Histological and immunochemical studies of oral leukoplakia: phenotype and distribution of immunocompetent cells.

The Phenotype and distribution of immunocompetent cells in oral leukoplakia with different levels of dysplasia were analyzed. Cells were identified in two compartments of the oral mucosa, the epithelium and subepithelial connective tissue. One hundred cases of neutral-buffered formalin-fixed paraffin embedded biopsy materials including 10 cases of acetone-fixed frozen tissue sections were studied immunohistochemically. In the main lymphoid population of each groups, the T lymphocytes predominated over the B lymphocytes. The lymphoid cells were present either as diffuse aggregates or organized in follicular patterns with or without germinal center-like structures. When present, B lymphocytes were seen to constitute the above mentioned structures. T lymphocytes made up the paracortical areas. A decrease in CD4/CD8 ratio was observed in cases with severe dysplasia. Specimens classified as mild to severe dysplasia presented a significant increase in the number of CD1a (+) dendritic Langerhans cells when compared with those of epithelial hyperplasia. A significant increase in macrophage count was also obtained in the subephitelial connective tissue of all dysplastic cases. A significant increase of CD57 (+) natural killer/killer cells in the subephitelial connective tissue and HLA-DR expression by the keratinocytes was observed in cases with severe dysplasia. Correlation and analysis of the results revealed an immunocellular reaction that varied according to the degree of dysplasia in oral leukoplakia. Immunologic events, i.e. decreased CD4/CD8 ratio, increased density of natural killer/killer cells and HLA-DR expression by keratinocytes, occurring simultaneously in severe dysplasia are speculated to be indicative of early malignant transformation.