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 .
 cytokine, CD28, IL-2 promoter, natural ligand CD80, IL-2, IL-2
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:
 cytokine, CD28, IL-2 promoter, natural ligand CD80, IL-2, IL-2