Rhoptry proteins (ROPs), secreted by specific rhoptry organelles of apicomplexan parasites, are determinants of parasite pathogenesis and sources of vaccine candidates. Twenty-eight ROPs of Eimeria tenella have been predicted by genomic approaches, and in the present study, E. tenella rhoptry protein 30 (EtROP30) was characterized. Subcellular localizations of EtROP30 in sporozoites and merozoites were in the apical complex and rhoptry-like bulb, suggesting that EtROP30 is a member of ROPs in E. tenella . Sequence analysis showed that EtROP30 contained an N-terminal secretory signal, a protein kinase domain with eight E. tenella -specific rhoptry kinase 1 subfamily (ROPK-Eten1) motifs, and a C-terminal nuclear localization sequence (NLS), making EtROP30 the only ROP that contains both a secretory signal and an NLS in E. tenella . Subsequent experiments showed that EtROP30 was a secreted protein in the sporozoite stage, relying on NLS for migration to the host nucleus. In addition, EtROP30 showed significantly higher expression levels in the parasite merozoite stage, indicating that EtROP30 plays a critical role during parasite reinvasion and development and may be a viable option as a vaccine candidate for anti-parasitic infection. The immunization protection efficacies of EtROP30 were evaluated. Significant improvements in mean body weight gain, reduction of cecum lesion score, and number of oocysts excreted were observed, indicating that EtROP30 has good immunogenicity against E. tenella . In the present study, a ROP of E. tenella with secretory and nuclear localization characteristics has been identified, and proved to be an effective vaccine candidate against this parasite.
Malaria is one of the deadliest infectious diseases threatening half of the world population. With the deterioration of the parasiticidal effect of the current antimalarials, novel approaches such as screening of more specific inhibitors and targeted delivery of drugs have been under intensive research. Herein, we prepare hollow mesoporous ferrite nanoparticles (HMFNs) of 200 nm with ferromagnetic properties using a one-pot hydrothermal reaction. A magnetically targeted drug-delivery system coloaded with artemisinin in the inner magnetite shell and heparin on the outer mesoporous shell (HMFN@ART@HEP) is developed. Specific targeting of the magnetic nanoparticles to the parasite-infected erythrocytes is achieved by the attraction between the HMFNs and hemozoin (paramagnetic), a vital metabolite of plasmodium in the erythrocytic stage. With the hemozoin production reaching the maximum during the schizont period of the parasite, HMFN@ART@HEPs are adsorbed to the infected red blood cells (iRBCs), which not only interferes with the release of merozoites but also significantly enhances the inhibitory efficacy due to the increased local concentration of artemisinin. Subsequently, the heparin coated on the surface of the nanoparticles can efficiently interfere with the invasion of freshly released merozoites to new RBCs through the specific interaction between the parasite-derived ligands and heparin, which further increases the inhibitory effect on malaria. As a cluster of heparin, heparin-coated nanoparticles provide stronger blocking capability than free heparin, resulting from multivalent interactions with surface receptors on merozoite. Thus, we have developed a HMFN-based delivery system with considerable antimalarial efficacy, which is a promising platform for treatment against malaria.
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