5745
In many circumstances it is difficult to distinguish the effects of CD28 from subsequent actions of cytokines , such as IL-2 , on T cell proliferation .
 IL-2, cytokines, CD28
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:
 IL-2, cytokines, CD28