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 .
 CD4, p56(lck), Fas, -Fas ligand, CD4
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 CD4, p56(lck), Fas, -Fas ligand, CD4