4553
In the current studies, IL-2 production by T cells from elderly (mean 78 years) and young (mean 37 years) humans was measured in cultures stimulated with PHA , PHA plus PMA , crosslinked anti-CD3 mAB OKT3 plus PMA , or PMA plus ionomycin .
 PHA, IL-2, T cells, PHA
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:
 PHA, IL-2, T cells, PHA