NOD1 and head and neck squamous cell carcinoma: NOD1 mainly recognizes γ-D-glu-meso-diaminopimelic acid-containning peptidoglycans (PGNs) in the cell wall of gram-negative bacteria and is highly expressed in several malignancies such as cervical cancer, colon cancer, and head and neck squamous cell carcinoma.56–58 However, a specific role for NOD1 in P. gingivalis-infection induced stemness acquisition of OSCC cells has not been identified.