Evaluation of immune responses and allergenic risks to different adjuvants in an OVA-based immunisation model using BALB/c mice

Abstract Objectives Adjuvants play a crucial role in enhancing vaccine efficacy by engaging the innate immune system and shaping a robust adaptive response. However, some adjuvants can also influence allergenicity by promoting Th2-biased responses, potentially increasing the risk of allergic sensitization depending on their mode of action. Methods In this study, we investigated the immunogenic properties of various FDA-approved adjuvants using ovalbumin (OVA) as a model antigen. BALB/c mice were immunized with different formulations of OVA combined with Alum, Freund's Adjuvant, and MF59 to assess their immunostimulatory effects. A total of nine experimental groups were evaluated, including two different doses of Alum. To assess the allergenic potential of these formulations, we analysed IgG1, IgG2a, and IgG2b responses, allowing us to evaluate the balance between Th1- and Th2-mediated immunity. Results CFA induced the strongest anti-OVA IgG1 response, while MF59 caused a short-lived response. OVA + 0.1 mg Alum group produced higher IgG1 response than the OVA + 0.2 mg group. CFA also strongly triggered Th1 immunity, with high IgG2a/IgG2b levels, while Alum elicited a low IgG2a/IgG2b response. No IgG2a/IgG2b response was seen in other groups. Conclusion The OVA + CFA group induced the highest IgG1 response, with IgG2a and IgG2b modulating the Th1-biased immune response. MF59 caused a rapid decline in IgG1 and promoted a Th2 response, with no IgG2a or IgG2b detected. The OVA + 0.1 mg Alum group showed a higher IgG1 response than the OVA + 0.2 mg group, highlighting the importance of optimizing the alum/antigen ratio. Alum triggered a strong Th2 response and a weak Th1 response, resulting in low IgG2a and IgG2b levels.