Muramyl Dipeptide (MDP)

Muramyl dipeptide is a peptidoglycan constituent of both Gram positive and Gram negative bacteria. It is composed of N-acetylmuramic acid linked by its lactic acid moiety to the N-terminus of an L-alanine D-isoglutamine dipeptide. It can be recognized by the immune system as a PAMP and activate the NALP3 inflammasome which in turn leads to cytokine activation, especially IL-1α and IL-1β. Muramyl dipeptide (MDP) is a synthetic immunoreactive peptide consisting of N-acetyl muramic acid attached to a short amino acid chain of L-Ala-D-isoGln. It was first identified in bacterial cell wall peptidoglycan as an active component in Freund’s complete adjuvant. In the cell, MDP is detected by NOD2, a cytoplasmic receptor belonging to the human innate immune system. NOD2 mutations are frequently observed in patients with Crohn’s disease, an autoimmune disorder, suggesting the significance of the MDP-NOD2 pathway in activating immunity.