Mathematical modelling to restore circulating IGF-1 concentrations in children with Crohn's disease-induced growth failure: a pharmacokinetic study

OBJECTIVES

Children with Crohn's disease grow poorly, and inflammation depresses the response of insulin-like growth factor-1 (IGF-1) to growth hormone. Correcting the inflammation normalises growth velocity; however, removing inflammation cannot be achieved in all children. Our lack of understanding of IGF-1 kinetics has hampered its use, particularly as high IGF-1 concentrations over long periods may predispose to colon cancer. We hypothesised that mathematical modelling of IGF-1 would define dosing regimes that return IGF-1 concentrations into the normal range, without reaching values that risk cancer.

DESIGN

Pharmacokinetic intervention study.

SETTING

Tertiary paediatric gastroenterology unit.

PARTICIPANTS

8 children (M:F; 4:4) entered the study. All completed: 5 South Asian British; 2 White British; 1 African British.

INCLUSION CRITERIA

Children over 10 years with active Crohn's disease (C reactive protein >10 mg/l or erythrocyte sedimentation rate >25 mm/h) and height velocity <-2 SD score.

EXCLUSION CRITERIA

closed epiphyses; corticosteroids within 3 months; neoplasia or known hypersensitivity to recombinant human IGF-1 (rhIGF-1).

INTERVENTIONS

Subcutaneous rhIGF-1 (120 μg/kg) per dose over two admissions: the first as a single dose and the second as twice daily doses over 5 days.

PRIMARY OUTCOME

Significant increase in circulating IGF-1.

SECONDARY OUTCOMES

Incidence of side effects of IGF-1. A mathematical model of circulating IGF-1 (Ac) was developed to include parameters of endogenous synthesis (Ksyn); exogenous uptake (Ka) from the subcutaneous dose (As): and IGF-1 clearance: where dAc/dt=Ksyn - Kout×Ac+Ka×As.

RESULTS

Subcutaneous IGF-1 increased concentrations, which were maintained on twice daily doses. In covariate analysis, disease activity reduced Ksyn (p<0.001). Optimal dosing was derived from least squares regression fitted to a dataset of 384 Crohn's patients, with model parameters assigned by simulation.

CONCLUSIONS

By using age, weight and disease activity scaling in IGF-1 dosing, over 95% of children will have normalised IGF-1 concentrations below +2.5 SDs of the normal population mean, a level not associated with cancer risk.

Dietary regulation of gene expression

PURPOSE OF REVIEW

The intestine has traditionally been assumed to process food by digestion and absorption. The possibility that the intestine or other genes in the body respond to diet has only slowly been appreciated.

RECENT FINDINGS

This review examines recent evidence that nutrients act on genes in the intestine and in distant sites such as the brain, liver, and skeletal muscle. The article reviews how nutrients affect genes involved in cancer in the intestine; it also studies dietary effects on inflammatory pathways and changes in the brain. Studies in the liver have given insights as to how amino acids may regulate gene promoter activity. Finally, target of rapamycin, an epigenetic regulator, links nutrition to histone acetylation, a key event in gene expression.

SUMMARY

The evidence that nutrients regulate gene expression continues to increase.

Interleukin-1beta (IL-1beta) and IL-6 modulate insulin-like growth factor-binding protein (IGFBP) secretion in colon cancer epithelial (Caco-2) cells

Chronic inflammation is characterised by modifications in cytokine concentrations, whereas growth is mainly dependent on the GH-IGF axis. IGF-I bioavailability is modulated by a family of IGF-binding proteins (IGFBPs). The aim of the present study was to evaluate the interactions among interleukin-1beta (IL-1beta), IL-6 and IGFBP secretion by intestinal cells to assess whether cytokines modulate IGFBP secretion, and in turn IGF-I and IGF-II bioavailability. The human colon carcinoma derived cell line Caco-2 was used as an in vitro model for its capacity to differentiate spontaneously. Experiments were carried out on day 4 (undifferentiated state) and day 14 (differentiated state) after plating. Carcinoembryonic antigen (CEA) was used as a marker of differentiation and increased in the conditioned media (CM) from days 4 to 14 (0.2+/-0.01 ng/ml per 10(5) cells vs 3.3+/-0.2 ng/ml per 10(5) cells, P<0.05). IGFBP-2 and IGFBP-4 secretion decreased concomitantly. Cells were stimulated with IL-1beta and IL-6 at 1, 10 and 50 ng/ml, and with IL-1beta and IL-6 in combination at the same dose of 1 and 10 ng/ml. IGF-I at 50 ng/ml was used as a control. Caco-2 cells expressed and secreted mainly IGFBP-2 and IGFBP-4 into the CM. On day 4, IL-1beta (1 ng/ml) and IL-6 (10 and 50 ng/ml) reduced IGFBP-2 by 29+/-8%, and by 32+/-9 and 38+/-8% respectively (P<0.05). IGFBP-4 was also reduced by IL-1beta at 1 and 50 ng/ml (-14+/-4% and -46+/-11% vs serum free medium (SFM) respectively, P<0.05), and IL-6 at 50 ng/ml (-46+/-15%, P<0.05). Both IGFBP-2 and IGFBP-4 were reduced by IL-1beta and IL-6 in combination at 1 and 10 ng/ml (P<0.05). On day 14, IGFBP-2 band intensity was reduced at 10 ng/ml of IL-1beta (-22+/-15% vs SFM, P<0.05) and at 50 ng/ml of both cytokines (-33%+/-8% and -13%+/-13% vs baseline respectively, P<0.05). IGFBP-4 band intensity decreased with 10 and 50 ng/ml of IL-1beta (-35+/-11% and -46+/-15% vs SFM respectively) and IL-6 (-36%+/-10% and -46+/-15% vs SFM respectively). IL-1beta and IL-6 in combination at 1 and 10 ng/ml reduced both IGFBP-2 and IGFBP-4.In conclusion, IGFBP-2 and IGFBP-4 secretion in CM decreased with Caco-2 cell differentiation. IGFBP-2 and IGFBP-4 were significantly decreased by IL-1beta and IL-6 treatment in both the undifferentiated and differentiated state. Furthermore, these cytokines increased cell proliferation whereas total protein content was significantly reduced only at the higher concentrations of IL-6 and IL-1beta. These findings suggest that interleukins modulate the IGF-IGFBP system in Caco-2 cells in vitro.

Nutritional factors and immune functions of gut epithelium

The intestinal epithelium acts as a barrier to the external environment contained within the lumen of the gut. It also transports solutes for nutrition and for immunological surveillance. The present review develops the hypothesis that changes in diet, through the composition of the lumen environment, alter the expression of genes in the epithelium. These genes include those that encode for proteins that signal to the mucosal immune system. Directly changing the expression of signalling molecules in the intestinal epithelium using transgenic techniques alters immune function. For example, up regulation of the chemokine macrophage inflammatory protein-2 increases neutrophil recruitment. Furthermore, lumen molecules such as short-chain fatty acids regulate chemokine expression by epithelial cells. By this means, the epithelium acts as a transducing monolayer signalling between the contents of the intestine and the mucosal immune system.

MIP-2 secreted by epithelial cells increases neutrophil and lymphocyte recruitment in the mouse intestine

BACKGROUND

Invasion of the intestinal mucosa by leucocytes is a characteristic of intestinal inflammation but the role of the epithelium in orchestrating this recruitment has not been examined in vivo. Cultured intestinal epithelial cells secrete a wide variety of chemokines, often in response to agents present in the intestinal lumen. Macrophage inflammatory protein 2 (MIP-2) is a chemokine that attracts neutrophils, and its secretion from intestinal epithelial cells is enhanced by inflammatory stimuli such as interleukin 1beta. We hypothesised that the production of MIP-2 by epithelial cells would increase leucocyte migration into the intestine.

AIM

To study the effects of a chemokine secreted from intestinal epithelial cells in vivo.

METHODS

MIP-2 was expressed in the mouse intestinal epithelium using an epithelial cell specific promoter from the gene encoding the intestinal fatty acid binding protein. The intestines of these transgenic mice were then analysed.

RESULTS

Epithelial cells from transgenic mice expressed MIP-2 but wild-type mice did not. Neutrophil recruitment, examined by myeloperoxidase (MPO) staining and total MPO activity per unit weight of intestine, was significantly increased in transgenic mice in both the small intestine and proximal colon, and this was blocked by anti-MIP-2 antibody treatment. Both intraepithelial and lamina propria lymphocytes were also increased in transgenic mice. They showed chemotactic activity to MIP-2 in the Boyden chambers and expressed MIP-2 receptor (CXCR-2) mRNA confirmed by reverse transcription-polymerase chain reaction.

CONCLUSION

These experiments are the first to show a functional role for epithelial chemokines in vivo and reveal an unexpected role for the neutrophil chemokine MIP-2 in controlling mucosal lymphocyte migration.

Absence of Toll-like receptor 4 explains endotoxin hyporesponsiveness in human intestinal epithelium

BACKGROUND

The Toll protein in Drosophila regulates dorsal ventral patterning during embryogenesis, and participates in antibacterial and antifungal host defense. Mammalian homologues are termed Toll-like receptors and, to date, nine have been cloned (TLRI-9) in humans. They are characterized by extracellular leucine-rich repeats and a cytoplasmic domain similar to the interleukin 1 receptor. Both TLR2 and TLR4 recognize various bacterial cell wall components including lipopolysaccharide (LPS). This results in the activation of the NFkappaB pathway. Peripheral blood mononuclear cells (PBMCs) express both TLR2 and TLR4. The authors hypothesized that the expression of TLR 2 and TLR4 in human intestinal epithelial cells differs from PBMCs because of the abundance of LPS in the intestinal lumen.

METHODS

Epithelial cells were isolated from Caco-2 cells, fetal gut explants, and small bowel resection specimens using Hanks/ethylenediamine tetraacetic acid solution. PBMCs were used as positive controls. Ribonucleic acid (RNA) was isolated using the TRIzol method. Standard reverse transcription-polymerase chain reaction examined TLR2 and TLR4 messenger RNA (mRNA) expression. NFkappaB expression was determined using a luciferase reporter assay.

RESULTS

TLR2 mRNA was highly expressed in PBMCs and was present in all human intestinal epithelial cells. TLR4 mRNA was detected only in PBMCs. TLR4 is not present in epithelium from children with inflammatory bowel disease. In Caco-2 cells, significant NFkappaB activation in response to LPS occurred only in the presence of TLR4 introduced by complementary deoxyribonucleic acid transfection.

CONCLUSION

Absence of TLR4 is associated with endotoxin hyporesponsiveness of intestinal epithelial cells. TLR4 is not directly involved in inflammation of the intestinal epithelium. Although TLR2 is normally present in the epithelial cell, it plays a limited role in inflammation. It may be activated during conditions in which bacterial cell wall concentrations within the intestine are pathologically high.

Dietary regulation of intestinal gene expression

We are becoming increasingly aware of inherited genetic abnormalities as causes of disease. However, alterations in gene expression can also contribute to other disease processes. Recently it has been suggested that our environment may alter such genes and thus be a direct influence on disease. Diet is a potent mechanism for altering the environment of cells of most organs, particularly the gastrointestinal tract. This review addresses the influence of nutritional factors on intestinal gene regulation. These influences include insulin, which is not a dietary component but responds to dietary changes, and butyrate, a short chain fatty acid produced by normal intestinal flora. Manipulation of diet may be a means of treating intestinal disorders. Nutritional treatment therefore is also discussed in the light of its effect on gene expression.

Interferon gamma induces enterocyte resistance against infection by the intracellular pathogen Cryptosporidium parvum

BACKGROUND & AIMS

Interferon (IFN)-gamma plays an important role in the immunologic control of infection by the protozoan enteropathogen Cryptosporidium parvum. We tested the hypothesis that IFN-gamma may directly inhibit infection of enterocytes by this pathogen.

METHODS

HT-29, Caco-2, and H4 human enterocyte cell lines were grown in monolayers and incubated with IFN-gamma before exposure with C. parvum. IFN-gamma receptor expression in the cell lines was determined by Western blot analysis.

RESULTS

IFN-gamma inhibited C. parvum infection of both HT-29 and Caco-2 cells but not H4 cells. Response to IFN-gamma was related to the expression of the IFN-gamma receptor in the respective cell lines. The effect of IFN-gamma was partially reversed by inhibition of the JAK/STAT signaling pathway. IFN-gamma mediated its action by at least 2 mechanisms: (1) inhibition of parasite invasion and (2) by modification of intracellular Fe(2+) concentration. No role for tryptophan starvation or nitric oxide synthase activity was found. TNF-alpha and IL-1beta also had anti-C. parvum activity but had no synergistic effect with IFN-gamma.

CONCLUSIONS

IFN-gamma directly induces enterocyte resistance against C. parvum infection; this observation may have important consequences for our understanding of the mucosal immune response to invasive pathogens.

Transforming growth factor-beta: an important cytokine in the mucosal immune response

Cytokines are important mediators in the intestine regulating both oral tolerance and mucosal inflammation. Central to this immune-regulatory role is the cytokine transforming growth factor-beta (TGF-beta). Oral tolerance and inflammatory responses in the gut are regulated through the balance of the Th1, Th2, and Th3 lymphocyte responses--a balance influenced strongly by TGF-beta. TGF-beta also modulates B-cell responses by increasing the production of immunoglobulin A (IgA) while decreasing the production of IgG, IgM, and IgE. In intestinal epithelial cells, TGF-beta activates signal transduction pathways resulting in the inhibition of proliferation and tumorigenesis. Currently, these signaling pathways are being dissected at the molecular level.

Butyrate upregulates stromelysin-1 production by intestinal mesenchymal cells

Nutritional factors and resident bacteria participate in the pathogenesis of intestinal inflammation. However, the ways in which bacteria and complex diets might modulate matrix metalloproteinase (MMP) production are unknown. We hypothesized that butyrate might enhance production of MMPs, thus amplifying their response to signals in inflammatory conditions. Human mesenchymal cells were incubated with butyrate and then stimulated with cytokines. MMPs and inhibitors were studied by Western blotting and quantitative RT-PCR. Acetylation of histones was examined in Triton X acetic acid-urea gels by PAGE. We showed that butyrate selectively enhanced the protein production and mRNA expression of stromelysin-1 in tumor necrosis factor-alpha- or interleukin-1beta-stimulated mesenchymal cells. Butyrate alone did not induce any change in MMP production or mRNA expression. It increased the acetylation of histones in mesenchymal cells. Furthermore, acetylation of histones (induced by trichostatin A) reproduced the effects of butyrate. Although butyrate is a major source of nutrient for the colonic epithelial cells, it modulates intestinal inflammation through the secretion of stromelysin-1 in stimulated stromal cells via the inhibition of histone deacetylase.

Butyrate switches the pattern of chemokine secretion by intestinal epithelial cells through histone acetylation

BACKGROUND

Butyrate, a fermentation product of intestinal bacteria, modifies chromatin structure through histone acetylation, thereby altering gene transcription. IL-8 and MCP-1 are chemokines, expressed by intestinal epithelial cells, which attract neutrophils and monocytes, respectively. We hypothesized that butyrate may alter IL-8 and MCP-1 expression by intestinal epithelial cells through histone acetylation.

MATERIALS AND METHODS

IL-8 and MCP-1 expression was measured by ELISA and RNA transfer blots. Acetylated histones were separated on acetic acid-urea-triton gels. Butyrate was compared to Trichostatin-A, a specific inhibitor of histone deacetylase and to other short chain fatty acids.

RESULTS

Caco-2 cells constitutively secreted MCP-1 but not IL-8. Butyrate reversibly decreased MCP-1 secretion. In contrast, butyrate increased IL-8 production. The effects of butyrate and Trichostatin-A were greater when cells were stimulated with IL-1beta. Butyrate and Trichostatin-A both increased histone acetylation. Trichostatin-A and other short chain fatty acids altered chemokine secretion according to their effect on histone acetylation.

CONCLUSIONS

Butyrate reversibly switches chemokine secretion by epithelial cells through histone acetylation. We speculate that butyrate carries information from resident bacteria to epithelial cells. Epithelial cells transduce this signal through histone acetylation, modulating the secretion of chemokines.

Nutrient regulation of intestinal gene expression

This review examines recent advances in the dietary modulation of gene expression in the gastrointestinal tract. We have chosen to concentrate on individual genes and examine what is known about their regulation, attempting to link different studies together.

Vascular endothelial growth factor (VEGF) is present in human breast milk and its receptor is present on intestinal epithelial cells

VEGF (vascular endothelial growth factor) is a multifunctional cytokine active on blood vessel cells. The present study measured VEGF in the aqueous phase of human milk and examined how the concentration varied with gestational age and the duration of lactation after birth. We hypothesized that VEGF-specific receptors were present on the apical surface of intestinal epithelial cells. The concentration of monomeric VEGF (containing 165 residues) measured by ELISA in the breast milk was 2 orders of magnitude greater than that measured in the serum of normal adults. The VEGF165 concentration in the first week of lactation was greater in the breast milk of mothers of full-term than in preterm babies (p < 0.05). The concentration in the breast milk of mothers of full-term infants decreased (p < 0.01) after the first week of lactation. Scatchard analysis of radioligand-receptor binding showed the presence of specific receptors for 125I-VEGF165 on the surface of Caco-2, an intestinal epithelial cell line, with a kd of 2.85 to 4 nM. Reverse transcriptase PCR of Caco-2 cell RNA showed mRNA for the VEGF receptor flt-1. In conclusion, VEGF is present in high concentrations in breast milk and binds to specific receptors on cells derived from intestinal epithelium.

The physicochemical environment of the neonatal intestine

Dietary intake, bacterial metabolites, and the secretion of factors (eg, proteins, electrolytes, lipid-soluble molecules, and water) by the body each contribute to the physicochemical environment of the gastrointestinal tract. Peristalsis regulates the changes along the length of the intestine. However, coordinated peristaltic responses develop as premature infants mature. In addition, the physicochemical environment of the center of the intestinal lumen differs from that of the epithelial surface. The area adjacent to the small intestinal epithelium is more acid than the bulk phase. Na+/H+ exchange antiporters in the epithelial cell apical membrane generate this acidity. Mucus maintains the acid microclimate by preventing free diffusion of hydrogen ions into the bulk phase. Development also affects these mechanisms. Changes in the lumenal environment may alter the synthesis of signaling molecules expressed by the intestinal epithelium. Thus, the epithelium, through changes in gene regulation, may act as an active interface that transmits information about the composition of the intestinal lumen to the mucosal immune system. Premature neonates are at risk of necrotizing enterocolitis, a disease almost exclusively associated with oral feeds. The pathogenesis of this condition may, in part, be due to the immaturity of the interactions between the physicochemical environment of the lumen and intestine.

Increased interleukin-8 (IL-8) in rectal dialysate from patients with ulcerative colitis: evidence for a biological role for IL-8 in inflammation of the colon

OBJECTIVE

Infiltration of neutrophils and their release of toxic reactive oxygen species (ROS) in the colonic mucosa are associated with tissue damage in ulcerative colitis (UC). This neutrophil migration may be induced by chemoattractants, such as cytokines, in the colonic milieu. One such chemoattractant is interleukin-8 (IL-8), a neutrophil chemokine that is present at high concentrations in inflamed mucosa. However, the functional significance of IL-8 in neutrophil attraction and activation in UC has not been established. We hypothesized that IL-8 in the colonic lumen of patients with UC primes neutrophils, leading to their attraction and activation.

METHODS

The colonic milieu was sampled by rectal dialysis. Using a semi-permeable membrane with a molecular weight cut-off of 12 kDa, dialysis solution was placed in the rectum and allowed to equilibrate over a 4-h period with the colonic milieu of controls or of patients with UC. IL-8 concentrations were measured by ELISA. Two functions of healthy neutrophils (PMN) were measured: expression of CD11-b surface adhesion molecules (by flow cytometry), and production of ROS (by both chemiluminescence and cytochrome C reduction assays). Neutrophil functions after exposure to rectal dialysates or n-formyl-methionyl-leucyl-phenylalanine (fMLP) were assessed before and after adding anti-IL-8 antibody or the fMLP blocker BMLP.

RESULTS

IL-8 concentrations in dialysates from patients with active UC were significantly higher than in controls and correlated with disease activity. UC dialysates significantly increased ROS production and CD11-b expression by neutrophils and anti-IL-8 antibody partially (50%) inhibited these stimulatory effects of UC dialysates. Preincubation of neutrophils with UC dialysates significantly potentiated the fMLP-induced rise in ROS and anti-IL-8 antibody completely abolished this priming effect.

CONCLUSIONS

The colonic milieu, sampled by rectal dialysis, from patients with active UC can both activate and prime neutrophils in vitro. High concentrations of IL-8 in the colonic lumen of UC patients are partially responsible for the activating effects of rectal dialysates, and account for all of its priming effects. These findings provide direct evidence for a role for IL-8 in inflammatory bowel disease.

Growth in Crohn's disease

Abnormal linear growth is frequent in children and adolescents with Crohn's disease. The typical pattern is of growth retardation associated with delayed skeletal maturation. Puberty is also frequently delayed. Over 50% of patients may have a subnormal height velocity, and approximately 25% will have short stature. The endocrine status is characterized by normal growth hormone secretion and a slightly subnormal serum level of insulin-like growth factor I, which is related to nutritional status. Principal therapeutic options are intestinal resection for localized disease, and enteral nutrition--using a polymeric diet--for more widespread disease, particularly involving the small intestine. Growth responses to both modalities are often excellent and produce considerable psychological benefit. Optimum therapy is achieved by close collaboration between gastroenterologists and endocrinologists, and by the use of auxological methods to document pre- and post-therapeutic management.

Dietary regulation of genes expressed in the developing intestinal epithelium

Gene expression is central to the pathogenesis of many disorders. An ability to alter the expression of genes would, if their relation to disease processes were fully understood, constitute a new modality of treatment. This lecture examines the evidence that nutritional factors can regulate genes in the gastrointestinal epithelium and it discusses the physiologic relevance of such alterations in gene expression. Dietary regulation of the genes expressed by the epithelium confers 3 fundamental advantages for mammals. It enables the epithelium to adapt to the luminal environment to better digest and absorb food; it provides the means whereby breast milk can influence the development of the gastrointestinal tract; and, when the proteins expressed by the epithelium act on the immune system, it constitutes a signaling mechanism from the intestinal lumen to the body's defenses. Each of these mechanisms is amenable to manipulation for therapeutic purposes.

Treatment of orofacial and ileo-colonic Crohn's disease with total enteral nutrition

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Short-chain fatty acids regulate IGF-binding protein secretion by intestinal epithelial cells

Gastrointestinal epithelial cells secrete insulin-like growth factor (IGF)-binding proteins (IGFBPs), which modulate the actions of IGFs on cell proliferation and differentiation. Short-chain fatty acids are bacterial metabolites from unabsorbed carbohydrate (including fiber). We hypothesized that they may alter the pattern of IGFBPs secreted by epithelial cells as part of a wider phenomenon by which luminal molecules regulate gastrointestinal epithelial cell signaling. The intestinal epithelial cell line, Caco-2, predominantly secretes IGFBP-3; however, butyrate increased the secretion of IGFBP-2 in a dose-dependent and reversible manner. Butyrate decreased the secretion of IGFBP-3. Butyrate altered only the synthesis and not the cell sorting of IGFBPs because 1) the secretion of IGFBPs remained polarized despite changes in their rates of production, and 2) IGFBP secretion corresponded to mRNA accumulation. The ability of short-chain fatty acids or the fungicide trichostatin A to stimulate IGFBP-2 correlated with their actions on histone acetylation. In conclusion, intestinal epithelial cells respond to short-chain fatty acids by altering secretion of IGFBPs.

The central role of chemokines (chemotactic cytokines) in the immunopathogenesis of ulcerative colitis and Crohn's disease

The final composition of leukocytes present in a site of inflammation in response to chemokine stimulation and activation may depend on both the nature of the secreted chemokines as well as the relative expression of the multitude of specific chemokine cell surface receptors on many different cell types. Because related receptors with different affinities and cross-reactive binding capabilities are present on each type of leukocyte, relative differences in receptor distribution and receptor affinity for specific chemokines may significantly influence which cells are ultimately attracted to and activated by each individual chemokine. Production of IL-8, MCP-1, and ENA-78 by endothelial cells, LPMNC, and epithelial cells in IBD could establish a chemotactic gradient capable of influencing the increased migration of monocytes/macrophages, granulocytes, and lymphocytes from the blood stream through the endothelium into both the mucosa and submucosa during chronic IBD. The ability of chemokines to induce chemotaxis, leukocyte activation, granule exocytosis, increased production of metalloenzymes, and up-regulation of respiratory burst activity indicates that there may be a variety of different mechanisms by which chemokines could markedly increase chronic inflammation and chronic intestinal tissue destruction in IBD.

Butyrate enhances interleukin (IL)-8 secretion by intestinal epithelial cells in response to IL-1beta and lipopolysaccharide

Intestinal epithelial (Caco-2) cells secrete the chemokine, IL-8, after stimulation with IL-1beta, but not after lipopolysaccharide. Butyrate is a short chain fatty acid derived from the metabolism of intestinal contents by gut bacteria. Butyrate concentrations reflect, therefore, the bacterial microenvironment established within the intestine. We hypothesized that butyrate may alter the secretion of IL-8 by intestinal epithelial cells in response to stimulation by IL-1beta or lipopolysaccharide. Caco-2 cells were incubated in varying concentrations of sodium butyrate (0-20 mM) for 24 h before stimulation with lipopolysaccharide or IL-1beta. IL-8 secretion was measured over 24 h by ELISA. IL-8 mRNA accumulation was detected by Northern blots. Lipopolysaccharide induced the secretion of IL-8 only after Caco-2 cells cells had been cultured with sodium butyrate. Furthermore, butyrate significantly enhanced IL-8 secretion by cells stimulated with IL-1beta. Butyrate also increased IL-8 mRNA accumulation in stimulated Caco-2 cells. Intestinal epithelial cells can, therefore, be primed by butyrate to become activated by lipopolysaccharide and proinflammatory cytokines. This may represent a mechanism by which intestinal epithelial cells can regulate intestinal inflammation in response to changes in the intestinal milieu.

Macrophage inflammatory protein-2: chromosomal regulation in rat small intestinal epithelial cells

Nonpathogenic, resident bacteria participate in the pathogenesis of inflammation in the small intestine, but the molecular messages produced by such bacteria are unknown. Inflammatory responses involve the recruitment of specific leukocyte subsets. We, therefore, hypothesized that butyrate, a normal bacterial metabolite, may modulate chemokine secretion by epithelial cells, by amplifying their response to proinflammatory signals. We studied the expression of the chemokine, macrophage inflammatory protein-2 (MIP-2) by the rat small intestinal epithelial cell line, IEC-6. Cells were stimulated with lipopolysaccharide or with interleukin 1beta (IL-1beta) and incubated with sodium butyrate. Acetylation of histones was examined in Triton X acetic acid-urea gels by PAGE. Unstimulated IEC-6 cells did not secrete MIP-2. However, lipopolysaccharide and IL-1beta induced MIP-2 expression. Butyrate enhanced MIP-2 secretion both in lipopolysaccharide-stimulated and IL-1beta-stimulated enterocytes; but butyrate alone did not induce MIP-2 expression. Butyrate increased the acetylation of histones extracted from the nuclei of IEC-6 cells. Furthermore, acetylation of histones (induced by trichostatin A, a specific inhibitor of histone deacetylase) enhanced MIP-2 expression by cells stimulated with IL-1beta. In conclusion, trichostatin A reproduced the effects of butyrate on MIP-2 secretion. Butyrate, therefore, increases MIP-2 secretion in stimulated cells by increasing histone acetylation. We speculate that butyrate carries information from bacteria to epithelial cells. Epithelial cells transduce this signal through histone deacetylase, modulating the secretion of chemokines.

Diet and gene expression in the intestine

Gene expression is central to the pathogenesis of many disorders. An ability to alter the expression of genes would, if their relationship to disease processes were fully understood, constitute a new modality of treatment. This review examines the evidence that nutritional factors can regulate genes in the gastrointestinal epithelium and it discusses the physiological relevance of such alterations in gene expression. Dietary regulation of the genes expressed by the epithelium confers three fundamental advantages for mammals. It enables the epithelium to adapt to the luminal environment to digest and absorb food better; it provides the means whereby mother's milk can influence the development of the gastrointestinal tract; when the proteins expressed by the epithelium act on the immune system, it constitutes a signalling mechanism from the intestinal lumen to the body's defences. Each of these mechanisms is amenable to manipulation for therapeutic purposes.

Growth factors in breast milk and their effect on gastrointestinal development

Breast milk contains various biologically active factors including, hormones, peptide growth factors, and cytokines. Epidermal growth factor (EGF) and insulinlike growth factor-I (IGF-I) are two of the major milk-derived peptide growth factors. Colostrum contains higher levels of these growth factors than mature milk does, and, these factors are relatively resistant to proteolysis and stable in the G-I tract. There are specific receptors found in G-I mucosa. Luminal EGF and IGF-I stimulate growth and development of gastrointestinal tract. Intestinal epithelial Caco-2 cells are a good model for studying physiological roles of exogenous growth factors in the G-I development. Effect of EGF and IGF-I on proliferation, differentiation, and IGF-binding protein (IGFBP) production of intestinal Caco-2 cells were studied. Both EGF and IGF-I increased cell proliferation in dose dependent manner. The number of IGF-I receptors on Caco-2 cells increased after differentiation, in contrast to EGF binding which was reported to decrease. Caco-2 cells produced at least three IGFBPs, namely IGFBP-2, -3, and -4. The profile of these IGFBPs varied with differentiation. Secretion of IGFBP-2 and -3 increased with differentiation, but IGFBP-4 diminished. IGF-I stimulated mainly IGFBP-3 production, while EGF stimulated predominantly IGFBP-4. The effects of IGF-I and EGF on IGFBP secretion diminished with increasing cell differentiation. Thus, the interaction between intestinal epithelial cells and extrinsic growth factors are complex and the stage of differentiation is an important determinant of this phenomenon.

Human fetal enterocytes in vitro: modulation of the phenotype by extracellular matrix

The differentiation of small intestinal epithelial cells may require stimulation by microenvironmental factors in vivo. In this study, the effects of mesenchymal and luminal elements in nonmalignant epithelia] cells isolated from the human fetus were studied in vitro. Enterocytes from the human fetus were cultured and microenvironmental factors were added in stages, each stage more closely approximating the microenvironment in vivo. Four stages were examined: epithelial cells derived on plastic from intestinal culture and grown as a cell clone, the same cells grown on connective tissue support, primary epithelial explants grown on fibroblasts with a laminin base, and primary epithelial explants grown on fibroblasts and laminin with n-butyrate added to the incubation medium. The epithelial cell clone dedifferentiated when grown on plastic; however, the cells expressed cytokeratins and villin as evidence of their epithelial cell origin. Human connective tissue matrix from Engelbreth-Holm-Swarm sarcoma cells (Matrigel) modulated their phenotype: alkaline phosphatase activity increased, microvilli developed on their apical surface, and the profile of insulin-like growth factor binding proteins resembled that secreted by differentiated enterocytes. Epithelial cells taken directly from the human fetus as primary cultures and grown as explants on fibroblasts and laminin expressed greater specific enzyme activities in brush border membrane fractions than the cell clone. These activities were enhanced by the luminal molecule sodium butyrate. Thus the sequential addition of connective tissue and luminal molecules to nonmalignant epithelia] cells in vitro induces a spectrum of changes in the epithelial cell phenotype toward full differentiation.

Developmental differences in the expression of the cholera toxin sensitive subunit (Gs alpha) of adenylate cyclase in the rat small intestine

BACKGROUND

The stimulatory guanosine triphosphate (GTP) binding protein alpha subunit (Gs alpha) of adenylate cyclase is the target protein for cholera toxin.

AIMS/METHODS

The expression of this signal transducer was analysed in the small intestine of developing rats by RNA transfer (northern blot) analysis by immunoblotting, and by ADP-ribosylation of membrane proteins.

RESULTS

Intestinal Gs alpha mRNA (about 1.9 kb) was increased in the neonate compared with the adult rat. Two isoforms of Gs alpha proteins, a 45,000 and a 52,000 form, were expressed in the small intestinal epithelial cell and both were ADP-ribosylated by cholera toxin. A significant increase in the larger isoform (52,000) and in its ribosylation was noted in the 2 week old suckling compared with post-weaned older animals. The protein content or ribosylation of the smaller form (45,000) did not significantly change with age.

CONCLUSION

These data show that a developmental decline of intestinal Gs alpha expression seems to be, in part, regulated at the mRNA level. An increased Gs alpha expression in the immature intestine may help to explain a previously reported, dose dependent increased adenylate cyclase response and an increase in fluid secretion to cholera toxin in neonates compared with adults.

Development of immune function in the intestine and its role in neonatal diseases

This review has traced the ontogeny of the human mucosal immune system, speculating that appropriate gut immune responses are essential in preventing many significant neonatal enteric diseases. Because the gastrointestinal tract serves as the portal of entry for many potential antigens, its mucosal immune function is essential in controlling antigenic responses and ensuring systemic tolerance. A thorough under standing of the development of the entire immune system is essential in defining intestinal mucosal immune function. From the protective barrier covering the enterocyte to the intraepithelial T lymphocytes, these components work together to limit antigen passage from the gut lumen to the underlying immune cells and, thus, promote normal immunity and tolerance. When abnormalities exist or when this immune barrier has not matured fully, conditions afflicting newborns, especially preterm infants, occur. Necrotizing enterocolitis, milk-protein enteropathy, and enteric bacterial infections are only three clinical examples of how aberrant gut immune-mediated defenses may have a significant role in their pathogenesis. In clinical practice, it is not only important to recognize these conditions at their onset but also to understand the basis for the underlying illness and identify newborns who are at an increased risk of acquiring them.

Exogenous nucleotides alter the proliferation, differentiation and apoptosis of human small intestinal epithelium

The turnover of intestinal epithelial cells is a finely regulated process extending from undifferentiated crypt stem cells to terminally differentiated villus cells. The final phase of this maturation process is apoptosis and extrusion. Recent studies have shown that programmed cell death (PCD) occurs not only in senescent cells and in rapidly developing tissues but also in response to cellular stress preventing damaged cells from entering uncontrolled proliferation without repair. This study examined the role of exogenous nucleotides on cell proliferation, differentiation and apoptosis in organ cultures of human fetal small intestine. The addition of adenosine monophosphate (AMP), a putative stress reactant, to the culture media resulted in the suppression of crypt cell proliferation followed by the restoration of differentiation and the induction of apoptosis across a broad range of villus epithelium when compared with controls without added nucleotide. In contrast, the addition to cytidine monophosphate (CMP) to the culture media did not increase apoptosis, despite the nucleotide being taken up by the fetal small intestine in a similar dose- and time-dependent manner to AMP. Furthermore, Bax mRNA, an apoptosis-inducer gene, was increased with addition of AMP, suggesting that the induction of apoptosis may be channeled through the p53 pathway. These results suggest that a specific exogenous nucleotide, AMP, may have an important role in controlling the dynamic balance of cellular turnover in the developing human small intestine.

Differentiation and polarity alter the binding of IGF-I to human intestinal epithelial (Caco-2) cells

This study examined whether insulin-like growth factor-I (IGF-I) bound to specific functioning IGF receptors on the surface of Caco-2 cells and how this binding was affected by the differentiation and polarity of these cells. IGF-I, which increased cell proliferation in a dose-dependent manner, bound to a specific receptor on the surface of Caco-2 cells. Affinity cross-linking with labeled IGF-I followed by reducing sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed M(r)s at 135,000, 270,000 and 355,000 bands, which was inhibited by unlabeled IGF-I. A Scatchard analysis of radioligand-receptor binding showed the presence of a single class of receptors with high affinity for IGF-I. This class of receptors was specific for IGF-I, the affinity of IGF-I to the receptor being four and 150 times greater than IGF-II and insulin, respectively. There was no difference in the affinity of IGF-I to type 1 IGF receptors between less-differentiated [dissociation constant (Kd) = 3.81 nM] and well-differentiated cells (Kd = 3.78 nM); however, well-differentiated cells showed a 2.4-fold higher maximum number of binding sites (Bmax) than less-differentiated cells (3.45 vs. 1.44 x 10(4) sites/cell), indicating an increase in the density of IGF-I receptors with differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron saturation alters the effect of lactoferrin on the proliferation and differentiation of human enterocytes (Caco-2 cells)

Recent studies have indicated that lactoferrin may act as a cell mitogen. The effect of human and bovine lactoferrins on the proliferation and differentiation of a human intestinal epithelial cell line (Caco-2) was investigated and compared with that of human transferrin. Caco-2 cells were cultured in serum-free media supplemented with both iron-unsaturated and -saturated forms of the iron-binding proteins. Cell proliferation and differentiation were evaluated by examining growth curves and measuring sucrase and alkaline phosphatase activities of brush border membrane fractions, respectively. The iron-binding status of lactoferrins and transferrin affected the proliferation of Caco-2 cells. The iron-saturated forms of human (S-hLf), bovine (S-bLf) lactoferrins and human transferrin (S-hTf) enhanced cell proliferation, while iron-unsaturated forms (U-hLf, U-bLf, and U-hTf) suppressed it. Iron-binding status also determined the effect of lactoferrin and transferrin on cellular differentiation, but this effect differed for different brush border enzymes. S-hTf enhanced sucrase activity more than S-hLF or S-bLf. Both U-hLf and U-bLf markedly suppressed sucrase activity. U-hTf suppressed alkaline phosphatase activity appreciably, while the other iron-binding proteins showed no significant effect on it. Lactoferrin and transferrin may modulate the proliferation and differentiation of intestinal epithelial cells, but their efficacy depends on their saturation with iron.

Profile of IGF-binding proteins secreted by intestinal epithelial cells changes with differentiation

Previous reports have shown that gastrointestinal epithelial cells produce insulin-like growth factor-binding proteins (IGF-BP), which modulate the actions of IGF. This study aims to examine the relationship between differentiation and IGF-BP secretion by human intestinal epithelial cells and the effect of growth factors on their production. Caco-2 cells were cultured in serum-free media. IGF-BP secretion into the incubation media was analyzed by Western ligand blotting and immunoblotting. Caco-2 cells produced IGF-BP-2, IGF-BP-3, and IGF-BP-4. Secretion of IGF-BP-2 and IGF-BP-3 increased with differentiation, but IGF-BP-4 secretion diminished. The effect of exogenous growth factors on IGF-BP secretion was maximal at earlier stages of differentiation. IGF-I stimulated mainly IGF-BP-3 production, but epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) stimulated predominantly IGF-BP-4 secretion. Adding an anti-EGF receptor antibody to block autocrine TGF-alpha activity inhibited IGF-BP-4 production but stimulated IGF-BP-2 and IGF-BP-3. In conclusion, the profile of IGF-BP secretion changes with differentiation. IGF-I and EGF (or TGF-alpha) stimulate different types of IGF-BP, with autocrine TGF-alpha activity being a factor affecting IGF-BP production during differentiation.

New approaches to the study of human pediatric disease

The intestinal epithelium may modulate childhood gastrointestinal disease activity, particularly in chronic inflammatory bowel disease. The epithelium is in direct contact with the intestinal lumen and is ideally placed to act as a communication between the intestinal environment and the immune cells of the mucosa. Interaction is possible through the production of cytokines by enterocytes and the expression of surface molecules on the basolateral membrane. The study of how luminal contents can modulate enterocyte gene expression is central to this process, but the molecular mechanisms by which such interactions occur are not well understood. This review discusses possible molecular pathways between the intestinal lumen and the enterocyte and how they can be examined experimentally. Finally, the importance of enterocyte gene expression in human health and disease is reviewed.

Uptake, transport and metabolism of exogenous nucleosides in intestinal epithelial cell cultures

The uptake and transport of nucleosides (adenosine, cytidine, guanosine, thymidine, uridine and inosine) were examined in intestinal cell lines (Caco-2 and IEC-6). Well-differentiated Caco-2 cells took up significantly more uridine and thymidine than less-differentiated cells over 24 h. These differences were reflected in the resulting trichloroacetic acid-soluble (nucleotide, nucleoside and nucleobase) pool sizes rather than in differences in nucleic acid incorporation. IEC-6 cells have smaller soluble pools than Caco-2 cells, and the uptake of nucleosides over 60 min reflected this difference. Caco-2 cells transported significantly more thymidine, cytidine, guanosine, adenosine and inosine into acid-soluble pools than IEC-6 cells. Caco-2 cells were grown on filters to examine the transcellular transport of nucleosides and to examine the chemical form in which nucleosides appeared at the basolateral aspect of the cell monolayer. The pattern of transport varied for individual nucleosides. The transport of cytidine and guanosine was significantly greater in the apical-to-basolateral direction than in the opposite direction over 2 h. No purine nucleoside was transported intact across the Caco-2 cell monolayer in either direction, with the majority of the transported material appearing as nucleobases. Nucleobases also represented the main metabolites of pyrimidines transported. However, some cytidine and uridine were detectable, but each constituted < 20% of transported material. Nucleosides are therefore transported by enterocytes but metabolized during transport.

Unusual colitides

Colitis is an important cause of abdominal pain and diarrhoea and is the main cause of blood and mucus in the stool. The inflammation can be due to infectious or to non-infectious causes, most commonly ulcerative colitis and Crohn's disease. However, a wide variety of rarer causes of colitis also present in childhood. These include colitis or enterocolitis secondary to Hirschsprung's disease and metabolic disorders (which include Hermansky-Pudlak syndrome, glycogen storage disease type 1b and pellagra). Primary inflammation of the colon is seen in microscopic and collagenous colitis, ulcerating enterocolitis of infancy, allergic colitis and autoimmune enteropathy. The histological pattern of each of these diseases has a characteristic picture and separates them from each other from ulcerative colitis and Crohn's disease. The pathophysiology of these rare forms of colitis in childhood is not clear; but in the future they may give us an insight into the pathogenesis of large bowel inflammation, particularly when the colitis occurs secondary to an established disease.

Nucleotide uptake and metabolism by intestinal epithelial cells

The epithelial cells of the gastrointestinal tract are the first to encounter ingested nucleotides. Enterocytes metabolize or transport nucleotides (often partially metabolized) to other cell types. Nucleotides may also affect enterocyte gene expression. These interactions in intestinal cell lines (Caco-2 and IEC-6 cells) are described. Nucleotides and nucleosides are efficiently taken up by neoplastic cells (Caco-2) and substantially metabolized during absorption by epithelial monolayers. In nonmalignant cells (IEC-6), nucleotide pools are smaller than enterocytes of neoplastic origin (Caco-2). Consequently, cell proliferation in IEC-6 cells is more dependent on an external supply of nucleotides. Cell differentiation was examined by measuring brush border enzyme activities (sucrase, lactase and alkaline phosphatase). Nucleotides enhanced the expression of brush border enzymes in carcinoma cells only when stressed by glutamine deprivation. IEC-6 cells, which are poorly differentiated in optimal media, require basement membrane (Matrigel) for expression of brush border enzymes. Under these conditions, adding nucleotides to the culture medium enhanced enzyme activity. In addition to being substrates for intestinal absorption, nucleotides may affect enterocyte differentiation.

Insulin-like growth factor binding protein profile secreted by human intestinal epithelial cells varies with polarity

The actions of insulin-like growth factors (IGFs) are modulated by interaction with a family of secreted binding proteins (IGFBPs). We have now demonstrated in intestinal epithelial cells (Caco-2) that the secretion of different members of this family depends on the cell surface secreting them. Polarized monolayers of cells secreted IGFBP-3 mainly into the medium adjacent to the apical surface, while IGFBP-2 was secreted predominantly through the basolateral surface. The secretion of IGFBP-1 and -4 was equivalent from both surfaces. However, administration of epidermal growth factor (EGF) induced polarized secretion of IGFBP-4 by increasing secretion from the apical surface more than from the basolateral aspect. It did not affect the polarity of the other IGFBPs. We believe that this is the first evidence that epithelial cells can interact with extrinsic agents in a polarized fashion at sites other than the membrane surface.

Ontogeny of Ia messenger RNA in the mouse small intestinal epithelium is modulated by age of weaning and diet

BACKGROUND

Exogenous antigenic peptides are presented to T cells by class II major histocompatibility complex (Ia) molecules on the surface of antigen-presenting cells. Class II-associated invariant chain (Ii) is also required for effective antigen presentation. Because messenger RNAs (mRNAs) for Ii chain and for class II I-A beta chain appear in the mouse intestinal epithelium after weaning, experiments were conducted to test the effect of age of weaning and diet on the appearance of Ia and Ii mRNA.

METHODS

Four litters were split at day 17; one half was weaned and the other remained with the mother until day 24. On day 23, 25, 27, and 29, enterocytes were isolated from full-length small intestine by vascular perfusion with 30 mmol/L ethylenediaminetetraacetic acid, and the RNA was extracted.

RESULTS

Appearance of Ii and I-A beta was significantly delayed by late weaning, as judged by RNA hybridization blots (Ii chain) and complementary DNA amplification (I-A beta chain). In mice on elemental diets, the appearance of Ii and I-A beta chain was delayed compared with littermates reared on standard chow. Ii mRNA failed to appear in mice maintained on the elemental diet by day 40, despite normal growth.

CONCLUSIONS

Appearance of mRNA for both Ia and Ii depends on the introduction of a complex diet and not the "stress" of weaning or elimination of breast milk. Introduction of foreign dietary antigens or development of an altered intestinal flora may contribute to this process.

Differential regulation of B7 mRNA in enterocytes and lymphoid cells

To investigate the molecular details of antigen presentation by cells of lymphoid or epithelial origin, we compared B7 mRNA regulation in intestinal epithelium with that in spleen, since both cell types express class II major histocompatibility complex (MHC) and present antigen. As measured by cDNA amplification using sequence-specific primers, I-A beta mRNA content was found to be similar in mouse full-thickness small intestine, isolated intestinal epithelial cells and spleen. However, in contrast to I-A beta, B7 mRNA intestinal epithelial cell content was markedly lower than in spleen and whole small bowel; cardiac RNA was negative for both sequences. Administration of intraperitoneal interferon-gamma (IFN-gamma) (10(5) U daily for 2 days) to adult mice resulted in an increase in I-A beta mRNA in epithelial cells, but did not alter levels of B7 mRNA. In addition, exposure of the IEC-6 rat cell line to the IFN-gamma resulted in a dose-dependent increase in I-A beta mRNA without altering levels of B7 mRNA. Thus, an apparent dichotomy exists in regulation of B7 and I-A beta gene expression in rodent intestinal epithelial cells. Since maximal T-cell response to splenocytes depends on B7, the absence of B7 mRNA in intestinal epithelium may be a factor in determining why antigen-presenting enterocytes normally do not elicit damaging T-cell proliferative responses.

Endopeptidase inhibition and intestinal antigen processing in mice

The role of gastrointestinal digestive processes in the systemic availability of ingested protein antigens was examined by feeding the trypsin inhibitor aprotinin intragastrically to mice and measuring uptake of ovalbumin and 14C-polyethylene glycol (MW 4000) from the gastrointestinal tract. Trypsin and chymotrypsin activities in the intestinal lumen were significantly reduced by aprotinin feeding. Aprotinin slowed stomach emptying, but radioimmunoassays for immunoreactive ovalbumin in the serum of mice prefed aprotinin showed 12-fold elevations within 1 hr after ovalbumin feeding. Uptake of a nonmetabolized macromolecular probe, 14C-polyethylene glycol-4000, increased less than two-fold when fed with aprotinin under the same conditions, indicating that the increased uptake of immunoreactive ovalbumin was not due to changes in intestinal permeability. The results show that inhibition of luminal proteolysis caused significant increases in the serum concentration of immunoreactive ovalbumin, indicating that acute inhibition of luminal proteases permits larger quantities of relatively intact protein to interact with mucosal absorptive surfaces. These results support the hypothesis that pancreatic proteases modulate antigen absorption from the lumen in adult animals.

Uptake and transport of macromolecules by the intestine: possible role in clinical disorders (an update)

The intestine is exposed to a wide variety of macromolecules. Because macromolecules are antigenic, mechanisms have evolved in the gastrointestinal tract to regulate their absorption. Macromolecular uptake can be beneficial in delivering essential factors for growth and in sampling the antigenic milieu of the gastrointestinal tract. Specific transport mechanisms exist to execute this physiological absorption. However, inappropriate and uncontrolled antigen transport may occur in disease states or as a prelude to disease states in the gastrointestinal tract. Such transport may result in immune responses that are harmful. This review examines physiological transport of macromolecules through epithelia and through M cells. It also considers uncontrolled transport and its relation to disease states. The review concludes with an examination of the interrelationship between antigen transport and an altered immune system in the establishment of gastrointestinal disease.

Ontogeny of class II MHC mRNA in the mouse small intestinal epithelium

MHC Class II (Ia) and invariant chain cooperate in the presentation of exogenous antigen by antigen presenting cells to T-helper cells. Both glycoproteins have been identified in the small intestine of the mature mouse. In this study, we examine the ontogeny of mRNA for three molecules; (Ii31, Ii41 and I-A beta) in whole intestine and in isolated epithelial cells. When RNA from whole intestine was analysed in northern blots using cDNA probe, Ii31 mRNA was present in Day 10 mice and at each 5 day time point thereafter; Ii41 and I-A beta were not detected by this technique. To examine ontogeny of Ii chain mRNA in enterocytes, RNA was purified from an enriched population of epithelial cells isolated after systemic perfusion with 30 mM EDTA in Day 21 and Day 28 and adult mice. Ii chain mRNA was not detected until Day 28 by blot hybridization. Reverse transcription of mRNA and amplification of the resultant cDNA by PCR revealed Ii41 and I-A beta as well as Ii31. RNA from Day 21 epithelial cells required five additional amplification cycles to attain cDNA levels equivalent to those found in Day 28 cells for Ii chain, and 10 additional cycles for I-A beta. In conclusion, Ii31, Ii41 and I-A beta mRNA increase rapidly in the enterocyte after weaning.

Response to autoimmune enteropathy to cyclosporin A therapy

Small bowel enteropathies that are associated with an autoimmune process are often resistant to treatment. Two children with autoimmune enteropathy were treated with cyclosporin A for eight months. Both improved, as assessed by growth, small intestinal mucosal morphology, and carbohydrate absorption. Cyclosporin A is useful in the treatment of autoimmune enteropathy. This report also suggests that T cell activation (which is suppressed by cyclosporin A) is important in the pathogenesis of this condition.

Intractable ulcerating enterocolitis of infancy

Five children (three boys, two girls) presenting in the first year of life with intractable diarrhoea had a number of features in common. All had ulcerating stomatitis, four had partial villous atrophy on small intestinal biopsy, all had colitis characterised by large ulcers with overhanging edges, and four had severe perianal disease; no stool pathogens were detected. Treatment with steroids, sulphasalazine, and azathioprine was unsuccessful. All five required subtotal colectomy. Four were children of consanguinous marriages, two were siblings of Pakistani origin, two were cousins of Arab origin, and the fifth was Portuguese. Although the diagnoses of Behçet's disease and Crohn's disease were considered, it appears that these children represent a distinct inherited condition affecting the whole gastrointestinal tract, particularly the colon.