Abstract:Dendritic cells(DCs) show two morphological forms,the mature and immature forms;the former is the potent antigen-presenting cells(APC) initiating the primary immune responses,while the latter processes different properties from the former and has the ability to induce T cell tolerance Coxiella burnetti(Cb) is an obligate intracellular microorganism and its mechanism by which this bacterium evades the action of immune clearance of host during persistent infection is still unknown.In the present study,mononuclear cells were isolated from human peripheral blood and cultivated in media containing GM-CSF and IL-4 to generate the immature DCs.The immature DCs generated were stimulated with the Xingqiao strain of Cb(an isolate in China and an virulent phase I strain with full-length LPS) and LPS-removed Cbs with LPS of E.coli used as the positive control.Meanwhile,the expressions of surface molecules on the stimulated DCs,such as CD40,CD58,CD80,CD83 and CD86,were analyzed with FACS.It was demonstrated that the expression levels of these surface molecules on DCs pulsed with LPS-removed Cbs were approached to that of E.coli LPS-pulsed DCs and significantly higher than that of the un-stimulated DCs.However,the expression of these surface molecules of Cbs or Cb LPS-pulsed DCs was dramatically lower compared with that of E.coli LPS-pulsed DCs.It is apparent that the virulent phase I C.burnetti with full-length LPS is unable to activate DCs,but the LPS-removed C.burnetti possess this ability.This result suggests that LPS can block the surface molecules of C.burnetti interacting with DCs and these molecules are necessary for the activation ofDCs.The presence of LPS is beneficial for the immune evasion strategy of virulent phase I strain of C.burnetti.