Evaluation of Adjuvant Effectiveness of Alum-Propranolol Mixture on the Immunogenicity of Excreted/Secreted Antigens of Toxoplasma gondii RH Strain

Purpose: The introduction of novel adjuvants is an important step in attempts to develop a safe and more efficient vaccine. The present study was performed to determine whether the use of a mixed beta-adrenergic receptor antagonist propranolol (PRP) and aluminum (alum), as an adjuvant, have efficacy for Toxoplasma gondii vaccine to induce protective immunity in a mouse model.

Methods: Female BALB/c mice divided into five groups were immunized with excretorys-ecretory antigens (ESA) vaccine, alum-ESA vaccine, PRP-ESA vaccine, and alum-PRP ESA vaccine, as well as with phosphate buffered saline (PBS), as a negative control group. The immune responses were evaluated by lymphocyte proliferation assay for measuring delayedtype hypersensitivity (DTH) response and by cytokine assay for evaluating IFN-γ and IL-5 levels. The survival rate of mice in all groups was assessed during a three-week monitoring period after an intraperitoneal challenge with T. gondii tachyzoites.

Results: The results showed that mice immunized with PRP, as an adjuvant, could secret a higher level of IFN-γ, which was significant in comparison to other groups. However, mice vaccinated with alum-precipitated ESA antigen had ability to produce an elevated level of IL-5 compared to other mouse groups (P ≤ 0.05). Moreover, alum-PRP co-administration together with ESA vaccine resulted in the longer survival of mice.

Conclusion: The findings of this study revealed that the combination of alum-PRP adjuvants and ESA vaccine of T. gondii elicits both humoral and cellular immune responses, which are comparable to either alum or PRP alone.