The expression of cell surface MHC class I heavy and light chain molecules in pre-malignant and malignant lesions of the oral mucosa.

Major histocompatibility complex (MHC) class I antigenic expression was examined on epithelial cell surfaces in normal oral mucosa, non-specific oral keratoses, dysplastic epithelium adjacent to carcinomas and in invasive tumour islands of squamous cell carcinomas, using antibodies to HLA-A,B,C shared determinant antigen and beta 2 microglobulin (beta 2m). HLA-A,B,C antigens were present in the basal and lower spinous cells in normal and dysplastic epithelium and in the non-specific keratoses, but in a minority of carcinomas staining was disorganized and absent at the periphery of tumour islands. beta 2m staining was present in the basal and lower spinous epithelial cells in all tissues; staining was lost progressively with increasing dilution of the primary antibody until it was completely lost in the invasive carcinoma tissue at 1:400, in dysplastic epithelium at 1:800 and in non-specific keratoses at 1:3200; in contrast, staining persisted in normal tissues at greater than 1:3200 anti-beta 2m dilution. Loss of beta 2m staining in the dysplastic epithelial tissues correlated broadly with the degree of cellular atypia. The results suggest that there are decreased concentrations of cell surface beta 2m in potentially malignant and malignant epithelial tissues, with normal concentrations of MHC class I heavy chains.