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To prove the involvement of CCR5 deletion in lowered nociception , we examined pain reactions with CCR5 WT mice following treatment of a CCR5 antagonist ( D - Ala ( 1 ) - peptide T - NH ( 2 , ) DAPTA ) .
 D - Ala ( 1 ) - peptide T - NH ( 2 , ), DAPTA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 D - Ala ( 1 ) - peptide T - NH ( 2 , ), DAPTA