7793
The human monoblastic cell line , U937 was differentiated to macrophages by the treatment with either phorbol 12-myristate 13-acetate ( PMA ) , retinoic acid ( RA ) , or vitamin D3 ( VitD3 ) .
 ( cell line: U937, None) , ( cell line: human monoblastic cell line, None) , ( cell type: macrophages, 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 line: U937, None) , ( cell line: human monoblastic cell line, None) , ( cell type: macrophages, None) 