7496
Optimal T cell activation requires two signals, one generated by TCR and another by the CD28 costimulatory receptor .
 TCR, CD28 costimulatory receptor
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:
 TCR, CD28 costimulatory receptor