14456
Nucleotide oligomerization domain - containing protein 2 ( Nod2 ) , an innate immune receptor , recognizes bacterial cell - wall peptidoglycan ( PGN ) , the minimum ligand of which is muramyl dipeptide ( MDP ) .
 Nucleotide, muramyl dipeptide, MDP
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Nucleotide, muramyl dipeptide, MDP