and Chinese indigenous chickens. Allele G of 1418G > A and allele T of 2462T > C predominated in the Chinese indigenous breed, whereas alleles A and C predominated in the White Leghorn breed. Association analyses revealed that birds with the GG genotype of SNP 1418G > A or the TT genotype of SNP 2462T > C had significantly higher antibody responses to Newcastle disease virus (NDV_S/P; P < 0.01) than carriers of the A allele (GA and AA) or the C allele (TC), respectively. Real-time PCR further revealed that ROBO2 expression in the spleens of the birds with higher antibody responses (GG and TT genotypes at SNP 1418 and 2462, respectively) was significantly higher than in the spleens of birds with the AA and AG genotypes at SNP 1418 or the TC genotype at SNP 2462 (P < 0.01). The results demonstrated that genetic variation at the ROBO2 gene plays a key role in the immune response to Newcastle disease virus, and SNP 1418G > A and 2462T > C can be used as genetic markers for the selection of chickens with stronger immune responses to Newcastle disease virus.

In vitro rapid clearance of infectious bursal disease virus in peripheral blood mononuclear cells of chicken lines divergent for antibody response might be related to the enhanced expression of proinflammatory cytokines

Infectious bursal disease (IBD) is an acute and highly contagious viral disease of young chickens caused by infectious bursal disease virus (IBDV). An effective way to control IBDV would be to breed chickens with a reduced susceptibility to IBDV infection. In the present work, we used chickens selected for high and low specific responses to sheep red blood cells (SRBC) (H and L, respectively) to assess the susceptibility of differential immune competent animals to IBDV infection. The peripheral blood mononuclear cells (PBMCs) of high SRBC line (HL) and low SRBC line (LL) were infected with IBDV and viral RNA loads were determined at different time post-IBDV infection. Chicken orthologues of the T helper 1 (Th1) cytokines, interferon-γ (IFN-γ) and interleukin-2 (IL-2); a Th2 cytokine, IL-10; a pro inflammatory cytokine, IL-6; the CCL chemokines, chCCLi2, chCCLi4 and chCCLi7; colony stimulating factor, GM-CSF; and a anti-inflammatory cytokine, transforming growth factor β-2 (TGFβ-2) were quantified. The expression of chCCLi2, chCCLi4 and chCCLi7 was significantly higher in L line as compared to H line. However, in H line the viral RNA loads were significantly lower than in L line. Therefore, the upregulated chemokines might be associated with the susceptibility to IBDV. The expression of IFN-γ, IL-2 and IL-6 was significantly higher in H line as compared to L line. We assume that the higher proinflammatory cytokines expression in H line might be related to the rapid clearance of virus from PBMCs. Significantly higher levels of IL-10 and TGFβ-2 mRNAs in L line might be related to the pathogenesis of IBDV. In conclusion, selection for antibody responses appears to influence the expression profiles of chemokines and cytokines against IBDV. Further, the selection for high SRBC response might improve the immuno-competence of chickens against IBDV.

Differences in genetic background influence the induction of innate and acquired immune responses in chickens depending on the virulence of the infecting infectious bursal disease virus (IBDV) strain

Previous studies and field observations have suggested that genetic background influences infectious bursal disease virus (IBDV) pathogenesis. However, the influence of the virulence of the infecting IBDV strain and the mechanisms underlying the differences in susceptibility are not known. In the present study IBDV pathogenesis was compared between specific-pathogen-free layer-type (LT) chickens, which are the most susceptible chicken for IBDV and have been used as the model for pathogenesis studies, and broiler-type (BT) chickens, which are known to be less susceptible to clinical infectious bursal disease (IBD). The innate and acquired immune responses were investigated after inoculation of an intermediate (i), virulent (v) or very virulent (vv) strain of IBDV. IBDV pathogenesis was comparable among genetic backgrounds after infection with iIBDV. After infection with vIBDV and vvIBDV, LT birds showed severe clinical disease and mortality, higher bursal lesion scores and IBDV-antigen load relative to BT birds. Circulating cytokine induction varied significantly in both timing and quantity between LT and BT birds and among virus strains (P<0.05). Evaluation of different immune cell populations by flow-cytometric analysis in the bursa of Fabricius provided circumstantial evidence of a stronger local T cell response in BT birds vs. LT birds after infection with the virulent strain. On the other hand, LT birds showed a more significant increase in circulating macrophage-derived immune mediators such as total interferon (IFN) and serum nitrite than BT birds on days 2 and 3 post-vIBDV infection (P<0.05). Stronger stimulation of innate immune reactions especially after vIBDV infection in the early phase may lead to faster and more severe lesion development accompanied by clinical disease and death in LT chickens relative to BT chickens. Interestingly, no significant differences were seen between genetic backgrounds in induction of the IBDV-specific humoral response: timing of IBDV-antibody induction and antibody levels were comparable between BT and LT birds. This study clearly demonstrates a significant influence of chickens' genetic background on disease outcome. The difference between backgrounds in IBDV susceptibility is further influenced by the virulence of the infecting virus strain.

Emerging diseases, zoonoses and vaccines to control them

Vaccination, when available, is undoubtedly the most cost-effective means of preventing and controlling, and even eradicating, infectious diseases. In recent years vaccination has also been used for other purposes in animal health, production and welfare, e.g. immunocastration. Vaccination of animals serves many different purposes, such as controlling animal infections and infestations, thus improving animal health and welfare; controlling anthropozoonoses and food poisoning in humans, thereby protecting public health; solving problems associated with antibiotic and anthelmintic resistance; helping to leave food-producing animals free of chemical residues; protecting the environment and biodiversity and ensuring animal farming sustainability. The problem is nevertheless more complex when facing emerging or re-emerging infections particularly zoonotic ones.

Stress response differences and disease susceptibility reflected by heterophil to lymphocyte ratio in turkeys selected for increased body weight

Three genetic lines of turkeys were compared for their responses to Escherichia coli challenge following dexamethasone injection (Dex) or E. coli challenge preceding transport stress (TS). The turkey lines were a slow growing line selected for increased egg production (Egg line), a fast growing line selected for increased 16-wk BW (F line), and a commercial line (Comm line). At 14 wk of age, the Dex group was treated with 3 injections of 2 mg of Dex/kg of BW followed by airsac challenge with 100 cfu of E. coli. The TS group was given the same E. coli challenge at 1 x 10(4) cfu/bird without Dex treatment, and was subjected to transport stress, including 12 h of holding time in a transport vehicle, 8 d after the challenge. All treated birds and untreated control birds were bled at the same time, which was 1 d after transport and 9 d after challenge with E. coli. The main effect mean (MEM) total leukocyte counts (WBC) and the percentages of eosinophils (Eos) and basophils (Baso) were the same for all 3 lines; however, the MEM percentages of heterophils (Het) and monocytes (Mono) and the heterophil/lymphocyte ratio (H/L) were lower and the percentage of lymphocytes (Lym) was higher in the Egg line compared with the 2 fast-growing lines. Both stress treatments increased WBC, Het, and H/L and decreased Lym in all 3 lines; however, these effects were significantly greater in both fast growing lines compared with the Egg line. Sixteen-week BW was unaffected by either treatment in the Egg line and was decreased by both treatments in the Comm line and by the Dex treatment in the F line. Main effect mean airsacculitis score (AS) was not affected by line and was significantly increased by TS and Dex treatments. Neither treatment affected AS of the Egg line birds, whereas Dex treatment increased AS of the F line, and both Dex and TS increased AS of the Comm line. Mortality was significantly higher in the Comm line compared with the Egg line and was intermediate in the F line. The differences between these lines in their disease resistance and physiological response to stress in 2 stress models suggests that increasing selection for BW of turkeys is accompanied by changes in the stress response resulting in increased susceptibility to opportunistic bacterial infection.

Directional selection for specific sheep cell antibody responses affects natural rabbit agglutinins of chickens

Agglutination data from generations 8 through 19 indicate that bidirectional selection for specific SRBC antibody responses was successful in a line cross of ISA x Warren medium heavy layers. After 11 generations titers of the high SRBC selected line (H line) were nearly 1:32,000; those of the low SRBC selected line (L line) were less than 1:2, but titers of the randombred control line remained stable at 1:32. Directional SRBC selection also affected levels of a naturally occurring rabbit cell agglutinating antibody (RRBC), presumably the avian form of alpha-galactose antibody (anti-Gal). This indirect response was biphasic and opposite in direction to the SRBC responses through generation 14 after which anti-Gal titers of all 3 lines increased. At generation 19, line H had the highest agglutinin titers; of both types, control line was intermediate, and line L was lowest. The correlation between SRBC and RRBC titers was 0.43 (P = 0.0). Females had higher titers than males, but the difference was only significant for the SRBC antibody (P = 0.028). Qualitative changes in anti-Gal accompanied SRBC selection. Rabbit agglutinins of 4 types were recognizable: classic, granular, annular, and one negative or very weak reaction. The score type means in line L were highest, in the control line were intermediate, and in line H were lowest, suggesting avidity differences now exist among these lines. The results show integration of natural and acquired immune systems because selection for one temporarily affected the other. Given the importance of anti-Gal in primates, our results should stimulate further study of this antibody in poultry species.

Microsatellite markers associated with quantitative trait loci controlling antibody response to Escherichia coli and Salmonella enteritidis in young broilers

A unique resource population was produced to facilitate detection of microsatellite markers associated with quantitative trait loci controlling antibody (Ab) response in broiler chickens. Three F1 males were produced by mating two lines divergently selected on Ab response to Escherichia coli vaccination. Each F1 male was mated with females from four genetic backgrounds: F1, high-Ab line (HH), low-Ab line and commercial line, producing three resource families, each with four progeny types. About 1700 chicks were immunized with E. coli and Salmonella enteritidis vaccines. Selective genotyping was conducted on the individuals with highest or lowest average Ab to E. coli and S. enteritidis within each progeny type in each sire family. Twelve markers were significantly associated with Ab to E. coli and six of them were also associated with Ab to S. enteritidis, mostly exhibiting a similar low effect (approximately 0.35 phenotypic SD) in all progeny types. Four markers exhibited a highly significant and much larger effect (approximately 1.7 SD), but only in progeny of females from the HH, suggesting that a backcross to the high parental line should be preferred over the commonly used F2 population. Results from two markers suggested a quantitative trait locus on chromosome 2 around 400 cM. The marker MCW0083, significant in two sire families, is closely linked to the bone morphogenetic protein 2 (BMP2) gene, known to be associated with the control of T-cell transformation in humans.