[Effect of Spatholobi Caulis extract from ethyl acetate on immune killing function of NK cells]

This study aims to investigate the regulatory effect of the Spatholobi Caulis extract from ethyl acetate(SEA) on natural killer(NK) cells under physiological conditions and elucidate the underlying mechanism. The C57BL/6 mice were randomized into NC and SEA groups, and NK-92 cells were respectively treated with 0, 25, 50, and 100 μg·mL~(-1) SEA. The body weight and immune organ index of the mice were compared between groups. The lactate dehydrogenase(LDH) assay was employed to examine the cytotoxicity of NK-92 cells treated with SEA and the killing activity of mouse NK cells against YAC-1 cells. The cell-counting kit-8(CCK-8) was used to examine the impact of SEA on the proliferation of NK-92 cells. Flow cytometry was employed to measure the number of NK cells in the peripheral blood as well as the expression levels of natural killer group 2 member A(NKG2A) and natural killer group 2 member D(NKG2D). The enzyme-linked immunosorbent assay(ELISA) was performed to determine the interferon(IFN)-γ secretion in the serum. Semi-quantitative PCR was conducted to determine the mRNA levels of NKG2A, NKG2D, and IFN-γ in spleen cells. Western blot was employed to investigate the involvement of phosphoinositide 3-kinase(PI3K)/extracellular regulated protein kinase 1(ERK1) signaling pathway. The results showed that SEA exhibited no adverse effects on the body, while significantly enhance the number of NK cells and augment the cytotoxicity of NK-92 cells against YAC-1 cells. Moreover, it suppressed the expression of NKG2A, enhanced the expression of NKG2D, promoted IFN-γ secretion, and upregulated the protein levels of PI3K and ERK. The findings suggest that SEA has the potential to enhance the immune recognition and effector function of NK cells by increasing the cell number, modulating the expression of functional receptors, and promoting IFN-γ secretion via the PI3K/ERK signaling pathway.