Objectives: The aim of this study was to develop a precise method to quantify mast cells in oral lichen planus (OLP). OLP is a dermatologic disease that can occur in the oral mucosa. Some cases are not true OLP but rather lichenoid lesions that occur as a result of contact with dental restorative materials, medication use or oral habits. OLP lesions are characterized by a band-like inflammatory infiltrate in the lamina propria comprised almost exclusively of T-lymphocytes. However, mast cells have been observed in varying numbers with special stains. Quantification of mast cells in this infiltrate has been problematic due to the dense inflammation.

Methods: Archived paraffin tissues from 62 OLP subjects were used. 5-µm sections were stained with toluidine blue (Sigma-Aldrich; St. Louis, MO) for mast cell-specific metachromasia or with a monoclonal mouse anti-human mast cell tryptase antibody (Dako; Carpinteria, CA). Tissue area was divided into 1mm² grid squares using a Lovin micro-slide field finder (Gurley; Troy, NY). Grid squares containing at least 50% epithelial or lamina propria tissue were identified. Four of these grid squares were selected at random from each slide for quantification.

Results: Cell counts were compared by a paired t-test. The average difference between the two methods was 18.9 (p<0.05).

Conclusions: There is a significant difference in the cell counts achieved with each method at a level of 0.05. Immunohistochemical detection of mast cells appears to be a more concise method than conventional toluidine blue staining for quantifying mast cells within dense inflammatory infiltrate such as that seen in OLP. Additionally, further characterization of mast cells in OLP may provide a way to differentiate OLP from lichenoid lesions of different etiology.

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