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In EBV infection most of the changes, including the early induction of cyclin D2 , are dependent on expression of EBV genes , but an alteration in the E2F-4 profile was partly independent of viral gene expression , presumably occurring in response to signal transduction activated when the virus binds to its receptor, CD21 .
 EBV genes, CD21, cyclin D2, E2F-4
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:
 EBV genes, CD21, cyclin D2, E2F-4