Expression of secretory leukocyte protease inhibitor in middle ear cholesteatoma

Secretory leukocyte protease inhibitor (SLPI) is a cationic protein and a member of the innate immunity-associated protein family. The main function of SLPI is to protect local tissue against the detrimental consequences of inflammation. We undertook this study to investigate the expression of SLPI in human middle ear cholesteatoma tissue as compared with normal external auditory canal skin. Cholesteatoma tissues and external auditory canal skin samples were obtained from eight patients during middle ear surgery. The expression levels of SLPI mRNA and protein were evaluated by real-time reverse transcription-polymerase chain reaction (RT-PCR) and western blotting. Immunohistochemical staining was performed in both tissue groups using anti-SLPI antibody. Real-time RT-PCR showed that SLPI mRNA levels in cholesteatoma tissues were increased 7.8-fold on average as compared with normal auditory canal skin. Western blotting analysis showed that SLPI protein expression in cholesteatoma epithelium is up-regulated versus external auditory canal skin epithelium. Immunohistochemical staining for SLPI showed that SLPI is expressed mainly in the stratum granulosum and in subepithelial inflammatory cells. These findings imply that SLPI contributes to host protection against inflammatory cell and destructive enzymes in the chronic inflammatory state of cholesteatoma by affecting the innate immune system.