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It is interesting that in humans and rats , cortical thymocytes undergoing negative selection can still induce IL-2R alpha expression and even be rescued in vitro, if exogenous IL-2 is provided.
 protein: exogenous IL-2; protein: IL-2R alpha; cell type: cortical thymocytes
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:
 protein: exogenous IL-2; protein: IL-2R alpha; cell type: cortical thymocytes