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The immune response to the X protein of human hepatitis B virus ( HBV ) was studied by epitope mapping by using a set of MS2-HBx fusion proteins and synthetic peptides .
 protein: MS2-HBx fusion proteins; protein: X protein
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 protein: MS2-HBx fusion proteins; protein: X protein