Geru Tao

An Eimeria vaccine candidate based on Eimeria tenella immune mapped protein 1 and the TLR-5 agonist Salmonella typhimurium FliC flagellin.

Immune mapped protein-1 (IMP1) is a new protective protein in apicomplexan parasites, and exits in Eimeria tenella. But its structure and immunogenicity in E. tenella are still unknown. In this study, IMPI in E. tenella was predicted to be a membrane protein. To evaluate immunogenicity of IMPI in E. tenella, a chimeric subunit vaccine consisting of E. tenella IMP1 (EtIMP1) and a molecular adjuvant (a truncated flagellin, FliC) was constructed and over-expressed in Escherichia coli and its efficacy against E. tenella infection was evaluated. Three-week-old AA broiler chickens were vaccinated with the recombinant EtIMP1-truncated FliC without adjuvant or EtIMP1 with Freunds Complete Adjuvant. Immunization of chickens with the recombinant EtIMP1-truncated FliC fusion protein resulted in stronger cellular immune responses than immunization with only recombinant EtIMP1 with adjuvant. The clinical effect of the EtIMP1-truncated FliC without adjuvant was also greater than that of the EtIMP1 with adjuvant, which was evidenced by the differences between the two groups in body weight gain, oocyst output and caecal lesions of E. tenella-challenged chickens. The results suggested that the EtIMP1-flagellin fusion protein can be used as an effective immunogen in the development of subunit vaccines against Eimeria infection. This is the first demonstration of antigen-specific protective immunity against avian coccidiosis using a recombinant flagellin as an apicomplexan parasite vaccine adjuvant in chickens.

Transgenic Eimeria tenella as a vaccine vehicle: expressing TgSAG1 elicits protective immunity against Toxoplasma gondii infections in chickens and mice

The surface antigen 1 of Toxoplasma gondii (TgSAG1) is a major immunodominant antigen and is widely considered an ideal candidate for the development of an effective recombinant vaccine against toxoplasmosis. Eimeria tenella, an affinis apicomplexan parasite with T. gondii, is a potential vaccine vector carrying exogenous antigens that stimulates specific immune responses. Here, we engineered TgSAG1 into E. tenella and obtained a stably transfected E. tenella line (Et-TgSAG1). We found TgSAG1 localized on the cell surface of Et-TgSAG1, which is similar to its native distribution in T. gondii tachyzoites. We immunized the chickens with Et-TgSAG1 orally and detected TgSAG1-specific immune responses, which partly reduced T. gondii infection. In the mouse model, we immunized the mice with Et-TgSAG1 sporozoites intraperitoneally and challenged them with T. gondii tachyzoites RH strain. We found that the mice immunized with Et-TgSAG1 showed a TgSAG1 specific Th 1-dominant immune response and a prolonged survival time compared with wild-type E. tenella and non-immunized mice. Collectively, our results demonstrated that Et-TgSAG1, utilized as a recombinant vaccine against toxoplasmosis, could be applied in both chickens and mice. Our findings also provide a promising persuasion for the development of transgenic Eimeria as vaccine vectors for use in birds and mammals.

Self-cleaving 2A peptide from porcine teschovirus-1 mediates cleavage of dual fluorescent proteins in transgenic Eimeria tenella.

The “self-cleaving” 2A sequence of picornavirus, which mediates ribosome-skipping events, enables the generation of two or more separate peptide products from one mRNA containing one or more “self-cleaving” 2A sequences. In this study, we introduced a single 2A sequence of porcine teschovirus-1 (P2A) linked to two fluorescent protein genes, the enhanced yellow fluorescent protein (EYFP) gene and the red fluorescent protein (RFP) gene, in a single cassette into transgenic Eimeria tenella (EtER). As expected, we obtained two separated protein molecules rather than a fused protein, although the two molecules were translated from the same mRNA carrying a single “self-cleaving” 2A sequence. Importantly, RFP led by a secretion signal was secreted into parasitophorous vacuoles, while EYFP localized mainly to the nucleus of EtER. Our results demonstrate that the “self-cleaving” 2A sequence actively mediated cleavage of polyproteins in the apicomplexan parasite E. tenella.

Chicken IgY Fc expressed by Eimeria mitis enhances the immunogenicity of E. mitis

BackgroundEimeria species are obligate intracellular apicomplexan parasites, causing great economic losses in the poultry industry. Currently wild-and attenuated- type anticoccidial vaccines are used to control coccidiosis. However, their use in fast growing broilers is limited by vaccination side effects caused by medium and/or low immunogenic Eimeria spp. There is, therefore, a need for a vaccine with high immunogenicity for broilers.MethodsThe avian yolk sac IgY Fc is the avian counterpart of the mammalian IgG Fc, which enhances immunogenicity of Fc-fusion proteins. Here, we developed a stable transgenic Eimeria mitis expressing IgY Fc (Emi.chFc) and investigated whether the avian IgY Fc fragment enhances the immunogenicity of E. mitis. Two-week-old broilers were immunized with either Emi.chFc or wild type Eimeria and challenged with wild type E. mitis to analyze the protective properties of transgenic Emi.chFc.ResultsChickens immunized with Emi.chFc had significantly lower oocyst output, in comparison with PBS, mock control (transgenic E. mitis expressing HA1 from H9N2 avian influenza virus) and wildtype E. mitis immunized groups after challenge, indicating that IgY Fc enhanced the immunogenicity of E. mitis.ConclusionsOur findings suggest that IgY Fc-expressing Eimeria may be a better coccidiosis vaccine, and transgenic Eimeria expressing Fc-fused exogenous antigens may be used as a novel vaccine-delivery vehicle against a wide variety of pathogens.

High pathogenicity and strong immunogenicity of a Chinese isolate of Eimeria magna Perard, 1925

Coccidia infection of rabbits with one or several species of parasites of the genus Eimeria causes coccidiosis, a disease leading to huge economic losses in the rabbit industry. Eimeria magna, one of the causal agents of rabbit coccidiosis, was characterized as mildly pathogenic and moderately immunogenic in previous studies. In this study, we identified a Chinese isolate of E. magna by testing its biological features (oocyst morphology and size, prepatent time) and sequencing its internal transcribed spacer 1 (ITS-1) DNA fragment. This isolate is highly pathogenic; infection of rabbits with only 1×102 oocysts caused a 55% reduction in weight gain in 14days. In addition, immunization with 1×102 oocysts prevented body weight loss against re-infection with 5×104 oocysts, indicating the high immunogenicity of this isolate. Our study described the distinctive phenotype of the Chinese isolate of E. magna and contributed to the research of geographic variation of rabbit coccidia.

Transgenic Eimeria magna Pérard, 1925 Displays Similar Parasitological Properties to the Wild-type Strain and Induces an Exogenous Protein-Specific Immune Response in Rabbits (Oryctolagus cuniculus L.)

Rabbit coccidiosis causes great economic losses to world rabbitries. Little work has been done considering genetic manipulation on the etiological agents, rabbit Eimeria spp. In this study, we constructed a transgenic line of Eimeria magna (EmagER) expressing enhanced yellow fluorescent protein (EYFP) and red fluorescent protein (RFP) using regulatory sequences of Eimeria tenella and Toxoplasma gondii. We observed the life cycle of EmagER and confirmed that the transgenic parasites express exogenous proteins targeted to different cellular compartments throughout the entire life cycle. EYFP was expressed mainly in the nucleus and RFP both in the nucleus and cytoplasm. Then, coccidia-free, laboratory-reared 40-day-old rabbits were primarily infected with either EmagER or wild-type strain oocysts and challenged with the wild-type strain. EmagER showed similar reproductivity and immunogenicity to the wild-type strain. Finally, we examined the foreign protein-specific immune response elicited by EmagER. Rabbits were immunized with either transgenic or wild-type oocysts. Immune response against parasite-soluble antigen, EYFP and RFP in spleen, and mesenteric lymph nodes were detected by quantitative real-time PCR. The relative expression level of IFN-γ, IL-2, and TNF-α were higher in EmagER-immunized rabbits than wild-type parasites-immunized rabbits after stimulation with EYFP and RFP. Our study confirmed that a specific immune response was induced by the exogenous protein expressed by EmagER and favored future studies on application of transgenic rabbit coccidia as recombinant vaccine vectors.

Stable Transfection of Eimeria intestinalis and Investigation of Its Life Cycle, Reproduction and Immunogenicity

Rabbit coccidiosis, caused by infection of Eimeria spp. is one of the most severe parasitic diseases in rabbits. Eimeria intestinalis is one of the most immunogenic species in rabbit coccidia. Due to the lack of genomic information and unsuccessful in vitro cultivation, genetic manipulation of rabbit coccidia lagged behind other apicomplexan parasites. Using regulatory sequences from E. tenella, we obtained a transgenic line of E. intestinalis expressing yellow fluorescent protein (YFP). YFP was continuously expressed throughout the whole life cycle. Morphological features of E. intestinalis in different developmental stages were dynamically observed with the transgenic line. Some important features in the endogenous development stages were observed. Trophozoites were found as early as 4 h post inoculation. Two types of schizonts and merozoites were observed in first three of the four schizogonies. Beside jejunum and ileum, gametogony stage and oocysts were also found in the duodenum and vermiform appendix. In addition, the transgenic strain was highly immunogenic but less pathogenic than the wild type. Considering the high immunogenicity of E. intestinalis and amenability to transfection with foreign genes, transgenic E. intestinalis could be a promising oral eukaryotic vaccine vector.

Molecular analysis of single oocyst of Eimeria by whole genome amplification (WGA) based nested PCR.

PCR-based molecular tools are widely used for the identification and characterization of protozoa. Here we report the molecular analysis of Eimeria species using combined methods of whole genome amplification (WGA) and nested PCR. Single oocyst of Eimeria stiedai or Eimeriamedia was directly used for random amplification of the genomic DNA with either primer extension preamplification (PEP) or multiple displacement amplification (MDA), and then the WGA product was used as template in nested PCR with species-specific primers for ITS-1, 18S rDNA and 23S rDNA of E. stiedai and E. media. WGA-based PCR was successful for the amplification of these genes from single oocyst. For the species identification of single oocyst isolated from mixed E. stiedai or E. media, the results from WGA-based PCR were exactly in accordance with those from morphological identification, suggesting the availability of this method in molecular analysis of eimerian parasites at the single oocyst level. WGA-based PCR method can also be applied for the identification and genetic characterization of other protists.

A Novel Vaccine Delivery Model of the Apicomplexan Eimeria tenella Expressing Eimeria maxima Antigen Protects Chickens against Infection of the Two Parasites

Vaccine delivery is critical in antigen discovery and vaccine efficacy and safety. The diversity of infectious diseases in humans and livestock has required the development of varied delivery vehicles to target different pathogens. In livestock animals, previous strategies for the development of coccidiosis vaccines have encountered several hurdles, limiting the development of multiple species vaccine formulations. Here, we describe a novel vaccine delivery system using transgenic Eimeria tenella expressing immunodominant antigens of Eimeria maxima. In this delivery system, the immune mapped protein 1 of E. maxima (EmIMP1) was delivered by the closely related species of E. tenella to the host immune system during the whole endogenous life cycle. The overexpression of the exogenous antigen did not interfere with the reproduction and immunogenicity of transgenic Eimeria. After immunization with the transgenic parasite, we detected EmIMP1’s and E. maxima oocyst antigens’ specific humoral and cellular immune responses. In particular, we observed partial protection of chickens immunized with transgenic E. tenella against subsequent E. maxima infections. Our results demonstrate that the transgenic Eimeria parasite is an ideal coccidia antigen delivery vehicle and represents a new type of coccidiosis vaccines. In addition, this model could potentially be used in the development of malaria live sporozoite vaccines, in which antigens from different strains can be expressed in the vaccine strain.

A new species of Eimeria (Apicomplexa: Eimeriidae) from Californian rabbits in Hebei Province, China

Rabbit coccidiosis is caused by infection with one or usually several Eimeria species, parasitizing in hepatobiliary ducts or intestinal epithelium of rabbits. To date, 11 species of rabbit coccidia have been well documented. Here we report a new species of Eimeria from rabbits. Sporulated oocysts were ellipsoidal to slightly ovoidal, 37.4 (32.6-41.2) μm in length, 23.5 (20.9-25.5) μm in width, with a shape index (length/width) 1.6 (1.43-1.91) and smooth, bilayered, homogeneously thick wall. The micropyle was obvious and with an inner diameter of 6.2 (5.0-7.5) μm. Both oocyst residuum and polar granule were absent. Sporocysts were ellipsoidal to elongate, 17.2 (13.2-20.0) μm long and 8.4 (7.5-9.1) μm wide, with a shape index (length/width) of 2.1 (1.74-2.21) and the presence of Stieda body and sporocyst residuum. The prepatent period was 132h. Phylogenetic analysis showed that 18S rDNA sequence of the new species clustered together with the 11 rabbit Eimeria species into a clade. However, ITS-1 sequence of the new species shared low similarities (27.1%-30%) with those of 11 rabbit Eimeria species. As the data above supported the erection of a new species, we named it as Eimeria kongi n. sp., in honor of Fanyao Kong, a Chinese parasitologist. The finding of the new species has important implications for the diagnosis and prevention of rabbit coccidiosis.