Intestinal Epithelial Response Research Articles

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.

Enteroinvasive bacteria directly activate expression of iNOS and NO production in human colon epithelial cells.

In these studies, we investigated whether bacterial infection of human colon epithelial cells is a sufficient stimulus to upregulate epithelial cell expression of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production. Human colon epithelial cells (Caco-2 and HT-29) rapidly upregulated iNOS mRNA and protein expression and NO production after infection with enteroinvasive Escherichia coli, Salmonella dublin, or Shigella flexneri but not after infection with noninvasive E. coli or an invasion-deficient mutant of S. dublin. Bacterial infection in the absence of added cytokines was as potent or more potent a stimulus of iNOS expression and NO production as stimulation of cells with combinations of cytokines known to strongly upregulate this epithelial cell response. Enteroinvasive E. coli increased epithelial NO production to a greater extent than S. dublin, although S. dublin was a stronger stimulus of epithelial cell interleukin-8 (IL-8) production. After enteroinvasive E. coli infection of polarized epithelial cell monolayers, nitrite, a stable NO end product, was released predominately into the apical compartment early after infection, whereas IL-8 was released in parallel into the basolateral compartment. These studies suggest NO and/or its redox products are an important component of the intestinal epithelial cell response to microbial infection.

Ion, fluid and charge transport across Necturus intestinal epithelium in response to alanine.

Fluxes of Na, Cl and volume were followed across Necturus small intestine under zero voltage clamp. 20 mM L-alanine doubles the net Na and fluid transfer. Although there is a ouabain-sensitive Na pump present in Necturus a major fraction of the net Na flux can be measured for an hour after application of 10(-3) M ouabain. Collected fluid transferred by the epithelium is quasi-isotonic over a range of luminal osmolarities from 100 to 250 milliosmolar in alanine saline. The net Na fluxes account for the Na found in this transported fluid. Fluid transfer also shows a large ouabain-insensitive fraction after the addition of alanine. Compartmental analysis of 22Na-loaded epithelium was used to separate cellular and paracellular fluxes. The estimated Na concentration in the cell derived from its Na content is 9-10 mM, in agreement with that determined with microelectrodes. The Na efflux from cell to serosa is stimulated by alanine, but this increase accounts for only a quarter of the simultaneous rises in Na, fluid and current flow across the epithelium. The increase of Na efflux from the cell induced by alanine is apparently insensitive to ouabain although the cell Na content rises to circa 20 mM but no higher even after 20 hr. From the initial rate of rise of Na in the cell on treatment with ouabain the activity of the Na pump can be estimated to be approximately 92 pM/cm2 . sec, a value much smaller than the transepithelial net flux. The results are not consistent with the standard model in which Na-alanine influx stimulates the Na pump and enhances fluid transport by osmotic coupling in the lateral interspace system. A scheme is proposed based upon that for absorption in Necturus gallbladder by which alanine stimulates an active paracellular fluid transfer driven by motile elements of the junction.

Immunocytochemical expression of the 70 kD heat shock protein in ischaemic bowel disease.

Heat shock proteins (HSPs) are a family of polypeptides which are induced in response to diverse forms of cell injury including hyperthermia, anoxia, ethanol, heavy metals, and others, with a presumably protective function. Among several species of HSPs, the 70 kD protein (HSP70) is the most abundant and consistently induced in mammalian cells. Anti-HSP70 monoclonal antibody and a standard immunocytochemical method were used to study the expression of HSP70 in 28 surgical specimens of small and large intestines from patients with ischaemic bowel disease. Strong immunoreactivity was observed in viable, regenerating cells of both the crypt and surface epithelium within or adjacent to the necrotic foci in 86 per cent of the ischaemic bowel specimens. Staining was mostly cytoplasmic, but focally both cytoplasmic and nuclear. Smooth muscle cells of the muscularis mucosae in the ischaemic areas of some cases also showed immunoreactivity. On the other hand, HSP70 was not expressed in control specimens of small and large intestine or in colonic specimens of Crohn's disease, ulcerative colitis, and adenocarcinoma. These findings suggest a possible role of HSP70 in intestinal epithelial and smooth muscle cell response to ischaemic injury, especially in the recovery phase.

Human eosinophils migrate across an intestinal epithelium in response to platelet-activating factor

Background/Aims: Transmigration of eosinophils across intestinal epithelia occurs in a variety of mucosal inflammatory disorders and results in the formation of crypt abscesses containing eosinophils. However, the conditions required to drive transepithelial migration of eosinophils are not understood. Methods: This study investigated eosinophil migration across intestinal epithelia using purified eosinophils and confluent monolayers of the human intestinal epithelial cell line T84. Results: Unactivated eosinophils (i.e., no granulocyte/macrophage colony-stimulating factor [GM-CSF] preexposure) did not migrate across T84 monolayers in the presence of transepithelial gradients of C5a, n-formyl-methionyl-leucyl-phenylalanine (fMLP), or platelet-activating factor (PAF). In contrast, activation of eosinophils by coincubation or pretreatment with GM-CSF enabled transepithelial migration in response to PAF but not to C5a or fMLP gradients in a time- and dose-dependent fashion. Specificity was confirmed by both the PAF receptor antagonist WEB-2086 and the PAF enantiomer 2-lyso-β-acetyl-γ-O-hexadecyl. Finally, addition of functionally inhibitory monoclonal antibodies to CD11b but not CD11a, very late activation antigen (VLA-4), or intracellular adhesion molecule 1 inhibited eosinophil migration. Conclusions: These studies establish that physiologically directed migration of eosinophils across model epithelia occurs but that this process is governed by the state of eosinophil activation, the specific chemotactic gradient imposed, and the availability of specific surface integrins to participate in putative eosinophil-epithelial adhesion steps.

In vivo immediate early gene expression induced in intestinal and colonic mucosa by feeding

Since the gut responds rapidly to food intake, the levels of expression of several immediate early genes were measured in mucosa from small and large intestine of rats starved for 3 days or refed. Within 1 h of refeeding, jejunal and ileal c-fos, jun B and zif/268 mRNA and colonil zif/268 dramatically increased. The zif/268 gene in jejunum corresponded in size to the full-length cDNA but. in ileum, an RNA band of about 1.2 kb in size increased greatly after feeding. This represents a physiologic in vivo model for the study of gene regulation associated with intestinal epithelial cellular responses to feeding.