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The production of human immunodeficiency virus type 1 ( HIV-1 ) progeny was followed in the U937 promonocytic cell line after stimulation either with retinoic acid or PMA , and in purified human monocytes and macrophages .
 cell line: U937 promonocytic cell line
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 cell line: U937 promonocytic cell line