5450
In B7.1 -positive B cells , this element bound several members of the NF-kappaB family , transcription factors already implicated in signal transduction pathways relevant to B7.1 expression .
 ( protein: NF-kappaB family, None) , ( cell type: B7.1 -positive B cells, None) , ( protein: B7.1, None) , ( protein: transcription factors, None) , ( protein: B7.1, 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:
 ( protein: NF-kappaB family, None) , ( cell type: B7.1 -positive B cells, None) , ( protein: B7.1, None) , ( protein: transcription factors, None) , ( protein: B7.1, None) 