NOD2 and colitis: Peptidoglycan and derived muropeptides in L. salivarius showed protective effect in murine colitis mice model through induction of pathogen-associated molecular pattern receptors such as Nod2 [37], which recognizes intracellular muramyl dipeptide of a peptidoglycan constituent [38], suggesting the relevance of peptidoglycan structure to the immune-augmenting activity of L. casei ATCC 27139.