621
Endothelial cell culture supernatants separated by ultrafiltration and ultracentrifugation from cells treated with EPO and IL - 3 significantly reduced thymidine incorporation into erythroid cells as compared to identical fractions obtained from the media of cells cultured with EPO alone .
 thymidine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 thymidine