Possible roles of il-33 in periodontal diseases: Porphyromonas gingivalis induced il-33 in human gingival epithelial cells

In the oral mucosa, epithelial cells work not only as a physical barrier to pathogens, but also play a pivotal role in initiating immune responses to microbes. Interleukin (IL)-33, a member of the IL-1 family, is constitutively expressed in epithelial cells and amplifies Th2-type inflammatory immune responses. We found that IL-33 was detected in the inflamed gingival epithelium from chronic periodontitis patients, and periodontopathic Porphyromonas gingivalis strongly increased expressions of IL-33 mRNA and molecules in human gingival epithelial cells. In contrast, fimbriae, a lipopeptide and lipopolysaccharide derived from P. gingivalis were not active in this respect. Protease inhibitors specific for gingipains efficiently inhibited the induction of IL-33 mRNA by stimulation with P. gingivalis. Furthermore, P. gingivalis KDP136, a gingipains-null mutant, did not increase IL-33 mRNA expression. We also demonstrated that P. gingivalis upregulated IL-33 mRNA expression through protease-activated receptor-2, phospholipase C, mitogen-activated protein kinase p38 and NF-?B. IL-33 is suggested to negatively regulate antimicrobial peptide LL-37, resulting in attenuation of innate immune responses of gingival epithelial cells in chronic periodontitis. Possible roles of IL-33 in inflammation in the oral mucosa are discussed.