A Toxoplasma gondii mutant highlights the importance of translational regulation in the apicoplast during animal infection

Protection against Eimeria intestinalis infection in rabbits immunized with the recombinant elongation factors EF1α and EFG

Eimeria intestinalis is the most pathogenic species of rabbit coccidiosis, causing weight loss, diarrhea, and even acute death. The currently used anticoccidial drugs against E. intestinalis in rabbits are associated with drug resistance and residues. Immunological control might be a potential alternative. We cloned and expressed the E. intestinalis recombinant EF1α and EFG (rEi-EF1α and rEi-EFG, respectively). Rabbits were immunized subcutaneously every 14 days with 100 µg of rEi-EF1α and rEi-EFG and followed by 5 × 104 E. intestinalis sporulated oocysts orally challenge. Serum samples were collected every 7 days to measure the levels of specific antibodies and cytokines. On post-challenge day 14, rabbits were sacrificed and the anticoccidial index was evaluated. The rabbits of PBS challenged groups exhibited anorexia, diarrhea, marked intestinal wall thickening, and white nodules that formed patches, while rabbits from the rEi-EF1α or rEi-EFG challenged group exhibited milder symptoms. The rEi-EF1α group showed a 75.18% oocyst reduction and 89.01%wt gain; the rEi-EFG group had a 60.58% oocyst reduction and 56.04%wt gain. After vaccination, specific IgG levels increased and stayed high (P < 0.05). The IL-4 and IL-2 levels of rEi-EF1α immunized groups showed a significant increase after immunization (P < 0.05). Both rEi-EF1α and rEi-EFG could induce humoral and cellular immune responses. In contrast, rabbits immunized with rEi-EF1α were better protected from challenge by E. intestinalis than rEi-EFG.

Rhoptry protein 5 (ROP5) Is a Key Virulence Factor in Neospora caninum

Neospora caninum, of the Apicomplexa phylum, is a common cause of abortions in cattle and nervous system dysfunction in dogs. Rhoptry proteins of Apicomplexa play an important role in virulence. The objectives of this study were to study functions of NcROP5 in N. caninum by deleting the NcROP5 gene from the wild Nc-1 strain. We selected NcROP5 in ToxoDB and successfully constructed an NcROP5 gene-deleted vector, pTCR-NcROP5-CD KO. Then we screened the NcROP5 knockout strains (ΔNcROP5) at the gene, protein and transcription levels. Plaque assay, host cell invasion assay and intracellular proliferation test showed that the ΔNcROP5 strain had less plaque space, weakened invasion capacity and slower intracellular growth. Animal testing showed significantly lower cerebral load of ΔNcROP5 than the load of the Nc-1 strain, as well as a loss of virulence for the ΔNcROP5 strains. Phenotypic analyses using the label-free LC-MS/MS assay-based proteomic method and KEGG pathway enrichment analysis showed a reduction of NcGRA7 transcription and altered expression of multiple proteins including the apicomplexan family of binding proteins. The present study indicated that ROP5 is a key virulence factor in N. caninum in mice. The proteomic profiling of Nc-1 and ΔNcROP5 provided some data on differential proteins. These data provide a foundation for future research of protein functions in N. caninum.

Toxoplasma gondii upregulates interleukin-12 to prevent Plasmodium berghei-induced experimental cerebral malaria

A chronic infection with the parasite Toxoplasma gondii has previously been shown to protect mice against subsequent viral, bacterial, or protozoal infections. Here we have shown that a chronic T. gondii infection can prevent Plasmodium berghei ANKA-induced experimental cerebral malaria (ECM) in C57BL/6 mice. Treatment with soluble T. gondii antigens (STAg) reduced parasite sequestration and T cell infiltration in the brains of P. berghei-infected mice. Administration of STAg also preserved blood-brain barrier function, reduced ECM symptoms, and significantly decreased mortality. STAg treatment 24 h post-P. berghei infection led to a rapid increase in serum levels of interleukin 12 (IL-12) and gamma interferon (IFN-γ). By 5 days after P. berghei infection, STAg-treated mice had reduced IFN-γ levels compared to those of mock-treated mice, suggesting that reductions in IFN-γ at the time of ECM onset protected against lethality. Using IL-10- and IL-12βR-deficient mice, we found that STAg-induced protection from ECM is IL-10 independent but IL-12 dependent. Treatment of P. berghei-infected mice with recombinant IL-12 significantly decreased parasitemia and mortality. These data suggest that IL-12, either induced by STAg or injected as a recombinant protein, mediates protection from ECM-associated pathology potentially through early induction of IFN-γ and reduction in parasitemia. These results highlight the importance of early IL-12 induction in protection against ECM.

Fusidic acid is an effective treatment against Toxoplasma gondii and Listeria monocytogenes in vitro, but not in mice

Fusidic acid is a bacteriostatic antibiotic that inhibits the growth of bacteria by preventing the release of translation elongation factor G (EF-G) from the ribosome. The apicomplexan parasite Toxoplasma gondii has an orthologue of bacterial EF-G that can complement bacteria and is necessary for parasite virulence. Fusidic acid has been shown to be effective in tissue culture against the related pathogen Plasmodium falciparum, and current drug treatments against T. gondii are limited. We therefore investigated the therapeutic value of fusidic acid for T. gondii and found that the drug was effective in tissue culture, but not in a mouse model of infection. To determine whether this trend would occur in another intracellular pathogen that elicits a T helper 1-type immune response, we tested the efficacy of fusidic acid for the bacterium Listeria monocytogenes. Similar to its effects on T. gondii, fusidic acid inhibits the growth of L. monocytogenes in vitro, but not in mice. These findings highlight the necessity of in vivo follow-up studies to validate in vitro drug investigations.