7255
The contact of natural killer (NK) cells with foreign cells and with certain virus-infected or tumor cells triggers the cytolytic machinery of NK cells .
 ( cell type: foreign cells, None) , ( cell type: NK cells, None) , ( cell type: natural killer (NK) cells, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( cell type: foreign cells, None) , ( cell type: NK cells, None) , ( cell type: natural killer (NK) cells, None) 