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Using reverse-transcription PCR differential display , we isolated an mRNA species expressed in IL-2 -but not IL-12 -stimulated NK cells .
 ( protein: IL-2, None) , ( RNA: mRNA species, None) , ( protein: IL-12, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: IL-2, None) , ( RNA: mRNA species, None) , ( protein: IL-12, None) 