Increased submucosal factor XII la-positive dendrocytes in oral lichen planus

Factor XIIIa +“dendrocytes”, normal residents of the submucosa and dermis. are a morphologically and phenotypically distinctive subset of the monocyte-macrophage system. Because these cells arc believed to participate in the regulation of immune responses, we postulated that they may play a role in the pathogenesis of lichen planus, a condition of immune dysregulation. Tissue sections of oral lichen planus were evaluated immunohistochemically for evidence of differences in dendrocyte populations in lesional and non-lesional areas from the same patient. In addition to factor XIIIa, sections were stained for antigens (CD68, S-100 protein, CD36) that may be expressed by other cells that occasionally exhibit dendritic profiles. CDI8 (found on leukocytes and dendrocytes) and its ligand ICAM-I (intercellular adhesion molecule) were also identified in sections to determine if these antigens are operative in lichen planus. Results showed that XIIIa + dendrocytes were significantly increased in number (and size) in lichen planus. The mean number of dendrocytes in connective tissue subjacent to basement membrane (0.064 mm²) was 27 in lichen planus as compared to 10 in adjacent unaffected tissue. Similar increases were also evident in connective tissue deep to this zone (mean of 20 dendrocytes vs. mean of 8). CD68+ macrophages were also abundant in the lichen planus infiltrate, and S-100 + connective tissue cells were frequently seen. CD36 + dendritic cells were seen in relatively small numbers in the same sites where dendrocytes were found. ICAM-I + connective tissue dendritic cells of undetermined lineage were also evident in the diseased areas. Endothelial cells in and around the infiltrate were strongly reactive to anti-ICAM-1. Basal and parabasal keratinocytes overlying the lymphoid infiltrates were also strongly ICAM-1 +. It appears that XIIIa + dendrocytes have a role in the immunologic mechanisms of lichen planus, and that these cells may be acting in concert with other immunocompetent cells, such as macrophages and S-100 + epithelial dendritic cells, to activate T lymphocytes. ICAM-I expression by dendrocytes. endothelial cells, and keratinocytes may facilitate leukocyte migration to, and retention in. the disease focus.