Gitonin, a spirostanol glycoside, acts as a mucosal adjuvant to enhance antigen-specific mucosal and systemic immune responses in mice.

Despite advances in contemporary medicine, infectious diseases remain a substantial threat to global health. Mucosal vaccines, which elicit immune responses at the mucosal surfaces from where the majority of pathogens enter the body, present advantages over traditional injectable vaccines that primarily induce systemic immunity. However, development of effective mucosal vaccines is impeded by the lack of safe and potent mucosal adjuvants that can enhance antigen-specific immune responses without provoking excessive inflammation. Unlike the extensively studied triterpene saponins, spirostanol glycosides, such as gitonin, represent a distinct category of potential mucosal adjuvants with largely uncharacterized immunological properties. We demonstrated that intranasal administration of gitonin in conjunction with ovalbumin induced robust antigen-specific mucosal IgA and systemic IgG responses in mice without provoking significant local inflammation. Initially, we hypothesized that gitonin might have exerted its effects through the release of damage-associated molecular patterns (DAMPs), similar to our previously characterized cationic liposome adjuvants. However, based on in vitro studies, our findings indicate that gitonin operates via alternative mechanisms, as evidenced by minimal cellular infiltration observed at the site of administration. Our findings indicate that gitonin is a promising candidate for the development of vaccines that target mucosal membranes. It possesses a well-defined structure, demonstrates safety in applications, and effectively enhances the immune response, primarily by promoting a Th2-type response. These characteristics make gitonin particularly suitable to be developed as a mucosal adjuvant against infectious diseases that affect the respiratory tract and other mucosal surfaces, where maintaining balanced humoral immunity is essential for protection.