Role of interleukin-33 in the clinical pathogenesis of chronic apical periodontitis

Objective This study investigated interleukin (IL)-33 expression in chronic apical periodontitis (CAP) lesions and possible relationships with receptor activator of nuclear factor kappa-Beta ligand (RANKL) and osteoprotegerin (OPG). Methods Inflammatory cell infiltration in CAP lesions and samples of healthy periapical tissue (n = 30 each) was evaluated by hematoxylin and eosin staining. IL-33, RANKL, and OPG expression levels were assessed by immunohistochemistry and real-time PCR. In CAP lesions alone, relationships between mRNA level of IL-33 and mRNA levels of both RANKL and OPG were analyzed by Spearman rank correlation. Results Histological analysis revealed a large number of inflammatory cells in CAP lesions, and immunohistochemistry revealed IL-33-positive cells. There were more IL-33- and RANKL-positive cells in CAP lesions than in healthy periapical tissue, whereas there were fewer OPG-positive cells in CAP lesions than in healthy periapical tissue. In CAP lesions alone, IL-33 mRNA level was negatively correlated with mRNA level of RANKL and positively correlated with mRNA level of OPG. Conclusions IL-33 is highly expressed in CAP lesions, where it is negatively correlated with RANKL and positively correlated with OPG expression. IL-33 may protect against bone resorption via RANKL suppression and OPG induction, and constitutes a potential target for CAP treatment.