12251
Forty-eight hours after transfection , EC were stimulated with NK cells or NK cell membrane extracts for 7 hr and activation was measured by a luciferase assay .
 ( cell type: EC, None) , ( protein: luciferase, None) , ( cell type: NK cells, None) , ( cell type: NK cell membrane extracts, 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: EC, None) , ( protein: luciferase, None) , ( cell type: NK cells, None) , ( cell type: NK cell membrane extracts, None) 