PLK:Δgra9 Live Attenuated Strain Induces Protective Immunity Against Acute and Chronic Toxoplasmosis

Toxoplasma gondii gra5 deletion mutant protects hosts against Toxoplasma gondii infection and breast tumors

Toxoplasma gondii is the causative agent of toxoplasmosis, a zoonotic disease that poses a threat to human health and a considerable loss to livestock farming. At present, clinical therapeutic drugs mainly target T. gondii tachyzoites and fail to eradicate bradyzoites. Developing a safe and effective vaccine against toxoplasmosis is urgent and important. Breast cancer has become a major public health problem and the therapeutic method needs to be further explored. Many similarities exist between the immune responses caused by T. gondii infection and the immunotherapy for cancers. T. gondii dense granule organelles secrete immunogenic dense granule proteins (GRAs). GRA5 is localized to the parasitophorous vacuole membrane in the tachyzoite stage and the cyst wall in the bradyzoite stage. We found that T. gondii ME49 gra5 knockout strain (ME49Δgra5) was avirulent and failed to form cysts but stimulated antibodies, inflammatory cytokines, and leukocytes infiltration in mice. We next investigated the protective efficacy of ME49Δgra5 vaccination against T. gondii infection and tumor development. All the immunized mice survived the challenge infection of either wild-type RH, ME49, VEG tachyzoites, or ME49 cysts. Moreover, ME49Δgra5 tachyzoite inoculation in situ attenuated the growth of murine breast tumor (4T1) in mice and prevented 4T1's lung metastasis. ME49Δgra5 inoculation upregulated the levels of Th1 cytokines and tumor-infiltrating T cells in the tumor microenvironment and triggered anti-tumor responses by increasing the number of natural killer, B, and T cells, macrophages, and dendritic cells in the spleen. Collectively, these results suggested that ME49Δgra5 was a potent live attenuated vaccine against T. gondii infection and breast cancer.

Live-attenuated ME49Δcdpk3 strain of Toxoplasma gondii protects against acute and chronic toxoplasmosis

Toxoplasmosis, a common parasitic disease, is caused by Toxoplasma gondii, which infects approximately 30% of the world’s population. This obligate intracellular protozoan causes significant economic losses and poses serious public health challenges worldwide. However, the development of an effective toxoplasmosis vaccine in humans remains a challenge to date. In this study, we observed that the knockout of calcium-dependent protein kinase 3 (CDPK3) in the type II ME49 strain greatly attenuated virulence in mice and significantly reduced cyst formation. Hence, we evaluated the protective immunity of ME49Δcdpk3 as a live attenuated vaccine against toxoplasmosis. Our results showed that ME49Δcdpk3 vaccination triggered a strong immune response marked by significantly elevated proinflammatory cytokine levels, such as IFN-γ, IL-12, and TNF-α, and increased the percentage of CD4⁺ and CD8⁺ T-lymphocytes. The high level of Toxoplasma-specific IgG was maintained, with mixed IgG1/IgG2a levels. Mice vaccinated with ME49Δcdpk3 were efficiently protected against the tachyzoites of a variety of wild-type strains, including type I RH, type II ME49, Chinese 1 WH3 and Chinese 1 WH6, as well as the cysts of wild-type strains ME49 and WH6. These data demonstrated that ME49Δcdpk3 inoculation induced effective cellular and humoral immune responses against acute and chronic Toxoplasma infections with various strains and was a potential candidate to develop a vaccine against toxoplasmosis.

The Cross-Species Immunity During Acute Babesia Co-Infection in Mice

Babesiosis causes high morbidity and mortality in immunocompromised individuals. An earlier study suggested that lethal Babesia rodhaini infection in murine can be evaded by Babesia microti primary infection via activated macrophage-based immune response during the chronic stage of infection. However, whether the same immune dynamics occur during acute B. microti co-infection is not known. Hence, we used the mouse model to investigate the host immunity during simultaneous acute disease caused by two Babesia species of different pathogenicity. Results showed that B. microti primary infection attenuated parasitemia and conferred immunity in challenge-infected mice as early as day 4 post-primary infection. Likewise, acute Babesia co-infection undermined the splenic immune response, characterized by the significant decrease in splenic B and T cells leading to the reduction in antibody levels and decline in humoral immunity. Interestingly, increased macrophage and natural killer splenic cell populations were observed, depicting their subtle role in the protection. Pro-inflammatory cytokines (i.e. IFN-γ, TNF-α) were downregulated, while the anti-inflammatory cytokine IL-10 was upregulated in mouse sera during the acute phase of Babesia co-infection. Herein, the major cytokines implicated in the lethality caused by B. rodhaini infection were IFN- γ and IL-10. Surprisingly, significant differences in the levels of serum IFN- γ and IL-10 between co-infected survival groups (day 4 and 6 challenge) indicated that even a two-day delay in challenge infection was crucial for the resulting pathology. Additionally, oxidative stress in the form of reactive oxygen species contributed to the severity of pathology during acute babesiosis. Histopathological examination of the spleen showed that the erosion of the marginal zone was more pronounced during B. rodhaini infection, while the loss of cellularity of the marginal zone was less evident during co-infection. Future research warrants investigation of the roles of various immune cell subtypes in the mechanism involved in the protection of Babesia co-infected hosts.

Toxoplasma gondii and Neospora caninum Infections in Stray Cats and Dogs in the Qinghai–Tibetan Plateau Area, China

Simple Summary

Diseases caused by parasites have introduced serious threats to human health and the development of animal husbandry in the Qinghai–Tibetan Plateau Area (QTPA), such as toxoplasmosis caused by Toxoplasma gondii and neosporosis caused by Neospora caninum. However, information on the epidemiology of toxoplasmosis and neosporosis in stray cats and dogs which are the definitive hosts of T. gondii and N. caninum in the QTPA is limited. The aim of this study was to establish a detailed record of the seroprevalence of T. gondii and N. caninum-specific IgG and IgM antibodies in serum samples and the molecular epidemiology in feces from stray cats and dogs in the plateau area. The results revealed that stray cats and dogs in the QTPA, China present both T. gondii and N. caninum infection through the antibodies and antigen detection of the indirect ELISA tests and qPCRs. The present study suggests the prevalence of acute neosporosis and chronic re-emergence of toxoplasmosis in stray cats and dogs in the testing area. To the best of our knowledge, this is the first report of T. gondii and N. caninum infection in cats and dogs in the QTPA, and the first determination of N. caninum infection in cats in China. In conclusion, stray cats and dogs play key roles in the transmission and prevalence of T. gondii and N. caninum in the plateau area.

Abstract

Toxoplasma gondii and Neospora caninum belong to the Apicomplexan protozoa which is an obligate intracellular parasite, causing toxoplasmosis and neosporosis throughout the world. Cats and dogs are the definitive hosts of these two parasites. However, information on the epidemiology of toxoplasmosis and neosporosis in stray cats and dogs in the Qinghai–Tibetan Plateau Area (QTPA) is limited, and little is known about the diversity of the diseases. Therefore, the aim of this study was to perform indirect ELISA tests based on recombinant TgSAG1, TgGRA1, NcSAG1 and NcGRA7 proteins to establish a detailed record of the seroprevalence of T. gondii and N. caninum-specific IgG and IgM antibodies in serum samples and to develop qPCR amplification based on TgB1 and NcNc5 genes to conduct molecular epidemiology in feces from stray cats and dogs in the QTPA. In the current study, a total of 128 cat serum samples were analyzed through serological tests in which 53 (41.4%) and 57 (44.5%) samples were found positive for T. gondii specific-IgG and IgM antibodies, and 2 (1.6%) and 74 (57.8%) samples were confirmed positive for N. caninum specific-IgG and IgM antibodies, respectively. Out of 224 stray dog sera, 59.8% and 58.9% were recorded as positive against anti-Toxoplasma IgG and IgM antibodies, 17.9% and 64.7% were detected positive against Neospora IgG and IgM. On the other hand, 1 of 18 cat fecal samples was successfully amplified within the Ct value of 10 to 30 while no cat was positive for neosporosis. Moreover, a higher prevalence of toxoplasmosis in stray dogs (14.5%, 16/110) than of neosporosis (5.5%, 6/110) with different parasite numbers were found. Further analysis showed that no significant sex differences were found nor between the overall infection rates of T. gondii and N. caninum in this study. This study suggests that stray cats and dogs play key roles in the transmission and prevalence of T. gondii and N. caninum in the plateau area.

Mining the Proteome of Toxoplasma Parasites Seeking Vaccine and Diagnostic Candidates

Simple Summary

The One Health concept to toxoplasmosis highlights that the health of humans is closely related to the health of animals and our common environment. Toxoplasmosis outcomes might be severe and fatal in patients with immunodeficiency, diabetes, and pregnant women and infants. Consequently, the development of effective vaccine and diagnostic strategies is urgent for the elimination of this disease. Proteomics analysis has allowed the identification of key proteins that can be utilized in the development of novel disease diagnostics and vaccines. This work presents relevant proteins found in the proteome of the life cycle-specific stages of Toxoplasma parasites. In fact, it brings together the main functionality key proteins from Toxoplasma parasites coming from proteomic approaches that are most likely to be useful in improving the disease management, and critically proposes innovative directions to finally develop promising vaccines and diagnostics tools.

Abstract

Toxoplasma gondii is a pathogenic protozoan parasite that infects the nucleated cells of warm-blooded hosts leading to an infectious zoonotic disease known as toxoplasmosis. The infection outcomes might be severe and fatal in patients with immunodeficiency, diabetes, and pregnant women and infants. The One Health approach to toxoplasmosis highlights that the health of humans is closely related to the health of animals and our common environment. The presence of drug resistance and side effects, the further improvement of sensitivity and specificity of serodiagnostic tools and the potentiality of vaccine candidates to induce the host immune response are considered as justifiable reasons for the identification of novel targets for the better management of toxoplasmosis. Thus, the identification of new critical proteins in the proteome of Toxoplasma parasites can also be helpful in designing and test more effective drugs, vaccines, and diagnostic tools. Accordingly, in this study we present important proteins found in the proteome of the life cycle-specific stages of Toxoplasma parasites that are potential diagnostic or vaccine candidates. The current study might help to understand the complexity of these parasites and provide a possible source of strategies and biomolecules that can be further evaluated in the pathobiology of Toxoplasma parasites and for diagnostics and vaccine trials against this disease.