Protective immune response against Toxoplasma gondii elicited by a novel yeast-based vaccine with microneme protein 16

Toxoplasma gondii is an obligate intracellular protozoan that can invade all eukaryotic cells and infect all warm-blood animals, causing the important zoonosis toxoplasmosis. Invasion of host cells is the key step necessary for T. gondii to complete its life cycle and microneme proteins play an important role in attachment and invasion of host cells. Microneme protein 16 (TgMIC16) is a new protective protein in T. gondii and belongs to transmembrane microneme proteins (TM-MIC). The TM-MICs are released onto the parasite's surface as complexes capable of interacting with host cell receptors. In the present study, we expressed the TgMIC16 protein on the surface of Saccharomyce cerevisiae (pCTCON2-TgMIC16/EBY100) and evaluated it as a potential vaccine for BALB/c mice against challenge infection with the RH strain of T. gondii. We immunized BALB/c mice both orally and intraperitoneally. After three immunizations, the immune response was evaluated by measuring antibody levels, lymphocyte proliferative responses, percentages of CD4+ and CD8+ T lymphocytes, cytokine production, and the survival times of challenged mice. The results showed that the pCTCON2-TgMIC16/EBY100 vaccine stimulated humoral and cellular immune responses. In addition, mice immunized with the pCTCON2-TgMIC16/EBY100 vaccine showed increased survival times compared with non-immunized controls. In summary, TgMIC16 displayed on the cell surface of S. cerevisiae could be used as potential vaccine against toxoplasmosis.