A systematic review on efficiency of microneme proteins to induce protective immunity against Toxoplasma gondii

Toxoplasma gondii is an intracellular parasite infecting almost all warm-blooded animals. Many studies on vaccination have been performed previously, and micronemal proteins (MICs) have crucial importance in this regard. The current review aims to reveal the efficiency of MICs as target antigen, adjuvants, animal models (species/strain), T. gondii strains for challenge infection, and routes of vaccine to prevent Toxoplasma infection. A comprehensive literature search was performed on April 18, 2018, in several known databases. Studies were included when evaluating vaccines based on MIC against T. gondii compared to that of a control group. Two independent researchers done the search process, study choice, and data extraction. A total of 28 articles published were selected for further analysis. Among them, 57.03% of the studies focused on MIC3 and its epitopes. SAG1 was further used in cocktail vaccines compared to other antigens. GM-CSF and Freund's complete were the predominant adjuvants used. BALB/c mice have been introduced as a proper model for lethal challenge. Virulent T. gondii (RH) was utilized more than other strains for challenge. Among MICs, the results of vaccination with MIC1-4, MIC6, and PLP1 demonstrated significantly strong humoral and cellular immunity, increased survival time, and reduced cyst burden in the mice. This review summarizes the latest results on MIC-based vaccines and presents that the most effective vaccination procedure is the administration of the cocktail vaccines. Our survey can serve as a basis for further studies to develop more efficient novel vaccines against T. gondii for animals and humans.