Lichen planus: immunologic and morphologic identification of the submucosal infiltrate.

The purpose of this investigation was to specifically identify T cells, B cells, and histiocytes in the infiltrate typically seen in lichen planus. In frozen tissue sections, AET-treated sheep erythrocytes formed immunologic rosettes with the lymphocytes in the infiltrate, designating them as T cells. Rosette assays with reagent erythrocytes, IgGEA, IgMEA, IgMEAC, and E resulted in nonadherence, indicating a lack of B cells and macrophages, and indirectly implicating them as T cells. Scanning electron microscopy of the cellular infiltrate, in situ, showed that the cells had smooth, nonvillous surfaces. These observations were consistent with a T cell origin and were considered supportive of the immunologic data. The results of this investigation support the hypothesis that lichen planus is a disease mediated by thymus-dependent lymphocytes.