Discovery of a previously undescribed immunopotentiator:identification and immune-stimulating activity of saponins from Hylomecon japonica (Thunb.) Prantl & Kündig.

The total saponins from Hylomecon japonica (Thunb.) Prantl & Kündig were found to exhibit significant immune-stimulating activity. This finding prompted the bioassay-guided isolation of ten triterpenoid saponins from the herb, including six previously undescribed saponins (1-6) and four known ones (7-10). Their chemical structures were unambiguously determined through comprehensive spectroscopic data analysis. Initial screening revealed that compounds 1-3 did not exhibit cytotoxic effects on splenic lymphocytes in vitro, and compound 2 demonstrated significant proliferative activity. Further, flow cytometry analysis showed that compound 2 significantly increased the expression levels of CD80, CD86, and MHC II on the surface of bone marrow-derived dendritic cells (BMDCs), suggesting its potential to promote BMDCs maturation. Moreover, ELISA and RT-qPCR assays indicated that compound 2 enhanced the production of immune cytokines IFN-γ, IL-2, and TNF-α, and upregulated the expression of immune-related genes IFN-γ, NF-κB, and TLR4 in BMDCs. Additionally, mixed lymphocyte reaction (MLR) experiments confirmed that compound 2 amplified the T cell-mediated immune response facilitated by BMDCs. These findings establish a fundamental basis for investigating immune-enhancing effect of triterpenoids.