Inflammatory and Anti-inflammatory Reactions in Periapical Granulomas

Objectives: Bacterial lipopolysaccharide, which is a strong virulent factor, induces cytokines and growth factors from inflammatory cells such as macrophages, lymphocytes and endothelial cells. Infiltration of inflammatory cells could be controlled by the inflammatory reaction of endothelial cells. Objectives of this study were to know the inflammatory mechanisms of endothelial cells in periapical granulomas by the analysis of receptor for advanced glycation end products (RAGE) and inducible nitric oxide synthase (iNOS) as inflammatory mediators, and vascular endothelial cadherin (VE-cadherin) as vascular integrity.
Methods: Surgically removed periapical lesions were analyzed by hematoxylin-eosin stains using the paraffin section. Only periapical granulomas were examined in this study. To detect RAGE, iNOS and VE-cadherin expression, immunohistochemistry using cryostat sections of periapical granulomas were performed. In addition, mRNA was extracted from the cryostat sections, and real-time PCR using specific primers was then conducted. This study was approved by an ethics committee in our university, and written consent was obtained from patients prior to the collection of the lesions.
Results: Of 37 specimens, 33 was histologically determined as periapical granulomas. The rest of the specimens showed epithelial cell layer and cholesterol crystal; therefore, these were diagnosed as radicular cysts and were excluded from this study. Endothelial cells as well as macrophages, lymphocytes and fibroblasts showed protein expression of RAGE, iNOS and VE-cadherin. Real-time PCR analysis demonstrated that RAGE, iNOS and VE-cadherin mRNA was expressed in periapical granulomas; however, iNOS expression was higher than VE-cadherin.
Conclusions: We found that endothelial cells in periapical granulomas exhibit not only the expression of inflammatory mediators but also vascular integrity, suggesting that endothelial cells control the infiltration of inflammatory cells. The data suggested the possibility that endothelial cells may play a central role in inflammatory and anti-inflammatory reactions.