Abstract: Objective:To investigate the effect of Mycobacterium tuberculosis(Mtb) on the function of mouse bone marrow derived dendritic cells(DC).Methods:DC were divided into 4 groups,lipopolysaccharide(LPS)-treated group,Mtb-treated group,inactivated Mtb-treated group and control group.Cytokines including interleukin(IL)-6,IL-12 and tumor necrosis factor α secretion of infected cells were examined by ELISA method.And the expression of surface molecules of infected DC including major histocompatibility complex class Ⅱ,CD40,CD80 and CD86 were detected by flow cytometry.Results:About 5×10⁶ to 1×10⁷ DC were obtained from bone marrow of one mouse,and the purity of DC was more than 85%.The cells had the typical morphology of DC.The expressions of major histocompatibility complex class Ⅱ,CD40,CD80 and CD86 on stimulated DC increased in LPS-treated group,Mtb-treated group,inactivated Mtb-treated group in contrast to control group;while the percentage of the upregulation of surface molecules in Mtb-treated DC was significantly lower than that of LPS or inactivated Mtb-treated DC.The cytokine levels in all groups significantly increased,and IL-6,IL-12 and tumor necrosis factor α secretions of DC infected by Mtb were significantly lower than those of LPS or inactivated Mtb-treated DC.Conclusions:Mtb can decrease the antigen presenting function through interfering the secretion of cytokines and inhibiting maturation of DC,and consequently suppress DC and T cell activation and result in the more serious damage of host.