18749
Serum depletion studies confirmed that neutralization was gp120 - directed and that sera from animals immunized with gp120 contained lower amounts of CD4bs - directed antibodies than corresponding sera from animals immunized with b121a / b122a .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None