8008
Rat spleen and peripheral blood lymphocytes express progesterone receptors whose concentration is increased greatly during the early phase of pregnancy .
 progesterone receptors, peripheral blood lymphocytes
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:
 progesterone receptors, peripheral blood lymphocytes