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We show here that estrogens also reduce the number of erythroid progenitor cells in primary human bone marrow cultures .
 primary human bone marrow cultures, erythroid progenitor cells
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:
 primary human bone marrow cultures, erythroid progenitor cells