Lipid Monolayer Compression Isotherms for Characterization of Adjuvant Mechanisms of Action

While vaccination is abundant in modern healthcare, the crucial adjuvant-cell interaction mechanism evades researchers. Vaccine safety and efficacy can be improved through the incorporation of adjuvants which enhance the immune response towards a specific antigen. As modern vaccine antigens become highly purified and less immunogenic, the need for safe yet effective adjuvants increases. While there are many supported theories regarding adjuvant mechanisms, none are universally agreed upon. This project investigates lipid-adjuvant interactions to better understand the underlying adjuvant mechanisms of action. Using a Langmuir trough, a lipid monolayer is exposed to an adjuvant-containing subphase and the resultant surface pressure is recorded throughout a compression cycle. Additionally, the compression cycle is observed and characterized using fluorescence microscopy. This investigation focuses on the most prevalent alum-based adjuvants Alhydrogel® (AH) and Adju-Phos® (AP). The findings support previous theories that certain adjuvants induce an immune response through lipid sorting and reorganization of the lipid bilayer. Combining compression isotherms with fluorescence imaging suggests that AH disrupts the molecular packing in the lipid monolayer while AP increases the packing density. The different behaviors of these adjuvants with model lipid membranes suggest different mechanisms of antigen delivery, which may affect the subsequent immune response.