7691
Despite this drastic effect in vivo, the in vitro immortalization of erythropoietin-dependent erythroid progenitors unexpectedly occurred at low frequency, and all four cell lines established expressed both erythrocytic (globins) and megakaryocytic markers ( glycoprotein IIb , platelet factor 4 ) as well as Spi-1 and Fli-1 transcripts at permissive temperature .
 cell lines, platelet factor 4, glycoprotein IIb, Spi-1, erythropoietin-dependent erythroid progenitors, Fli-1 transcripts
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:
 cell lines, platelet factor 4, glycoprotein IIb, Spi-1, erythropoietin-dependent erythroid progenitors, Fli-1 transcripts