A Histochemical and Immunohistochemical Study of Mucous Cyst—with Special Reference to Mucoid Substance and Characteristics of Inflammation—

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Mucous cysts are relatively common lesions in the oromaxillofacial region. A mucous cyst is composed of a mucoid substance and foamy mononuclear macrophages (mucinophages), with inflammatory cell infiltration and the overgrowth of blood vessels and fibrous tissue forming a mucoid granuloma. Although the mucoid substance characteristics and the inflammatory characteristics are thought to be important factors, details of the histopathogenesis in relation to the mucinophages remain unclear. Therefore, the present study was conducted to investigate the pathogenesis of mucous cysts with reference to the histochemical and immunohistochemical characteristics of thirteen cases and a review of the literature. Lectin histochemistry and immunohistochemistry showed that mucinophages gave a strong reaction to concanavalin A and lysozyme, and a weak or negative reaction to wheat germ agglutinin. In contrast, the mucoid substance, salivary ducts and acinar cells were strongly to weakly reactive to wheat germ agglutinin and weakly or negatively reactive to concanavalin A. The reactivity to the other lectins and salivary markers in mucous cysts was similar with those in the salivary gland tissues. These results suggested that mucoid degeneration resulted from phagocytosis by the mucinophages and that the mucoid substance in mucous cysts was derived from the saliva. The cell rate of CD68-positive mucinophages was higher in mucous cysts than in control tissues. The cell rates of panT-positive T-cells and panB-positive B-cells were lower in mucous cysts than in control tissues. In addition, the count of mast cells showing metachromasia with toluidine blue at pH 2.5 in mucous cysts was equal to that in control tissues. For immunoglobulin-producing plasma cells, the IgE positivity rate was higher in mucous cysts than in control tissues, whereas the IgA positivity rate was lower in mucous cysts than in control tissues. These results suggested that the accumulation of mucinophages, which had phagocytotic and antigen-presenting abilities, was mainly associated with the pathogenesis of the mucous cyst, in addition to a local T-cell-mediated cellular immune mechanism or to an acute allergic immunoresponse by IgE-producing cells and mast cells.