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).
 cell surface CD4, gp120-anti-gp120 immune complexes, 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:
 cell surface CD4, gp120-anti-gp120 immune complexes, CD4