Lichen planus (LP) is a mucocutaneous disease for which the etiology and pathogenesis are poorly understood. We performed an immunohistochemical study on formalin-fixed tissue sections of 10 cases of LP using subsets of antibodies to lymphocytes (LCA, CD3, OPD4-CD4, L26, LN1 and Leu-7), and monocyte-macrophages lysozyme, KP1-Mac, Factor XIIIa (FXIIIa) and S-100 protein. Six cases showed typical histological features of active LP, two cases showed features of active and inactive LP, and two cases showed only inactive LP. In active LP, scattered T cells (CD3+ and pan T cells) were present in the epidermis, whereas large numbers of CD3+ T cells were present at the dermoepidermal junction and in the dermis. Approximately 40percnt; of the T cells at the dermoepidermal junction were of the helper/inducer subset, whereas sim;80percnt; of those in the dermis were CD4 positive (helper/ inducer T cells). Occasional B cells were present in the dermis only. Increased numbers of S-100-positive Langerhans cells, macrophages expressing lysozyme, and FXIIIa dendritic cells were present in the epidermis and dermis. The inactive lesions showed the presence of a few epidermal Langerhans cells and a mild infiltrate of T cells (helper/inducer subset). These results suggest that in addition to different subsets of T cells and macrophages, including Langerhans cells, dermal dendritic cells expressing Factor XIIIa and lysozyme-positive histiocytes play an important role in lichen planus. They may participate in the destruction and subsequent regeneration of the basal layer of the epidermis, or alternatively may be activated as a result of destruction of the basement membrane in LP.
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