11618
Substitutions in the YFV Ag - binding region ( ABR ) occur at four of the eight highly conserved residues that are essential for binding of peptide - Ag in the class Ia molecules .
 YFV, Ag - binding region, ABR
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 YFV, Ag - binding region, ABR