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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-016-0351-z) contains supplementary material, which is available to authorized users.

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.

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Coccidiosis, caused by different species of parasites, is an economically important disease of poultry and livestock worldwide. Here we report previously unknown alterations in the gut microbes and metabolism of BALB/c mice infected with Specifically, we observed a significant shift in the abundance of cecal bacteria and disrupted metabolism in parasitized animals. The relative abundances of bacterium NK4A136,, , and declined in response to infection, whereas, ,, , and were increased. Carbohydrate and amino acid metabolites in the serum samples of infected mice were significantly altered compared to naïve controls. Levels of amino acids, including asparagine, histidine, l-cysteine, tryptophan, lysine, glycine, serine, alanine, proline, ornithine, methionine, and valine, decreased on day 7 postinfection before returning to baseline on day 14. In addition, increased levels of indolelactate and mannitol and a reduced amount of oxalic acid indicated impaired carbon metabolism upon parasitic infection. These data demonstrate that intestinal coccidial infection perturbs the microbiota and disrupts carbon and nitrogen metabolism.

Chicken coccidiosis, caused by Eimeria sp., occurs in almost all poultry farms and causes huge economic losses in the poultry industry. Although this disease could be controlled by vaccination, the reduced feed conservation ratio limits the widespread application of anticoccidial vaccines in broilers because some intermediate and/or low immunogenic Eimeria sp. only elicit partial protection. It is of importance to enhance the immunogenicity of these Eimeria sp. by adjuvants for more effective prevention of coccidiosis. Cytokines have remarkable effects on the immunogenicity of antigens. Interleukin 2 (IL-2), for example, significantly stimulates the activation of CD8+ T cells and other immune cells. In this study, we constructed a transgenic Eimeria mitis line (EmiChIL-2) expressing chicken IL-2 (ChIL-2) to investigate the adjuvant effect of ChIL-2 to enhance the immunogenicity of E. mitis against its infection. Stable transfected EmiChIL-2 population was obtained by pyrimethamine selection and verified by PCR, genome walking, western blotting and indirect immunofluorescence assay. Cellular immune response, E. mitis-specific IFN-γ secretion lymphocytes in the peripheral blood mononuclear cells, stimulated by EmiChIL-2 was analyzed by enzyme-linked immunospot assay (ELISPOT). The results showed that EmiChIL-2 stimulated a higher cellular immune response compared with that of the wild-type parasite infection in chickens. Moreover, after the immunization with EmiChIL-2, elevated cellular immune response as well as reduced oocyst output were observed These results indicated that ChIL-2 expressed by Eimeria sp. functions as adjuvant and IL-2 expressing Eimeria parasites are valuable vaccine strains against coccidiosis.