Global gene expression analysis of chicken caecal response to Campylobacter jejuni

Avian campylobacteriosis, prevalence, sources, hazards, antibiotic resistance, poultry meat contamination, and control measures: a comprehensive review

Avian campylobacteriosis is a vandal infection that poses human health hazards. Campylobacter is usually colonized in the avian gut revealing mild signs in the infected birds, but retail chicken carcasses have high contamination levels of Campylobacter spp. Consequently, the contaminated avian products constitute the main source of human infection with campylobacteriosis and result in severe clinical symptoms such as diarrhea, abdominal pain, spasm, and deaths in sensitive cases. Thus, the current review aims to shed light on the prevalence of Campylobacter in broiler chickens, Campylobacter colonization, bird immunity against Campylobacter, sources of poultry infection, antibiotic resistance, poultry meat contamination, human health hazard, and the use of standard antimicrobial technology during the chicken processing of possible control strategies to overcome such problems.

Transcriptomic analysis of caecal tissue in inbred chicken lines that exhibit heritable differences in resistance to Campylobacter jejuni

BACKGROUND

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans and the handling or consumption of contaminated poultry meat is a key source of infection. Selective breeding of poultry that exhibit elevated resistance to Campylobacter is an attractive control strategy. Here we studied the global transcriptional response of inbred chicken lines that differ in resistance to C. jejuni colonisation at a key site of bacterial persistence.

RESULTS

Three-week-old chickens of line 6₁ and N were inoculated orally with C. jejuni strain M1 and caecal contents and tonsils were sampled at 1 and 5 days post-infection. Caecal colonisation was significantly lower in line 6₁ compared to line N at 1 day post-infection, but not 5 days post-infection. RNA-Seq analysis of caecal tonsils of both lines revealed a limited response to C. jejuni infection compared to age-matched uninfected controls. In line N at days 1 and 5 post-infection, just 8 and 3 differentially expressed genes (DEGs) were detected (fold-change > 2 and false-discovery rate of < 0.05) relative to uninfected controls, respectively. In the relatively resistant line 6₁, a broader response to C. jejuni was observed, with 69 DEGs relating to immune regulation, cell signalling and metabolism at 1 day post-infection. However, by day 5 post-infection, no DEGs were detected. By far, the greatest number of DEGs were between uninfected birds of the two lines implying that differential resistance to C. jejuni is intrinsic. Of these genes, several Major Histocompatibility Complex class I-related genes (MHCIA1, MHCBL2 and MHCIY) and antimicrobial peptides (MUC2, AvBD10 and GZMA) were expressed to a greater extent in line N. Two genes within quantitative trait loci associated with C. jejuni colonisation were also more highly expressed in line N (ASIC4 and BZFP2). Quantitative reverse-transcriptase PCR analysis of a subset of transcripts confirmed the RNA-Seq results.

CONCLUSIONS

Our data indicate a limited transcriptional response in the caecal tonsils of inbred chickens to intestinal colonisation by Campylobacter but identify a large number of differentially transcribed genes between lines 6₁ and N that may underlie variation in heritable resistance to C. jejuni.

The Probiotic Lactobacillus fermentum Biocenol CCM 7514 Moderates Campylobacter jejuni-Induced Body Weight Impairment by Improving Gut Morphometry and Regulating Cecal Cytokine Abundance in Broiler Chickens

Simple Summary

High consumption of chicken meat and derived products has been associated with Campylobacter jejuni infections in humans. Probiotics have been exploited successfully with the aim of preventing colonization by unwanted microorganisms in birds. In this research, we investigated the effects of Lactobacillus fermentum Biocenol CCM 7514 supplementation on body weight, morphometry of the intestine and the cecal cytokine response. Probiotic-treated chickens showed higher body weight values than those exposed to C. jejuni or reared under control conditions. These differences in body weight were correlated to the overall characteristics of the small intestine, with larger villi and deeper crypts, observed in chickens administered with L. fermentum; such conditions are known to favor nutrient absorption. Likewise, body weight proved to be correlated to transcript abundance of IL-1β and IL-13. In probiotic-treated birds, such factors were upregulated in comparison to what was detected in C. jejuni-infected chickens; these interleukins are considered crucial in the response to invading pathogens. Clearly, these results show that administration of this probiotic strain lessens the negative effects elicited by C. jejuni and ultimately improves chicken body weight.

Abstract

This research was conducted to investigate if the administration of the probiotic Lactobacillus fermentum could influence body weight, intestinal morphometry and the cecal cytokine response in Campylobacter jejuni-infected chickens. Seventy-two 1-day old COBB 500 male chicks were allocated randomly into four experimental groups. (I) Control group (C), in which chicks were left untreated. (II) LB group, treated with L. fermentum. (III) Cj group, infected with C. jejuni and (IV) coexposure group in which both bacteria were administered. Body weight was registered and then all birds were slaughtered; samples from the small intestine and caecum were collected at 4- and 7-days post infection. The experiment lasted eleven days. Villi height and crypt depth ratios of the duodenum, jejunum and ileum were evaluated using appropriate software, while reverse transcription quantitative PCR (RT-qPCR) was utilized for assessing transcript levels of key cecal inflammatory cytokines (IL-1β, IL-18, IL-17, IL-15, IL13 and IL-4). Campylobacter-infected birds showed lower body weight values than those supplemented with the probiotic; these birds, in turn, proved to be heavier than those reared under control conditions. L. fermentum administration improved morphometrical parameters of the duodenum, jejunum and ileum; in general, villi were larger and crypts deeper than those identified in control conditions. Moreover, the negative effects elicited by C. jejuni were not observed in chickens exposed to the probiotic. Significant differences were also determined with regards to transcript abundance of all evaluated cytokines in the caecum. C. jejuni induced a downregulation of the studied interleukins; however, such a response was heightened by administration of L. fermentum, with an increase rate of transcription that promoted a more effective response to a C. jejuni infection. The effects of experimental treatments proved to vary between sampling points. Conclusively, these results demonstrate that L. fermentum lessens the negative effects elicited by C. jejuni on body weight by alleviating the impact on intestinal morphometry and cecal cytokine response, which ultimately improve chicken growth performance.

Quantitative trait loci and transcriptome signatures associated with avian heritable resistance to Campylobacter

Campylobacter is the leading cause of bacterial foodborne gastroenteritis worldwide. Handling or consumption of contaminated poultry meat is a key risk factor for human campylobacteriosis. One potential control strategy is to select poultry with increased resistance to Campylobacter. We associated high-density genome-wide genotypes (600K single nucleotide polymorphisms) of 3000 commercial broilers with Campylobacter load in their caeca. Trait heritability was modest but significant (h² = 0.11 ± 0.03). Results confirmed quantitative trait loci (QTL) on chromosomes 14 and 16 previously identified in inbred chicken lines, and detected two additional QTLs on chromosomes 19 and 26. RNA-Seq analysis of broilers at the extremes of colonisation phenotype identified differentially transcribed genes within the QTL on chromosome 16 and proximal to the major histocompatibility complex (MHC) locus. We identified strong cis-QTLs located within MHC suggesting the presence of cis-acting variation in MHC class I and II and BG genes. Pathway and network analyses implicated cooperative functional pathways and networks in colonisation, including those related to antigen presentation, innate and adaptive immune responses, calcium, and renin–angiotensin signalling. While co-selection for enhanced resistance and other breeding goals is feasible, the frequency of resistance-associated alleles was high in the population studied and non-genetic factors significantly influenced Campylobacter colonisation.

Effects of Lactobacillus Fermentum Supplementation on Body Weight and Pro-Inflammatory Cytokine Expression in Campylobacter Jejuni-Challenged Chickens

Due to the interest in using probiotic bacteria in poultry production, this research was focused on evaluating the effects of Lactobacillus fermentum Biocenol CCM 7514 administration on body weight gain and cytokine gene expression in chickens challenged with Campylobacter jejuni. One-hundred and eight 1-day old COBB 500 broiler chickens were equally assigned to four experimental groups at random. In the control group (C) chicks were left untreated, whereas in groups LB and LBCj a suspension of L. fermentum was administered. A suspension of C. jejuni was subsequently applied to groups Cj and LBCj. Body weight was registered, and the individuals were later slaughtered; cecum samples were collected at 12, 36 and 48 h post-infection (hpi). The entire experiment lasted seven days. Reverse transcription quantitative PCR (RT-qPCR) was used to determine expression levels of IL-1β, IL-15, IL-17, and IL-18 at each time point. Pathogen-infected individuals were observed to weigh significantly less than those fed with the probiotic. Significant differences were also found in transcript abundance; expression of IL-15 was downregulated by the probiotic and upregulated by C. jejuni. The effects of bacterial treatments were time-dependent, as the expression profiles differed at later stages. The present outcomes demonstrate that L. fermentum both reduces the impact of C. jejuni infection on chicken body weight and regulates positively pro-inflammatory cytokine expression, which ultimately increase bird well-being and improves production.

Campylobacter-derived ligands induce cytokine and chemokine expression in chicken macrophages and cecal tonsil mononuclear cells

Campylobacter jejuni colonizes the chicken gut at a high density without causing disease. However, consumption of poultry products contaminated with this bacterium causes gastroenteritis in humans. Therefore, it is critically important to reduce the Campylobacter burden in poultry products to prevent transmission to humans. Evidence indicates that enhancing intestinal mucosal immune responses is of paramount importance for preventing or reducing Campylobacter colonization in chickens. In view of this, the present study was undertaken to evaluate host responses to different C. jejuni-derived ligands, including lipooligosaccharide (LOS), outer membrane proteins (OMPs), and genomic DNA, with the ultimate goal of identifying a ligand with potent immunostimulatory capacity to serve as a mucosal vaccine adjuvant against enteric infections in chickens. The results revealed that C. jejuni pathogen-associated molecular patterns (PAMPs) varied in their ability to induce the expression of cytokines and chemokines in chicken macrophages and cecal tonsil mononuclear cells and nitric oxide production in macrophages. In addition, C. jejuni OMPs demonstrated superior activity over LOS and DNA ligands in eliciting cytokine expression associated with T helper (Th)1 and Th2 responses (interferon [IFN]-γ and interleukin [IL]-13, respectively), in addition to expression of pro-inflammatory cytokines (IL-1β), chemokine (CXCLi2), and regulatory cytokines (IL-10 and TGFβ1/4) in cecal tonsil cells. Importantly, in addition to their ability to induce innate responses, OMPs could also function as antigens to elicit C. jejuni-specific antibody responses and thereby confer dual protection against C. jejuni infection. Further studies are required to assess the protective efficacy of C. jejuni OMPs against C. jejuni infection in chickens.

Indole Treatment Alleviates Intestinal Tissue Damage Induced by Chicken Coccidiosis Through Activation of the Aryl Hydrocarbon Receptor

Indoles, as the ligands of aryl hydrocarbon receptor (AhR), have been shown to possess immune-modulating property in terms of the balancing between regulatory T cells (Treg) and T helper 17 cells (Th17) activities. In the present study, we examined the effects of dietary indoles, 3,3′-diindolylmethane (DIM) and indole-3-carbinol (I3C), on CD4⁺T cell population and functions in chickens. Furthermore, the effects of dietary DIM treatment on chicken coccidiosis caused by an apicomplexan parasite were investigated. Dietary treatment of healthy chickens with DIM and I3C induced increased CD4⁺CD25⁺ (Treg) cells and the mRNA expression of IL-10, while decreasing number of CD4⁺IL-17A⁺ (Th17) cells and Th17-related cytokines transcripts expression in the intestine. In addition, we explored the role of AhR in indole-treated splenic lymphocytes by using AhR antagonist and our results suggested that DIM is a ligand for chicken AhR. In chicken coccidiosis, treatment of DIM increased the ratio of Treg/Th17 cells and significantly reduced intestinal lesion although no significant changes in body weight and fecal oocyst production were noted compared to non-treated control group. These results indicate that DIM is likely to affect the ratios of Treg/Th17 reducing the level of local inflammatory response induced by Eimeria or facilitate repairing process of inflamed gut following Eimeria infection. The results described herein are thus consistent with the concept that AhR ligand modulates the T cell immunity through the alteration of Treg/Th17 cells with Treg dominance. To our knowledge, present study is the first scientific report showing the effects of dietary indole on T cell immunity in poultry species.

Intestinal colonization and acute immune response in commercial turkeys following inoculation with Campylobacter jejuni constructs encoding antibiotic-resistance markers

Consumption of contaminated poultry products is one of the main sources of human campylobacteriosis, of which Campylobacter jejuni subsp. jejuni (C. jejuni) is responsible for approximately 90% of the cases. At slaughter, the ceca of commercial chickens and turkeys are the main anatomical site where C. jejuni asymptomatically colonizes. We have previously colonized commercial turkey poults with different isolates of C. jejuni and evaluated different media to best enumerate Campylobacter from intestinal samples, but the host-response is unknown in turkeys. Enumeration of Campylobacter (colony forming units (cfu)/gram of intestinal contents) can be challenging, and can be confounded if animals are colonized with multiple species of Campylobacter. In order to precisely enumerate the C. jejuni isolate used to experimentally colonize turkeys, constructs of C. jejuni (NCTC 11,168) were tagged with different antibiotic resistance markers at the CmeF locus (chloramphenicol (CjCm) or kanamycin (CjK)). We sought to examine the kinetics of intestinal colonization using the antibiotic resistant constructs, and characterize the immune response in cecal tissue of turkeys. In vitro analysis of the tagged antibiotic-resistant constructs demonstrated no changes in motility, morphology, or adherence and invasion of INT-407 cells compared to the parent isolate NCTC 11,168. Two animal experiments were completed to evaluate intestinal colonization by the constructs. In experiment 1, three-week old poults were colonized after oral gavage for 14 days, and CjCm and CjK cfu were recovered from cecal, but not ileal contents. In experiment 2, nine-week old poults were orally inoculated with CjCm, and the abundance of CjCm cfu/g of cecal contents significantly decreased beyond 14 days after inoculation. Significant lesions were detected in CjCm colonized poults at day 2 post-colonization. Using immunohistochemistry, Campylobacter antigen was detected in between cecal villi by day 7 of CjCm colonized poults. Quantitative RT-PCR of CjCm-colonized cecal tissue demonstrated significant down-regulation of IL-1β, IL-10 and IL-13 mRNA, and significant up-regulation of IL-6, IL-8, IL-17 A, IL-22 and IFNγ mRNA on day 2, and for some on day 7 post-colonization. All differentially expressed genes were similar to mock-infected poults by day 14. These data suggest that C. jejuni induced a brief inflammatory response in the cecum of poults that quickly resolved. Results from this study provide valuable insight into host-response and persistent colonization of the turkey cecum. These findings will help to develop and test strategies to promote food safety in commercial turkeys.

Purification and Characterization of a Novel Anti-Campylobacter Bacteriocin Produced by Lactobacillus curvatus DN317

The lactic acid bacteria (LAB) microbiota of Saudi chicken ceca was determined. From 60 samples, 204 isolates of lactic acid bacteria were obtained. Three isolates produced antimicrobial activities against Campylobacter jejuni, Listeria monocytogenes, and Bacillus subtilis. The isolate DN317, which had the highest activity against Campylobacter jejuni ATCC 33560, was identified as Lactobacillus curvatus (GenBank accession numbers: KX353849 and KX353850). Full inhibitory activity was observed after a 2-h incubation with the supernatant at pH values between 4 and 8. Only 16% of the activity was conserved after a treatment at 121 °C for 15 min. The use of proteinase K, pepsin, chymotrypsin, trypsin, papain, and lysozyme drastically reduced the antimicrobial activity. However, lipase, catalase, and lysozyme had no effect on this activity. The active peptide produced by Lactobacillus curvatus DN317 was purified by precipitation with an 80% saturated ammonium sulfate solution, and two steps of reversed phase HPLC on a C18 column. The molecular weight of this peptide was 4448 Da as determined by MALDI-ToF. N-terminal sequence analysis using Edman degradation revealed 47 amino acid residues (UniProt Knowledgebase accession number C0HK82) revealing homology with the amino acid sequences of sakacin P and curvaticin L442. The antimicrobial activity of the bacteriocin, namely curvaticin DN317, was found to be bacteriostatic against Campylobacter jejuni ATCC 33560. The use of microbial antagonism by LAB is one of the best ways to control microorganisms safely in foods. This result constitutes a reasonable advance in the antimicrobial field because of its potential applications in food technology.

Invasive behavior of Campylobacter jejuni in immunosuppressed chicken

Campylobacter jejuni is a predominant cause of gastroenteritis in humans but rather harmless in chickens. The basis of this difference is unknown. We investigated the effect of the chicken immune defense on the behavior of C. jejuni using glucocorticoid (GC)-treated and mock-treated 17-day old Ross 308 chicken bearing in mind that GCs have immunosuppressive effects and dampen the innate immune response. The effect of GC administration on the behavior of C. jejuni was compared with that on infection with Salmonella Enteritidis to address possible microbe-associated differences. Our results revealed that GC treatment fastened the intestinal colonization of C. jejuni (p < 0.001) and enhanced its dissemination to the liver (p = 0.007). The effect of GC on intestinal colonization of S. Enteritidis was less pronounced (p = 0.033) but GC did speed up the spread of this pathogen to the liver (p < 0.001). Cytokine transcript analysis showed an up to 30-fold reduction in baseline levels of IL-8 mRNA in the cecal (but not spleen) tissue at Day 1 after GC treatment (p < 0.005). Challenge with C. jejuni strongly increased intestinal IL-8, IL-6, and iNOS transcript levels in the non-GC treated animals but not in the GC-treated birds (P < 0.005). In vitro assays with chicken macrophages showed that GC dampened the TLR agonist- and C. jejuni induced-inflammatory gene transcription and production of nitric oxide (P < 0.005). Together, the results support the hypothesis that C. jejuni has the intrinsic ability to invade chicken tissue and that an effective innate immune response may limit its invasive behavior.

Effect of Mycoplasma synoviae and lentogenic Newcastle disease virus coinfection on cytokine and chemokine gene expression in chicken embryos

Mycoplasma synoviae and Newcastle disease virus (NDV) are 2 avian pathogens that cause modulation in expression of a variety of cytokine and chemokine genes in chickens. However, there is limited data about gene modulation after coinfection with these 2 pathogens and even less data about gene modulation after infection of chicken embryos. In this study, the effect of M. synoviae type strain WVU 1853 and lentogenic LaSota vaccine strain of NDV infection on cytokine and chemokine gene expression in chicken embryos was analyzed in the liver, spleen, bursa of Fabricius, and thymus by using quantitative real-time PCR. Three types of infection were performed; infection with M. synoviae on d 10, infection with NDV on d 17; and consecutive infection with both pathogens, where M. synoviae was inoculated on d 10 and NDV on d 17. Thus, simulation of consecutive infection that may occur after NDV infection of the M. synoviae-infected host was performed. Mycoplasma synoviae infection of embryos resulted in intensive upregulation of cytokine and chemokine genes, including interferon (IFN)-γ, IL-1β, IL-6, IL-12p40, IL-16, IL-18, MIP-1β (CCL4), inducible nitric oxide synthase (iNOS), XCL1, and lipopolysaccharide-induced tumor necrosis factor-α factor (LITAF), with different expression profiles in the 4 organs. Inoculation of lentogenic NDV significantly upregulated IFN-γ, IL-6, and IL-16 genes in spleen and IFN-γ, IL-1β, IL-2, IL-16, IL-21, XCL1, and MIP-1β (CCL4) genes in the thymus, but to a lesser extent than M. synoviae. However, no genes were upregulated by NDV in the liver and bursa of Fabricius. Overall effect of NDV inoculation, regarding the number of modulated cytokine and chemokine genes and the extent of expression, was lower than M. synoviae. When NDV was introduced after on-going M. synoviae infection, most M. synoviae-induced cytokine and chemokine genes were significantly downregulated. This study provides the first evidence in chicken embryos that consecutive infection with NDV could suppress expression of cytokine and chemokine genes being significantly upregulated by the previous M. synoviae infection.

Genome-wide association analysis of avian resistance to Campylobacter jejuni colonization identifies risk locus spanning the CDH13 gene

The enteropathogen Campylobacter jejuni is a major worldwide health and economic burden, being one of the leading causes of bacterial gastroenteritis and commonly linked to postinfectious onset of autoimmune disease. Chickens are a major vector for human infection and even though variation in avian colonization level is heritable, no previous studies have identified regions of the genome associated with colonization resistance. We performed a genome-wide association study of resistance to C. jejuni colonization in the avian intestine by controlling for population structure, which revealed a risk locus with genome-wide significance spanning the T-cadherin (CDH13) gene. A second possible risk locus was also identified close to calmodulin (CALM1), a calcium-activated modulator of cadherin function. In addition, gene expression analysis of mRNA sequencing profiles revealed that the relative expression of the two genes is significantly associated with colonization resistance. Functional studies have previously demonstrated involvement of cadherins and calmodulin in C. jejuni intracellular invasion and colonization of human intestinal epithelial cells in vitro. Consistent with this finding, our analysis reveals that variation surrounding these genes is associated with avian colonization resistance in vivo and highlights their potential as possible targets for control of the bacterium in avian and human populations.

Induction of chicken cytokine responses in vivo and in vitro by lipooligosaccharide of Campylobacter jejuni HS:10

Campylobacter jejuni is a pathogen of the gastrointestinal tract of humans, but colonizes chickens for prolonged periods without causing disease. It is unclear what host and bacterial mechanisms maintain a non-inflammatory state in chickens. The present work was undertaken to characterize cytokine responses of chickens to purified lipooligosaccharide (LOS) of C. jejuni HS:10. Chickens were injected with purified LOS, and expression of interleukin (IL)-1β (pro-inflammatory cytokine), IL-8 (pro-inflammatory chemokine), interferon (IFN)γ (Th1-like cytokine), IL-10 (immune regulatory/anti-inflammatory cytokine) and IL-13 (Th2-like cytokine) was evaluated in spleen using quantitative RT-PCR, up to 24h post-injection. In an in vitro study, splenocytes were incubated with LOS, and cytokine expression followed up to 18 h. Chickens injected with LOS had increased expression of IL-1β up to 24h later. Expression of IL-8 was significantly increased at 2h but then declined below baseline. Expression of IFNγ and IL-10 was increased significantly at 2h, but declined thereafter. Splenocytes incubated with LOS had increased expression of IL-1β and IL-8 up to 18 h of incubation. Expression of IFNγ was increased at 6 and 18 h, IL-10 was increased at 2h, but expression of IL-13 did not differ significantly up to 18h. It is concluded that LOS of C. jejuni can induce expression of pro-inflammatory IL-1β and IL-8, as well as IFNγ and IL-10 in chickens. More extensive studies with more prolonged exposure to LOS are needed to further clarify the interaction between C. jejuni and the chicken host.

Avian resistance to Campylobacter jejuni colonization is associated with an intestinal immunogene expression signature identified by mRNA sequencing

Campylobacter jejuni is the most common cause of human bacterial gastroenteritis and is associated with several post-infectious manifestations, including onset of the autoimmune neuropathy Guillain-Barré syndrome, causing significant morbidity and mortality. Poorly-cooked chicken meat is the most frequent source of infection as C. jejuni colonizes the avian intestine in a commensal relationship. However, not all chickens are equally colonized and resistance seems to be genetically determined. We hypothesize that differences in immune response may contribute to variation in colonization levels between susceptible and resistant birds. Using high-throughput sequencing in an avian infection model, we investigate gene expression associated with resistance or susceptibility to colonization of the gastrointestinal tract with C. jejuni and find that gut related immune mechanisms are critical for regulating colonization. Amongst a single population of 300 4-week old chickens, there was clear segregation in levels of C. jejuni colonization 48 hours post-exposure. RNAseq analysis of caecal tissue from 14 C. jejuni-susceptible and 14 C. jejuni-resistant birds generated over 363 million short mRNA sequences which were investigated to identify 219 differentially expressed genes. Significantly higher expression of genes involved in the innate immune response, cytokine signaling, B cell and T cell activation and immunoglobulin production, as well as the renin-angiotensin system was observed in resistant birds, suggesting an early active immune response to C. jejuni. Lower expression of these genes in colonized birds suggests suppression or inhibition of a clearing immune response thus facilitating commensal colonization and generating vectors for zoonotic transmission. This study describes biological processes regulating C. jejuni colonization of the avian intestine and gives insight into the differential immune mechanisms incited in response to commensal bacteria in general within vertebrate populations. The results reported here illustrate how an exaggerated immune response may be elicited in a subset of the population, which alters host-microbe interactions and inhibits the commensal state, therefore having wider relevance with regard to inflammatory and autoimmune disease.

A tolerogenic mucosal immune response leads to persistent Campylobacter jejuni colonization in the chicken gut

Campylobacter enteritis is the most reported zoonotic disease in many developed countries where it imposes a serious health burden. Campylobacter transmission to humans occurs primarily through the chicken vector. Chicks are regarded as a natural host for Campylobacter species and are colonized with C. jejuni in particular. But despite carrying a very high bacterial load in their gastrointestinal tract, these birds, in contrast to humans, do not develop pathological signs. It seems that in chickens C. jejuni principally harbors in the cecal mucosal crypts, where an inefficient inflammatory response fails to clear the bacterium from the gut. Recent intensive research resulted in an increased insight into the cross talk between C. jejuni and its avian host. This review discusses the chicken intestinal mucosal immune response upon C. jejuni entrance, leading to tolerance and persistent cecal colonization. It might in addition provide a solid base for further research regarding this topic aiming to fully understand the host-bacterium dynamics of C. jejuni in chicks and to develop effective control measures to clear this zoonotic pathogen from poultry lines.