OBJECTIVETo investigate the effect of blocking the inhibitory receptors KIR2DL1 and KIR2DL2/2DL3 with monoclonal antibody on cytotoxic activity of human NK cells.

METHODSHuman peripheral blood NK cells were isolated by Rosettesep NK sorting kit. The cytotoxic activity of NK cells against human leukemia NB4, K-562, Raji cells and allogeneic mature or dendritic cells (DCs) was detected before or after KIR2DL1 and KIR2DL2/2DL3 were blocked. The effect of NK cells on T lymphocyte proliferation was detected by mixed lymphocyte reaction and TGF-β1 concentration in culture supernatant was measured.

RESULTSThe cytotoxicity of NK cells to NB4 cells was augmented with increasing concentration of the antibody. Combination of both antibodies enhanced killing activity of NK cells. NK cells had strong cytotoxicity to K-562 cells, but were not enhanced by the blockade of inhibitory receptors. The cytotoxicity to Raji cells was not evidently augmented. The cytotoxicity of NK cells to mature DC was enhanced remarkably with the increase of concentration of the antibodies (2.20% ±1.10% compared with 37.59% ±5.06%, P<0.05). In mixed lymphocyte reaction, the blockade of two antibodies enhanced the inhibition effect of NK cells on T cell proliferation (77.85% ± 8.31% compared with 43.05% ± 5.95%, P<0.05) and the content of TGF-β1 in the supernatant was increased.

CONCLUSIONThe cytotoxic effects of human NK cells against target cells were significantly enhanced with the blockade of inhibitory KIR receptor; and the cytokine TGF-β1 secreted by NK cells further inhibits T cells proliferation.