Nanocurcumin as an adjuvant in killed Toxoplasma gondii vaccine formulation: An experience in BALB/c mice

Toxoplasma gondii (T. gondii) remains as one of the controversial infections in the world. T. gondii is an important obligate intracellular protozoan parasite in the immune-deficient patients and pregnant women, sometimes leading to death and abortion, respectively. Herein, the adjuvant activity of nanocurcumin was assessed in the T. gondii killed vaccine model in BALB/c mice. In this study, 144 BALB/c mice were included in 8 groups and administered with different regimens of the vaccine; vac+30, 20 mg/kg of curcumin and nanocurcumin, vac + Freund's adjuvant, killed vac, vac + Alum adjuvant, and PBS via the subcutaneous route of immunization for three times with two-week intervals. Two weeks after the last immunization, the splenocytes' culture supernatant was evaluated for IL-4, IFN-γ, IL-2 and TNF-α cytokines and IFN-γ/IL-4, IFN-γ/TNF-α, and IL-2/IL-4 cytokine ratios using commercial ELISA kits. Specific total IgG antibodies, IgG1, and IgG2a were assessed with an optimized ELISA. Then the survival rate was determined 10 days after the experimental challenge. The results showed that the vaccine formulation in nanocurcumin at 20 mg/kg significantly increases IFN-γ cytokine and IFN-γ/IL4, IFN-γ/TNFα, and IL-2/IL4 ratios versus the vaccine formulated in curcumin, killed vaccine, and PBS group. In addition, specific total IgG antibody response showed that the vaccine formulated in nanocurcumin was more potent than that formulated in curcumin in the induction of humoral immune responses. Furthermore, results from the experimental challenge showed that nanocurcumin at a dose of 20 mg/kg could promote the life span of mice approximately by 12% versus the killed vaccine group. The present study showed that nanocurcumin in the vaccine formulation not only is more bioactive than curcumin in the modulation of cellular and humoral immune responses, but also provides more protectivity rate in the vaccinated mice on the killed T. gondii vaccine model. It seems that nanocurcumin can be used as an immunomodulator in vaccine formulation or as part of a complex adjuvant.