Eimeria tenella: Interleukin 17 contributes to host immunopathology in the gut during experimental infection
Graphical abstract
Highlights
► Provide data of dynamic change of Th17-related cytokines during E. tenella infection. ► Reduced fecal oocysts shedding was observed in IL-17 neutralized chicken. ► Enhanced body weight gain was observed in IL-17 neutralized chicken. ► Neutrophils recruitment was diminished in IL-17 neutralized chicken. ► Augmented IFN-γ and IL-12 was shown in IL-17 neutralized chicken.
Introduction
Th17 cells have been identified as a new subpopulation of CD4+ T cells (Korn et al., 2009). A hallmark of Th17 cells is the production of IL-17A (also called IL-17), a proinflammatory cytokine. Th17 differentiation is regulated by the transcription factors signal transducer and activator of transcription 3 (STAT-3), retinoic acid receptor-related orphan receptor-γt (RORγt) and aryl hydrocarbon receptor, and is driven by transforming growth factor-β (TGF-β), IL-1 and IL-6 (Gaffen, 2009). Moreover, IL-23 also plays a critical role in the differentiation of Th17 cells and leads to the further maturation of Th17 cells (Bettelli et al., 2006). The hallmark cytokines of Th1 and Th2 cells, IFN-γ and IL-4, can inhibit the IL-23-driven expansion of Th17 cells (Harrington et al., 2005, Park et al., 2005). Similarly, IL-17 can suppress Th1 cell differentiation in the presence of exogenous IL-12 in vitro (Nakae et al., 2007).
IL-17 and Th17 cells play important roles in several diseases (Kelchtermans et al., 2009, O’Connor et al., 2009). Th17 cells largely promote inflammation by recruiting neutrophils and inducing production of several pro-inflammatory mediators, including IL-1, IL-6, TNF-α, and chemokines (Kolls and Linden, 2004, Korn et al., 2009). The protective function of Th17 and their effector cytokines in various infectious diseases has also been reported. For example, Mycobacterium tuberculosis (Khader et al., 2007), Candida albicans (Huang et al., 2004) and Klebsiella pneumonia (Aujla et al., 2008), can trigger a strong Th17 response that mediates protective effects. These observations indicate that Th17 cells and their effector cytokines have both pathologic and protective roles during inflammation and infections.
Recently studies have shown Th17 cells have been involved in protozoal infection diseases. Similarly, controversial results are shown in protozoan infection studies. Several studies have also demonstrated that Th17 cells may mediate the host defense against Trypanosoma cruzi (Miyazaki et al., 2010), Pneumocystis carinii (Rudner et al., 2007) and Toxoplasma gondii (Kelly et al., 2005), and other studies demonstrated they promoted pathogenesis in human cutaneous leishmaniasis (Bacellar et al., 2009) and in T. gondii infection (Guiton et al., 2010). These studies suggest that the role of Th17 cells in parasitic diseases remains to be elucidated.
Eimeria tenella is an intracellular apicomplexan parasite of chickens. It can lead to malabsorption, reduced body weight gains and decreased efficiency of feed conversion of poultry resulting in significant economic losses (Shirley et al., 2005). Extensive experimental evidence shows that cell-mediated (Th1 cell-mediated) immunity represents the main component of protective immunity against Eimeria parasites (Dalloul and Lillehoj, 2006, Lillehoj and Lillehoj, 2000). The pro-inflammatory cytokines, IL-12 and IFN-γ, play a critical role in mediating protective immunity against Eimeria parasites (Dalloul and Lillehoj, 2006, Lillehoj and Lillehoj, 2000). In addition, these cytokines also stimulate the differentiation and proliferation of Th1 cells (Lee et al., 2010).
Despite the importance of coccidiosis in poultry, the immunological mechanism associated to E. tenella infection is not fully established. Although the transcript expression levels of IL-17 were measured in Eimeria-infected chickens in several studies (Hong et al., 2006a, Hong et al., 2006b, Zhang et al., 2012), there has been as yet no reports on the role of IL-17 and Th17 cells in resistance to E. tenella. The primary objective of this study was to determine whether experimental E. tenella infection induces the production of Th17-associated genes (STAT-3, IL-1β, IL-6, IL-17 and TGF-β) and whether IL-17 plays any significant role in the pathogenesis of the diseases or protection against infection.
Section snippets
Chickens
Day-old Arbor Acre (AA) broiler chickens obtained from the Huadu Broiler Hatchery (Beijing, China) were reared in a coccidia-free laboratory, housed in wire cages. Three-week-old White Leghorn specific pathogen-free (SPF) chickens were obtained from China Vital River Laboratories, and housed within poultry isolators (Jin Hang, China). Chickens were provided free access to feed and water. All animal experiments were carried out in compliance with current Chinese ethical legislation.
Parasites
Parental
Th17 responses associated cytokins expression during E. tenella infection
To determine the role of chicken IL-17, we first detected whether Th17 differentiation associated cytokines were expressed during the early infection of E. tenella. Results were presented in Fig. 1. All Th17-associated cytokines were up-regulated in the infected chickens compared with the uninfected control during the first 72 hpi (Fig. 1.). The transcripts of STAT-3, IL-1β, IL-6, and IL-17 showed robust upregulation, peaking at 6 hpi and declining thereafter, whereas TGF-β mRNA level showed
Discussion
Th17 cells have been shown to play a pivotal role in host defense against microbial infection (Kelchtermans et al., 2009, O’Connor et al., 2009). Although previous studies showed infection with Eimeria lead to the production of high levels of IL-17 (Hong et al., 2006a, Hong et al., 2006b, Min and Lillehoj, 2002), the role of IL-17 in E. tenella infection remains unknown, and controversial results of IL-17 roles showed in T. gondii infection make it more interesting to find out the contribution
Competing interests
The authors have declared that no competing interests exist.
Acknowledgments
This research was supported by the Joint Project of Natural Science Foundation of China and the Natural Science Foundation of Guangdong Province (No. U0831004 to J.P. Cai). We are also greatly indebted to the technical staff of our laboratory for their assistance during this study.
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