7111
PROBLEM: Due to the lack of classical HLA antigens on the trophoblast, fetal antigens are possibly presented in a non major histocompatibility complex ( MHC ) restricted way .
 ( protein: classical HLA antigens, None) , ( protein: fetal antigens, None) , ( protein: MHC, None) , ( protein: major histocompatibility complex, 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: classical HLA antigens, None) , ( protein: fetal antigens, None) , ( protein: MHC, None) , ( protein: major histocompatibility complex, None) 