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Activation of the CD28 surface receptor provides a major costimulatory signal for T cell activation resulting in enhanced production of interleukin-2 ( IL-2 ) and cell proliferation .
 CD28, CD28 surface receptor, IL-2, interleukin-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:
 CD28, CD28 surface receptor, IL-2, interleukin-2