Loss of epithelial L1 expression is associated with cellular invasion of oral squamous cell carcinomas

Recent studies have suggested that the epithelial expression of two leukocyte-related proteins, human class II HLA-DR antigen and myelomonocytic L1 antigen, depends on a certain state of cellular maturation and differentiation. We have studied HLA-DR and L1 expression in oral squamous cell carcinomas. The epithelial distribution of these proteins was evaluated in relation to differentiation alterations by two-color immunofluorescence staining with cytokeratins (K14 and K13) as a baseline. HLA-DR was infrequently expressed in oral carcinomas, apparently being unrelated to the degree of differentiation and the subepithelial leukocyte infiltration. L1 was generally present in oral epithelium but disappeared in the most invasive cells of carcinomas. These cells were also K14 and K13 negative suggesting an abnormal state of differentiation. L1 has been suggested to have an inhibitory effect on casein kinases I and II, enzymes possibly associated with cell proliferation; it might therefore exert an inhibitory effect on tumor growth. Its absence could be an interesting aspect of the invasiveness of oral carcinoma cells.