Introduction: Oral Lichen planus (OLP) is chronic inflammatory oral mucosal disease of unknown etiology. Basement membrane damage and T-cell migration in OLP may be mediated by matrix metalloproteinases (MMPs). We examined the expression of matrix metalloproteinase 9 to support this hypothesis.
Materials and methods: The study population consisted of 71 patients with OLP and 10 control patients with oral fibromas. Indirect immunohistochemistry was used for detection of MMP 9 expression (polyclonal rabbit anti-human MMP antibody).
Results: In all cases of OLP, the MMP-9 expression was seen mainly in the area oflymphocytic inflammatory infiltrate in the lamina propria including lymphocytes within the overlying epithelium. In addition, it was observed in the epithelial keratinocytes, particularly in the stratum basale and stratum spinosum with occasional positivity in the superficial layer. Fibroblasts and endothelium of small vessels in the lamina propria showed MMP9 expression as well. In all cases of oral mucosal fibromas, the MMP-9 expression was seen only in fibroblasts and in endothelium of small vessels with occasional positivity within the overlying epithelium. It remains unclear, whether MMP-9 is directly connected to OLP pathogenesis.