Abstract
Toxoplasma gondii is a ubiquitous apicomplexan protozoan parasite that can infect all warm-blooded animals, causing toxoplasmosis. Thus, efficient diagnosis methods for acute T. gondii infection are essential for its management. Circulating antigens (CAgs) are reliable diagnostic indicators of acute infection. In this study, we established a mouse model of acute T. gondii infection and explored new potential diagnostic factors. CAgs levels peaked 60 h after T. gondii inoculation and 31 CAgs were identified by immunoprecipitation-liquid chromatography-tandem mass spectrometry, among which RuvB-like helicase (TgRuvBL1), ribonuclease (TgRNaseH1), and ribosomal protein RPS2 (TgRPS2) were selected for prokaryotic expression. Polyclonal antibodies against these three proteins were prepared. Results from indirect enzyme-linked immunosorbent assay indicated that anti-rTgRuvBL1, anti-rTgRNase H1, and anti-rTgRPS2 mouse sera were recognized by natural excretory-secretory antigens from T. gondii tachyzoites. Moreover, immunofluorescence assays revealed that TgRuvBL1 was localized in the nucleus, while TgRNase H1 and TgRPS2 were in the apical end. Western blotting data confirmed the presence of the three proteins in the sera of the infected mice. Moreover, mice immunized with rTgRuvBL1 (10.0 ± 0.30 days), TgRNaseH1 (9.67 ± 0.14 days), or rTgRPS2 (11.5 ± 0.34 days) had slightly longer lifespan when challenged with a virulent T. gondii RH strain. Altogether, these findings indicate that these three proteins can potentially be diagnostic candidates for acute toxoplasmosis. However, they hold poor protective potential against highly virulent T. gondii infection.
Highlights
Toxoplasma gondii is an obligatory intracellular protozoan parasite that infects virtually any warm-blooded animal, including a third of the human population (Montoya and Liesenfeld, 2004)
The results of indirect enzyme-linked immunosorbent assay (ELISA) and immunoblotting assays indicated that anti-excretory-secretory antigens (ESA) mouse and rabbit sera could identify numerous ESA components with good immunogenicity
These results showed that the double-PcAb sandwich ELISA was sufficiently sensitive
Summary
Toxoplasma gondii is an obligatory intracellular protozoan parasite that infects virtually any warm-blooded animal, including a third of the human population (Montoya and Liesenfeld, 2004). Infection is mainly acquired by ingestion of undercooked meats containing T. gondii cysts (Hide et al, 2009). The parasite causes lifelong infections by converting from rapidly dividing tachyzoites into encysted slow-growing bradyzoites, mainly localizing to the brain, and muscle tissues (Hunter and Sibley, 2012; Wohlfert et al, 2017). A latent infection may be reactivated via immune suppression (Dupont et al, 2020). Toxoplasmosis is usually asymptomatic in immunocompetent persons, but it can cause life-threatening infections in immunocompromised individuals and developing fetuses. Timely and effective diagnosis of acute T. gondii infection is imperative
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