Protective response mediated by immunization with recombinant proteins in a murine model of toxocariasis and canine infection by Toxocara canis

Cloning, bioinformatics analysis, and expression of the ubiquitin 2 (ubq-2) gene from the dog roundworm Toxocara canis

Toxocariasis, caused by the dog roundworm Toxocara canis, is a globally distributed zoonotic parasitic disease that poses a significant threat to veterinary and public health. The ubiquitin plus an L40 ribosomal protein (UBQ-2) in parasites plays a crucial role in protein degradation and meiotic divisions, thereby affecting parasite development, survival, and parasite-host interactions. In this study, we identified for the first time a full-length cDNA encoding the UBQ-2 protein from the T. canis-omic dataset, called Tcubq-2. After cloning and sequencing, we conducted sequence analysis and structural modeling of TcUBQ-2 using online bioinformatics tools. The recombinant TcUBQ-2 protein (rTcUBQ-2) was prokaryotically expressed and subjected to Western blot analysis to assess its antigenicity and immunoreactivity. Additionally, we performed immunolocalization of the endogenous protein in adult T. canis and evaluated its serodiagnostic potential using sera from naïve and infected mice and dogs. Our results showed that the complete cDNA sequence of Tcubq-2 was 387 bp in length and encoded a polypeptide of 128 amino acids, lacking both an N-terminal signal sequence and a transmembrane domain. Sequence and phylogenetic analyses showed that TcUBQ-2 shared the closest genetic distance with its homologs in Parascaris univalens and Ascaris suum. Real-time quantitative PCR and Western blotting revealed an expression peak of TcUBQ-2 in the intestine-hatched second-stage (L3) larvae compared to other developmental stages of T. canis. Tissue localization of endogenous TcUBQ-2 revealed its broad distributions in the body wall, muscle, gut epithelium, and microvilli of adult T. canis, with gender-specific expression in the uterus, ovary, and non-embryonated eggs of females. Based on its strong immunogenic properties, a recombinant TcUBQ-2 (rTcUBQ-2)-based ELISA was established and exhibited a sensitivity of 100% and a specificity of 95.8% to detect anti-T. canis mouse sera and a sensitivity of 79.2% and a specificity of 83.3% to detect anti-T. canis dog sera, respectively. This study presents a comprehensive bioinformatics analysis of the dog roundworm TcUBQ-2, and its strong serodiagnostic performance suggests that rTcUBQ-2 has the potential to be developed into an ELISA-based serological test for detecting toxocariasis in dogs and other accidental hosts, including humans.

Enhanced protective immunity against Baylisascaris schroederi infection in mice through a multi-antigen cocktail vaccine approach

Baylisascaris schroederi is among the most severe intestinal nematodes affecting giant pandas. Developing effective and secure vaccines can be used as a novel strategy for controlling repeated roundworm infection and addressing drug resistance. In our previous study, three recombinant antigens (rBsHP2, rBsGAL, and rBsUP) exhibited promising effects against B. schroederi infection in the mice model. This study extends the findings by formulating four-form cocktail vaccines (GAL+UP, HP2+UP, GAL+HP2, and GAL+HP2+UP) using three B. schroederi recombinant antigens to improve protection in mice further. Additionally, the protective differences after immunizing mice with different doses of cocktail antigens (150 μg, 100 μg, and 50 μg) were analyzed. Administration of rBs(GAL+UP), rBs(HP2+UP), rBs(GAL+HP2), and rBs(GAL+HP2+UP) significantly reduced liver and lung lesions, along with a decrease in L3 larvae by 83.7%, 82.1%, 76.4%, and 75.1%, respectively. These vaccines induced a Th1/Th2 mixed immunity, evidenced by elevated serum antibody levels (IgG, IgG1, IgG2a, IgE, and IgA) and splenocyte cytokines [interferon gamma (IFN-γ), interleukin (IL)-5, and IL-10]. Furthermore, varying cocktail vaccine dosages did not significantly affect protection. The results confirm that a 50 μg rBs(GAL+UP) dosage holds promise as a better candidate vaccine combination against B. schroederi infection, providing a basis for developing the B. schroederi vaccine.

Evaluation of the immunoprotective effects of eight recombinant proteins from Baylisascaris schroederi in mice model

BACKGROUND

Baylisascaris schroederi is the most common and harmful intestinal parasitic nematode of giant pandas, causing ascariasis. Although drug deworming is the main measure to control ascariasis in captive giant pandas, prolonged and repeated use of deworming drugs might induce resistance in nematodes and drug residues in giant pandas. Therefore, developing a safe and effective vaccine might provide a novel strategy to prevent ascariasis in captive giant pandas.

METHODS

Four highly expressed secretome genes encoding excretory and secretory proteins of B. schroederi, including transthyretin-like protein 46 (BsTLP), uncharacterized protein (BsUP), hypothetical protein 1 (BsHP1), and hypothetical protein 2 (BsHP2) and four functional genes [(encoding Galectin (BsGAL), glutathione S-transferase (BsGST), fatty acid-binding protein (BsFABP), and thioredoxin peroxidase (BsTPX)] were identified based on genome and transcriptome databases of B. schroederi and used to construct recombinant proteins via prokaryotic expression. Kunming mice were vaccinated subcutaneously twice with the recombinant proteins (50 μg/mouse) mixed with Quil A adjuvant with a 2-week interval and then orally challenged with 3000 infective eggs. The immunoprotective effects of the eight recombinant proteins on mice were assessed comprehensively using surface lesion histology scores of the mouse liver and lung, larval worm reduction, serum antibody levels (IgG, IgE, IgA, IgG1, and IgG2a), and cytokine production [interferon gamma (IFN-γ), interleukin (IL)-2, IL-4, IL-5, and IL-10].

RESULTS

Mice vaccinated with recombinant (r)BsUP (76.5%), rBsGAL (74.7%), and rBsHP2 (71.5%) showed a significant (P < 0.001) reduction in the larval worm rate compared with that in the adjuvant control. Besides, the surface lesions in the liver and lung of the vaccinated mice were alleviated. Serum levels of total IgG, IgE, IgA, IgG1, IgG2a, and cytokines, including IL-10, IL-5, and IFN-γ, were significantly higher (P < 0.001) than those in the control group.

CONCLUSIONS

The results showed that candidate three vaccines (rBsUP, rBsGAL, and rBsHP2) could provide effective protection against egg infection in mice associated with a mixed Th1/2-type immune response.