The Immunoregulatory Role Of Indoleamine 2, 3-dioxygenase In T-lymphocyte Killing Hepatocellular Carcinoma Cell

Objects Indoleamine 2,3-dioxygenase(IDO)catalyzes the rate-limiting step of tryptophan degradation along the kynurenine pathway , and both the reduction in local tryptophan concentration and the production of immunomodulatorytryptophan metabolites contribute to the immunosuppressive effects of IDO. Rencent studies have focused on immunoregulatory role of IDO in mononuclear cells. To seek the new way of curing hepatocellular carcinoma, we investigated the role of IDO in anticancer immune responses.Methods T-lymphocytes freshly isolated from healthy people and HepG2 cell were cocultured, and IDO inhibitor (1-methyl-tryptophan,1-MT) or exogenous IDO was added to make an intervening experiment. The level of IDO mRNA expression in HepG2 cell cocultured with T-lymphocyte was detected by RT-PCR;the apoptosis rate of HepG2 cell cocultured with T-lymphocyte was analyzed by flow cytometer; the cytotoxicity of T-lymphocyte against HepG2 cell was examined by MTT assay.Results 1.In HepG2 cell studied, IDO mRNA was not expressed under normal culture conditions. A low level of IDO mRNA expression was detectable in T-lymphocyte under normal culture conditions. The IDO mRNA was expressed exclusively when HepG2 cell was cultured with T-lymphocyte. The level of IDO mRNA expression in HepG2 cells cultured with T-lymphocyte was especially higher than that in na?ve T-lymphocyte. And the level of IDO mRNA expression was faintly induced after addition of 1-MT, but that was not altered by exogenous IDO.2.The earlier apoptosis rate of HepG2 cell in control group was (3.48±0.34)% and 1-MT(1.25 mmol/l,2.5 mmol/l,5mmol/l) group was respectively(7.82±0.41)%,(18.62±0.42)%,(25.32±0.40)%, the earlier apoptosis rate of HepG2 cell was significantly higher in cocultured condition with 1-MT group than without 1-MT group; the exogenous IDO (0.05 mmol/l,0.5 mmol/l,5mmol/l) group was respectively(3.32±0.35)%,(3.46±0.40)%,(2.75±0.26)%, it was considered statistically significant compared with control group when the concentration of exogenous IDO was 5mmol/l.3.The cytotoxicity of T-lymphocyte against HepG2 cell in control group was (17.36±1.24)%,and 1-MT(1.25 mmol/l,2.5 mmol/l,5mmol/l) group was respectively(25.48±1.48)%,(32.89±1.73)%,(42.04±2.16)%, there was a significant increase in the cytotoxicity of T-lymphocyte against HepG2 cell in cocultured condition with 1-MT group than without 1-MT group; the exogenous IDO (0.05 mmol/l,0.5 mmol/l,5mmol/l) group was respectively(17.30±0.52)%,(17.48±1.08)%,(15.74±0.79)%, it was considered statistically significant compared with control group when the concentration of exogenous IDO was 5mmol/l, too.Conclusions These results suggest that IDO from HepG2 cell and some concentration of exogenous IDO can suppress the cytotoxicity of T-lymphocyte against HepG2 cell and the earlier apoptosis rate of HepG2 cell , which may be contributing to hepatocellular carcinoma immune escape , but 1-MT can reverse the immunoregulatory role. In the future, it maybe become a new target for treatment of hepatocellular carcinoma.