Interleukin-18 and oral mucosal immunity

Oral mucosal cells such as epithelial cells and fibroblasts are the first cells encountered by bacteria in our body. In addition to acting as a physical barrier, oral mucosal cells appear to express adhesion molecules and secrete many proinflammatory mediators, implying that the cells actively participate in mucosal immunity. Oral epithelial cells express a precursor form of interleukin (IL)-18, an important regulator of innate and acquired immune responses. An active form of IL-18 was secreted from the cells on co-stimulation with neutrophil proteinase 3 (PR3) and lipopolysaccharide after interferon-γ-priming. Subsequently, it was evident that neutrophil serine proteases including PR3 activate oral mucosal cells through protease-activated receptor-2 (PAR-2) pathway and play a critical role in IL-18 induction in vivo. These results indicate that induction of IL-18 and PAR-2 activation by neutrophil serine proteases may be critical in regulation of oral mucosal immunity.