4695
Neutralizing antiserum against IFN-gamma , but not other cytokines tested, blocked activation of the factor almost completely, and IFN-gamma was found in the culture supernatants of stimulated cells at levels at which recombinant IFN-gamma could activate the factor in naive cells .
 IFN-gamma, cytokines, IFN-gamma, naive cells, IFN-gamma, stimulated cells
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:
 IFN-gamma, cytokines, IFN-gamma, naive cells, IFN-gamma, stimulated cells