6886
We have demonstrated that the cross-linking of cell surface CD4 by gp120-anti-gp120 immune complexes or heat-inactivated HIV-1 ( iHIV-1 ) is sufficient to trigger activation signals leading to virus reactivation (9).
 ( protein: cell surface CD4, None) , ( protein: gp120-anti-gp120 immune complexes, None) , ( protein: CD4, 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: cell surface CD4, None) , ( protein: gp120-anti-gp120 immune complexes, None) , ( protein: CD4, None) 