Stromal expression of matrix metalloprotease-9 in middle ear cholesteatomas

Background: Matrix metalloprotease-9 (MMP-9) plays an important role in the degradation of extracellular matrix (ECM). In cholesteatoma there are sign ificant changes in the composition of the ECM, supporting the view of a dis turbed cell-ECM interaction. it has been reported that in cholesteatoma tis sues, MMP-9 is: expressed in epithelial cells but not in stromal cells. In this study, we report conflicting results regarding the identity of the cho lesteatoma cells that express MMP-9. Methods: An immunohistochemical assay was performed to examine the expressi on of MMP-9 in 35 cases (formalin-fixed paraffin-embedded sections) of chol esteatoma. using an MMP-9-specific monoclonal antibody. Results: In all cholesteatomas examined, MMP-9 was expressed in the stromal cells hut not in the epithelial cells. MMP-9 immunostaining was undetectab le in external auditory meatal skin (n = 5) and tympanic membrane (n = 3). Conclusions: These results suggest that the MMP-9 expressed in stromal cell s may be involved in the disturbed cell-ECM interaction associated with the process of cholesteatoma formation.