Abstract: Objective: The purpose of this study was to investigate the effect of interleukin-1β (IL-1β), the key factor of dental pulp inflammation, on the synthesis and secretion of MMP-9 of human pulp cells in vitro. Methods: Human pulp cells were separated and cultured in vitro. Cells of 4th-8th generation were incubated in 6 wells plates and divided into two groups. The cells in experimental group were treated with IL-1β, while the cells in control group were not. The streptavidin peroxdase conjugated method was applied to investigate immunohistochemical positive stained rate of cells and the distribution of positive stained particles. immunohistochemical The gelatin zymography method was also applied to investigate the expression of MMP-9 in human dental pulp cells with IL-1β or not, and gelatin zymography to examine the production of MMPs by dental pulp cell in course of cultures by the number of integrated optical density. Results: The results of immunohistochemical method and gelatin zymography revealed that MMP-9 were expressed in normal human dental pulp cells, and IL-1β could increase this level significantly（P＜0.01）. The immunohistochemical positive stained particles were found mainly in the cytoplasm, while a few of them were found in the extra-cellular matrix. Upon treated with IL-1β, the cells demonstrate significantly elevated levels of synthesis and secretion of MMP-9, showing the higher number of integrated optical density（P＜0.01）. Conclusion: MMP-9 is probably one of the matrix-degrading MMPs in dental pulp. IL-1β could have the potential to stimulate the production of MMP-9 in human pulp cells and thus result in the inflammation of dental pulp.

Key words: pulp cell, matrix metallproteinase, interleukin-1β, immunohistochemical, gelatin zymography