A mucoprotein with colon-specific determinants

Monoclonal antibody G47 engineered to be reactive with colorectal tumor mucin

We have previously shown that the normal adult colon produces a sialomucin containing the core trisaccharide 1,3 N-acetylgalactosamine. This structure was shown to be the epitope for a polyclonal antiserum that demonstrated colon "specific" activity. Antiserum binding is dependent upon the presence of O-acetylated sialic acids present at high concentrations in normal adult colon tissue. However, O-acetylation of sialic acids is decreased in colorectal cancer. Indeed, approximately 50% of colorectal carcinomas are nonreactive with this antiserum. In the current work, we used a de-O-acetylated, normal colon mucin as immunogen to generate monoclonal antibody (MAb) G47. Untreated normal colon mucins having a high O-acetylated sialic acid content were essentially nonreactive with G47. Removal of O-acetyl groups by saponification generated a reactive mucin derivative while subsequent treatment with neuraminidase abolished reactivity. By immunoperoxidase procedures MAb-G47 was reactive with approximately 85% of colorectal tumors while exhibiting relatively low reactivity with normal colon tissue. Mucins isolated from normal colon had on average less than 10% of the specific epitope as compared with mucins derived from colorectal tumors (p < 0.01). Initial immunohistochemical studies on tumors of noncolonic origin revealed few positive cases. The potential of MAb-G47 to assist in the diagnosis and/or prognosis of colorectal cancer is now being studied.

Precursors of colorectal carcinoma. Biopsy and biologic markers

The term biologic marker (biomarker) of colorectal cancer refers in this article to an early preclinical phenotypic characteristic that relates to the risk for developing this cancer. Putative biologic markers in the normal colorectal mucosa of patients at risk include abnormal cell proliferation as determined by kinetic studies, ornithine decarboxylase activity, and polyamine synthesis. Alterations of mucin synthesis have been studied using both histochemical stains and lectin-binding techniques. Blood group and related carbohydrate antigens also have been evaluated as potential biomarkers in the normal mucosa. Biopsy small (less than 5 mm) polyps encountered at endoscopy has become a standard practice. Although a small polyp found to be an adenoma has a low likelihood of harboring high-grade dysplasia or invasive carcinoma, it represents an indicator of risk for colorectal neoplasia. Hyperplastic polyps, however, even though they have certain epidemiologic associations with colorectal neoplasia, are controversial as putative biomarkers of clinical relevance. Current research supports a concept of a field defect of the colorectal mucosa at risk for neoplasia, which may be identified by phenotypic abnormalities of the normal mucosa and the development of small adenomas.

Enzyme-linked immunosorbent assay for ileal human goblet cell mucin

A sandwich ELISA for measuring ileal human goblet cell mucin has been developed with a linear response range 0.2 to 1.5 ng mucin protein. It can be used to quantitate the mucin present in dilute and unpurified samples without interference from other glycoproteins and proteins. Reduction of the mucin decreased the reactivity by only 14% indicating that the assay reacts almost as well with mucin glycopeptides as with native mucin. The assay has the advantages over previously described immunoassays for mucin of giving a result in 6 h, detecting slightly lower concentrations of mucin, and is more sensitive, quantitative and specific than the traditional protein or periodic acid-Schiff assays used for glycoproteins.

Organ specific antigens of the human gastrointestinal tract

We previously reported the characterization of a normal adult colonic mucin antigen which contained an organ specific immunodeterminant [Tissue Antigen 11, 362 (1978)]. In the present study we have investigated mucins produced at other levels of the gastrointestinal tract in order to determine if regional specificities exist. Mucins were isolated from normal adult stomach, jejunum, ileum and colon and used to prepare antisera in rabbits. By radioimmunoassay at least four distinct specificities were observed. Gastric, ileal and colonic mucins were shown to contain immunodeterminants which were organ specific. Antiserum directed toward jejunal mucin determinants was reactive with the entire gastrointestinal tract. However, by heterologous inhibition analyses employing purified mucins as inhibiting antigens, the anti-jejunum antiserum was shown to be capable of discriminating a determinant present in much higher epitope density within small intestinal mucins as compared to mucins of the stomach and colon. Thus, it appeared that immunologic determinants present within mucin type glycoproteins of the gastrointestinal tissues exhibit anatomic specificity. In each case the structure of the immunodeterminant was, or was dependent upon the presence of a sialic acid derivative.

Colonic and gastric mucus-associated antigens: a comparative immunohistological study in precancerous and cancerous rat intestinal mucosa

Gastric M1 antigens were previously shown to be oncofetal markers for the colon in man and in the rat. They were observed very early during carcinogenesis in goblet cells of precancerous colonic mucosa; using an immunohistological method, we found that M1 were produced in 68% (41/60) of colonic adenocarcinomas and in 33% (21/63) of duodenal adenocarcinomas. M3C antigen has been described as being associated with human colonic mucus; in the rat it is restricted to the proximal colon. We found that M3C was produced in 91% (55/60) of colonic adenocarcinomas and in 15% (8/53) of duodenal adenocarcinomas. Before tumor appearance, M3C was sometimes expressed by goblet cells of the distal colon. We could not find it during fetal life. We have concluded that mucus-associated antigens can characterize modifications in cell differentiation in rat colonic carcinomas.

Clinical aspects of gastrointestinal mucus

In such a bird's eye view of a very complicated and complex literature it is inevitable that significant contributions, particularly from earlier investigators, will have been overlooked. We have tried, however, to provide a reasonable framework for the many presentations and discussions which will take place at this conference. As in the past, it is evident that much needs to be done to reconcile the excellent histochemical studies of gastrointestinal mucus in many diseases with the increasing knowledge of mucin structure and composition. This will only be achieved by extraction of highly pure mucin from diseased bowel. In this regard, post mortem material provides an opportunity for mucin researchers which is not available to workers in other fields because of relative freedom from decomposition. The wedding of mucin technology with immunology is also a major priority. Immunoassay techniques provide the answer to quick and accurate product identification in secretion studies. Specific monoclonal antibodies will provide the route to structural differentiation of antigens in complex mixtures. It is also evident that we must seek to develop a variety of controllable models for the study of functional parameters of mucus in physiological conditions, parasite rejection, neoplasia and inflammatory states. Promising initiatives have been touched upon in this review, but these must only be the beginning. One must conclude, however, by recognizing that advances in knowledge have been truly remarkable since the last conference in 1976. One senses that some of the keys which will one day unlock the gates of this "ill-defined" kingdom are already in hand, while the remainder are at least within reach.

Intestinal M3 antigen, a marker for the intestinal-type differentiation of gastric carcinomas

The mucus-associated intestinal M3 antigen, normally restricted to intestinal goblet cells, was found in 35 out of 100 gastric adenocarcinomas belonging to intestinal (19/64) as well as diffuse (16/36) types according to Laurén's classification. often accompanying the other mucus-associated gastric M1 and M2 antigens. This M3 antigen was predominant over the gastric M antigens in 25 of these 35 tumors; 18 of these belonged to the histological intestinal type. According to the WHO classification, the M3 antigen was found to predominate in all mucinous adenocarcinomas (7/7), was never present in the undifferentiated carcinomas (0/8), but was also found in some tubulo-papillar (16/57) and signet-ring cell (12/27) adenocarcinomas. This antigen could be used as a new criterion and incorporated into a point system containing morphological and tumor cell behavioral considerations; then it would appear to be a good marker for intestinal-type differentiation. Indeed, 22 of these 25 gastric adenocarcinomas which produced predominantly M3 antigen showed such an intestinal-like differentiation. The M antigen pattern of gastric carcinoma suggested a duodenal rather than colonic-type differentiation.

Further characterization of CSAp, an antigen associated with gastrointestinal and ovarian tumors

Colon-specific antigen-p, or CSAp, was originally extracted from GW-39 tumors, which are human colonic carcinomas serially transplanted in golden hamsters, and antibodies to CSAp have been produced in the same animal hosts. By means of immunodiffusion and a hemagglutination-inhibition assay, CSAp has been found to be restricted to adult and fetal small intestine, neoplastic gastric and colonic tissues, inflamed colon, and cystic mucinous tumors of the ovary. CSAp was shown to be distinct from blood group antigens, including Lea and Leb blood group substances, liver ferritin, AFP, CEA, CSA, CMA, ZGM, and BOFA, and to have the electrophoretic mobility of an alpha2-globulin. Gel filtration studies indicated that CSAp in GW-39 tumor, primary human colonic carcinoma, and ovarian cancer mucinous cyst fluid had a peak molecular size range of 70,000--110,000. Quantitation of CSAp in 214 tissue specimens by the hemagglutination-inhibition assay revealed a progressive increase in fetal, inflamed, and neoplastic intestine, such that CSAp in colonic tumors was increased over normal colon tissue. Thus, CSAp appears to be an organ-specific antigen showing increased levels in some gastrointestinal and ovarian neoplasms, as well as in specimens with colitis.