TGM2 and periodontitis: They experimentally evaluated the lower expression of TG2 in cultured normal human than in patient-derived human periodontal ligament (HPDL) cells, its nuclear factor-kappaB (NF-κB) receptor activator ligand (RANKL)/secretory bone The ratio of protectin (RANKL/OPG) was also relatively low, and the ratio of RANKL/OPG in HPDL cells of patients with periodontitis was positively correlated with the expression level of TG2 gene.