Isolation of coccidian enteroepithelial stages of Toxoplasma gondii from the intestinal mucosa of cats by Percoll density-gradient centrifugation

Toxoplasma invasion delayed by TgERK7 eradication

Toxoplasma gondii causes serious clinical toxoplasmosis in humans mostly due to its asexual life cycles, which can be artificially divided into five tightly coterminous stages. Any radical or delay for the stage will result in tremendous changes immediately behind. We previously demonstrated that TgERK7 is associated with the intracellular proliferation of T. gondii, but during the process, other stages before were not meanwhile determined. To further clarify the function of ERK7 gene in T. gondii, the complemental strain of ΔTgERK7 tachyzoites created previously was engineered via electric transfection with the recombinant pUC/Tgerk7 plasmid, named pUC/TgERK7 strain in this study, and was used together with ΔTgERK7 and wild-type GT1 strains to retrospect the phenotypic changes including invasion and attachment. The results showed that TgERK7 protein can be re-expressed in the ΔTgERK7 tachyzoites and eradication of this protein leads to significantly lower invasion of T. gondii at 1 h and 2 h post-infection (P < 0.05), which is the key factor causing the following slow intracellular proliferation, in comparison with wild-type GT1 and pUC/TgERK7 parasites; noteworthily, at other early time points including 15 min for attachment assay was no statistical difference (P > 0.05). The data suggested that ERK7 protein in T. gondii is an important virulence factor that participates in the invasion of this parasite.

Visualization of IL-22-expressing Lymphocytes Using Reporter Mice

Reporter mice have been widely used to observe the localization of expression of targeted genes. This protocol focuses on a strategy to establish a new transgenic reporter mouse model. We chose to visualize interleukin (IL) 22 gene expression because this cytokine has important activities in the intestine, where it contributes to repair tissues damaged by inflammation. Reporter systems offer considerable advantages over other methods of identifying products in vivo. In the case of IL-22, other studies had first isolated cells from tissues and then re-stimulated the cells in vitro. IL-22, which is normally secreted, was trapped inside cells using a drug, and intracellular staining was used to visualize it. This method identifies cells capable of producing IL-22, but it does not determine whether they were doing so in vivo. The reporter design includes inserting a gene for a fluorescent protein (tdTomato) into the IL-22 gene in such a way that the fluorescent protein cannot be secreted and therefore remains trapped inside the producing cells in vivo. Fluorescent producers can then be visualized in tissue sections or by ex vivo analysis through flow cytometry. The actual construction process for the reporter included recombineering a bacterial artificial chromosome that contained the IL-22 gene. This engineered chromosome was then introduced into the mouse genome. Homeostatic IL-22 reporter expression was observed in different mouse tissues, including the spleen, thymus, lymph nodes, Peyer's patch, and intestine, by flow cytometry analysis. Colitis was induced by T-cell (CD4+CD45RBhigh) transfer, and reporter expression was visualized. Positive T cells were first present in the mesenteric lymph nodes, and then they accumulated inside the lamina propria of the distal small intestine and colon tissues. The strategy using BACs gave good-fidelity reporter expression compared to IL-22 expression, and it is simpler than knock-in procedures.

Toxoplasma gondii merozoite gene expression analysis with comparison to the life cycle discloses a unique expression state during enteric development

BACKGROUND

Considerable work has been carried out to understand the biology of tachyzoites and bradyzoites of Toxoplasma gondii in large part due to in vitro culture methods for these stages. However, culturing methods for stages that normally develop in the gut of the definitive felid host, including the merozoite and sexual stages, have not been developed hindering the ability to study a large portion of the parasite's life cycle. Here, we begin to unravel the molecular aspects of enteric stages by providing new data on merozoite stage gene expression.

RESULTS

To profile gene expression differences in enteric stages we harvested merozoites from the intestine of infected cats and hybridized mRNA to the Affymetrix Toxoplasma GeneChip. We analyzed the merozoite data in context of the life cycle by comparing it to previously published data for the oocyst, tachyzoite, and bradyzoite stages. Principal component analysis highlighted the unique profile of merozoites, placing them approximately half-way on a continuum between the tachyzoite/bradyzoite and oocyst samples. Prior studies have shown that antibodies to surface antigen one (SAG1) and many dense granule proteins do not label merozoites: our microarray data confirms that these genes were not expressed at this stage. Also, the expression for many rhoptry and microneme proteins was drastically reduced while the expression for many surface antigens was increased at the merozoite stage. Gene Ontology and KEGG analysis revealed that genes involved in transcription/translation and many metabolic pathways were upregulated at the merozoite stage, highlighting unique growth requirements of this stage. To functionally test these predictions, we demonstrated that an upstream promoter region of a merozoite specific gene was sufficient to control expression in merozoites in vivo.

CONCLUSIONS

Merozoites are the first developmental stage in the coccidian cycle that takes place within the gut of the definitive host. The data presented here describe the global gene expression profile of the merozoite stage and the creation of transgenic parasite strains that show stage-specific expression of reporter genes in the cat intestine. These data and reagents will be useful in unlocking how the parasite senses and responds to the felid gut environment to initiate enteric development.

Toxoplasma gondii merozoite gene expression analysis with comparison to the life cycle discloses a unique expression state during enteric development

Background

Considerable work has been carried out to understand the biology of tachyzoites and bradyzoites of Toxoplasma gondii in large part due to in vitro culture methods for these stages. However, culturing methods for stages that normally develop in the gut of the definitive felid host, including the merozoite and sexual stages, have not been developed hindering the ability to study a large portion of the parasite’s life cycle. Here, we begin to unravel the molecular aspects of enteric stages by providing new data on merozoite stage gene expression.

Results

To profile gene expression differences in enteric stages we harvested merozoites from the intestine of infected cats and hybridized mRNA to the Affymetrix Toxoplasma GeneChip. We analyzed the merozoite data in context of the life cycle by comparing it to previously published data for the oocyst, tachyzoite, and bradyzoite stages. Principal component analysis highlighted the unique profile of merozoites, placing them approximately half-way on a continuum between the tachyzoite/bradyzoite and oocyst samples. Prior studies have shown that antibodies to surface antigen one (SAG1) and many dense granule proteins do not label merozoites: our microarray data confirms that these genes were not expressed at this stage. Also, the expression for many rhoptry and microneme proteins was drastically reduced while the expression for many surface antigens was increased at the merozoite stage. Gene Ontology and KEGG analysis revealed that genes involved in transcription/translation and many metabolic pathways were upregulated at the merozoite stage, highlighting unique growth requirements of this stage. To functionally test these predictions, we demonstrated that an upstream promoter region of a merozoite specific gene was sufficient to control expression in merozoites in vivo.

Conclusions

Merozoites are the first developmental stage in the coccidian cycle that takes place within the gut of the definitive host. The data presented here describe the global gene expression profile of the merozoite stage and the creation of transgenic parasite strains that show stage-specific expression of reporter genes in the cat intestine. These data and reagents will be useful in unlocking how the parasite senses and responds to the felid gut environment to initiate enteric development.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-350) contains supplementary material, which is available to authorized users.

Toxoplasma gondii: Cross-immunity against the enteric cycle

Eight of nine cats inoculated with strain ME-49 and challenged with three different strains of Toxoplasma were immune to oocyst shedding, as ascertained with bioassays of their feces. In a second experiment, only toxoplasma asexual stages were seen in H&E stained gut sections of cats treated with suppressive doses of sulfamerazine and pyrimethamine starting 2 days after oral inoculation with cysts of the strain ME-49 and killed 6 days later. In a third experiment, four cats were similarly inoculated and treated for 20 days. Six weeks later, the cats received an oral homologous challenge with cysts, and none shed toxoplasma oocysts. An acceptable level of cross-protection was achieved with strain ME-49, and therefore, it can be used as a candidate strain from which antigens could be tested for enteric protection.

Isolation of Neospora caninum from the brain of a pregnant sheep

Neospora caninum was isolated from the brain of a naturally infected pregnant sheep by inoculation of immunodeficient mice with a homogenate of the brain tissue. The ewe showed no clinical signs. Tachyzoites were observed in the tissues of the nu/nu mice injected with the brain tissue homogenate and the diagnosis was confirmed by immunohistochemical staining with anti-N. caninum antibodies and by detecting N. caninum-specific DNA by polymerase chain reaction.

Trail antigen in Eimeria stiedai sporozoites associated with a thrombospondin-related motif and the entry of cultured cells

In order to examine the antigenic similarity and specificity of the trail antigen of Eimeria stiedai and Etp 100, a microneme protein of Eimeria tenella, monoclonal antibodies to the trail antigen of E. stiedai sporozoites were selected by an indirect immunofluorescent antibody method. The monoclonal antibody of one clone, 3D10, reacted with the anterior portion of non-fixed sporozoites. By immunoblotting, the monoclonal antibody was found to react with a 100 kDa antigen of E. stiedai sporozoites, and a 117 kDa antigen of E. tenella sporozoites and merozoites. It was also found to react with a recombinant protein with thrombospondin-/properdin-like motifs homologous to E. tenella microneme protein Etp 100. The monoclonal antibody significantly inhibited the penetration of E. stiedai sporozoites into cultured rabbit hepatobiliary epithelial cells. These results suggest that E. stiedai sporozoites have a trail antigen, located in the anterior region on the outer surface of the sporozoites, which has an epitope with thrombospondin-/properdin-like motifs similar to E. tenella microneme protein Etp 100. This protein may play an important functional role in the process of penetration of host cells.

A 14-3-3 protein homologue is expressed in feline enteroepithelial-stages of Toxoplasma gondii

Fourteen cDNA clones encoding epitopes of proteins of Toxoplasma gondii feline enteroepithelial-stages parasites were isolated and expressed in Escherichia coli in an effort to determine the antigenecity of the parasites. Sequence analysis showed that four of the cDNA clones had a 930-bp open-reading frame encoding a product showing similarity to the 14-3-3 protein mRNA sequence.(1) Southern hybridization of DIG-labeled positive clone with T. gondii genomic DNA cleaved with EcoRI, BamHI and HindIII resulted in one or two bands in each case. In an immunofluorescence assay, polyclonal and monoclonal antibodies raised against the expressed protein showed strong reactivity with feline enteroepithelial-stages parasites and sporozoites. In a complementation assay in which a plasmid carrying the protein-coding region of the isolated cDNA was introduced into a Saccharomyces cerevisiae mutant, strain DS9-22, the expressed protein showed complementation of the function of the 14-3-3 protein in yeast transformants. These findings suggest that T. gondii parasites produce a protein showing partial homology with members of the 14-3-3 protein family and this protein is expressed in feline enteroepithelial-stages parasites.

Antigens expressed in feline enteroepithelial-stages parasites of Toxoplasma gondii

In an investigation aimed to identify Toxoplasma gondii antigens expressed in feline enteroepithelial-stages parasites, a cDNA library was constructed and fourteen positive clones were isolated by immunoscreening using sera from cats immunized with feline enteroepithelial-stages parasites. By DNA sequence homology analysis, these fourteen isolated clones were classified into four groups: hypoxanthine-guanine phosphoribosyl transferase (HGPRT) cDNA, heat shock protein 70 (HSP70) cDNA, 14-3-3 protein homologue cDNA, and cDNA encoding an unknown product. In an indirect immunofluorescence antibody test, sera from mice immunized with the recombinant protein encoded by the cDNA for HGPRT, HSP70, 14-3-3 protein, or the unknown product each showed a relatively high level of immunoreactivity with feline enteroepithelial-stages parasites.

Sex allocation and population structure in apicomplexan (protozoa) parasites

Establishing the selfing, rate of parasites is important for studies in clinical and epidemiological medicine as well as evolutionary biology Sex allocation theory offers a relatively cheap and easy way to estimate selfing rates in natural parasite populations. Local mate competition (LMC) theory predicts that the optimal sex ratio (r*; defined as proportion males) is related to the selfing rate (s) by the equation r* = (1-s)/2. In this paper, we generalize the application of sex allocation theory across parasitic protozoa in the phylum Apicomplexa. This cosmopolitan phylum consists entirely of parasites, and includes a number of species of medical and veterinary importance. We suggest that LMC theory should apply to eimeriorin intestinal parasites. As predicted, data from 13 eimeriorin species showed a female-biased sex ratio, with the sex ratios suggesting high levels of selfing (0.8-1.0). Importantly, our estimate of the selfing rate in one of these species, Toxoplasma gondii, is in agreement with previous genetic analyses. In contrast, we predict that LMC theory will not apply to the groups in which syzygy occurs (adeleorins, gregarines and piroplasms). Syzygy occurs when a single male gametocyte and a single female gametocyte pair together physically or in close proximity, just prior to fertilization. As predicted, data from four adeleorin species showed sex ratios not significantly different from 0.5.

Antibody reactivity in mice and cats to feline enteroepithelial stages of Toxoplasma gondii

The reactivity of antibodies in mice and cats to feline enteroepithelial stages of Toxoplasma gondii was examined by means of an indirect immunofluorescent antibody test. Mice immunized with feline enteroepithelial stage (FES) parasites produced antibodies not only against FES, but also against tachyzoites, sporozoites/oocysts, tissue cysts and one part of the infected feline enterocytes. After absorption with tachyzoites, the titer of antibodies reactive to enterocytes was significantly reduced. In contrast, the titer of antibodies reactive to FES remained unchanged. The antibodies from cats immunized with FES, reacted specifically to FES, but not to tachyzoites, tissue cysts or enterocytes. These results suggest that FES parasites may have stage-specific antigen(s).

Infectivity of feline enteroepithelial stages of Toxoplasma gondii isolated by Percoll-density gradient centrifugation

The infectivity of the feline enteroepithelial stages of Toxoplasma gondii isolated by Percoll-density gradient centrifugation was examined by the trypan blue dye exclusion method by assaying their penetration into feline fibroblast cells in vitro and by inoculation of the intestinal mucosa of cats. A large population of the parasites showed trypan blue dye exclusion activity. When feline fibroblast cells were inoculated with feline enteroepithelial stage parasites, no intracellular parasites were found 18 h post-inoculation. Kittens inoculated intraduodenally with 2 x 10(6) feline enteroepithelial stage parasites shed oocysts between 2 and 8 days post-inoculation. These results indicate that the isolated feline enteroepithelial stage parasites display infectivity towards enterocytes of cats and are capable of gametogenesis.

Positive evidence that anti-Toxoplasma gondii IgA antibody exists in the intestinal tract of infected cats and exerts protective activity against the infection

The presence of anti-Toxoplasma gondii IgA antibody in the feces and intestinal tract of cats infected with this parasite was demonstrated using an immunoblotting assay. Cats (n = 5) were inoculated orally with T. gondii cysts and supernatants of feces and washings of the intestinal tract were assayed for secretory IgA specific for the parasite. The secretory IgA detected recognized tachyzoite antigens of m.w. 24, 34, 38 and 43 kDa and one sporozoite antigen of m.w. 24 kDa. No reactivity was shown against bradyzoites or enteroepithelial stage parasites. Tachyzoites preincubated with washings of the intestinal tract of infected cats showed decreased activity in penetration of feline fibroblast cells, as compared to tachyzoites preincubated with similar washings derived from non-infected cats. The addition of either anti-cat IgA or anti-cat IgG to the washings had no effect on the inhibitory activity which reduced the parasite's cell-penetration activity. However, the addition of both anti-cat IgA and anti-cat IgG to the washings diminished the inhibitory activity. These results suggest that anti-T. gondii antibodies of both classes, secretory IgA and IgG, exist in the intestinal tract of infected cats and these may be capable of preventing infection.