Abstract
Avian coccidian parasites exhibit a high degree of site specificity in different Eimeria species. Although the underlying mechanism is unclear, an increasing body of evidence suggests that site specificity is due to the interaction between microneme proteins (MICs) and their receptors on the surface of target host cells. In this study, the binding ability of E. tenella MICs (EtMICs) to different intestinal tissue was observed by immunofluorescence to identify the key surface molecule on the parasite responsible for the site specificity. Subsequently, we identified the corresponding host-cell receptors by yeast two-hybrid screening and glutathione-S-transferase pull-down experiments and the distribution of these receptors was observed by immunofluorescence in chicken intestinal tissues. Finally, we evaluated the efficacy of receptor antiserum against the infection of E. tenella in chickens. The results showed that EtMIC3 could only bind to the caecum while EtMIC1, EtMIC2, and EtAMA1 did not bind to any other intestinal tissues. Anti-serum to EtMIC3 was able to block the invasion of sporozoites with a blocking rate of 66.3%. The receptors for EtMIC3 were BCL2-associated athanogene 1 (BAG1) and Endonuclease polyU-specific-like (ENDOUL), which were mainly distributed in the caecum. BAG1 and ENDOUL receptor antiserum reduced weight loss and oocyst output following E. tenella infection, showing partial inhibition of E. tenella infection. These data elucidate the mechanism of site specificity for Eimeria infection and reveal a potential therapeutic avenue.
Highlights
Chicken Eimeria are obligate intracellular parasitic protozoa that develop within intestinal epithelial cells of chickens
Preparations of recombinant proteins and antiserum of rEtMICs Recombinant proteins of EtMIC3, EtMIC2, Recombinant proteins of EtAMA1 (rEtAMA1) and E. tenella MIC1 (EtMIC1) were harvested from E. coli host
Antiserum of recombinant proteins of EtMIC3 (rEtMIC3), Recombinant proteins of EtMIC2 (rEtMIC2), rEtAMA1, Recombinant proteins of EtMIC1 (rEtMIC1) and pET-32a tag protein were obtained from rats vaccinated with the corresponding recombinant proteins and Enzyme-linked Immunosorbent Assay (ELISA) assay revealed that their titres were 2 13, 218, 218, 219 and 218 respectively
Summary
Chicken Eimeria are obligate intracellular parasitic protozoa that develop within intestinal epithelial cells of chickens. Avian Eimeria exhibits a high degree of site specificity in the chicken intestine. Site specificity is so strict that Eimeria parasite infection by intravenous, intramuscular, or intraperitoneal injections routes cause infections in the same region of the intestine as the oral route [7, 10]. In the early stage of infection by Eimeria, microneme proteins (MICs) are secreted to participate in adhesion to the host cell. The authors found only EtMIC3 was detected in the cellbound protein fraction They documented that EtMIC3 bound to α-2,3-sialyl glycan sequences present on the surface of MDBK cell through inhibition experiments in vitro and considered EtMIC3 as a major determinant of site specificity of E. tenella [8]. Whether EtMIC3 is the key molecule for site specificity in the natural chicken host is unclear and its receptor in the caecal epithelium remains to be elucidated
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