Squalene-based oil-in-water emulsion immunostimulatory pathway

Squalene-based oil-in-water emulsions (notably MF59, AS03, AddaVax) are widely used vaccine adjuvants that enhance the immunogenicity of co-administered antigens by triggering local innate immune mechanisms at the site of injection and in draining lymph nodes[3][4][5]. These emulsions recruit and activate innate immune cells (monocytes, dendritic cells, neutrophils), facilitate the production of pro-inflammatory cytokines, and promote antigen presentation and cross-presentation to T cells, including CD8+ cytotoxic and CD4+ T follicular helper cell subsets[2][3][4][6]. Their adjuvant effect involves multiple molecular pathways, including RIPK3-dependent necroptosis, caspase activation, and, when present, α-tocopherol-mediated enhancement of Tfh cell responses[3][6]. Collectively, these mechanisms drive robust humoral and cellular adaptive immunity, critical for vaccine effectiveness. This pathway does not correspond to a single molecular target but encompasses a set of immunological events triggered by the physical and chemical properties of squalene emulsions.

Other names

Squalene-based emulsion adjuvant pathwaySqualene oil-in-water adjuvant mechanismMF59/AS03 adjuvant immunological effectSqualene emulsion-induced immune activation

Recruitment of monocytes, neutrophils, eosinophils, and dendritic cells to the injection site and draining lymph nodes[4][5]; Induction of pro-inflammatory cytokines (e.g., IL-6, IL-12, TNF) and chemokines for cellular recruitment[3][4][5]; Enhanced antigen uptake and cross-presentation by dendritic cells, notably Batf3-dependent CD8+ DCs[3]; Activation of RIPK3-dependent necroptotic and apoptotic pathways contributing to T cell priming[3]; Caspase activation and induction of IL-18, facilitating Th1-type and CD8+ T cell responses[2][3]; Promotion of T follicular helper cell generation (especially when α-tocopherol is included, as in AS03 and A-910823)[6]