13420
These observations demonstrate that CD4 signaling mediates HIV-induced apoptosis by a mechanism independent of Fas -Fas ligand interaction , does not require p56(lck) signaling , and may involve a critical region for CD4 dimerization .
 ( protein: CD4, None) , ( protein: p56(lck), None) , ( protein: Fas, None) , ( protein: -Fas ligand, 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: CD4, None) , ( protein: p56(lck), None) , ( protein: Fas, None) , ( protein: -Fas ligand, None) , ( protein: CD4, None) 