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The CD4 coreceptor interacts with non-polymorphic regions of major histocompatibility complex class II molecules on antigen-presenting cells and contributes to T cell activation .
 ( protein: CD4 coreceptor, None) , ( protein: non-polymorphic regions, None) , ( cell type: antigen-presenting cells, None) , ( protein: major histocompatibility complex class II molecules, 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: CD4 coreceptor, None) , ( protein: non-polymorphic regions, None) , ( cell type: antigen-presenting cells, None) , ( protein: major histocompatibility complex class II molecules, None) 