Leukotriene A4-hydrolase expression and leukotriene B4 levels in chronic inflammation of bacterial origin -: Immunohistochemistry and reverse-phase high-performance liquid chromatography analysis of oral mucosal epithelium

Chronic inflammation of the oral epithelium of bacterial origin is associated with elevated leukotriene B-4 (LTB4) levels, We investigated leukotriene A(4) (LTA(4))-hydrolase expression and LTB4 levels in oral epithelium in relation to the clinical disease manifestation and immunohistopathology and LTA(4)-hydrolase expression in cultured oral keratinocytes. In 11 patients, three different types of biopsy specimens of the oral mucosa tissues were examined. Each sample was divided, and one-half was analysed using immunohistochemistry with antibodies to LTA(4)-hydrolase, CD1a, CD3, CD19, macrophages/monocytes and granulocytes. The other half of the sample was homogenised and analysed using reverse-phase high-performance liquid chromatography to determine LTB4 levels. We found strong LTA(4)-hydrolase expression in basal cells of the oral epithelium from tissue samples that appeared clinically healthy; however, histologically a mild chronic inflammation was observed. In contrast, patients with symptoms of an inflammation of the oral mucosa showed only weak LTA(4)-hydrolase staining of the epithelial cell layers, but strong immunoreactivity in endothelial and invading inflammatory cells. LTB4 levels were elevated in inflamed tissues compared with non-inflamed controls. Most significantly, there was a strong association between the immunohistochemical detection of the enzyme, LTB4 levels, cellular infiltration and the clinical disease manifestations. In vitro experiments indicated that LTA(4)-hydrolase expression may be induced by bacterial contamination. This study suggests that LTA(4)-hydrolase expression and elevated LTB4 levels in oral mucosal epithelium are integral parts of the induction and progression of chronic inflammatory reactions. Epithelial cells may participate in early stages of inflammation as a source of LTB4.