The pathogenesis of lichen planus.

The histological features of lichen planus (LP) are characterized by typical epidermal changes with dermal lymphocytes that are mostly Ia positive T cells. In order to find out whether the primary event of LP is damage to basal keratinocytes or a delayed hypersensitivity reaction in which an as yet unidentified antigen activates T lymphocytes that destroy keratinocytes, we transplanted skin obtained from six patients with LP. Two millimetre punch and split thickness of grafts were obtained from involved and uninvolved areas from each patient and grafted onto nude mice. Biopsies were taken from the grafts at 14 and 21 days after transplantation for histological and immunofluorescence studies and after 6 weeks for Dopa incubation for melanocyte populations. A complete disappearance of the pathological changes of LP was found 21 days following grafting. An increased number of melanocytes was noted. This indicates that the pathogenesis of LP may not be due to an inherent change in the epidermal cells, but rather to the migration of cellular elements of the immune system.