Background: Hydatid disease caused by the larval stage ofEchinococcus granulosus is endemic in many area of the world.Experimental hydatidosis by inoculation of protoscolecesin mice is the current model to study the interactions between the immune system and the parasite.During the early infection stage (until day 20), parasite utilizes evasion mechanisms to survive in an immunological hostile environment.Among the various evasion mechanisms, our team focuses on the change of NK cells function during the early infection stage, and try to find whether inhibitory factor TGF-β secretion involved in this event.Through the use of inhibitor of TGF-β receptor, the effort of TGF-β on NK cells functional change during the early infection is further revealed.