Gut microbiome and symptoms in females with irritable bowel syndrome: a cross-sectional analysis.

Irritable bowel syndrome (IBS), a disorder of gut-brain interaction, is associated with abdominal pain and stool frequency/character alterations that are linked to changes in microbiome composition. We tested whether taxa differentially abundant between females with IBS vs healthy control females (HC) are associated with daily gastrointestinal and psychological symptom severity. Participants (age 18-50 year) completed a 3-day food record and collected a stool sample during the follicular phase. They also completed a 28-day diary rating symptom intensity; analysis focused on the three days after the stool sample collection. 16S rRNA gene sequencing was used for bacterial identification. Taxon abundance was compared between IBS and HC using zero-inflated quantile analysis (ZINQ). We found that females with IBS (n = 67) had greater Bacteroides abundance (q = 0.003) and lower odds of Bifidobacterium presence (q = 0.036) compared to HC (n = 46) after adjusting for age, race, body mass index, fibre intake, and hormonal contraception use. Intestimonas, Oscillibacter, and Phascolarctobacterium were more often present and Christensenellaceae R-7 group, Collinsella, Coprococcus 2, Moryella, Prevotella 9, Ruminococcaceae UCG-002, Ruminococcaceae UCG-005, and Ruminococcaceae UCG-014 were less commonly present in IBS compared to HC. Despite multiple taxon differences in IBS vs HC, we found no significant associations between taxon presence or abundance and average daily symptom severity within the IBS group. This may indicate the need to account for interactions between microbiome, dietary intake, metabolites, and host factors.

Systematic Analysis of Mobile Genetic Elements Mediating ß-Lactamase Gene Amplification in Noncarbapenemase-Producing Carbapenem-Resistant Enterobacterales Bloodstream Infections.

Noncarbapenemase-producing carbapenem-resistant Enterobacterales (non-CP-CRE) are increasingly recognized as important contributors to prevalent carbapenem-resistant Enterobacterales (CRE) infections. However, there is limited understanding of mechanisms underlying non-CP-CRE causing invasive disease. Long- and short-read whole-genome sequencing was used to elucidate carbapenem nonsusceptibility determinants in Enterobacterales bloodstream isolates at MD Anderson Cancer Center in Houston, Texas. We investigated carbapenem nonsusceptible Enterobacterales (CNSE) mechanisms (i.e., isolates with carbapenem intermediate resistance phenotypes or greater) through a combination of phylogenetic analysis, antimicrobial resistance gene detection/copy number quantification, porin assessment, and mobile genetic element (MGE) characterization. Most CNSE isolates sequenced were non-CP-CRE (41/79; 51.9%), whereas 25.3% (20/79) were Enterobacterales with intermediate susceptibility to carbapenems (CIE), and 22.8% (18/79) were carbapenemase-producing Enterobacterales (CPE). Statistically significant copy number variants (CNVs) of extended-spectrum ß-lactamase (ESBL) genes (Wilcoxon Test; P-value < 0.001) were present in both non-CP-CR E. coli (median CNV = 2.6×; n = 17) and K. pneumoniae (median CNV = 3.2×, n = 17). All non-CP-CR E. coli and K. pneumoniae had predicted reduced expression of at least one outer membrane porin gene (i.e., ompC/ompF or ompK36/ompK35). Completely resolved CNSE genomes revealed that IS26 and ISEcp1 structures harboring blaCTX-M variants along with other antimicrobial resistance elements were associated with gene amplification, occurring in mostly IncFIB/IncFII plasmid contexts. MGE-mediated ß-lactamase gene amplifications resulted in either tandem arrays, primarily mediated by IS26 translocatable units, or segmental duplication, typically due to ISEcp1 transposition units. Non-CP-CRE strains were the most common cause of CRE bacteremia with carbapenem nonsusceptibility driven by concurrent porin loss and MGE-mediated amplification of blaCTX-M genes. IMPORTANCE Carbapenem-resistant Enterobacterales (CRE) are considered urgent antimicrobial resistance (AMR) threats. The vast majority of CRE research has focused on carbapenemase-producing Enterobacterales (CPE) even though noncarbapenemase-producing CRE (non-CP-CRE) comprise 50% or more of isolates in some surveillance studies. Thus, carbapenem resistance mechanisms in non-CP-CRE remain poorly characterized. To address this problem, we applied a combination of short- and long-read sequencing technologies to a cohort of CRE bacteremia isolates and used these data to unravel complex mobile genetic element structures mediating ß-lactamase gene amplification. By generating complete genomes of 65 carbapenem nonsusceptible Enterobacterales (CNSE) covering a genetically diverse array of isolates, our findings both generate novel insights into how non-CP-CRE overcome carbapenem treatments and provide researchers scaffolds for characterization of their own non-CP-CRE isolates. Improved recognition of mechanisms driving development of non-CP-CRE could assist with design and implementation of future strategies to mitigate the impact of these increasingly recognized AMR pathogens.

GABA-producing Bifidobacterium dentium modulates visceral sensitivity in the intestine.

BACKGROUND: Recurrent abdominal pain is a common and costly health-care problem attributed, in part, to visceral hypersensitivity. Increasing evidence suggests that gut bacteria contribute to abdominal pain perception by modulating the microbiome-gut-brain axis. However, specific microbial signals remain poorly defined. γ-aminobutyric acid (GABA) is a principal inhibitory neurotransmitter and a key regulator of abdominal and central pain perception from peripheral afferent neurons. Although gut bacteria are reported to produce GABA, it is not known whether the microbial-derived neurotransmitter modulates abdominal pain. METHODS: To investigate the potential analgesic effects of microbial GABA, we performed daily oral administration of a specific Bifidobacterium strain (B. dentiumATCC 27678) in a rat fecal retention model of visceral hypersensitivity, and subsequently evaluated pain responses. KEY RESULTS: We demonstrate that commensal Bifidobacterium dentium produces GABA via enzymatic decarboxylation of glutamate by GadB. Daily oral administration of this specific Bifidobacterium (but not a gadB deficient) strain modulated sensory neuron activity in a rat fecal retention model of visceral hypersensitivity. CONCLUSIONS & INFERENCES: The functional significance of microbial-derived GABA was demonstrated by gadB-dependent desensitization of colonic afferents in a murine model of visceral hypersensitivity. Visceral pain modulation represents another potential health benefit attributed to bifidobacteria and other GABA-producing species of the intestinal microbiome. Targeting GABAergic signals along this microbiome-gut-brain axis represents a new approach for the treatment of abdominal pain.

Melanin-concentrating hormone (MCH) modulates C difficile toxin A-mediated enteritis in mice.

OBJECTIVE: Melanin-concentrating hormone (MCH) is a hypothalamic orexigenic neuropeptide that regulates energy balance. However, the distribution of MCH and its receptor MCHR1 in tissues other than brain suggested additional, as yet unappreciated, roles for this neuropeptide. Based on previous paradigms and the presence of MCH in the intestine as well as in immune cells, its potential role in gut innate immune responses was examined. METHODS: In human intestinal xenografts grown in mice, changes in the expression of MCH and its receptors following treatment with Clostridium difficile toxin A, the causative agent of antibiotic-associated diarrhoea in hospitalised patients, were examined. In colonocytes, the effect of C difficile toxin A treatment on MCHR1 expression, and of MCH on interleukin 8 (IL8) expression was examined. MCH-deficient mice and immunoneutralisation approaches were used to examine the role of MCH in the pathogenesis of C difficile toxin A-mediated acute enteritis. RESULTS: Upregulation of MCH and MCHR1 expression was found in the human intestinal xenograft model, and of MCHR1 in colonocytes following exposure to toxin A. Treatment of colonocytes with MCH resulted in IL8 transcriptional upregulation, implying a link between MCH and inflammatory pathways. In further support of this view, MCH-deficient mice developed attenuated toxin A-mediated intestinal inflammation and secretion, as did wild-type mice treated with an antibody against MCH or MCHR1. CONCLUSION: These findings signify MCH as a mediator of C difficile-associated enteritis and possibly of additional gut pathogens. MCH may mediate its proinflammatory effects at least in part by acting on epithelial cells in the intestine.

Neuro-glial crosstalk in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a multifactorial disease in which environmental, immune and genetic factors are involved in the pathogenesis. Although biological therapies (antibodies anti-tumour necrosis factor-alpha or anti-integrin) have considerably improved the symptoms and quality of life of IBD patients, some drawbacks have emerged limiting their long-term use. In addition, prevention of relapses and treatment of resistant ulcers remains a clinical challenge. In this context, a better understanding of the pathophysiology of IBD and the development of novel therapeutic intervention would benefit from further basic and preclinical research into the role of the cellular microenvironment and the interaction between its cellular constituents. In this context, the role of the enteric nervous system (ENS) in the regulation of the intestinal epithelial barrier (IEB) and the gut immune response has fuelled an increased interest in the last few years. Recent advances, summarized in this review, have highlighted the ENS as playing a key role in the control of IEB functions and gut immune homeostasis, and that alterations of the ENS could be directly associated in the development of IBD and its associated symptoms.

Enteric glia inhibit intestinal epithelial cell proliferation partly through a TGF-beta1-dependent pathway.

Although recent studies have shown that enteric neurons control intestinal barrier function, the role of enteric glial cells (EGCs) in this control remains unknown. Therefore, our goal was to characterize the role of EGCs in the control of intestinal epithelial cell proliferation using an in vivo transgenic and an in vitro coculture model. Assessment of intestinal epithelial cell proliferation after ablation of EGCs in transgenic mice demonstrated a significant increase in crypt cell hyperplasia. Furthermore, mucosal glial network (assessed by immunohistochemical detection of S-100beta) is altered in colon adenocarcinoma compared with control tissue. In an in vitro coculture model of subconfluent Caco-2 cells seeded onto Transwell filters with EGCs, Caco-2 cell density and [3H]thymidine incorporation were significantly lower than in control (Caco-2 cultured alone). Flow cytometry analysis showed that EGCs had no effect on Caco-2 cell viability. EGCs induced a significant increase in Caco-2 cell surface area without any sign of cellular hypertrophy. These effects by EGCs were also seen in various transformed or nontransformed intestinal epithelial cell lines. Furthermore, TGF-beta1 mRNA was expressed, and TGF-beta1 was secreted by EGCs. Exogenously added TGF-beta1 reproduced partly the EGC-mediated effects on cell density and surface area. In addition, EGC effects on Caco-2 cell density were significantly reduced by a neutralizing TGF-beta antibody. In conclusion, EGCs have profound antiproliferative effects on intestinal epithelial cells. Functional alterations in EGCs may therefore modify intestinal barrier functions and be involved in pathologies such as cancer or inflammatory bowel diseases.

Enterocolitis induced by autoimmune targeting of enteric glial cells: a possible mechanism in Crohn's disease?

Early pathological manifestations of Crohn's disease (CD) include vascular disruption, T cell infiltration of nerve plexi, neuronal degeneration, and induction of T helper 1 cytokine responses. This study demonstrates that disruption of the enteric glial cell network in CD patients represents another early pathological feature that may be modeled after CD8(+) T cell-mediated autoimmune targeting of enteric glia in double transgenic mice. Mice expressing a viral neoself antigen in astrocytes and enteric glia were crossed with specific T cell receptor transgenic mice, resulting in apoptotic depletion of enteric glia to levels comparable in CD patients. Intestinal and mesenteric T cell infiltration, vasculitis, T helper 1 cytokine production, and fulminant bowel inflammation were characteristic hallmarks of disease progression. Immune-mediated damage to enteric glia therefore may participate in the initiation and/or the progression of human inflammatory bowel disease.

Developmental regulation of intestinal epithelial hydrolase activity in human fetal jejunal xenografts maintained in severe-combined immunodeficient mice.

Intestinal epithelial brush border hydrolases are important and sensitive enzyme markers of gastrointestinal development and function. Little is know about the mechanisms that regulate the induction of these enzymes during human fetal development, as these events occur primarily in utero. The present work used ectopically grafted human fetal jejunal xenografts (median age,13.3 wk of gestation), maintained in severe-combined immunodeficient mice, to study the differential expression of five different hydrolases after 10 wk of xenotransplantation. The spatio-temporal distribution of brush border alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, lactase-phlorizin hydrolase, and dipeptidyl peptidase IV enzyme activities were measured quantitatively using scanning microdensitometry along the crypt-villus axes of fetal, xenograft, and pediatric (median age, 34 mo) biopsies. Ectopic grafting of fetal jejunum closely recapitulated the development of these enzymes in utero, with alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, and dipeptidyl peptidase IV enzyme activities closely matching the spatio-temporal distribution and levels recorded in pediatric duodenal biopsies. Lactase-phlorizin hydrolase was the only enzyme not to reach values recorded in pediatric brush border membranes, although activities were significantly (5.6-fold) higher than in pretransplanted fetal bowel. Human jejunal xenografts therefore demonstrate an appropriate developmental induction of brush border hydrolase activity and may represent a useful model to study trans-acting factors that promote human epithelial differentiation and function in vivo. Characterization of such agents may be of potential therapeutic use in the treatment of diseases associated with gastrointestinal immaturity, notably necrotizing enterocolitis.

Morphology and enzyme activities of the small intestine are modulated by dietary protein source in the preruminant calf.

A study was undertaken to assess the impact of the protein nature and soya antigenicity on the morphology and some enzyme activities of the jejunum in preruminant calves. Twenty Holstein calves fitted with a duodenal cannula were fed a liquid diet based on skimmed milk powder (SMP) for 2 weeks. They were then switched onto diets containing a mixture of SMP and either antigenic heated soybean flour (HSF; n = 12) or hypo-antigenic soya protein concentrate (SPC; n = 8) for 8 weeks, after which they were reverted back to the SMP diet for 2 weeks. The diets contained similar amounts of digestible nitrogen and energy, and were fed at a rate of 55 g DM/kg(0.75)/d. Proximal jejunal biopsies were collected just before (week 0), during (weeks 2 and 8) and after (week 10) feeding of the soya-based diets, and were used for morphology measurements and the determination of total alkaline phosphatase, lactase, amino-peptidases A and N, and dipeptidyl peptidase IV activities. Feed intake and growth were similar between the HSF and SPC groups during the experimental period. The effects of antigenicity and the antigenicity x time interaction were never significant (P > 0.05). Villus height decreased (P < 0.01) between weeks 0 and 2, and increased (P < 0.05) between weeks 8 and 10. Villus width increased between weeks 2 and 8 (P < 0.001). Crypt depth also increased between weeks 0 and 2 (P < 0.001). Specific activities of alkaline phosphatase (P < 0.01) and amino-peptidase N (P < 0.05) decreased between weeks 0 and 2. Conversely, those of alkaline phosphatase (P < 0.0001), lactase (P < 0.01) and dipeptidyl-peptidase IV (P < 0.0001) increased between weeks 8 and 10. Specific activities for lactase and amino-peptidase N decreased (P < 0.01) between weeks 2 and 8. The treatments had little effects on the amino-peptidase A activity. In conclusion, the present work demonstrated that soybean protein markedly depressed the morphology and most enzyme activities of the calf small intestine. On the contrary, the in vitro antigenicity of soybean protein had little influence on these parameters in this study.

Autoimmune enteropathy with distinct mucosal features in T-cell activation deficiency: the contribution of T cells to the mucosal lesion.

BACKGROUND: Autoimmune enteropathy is normally characterised by crypt hyperplastic villous atrophy with enterocyte autoantibodies, activation of mucosal lymphocytes and increased epithelial HLA-DR. This case involved a severely affected Portuguese infant who was found to have lymphocyte activation deficiency and demonstrated correspondingly distinct mucosal features. METHODS: A female infant of nonconsanguineous parents was treated for vomiting and diarrhoea, first with milk exclusion and then with parenteral nutrition. Lymphocyte subsets and immunoglobulin concentrations were normal, but in vitro testing showed no activation in response to phytohaemagglutinin, Candida, or purified protein derivative, although the response to interleukin (IL)-2 was intact. Interleukin-2 deficiency was excluded. Analysis of jejunal biopsy specimens revealed only mild villous blunting with absent goblet cells, normal epithelial proliferation, and no crypt hyperplasia. The dense infiltrate of CD8+ and CD4+ T lymphocytes showed normal CD2 and CD3 expression but no activation or proliferation markers. HLA-DR was not increased on epithelium or lymphocytes. Thus, in addition to in vitro evidence for lymphocyte activation deficiency, the mucosal specimens showed no evidence of in situ T-cell activation. RESULTS: After development of overwhelming septicaemia, the patient died at 18 months, just before a planned bone marrow transplant. CONCLUSIONS: These findings confirm significant heterogeneity within autoimmune enteropathy. Formal immune function testing should be performed in all affected infants to identify T-cell activation deficiencies. The distinct mucosal findings suggest that activated T cells usually induce the crypt hyperplastic villous atrophy characteristic of classic autoimmune enteropathy.

Characterization of candidate live oral Salmonella typhi vaccine strains harboring defined mutations in aroA, aroC, and htrA.

The properties of two candidate Salmonella typhi-based live oral typhoid vaccine strains, BRD691 (S. typhi Ty2 harboring mutations in aroA and aroC) and BRD1116 (S. typhi Ty2 harboring mutations in aroA, aroC, and htrA), were compared in a number of in vitro and in vivo assays. BRD1116 exhibited an increased susceptibility to oxidative stress compared with BRD691, but both strains were equally resistant to heat shock. Both strains showed a similar ability to invade Caco-2 and HT-29 epithelial cells and U937 macrophage-like cells, but BRD1116 was less efficient at surviving in epithelial cells than BRD691. BRD1116 and BRD691 were equally susceptible to intracellular killing within U937 cells. Similar findings were demonstrated in vivo, with BRD1116 being less able to survive and translocate to secondary sites of infection when inoculated into the lumen of human intestinal xenografts in SCID mice. However, translocation of BRD1116 to spleens and livers in SCID mice occurred as efficiently as that of BRD691 when inoculated intraperitonally. The ability of BRD1116 to increase the secretion of interleukin-8 following infection of HT-29 epithelial cells was comparable to that of BRD691. Therefore, loss of the HtrA protease in S. typhi does not seem to alter its ability to invade epithelial cells or macrophages or to induce proinflammatory cytokines such as IL-8 but significantly reduces intracellular survival in human intestinal epithelial cells in vitro and in vivo.

Apoptosis of human intestinal epithelial cells after bacterial invasion.

Epithelial cells that line the human intestinal mucosa are the initial site of host invasion by bacterial pathogens. The studies herein define apoptosis as a new category of intestinal epithelial cell response to bacterial infection. Human colon epithelial cells are shown to undergo apoptosis following infection with invasive enteric pathogens, such as Salmonella or enteroinvasive Escherichia coli. In contrast to the rapid onset of apoptosis seen after bacterial infection of mouse monocyte-macrophage cell lines, the commitment of human intestinal epithelial cell lines to undergo apoptosis is delayed for at least 6 h after bacterial infection, requires bacterial entry and replication, and the ensuing phenotypic expression of apoptosis is delayed for 12-18 h after bacterial entry. TNF-alpha and nitric oxide, which are produced as components of the intestinal epithelial cell proinflammatory program in the early period after bacterial invasion, play an important role in the later induction and regulation of the epithelial cell apoptotic program. Apoptosis in response to bacterial infection may function to delete infected and damaged epithelial cells and restore epithelial cell growth regulation and epithelial integrity that are altered during the course of enteric infection. The delay in onset of epithelial cell apoptosis after bacterial infection may be important both to the host and the invading pathogen since it provides sufficient time for epithelial cells to generate signals important for the activation of mucosal inflammation and concurrently allows invading bacteria time to adapt to the intracellular environment before invading deeper mucosal layers.

Mucin gene expression in human embryonic and fetal intestine.

BACKGROUND: The intestinal epithelium is covered by a continuous layer of mucus which is secreted by well differentiated epithelial cells. Disregulation of the expression of mucins has been reported to have possible implications in the neoplastic process which affects intestinal mucosae. It is well known that preneoplastic and neoplastic tissues can express fetal phenotypic characteristics. AIMS: To assess whether the expression of mucin genes in the intestinal tract is linked to the stage of cellular differentiation and tissue development, by studying the expression of six mucin genes in human fetal small intestine and colon, and also adult tissues. METHODS: In situ hybridisation was used to study mRNA expression of MUC2, MUC3, MUC4, MUC5B, MUC5AC, and MUC6 in 32 human embryos and fetuses (6.5-27 weeks gestation). Normal adult mucosae were used as controls. RESULTS: Three mucin genes, MUC2, MUC4, and MUC5AC, were differently expressed in fetal intestine compared with expression in normal adults. CONCLUSION: These differences in mucin gene expression suggest a possible regulatory role for these products in intestinal epithelial cell differentiation.

Fulminant jejuno-ileitis following ablation of enteric glia in adult transgenic mice.

To investigate the roles of astroglial cells, we targeted their ablation genetically. Transgenic mice were generated expressing herpes simplex virus thymidine kinase from the mouse glial fibrillary acidic protein (GFAP) promoter. In adult transgenic mice, 2 weeks of subcutaneous treatment with the antiviral agent ganciclovir preferentially ablated transgene-expressing, GFAP-positive glia from the jejunum and ileum, causing a fulminating and fatal jejuno-ileitis. This pathology was independent of bacterial overgrowth and was characterized by increased myeloperoxidase activity, moderate degeneration of myenteric neurons, and intraluminal hemorrhage. These findings demonstrate that enteric glia play an essential role in maintaining the integrity of the bowel and suggest that their loss or dysfunction may contribute to the cellular mechanisms of inflammatory bowel disease.

Human intestinal epithelial cells respond to Cryptosporidium parvum infection with increased prostaglandin H synthase 2 expression and prostaglandin E2 and F2alpha production.

Cryptosporidium parvum is an important cause of diarrhea in humans and several animal species. Prostaglandins play a central role in regulating intestinal fluid secretion in animal models of cryptosporidiosis, but their cellular sources and mechanisms of induction are unclear. Here, we show that C. parvum infection directly activates prostaglandin H synthase 2 expression and prostaglandin E2 and F2alpha production in human intestinal epithelial cells.

Cryptosporidium parvum infection of human intestinal epithelial cells induces the polarized secretion of C-X-C chemokines.

Cryptosporidium parvum infects intestinal epithelial cells and does not invade deeper layers of the intestinal mucosa. Nonetheless, an inflammatory cell infiltrate that consists of neutrophils and mononuclear cells is often present in the lamina propria, which underlies the epithelium. This study investigated the host epithelial cell response to C. parvum by assessing in vitro and in vivo the expression and production of proinflammatory cytokines by intestinal epithelial cells after infection. The human colon epithelial cell lines HCT-8 and Caco-2 and human intestinal xenografts in SCID mice were infected with C. parvum. The expression and secretion of the C-X-C chemokines interleukin-8 (IL-8) and GROalpha were determined by reverse transcription-PCR analysis and enzyme-linked immunosorbent assay. Our results demonstrate that upregulated expression and secretion of IL-8 and GROalpha after C. parvum infection of intestinal epithelial cells first occurred 16 to 24 h after infection and increased over the ensuing 1 to 2 days. The kinetics of C-X-C chemokine production by C. parvum-infected epithelial cells contrast markedly with the rapid but transient expression of C-X-C chemokines by epithelial cells infected with invasive enteric bacteria. C-X-C chemokine secretion in C. parvum-infected epithelial cells occurred predominantly from the basolateral surface in polarized monolayers of Caco-2 cells grown in Transwell cultures, whereas cell lysis occurred at the apical surface. The basolateral secretion of IL-8 and GROalpha from C. parvum-infected epithelial cells suggests that C-X-C chemokines produced by those cells contribute to the mucosal inflammatory cell infiltrate in the underlying intestinal mucosa.

Role of intestinal epithelial cells in the host secretory response to infection by invasive bacteria. Bacterial entry induces epithelial prostaglandin h synthase-2 expression and prostaglandin E2 and F2alpha production.

Increased intestinal fluid secretion is a protective host response after enteric infection with invasive bacteria that is initiated within hours after infection, and is mediated by prostaglandin H synthase (PGHS) products in animal models of infection. Intestinal epithelial cells are the first host cells to become infected with invasive bacteria, which enter and pass through these cells to initiate mucosal, and ultimately systemic, infection. The present studies characterized the role of intestinal epithelial cells in the host secretory response after infection with invasive bacteria. Infection of cultured human intestinal epithelial cell lines with invasive bacteria, but not noninvasive bacteria, is shown to induce the expression of one of the rate-limiting enzymes for prostaglandin formation, PGHS-2, and the production of PGE2 and PGF2alpha. Furthermore, increased PGHS-2 expression was observed in intestinal epithelial cells in vivo after infection with invasive bacteria, using a human intestinal xenograft model in SCID mice. In support of the physiologic importance of epithelial PGHS-2 expression, supernatants from bacteria-infected intestinal epithelial cells were shown to increase chloride secretion in an in vitro model using polarized epithelial cells, and this activity was accounted for by PGE2. These studies define a novel autocrine/paracrine function of mediators produced by intestinal epithelial cells in the rapid induction of increased fluid secretion in response to intestinal infection with invasive bacteria.

Pig lymphocytes utilise mouse MAdCAM-1 to enter fetal gut xenografts in SCID mice.

Ileocecal junction (ICJ) and proximal intestine (PI) fragments from CD45(323-) allovariant fetal pigs were grafted subcutaneously into SCID mice. The xenografts were examined 8-12 weeks later using two-color immunohistology and the ICJ, but not PI, xenografts were found to contain three types of vessels. The first (the majority) was lined with mouse endothelium (mAb 9F1+), the second was lined with pig endothelium, and the third was chimeric. The ICJ vessels were specifically lined with mouse endothelium expressing MAdCAM-1, the mucosal addressin. Vessels lined with pig endothelium alone did not express the MAdCAM-1 epitopes. Radiolabeled allovariant pig peripheral blood lymphocytes (PBL) were introduced i.v. into the xenografted SCID mice, and entry into xenografts studied. Pig PBL were occasionally seen in MECA-367+ vessel walls after 4 h and within the ICJ but not PI xenografts after 24 h. This entry was specifically blocked by coinjection of the anti-MAdCAM-1 mAb MECA-367. The results demonstrate reendothelialization of xenografts by host endothelium that expresses its own addressin and is functional for xenogenic PBL.

The life and times of an intestinal M cell.

Intestinal M cells are specialized epithelial antigen-sampling cells, strategically located over mucosal lymphoid follicles. They regulate the entry of antigen required for mucosal immune responses. There are several potential mechanisms involved in the induction of intestinal M cells. Both luminal antigen and B cells appear to have an influence on these altered epithelial differentiation pathways.