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However , using a full length bacterial IgG display system , we have isolated aglycosylated Fc domains with mutations that confer up to a 160 - fold increase in the affinity toward the low affinity Fc gamma RIIa - R131 allele as well as high selectivity against binding to the remarkably homologous human inhibitory receptor , Fc gamma RIIb .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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