Immune System Activation via Oil-in-Water Emulsion Adjuvant (O/W Emulsion Adjuvant)

Oil-in-water (O/W) emulsion adjuvants are vaccine components designed to enhance the immune response to co-administered antigens. These emulsions consist of tiny droplets of oil (commonly squalene) dispersed in water, stabilized by surfactants. They act primarily by creating a local inflammatory environment at the injection site, which recruits antigen-presenting cells (APCs). The adjuvant effect is not solely attributable to any single component but rather the emulsion structure itself. MF59 does not activate Toll-like receptors directly but requires MyD88 signaling for its activity through an alternative pathway. O/W emulsions induce both humoral and cellular immune responses. Squalene-based O/W emulsions like MF59 have been safely used in pandemic influenza vaccines since 2009 and continue to be included in seasonal flu shots as well as under investigation for COVID-19 vaccines.

Other names

Oil-in-Water Emulsion AdjuvantsMF59Squalene-based Adjuvant

Recruitment/activation of APCs; enhanced antigen uptake; induction of local inflammation; MyD88-dependent signaling; promotes both humoral/cellular immunity