7226
The secondary lymphoid tissues are located at strategic sites where foreign antigens can be efficiently brought together with immune system regulatory and effector cells .
 ( protein: foreign antigens, 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: foreign antigens, None) 