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To overcome the difficulty in obtaining quiescent monocytes , we studied the ability of promonocytic THP-1 cells to activate endothelial cells .
 ( cell type: endothelial cells, None) , ( cell type: quiescent monocytes, None) , ( cell line: promonocytic THP-1 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: endothelial cells, None) , ( cell type: quiescent monocytes, None) , ( cell line: promonocytic THP-1 cells, None) 