Establishment of an in vitro chicken epithelial cell line model to investigate Eimeria tenella gamete development and the epithelial cell response to the infection
Résumé
Eimeria tenella infection is responsible for important economic losses in poultry farming worldwide. The life-cycle of E. tenella is monoxenous; infection occurs in chicken caecal epithelial cells. However, in vitro, the complete life-cycle of the parasite has only been propagated successfully in primary chicken kidney cells; no cell line model has been able to consistently support the development of the sexual stages of the parasite. We therefore sought to develop a new model to study E. tenella gametogony in vitro using a recently characterised chicken cell line (CLEC-213) exhibiting an epithelial cell phenotype. CLEC-213 were infected with sporozoites from a precocious strain or with second generation merozoites (merozoites II) from wild type strains. Sexual stages of the parasite were determined both at the gene and protein levels. In addition, the early cell response to Eimeria tenella was studied by RT-qPCR and compared to in vivo experiments. We show for the first time in CLEC-213, that sporozoites from a precocious strain of E. tenella were able to develop to gametes, as verified by measuring gene expression and by using antibodies to a microgamete-specific protein (EtFOA1: flagellar outer arm protein 1) and a macrogamete-specific protein (EtGAM-56), but oocysts were not observed. However, both gametes and oocysts were observed when cells were infected with merozoites II from wild type strains, demonstrating that completion of the final steps of the parasite cycle is possible in CLEC-213 cells. Concerning the epithelial response to the infection, an increase in gene expression related to inflammatory mediators (CXCLi2, CCL20, CSF2) was observed in vitro at the stage of schizont I and in vivo at early time of infection. Then, the epithelial cell line CLEC-213 constitutes a useful avian tool for studying Eimeria epithelial cell interactions and the effect of drugs on E. tenella invasion, merogony and gametogony.