Macrophage Stimulation as a Useful Approach for Immunoscreening of Potential Vaccine Candidates Against Toxoplasma gondii and Neospora caninum Infections

Immunogenicity and protective efficacy of recombinant chimeric antigens based on surface proteins of Toxoplasma gondii

Introduction

Toxoplasmosis is caused by the opportunistic, cosmopolitan protozoan Toxoplasma gondii is one of the most common parasitoses in the world. This parasite can pose a threat to people with immunodeficiency but also to the fetus, since the invasion can lead to miscarriages. Moreover, this parasite can contribute to economic losses in livestock farming. These problems lead to the implementation of new, safe solutions for the development of effective toxoplasmosis immunoprophylaxis.

Methods

In this work, newly produced recombinant trivalent chimeric proteins of T. gondii, based on SAG1-SAG2 recombinant chimeric antigen that differ in one terminal antigenic component, were tested in terms of their ability to induce an effective post-vaccination response. Antigens were tested in vitro to assess their ability to elicit APC cells response and further mice of the C3H/HeOuJ strain were immunized using those antigens, to evaluate their immunogenicity and immunoprotective effect in vivo. Two weeks after the last dose mice were either sacrificed to assess selected parameters of the immune response or infected with T. gondii DX strain to determine the degree of protection one month later.

Results

The results of serological tests revealed a high level of serum IgG antibodies specific for the native T. gondii TLA antigens. TLA-stimulated splenocytes produced cytokines that are important in inhibiting protozoal invasion. Additionally, CD3+ CD4+ and CD3+ CD8+ T cell subpopulations of splenocytes were analysed by flow cytometry. One month after experimental infection mice were sacrificed, and their brains were isolated to count T. gondii tissue cyst. Immunization of mice with recombinant trivalent chimeric proteins of T. gondii resulted in reduction of tissue cyst burden rates reaching even 74%.

Discussion

The obtained results demonstrate strong immunogenicity of the studied proteins and will allow to select candidates for further research aimed at increasing the immunoprotective properties of experimental vaccines against toxoplasmosis based on T. gondii chimeric antigens.

Exploiting the Macrophage Production of IL-12 in Improvement of Vaccine Development against Toxoplasma gondii and Neospora caninum Infections

Toxoplasmosis and neosporosis are major protozoan diseases of global distribution. Toxoplasma gondii is the cause of toxoplasmosis, which affects almost all warm-blooded animals, including humans, while Neospora caninum induces neosporosis in many animal species, especially cattle. The current defective situation with control measures is hindering all efforts to overcome the health hazards and economic losses of toxoplasmosis and neosporosis. Adequate understanding of host-parasite interactions and host strategies to combat such infections can be exploited in establishing potent control measures, including vaccine development. Macrophages are the first defense line of innate immunity, which is responsible for the successful elimination of T.gondii or N. caninum. This action is exerted via the immunoregulatory interleukin-12 (IL-12), which orchestrates the production of interferon gamma (IFN-γ) from various immune cells. Cellular immune response and IFN-γ production is the hallmark for successful vaccine candidates against both T. gondii and N. caninum. However, the discovery of potential vaccine candidates is a highly laborious, time-consuming and expensive procedure. In this review, we will try to exploit previous knowledge and our research experience to establish an efficient immunological approach for exploring potential vaccine candidates against T. gondii and N. caninum. Our previous studies on vaccine development against both T. gondii and N. caninum revealed a strong association between the successful and potential vaccine antigens and their ability to promote the macrophage secretion of IL-12 using a murine model. This phenomenon was emphasized using different recombinant antigens, parasites, and experimental approaches. Upon these data and research trials, IL-12 production from murine macrophages can be used as an initial predictor for judgment of vaccine efficacy before further evaluation in time-consuming and laborious in vivo experiments. However, more studies and research are required to conceptualize this immunological approach.