NOD1 and NOD2 Mediate Sensing of Periodontal Pathogens

In bacterial infection, Nucleotide-binding Oligomerization Domain (NOD) 1 and NOD2 induce innate immune responses by recognizing fragments of the bacterial component peptidoglycan (PGN). To determine the roles of these receptors in detection of periodontal pathogens, we stimulated human embryonic kidney cells expressing NOD1 or NOD2 with heat-killed Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum or their soluble PGNs (sPGNs). All bacteria and their sPGNs could stimulate activation of NF-kappaB. However, there were differences in NOD1- and NOD2-stimulatory activities among the species of bacteria. P. gingivalis showed weaker NOD1- and NOD2-stimulatory activities than did other bacteria. These differences in activities were confirmed by production of interleukin-8 from oral epithelial cells stimulated with sPGNs. These findings indicate that both NOD1 and NOD2 might be involved in the recognition of periodontal pathogens, and that the weak NOD-stimulatory property of P. gingivalis might be helpful for survival in the periodontal pocket.