Previous studies have suggested that the cell type-specific host immune response to P. gingivalis infection is closely linked to the activation of pattern recognition receptors (PRRs).54 NODs are a group of intracellular pattern-recognition proteins that recognize invading pathogens and induce host responses to limit bacterial infection.55 In the present study, P. gingivalis upregulated the expression of NOD1 but not NOD2. This evidence concerns the gene NOD2 and bacterial infectious disease.