Immune responses to an Eimeria acervulina infection in different broilers lines

Transcriptomic analysis uncovers a biphasic response to precocious Eimeria acervulina infection in chicken duodenal tissue

Live anticoccidial vaccines, either formulated with unattenuated or attenuated Eimeria parasites, are powerful stimulators of chicken intestinal immunity. Little is known about the dynamics of gene expression and the corresponding biological processes of chicken responses against infection with precocious line (PL) of Eimeria parasites. In the present study, we performed a time-series transcriptomic analysis of chicken duodenum across 15 time points from 6 to 156 hours post-infection (p.i.) with PL of E. acervulina. A high-quality profile showing two distinct changes in chicken duodenum mRNA expression was generated during the infection of Eimeria. Early response revealed that activation of the chicken immune response was detectable from 6 h.p.i., prominent genes triggered during the initiation of asexual and sexual parasite growth encompass immune regulatory effects, such as interferon gamma (IFN-γ), interferon regulatory factor 1 (IRF1), and interleukin-10 (IL10). The late response was identified significantly associating with maintaining cellular structure and activating lipid metabolic pathways. These analyses provide a detailed depiction of the biological response landscape in chickens infected by the PL of E. acervulina, contributing significant insights for the investigation of the host-parasite interactions and the management of parasitic diseases.

Behavior and Immune Response of Conventional and Slow-Growing Broilers to Salmonella Typhimurium

Fast growth rate in broiler chickens comes with welfare concerns and the contribution of growth rate to pathogen resistance and sickness behavior is relatively unknown. The objective of this study was to evaluate physiological and behavioral responses of conventional (CONV) and slow-growing (SG) male broilers challenged with Salmonella Typhimurium. CONV (n = 156) and SG (n = 156) chicks were raised in a pen with wood litter shavings until day 7 of age, when birds were transferred to 24 isolators (n = 11 chicks/isolator). On day 14 of age, half of the birds (n = 12 isolators) were challenged with S. Typhimurium (ST) and the other half (n = 12 isolators) received a control (C). On days 7, 13, 17, 21, and 24, body weight was recorded, and blood, jejunum and ileum sections were collected from 2 birds/isolator (n = 48 birds/sampling) to measure plasma IgA and IgG and intestinal histomorphology, respectively. On days 12, 16, 21, and 23, video was recorded to evaluate bird postures (sitting, standing, or locomoting) and behaviors (eating, drinking, preening, stretching, sham foraging, allopreening, and aggression). CONV birds were 70 g heavier (p = 0.03) on day 21 and 140 g heavier (p = 0.007) on day 24 than SG. On day 7, CONV jejunum villus height and crypt depth were 22 and 7 μm greater (p ≤ 0.001), respectively, than SG. On day 24, ST ileum villus height was 95 μm shorter (p = 0.009) than C. IgA increased after day 17 for all birds and at day 21, CONV IgA was greater (p = 0.01) than SG. Although SG IgG was 344 μg/ml greater (p = 0.05) than CONV on day 7, CONV IgG increased with age (p < 0.0001) to greater (p ≤ 0.03) concentrations than SG on day 21 and day 24 by 689 μg/ml and 1,474 μg/ml, respectively, while SG IgG remained at similar concentrations after day 13. Generally, a greater proportion of birds sham foraged as they aged (p < 0.0001). A greater proportion of CONV tended to sit (p = 0.09) and fewer locomoted (p < 0.0001) than SG as they aged. The results illustrate conventional and slow-growing broilers differ in their behavior, immunity, and response to Salmonella.

Dual RNA-seq transcriptome analysis of caecal tissue during primary Eimeria tenella infection in chickens

BACKGROUND

Coccidiosis is an infectious disease with large negative impact on the poultry industry worldwide. It is an enteric infection caused by unicellular Apicomplexan parasites of the genus Eimeria. The present study aimed to gain more knowledge about interactions between parasites and the host immune system during the early asexual replication phase of E. tenella in chicken caeca. For this purpose, chickens were experimentally infected with E. tenella oocysts, sacrificed on days 1-4 and 10 after infection and mRNA from caecal tissues was extracted and sequenced.

RESULTS

Dual RNA-seq analysis revealed time-dependent changes in both host and parasite gene expression during the course of the infection. Chicken immune activation was detected from day 3 and onwards with the highest number of differentially expressed immune genes recorded on day 10. Among early (days 3-4) responses up-regulation of genes for matrix metalloproteinases, several chemokines, interferon (IFN)-γ along with IFN-stimulated genes GBP, IRF1 and RSAD2 were noted. Increased expression of genes with immune suppressive/regulatory effects, e.g. IL10, SOCS1, SOCS3, was also observed among early responses. For E. tenella a general up-regulation of genes involved in protein expression and energy metabolism as well as a general down-regulation genes for DNA and RNA processing were observed during the infection. Specific E. tenella genes with altered expression during the experiment include those for proteins in rhoptry and microneme organelles.

CONCLUSIONS

The present study provides novel information on both the transcriptional activity of E. tenella during schizogony in ceacal tissue and of the local host responses to parasite invasion during this phase of infection. Results indicate a role for IFN-γ and IFN-stimulated genes in the innate defence against Eimeria replication.

Kinetics of the Cellular and Transcriptomic Response to Eimeria maxima in Relatively Resistant and Susceptible Chicken Lines

Eimeria maxima is a common cause of coccidiosis in chickens, a disease that has a huge economic impact on poultry production. Knowledge of immunity to E. maxima and the specific mechanisms that contribute to differing levels of resistance observed between chicken breeds and between congenic lines derived from a single breed of chickens is required. This study aimed to define differences in the kinetics of the immune response of two inbred lines of White Leghorn chickens that exhibit differential resistance (line C.B12) or susceptibility (line 15I) to infection by E. maxima. Line C.B12 and 15I chickens were infected with E. maxima and transcriptome analysis of jejunal tissue was performed at 2, 4, 6 and 8 days post-infection (dpi). RNA-Seq analysis revealed differences in the rapidity and magnitude of cytokine transcription responses post-infection between the two lines. In particular, IFN-γ and IL-10 transcript expression increased in the jejunum earlier in line C.B12 (at 4 dpi) compared to line 15I (at 6 dpi). Line C.B12 chickens exhibited increases of IFNG and IL10 mRNA in the jejunum at 4 dpi, whereas in line 15I transcription was delayed but increased to a greater extent. RT-qPCR and ELISAs confirmed the results of the transcriptomic study. Higher serum IL-10 correlated strongly with higher E. maxima replication in line 15I compared to line C.B12 chickens. Overall, the findings suggest early induction of the IFN-γ and IL-10 responses, as well as immune-related genes including IL21 at 4 dpi identified by RNA-Seq, may be key to resistance to E. maxima.

Dietary supplementation with anti-IL-10 antibody during a severe Eimeria challenge in broiler chickens

Attenuation of host IL-10 activity during Eimeria infection may elicit a robust Th1 response to eliminate the parasite from the gut epithelium. An experiment was conducted to study the effects of feeding IL-10 neutralizing antibody delivered via a dried egg product (DEP) on growth performance, immune responsivity, and gut health outcomes during a severe challenge with either Eimeria acervulina (study 1) or Eimeria tenella (study 2) following FDA CVM #217 protocol to test anticoccidial products. A total of 720 male Ross 308 chicks were used in each study, with 15 replicate cages of 12 birds and the following 4 treatments: sham-inoculated (uninfected) control diet (UCON), Eimeria-infected control diet (ICON), and Eimeria-infected control diet supplemented with DEP at 2 levels (165 [I-165] or 287 [I-287] U/tonne in study 1 and 143 [I-143] or 287 [I-287] U/tonne in study 2). Individual birds assigned to infected treatment groups received a single oral dose of either 200,000 E. acervulina (study 1) or 80,000 E. tenella (study 2) oocysts at 12 d of age (i.e., d post inoculation [DPI] 0), whereas uninfected birds were sham-inoculated with tap water. A one-way ANOVA was performed on outcomes including growth performance, hematology, serum chemistry profiles, immunophenotyping profiles, and intestinal lesion scores. In both studies, DPI 0 to 7 weight gain, feed intake, and feed conversion ratio were worse (P < 0.05) in all infected groups compared with the UCON group. Compared with ICON, DEP supplementation elicited no differences on overall growth performance. Histopathology and lesion scores revealed severe damage to the gut epithelium owing to the Eimeria challenge, yet DEP supplementation did not improve these outcomes or oocyst shedding, hematological measurements, or serum chemistry. However, DEP supplementation improved (P < 0.05) the percentage of circulating CD3⁺ cells at 6 DPI in study 2. These results indicate that DEP does not appear to elicit a coccidiostatic effect during a severe infection with E. acervulina or E. tenella.

Comparing performance and resistance of two broilers breeds challenged by Eimeria acervulina

The proposal on the ban of anticoccidials drugs from poultry feed highlights the importance of broiler breeders resistance to Eimeria as a criteria for animal genetic selection. The aim of this study was to compare the resistance between two commercial broiler breeds to Eimeria acervulina. Eight hundred male chicks from two commercial breeds (400 animals each) were housed from 1-42 days of age and randomly divided into 4 treatments with 8 replicates of 25 birds each. Following a factorial design, the treatments were AU, BU (breed A and B, unchallenged), AC and BC (breed A and B, challenged at 14 days of age by gavage with 1 × 106 oocysts of a field strain of E. acervulina). From 1-42 days, feed intake, body weight gain (BWG), feed conversion ratio (FCR), feed efficiency and mean weight (MW) were weekly measured. For the clinical evaluation, feces were sampled from 18 to 24 days for the counting of excreted oocysts and twenty birds per treatment were euthanized at 20 days of age for the scoring of macroscopic lesions in the gut. The breeds did not show statistical differences in performance after the Eimeria challenge in all phases. Breed A presented a higher increase in FCR from 21 to 45 days in comparison to the breed B, which presented a deeper reduction in FI, BWG and MW at all periods post-infection when compared to the breed A. Despite of the challenge, breed A presented better performance indexes (P < 0.05) up to the 28 days of age in comparison to the breed B, however, no significant difference in performance was detected between the breeds at the final age of 42 days. Regardless of the breed, the challenged birds presented significant worsens in all performance parameters from 14 to 42 days of age. The breed B presented a higher (P < 0.05) fecal count of oocysts from 19 to 21 days and higher (P < 0.05) score of macroscopic lesions in the gut at 21 days in comparison to the breed A. The clinical evaluation pointed out a lower resistance of the breed B to the E. acervulina challenge, which could result in significant impacts on the performance in field production conditions.

Poultry Coccidiosis: Design and Interpretation of Vaccine Studies

Eimeria infection impacts upon chicken welfare and economic productivity of the poultry sector. Live coccidiosis vaccines for chickens have been available for almost 70 years, but the requirement to formulate blends of oocysts from multiple Eimeria species makes vaccine production costly and logistically demanding. A multivalent vaccine that does not require chickens for its production and can induce protection against multiple Eimeria species is highly desirable. However, despite the identification and testing of many vaccine candidate antigens, no recombinant coccidiosis vaccine has been developed commercially. Currently, assessment of vaccine efficacy against Eimeria, and the disease coccidiosis, can be done only through in vivo vaccination and challenge experiments but the design of such studies has been highly variable. Lack of a "standard" protocol for assessing vaccine efficacy makes comparative evaluations very difficult, complicating vaccine development, and validation. The formulation and schedule of vaccination, the breed of chicken and choice of husbandry system, the species, strain, magnitude, and timing of delivery of the parasite challenge, and the parameters used to assess vaccine efficacy all influence the outcomes of experimental trials. In natural Eimeria infections, the induction of strong cell mediated immune responses are central to the development of protective immunity against coccidiosis. Antibodies are generally regarded to be of lesser importance. Unfortunately, there are no specific immunological assays that can accurately predict how well a vaccine will protect against coccidiosis (i.e., no "correlates of protection"). Thus, experimental vaccine studies rely on assessing a variety of post-challenge parameters, including assessment of pathognomonic lesions, measurements of parasite replication such as oocyst output or quantification of Eimeria genomes, and/or measurements of productivity such as body weight gain and feed conversion rates. Understanding immune responses to primary and secondary infection can inform on the most appropriate immunological assays. The discovery of new antigens for different Eimeria species and the development of new methods of vaccine antigen delivery necessitates a more considered approach to assessment of novel vaccines with robust, repeatable study design. Careful consideration of performance and welfare factors that are genuinely relevant to chicken producers and vaccine manufacturers is essential.

Genotype-associated differences in bursal recovery after infectious bursal disease virus (IBDV) inoculation

T-cell immune responses were shown to play an important role in the regulation of infectious bursal disease virus (IBDV) replication and development of lesions in the bursa of Fabricius (BF) (bursal lesions) but also in the recovery from the infection. Studies suggested that the host-genotype influences T-cell responses during the acute phase of infection. Genotype-related differences in the recovery phase were not investigated so far. The present study used commercial broiler- (BT), layer- (LT), dual-purpose type (DT) chicken lines as well as a specific pathogen free (SPF) LT chicken as a reference for comparison of T-cell related differences in IBDV-immunopathogenesis not only in the early phase post inoculation (pi) but also in the recovery phase. The Deventer formula was used to determine the optimal time point of inoculation with an intermediate plus IBDV strain when maternally derived antibody (MDA) titers were below the calculated breakthrough level of the virus for all genotypes. Differences in the bursal lesion development, intrabursal CD4+ and CD8+ T-cell accumulation and numbers of IBDV-positive cells were determined. In addition, anti-IBDV antibody development and the relative amount of anti-inflammatory cytokine mRNA were recorded until 28 days post IBDV inoculation. Differences between the genotypes were observed in the duration and magnitude of bursal lesions, CD4+ and CD8+ T-cell infiltration as well as the presence of anti-inflammatory Interleukin (IL)-10 and Transforming growth factor (TGF) β4 cytokine mRNA (P < 0.05). While the investigated immune parameters were comparable between the genotypes at seven days pi, during 14, 21 and 28 days pi a delayed recovery process in LT and DT chickens compared to BT chickens was observed (P < 0.05). Furthermore, the age and residual MDA levels had a genotype-dependent influence on the onset of the anti-IBDV specific humoral and T-cell mediated immune responses. This study suggests, that the impact of T-cell immunity on the recovery process after IBDV infection may need to be considered further for the development of new breeding programs for disease resistant chicken lines.

Differential immune response to Eimeria maxima infection in fast- and slow-growing broiler genotypes

Very little has been reported comparing resistance to coccidiosis in fast or slow growing broilers, the latter of which are becoming more prevalent in the broiler industry. We examined mRNA expression in the intestines of fast and slow growing broilers following Eimeria infection. We show that by day 13 post-infection (d pi) with 2500 or 7000 oocysts of Eimeria maxima, slower-growing (Ranger Classic) broilers significantly (P < 0.01) upregulated expression of proinflammatory cyclooxygenase genes (LTB4DH, PTSG1 and PTSG2) above that detected in fast growing (Ross 308) broilers. Expression of CD8α mRNA was downregulated in Ross 308 at day 6d pi with either 2500 or 7000 oocysts of E maxima (P < 0.05), compared to uninfected controls, but was not differentially expressed in Ranger Classic. CD4 genes were not differentially expressed in either chicken line infected with either infectious oocyst dose at d6 pi, compared to uninfected controls. However, at d13 pi, CD4 expression was significantly upregulated in both chicken lines infected with either infectious oocyst dose, compared to uninfected controls (P < 0.05) but this was significantly greater in Ranger Classic broilers compared to Ross 308 (P < 0.05). At d13 pi, expression of CD3 chains (required for T lymphocyte activation) was significantly increased in Ranger Classic compared to Ross 308, infected with either oocyst dose (P < 0.05-0.01). Expression of IL-2 and IL-15 mRNA, required for T lymphocyte proliferation was also significantly upregulated, or maintained longer, in Ranger Classic broilers compared to Ross 308. These differences in immune response to E maxima corresponded with a reduction in E maxima genome detected in the intestines of Ranger Classic compared to Ross 308.

Does selection for growth rate in broilers affect their resistance and tolerance to Eimeria maxima?

Chickens exhibit varied responses to infection with Eimeria parasites. We hypothesise that broilers selected for increased growth rate will show lower resistance and tolerance to a coccidian challenge. 288 chickens of fast (F) or slow (S) growing lines were inoculated with 0 (control), 2500 (low-dose), or 7000 (high-dose) sporulated E. maxima oocysts at 13 days of age in two consecutive rounds. Gain and Intake were measured daily and their values relative to BW at the point of infection were calculated over the pre-patent (days 1-4 post-infection), acute (d5-8 pi), and recovery (d9-12 pi) phases of infection to assess the impact of infection. Levels of plasma carotenoids, vitamins E and A, long bone mineralisation, caecal microbiota diversity indices, and histological measurements were assessed at the acute (d6 pi) and recovery stage (d13 pi). In addition, we measured the levels of nitric oxide metabolites and the number of parasite genome copies in the jejunumat d6pi. In absolute terms F birds grew 1.42 times faster than S birds when not infected. Infection significantly reduced relative daily gain and intake (P < 0.001), with the effects being most pronounced during the acute phase (P < 0.001). Levels of all metabolites were significantly decreased, apart from NO which increased (P < 0.001) in response to infection on d6pi, and were accompanied by changes in histomorphometric features and the presence of E. maxima genome copies in infected birds, which persisted to d13pi. Furthermore, infection reduced tibia and femur mineralisation, which also persisted to d13pi. Reductions in measured variables were mostly independent of dose size, as was the level of parasite replication. The impact of infection was similar for S and F-line birds for all measured parameters, and there were no significant interactions between line x dose size on any of these parameters. In conclusion, our results suggest that line differences in productive performance do not influence host responses to coccidiosis when offered nutrient adequate diets.

Monitoring of local CD8β-expressing cell populations during Eimeria tenella infection of naïve and immune chickens

The purpose of this study was to monitor abundance and activation of local CD8β-expressing T-cell populations during Eimeria tenella infections of naïve chickens and chickens immune by previous infections. Chickens were infected with E. tenella up to three times. Caecal T-cell receptor (TCR) γ/δ-CD8β+ cells (cytotoxic T lymphocytes; CTL) and TCRγ/δ+CD8β+ cells were characterized with respect to activation markers (blast transformation, CD25 and cell surface CD107a). Cells were also induced to degranulate in vitro as a measure of activation potential. Major findings included a prominent long-lasting, up to 6 weeks, increase in the proportion of CTL among caecal CD45+ cells in the later stages after primary E. tenella infection. These CTL also showed clear signs of activation, that is blast transformation and increased in vitro induced degranulation. At second and third E. tenella infection, chickens showed strong protective immunity but discrete signs of cellular activation were observed, for example increased in vitro induced degranulation of CTL. Thus, primary E. tenella infection induced clear recruitment and activation of local CTL. Upon subsequent infections of strongly immune chickens cellular changes were less prominent, possibly due to lower overall numbers of cells being activated because of the severe restriction of parasite replication.

Influence of dietary amino acid reductions and Eimeria acervulina infection on growth performance and intestinal cytokine responses of broilers fed low crude protein diets

Two experiments were conducted to evaluate the influence of Eimeria acervulina infection on growth performance, plasma carotenoids, and intestinal cytokine responses of broilers fed low crude protein (LCP) diets with reduced concentrations of selected amino acids (AA). Experiment 1 was conducted to validate a dietary formulation approach in which broilers were fed 1 of 5 diets including a 19.0% CP corn-soybean meal based (CSBM) diet, a LCP control diet (16.7% CP) that matched the AA profile of the CSBM diet, and 3 LCP diets with 30% reductions in standardized ileal digestible concentrations of TSAA, Lys, or Thr from 14 to 23 d post-hatch. Body weight gain and G:F were greatest (P < 0.05) and similar for broilers fed the CSBM and LCP control diets, whereas reductions in Thr, TSAA, and Lys each decreased (P < 0.05) G:F of broilers. In Experiment 2, birds were allotted to 18 treatment groups in a factorial arrangement of 9 dietary treatments × 2 infection states. Dietary treatments included a LCP control diet similar to that fed in Experiment 1 and 8 LCP diets with 40% individual reductions in TSAA, Lys, Thr, Val, Ile, Arg, Phe + Tyr, or Gly + Ser. Broilers received experimental diets from 10 d to 28 d post-hatch and were inoculated with 0 or 4.0 × 10⁵ sporulated E. acervulina oocysts at 15 d. Decreased (P < 0.05) growth performance (10 to 28 d) of broilers was observed with each AA reduction, except Phe + Tyr, compared with birds fed the LCP control diet. Body weight gain and G:F were lowest (P < 0.05) for birds fed diets reduced in Lys or Val. Eimeria acervulina decreased growth performance and plasma carotenoids of broilers, but effects varied among dietary treatment groups as indicated by diet × infection interactions (P < 0.05). Dietary AA reductions did not alter (P > 0.05) the increase in intestinal gene expression of interferon-γ, interleukin-1β, or interleukin-10 observed in E. acervulina-infected birds.

Effect of Eimeria acervulina infection history on the immune response and transmission in broilers

Heterogeneity in exposure to Eimeria spp. of chickens in a flock will result in differences between individual birds in oocyst output and acquired immunity, which subsequently affects transmission of the parasite in the population. The aim of this study was to quantify effects of previous infection of broilers with Eimeria acervulina on immune responses, oocyst output and transmission. A transmission experiment was carried out with pair-wise housed broilers, that differed in infection history. This "infection history" was achieved by establishment of a primary infection by inoculation of birds with 50,000 sporulated E. acervulina oocysts at day 6 of age ("primed"); the other birds did not receive a primary infection ("naïve"). The actual transmission experiment started at day 24 of age: one bird (I) was inoculated with 50,000 sporulated oocysts and was housed together with a non-inoculated contact bird (C). Oocyst excretion and parameters describing transmission, i.e. the number of infected C birds and time passed before start of excretion of C birds, were determined from day 28 to day 50 for six pairs of four different combinations of I and C birds (I-C): naïve-naïve, naïve-primed, primed-naïve and primed-primed. Immune parameters, CD4(+), CD8(+), αβTCR(+) and γδTCR(+) T cells and macrophages in duodenum, were determined in an additional 25 non-primed, non-inoculated control birds, and in the naïve-naïve and naïve-primed groups, each group consisting of 25 pairs. Although the numbers of CD4(+) T cells and γδTCR(+) T cells increased after primary infection, none of the immunological cell types provided an indication of differences in infectivity, susceptibility or transmission between birds. Oocyst output was significantly reduced in primed I and C birds. Transmission was reduced most in the primed-primed group, but nonetheless transmission occurred in all groups. This study also showed that acquired immunity significantly reduced oocyst output after inoculation and contact-infection, but not sufficiently to prevent transmission to contact-exposed birds.

Efficacy of DNA vaccines carrying Eimeria acervulina lactate dehydrogenase antigen gene against coccidiosis

The efficacies of DNA vaccines encoding either Eimeria acervulina lactate dehydrogenase (LDH) antigen or a combination of LDH antigen and chicken IL-2 or IFN-gamma were evaluated against chicken coccidiosis. Three vaccine plasmids pVAX-LDH, pVAX-LDH-IFN-gamma and pVAX-LDH-IL-2 were constructed using the eukaryotic expression vector pVAX1. Expressions of proteins encoded by plasmids DNA in vivo were detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot assay. Average body weight gain, oocyst output, survival rate and lesion scores were measured to evaluate the protective effects of vaccination on challenge infection. The results showed that DNA vaccines could obviously alleviate body weight loss, duodenal lesions, oocyst output and enhance oocyst decrease ratio. Anti-coccidial indexes (ACIs) of pVAX-LDH-IFN-gamma and pVAX-LDH-IL-2 groups were higher than that of other groups. Flow cytometric analysis of T lymphocytes in spleen and cecal tonsil demonstrated that DNA vaccines had significantly increased percentages of CD3(+) T cells compared with pVAX1 alone or TE buffer. The results provided the first proof that DNA vaccine carrying E. acervulina LDH antigen gene induced protective immunity against homologous infection and its effect could be enhanced by co-expression of chicken IL-2 or IFN-gamma.