Objective    To study the effect of DC-SIGN-ManLAM binding signal on the ability of dendritic cells (DCs) to activate naive

T lymphocytes with RNA interference（RNAi）.     Methods    Effective RNAi targeting human DC-SIGN molecules were used to construct lentivirus vectors. DC were divided into RNAi group

empty carrier group

and blank control group.  Changes of DC-SIGN molecules in DC were detected by flow cytometry

RT-PCR and Western blotting

respectively. In the presence of LPS

18 h after DC and naive T lymphocytes were co-cultured with ManLAM

mature markers of DC were detected by flow cytometry. The effect of DC-SIGNManLAM binding signal on the ability of DC to activate naive T lymphocytes toward Th1 differentiation was detected by ELISA.     Results    The titer of concentrated virus suspension was 1×10

9

TU/ml. The expression level of DC-SIGN on the surface of DC at mRNA and protein levels was significantly lower in RNAi group than in empty carrier group and blank control group. The mature markers of DC including CD86 (F=15.59

P=0.004)

CD83 (F=18.03

P=0.003)

and HLA-DR (F=7.684

P=0.022) were much more in RNAi group than in empty carrier group and blank control group. The IFN-γ (F=18.434

P=0.003) and IL-2（F=31.08

P=0.001）levels were significantly higher in RNAi group than in empty carrier group and blank control group after DC and naive T lymphocytes were co-cultured.      Conclusion    Down-regulation of DC-SIGN level with lentivirus vector can weaken the DC-SIGN-ManLAM binding signal

thus recovering the ability of DC to activate naive T lymphocytes. 