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Summary Monoclonal antibodies (McAbs) directed against the framework determinants of Class I and Class II products of the major histocompatibility complex (MHC) and against leucocyte differentiation antigens were used in an indirect immunoperoxidase technique to study their expression in normal, benign (adenomatous polyps) and malignant disease of the colon. Class I products (detected by the McAb 2AI) were strongly expressed on all cell types in normal and benign tissues but some carcinomas exhibited a heterogenous pattern of epithelial cell staining and 4/15 were completely negative. Class II products (detected by TDR3 1.1) were strongly expressed on cells (mainly B lymphocytes) within the lamina propria. In carcinomas TDR31.1 staining was mainly interstitial, but in 2/15, DR+ epithelial cells were also detected. In normal and benign tissues, leucocytes (reactive with 2D1) found predominantly in the lamina propria, comprised T cells mainly of the helper/inducer (OKT4) subset, DR+ cells in approx. equivalent proportion and a few OKM1+ cells mostly of macrophage morphology. Occasional intraepithelial lymphocytes were of cytotoxic/suppressor (OKT8) phenotype. In malignant neoplasms, there was wide inter and intra-tumour variation in the proportion of leucocytes which were heterogeneous with respect to cell type and confined mainly to the stroma. T cells were consistently predominant, but B cells and macrophages were also present. Two neoplasms showed unequivocal evidence of a shift (relative to peripheral blood) in favour of the OKT8+ subset, but in the majority of tumours OKT4+; and OKT8+ cells were present in roughly similar proportions. Natural killer cells (monitored with Leu7, HNK1) were virtually undetectable in both normal and malignant tissues. There were no apparent correlations between the extent and type of leucocyte infiltration, tumour differentiation or expression of MHC products. Some implications for the extrapolation of in vitro data on leucocyte function to the in vivo situation are discussed.

The results of a clinicopathologic study of 165 oral leukoplakia cases followed up over a period of years are presented. The histologic changes were correlated with the clinical appearance and subsequent clinical course. A certain relationship between the clinical type of leukoplakia and its histologic changes could be established. The type of keratinization varied according to the clinical appearance; hyperorthokeratosis was found in the majority of leukoplakia simplex and verrucosa, and hyperparakeratosis was found in the leukoplakia erosiva cases. Comparing the results of histologic examination with the subsequent clinical course, the hyperparakeratotic group showed a more unfavorable proportion of healing than the hyperorthokeratotic leukoplakias.

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