Composition of human colonic mucin. Selective alteration in inflammatory bowel disease

Intestinal trefoil factor binds to intestinal epithelial cells and induces nitric oxide production: priming and enhancing effects of mucin

Intestinal trefoil factor (ITF or TFF3), NO and epithelium-associated mucin have important roles in sustaining mucosal integrity in the gastrointestinal tract. In the present study we examined ITF-binding molecules on IEC-18 cells (an intestinal epithelial cell line) with the use of flow cytometry and localized these molecules on the cell surface by confocal microscopy. Furthermore, we studied the interaction of mucin and ITF and their co-operative effect on NO production by the epithelium. Stimulation of cells with mucin (5 mg/ml) for 90 min resulted in a 5-fold increase in ITF binding. Treatment of IEC-18 cells with actinomycin D or cycloheximide attenuated mucin-enhanced ITF binding. Ligand blot analysis confirmed the induction of ITF-binding protein in IEC-18 cells by mucin. These results indicate that transcriptional and translational mechanisms are involved in the effect of mucin. Treatment with ITF overnight resulted in a low level of nitrite production by the cells, a 5-fold increase over control, in a concentration-dependent manner. ITF-induced NO production was attenuated by 1400W, a selective type II nitric oxide synthase (NOS2) inhibitor. By immunoblotting we found that NOS2 was up-regulated by ITF treatment. Priming IEC-18 cells with mucin for 90 min enhanced the effect of ITF on NO production, suggesting that the up-regulation of ITF-binding molecules by mucin might be physiologically relevant. Taken together, these observations indicate (1) that ITF-binding molecules that are up-regulated by mucin exist on the intestinal epithelial surface, and (2) that ITF modulates epithelial NO production via the NOS2 pathway, which is enhanced by mucin.

Intestinal trefoil factor binds to intestinal epithelial cells and induces nitric oxide production: priming and enhancing effects of mucin

Intestinal trefoil factor (ITF or TFF3), NO and epithelium-associated mucin have important roles in sustaining mucosal integrity in the gastrointestinal tract. In the present study we examined ITF-binding molecules on IEC-18 cells (an intestinal epithelial cell line) with the use of flow cytometry and localized these molecules on the cell surface by confocal microscopy. Furthermore, we studied the interaction of mucin and ITF and their co-operative effect on NO production by the epithelium. Stimulation of cells with mucin (5 mg/ml) for 90 min resulted in a 5-fold increase in ITF binding. Treatment of IEC-18 cells with actinomycin D or cycloheximide attenuated mucin-enhanced ITF binding. Ligand blot analysis confirmed the induction of ITF-binding protein in IEC-18 cells by mucin. These results indicate that transcriptional and translational mechanisms are involved in the effect of mucin. Treatment with ITF overnight resulted in a low level of nitrite production by the cells, a 5-fold increase over control, in a concentration-dependent manner. ITF-induced NO production was attenuated by 1400W, a selective type II nitric oxide synthase (NOS2) inhibitor. By immunoblotting we found that NOS2 was up-regulated by ITF treatment. Priming IEC-18 cells with mucin for 90 min enhanced the effect of ITF on NO production, suggesting that the up-regulation of ITF-binding molecules by mucin might be physiologically relevant. Taken together, these observations indicate (1) that ITF-binding molecules that are up-regulated by mucin exist on the intestinal epithelial surface, and (2) that ITF modulates epithelial NO production via the NOS2 pathway, which is enhanced by mucin.

Abnormalities in mucin gene expression in Crohn's disease

Alterations in the structure and/or quantity of mucins could alter the barrier function of mucus and play a role in initiating and maintaining mucosal inflammation in Crohn's disease. To investigate the hypothesis of a mucin gene defect in Crohn's disease, we analyzed the expression of the different mucin genes in the ileal mucosa of patients with Crohn's disease and controls. mRNA expression levels were assessed by a quantitative dot blot analysis and compared (i) between healthy and involved ileal mucosa of patients with Crohn's disease and (ii) between healthy mucosa of patients with Crohn's disease and controls. Expression of the different mucin genes was heterogeneous among controls and patients with Crohn's disease, except for MUC6 in controls. Nevertheless, MUC1 mRNA expression was significantly decreased in the involved ileal mucosa of patients with Crohn's disease when compared to the healthy mucosa (p = 0.02). Moreover, the expression levels of MUC3, MUC4, and MUC5B were significantly lower in both healthy and involved ileal mucosa of patients with Crohn's disease compared to controls (p < or = 0.05). The decrease of expression levels of some mucin genes (more particularly MUC3, MUC4, and MUC5B) in both healthy and involved ileal mucosa suggests a primary or very early mucosal defect of these genes in CD.

Abnormalities in mucin gene expression in Crohn's disease

Alterations in the structure and/or quantity of mucins could alter the barrier function of mucus and play a role in initiating and maintaining mucosal inflammation in Crohn's disease. To investigate the hypothesis of a mucin gene defect in Crohn's disease, we analyzed the expression of the different mucin genes in the ileal mucosa of patients with Crohn's disease and controls. mRNA expression levels were assessed by a quantitative dot blot analysis and compared (i) between healthy and involved ileal mucosa of patients with Crohn's disease and (ii) between healthy mucosa of patients with Crohn's disease and controls. Expression of the different mucin genes was heterogeneous among controls and patients with Crohn's disease, except for MUC6 in controls. Nevertheless, MUC1 mRNA expression was significantly decreased in the involved ileal mucosa of patients with Crohn's disease when compared to the healthy mucosa (p = 0.02). Moreover, the expression levels of MUC3, MUC4, and MUC5B were significantly lower in both healthy and involved ileal mucosa of patients with Crohn's disease compared to controls (p < or = 0.05). The decrease of expression levels of some mucin genes (more particularly MUC3, MUC4, and MUC5B) in both healthy and involved ileal mucosa suggests a primary or very early mucosal defect of these genes in CD.

A novel gastric-cancer-associated mucin antigen defined by a monoclonal antibody A3D4

De-glycosylation of mucins may expose new tumor-associated core protein epitopes. In this study, to attempt to develop useful markers for gastric cancers, we have purified and de-glycosylated gastric mucin and tried to establish monoclonal antibodies (MAbs). A MAb designated A3D4 among established MAbs was shown to react with gastric cancer with high frequency, but not with normal gastric epithelium. Among normal digestive organs, only the colon and gall bladder were positive for MAb A3D4. The incidence of positivity in gastric cancer was 75% for intestinal-type adenocarcinoma (n = 28), 40% for solid-type adenocarcinoma (n = 5) and 33% for signet/scirrhous-type adenocarcinoma (n = 15). Interestingly, adenoma and intestinal metaplasia (IM) with chronic gastritis or peptic ulcer were negative for MAb A3D4, whereas 8 out of 13 cases (62%) of IM with gastric cancer was positive. Western-blot analysis using the lysate from normal colon tissues revealed a high-molecular-weight (> 300-kDa) smear-like band. Immunohistochemical analysis indicated that the reactivity of MAb A3D4 was clearly increased when tissue sections were pre-treated with periodic acid or O-glycanase, while it was decreased by pre-treatment with trypsin or protease V8. There was no reactivity with the synthetic peptide encompassing the tandem-repeat sequence of MUC2 or MUC3. These data suggest that MAb A3D4 detects a novel gastric-cancer-associated mucin antigen whose epitope may be peptide in nature.

Altered expression of mucins throughout the colon in ulcerative colitis

BACKGROUND/AIMS

Regional differences in the biology of the colonic epithelium may determine the extent of involvement by ulcerative colitis. Novel monoclonal antibodies (MAbs) were used in this study to investigate regional heterogeneity in the colonic mucosa.

METHODS

MAbs generated using a method of tolerisation against common antigens in the proximal colon and distal colon were used for immunoperoxidase staining, comparative histochemistry, immunoblotting, and slot-blot analysis.

RESULTS

The colon specific MAbs 5F1 (IgG3) and 6G4 (IgM) stained goblet cell contents throughout the normal distal colon but staining was markedly reduced in the proximal colon (p < 0.0001). In the distal colon of patients with ulcerative colitis, whether quiescent or actively inflamed, reactivity was reduced compared with controls (p < 0.05, p < 0.001 respectively). By contrast, an overall increase in staining was seen in the uninflamed proximal colon in ulcerative colitis compared with controls (p < 0.02). Comparative staining with high iron diamine and biochemical analyses indicated that MAb 6G4 was reactive with mucin bearing sulphate or O-acetylated sialic acid groups, or both.

CONCLUSIONS

Regional differences in the staining characteristics of normal colonic mucin have been shown using novel monoclonal antibodies. The pattern of mucin expression throughout the colon in ulcerative colitis is altered even in the absence of histological changes.

Healing the epithelium: solving the problem from two sides

The gastrointestinal epithelium produces a wide variety of peptides which may contribute to protection from injury as well as repair after injury occurs. Restitution, the initial phase of mucosal repair, is accomplished by rapid migration of the epithelium to re-establish surface epithelial continuity. A wide variety of growth factors and cytokines, which are produced both by the epithelium itself and by lamina propria cell populations, promote restitution in models of epithelial injury. These include members of the epidermal growth factor (EGF)/transforming growth factor (TGF)alpha, and the fibroblast growth factor (FGF) families, as well as a variety of cytokines (interleukin [IL]-1, IL-2, IL-4, IL-15, and interferon gamma) which interact with their cognate receptors on the intestinal epithelial basolateral surface. These growth factors and cytokines appear to promote restitution through a TGF beta-dependent pathway and act to both enhance expression of TGF beta and to entrance its bioactivation. In contrast, trefoil peptides, members of a recently recognized family of small proteins produced by goblet cells, both protect the epithelium and promote restitution following secretion onto the apical surface through mechanisms distinct from those peptides acting through TGF beta. Thus, rapid repair after epithelial injury is achieved through complementary mechanisms acting at the basolateral and apical surfaces of the epithelium.

Apoptosis of crypt epithelial cells in ulcerative colitis

In the colon of ulcerative colitis (UC) patients, apoptotic bodies have been recognized in routine histopathological preparations. To investigate the extent of the apoptosis, colonic biopsies were examined from involved and uninvolved areas of untreated active UC and from normal areas in patients with colonic polyps, utilizing various markers of apoptosis. The markers included DNA breaks detected by TUNEL, Fas (CD95/APO-1) and Fas ligand (Fas-L) localized by immunohistochemistry, electron microscopic features of apoptosis, and laddering of extracted DNA. Apoptosis marker positive cells were found mainly on the luminal epithelium of the normal colon and were present in active UC in crypts of involved and uninvolved areas of the colon, in addition to the luminal epithelium. The DNA extracted from active UC colon electrophoresed as a ladder. These findings suggest that the loss of epithelial cells in active UC occurs mainly by apoptosis in crypts of involved and adjacent uninvolved areas and that the Fas/Fas-L interaction is a mediator of the apoptosis.

Apoptosis of crypt epithelial cells in ulcerative colitis

In the colon of ulcerative colitis (UC) patients, apoptotic bodies have been recognized in routine histopathological preparations. To investigate the extent of the apoptosis, colonic biopsies were examined from involved and uninvolved areas of untreated active UC and from normal areas in patients with colonic polyps, utilizing various markers of apoptosis. The markers included DNA breaks detected by TUNEL, Fas (CD95/APO-1) and Fas ligand (Fas-L) localized by immunohistochemistry, electron microscopic features of apoptosis, and laddering of extracted DNA. Apoptosis marker positive cells were found mainly on the luminal epithelium of the normal colon and were present in active UC in crypts of involved and uninvolved areas of the colon, in addition to the luminal epithelium. The DNA extracted from active UC colon electrophoresed as a ladder. These findings suggest that the loss of epithelial cells in active UC occurs mainly by apoptosis in crypts of involved and adjacent uninvolved areas and that the Fas/Fas-L interaction is a mediator of the apoptosis.

Colonic mucins in ulcerative colitis: evidence for loss of sulfation

Colonic tissue obtained at surgery from control individuals and patients with ulcerative colitis was used to isolate mucins and to prepare mucin glycopolypeptides by pronase digestion. These were compared with mucins labelled with [35S] sulfate and [3H]-glucosamine after organ culture tissue samples from the same patients. A significant loss of mucin sulfation was detected in the colitis patients by both metabolic labelling and chemical analysis of the glycopolypeptides. A change in the size distribution of purified mucin oligosaccharides fractionated on BioGel P6 after release by beta-elimination was seen in both radiolabelled and non-labelled colitis mucins compared with controls. Amino acid analysis of the glycopolypeptides showed a close similarity to the expected ratio of serine:threonine:proline for MUC2 and did not vary between control and colitis groups. Analysis of the mucins confirmed > 90% purity in the labelling experiments, characteristic behaviour on density gradient centrifugation and agarose gel electrophoresis in control and ulcerative colitis groups and differences in sulfation and turnover at various sites in the normal colon.

Characterization of mucin in whole-gut lavage fluid obtained from patients with inflammatory bowel disease

Whole-gut lavage fluid, collected by administering an electrolyte lavage solution orally, was found to be an excellent and easily collectable source of abundant mucin. Furthermore, the biochemical features of the mucin from patients with ulcerative colitis and Crohn's disease were investigated. The mucin was separated into four fractions by Sepharose CL-4B, Sepharose CL-2B, and DEAE Sephacel chromatography. Compared with healthy subjects, the total yields of mucin from ulcerative colitis patients were low due to a deficiency of neutral mucin, whereas those from Crohn's disease patients were high, which was attributable mainly to high-molecular-weight mucin. The fucose and sulfate contents were low in ulcerative colitis, but only the former was low in Crohn's disease. The different biochemical features of the mucin obtained from whole gut lavage fluid appear to reflect mucosal pathological changes associated with inflammatory bowel disease.

Mucus glycoproteins and their role in colorectal disease

In this review, the nature and impact of progress in the study of mucins is outlined, emphasizing the current understanding of the structure and physiological function of these molecules in the colorectum. The use of new methods for preparation and separation has led to improvements in the analysis of mucins; these are detailed, as are their difficulties and pitfalls. Results obtained with these methods are correlated with long-established histochemical techniques and the use of chemical, lectin, and antibody reagents for general and specific detection of mucins in all procedures is described. Improvements in the detection and analysis of mucins in biopsy-size tissue samples and in larger numbers of individual clinical cases have now permitted a much wider approach to the pathological evaluation of mucin biology and progress with these techniques is outlined. The significance of the discovery of a family of mucin genes is presented and new concepts of mucin structure resulting from these studies are described. Bacterial degradation of the mucus layer at the surface of the colorectal mucosa is considered in line with the homeostatic relationship with mucosal mucin synthesis. Finally, the implications of abnormal mucins in colorectal disease are considered in the light of recent methodological advances.

Biosynthesis of human colonic mucin: Muc2 is the prominent secretory mucin

BACKGROUND/AIMS

Human colonic epithelium produces large amounts of mucin. The aim of this study was to examine mucin biosynthesis in the human colon.

METHODS

Human colonic mucin was isolated using CsCl density gradients, and polyclonal antiserum was raised. Biosynthesis of colonic mucins was studied by labeling colonic explants with 35S-labeled amino acids or [35S]sulfate and subsequent immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

The polyclonal antiserum specifically recognized colonic mucin, primarily reacting with peptide epitopes. Biosynthetic pulse/chase experiments showed a 35S-amino acid-labeled mucin precursor of about 600 kilodaltons, which was converted into a mature, glycosylated, and sulfated mucin and subsequently secreted into the medium. This mature mucin comigrated with isolated colonic mucin with an apparent molecular weight of 550 kilodaltons on SDS-PAGE, whereas gel filtration indicated that the molecular weight is actually much larger. Independent immunoprecipitation with an anti-Muc2 antiserum showed cross-reactivity with the 600-kilodalton precursor.

CONCLUSIONS

These results show the biosynthesis of a secretory colonic mucin for the first time. This mucin is synthesized as a precursor protein of approximately 600 kilodaltons, which, after glycosylation, is secreted as a glycoprotein with an apparent molecular weight of 550 kilodaltons on SDS-PAGE. It is very likely that this mucin is Muc2.

Colorectal mucin histochemistry in health and disease: a critical review

Neoplastic, inflammatory and regenerative processes affecting colorectal mucosa are associated with alterations in structure of epithelial mucin. This review collates mucin-, lectin-, and immuno-histochemical observations on colorectal mucins and introduces recent molecular genetic insights into the structure of the protein backbone of mucins. The numerous structural modifications uncovered by the various technical approaches have been reduced to a few manageable principles that are of relevance to both researcher and diagnostic pathologist. Particular attention is drawn to the need to appreciate the limited specificities of probes, the confounding influences of anatomical site and genetic factors (necessitating the use of appropriate positive and negative control tissues) and the precise location of secretory material. In the past, insufficient attention has been given to the effects of altered differentiation including metaplasia and differing lineage expression in epithelial disorders of growth. It is likely that certain changes loosely ascribed to goblet cell mucin, such as neo-expression of blood group antigens and anomalous expression of core carbohydrate structures, do not occur at all. Critical examination of available data point to only two consistent and unequivocal changes affecting goblet cell mucin in pathological processes: loss of O-acetyl substituents at sialic acid C4 and C7,8,9 and increased sialylation. Furthermore, there are no neoplasia-specific alterations in mucins documented to date. All neoplasia-associated changes have been described in non-neoplastic lesions also.

Trefoil peptides promote epithelial migration through a transforming growth factor beta-independent pathway

The trefoil peptides, a recently recognized family of protease-resistant peptides, expressed in a regional specific pattern throughout the normal gastrointestinal tract. Although these peptides have been hypothesized to act as growth factors, their functional properties are largely unknown. Addition of recombinant trefoil peptides human spasmolytic polypeptide (HSP), rat and human intestinal trefoil factor (RITF and HITF) to subconfluent nontransformed rat intestinal epithelial cell lines (IEC-6 and IEC-17), human colon cancer-derived cell lines (HT-29 and CaCO2) or nontransformed fibroblasts (NRK and BHK) had no significant effect on proliferation. However addition of the trefoil peptides to wounded monolayers of confluent IEC-6 cells in an in vitro model of epithelial restitution resulted in a 3-6-fold increase in the rate of epithelial migration into the wound. Stimulation of restitution by the trefoil peptide HSP was enhanced in a cooperative fashion by the addition of mucin glycoproteins purified from the colon or small intestine of either rat or man, achieving up to a 15-fold enhancement in restitution. No synergistic effect was observed by the addition of nonmucin glycoproteins. In contrast to cytokine stimulation of intestinal epithelial cell restitution which is mediated through enhanced TGF beta bioactivity, trefoil peptide, and trefoil peptide-mucin glycoprotein stimulation of restitution was not associated with alteration in concentrations of bioactive TGF-beta and was not affected by the presence of immunoneutralizing anti-TGF beta antiserum. Collectively, these findings suggest that the trefoil peptides which are secreted onto the lumenal surface of the gastrointestinal tract may act in conjunction with the mucin glycoprotein products of goblet cells to promote reestablishment of mucosal integrity after injury through mechanisms distinct from those which may act at the basolateral pole of the epithelium.

Thickness of adherent mucus gel on colonic mucosa in humans and its relevance to colitis

The thickness of adherent mucus gel on the surface of colonic mucosa was measured in surgically resected specimens from 46 'control' patients most of whom had carcinoma of the colon; 12 were from right colon, 17 left colon, and 21 from rectum. In addition specimens were examined from 17 patients with ulcerative colitis and 15 patients with Crohn's disease. In controls a continuous layer of mucus was readily seen on specially prepared sections viewed by phase contrast illumination. Mean values for right and left colon and rectum were 107 (48), 134 (68), and 155 (54) microns respectively with a significant difference between right colon and rectum (p = 0.015). Values in ulcerative colitis showed greater variation and in those areas with acute inflammation mucosa was denuded of the mucus layer. In contrast, values for Crohn's disease were normal or greater than normal in thickness--right colon 190 (83) microns compared with 107 48 microns, p = 0.0093. A series of validation experiments are described for the method used to measure mucus thickness. The possible role of mucus in the pathogenesis of inflammatory bowel disease is discussed.

Biosynthesis of two distinct types of mucin in HM3 human colon cancer cells

Mucins, high-M(r) glycoproteins with a large amount of O-glycosidically linked carbohydrate, protect the colonic epithelial surface and are altered in ulcerative colitis and colon cancer. At least two mucin genes, MUC2 and MUC3, are expressed at high levels in the human intestine. As an experimental model for studying the biosynthesis of human intestinal mucins, we used HM3 colon cancer cells. When mature mucins labelled with [3H]glucosamine or [3H]threonine were analysed by gel filtration, it was found that secreted mucins (M(r) > 10(8) were larger than soluble cellular mucins (M(r) approx. 5 x 10(6)). Only secreted mucin was sensitive to reduction. Both MUC2 and MUC3 proteins, identified by labelling with [3H]threonine or [35S]cysteine and immunoprecipitation with antibodies to synthetic mucin peptides, were already of large size (M(r) > 180,000) by the earliest labelling time (5 min). The MUC3 precursor was completely degraded by trypsin, but the MUC2 precursor had a trypsin-resistant fragment of M(r) approx. 240,000 containing threonine and cysteine. The trypsin-resistant MUC2 fragment contained N-linked carbohydrate, as indicated by a decrease in size as a result of peptidyl N-glycosidase digestion or tunicamycin treatment of HM3 cells. These results show that HM3 colon cancer cells produce at least two distinct human intestinal mucins. They also indicate that the mechanisms of biosynthesis of intestinal mucins differ from those of other mucin-like glycoproteins that have been studied.

Glycosylation and sulphation of colonic mucus glycoproteins in patients with ulcerative colitis and in healthy subjects

Studies have been made of mucus glycoprotein biosynthesis in different regions of the lower gastrointestinal tract in normal patients and those with ulcerative colitis (UC), active or inactive, by means of 3H-glucosamine (3H-GlcNH2)--35S-sulphate double labelling of epithelial biopsy specimens under culture conditions. The time based rate of 3H-GlcNH2 labelling of mucus in rectal tissue was similar to that in active or inactive UC whereas the rate of 35SO4(2) labelling was significantly increased in active disease. The 3H specific activities measuring the amount of isotopic incorporation into surface and tissue mucus glycoproteins were increased in patients with active UC compared with normal or inactive subjects. The 35S specific activities did not differ significantly between patients with active UC and those in remission. In the rectum, glycosylation of mucus glycoproteins decreases with the increasing age of the patient. Regional differences in 3H-labelling of mucus components are reported for ascending colon, transverse colon, sigmoid colon, and rectum. Sulphation (35S-labelling) was higher in all parts of the colon in left sided UC. Results point to accelerated glycosylation of core proteins in the active phase of UC.

Intestinal epithelial cells contribute to the enhanced generation of platelet activating factor in ulcerative colitis

Generation of platelet activating factor by intestinal mucosal epithelial cells and lamina propria mononuclear cells was evaluated to elucidate the possible role of this mediator in the pathogenesis of inflammatory bowel disease. Epithelial and lamina propria mononuclear cells were isolated from surgical specimens from control, Crohn's disease, and ulcerative colitis patients. Platelet activating factor was extracted from highly purified cell preparations with 80% ethanol after stimulation with and without 0.2 uM calcium ionophore A23187 and was measured by platelet aggregation assay. Both cell types generated platelet activating factor activity and this was generally comparable for epithelial and lamina propria cells. Basal and stimulated platelet activating factor activity of epithelial and lamina propria cells from ulcerative colitis but not Crohn's disease patients was appreciably higher than that of control. Stimulation with calcium ionophore increased appreciably platelet activating factor activity in lamina propria cells from all groups. In contrast, only epithelial cells from ulcerative colitis showed an appreciable increase after calcium ionophore induction. These results suggest that epithelial cells are important contributors to intestinal platelet activating factor generation under normal and inflammatory conditions and that epithelial cells actively play a part in the pathogenesis of ulcerative colitis.

The roles of enteric bacterial sialidase, sialate O-acetyl esterase and glycosulfatase in the degradation of human colonic mucin

Sialidase activity in normal faecal extracts showed a preference for mucin-related glycoprotein and oligosaccharide substrates, but the presence of two or more O-acetyl esters at positions C7-C9 on the sialic acids retarded the rate of hydrolysis. A specific sialate O-acetyl esterase was detected with a lower total activity relative to sialidase with mucin substrates and having a pH optimum of 7.8 and a KM of approximately 1 mM sialate O-acetyl ester. A specific glycosulfatase activity was found in faecal extracts using the substrate lactit-[3H]ol 6-O-sulfate with a pH optimum of pH 5.0 and a KM of approximately 1 mM. Faecal extracts from ulcerative colitis (UC) patients had higher sialate O-acetyl esterase and glycosulfatase activity, while mucin sialidase activity was unchanged. Metabolically labelled mucin isolated from UC patients contained less sulfate and had lower sialic acid O-acetylation compared with normal mucin. Colonic mucin was degraded more efficiently by faecal extracts from UC patients compared with normal extracts. The UC mucin was degraded more rapidly than the normal mucin by faecal enzyme extracts from both normal and UC subjects.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Experimental colitis in animal models

Colitis may be induced in animals by oral administration of sulfated polysaccharides (carrageenan, amylopectin sulfate, dextran sulfate), chemical irritation by rectal instillation of diluted acetic acid, delayed hypersensitivity reaction after sensitization to DNCB or after one single administration of TNBS, and Arthus reaction induced by intravenous injection of immune complexes after chemical irritation of the colon, and by chemoattractant peptides such as FMLP. It appears that all models of colon inflammation in the rat, mouse, or rabbit produce increased amounts of eicosanoids similar to that found in human colitis. Thus, animal studies provide useful information on the origin, regulation, and function of inflammatory mediators. However, with the possible exception of the cotton-top tamarin, no animal model of induced or spontaneous inflammation of the colon is analogous to human ulcerative colitis in etiology, course of disease activity, or histology (114). The observation that two different immune-mediated models gave similar results suggests that the colitis is not a specific response to delayed-type hypersensitivity or immune-complex-mediated reactions but rather an unspecific, stereotype response (125). The original disturbance may not determine the nature of the lesions ultimately produced but may instead serve as an initiator of a final common immunologic pathway.

Biochemical characterization of rat colonic mucins secreted in response to Entamoeba histolytica

Invasion of the colonic mucosa by Entamoeba histolytica trophozoites is preceded by colonic mucus depletion. The aim of our studies was to determine whether E. histolytica caused a differential secretion of mucin species in a rat colonic loop model. Mucus secretion in response to amoebae was followed by release of acid-precipitable 3H-glucosamine metabolically labelled glycoproteins and in vitro labelling of glycoprotein secretion with NaB3H4. The secretory response consisted of high-Mr goblet cell mucins and an increase in the secretion of low-Mr nonmucin glycoproteins as determined by Sepharose 4B column chromatography. High-Mr mucins subfractionated by Cellex-E (ECTEOLA) ion-exchange chromatography demonstrated a minor neutral and a major acidic mucin (greater than 98%) species. Marked differences between the neutral and acidic mucin species were indicated by immunogenicity and amino acid compositions. Thin-section histochemistry of rat colons confirmed secretion of neutral and acidic mucins in response to E. histolytica and demonstrated secretory activity from goblet cells from both the crypts and interglandular epithelium. E. histolytica mucus secretagogue activity was generalized and may function to deplete the host's protective mucus layer, facilitating invasion by the parasites.

The ion exchange properties of human post-mortem caecal and colonic mucus: the effect of sodium butyrate

This study examined Na+/H+ ion exchange of caecal and colonic mucus. Two distinct Na+/H+ ion exchange populations of caecal mucus were identified, one group being a cation exchanger and the other an anion exchanger, suggesting that caecal mucus has ampholyte properties responsive to changing physical and chemical properties of luminal contents. Mucus from the colon was consistently an anionic exchanger--this may aid water and electrolyte absorption in the colon. When mucus was incubated with sodium butyrate, the Na+/H+ ion exchange properties of the mucus were decreased.

Inflammatory mediators in chronic inflammatory bowel diseases

Crohn's disease and ulcerative colitis are chronic inflammatory bowel diseases (IBD) of unknown etiology. They are characterized by an activation of intestinal mononuclear cells. Cytokines play a crucial role in the regulation of the functions of these cells. An increased synthesis of the cytokines interleukin-1 (IL-1), interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF alpha), which are primarily synthesized by activated monocytes/macrophages has been described in patients with IBD. The synthesis of interleukin-2 (IL-2) and of interferon gamma (IFN gamma), which are produced by lymphocytes, on the other hand, has been found to be decreased. The published data are, however, not quite consistent. In patients with IBD there is not only a stimulation of the local cytokine production in the gut. The blood levels and the synthesis of the cytokines IL-1, IL-6 and TNF alpha by peripheral blood mononuclear cells are also increased, in particular in patients with Crohn's disease. Drugs, which are commonly used for the treatment of IBD impair the synthesis of these cytokines in monocytes/macrophages.

Ion exchange chromatography of purified colonic mucus glycoproteins in inflammatory bowel disease: absence of a selective subclass defect

Previous reports of a selective mucin subclass defect in ulcerative colitis have been reassessed using high performance chromatography (Superose 6 and Mono Q) for mucin purification and fractionation coupled with analysis of the fractions obtained using a combination of enzyme linked lectin and mucin antibody assays. Mucin samples purified from snap frozen rectal biopsy specimens obtained from patients with ulcerative colitis (n = 12), Crohn's disease (n = 5), and non-inflammatory bowel disease control subjects (n = 9) were subject to ion exchange chromatography using a continuous 0-0.35 mol/l NaCl salt gradient with a final 2.5 mol/l NaCl step. In all samples the major proportion (mean (SD) 86.7 (8.9)%) of the mucin detectable by wheat germ agglutinin binding eluted between 0.15 and 0.35 mol/l NaCl with no significant difference in elution profile between ulcerative colitis and control subjects. Significant elution of glycoprotein at less than 0.15 mol/l NaCl did occur, however, when a lower molecular weight mucin containing fraction which contained concanavalin A positive (glucose or mannose containing) material was analysed similarly. Similar ion exchange profiles were obtained when (3H)N-acetylglucosamine labelled mucins were studied after tissue culture of rectal biopsy specimens. No significant alteration in the ion exchange profile of purified mucins in ulcerative colitis has been shown in these studies. It is possible that the previously reported relative depletion of mucin subclass IV (eluting with 0.20 mol/l NaCl) may simply have reflected mucin depletion.

Intracellular variation of rat intestinal mucin granules localized by monoclonal antibodies

Monoclonal antibodies produced against rat small intestinal mucins were utilized to study variability of stored mucin granules within rat ileal goblet cells. Eleven antibody-secreting hybridoma cultures were produced; six of these uniformly labeled stored mucin granules in virtually all goblet cells, suggesting that some antigenic features are common to all granules. The other five stained goblet cells in the rat small intestinal epithelium nonuniformly. R803, R805, and R807 localized within almost all goblet cells but revealed differential labeling of centrally and peripherally located mucin granules. R804 uniformly labeled the mucin granules of most villous goblet cells; some of the crypt goblet cells were uniformly labeled, but the majority were only partially labeled, resulting in a mottled staining pattern. R808 stained only a small portion of crypt goblet cells; there is, however, an increase in both number of goblet cells labeled and in uniformity of staining of the stored granule mass from the base of the crypt to the surface, resulting in uniform labeling of virtually all goblet cells at the villus tip. This study demonstrates for the first time that rat small intestinal mucin granules are immunologically heterogeneous and nonuniformly distributed within the epithelium. Additionally, staining patterns within the stored granule mass suggest that structurally distinct subpopulations of mucin granules may exist within a single goblet cell.

Detection of distinct species in purified human respiratory mucin using monoclonal antibodies

The purpose of this investigation was to demonstrate the presence of different species (subpopulations) in the purified human tracheobronchial mucin (HTM-1). Mucin was highly purified from sputum specimens collected from a cystic fibrosis (CF) patient using a protocol involving sequential chromatography on Bio-Gel A-5m and hydroxylapatite columns. SDS-composite gel electrophoresis followed by periodic acid-Schiff's reagent staining was unable to detect mucin species. However, using enzyme-linked immunoelectrotransfer blot (EITB) method and polyclonal antibodies raised against HTM-1, at least four different migrating mucin species were detected. Further immunological characterization of these mucin species was carried out using a library of 16 monoclonal antibodies (MAbs) developed against the purified mucin. Nine MAbs belonged to the IgM class, two MAbs were IgG1, one IgG2a and remaining four were of the IgG3 subclass. Periodate oxidation of the mucin antigen was used to establish the nature of the mucin epitopes recognized by the MAbs. 11 MAbs recognized carbohydrate epitopes in the mucin molecule that were sensitive to periodate, while five MAbs reacted with periodate resistant carbohydrate epitopes or the protein portion of the mucin molecule. Enzyme-linked immunoelectrotransfer blot analysis of the MAbs against HTM-1 showed the presence of at least three distinct mucin species. Chromatography of the mucin on immunoaffinity columns (MAbs H(13.3), M(33.3) and CCK 061 conjugated to CNBr-activated Sepharose 4B), followed by ELISA and EITB analyses, established the mucin species recognized by the antibodies. These experiments further indicated that both unique and shared epitopes were present in the mucin species. These monoclonal antibodies may provide a promising approach to differentiate the secretory products of the tracheobronchial tree.

Characterization and heterogeneity of monoclonal antibodies directed to intestinal mucin derived from Crohn's disease small bowel

A panel of 12 monoclonal antibodies were produced by immunization of Balb/c mice with small bowel epithelial cells obtained from a patient with active well-documented Crohn's disease. The clones were derived by screening with immunofluorescence microscopy; those with staining patterns suggestive of mucin directed epitopes were chosen for study. Several distinct patterns of staining reactivity were noted, including reagents with homogeneous, luminal, heterogeneous and peripheral goblet cell activity. In addition, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis revealed reactivity to high molecular weight mucin. The reactive antigen was resistant to proteinase digestion. No endoneuraminidase activity was detected; however, one neuraminidase sensitive sialic acid epitope was demonstrated. Confirmation of glycoprotein epitopes was accomplished by testing purified mucins from several areas of the gastrointestinal tract by ELISA. Finally, individual small bowel goblet cell heterogeneity was demonstrated by immunofluorescence, Western blotting, and antibody affinity chromatography. These data demonstrate both by morphology and specific binding of antibody affinity chromatography a significant degree of small bowel goblet cell mucin heterogeneity.

Effect of reserpine on the histochemical and biochemical properties of rat intestinal mucin

Biochemical and histochemical parameters of intestinal mucins were examined in control and reserpine-treated rats. An assay for intestinal mucin sulfotransferase was developed and the activity shown to increase 3.4 times over control levels in rats given intraperitonal reserpine (0.5 mg/kg body wt) daily for 7 days. Histochemical staining of intestinal sections revealed an increase in sulfomucins in goblet cells of reserpine-treated rats. The effects were prominent as early as 1 day following injection, particularly in the distal third of the small intestine, and during the next 6 days these changes spread progressively to the middle and proximal thirds. After 3 days of treatment mucins were purified from each intestinal segment and compared to control mucins with respect to composition and [35S]NaSO4 incorporation. Although individual amino acid and carbohydrate molar ratios were unchanged, the total carbohydrate and sulfate content of mucins in treated animals was elevated (two to three times above control) in the middle and distal thirds of the intestine. In vivo [35S]SO4 incorporation into these mucins was also proportionaltely elevated, and was targetted to O-linked oligosaccharide side chains. These findings are consistent with an action of reserpine causing an increased production of mucin which is enriched in glycoprotein components bearing sulfated oligosaccharide chains. The relevance of these findings to the production of hypersulfated and hyperglycosylated mucins in cystic fibrosis is discussed.

Mucin and nonmucin secretagogue activity of Entamoeba histolytica and cholera toxin in rat colon

Depletion of colonic mucus occurs before invasion of the colonic mucosa by Entamoeba histolytica trophozoites. It is hypothesized that E. histolytica releases a mucus secretagogue; this was studied in a rat colonic loop model. In colonic loops exposed to live amebae, mucus secretion was quantitated by release of acid-precipitable [3H]glucosamine-labeled luminal glycoprotein and by specific immunoassay. Mucus secretion increased in dose-dependent fashion in response to greater than or equal to 1 X 10(5) trophozoites; cholera toxin (20 micrograms per loop), a known mucus secretagogue, elicited a similar response. Thin-section histological analysis of amebae and cholera toxin-exposed loops showed increased mucus release and streaming from mucosal goblet cells with cellular cavitation compared with control loops. Sepharose-4B chromatography of amebae and cholera toxin-stimulated glycoproteins demonstrated secretion of mucins and an 80%-90% increase in low-molecular-weight proteins. E. histolytica trophozoites and cholera toxin enhanced the secretion of preformed and newly synthesized mucin glycoproteins and stimulated colonic glycoprotein synthesis. The level of mucus secretion elicited by axenic E. histolytica strains correlated with their virulence in vivo and in vitro. The amebic secretagogue was released into the culture medium and was heat stable. Mucus secretagogue activity of E. histolytica may contribute to depletion or alteration of the protective mucus blanket, facilitating pathogenesis of invasive amebiasis.

Colonic glycoproteins in monozygotic twins with inflammatory bowel disease

Colonic glycoprotein composition was evaluated in monozygotic twins with inflammatory bowel disease using ion-exchange chromatography. Fifty-three individuals, 12 pairs and 1 single twin with ulcerative colitis and 14 pairs with Crohn's disease, were evaluated. Seven twin pairs were concordant for the presence of ulcerative colitis or Crohn's disease, whereas twin siblings of 10 ulcerative colitis probands and 9 Crohn's disease probands were not known to have inflammatory bowel disease. Content of one chromatographically defined component of colonic mucin, designated HCM species IV, was reduced in both patients with ulcerative colitis (1040 +/- 300 cpm/10,000 cpm total HCM) and their apparently healthy twins (1340 +/- 540 cpm/10,000 cpm total HCM) compared with control subjects (4030 +/- 1,000 cpm/10,000 cpm total HCM). Composition of mucin in Crohn's disease patients and their nonaffected twins was not significantly different than in controls. These observations suggest that altered profiles of mucin glycoprotein may be present before the onset of ulcerative colitis and may be genetically defined. Conversely, it appears that alterations in glycoproteins only are not sufficient to initiate mucosal inflammation.

Characterization of a sialic-acid-rich mucus glycoprotein secreted by a premalignant human colorectal adenoma cell line

The human colonic cell line PC/AA, derived from an adenoma, retains in vitro colonic cell differentiation, notably the production of mucus glycoproteins. The PC/AA adenoma cells produce an extracellular gel layer in culture. The PC/AA gel could be isolated by extraction of the cell cultures with guanidine hydrochloride. The extracted material was purified by gel filtration and caesium chloride density-gradient centrifugation and showed properties typical of mucus glycoproteins, namely, a carbohydrate content above 60% of dry weight rich in N-acetylgalactosamine and sialic acid and low in mannose; an amino acid composition with high serine threonine and proline content; a molecular weight above 1,000 kDa on Sepharose CL 4B chromatography and on SDS-polyacrylamide gel electrophoresis under reducing conditions (greater than 200 kDa); a buoyant density of approximately 1.48 g/ml and the release of oligosaccharides by the alkaline beta-elimination reaction. Comparison of the gel mucus glycoprotein purified from premalignant PC/AA cells with normal human colon mucin showed that it has a higher sialic acid content. This suggests that higher sialic acid levels may precede the development of malignancy.

High-performance size-exclusion chromatography of porcine colonic mucins. Comparison of Bio-Gel TSK 40XL and Sepharose 4B columns

A high-performance size-exclusion chromatography (HPSEC) method was developed for the separation of porcine colonic mucins using a Bio-Gel TSK 40XL HPSEC column (300 mm x 75 mm). In addition, porcine gastric and bovine submaxillary mucin preparations were used to describe more fully the separation characteristics of the HPSEC column. For comparison, the same preparations were also separated using a Sepharose 4B column (100 cm x 2.6 cm). The colonic and gastric mucins eluted in the void volume (V0) of both columns. Bovine submaxillary mucin was in the elution volume (Ve) of both columns. Analytical HPSEC of fractions (V0 and Ve) of the various preparations obtained by Sepharose 4B chromatography exhibited retention times identical to those for fractions obtained by HPSEC. After separation by both methods, purified mucins were obtained by CsCl2 density gradient ultracentrifugation; analytical HPSEC profiles, protein contents, and monosaccharide compositions of both gastric and colonic mucins from either column were similar. The HPSEC method, however, is ideally suited to separate microgram to milligram quantities of colonic mucin preparations quickly: 2 to 4 h, compared with 24 to 30 h for the Sepharose 4B method.

Binding of proteolytically-degraded human colonic mucin glycoproteins to the Gal/GalNAc adherence lectin of Entamoeba histolytica

Rat and human colonic mucin glycoproteins bind to the Gal/GalNAc adherence lectin on the surface of Entamoeba histolytica in vitro, thus inhibiting the organism from adhering to and lysing the target cells. Human colonic mucin glycoproteins were isolated by Sepharose 4B gel filtration chromatography, they were proteolytically degraded with trypsin, pronase, and papain, and the glycoprotein fractions were reisolated by Sephacryl S-200 gel filtration chromatography. Binding of the mucin glycoprotein fractions to amoebae was quantitated by the inhibition of adherence of Chinese hamster ovary cells to the surface of the amoebae. Trypsin and papain digests caused 40 and 20% reductions, respectively, in the excluded fractions (void volume) that contained all the carbohydrates; pronase digests resulted in extensive degradation of the mucin glycoprotein with the carbohydrate fractions eluting over 40% of the gel bed volume. 3H-labelled mucin glycoprotein and sodium dodecylsulfate-polyacrylamide gel electrophoresis confirmed the presence of the high molecular weight carbohydrate-rich glycoproteins with no subunits in the excluded fractions and the absence of sugars in the included peptides. Only the high molecular weight carbohydrate-containing fractions bind amoebae and inhibit amoebic adherence to Chinese hamster ovary cells. The trypsin digested mucins in the excluded volume were more efficient than the native undigested mucins in binding amoebae. The carbohydrate-containing fractions of the pronase digests were the least effective in binding amoebae and inhibiting adherence of Chinese hamster ovary cells. This suggests that proteolytically-degraded colonic mucins that are glycosylated, as well as the undegraded native mucin glycoproteins of the gut, may play a protective role in binding to amoebae, thus preventing contact of amoebae with mucosal epithelial cells and potential invasion.

The carbohydrate composition of mucin in colonic cancer

Mucins synthesized in colonic cancer are known to be different from those in the normal colon; however, the biochemical differences between these mucins have not been defined. We have purified mucins from samples of nonneoplastic (normal) human colon and colon cancer and found that the carbohydrate content of the cancer-associated mucins is 48% of that in the normal colon, including significant reductions in galactose, N-acetylglucosamine, N-acetylgalactosamine, and fucose. By subjecting the mucins to alkaline degradation, we determined that there are 19% fewer oligosaccharide chains per milligram of cancer-associated colonic mucin than there are in mucins from normal colons. We also found a reduction in mean oligosaccharide chain length in cancer-associated mucin (5.83 carbohydrate residues per chain) compared with those derived from normal colons (10.2 residues). Total and individual amino acid contents were greater in cancer-associated mucins, with the exception of three amino acids (threonine, serine, and proline), two of which represent the O-linked glycosylation sites for glycoproteins. Thus, mucins are aberrantly glycosylated in colon cancer, both in terms of the number and mean chain length of the oligosaccharide moiety. Because of their relative abundance in colonic tissue, mucins appear to be useful molecular species in the study of the derangements in protein glycosylation that occur during neoplasia.

Chemotactic peptide-induced acute colitis in rabbits

Bacterial chemotactic peptides from the intestinal lumen could potentially induce inflammation if they reached the mucosa. We tested several peptides chemotactic for different inflammatory cells, as well as a nonchemotactic peptide, bradykinin, for their ability to induce colitis in vivo in rabbits. These peptides were also assessed for their ability to stimulate release of the eicosanoids leukotrienes B4 and C4 and prostaglandin E2 from normal rabbit colons perfused ex vivo. Intracolonic administration of n-formyl-methionyl-leucyl-phenylalanine (chemotactic for neutrophils); its methyl ester (chemotactic for monocytes), and alanyl-glycyl-seryl-glutamic acid (chemotactic for eosinophils) all produced colitis (assessed grossly and histologically) within 4 days. Bradykinin did not induce colitis although it did release prostaglandin E2. n-Formyl-methionyl-leucyl-phenylalanine methyl ester induced the greatest degree of colitis in vivo and released prostaglandin E2 and leukotrienes ex vivo. n-Formyl-methionyl-leucyl-phenylalanine and alanyl-glycyl-seryl-glutamic acid induced comparable degrees of inflammation, but alanyl-glycyl-seryl-glutamic acid produced no eicosanoid release while n-formyl-methionyl-leucyl-phenylalanine released both prostaglandin E2 and leukotriene B4 and leukotriene C4 products from normal ex vivo perfused colons. Thus alanyl-glycyl-seryl-glutamic acid produces colitis independent of proinflammatory eicosanoids while eicosanoid release could contribute to colitis produced by n-formyl-methionyl-leucyl-phenylalanine methyl ester. This experimental model of colitis may reflect one possible etiology of inflammatory bowel disease in humans, when bacterial chemotactic peptides breach mucosal defenses in susceptible individuals.

Deglycosylation of neutral and acidic human colonic mucin

Human colonic mucin has been isolated from normal colonic mucosa by a phenol-water extraction procedure and purified by Sepharose 2B column chromatography. The mucin was further purified by cesium bromide density gradient centrifugation. Sodium dodecyl sulfate-polyacrylamide gel (5%) electrophoresis of this material showed high-molecular-weight mucin component(s) at the top of the gel. Chemical analyses of this preparation indicated a typical mucin profile of amino acids and carbohydrates. Ion-exchange chromatography resulted in the separation of two major fractions, one being more acidic than the other. Chemical deglycosylation of the purified preparation at 20 degrees C for 3 1/2 showed loss of sialic acid, fucose, galactose, and N-acetylglucosamine, whereas traces of N-acetylgalactosamine were still detected. High-pressure liquid chromatography of the deglycosylated material resulted in the purification of a major peptide, P1, with high levels of threonine, serine, and proline, resembling, in most respects, the profile of native mucin. The molecular weight of the peptide was determined to be approximately 97 kDa and serine was the single NH2 terminus.

Analysis of cancer-associated colonic mucin by ion-exchange chromatography: evidence for a mucin species of lower molecular charge and weight in cancer

Cancer-associated mucins in the colon are antigenically distinct and glycosylated differently from their normal counterparts. Mucin-rich glycoconjugate preparations were made from nine non-neoplastic colons, seven colon cancers, and two different xenografts from mucin-producing human colon cancer cell lines, and radiolabeled with 3H. The preparation was applied to a DEAE-cellulose ion-exchange column, and eluted with a discontinuous ascending NaCl gradient resulting in seven discrete fractions or 'species'. Over half of the 3H-labeled glycoconjugates from specimens of non-neoplastic colonic epithelium eluted in fraction V (eluted with 0.25 NaCl). Significantly less of the 3H-labeled glycoconjugates from specimens of colon cancer eluted in fraction V (34%, P less than 0.0005), and there were significant increases in glycoconjugates eluted in fractions IV (P less than 0.008), III (P less than 0.0005), and II (P less than 0.028). Additional samples were prepared without the radiolabeling procedures, chromatographed on a DEAE-cellulose ion-exchange column, and analyzed for monosaccharide content. Each of the fractions contained the monosaccharides expected in mucin-type glycoproteins, but only sialic acid was differentially expressed in the seven fractions or 'species', occurring principally in the more charged species. However, differences in sialic acid content were not sufficient to explain the differences in retention on the ion-exchange column, nor were differences in O-acetylation of the mucins. Mucin-type glycoconjugates from colon cancers are relatively less charged than those from the normal colon, and elute at lower ionic strengths. Of interest, cancer-associated mucins appear to be of lower molecular weight than their normal counterparts. Additional studies of oligosaccharide and apomucin structure will be required to explain the molecular basis of these differences in charge.

Ulcerative colitis: specific antibodies against a colonic epithelial Mr 40,000 protein

A colon tissue-bound disease specific IgG (CCA-IgG) antibody can be eluted from the colonic tissue of patients with ulcerative colitis (UC). CCA-IgG recognizes an Mr 40,000 protein present in both normal and diseased colon. Using an anti-Mr 40,000 murine monoclonal antibody this protein has been localized exclusively in colonic epithelial cells mainly along the baso-lateral domains of plasma membrane. Non-colonic epithelial tissues from 12 different organs including small intestine did not react with the anti-Mr 40,000 monoclonal antibody. The Mr 40,000 protein is present in the RPMI-4788 colon cancer cells but not in HeLa. The antibody dependent cell-mediated cytolysis by UC sera against RPMI-4788 cells was inhibited by anti-Mr 40,000 polyclonal antibody. These findings suggest that CCA-IgG and the Mr 40,000 colonic epithelial protein are involved in an autoimmune reaction and may be important in the pathogenesis of UC.

The colonic goblet cell and glycoprotein heterogeneity

Mucin glycoproteins are an important 'nonspecific' host defense at the interface of mucosal surface and lumen. However insights into structural and functional features of these enormously complex and heterogeneous glycoproteins have been markedly limited. In recent studies, the presence of several distinct colonic mucin glycoproteins has been demonstrated and their oligosaccharide side chains extensively characterized through conventional structural analysis and utilization of monoclonal antibodies. Glycoprotein diversity has been found to arise from previously unrecognized functional heterogeneity of colonic goblet cells. Rates of biosynthesis and secretion of different HCM glycoproteins appear to vary. In addition, a selective reduction in HCM glycoprotein IV has been demonstrated in specific association with ulcerative colitis. Finally preliminary studies suggest that additional alterations in colonic glycoconjugates may be present in ulcerative colitis mucosa.

Sensitization to epithelial antigens in chronic mucosal inflammatory disease: immunochemical similarity of macromolecules in human colonic epithelium with murine intestinal epithelial cell-associated components (ECAC)

In order to explore whether human intestinal epithelium contains cell-associated components that are organ-specific and therefore potentially autoantigenic, macromolecules were isolated in aqueous-soluble form from histologically normal human colonic epithelial cells, partially purified under nondenaturing conditions, then characterized biochemically and immunologically. Preparative non-SDS-polyacrylamide gel electrophoresis followed by electro-elution into a Tris-glycine buffer separated five human colonic fractions (yield 86%), all of which possessed an acidic isoelectric point (4.0-4.8) and a modest carbohydrate content (0.9-15%), resembling fractions of corresponding Rf similarly prepared from murine colonic epithelial cells. Immunological characterization suggested that two of the gel-purified fractions (B1, B2) isolated from colonic epithelium contained organ-specific determinants: (i) reactivity of B1/B2-specific immunoglobulin was not diminished by prior absorption with proteins from other epithelial surfaces (tracheal mucosal components) nor from normal serum; (ii) epitopes on ECAC B1 and B2 fractions were shared across species lines, with reactivity for the cross-reactive determinant being as much as 20-fold that of control protein; and (iii) localization studies with specific antibody showed an organ- and cell-restricted immunofluorescence pattern on freshly fixed human and murine mucosal epithelial tissue, using B1-specific monoclonal antibody. Given the reported binding of inflammatory bowel disease serum immunoglobulin and lamina propria mononuclear cells for murine ECAC determinants, our studies suggest these same antigens are present in human colonic epithelium, and are available as potential binding sites for antibody or lymphocytes participating in an autoaggressive immune response.

Altered lectin binding by colonic epithelial glycoconjugates in ulcerative colitis and Crohn's disease

Evidence is accumulating that colonic mucin glycoconjugates are altered in ulcerative colitis. In order to investigate this further, the lectin-binding properties of rectal glycoconjugates have been studied in ulcerative colitis, Crohn's disease, and controls using lectin-peroxidase histochemistry. Ten lectins were used including peanut agglutinin (PNA) which is known to bind to malignant and adenomatous but not normal colonic mucins. Eight of 21 ulcerative colitis rectal biopsies and 10 of 17 Crohn's disease rectal biopsies showed PNA positivity, particularly in the supranuclear region of surface epithelial cells. There was no correlation between PNA positivity and duration of disease or inflammation, and none of the biopsies showed evidence of dysplasia. This abnormality in epithelial cell glycoconjugates seems to be commonly present in nondysplastic mucosa and occurs in both ulcerative colitis and Crohn's disease. It may reflect a fundamental abnormality in mucus glycoprotein synthesis in inflammatory bowel disease.