Localization of substance P-induced upregulated interleukin-8 expression in human dental pulp explants

Aim To localize ex vivo expression of interleukin‐8 (IL‐8) induced by substance P (SP) in human dental pulps. Methodology Intact caries‐free, freshly extracted third molars (n = 20) were collected from patients (15–25 years old). The teeth were split and pulpal tissue was obtained and stored in Dulbecco’s modified Eagle medium. Human dental pulp tissue explants were stimulated with SP. Expression of IL‐8 in pulp explants was detected and localized by immunohistochemistry. Results Moderated IL‐8 immunoreactivities were detected mainly in the cell‐rich zone in pulp tissues 12 h after tumour necrosis factor alpha (TNF‐α) stimulation (positive controls), whereas only weak IL‐8 expression was observed in tissues stimulated with SP at the same time interval. These data did not differ from those in negative controls. Increased IL‐8 expression in pulp explants after 24 h of SP stimulation was noted compared with negative controls and located in fibroblast‐like cells, blood vessel‐associated cells and extracellular matrix in the central zone and cell‐rich zone of pulp explants. Tissues stimulated with TNF‐α for 24 h (positive controls) revealed weak IL‐8 immunoreactivities with altered cell morphology. Conclusions Substance P induces IL‐8 expression and was located in fibroblast‐like pulp cells, blood vessel‐associated cells and extracellular matrix of human dental explants. These data support the hypothesis that neuropeptide (SP) coordinates the modulation of pulpal inflammation via up‐regulating chemokine IL‐8.