Modest Protective Immune Responses Induced by a DNA Vaccine Expressing IMP1 of Toxoplasma gondii in BALB/c Mice

Toxoplasma gondii is a parasitic protozoan that infects nucleated cells and poses a major threat to human and animal health. Developing effective vaccines is critical for controlling toxoplasmosis. Immune Mapped Protein 1 (IMP1) is a protective antigen located on the plasma membrane of T. gondii. This study aimed to evaluate the efficacy of IMP1 as a DNA vaccine, either alone or combined with IL-12 as an adjuvant, in BALB/c mice. The use of IL-12 as an adjuvant was based on its well-documented ability to enhance Th1 immune responses in DNA vaccines against T. gondii. Mice were divided into five groups: group I served as a control (100 μL PBS), group II received empty pcDNA3.1, group III received pcIL12, group IV received pcTgIMP1, and group V received a combination of pcTgIMP1 and pcIL12 (50 μg each). Immunisation was administered three times on days zero, 14, and 28 with the same dose. Two weeks post-final vaccination, mice from each group were either challenged with a lethal dose of T. gondii for survival monitoring or euthanised for evaluating immune responses, including antibody levels, lymphocyte proliferation, and cytokine production. Results showed that mice immunised with pcIMP1 + pcIL-12 or pcTgIMP1 alone exhibited robust immune responses against Toxoplasmosis. These responses included elevated levels of IgG1 and IgG2a antibodies, a strong lymphoproliferative response, and higher levels of IFN-γ and IL-4 production compared to the other groups. Furthermore, mice immunised with pcIMP1 + pcIL-12 demonstrated prolonged survival times compared to the empty pcDNA3.1, pcIL-12 alone, and control groups (p < 0.05). Our finding underscores the potential of IMP1 as a vaccine candidate and highlights the adjuvant effect of IL-12 in enhancing protective immunity against toxoplasmosis.