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 .
 NF-kappaB family, B7.1 -positive B cells, B7.1, transcription factors, B7.1
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 NF-kappaB family, B7.1 -positive B cells, B7.1, transcription factors, B7.1