Altered expression of extracellular matrix proteins and integrins in oral lichen planus (OLP)

The immunohistochemical distribution of collagens type I, III, IV, V, VI, of undulin and tenascin, and of integrins alpha 2, alpha 3, alpha 4, alpha 5, alpha 6 and beta 4, was studied in 14 biopsies of oral lichen planus (OLP), 5 biopsies of orthokeratinized gingiva and 4 biopsies of oral fibrous hyperplasia. The localization of extracellular matrix proteins showed altered expression in OLP when compared to normal oral mucosa, with two principal patterns corresponding to the reticular or atrophic type. Whereas in the reticular type a focal loss of immunoreactivity for collagen types I, III, V, VI and undulin was noted in areas with a cellular infiltrate, in the atrophic variant almost complete loss of immunoreactivity of the subepithelial extracellular matrix was found. There was no clear correlation between the distribution of extracellular matrix proteins and their integrin receptors. The present findings suggest that the autoimmune reaction in OLP might not be primarily targeted to oral keratinocytes but to an unknown antigen in the connective tissue stroma. The changes in the subepithelial extracellular matrix associated with the inflammatory reaction might, especially in the atrophic variant, impair the cross-talk between epithelium and mesenchyme and favour both the loss of barrier function and the development of erosions in the clinical course of the disease.