Immunohistochemical characterisation of odontogenic cysts with mesenchymal and myofilament markers.

The aim of the present investigation was to analyse the fibroblast phenotype in the main groups of odontogenic cysts. We have examined the muscle differentiation markers alpha-smooth muscle actin (ASMA) and desmin and the presence of vimentin using immunocytochemistry. Fibroblasts of other cyst types, hyperplastic fibrous lesions, and from several normal sites were used as controls. All fibroblasts stained for vimentin, but a variable proportion of cyst wall fibroblasts were also positive for the antibody to ASMA. Their distribution was not random and two positive zones could be distinguished, an inner subepithelial layer and an outer region adjacent to the bone-facing surface. This staining pattern was observed for all the types of odontogenic cysts studied, although the subepithelial staining was more frequent in the presence of an inflammatory infiltrate. The contractile nature of these cells was supported by their ultrastructural appearance. Some non-odontogenic cysts showed subepithelial fibroblasts strongly labelled with ASMA; in the control tissues ASMA was negative except for pericytes and some groups of cells in supracrestal gingiva. These results demonstrate a distinct cell population with a myofibroblast phenotype in the odontogenic cyst wall and with a distribution which may enable them to contribute to wall elasticity constraining cyst expansion. Their presence in all types of odontogenic cyst studied would suggest that myofibroblast formation is independent of the pattern of cyst growth.