No abstract

We describe the production, immunochemical and immuno-histochemical characterization of monoclonal antibodies (MAbs) raised against the oncofetal small intestinal mucin antigen (SIMA). Four MAbs, reacting with distinct neuramini-dase-sensitive SIMA epitopes, were shown to define a novel differentiation-associated relationship of SIMA epitopes within the normal small intestinal villus. Using Swiss rolls of 15 entire colorectal cancer resections, inappropriate expression of SIMA epitopes was detected in all cancers, in adjacent transitional mucosa and remote morphologically normal mucosa, extending as far as resection margins (73%). SIMA expression, whether preexisting or reactive to the tumor, may predispose to malignant change and tumor recurrence.

SummaryThe colorectal adenoma-carcinoma sequence was examined in relation to the ectopic expression of the oncofoetal Small Intestinal Mucin Antigen (SIMA), to the development of morphologic changes in the adenoma and perineoplastic mucosa and to indices of malignant potential. Four anti-SIMA MAbs, which define a novel hierarchy of SIMA epitopes in the normal small intestine and adjacent to colorectal cancers, were used in a retrospective immunohistochemical study of Familial Adenomatous Polyposis (FAP, n = 183) and non-familial (n = 44) adenomas. Inappropriate expression of SIMA epitopes was first detected in mucosa adjacent to minute microadenomas larger than three glands, and with increase in size, in increasing amounts within adenomas themselves, but not with microadenomas smaller than three glands or regions of flat mucosa free of adenomas. SIMA epitope expressed in mucosa adjacent to adenomas preceded changes in perineoplastic morphology, which progressed with adenoma growth to resemble transitional mucosa (TM) adjacent to cancers. Thus, the onset of both SIMA expression and morphological changes in TM were consistent with reactive rather than pre-existing field change phenomena. The previously reported hierarchy of four SIMA epitopes (5C5, 3D4, 4D3, 6C5) was also consistently observed in the adenoma-carcinoma sequence, and applied to (i) the order of epitope detection, (ii) the number of positive adenomas and (iii) extent of staining; (iv) the height in the crypt and (v) distance from the adenoma to which epitopes were expressed in perineoplastic mucosa. These observations are consistent with a progression of changes in mucin composition with adenoma development. The percentage of positive adenomas and reactivity scores for each anti-SIMA MAb correlated with increasing adenoma size, degree of dysplasia and growth pattern. SIMA expression appears to predate the earliest reported oncogene and tumour suppressor gene changes, was persistent and increased throughout adenoma development. SIMA epitopes are thus markers of very early neoplastic change, whose expression correlates with malignant potential and may contribute to the accumulation of changes necessary for tumourigenesis.

This study has identified the expression in normal and neoplastic gastrointestinal (GI) tract of epitopes on the colonic mucin LIMA (large intestinal mucin antigen), which are unique markers of normal colonic differentiation. Six anti-LIMA monoclonal antibodies (MAbs) (22D4, 9B5, 2C3, 23B2, 46A2, and 10B3) were studied immunohistochemically in normal GI tract, colorectal adenomas, and colorectal and gastric cancers. All MAbs showed specificities consistent with distinct epitopes, five of which were neuraminidase-resistant and four periodate-sensitive. Each reacted with mucin in 60-100 per cent normal colons--MAbs 10B3 and 23B2 also with small intestinal mucin--but none with gastric mucin. Five MAbs showed crypt and regional gradients in normal colon, MAbs, 22D4, 9B5, and 2C3 showing a hierarchy of reactivities in the crypt. Individual adenomas showed decreasing goblet cell (GC) LIMA expression with increasing size. However, 30 per cent of familial adenomatous polyposis (FAP) patients had generalized background losses of 9B5 and 2C3 GC reactivity, retaining 22D4, whilst 44 per cent of non-FAP patients lost 22D4 GC reactivity, regaining 9B5 and 2C3--evidence for polymorphism of mucin expression. All colorectal cancers expressed LIMA epitopes (frequently weaker than normal), and three MAbs (22D4, 9B5, and 2C3) showed deeper than normal staining in adjacent crypts. Eighty-five per cent of gastric cancers also expressed LIMA epitopes.

We have investigated changes in mucin antigenicity and morphology in the perineoplastic mucosa adjacent to rare, predominantly non-mucosal gastrointestinal (GI) tumours. Twenty-nine tumours of small and large intestine, including primary mesenchymal and ectodermal tumours, were examined immunohistochemically using 11 monoclonal antibodies (MAbs) raised against SIMA and LIMA (small and large intestinal mucin antigens). Non-epithelial GI tumours were essentially non-reactive, while adjacent mucosa showed altered mucin expression and morphology, in particular, features of transitional mucosa (TM). Combinations of different SIMA epitopes were detected adjacent to all colorectal tumours, and, similarly, LIMA epitopes adjacent to small intestinal tumours. Specific patterns adjacent to certain tumours may reflect influences of factors produced by individual tumours on mucin composition. Altered antigenicity and morphology in TM thus appear to be reactive changes in response to a wide range of GI tumours, presumably as a consequence of factors secreted by the tumour and/or a host response to the tumour.