Adjuvant-active aqueous extracts from Artemisia rupestris L. improve immune responses through TLR4 signaling pathway

Activating innate immunity by an adjuvant is required in vaccine development. The study aims to investigate adjuvant effects of aqueous extracts of Artemisia rupestris L. (AEAR) in vivo and in vitro. ICR mice were subcutaneously administered with antigen and AEAR at various doses to evaluate their immune responses of antibodies, dendritic cells (DCs), regulatory T cells (Treg), splenic lymphocyte, and cytokine. The evaluation results showed that AEAR could largely increase titers of antigen-specific antibodies (IgG, IgG₁, and IgG_2a) and T cell proliferation. AEAR also increased expression of IFN-γ in CD8⁺T cells as well as IL-4 and INF-γ expression in CD4⁺T cells. Expression levels of MHC-II, CD40, CD80, and CD86 on DCs were significantly elevated, whereas the Treg frequency was significantly decreased. AEAR (200μg) showed remarkable adjuvant activity. Furthermore, AEAR enhanced MHC-II, CD40, CD80, and CD86 expression as well as the yields of TNF-α and IL-12 on DCs through toll-like receptor4 (TLR4) in vitro. Those results indicated that AEAR could serve as an efficacious immune stimulator for vaccines because it significantly enhanced specific immune responses by promoting DCs maturation and reduced Treg through TLR4 signaling pathway.