5746
Here, we report a model of CD28 costimulation using PMA plus the natural ligand CD80 that resulted in very limited stimulation of IL-2 , as evidenced by both cytokine production and IL-2 promoter stimulation .
 ( protein: cytokine, None) , ( protein: CD28, None) , ( DNA: IL-2 promoter, None) , ( protein: natural ligand CD80, None) , ( protein: IL-2, None) , ( protein: IL-2, 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: cytokine, None) , ( protein: CD28, None) , ( DNA: IL-2 promoter, None) , ( protein: natural ligand CD80, None) , ( protein: IL-2, None) , ( protein: IL-2, None) 