QS-21, an immunostimulatory saponin, is a potent vaccine adjuvant that stimulates both Th2 humoral and Th1 cell-mediated immune responses by interacting with antigen presenting cells (APCs) and T cells. Furthermore, QS-21 activates the NLRP3 inflammasome, leading to the release of cytokines IL-1β and IL-18, dependent on caspase-1.

Research on mouse antigen-presenting cells (APCs), specifically dendritic cells (DCs) and macrophages, has identified QS-21 as a stimulant for the NLRP3 inflammasome. This activation leads to the subsequent release of caspase-1-dependent proinflammatory cytokines, IL-1β/IL-18, which either support the maturation of Th17 cells or energize interferon-gamma (INF-γ)-mediated Th1 responses, respectively[3].