Effect of total flavonoids from the seeds of Astragali complanati on natural killer cell function

The seeds of Astragalus complanatus R.Br. (AC), a traditional Chinese medicine, have been extensively used for clinical treatment of liver and kidney complaints and tumors for more than a thousand years. It was believed that AC is warm and sweet in the most authoritative medical book of Ancient China "Compendium of Materia Medica". Our previous studies showed that the flavonoid component from the seeds of Astragalus complanatus (FAC) is mainly an active constituent and has the hepatoprotective effect, anti-liver fibrosis, and anti-tumor and immune enhancement.

The aim of this study was to investigate in vitro the regulation effect of FAC on NK cells function and possible mechanism of action.

The effect of FAC on the proliferation ability of NK-92 cells and the cytolysis of NK-92 cells to K562 and SMMC-7721 were measured by MTT assay and lactase dehydrogenase (LDH)-releasing assay, respectively. The phenotypical characterization (CD3, CD16 and CD56) and activation markers (CD25, CD69 and CD95) of NK-92 cell were detected by flow cytometry analysis. IFN-γ production of NK-92 cells stimulating by K562 cells was quantitated using ELISA. To explore the mechanism of action, mRNA and protein expressions of activating receptors (NKp30, NKp44, NKp46 and NKG2D) in NK-92 cells were detected by quantitative real-time PCR and flow cytometry analysis.

Our results demonstrated that FAC significantly promoted the proliferation and the cytotoxicity of NK-92 cells in a dose-dependent manner by enhancing IFN-γ and increasing the expression of the activation markers CD25 and CD69. In addition, FAC had not changed the NK-92 cells phenotypical characterization, but markedly enhanced the expression intensity of CD56. Furthermore, FAC significantly enhanced mRNA and protein expressions lever of NKp44 and NKG2D in NK-92 cells.

These results suggest that FAC upregulate the expressions of NKG2D, NKp44, which in turn influence NK-92 cells activation. FAC may serve as an immunostimulatory of NK cells for tumor treatment.