6068
B cells were purified from buffy coat preparations of healthy blood donors by positive selection using an anti CD20 monoclonal antibody and a MiniMACS separation unit .
 ( cell type: B cells, None) , ( protein: CD20, None) , ( protein: anti CD20 monoclonal antibody, 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:
 ( cell type: B cells, None) , ( protein: CD20, None) , ( protein: anti CD20 monoclonal antibody, None) 