Absence of leukocyte microchimerism in oral lichen planus (OLP): an in situ hybridisation study

Oral lichen planus (OLP) is a relatively common chronic inflammatory disease. The majority of patients are between 30 and 50 years of age with a higher incidence in females. The aetiology is unknown and various hypotheses on the pathogenic mechanisms, including autoimmunity, have been proposed over the years. In the present study, we investigated whether leukocyte microchimerism, a biological situation implicated in the aetiology of some autoimmune diseases, might play a role in the pathogenesis of OLP. We used in situ hybridisation to identify Y chromosome DNA in a series of formalin-fixed paraffin-embedded oral mucosa biopsies of women with established clinical and histological disease who had given birth to a male child. The positive control, two mucosal specimens from a man with OLP, showed over 90% of keratinocytes and cells within the inflammatory infiltrate, a positive nuclear signal. The negative control, biopsies from three women having carried only female foetuses and one nulliparous woman, all with OLP, did not show any nuclear signal. In the fifteen selected cases of OLP biopsies from women who had only male offspring, nucleated cells containing the Y chromosome were not detected within the chronic inflammatory infiltrate. These results suggest that unlike some other immunologically mediated diseases, leukocyte microchimerism does not seems to be involved in the pathogenesis of OLP.