Absorptive Enterocytes Research Articles

Inactivation of the transcription factor EIf3 in mice results in dysmorphogenesis and altered differentiation of Intestinal Epithelium

The mammalian small intestine is lined by a highly specialized epithelium that functions in the digestion and absorption of nutrients. The molecular mechanisms that direct intestinal epithelial cell morphogenesis and terminal differentiation are poorly understood. We have previously identified Elf3 (E74-like factor-3) as a member of the ETS transcription factor family strongly expressed in small intestinal epithelium. The aim of this study is to investigate the biological roles of Elf3 in vivo. Mice with a null mutation of Elf3 were generated through targeted gene disruption. Characterization of intestinal development was performed by histologic and immunohistochemical techniques. Targeted disruption of Elf3 resulted in fetal lethality of about 30% at around embryonic day 11.5. Seventy percent of the Elf3-deficent progeny were born and displayed severe alterations of tissue architecture in the small intestine, manifested by poor villus formation and abnormal morphogenesis and terminal differentiation of absorptive enterocytes and mucus-secreting goblet cells. Crypt cell proliferation, however, appeared intact in Elf3-deficient mice.Elf3-deficient enterocytes express markedly reduced levels of the transforming growth factor beta type II receptor (TGF-beta RII), an inducer of intestinal epithelial differentiation. Elf3 is an important regulator of morphogenesis and terminal differentiation of epithelial cell lineages in the small intestine.

Iron metabolism and requirements in early childhood: do we know enough?: a commentary by the ESPGHAN Committee on Nutrition.

*University of Lancashire, Lancashire, United Kingdom; †University of Milano, Milano, Italy; ‡University of Lund, Malmo, Sweden; §Hopital des Enfants Malades, Paris, France; Hopital Necker Enfants-Malades, Paris, France, ¶Umea University, Umea, Sweden; #University of Munich, Munich, Germany; **Free University of Amsterdam, Amsterdam, The Netherlands; ††Royal Veterinary and Agricultural University, Frederiksberg, Denmark; ‡‡CHUV University Hospital, Lausanne, Switzerland; §§University of Liege, Liege, Belgium; Medical University of Warsaw, Warsaw, Poland; and ¶¶University of Glasgow, Glasgow, United Kingdom

NHE3-dependent cytoplasmic alkalinization is triggered by Na(+)-glucose cotransport in intestinal epithelia.

Cytoplasmic pH (pH(i)) was evaluated during Na(+)-glucose cotransport in Caco-2 intestinal epithelial cell monolayers. The pH(i) increased by 0.069 +/- 0.002 within 150 s after initiation of Na(+)-glucose cotransport. This increase occurred in parallel with glucose uptake and required expression of the intestinal Na(+)-glucose cotransporter SGLT1. S-3226, a preferential inhibitor of Na(+)/H(+) exchanger (NHE) isoform 3 (NHE3), prevented cytoplasmic alkalinization after initiation of Na(+)-glucose cotransport with an ED(50) of 0.35 microM, consistent with inhibition of NHE3, but not NHE1 or NHE2. In contrast, HOE-694, a poor NHE3 inhibitor, failed to significantly inhibit pH(i) increases at <500 microM. Na(+)-glucose cotransport was also associated with activation of p38 mitogen-activated protein (MAP) kinase, and the p38 MAP kinase inhibitors PD-169316 and SB-202190 prevented pH(i) increases by 100 +/- 0.1 and 86 +/- 0.1%, respectively. Conversely, activation of p38 MAP kinase with anisomycin induced NHE3-dependent cytoplasmic alkalinization in the absence of Na(+)-glucose cotransport. These data show that NHE3-dependent cytoplasmic alkalinization occurs after initiation of SGLT1-mediated Na(+)-glucose cotransport and that the mechanism of this NHE3 activation requires p38 MAP kinase activity. This coordinated regulation of glucose (SGLT1) and Na(+) (NHE3) absorptive processes may represent a functional activation of absorptive enterocytes by luminal nutrients.

DMT1 gene expression and cadmium absorption in human absorptive enterocytes

Divalent metal transporter 1 (DMT1) is a transmembrane, proton-coupled metal ion transporter that is upregulated in the duodenum of iron-deficient rodents and in hereditary hemochromatosis patients, suggesting that it may constitute a key factor in the uptake of dietary iron. Functional expression studies in Xenopus oocytes have shown that DMT1 not only mediates transport of iron but also other divalent metal ions, including the toxic metal cadmium. In the present study, the correlation between the cadmium absorption process and gene expression of DMT1 was investigated in an experimental model of human absorptive enterocytes. Fully differentiated Caco-2 cells were grown in monolayers and treated with iron supplemented medium or control medium for 1, 3 or 7 days. At each time point, cadmium transport experiments across the Caco-2 cell monolayers were performed and gene expression of DMT1 measured. Iron treatment for 3 and 7 days resulted in a 50% reduction in the cadmium uptake and a 75% reduction in the transport of the metal across the basolateral membrane. No effects were observed at 24 h. Gene expression of DMT1 in the iron-treated Caco-2 cells was reduced by about 50% at 3 and 7 days and thus, correlated well with the uptake of cadmium. In summary, our results indicate that the uptake of cadmium into human absorptive enterocytes may be mediated by DMT1.

Role of M cells in intestinal barrier function.

M cells are known as specialized epithelial cells of the follicle-associated epithelium of the gastrointestinal tract. As M cells have a high capacity for transcytosis of a wide range of microorganisms and macromolecules, they are believed to act as an antigen sampling system. The primary physiological role of M cells seems to be the rapid uptake and presentation of particular antigens and microorganisms to the immune cells of the lymphoid follicle to induce an effective immune response. In contrast to absorptive enterocytes, M cells do not exert direct defense mechanisms to antigens and pathogens in the gut lumen. Therefore, they provide functional openings of the epithelial barrier. Although M cells represent a weak point of the epithelial barrier, even under noninflamed conditions, there seems to be a balance between antigen uptake and immunological response. The low number of M cells in the gastrointestinal tract and the direct contact to immune cells in the lamina propria usually prevent the occurrence of mucosal inflammation. During chronic intestinal inflammation we observe an increase of M cell number and apoptosis selectively in M cells. M cell damage seems to be responsible for the increase of the uptake of microorganisms that is observed during intestinal inflammation. Under inflammatory conditions in the intestine, the maintenance of the epithelial barrier is broken and M cells seem to play a major role during this process.

Translocation of Ribosomal Immunostimulant Through an In Vitro–Reconstituted Digestive Barrier Containing M‐Like Cells

Ribosomal preparations of pathogenic micro‐organisms of the upper respiratory tract can be delivered orally for the prevention of recurrent infectious episodes, because they induce mucosal and protective immune responses. The mechanism of mucosal barrier translocation is difficult to study in animal models, little is therefore known about this process. In order to circumvent these problems, we have examined the uptake of ribosomal preparations in three experimental systems that model human intestinal cells. We found that M‐like cells displayed a 8.7‐fold increase in the uptake of a ribosomal immunostimulant when compared to absorptive or crypt enterocyte‐like cells. The product was taken up, translocated, and delivered in the basolateral compartment by cultured M‐like cells. No translocation was observed across monolayers of T84 cells (model of crypt cells). Only minimal translocation occured through monolayers of Caco‐2 cells (model of absorptive enterocytes). This suggests that, in vivo, colyophilisat is delivered mainly through the M cells overlying lymphoid follicles (Peyer's patches) or nodules of the gut‐associated mucosal lymphoid tissue, which are the major inductor sites of mucosal responses. Use of the M‐like cell cultured model could be a key step for the development of even more efficient immunostimulators in animals and human.

Postabsorptive plasma citrulline concentration is a marker of absorptive enterocyte mass and intestinal failure in humans

Background & Aims: No blood marker assessing the functional absorptive bowel length has been identified. Plasma citrulline, a nonprotein amino acid produced by intestinal mucosa, is one candidate. We tested this hypothesis in adult patients with the short-bowel syndrome, whose condition can lead to intestinal failure. Methods: In 57 patients, after a minimal follow-up of 2 years subsequent to final digestive circuit modification, postabsorptive citrulline concentration was measured and parenteral nutrition dependence was used to define permanent (n = 37) and transient (n = 20) intestinal failure. Absorptive function, studied over a 3-day period, was evaluated by net digestive absorption for protein and fat (n = 51). Relations between quantitative values were assessed by linear regression analysis and cutoff citrulline threshold, for a diagnosis of intestinal failure by linear discriminant analysis. Cox model was used to compare citrulline threshold and anatomic variables of the short bowel as indicators of transient as opposed to permanent intestinal failure. Results: In patients with short-bowel syndrome, citrulline levels were lower than in controls (n = 51): 20 ± 13 vs. 40 ± 10 μmol/L (mean ± SD), respectively (P < 0.001). After multivariate analysis, citrullinemia was correlated to small bowel length (P < 0.0001, r = 0.86) and to net digestive absorption of fat, but to neither body mass index nor creatinine clearance. A 20-μmol/L threshold citrullinemia, (1) classified short bowel patients with permanent intestinal failure with high sensitivity (92%), specificity (90%), positive predictive value (95%), and negative value (86%); and (2) was a more reliable indicator (odds ratio, 20.0; 95% confidence interval, 1.9–206.1) than anatomic variables (odds ratio, 2.9; 95% confidence interval, 0.5–15.8) to separate transient as opposed to permanent intestinal failure. Conclusions: In patients with short-bowel syndrome, postabsorptive plasma citrulline concentration is a marker of functional absorptive bowel length and, past the 2-year adaptive period, a powerful independent indicator allowing distinction of transient from permanent intestinal failure.GASTROENTEROLOGY 2000;119:1496-1505

Functional and molecular responses of human intestinal Caco-2 cells to iron treatment

Divalent metal transporter 1 (DMT1), HFE, and stimulator of iron transport (SFT) are transmembrane proteins that have been implicated in the regulation of iron homeostasis. The objective of this study was to investigate whether absorption and transepithelial movement of iron correlated with gene expression of DMT1, HFE, and SFT in an experimental model of human absorptive enterocytes. Caco-2 cells were exposed to iron-supplemented media in either the presence or the absence of serum for 24, 72, and 168 h. At each time point, the uptake and transepithelial movement of iron were examined and gene expression of DMT1, HFE, and SFT was measured. Manganese and zinc absorption was also examined at 168 h. Iron treatment in the presence or absence of serum reduced the uptake and transepithelial movement of iron by approximately 50% after 72 and 168 h. No effect was observed at 24 h. The uptake and transepithelial movement of manganese were similar to those of iron at 168 h, whereas the effects on zinc were less pronounced. In the absence of serum, iron treatment was associated with a reduction of DMT1 expression by 50% at 72 and 168 h. HFE expression was dependent on serum, but iron treatment did not alter HFE expression. SFT expression was not affected by iron. Iron treatment decreased cellular uptake of iron, manganese, and zinc, suggesting that these metals may utilize the same apical transporter. The transepithelial movement of iron and manganese, but not of zinc, was reduced across iron-treated Caco-2 cells, suggesting that iron and manganese are regulated by the same mechanism at the basolateral membrane. The gene expression of DMT1, HFE, and SFT did not fully correlate with the functional responses of Caco-2 cells. This may have been a result of posttranscriptional regulation of these genes or regulation of other genes involved in the uptake and transepithelial movement of iron in Caco-2 cells.

Colorectal Polyps With Extensive Absorptive Enterocyte Differentiation

Colorectal Polyps With Extensive Absorptive Enterocyte Differentiation

Impaired stimulation of intestinal glucose absorption via hepatoenteral nerves in streptozotocin-diabetic rats.

In an ex situ organ perfusion system, that of the isolated nonrecirculating joint perfusion of rat small intestine and liver, insulin infused into the portal vein increased intestinal glucose absorption. This insulin action against the bloodstream can be blocked by TTX, indicating a propagation of the insulin signal via hepatoenteral nerves, which conforms with previous studies with atropine and carbachol. Insulin action could also be mimicked by dibutyryl cAMP (DBcAMP) acting directly on the absorptive enterocytes. Because autonomic neuropathy is a common late complication of diabetes mellitus, the possible impairment of these nerves in the diabetic state was studied in streptozotocin-diabetic rats. In the isolated joint intestine-liver perfusion, glucose was applied as a bolus into the lumen; its absorption was measured in the portal vein. In 5-day diabetic as well as in control rats, portal insulin, arterial carbachol, and arterial DBcAMP increased intestinal glucose absorption. In 3-mo diabetic rats portal insulin and arterial carbachol failed to stimulate glucose absorption, whereas arterial DBcAMP still did so, indicating an undisturbed function of the absorptive enterocytes. The lack of an effect of portal insulin and arterial carbachol and the unchanged action of DBcAMP in the chronically diabetic rats indicated that the signaling chain via the hepatoenteral nerves was impaired, which is in line with a diabetic neuropathy.

Receptor-mediated endocytosis of cobalamin (vitamin B12).

Dietary cobalamin (Cbl) (vitamin B12) is utilized as methyl-Cbl and the coenzyme 5'-deoxyadenosyl Cbl by cells of the body that have the enzymes methionine synthase and methyl malonyl CoA mutase, which convert homocysteine to methionine and methyl malonyl CoA to succinyl CoA, respectively. Prior to conversions and utilizations as the active alkyl forms of Cbl, dietary Cbl is absorbed and transported across cellular plasma membranes by two receptor-mediated events. First, dietary and biliary Cbl bound to gastric intrinsic factor (IF) presented apically to the ileal absorptive enterocytes is transported to the circulation by receptor-mediated endocytosis via apically expressed IF-Cbl receptor. Second, Cbl bound to plasma transcobalamin (TC) II is taken up from the circulation by all cells via a TC II receptor expressed in the plasma membrane of these cells, and in polarized cells via a TC II receptor expressed in the basolateral membranes. This review updates recent work and focuses on (a) the molecular and cellular aspects of Cbl binding protein ligands, IF and TC II, and their cell-surface receptors, IF-Cbl receptor and TC II receptor; (b) the cellular sorting pathways of internalized Cbl bound to IF and TC II in polarized epithelial cells; and (c) the absorption and transport disorders that cause Cbl deficiency.

Colorectal polyps with extensive absorptive enterocyte differentiation: histologically distinct variant of hyperplastic polyps.

The histologic classification of colorectal polyps is well established. However, practicing pathologists may still occasionally encounter colorectal polyps that are difficult to classify. We studied 6 colorectal polyps that showed uncommon histologic features that have not been described in the English language literature. The polyps were studied using standard hematoxylin-eosin stain, mucin histochemistry, and electron microscopy. The 6 polyps we studied showed extensive papillary and villous structures with alternating villi and crypts. The villi were lined by well-differentiated absorptive cells, whereas the crypts were lined by immature glandular cells, thus mimicking the histology of the small intestinal mucosa. These polyps appear to represent a variant of the hyperplastic polyp, in as much as cellular maturation (immature glandular cells differentiate into the mature surface absorptive cells) is the essential feature distinguishing hyperplastic polyps from adenomas.

Lectin-mediated bioadhesion: binding characteristics of plant lectins on the enterocyte-like cell lines Caco-2, HT-29 and HCT-8

In order to take advantage of the biorecognition between lectins and specific carbohydrates for targeted drug delivery, fluorescein-labelled lectins of different carbohydrate specificities were screened for binding to human colorectal carcinoma cell lines by flow cytometry and confocal microscopy. The lectin-binding rate increased as follows: Dolichos biflorus agglutinin, DBA<peanut agglutinin, PNA< Lens culinaris agglutinin, LCA< Solanum tuberosum lectin, STL< Ulex europaeus isoagglutinin I, UEA-I<wheat germ agglutinin, WGA (Caco-2); PNA<UEA-I<WGA (HT-29); DBA<UEA-I<WGA (HCT-8), thus reflecting the glycosylation pattern of the cells. Compared to the BSA-binding capacity of the cells, the extent of nonspecific binding was strongly dependent on the type of cell line and lectin under investigation being lower than 2% in the case of WGA, STL and UEA-I/Caco-2 and HT-29 cells. Whereas 50% of DBA was bound nonspecifically to Caco-2 cells, the interactions DBA/HCT-8 and PNA/HT-29 were due to nonspecific binding. By competitive inhibition of lectin-adhesion to the cells upon addition of the complementary carbohydrate, specificity of lectin-binding was confirmed except for the interaction of DBA/HCT-8 and PNA/HT-29. Following on from this work, we consider WGA-, STL- and UEA-I-mediated drug delivery to be a promising approach for peroral bioadhesive formulations adhering to absorptive enterocytes.

Defective Intracellular Processing of Lactase‐Phlorizin Hydrolase Protein in Rats Prenatally Exposed to Ethanol

We have previously shown that fetal exposure to ethanol in rats produces both structural and biochemical abnormalities in absorptive enterocytes. Among the indicators of injury are derangements in the expression of lactase-phlorizin hydrolase (LPH), which is an essential enzyme for the assimilation of milk. In an animal model of fetal alcohol syndrome, unsuckled newborn rats prenatally exposed to maternal ethanol revealed a 10- to 15-fold increase in the number of LPH mRNA molecules per absorptive enterocyte, compared with controls (Estrada et al., Alcohol. Clin. Exp. Res. 20:1662-1668, 1996). However, lactase activity per cell was similar in both groups. The aim of this study was to characterize the effect of prenatal exposure to ethanol on the processing of LPH mRNA and protein. RNase protection assays using 3'- and 5'-directed antisense RNA probes revealed that the LPH mRNA from ethanol-exposed pups is full length. However, metabolic labeling, followed by immunoprecipitation using an anti-LPH monoclonal antibody, demonstrated a significant alteration in LPH protein processing. Intestinal explants from 21-day ethanol-exposed fetuses that were chased 30 min after a [35S]methionine pulse showed greater amounts of newly synthesized LPH precursors (205 and 220 kDa) and low molecular weight degradation products than controls. However, despite the increases in LPH precursor, the amount of 130 kDa mature LPH was similar in ethanol-exposed and control explants. These data suggest an increase in intracellular degradation of LPH precursor in rats prenatally exposed to ethanol, which occurs before its insertion into the microvillus membrane. Biosynthesis of LPH appears to be upregulated at the transcriptional level, which overcomes the degradation of LPH precursor during processing.

O.74 Post absorptive plasma citrulline concentration is a biochemical marker of absorptive enterocyte mass in villous atrophy

O.74 Post absorptive plasma citrulline concentration is a biochemical marker of absorptive enterocyte mass in villous atrophy

Tubules of the trans Golgi apparatus visualized by immunoelectron microscopy.

Tubules constitute an integral part of the Golgi apparatus and have been shown to form a complex and dynamic network at its trans side. We have studied in detail structural features of the trans Golgi network and its relationship with the cisternal stack in thin sections of Lowicryl K4M embedded human absorptive enterocytes by immunolectron microscopy. Immunoreactive sites for alpha1,3 N-acetylgalactosaminyltransferase and blood group A substance were detectable throughout the cisternal stack and the entire trans Golgi network. Furthermore, the entire trans Golgi network was reactive for CMPase activity. Evidence for two kinds of tubules at the trans side of the Golgi apparatus was found: tubules that laterally connect adjacent and distant cisternal stacks, and others extending from central and lateral portions of trans cisternae to form the complex and extensive trans Golgi network. Trans cisternae showed often the peeling-off phenomenon and were continuous with the trans Golgi network. Both, trans cisternae and tubules of the trans Golgi network exhibited regionally buds and vesicles with a lace-like, non clathrin coat, previously reported by others in NRK cells, which contained glycoproteins with terminal N-acetylgalactosamine residues. These buds and vesicle are therefore involved in constitutive exocytosis.

Na-K-2Cl cotransporter gene expression and function during enterocyte differentiation. Modulation of Cl- secretory capacity by butyrate.

The basolateral Na-K-2Cl cotransporter (NKCC1) is a key component of the intestinal crypt cell secretory apparatus. Its fate during the transition to absorptive enterocyte and the potential impact of its altered expression on secretory output have not been addressed. In this report, NKCC1 mRNA was found to be expressed in rat jejunal crypt but not villus cells. Butyrate treatment of intestinal epithelial HT29 cells induced a differentiation pattern that recapitulated the rat intestinal crypt-villus axis, with NKCC1 mRNA levels decreasing in a time- and dose-dependent fashion in parallel with upregulation of apical brush-border markers. Butyrate but not acetate or proprionate decreased basal and cAMP-stimulated bumetanide-sensitive K+ (86Rb) uptake in both HT29 cells and the Cl--secreting T84 line. Butyrate markedly decreased transepithelial Cl- secretion in confluent T84 monolayers without effect on cAMP-regulated apical Cl- efflux. We conclude that NKCC1 regulation during enterocyte differentiation occurs at the level of gene expression, and that selective downregulation of NKCC1 gene expression and function by butyrate leads to a profound decrease in transepithelial Cl- secretion. These data emphasize the importance of NKCC1 in determining epithelial secretory capacity and suggest the possibility of modulation of the enterocytic transport phenotype as therapy for diarrheal disorders.

DISTINCT mRNA DISTRIBUTION PATTERNS IN HUMAN JEJUNAL ENTEROCYTES.

70 Although intracellular sorting of mRNAs has been demonstrated in several cellular systems, including oocytes, embryos, neurons, fibroblasts, and absorptive enterocytes, its importance in enterocyte differentiation is poorly understood. Previous studies from our laboratory have demonstrated that mRNAs are asymmetrically distributed in human intestinal epithelial cells, but in general co-localized with their encoded proteins. Most mRNA sorting studies indicate that cis-acting sequences responsible for mRNA localization are located in the 3′-untranslated region (3′UTR). The aims of this study were to characterize in human enterocytes the mRNA localization patterns of genes with distinctly different functions: villin, brush border myosin I (BBMI), Na+-dependent glucose co-transporter (SGLT1), and liver fatty acid binding protein (L-FABP), and to characterize the protein(s) that may be involved in the mRNA sorting process. Methods: mRNA distribution in formalin fixed human jejunal tissue sections was determined byin situ hybridization at high stringency using digoxigenin-labeled RNA probes. Gel-shift assays were used to study RNA-protein interactions in the 3′UTR. Results: The mRNAs for villin and BBMI, well-characterized apical microvillus cytoskeletal proteins, were unexpectedly sorted to the basal region of enterocytes, a different intracellular location than their encoded proteins. The mRNA for human SGLT1 was sorted to the apical region, a location near its encoded protein; and the mRNA for human L-FABP was distributed diffusely in the cytoplasm as is its encoded protein. Gel-shift assays indicated that a cytoplasmic protein in Caco-2 cells binds to the villin 3′UTR, suggesting that this region contains a protein-binding motif. Conclusions: This study not only demonstrates distinct mRNA sorting patterns in human absorptive enterocytes for villin, BBMI, SGLT1, and L-FABP, but also reveals for the first time that a dichotomy may exist between the distribution pattern of mRNA and that of its sorted protein. The observations further offer the opportunity to identify the mechanisms by which mRNAs are separately localized to apical and basal domains in absorptive enterocytes.

Asymmetrical localization of mRNAs in enterocytes of human jejunum.

Intracellular localization of specific mRNAs is known to be a mechanism for targeting proteins to specific sites within the cell. Previous studies from this laboratory have demonstrated co-localization of mRNAs and proteins for a number of genes in absorptive enterocytes of fetal rat intestine. The present study was undertaken to examine in human enterocytes the intracellular localization patterns of mRNAs for the microvillous membrane proteins lactase-phlorizin hydrolase (LPH), sucrase-isomaltase (SI), and intestinal alkaline phosphatase (IAP), and the cytoskeletal protein beta-actin. In sections of human jejunum, mRNAs were localized by in situ hybridization using digoxigenin-labeled anti-sense RNA probes. Both LPH and SI mRNAs were localized to the apical region of villous enterocytes, whereas IAP and beta-actin mRNAs were detected both apically and basally relative to the nucleus. Therefore, in contrast to LPH, SI, and beta-actin mRNAs, which co-localize with their encoded proteins, that of IAP is present in the basal region of the cell where IAP protein has not directly been demonstrated to be present. Absorptive enterocytes from humans possess the mechanisms for intracellular mRNA localization, but not all mRNAs co-localize with their encoded proteins.

Cytokine--intestinal epithelial cell interactions: implications for immune mediated bowel disorders.

The intestinal epithelial cell population is comprised of a dynamic continuum, ranging from undifferentiated, actively proliferating crypt cells, to mature absorptive villus enterocytes, lacking mitotic capacity. Under normal conditions, the constant loss of differentiated villus tip cells via apoptosis leads to a complete renewal of the epithelial cell population every few days. The physiological factors regulating enterocyte proliferation, maturation and apoptosis in health, as well as those that modulate these events in disease states remain largely unknown. It has been demonstrated in vitro that immature crypt cell proliferation is stimulated by factors such as TGF alpha and TNF alpha, whereas TFG beta and IFN gamma inhibit mitotic activity. Further studies showed that intestinal epithelial cells are able to produce and secrete several cytokines such as IL6, IL8, TNF alpha, TGF alpha and TGF beta, indicating the potential for autocrine and paracrine responses. A variety of immune mediated bowel disorders, including celiac disease, Crohn's disease and ulcerative colitis, are characterized by accelerated epithelial cell turnover and apoptosis, leading to altered crypt/villus morphology. There is increasing evidence that these changes, and the accompanying functional alterations of the bowel epithelium, are mediated by the cytokines released from infiltrating inflammatory cells, as well as from enterocytes themselves in an autocrine fashion.