T-cell Activation in Oral Lichen Planus Lesions

Purpose: OLP lesions are invaded by T cells, but characteristically lack B cells and NK cells. CD4+ outnumber CD8+ T cells by up to three-fold, and produce cytokines, which may significantly contribute to the apoptotic cell death of keratinocytes. OLP lesion infiltrating T cells are largely memory lymphocytes (CD45RA-, CD45RO+), but their state of activation remains to be fully characterized. Method: We performed an immunohistochemical study designed to test the state of activation of lymphocytes in reticular, compared to erosive OLP lesions. We used frozen sections from biopsies obtained from patients whose OLP status was confirmed by immunohistopathology. Sections were immunostained with horse radish peroxidase. Results: We confirm the histological disruption of the lamina propria by H & E stain, the presence of significant apoptosis by Annexin staining, and CD3+ T cell invasion in OLP lesions. We show a significant invasion of OLP lesions by activated lymphocytes, as determined by the expression of the a chain of the interleukin-2 receptor, CD25, and by CD69. Preliminary statistical analyses indicate more CD25+ and CD69+ cells in erosive, compared to reticular lesions. Conclusions: Our data to date strongly suggest, but do not definitely prove that invading T cells in OLP lesions are predominantly activated effector memory T cells. From a clinical and from a fundamental immunology viewpoint, a better understanding of the nature of resident T lymphocytes in OLP lesions at the different stages of the disease process could lead to new modes of treatment intervention. In fact, whether T cells found in OLP lesions are indeed resting or activated effectors could increase the level of understanding of the pathogenesis of OLP, and could make OLP a useful model for distinguishing central vs. local, and resting vs. effector memory T cells.