Heterophils isolated from chickens resistant to extra-intestinal Salmonella enteritidis infection express higher levels of pro-inflammatory cytokine mRNA following infection than heterophils from susceptible chickens

Comparative in vivo infection models yield insights on early host immune response to Campylobacter in chickens

Salmonella typhimurium and Campylobacter jejuni pose significant risks to human health and poultry are a major vector for infection. Comparative in vivo infection models were performed to compare the avian host immune response to both bacterial species. Forty-five commercial broiler chickens were orally challenged with either C. jejuni or S. typhimurium whilst 60 similar control birds were mock challenged in parallel. Birds were sacrificed at 0, 6, 20 and 48 h post-infection and cloacal swabs, blood and tissue samples taken. Peripheral blood leukocytes were isolated for flow cytometric analyses and RNA was extracted for gene expression profiling. Colonisation patterns were markedly different between the two bacterial species, with systemic colonisation of Campylobacter outside the gastrointestinal tract. Salmonella infection induced significant changes in circulating heterophil and monocyte/macrophage populations, whilst Campylobacter infection had no effect on the heterophil numbers but caused a significant early increase in circulating monocytes/macrophages. Toll-like receptor 1 (TLR1) gene expression was decreased, and avian beta-defensin (AvBD) gene expression (AvBD3, AvBD10 and AvBD12) was significantly increased in response to Salmonella infection (P < 0.05). In contrast, Campylobacter infection induced increased TLR21 gene expression but significantly reduced expression of seven antimicrobial peptide (AMP) genes (AvBD3, AvBD4, AvBD8, AvBD13, AvBD14, CTHL2 and CTHL3; P < 0.05). Considered together, microbiological, cellular and gene expression profiles indicate that the innate immune system responds differently to Salmonella and to Campylobacter infection. Furthermore, reduction in the expression of AMPs may play a role in the persistence of high level colonisation of the host by Campylobacter.

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.

Intestinal cytokine response of commercial source broiler chicks to Salmonella typhimurium infection

Development of molecular-based immunotherapeutic strategies for controlling Salmonella Typhimurium (ST) infection in poultry requires a better understanding of intestinal and cecal cytokine responses. Accordingly, an experiment was conducted to measure changes in intestinal cytokine expression when commercial source broiler chickens were challenged with a nalidixic acid-resistant ST. Ross broiler chicks were nonchallenged with ST (control treatment) or challenged by orally giving 7.8 x 10(6) cfu at 4 d of age (STC treatment). Each treatment consisted of 4 replicate pens with 14 chicks per pen. Expression levels of proinflammatory cytokines, interferon-gamma, and antiinflammatory interleukin (IL)-10 were determined at 5 and 10 d postchallenge (PC). Intestinal flushes were also collected from each treatment at 7 d PC to estimate IgA and IgG. Results showed an upregulation in IL-1beta mRNA in STC chicks at 5 d PC. By 10 d PC, the expression of IL-1beta was further increased and accompanied by an upregulation of IL-6 and interferon-gamma mRNA, whereas IL-10 mRNA expression decreased. It was concluded that ST induced an intestinal mucosal inflammatory response in commercial source broiler chicks less than 2 wk of age.

Flagellin and lipopolysaccharide up-regulation of IL-6 and CXCLi2 gene expression in chicken heterophils is mediated by ERK1/2-dependent activation of AP-1 and NF-κB signaling pathways

The Toll-like receptor agonists, flagellin (FLG) and lipopolysaccharide (LPS), stimulate chicken heterophils to induce the expression and secretion of pro-inflammatory cytokines by a mechanism involving the triggering of differential MEK-ERK signaling cascades. However, the translocation and activation of transcription factors potentially involved in the control of cytokine gene expression remains unknown. Herein, we examined the effects of FLG and LPS on the activation of the transcription factors NF-κB and AP-1 and their role in regulating heterophil activation leading to cytokine gene expression. Treatment of heterophils with either FLG or LPS induced a significant increase in DNA binding by the NF-κB family members p50, c-Rel, and RelB. Likewise, FLG and LPS induced a significant increase in DNA binding by the AP-1 family members c-Jun and JunD. The activation of both NF-κB and AP-1 was inhibited following treatment of heterophils with specific inhibitors of ERK1/2 (U0126 and PD098059), NF-κB (Bay 11-7086 and the cell-permeable NF-κB peptide, SN50), and AP-1 (Tanshinone IIA). Likewise, the up-regulation of gene expression of the pro-inflammatory cytokine, IL-6, and the inflammatory chemokine, CXCLi2, were inhibited when heterophils were treated with the same specific inhibitors. Taken together these data demonstrate that FLG and LPS stimulate the up-regulation of expression of IL-6 and CXCLi2 through an ERK1/2-dependent activation of both NF-κB and AP-1.

Global gene expression profile after Salmonella enterica Serovar enteritidis challenge in two F8 advanced intercross chicken lines

A chicken 13K cDNA microarray was used to profile global gene expression after Salmonella enteritidis (SE) challenge of young chickens. Two F8 advanced intercross lines (AIL), broiler by Leghorn, and broiler by Fayoumi, were studied. Day-old chicks were orally inoculated with SE, and spleens were harvested at day 7 or 8 post-inoculation. The SE bacteria burden in the spleen was quantified. The 20% high and 20% low SE burden birds within each AIL and harvest time were studied by microarray. The loop design was used for pair-comparison between high and low SE burden challenged birds and unchallenged birds, within each AIL and harvest time. The signal intensity of each gene was globally normalized and expressed on the natural log scale. A mixed model including line, treatment, time, array (random effect), dye, and all two-way interactions among treatment, time, and line was used to identify differentially expressed candidate genes at the 1% significance level. The results suggest that genetics, time, and interaction between genetics and time play important roles in gene regulation of SE infection and colonization in chickens. The differentially expressed genes identified in the current study are candidates for detailed hypothesis-driven investigation of genes determining resistance to SE 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.

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

Heterophils mediate acute protection against Salmonella in young poultry. We evaluated susceptibility of genetically distinct lines of broilers to systemic Salmonella enteritidis (SE) infections. SE was administered into the abdomen of day-old chickens (parental lines [A and B]; F1 reciprocal crosses [C and D]) to assess modulation of leukocytes and survivability of chickens. Line A was more resistant to SE than line B; likewise cross D was more resistant than cross C. Significantly more heterophils migrated to the abdominal cavity post-infection in the resistant lines. These data indicate that increased heterophil influx to the infection site contributes to increased resistance against systemic SE infections in neonatal chickens.

Lipopolysaccharide Binding Protein/CD14/TLR4-Dependent Recognition of Salmonella LPS Induces the Functional Activation of Chicken Heterophils and Up-Regulation of Pro-Inflammatory Cytokine and Chemokine Gene Expression in These Cells

Lipopolysaccharide (LPS) is the major pathogen-associated molecular pattern (PAMP) found in the cell wall of gram-negative bacteria and, in mammals, is recognized by the Toll-like receptor 4 (TLR4) in conjunction with the serum protein, lipopolysaccharide-binding protein (LBP), and the CD14 co-receptor. We have found that chicken heterophils constitutively express multiple TLRs including TLR4. Interestingly, ultrapure LPS from Salmonella minnesota directly induced the functional activation of heterophils without the presence of LBP. However, the role of LBP and CD14 in the recognition of LPS and the induction of innate immunity, including cellfunctional activation and the transcription of cytokine and chemokine genes in chicken heterophils, is not known. As previously seen, in the absence of chicken serum, heterophil exposure to ultrapure LPS from Salmonella minnesota stimulated an increased degranulation response. However, the presence of 5% chicken serum, presumed to be a source of LBP, increased heterophil degranulation by 84%. In addition, the presence of either soluble recombinant human LBP (rhLBP, 68%) or CD14 (39%) also induced the up-regulation of the heterophil degranulation response. Incubation of heterophils with either chicken serum or rhLBP also significantly induced the up-regulation of pro-inflammatory cytokine (IL-1beta, IL-6, and IL-18) and chemokine (CCLi4, CXCLi1, CXCLi2, and the CXC receptor 1) mRNA expression. Moreover, polyclonal antibodies directed against rat CD14 and human TLR4, but not antibodies against human TLR2, blocked LPS-mediated degranulation and up-regulation of the pro-inflammatory cytokine and chemokine mRNA expression. These data clearly demonstrate that LBP and CD14/TLR4 engagement is directly involved in LPS-mediated functional activation and innate immune gene expression in chicken heterophils.

Recombinant chicken IL-6 does not activate heterophils isolated from day-old chickens in vitro

Pro-inflammatory cytokines are produced as part of innate immunity. Increased resistance to extraintestinal Salmonella enteritidis (SE) has been associated with an increase in heterophil pro-inflammatory cytokine gene expression. Invasion of chicken epithelial cells by SE induces an 8- to 10-fold increase in interleukin (IL) -6 production. Infection with SE induces an influx of heterophils to the site of infection; therefore, we hypothesize heterophils would be responsive to IL-6. The objective was to determine the effects of COS cell-derived recombinant chicken interleukin 6 (rChIL-6) on in vitro functional activity of heterophils. Heterophils were incubated with rChIL-6 or mock-transfected COS cell supernatant and functional activity was assessed. Heterophils treated with rChIL-6 showed no functional differences compared to controls. These data indicate rChIL-6, alone, does not affect the functional activity of neonatal chicken heterophils in vitro. Therefore, the function of IL-6 in the local environment in response to SE invasion is still unknown.