The Effects Of Astragalus Polysaccharide On The Expression Of MICA In Leukemia Cell Lines And Its Impact On NK Cytotoxicity

Objective:Natural killer (NK) cells is a subset of lymphocytes that mainly participate in innate immunity, and also play a key role in the antitumor immune responses. The activating receptor NKG2D and its ligands NKG2D-L play an important role in the NK cell-mediated immune response to tumors. However, malignant blood cells in AML display low levels of ligands for the activating immunoreceptor NKG2D and can thus evade NK cells-mediated immune response. Consequently, it’s necessary for us to find a new pharmacologic approach to achieve the up-regulation of NKG2D-L-or the express of NKG2D-L that expressed at a low level on the surface of leukemia cell. These studies based on the observation of that if astragalus polysaccharides could increase the expression of MICA in HL-60, K562cells and enhance the cytotoxicity of NK cell against leukemia cell lines, and to find new targets for NK cell-based immunotherapy in leukemia.Methods:The different concentrations of astragalus polysaccharides incubated with the HL-60, K562cells, after48hours, the IC50of leukemic cell lines treating with APS was determined with the CCK-8assay and this concentration of APS was chosen to treat leukemic cell lines. The difference of the genes expression of MICA from leukemic cell line was determined by RT-PCR before and after treating with APS, and the difference of the expression of MICA molecules was assayed by flow cytometer before and after treating with APS. Cytotoxicities of NK cells against leukemic cell lines were analyzed by LDH releasing assay at different effector-to-target cell ratios (E:T) before and after treating with APS.Results:The MICA mRNA of HL-60cells after treating with APS is1.46±0.16times than that of before treating with APS; MICA mRNA of K562cells after treating with APS is2.26±0.34times than that of before (P<0.05). The protein expressions of MICA on HL-60cells and K562cells incubated with APS have respectively increased from (6.34±0.81)%,(42.29±1.57)%to (10.35±1.68)%,(65.02±2.24)%, the differences have statistical significance (P<0.05); the cytotoxic sensitivity of HL-60cells and K562cells to NK cells increased by treating with APS at the E:T ratio of5:1,10:1and20:1, the difference have statistical significance (P<0.05).Conclusion:1. The mRNA and protein of MICA on the surface of HL-60cells and K562cells after being treated by APS was significantly up-regulated;2. The APS could enhance the sensitivity of leukemia cells to NK cell through the up-expression of MICA on the surface of leukemia cell.