6590
Strikingly, despite the observed repertoire heterogeneity, all clones displayed a narrow range of MHC /peptide density requirements in cytotoxicity assays ( ED50 between 9 and 36 nM).
 ( protein: MHC, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: MHC, None) 