水通道蛋白3与紧密连接的相关性

目的:探讨水通道蛋白3(aquaporin 3,AQP3)对肠黏膜上皮细胞间紧密连接(tight junction,TJ)的影响,并探讨其可能的作用机制.方法:应用Caco-2细胞系在体外构建肠黏膜上皮屏障,构建沉默AQP3的shRNA慢病毒载体,建立稳定转染细胞系.实验分为3组:空白对照组(BLANK)、阴性对照组(NC)、AQP3干扰组(AQP3 shRNA).Western blot验证TJ相关蛋白Occludin以及Claudin-1的表达情况;并且采用免疫细胞化学法观察TJ相关蛋白的分布和结构变化.结果:RT-PCR及Western blot结果显示在Caco-2细胞系中成功沉默AQP3的表达.干扰组与对照组相比下降约75%.Western blot结果显示AQP3干扰组TJ相关蛋白Occludin以及Claudin-1的表达明显降低.免疫细胞化学结果显示Caco-2细胞间Occludin以及Claudin-1主要表达在细胞膜和/或胞浆中,Occludin和Claudin-1细胞间棕褐色颗粒减少,结构变模糊.相邻Caco-2细胞间TJ结构遭到破坏.结论:靶向AQP3的shRNA技术可以引起TJ的结构变化和相关蛋白的表达分布的异常.     

Campylobacter and IFNgamma interact to cause a rapid loss of epithelial barrier integrity

BACKGROUND: The intestinal epithelium is a single layer of polarized cells and is the primary barrier separating foreign antigen and underlying lymphoid tissue. IFNgamma alters epithelial barrier function during inflammation by disrupting tight cell junctions and facilitating the paracellular transport of luminal antigens. The aim of this work was to determine whether Campylobacter infection of cells exposed to IFNgamma would lead to greater disruption of cell monolayers and hence increased bacterial translocation. METHODS: Monolayers were polarized on Transwell polycarbonate membranes for 14 days and then cultured in the presence or absence of 100 U/mL IFNgamma. Campylobacter was added to the apical side of the monolayer at an MOI of 30. Transepithelial electrical resistance (TEER) was recorded and bacteria in the basal well counted every 2 hours. Cells were stained for occludin, actin, and nuclear DNA, and cell viability determined by measurement of apoptosis. RESULTS: In the presence of IFNgamma, TEER dropped significantly after 18 hours, indicating a reduction in barrier function. A further significant decrease was seen in the presence of both IFNgamma and Campylobacter, indicating a synergistic effect, and cellular morphology and viability were affected. Bacterial translocation across the monolayer was also significantly greater in the presence of IFNgamma. CONCLUSIONS: These combined effects indicate that Campylobacter infection concomitant with intestinal inflammation would result in a rapid and dramatic loss of epithelial barrier integrity, which may be a key event in the pathogenesis of Campylobacter-mediated colitis and the development of bloody diarrhea.     

Pollen proteolytic enzymes degrade tight junctions

BACKGROUND AND OBJECTIVE: Asthma and allergic rhinitis are significant, increasing causes of morbidity worldwide. Pollen, a major cause of seasonal rhinitis/conjunctivitis, carries proteolytic enzymes on its surface. We showed previously that peptidase allergens from house dust mites compromise epithelial barrier function by degrading the extracellular domains of the tight junction proteins, occludin and claudin, thus facilitating allergen delivery across epithelial layers. In this study, we aimed to determine whether peptidases from allergenic pollens should similarly be considered to have a role in disrupting tight junctions. METHODS: Diffusates from stored pollen of Giant Ragweed, White Birch and Kentucky Blue Grass, and fresh pollen from Easter Lily were applied to confluent monolayers of Madin-Darby canine kidney (MDCK) and Calu-3 cells in serum-free medium. Immunofluorescence was performed for the tight junction proteins, occludin, claudin-1 and ZO-1. The effect of pollen diffusate on occludin was studied by Western blotting, and enzymatic activity in the diffusates was demonstrated by zymography. The ability of protease inhibitors to block the action of the diffusate on tight junctions was investigated. RESULTS: Diffusates from all four allergenic pollens caused loss of immunofluorescence labelling for tight junction proteins on MDCK and Calu-3 cells. The effect was blocked by inhibitors of serine and cysteine proteases. Degradation of occludin was demonstrated by Western blotting and zymography indicated that diffusates contain proteolytic activity. CONCLUSIONS: Pollen peptidases directly or indirectly disrupt epithelial tight junctions, and this activity should be considered as a possible mechanism for facilitating allergen delivery across epithelia.     

Oral treatment with plecanatide or dolcanatide attenuates visceral hypersensitivity via activation of guanylate cyclase-C in rat models

AIM To investigate the effects of plecanatide and dolcanatide on maintenance of paracellular permeability, integrity of tight junctions and on suppression of visceral hypersensitivity. METHODS Transport of fluorescein isothiocyanate(FITC)-dextran was measured to assess permeability across cell monolayers and rat colon tissues. Effects of plecanatide and dolcanatide on the integrity of tight junctions in Caco-2 and T84 monolayers and on the expression and localization of occludin and zonula occludens-1(ZO-1) were examined by immunofluorescence microscopy. Anti-nociceptive activity of these agonists was evaluated in trinitrobenzene sulfonic acid(TNBS)-induced inflammatory as well as in non-inflammatory partial restraint stress(PRS) rat models. Statistical significance between the treatment groups in the permeability studies were evaluated using unpaired t-tests.RESULTS Treatment of T84 and Caco-2 monolayers with lipopolysaccharide(LPS) rapidly increased permeability, which was effectively suppressed when monolayers were also treated with plecanatide or dolcanatide. Similarly, when T84 and Caco-2 monolayers were treated with LPS, cell surface localization of tight junction proteins occludin and ZO-1 was severely disrupted. When cell monolayers were treated with LPS in the presence of plecanatide or dolcanatide, occludin and ZO-1 were localized at the cell surface of adjoining cells, similar to that observed for vehicle treated cells. Treatment of cell monolayers with plecanatide or dolcanatide without LPS did not alter permeability, integrity of tight junctions and cell surface localization of either of the tight junction proteins. In rat visceral hypersensitivity models, both agonists suppressed the TNBS-induced increase in abdominal contractions in response to colorectal distension without affecting the colonic wall elasticity, and both agonists also reduced colonic hypersensitivity in the PRS model. CONCLUSION Our results suggest that activation of GC-C signaling might be involved in maintenance of barrier function, possibly through regulating normal localization of tight junction proteins. Consistent with these findings, plecanatide and dolcanatide showed potent antinociceptive activity in rat visceral hypersensitivity models. These results imply that activation of GC-C signaling may be an attractive therapeutic approach to treat functional constipation disorders and inflammatory gastrointestinal conditions.     

The coxsackievirus and adenovirus receptor is a transmembrane component of the tight junction

The coxsackievirus and adenovirus receptor (CAR) mediates viral attachment and infection, but its physiologic functions have not been described. In nonpolarized cells, CAR localized to homotypic intercellular contacts, mediated homotypic cell aggregation, and recruited the tight junction protein ZO-1 to sites of cell-cell contact. In polarized epithelial cells, CAR and ZO-1 colocalized to tight junctions and could be coprecipitated from cell lysates. CAR expression led to reduced passage of macromolecules and ions across cell monolayers, and soluble CAR inhibited the formation of functional tight junctions. Virus entry into polarized epithelium required disruption of tight junctions. These results indicate that CAR is a component of the tight junction and of the functional barrier to paracellular solute movement. Sequestration of CAR in tight junctions may limit virus infection across epithelial surfaces.     

乌司他丁对乙醇诱导的肠黏膜屏障损伤的保护作用

目的探讨乌司他丁对乙醇诱导的肠黏膜屏障损伤的保护作用。方法培养Caco-2细胞至形成肠上皮细胞屏障模型,分为空白对照组、乙醇组(终体积浓度10%)和不同浓度乌司他丁治疗组(750 U/mL、1 500 U/mL、3 000 U/mL)。测定单层上皮的跨上皮细胞电阻(TEER)及荧光素钠透过率,免疫荧光法及蛋白质免疫印迹法(Western blot)检测紧密连接蛋白ZO-1在细胞单层的定位及表达量,透射电镜观察细胞紧密连接的超微结构。结果与对照组对比,乙醇组单层细胞的TEER降低(P0.001);荧光素钠透过率升高(P0.001);免疫荧光检测显示ZO-1蛋白表达断续不完整,荧光强度弱;Western blot检测显示ZO-1蛋白表达水平降低(P0.001);透射电镜结果示细胞刷状缘受损,排列紊乱,细胞间连接模糊。乌司他丁治疗组的上述指标均改善(P均0.05),其中3 000 U/mL乌司他丁组的改善最明显(P均0.05)。结论乌司他丁对乙醇诱导的肠单层上皮细胞屏障损伤具有保护作用。     

Interferon gamma induces translocation of commensal Escherichia coli across gut epithelial cells via a lipid raft-mediated process

BACKGROUND & AIMS: The "leaky gut" hypothesis proposes that leakage of enteric bacteria into the body resulting from disruption of the epithelial barrier is a critical step in the pathophysiology of various disorders such as inflammatory bowel disease and sepsis. However, the pathways and underlying mechanisms by which commensal bacteria cross the epithelial barrier in inflammatory conditions remain unclear. This study investigated the mechanisms of interferon gamma-mediated bacterial translocation across human colonic epithelial monolayers. METHODS: Caco-2 and T84 monolayers were exposed to interferon gamma. Barrier function was assessed by transepithelial electrical resistance and lucifer yellow permeability. Internalization and translocation of Escherichia coli strain C25 were measured by quantitative bacterial culture. Expression and distribution of junctional proteins were assessed by immunoblotting and confocal imaging. RESULTS: Minimal apical to basolateral translocation of C25 was observed in untreated T84 and Caco-2 monolayers. Interferon gamma caused a dramatic, dose-dependent increase in C25 translocation, which was uncoupled from cytokine-induced increases in paracellular permeability and disruption of tight junction proteins at low interferon gamma concentrations. These effects were associated with increased internalization of viable bacteria into, but not adherence to, Caco-2 cells. Interferon gamma-mediated bacterial translocation was abolished by pretreatment with the cholesterol-disrupting drugs filipin and methyl-beta-cyclodextrin, whereas these agents had no effect on infection of Caco-2 by the enteric pathogen Shigella sonnei. CONCLUSIONS: Normally poorly invasive enteric bacteria may, in situations of inflammatory stress, exploit lipid raft-mediated transcytotic pathways to cross the intestinal epithelium, and these effects may precede cytokine-induced disruption of tight junctions.     

IFN-gamma-induced TNFR2 expression is required for TNF-dependent intestinal epithelial barrier dysfunction

BACKGROUND & AIMS: Tumor necrosis factor (TNF) plays a critical role in intestinal disease. In intestinal epithelia, TNF causes tight junction disruption and epithelial barrier loss by up-regulating myosin light chain kinase (MLCK) activity and expression. The aim of this study was to determine the signaling pathways by which TNF causes intestinal epithelial barrier loss. METHODS: Caco-2 cells that were either nontransfected or stably transfected with human TNF receptor 1 (TNFR1) or TNFR2 and mouse colonocytes were used for physiologic, morphologic, and biochemical analyses. RESULTS: Colitis induced in vivo by adoptive transfer of CD4(+)CD45RB(hi) T cells was associated with increased epithelial MLCK expression and myosin II regulatory light chain (MLC) phosphorylation as well as morphologic tight junction disruption. In vitro studies showed that TNF caused similar increases in MLCK expression and MLC phosphorylation, as well as barrier dysfunction, in Caco-2 monolayers only after interferon (IFN)-gamma pretreatment. This reductionist model was therefore used to determine the molecular mechanism by which IFN-gamma and TNF synergize to cause intestinal epithelial barrier loss. IFN-gamma priming increased TNFR1 and TNFR2 expression, and blocking antibody studies showed that TNFR2, but not TNFR1, was required for TNF-induced barrier dysfunction. Transgenic TNFR2, but not TNFR1, expression allowed IFN-gamma-independent TNF responses. CONCLUSIONS: IFN-gamma primes intestinal epithelia to respond to TNF by inducing TNFR2 expression, which in turn mediates TNF-induced MLCK-dependent barrier dysfunction. The data further suggest that epithelial TNFR2 blockade may be a novel approach to restore barrier function in intestinal disease.     

Fatty acids and epithelial permeability: effect of conjugated linoleic acid in Caco-2 cells

Conjugated linoleic acid (CLA) is a collective term referring to the positional and geometric isomers of linoleic acid. This novel fatty acid has been shown to have a number of beneficial actions, including immunomodulatory, anticarcinogenic, and antiatherogenic effects. Tight junctions of epithelial cells determine epithelial membrane integrity and selective paracellular permeability to ions and macromolecules. Occludin and ZO-1 are integral structural components of the tight junction, which are involved in the biogenesis and functional integrity of the epithelial monolayer. This study investigated the effects of two isomers of CLA (cis-9 and trans-10 isomers) on Caco-2 cell transepithelial resistance (TER) development, paracellular epithelial permeability, and occludin and ZO-1 expression. Caco-2 cells were grown in media supplemented with 0.05 mM linoleic acid, cis-9 CLA, or trans-10 CLA for 21 days. The trans-10 CLA isomer delayed Caco-2 cell TER development, which is an in vitro measure of epithelial cell integrity, and increased paracellular epithelial permeability. Immunofluorescent staining of Caco-2 cell epithelial monolayers grown in media supplemented trans-10 CLA showed that the trans-10 CLA isomer altered distribution of occludin and ZO-1. The trans-10 CLA isomer delayed the acquisition of transepithelial resistance and altered the cellular distribution of occludin, which have important implications in relation to epithelial permeability.     

Modulation of barrier function during Fas-mediated apoptosis in human intestinal epithelial cells

BACKGROUND & AIMS: Intestinal epithelial cell apoptosis occurs continually without apparent permeability defects and is increased in response to intestinal inflammation. We hypothesized that increased, immune-mediated apoptosis during inflammation might result in barrier dysfunction of the epithelium. METHODS: T84 cells were cultured as a polarized monolayer and exposed to agonist antibody to Fas. Barrier function was assessed by transepithelial resistance and permeability measurements. Immunofluorescent staining was used to examine junctional protein expression. RESULTS: Fas expression is predominantly basolateral in polarized T84 monolayers. Basolateral cross-linking of the Fas receptor resulted in T84 cell apoptosis and a loss of 50% of the cells within 24 hours. Apoptosis was coincident with a decrease in transepithelial electrical resistance and increased flux of small but not large molecules. Preservation of barrier function was associated with dramatic rearrangement of tight junctions and desmosomal junctions in apoptotic monolayers. E-cadherin-mediated cell contact was maintained between intact cells in the monolayer, thus sealing gaps created by apoptotic cells. Apoptosis and barrier dysfunction could be prevented by caspase inhibition. CONCLUSIONS: Immune-mediated apoptosis of intestinal epithelial cells may contribute to the permeability defects associated with inflammatory conditions of the bowel, but the intestinal epithelium is remarkably resilient in the face of apoptosis.     

Restoration of impaired intestinal barrier function by the hydrolysed casein diet contributes to the prevention of type 1 diabetes in the diabetes-prone BioBreeding rat

Aims/hypothesis

Impaired intestinal barrier function is observed in type 1 diabetes patients and animal models of the disease. Exposure to diabetogenic antigens from the intestinal milieu due to a compromised intestinal barrier is considered essential for induction of the autoimmune process leading to type 1 diabetes. Since a hydrolysed casein (HC) diet prevents autoimmune diabetes onset in diabetes-prone (DP)-BioBreeding (BB) rats, we studied the role of the HC diet on intestinal barrier function and, therefore, prevention of autoimmune diabetes onset in this animal model.

Methods

DP-BB rats were fed the HC diet from weaning onwards and monitored for autoimmune diabetes development. Intestinal permeability was assessed in vivo by lactulose–mannitol test and ex vivo by measuring transepithelial electrical resistance (TEER). Levels of serum zonulin, a physiological tight junction modulator, were measured by ELISA. Ileal mRNA expression of Myo9b, Cldn1, Cldn2 and Ocln (which encode the tight junction-related proteins myosin IXb, claudin-1, claudin-2 and occludin) and Il-10, Tgf-ß (also known as Il10 and Tgfb, respectively, which encode regulatory cytokines) was analysed by quantitative PCR.

Results

The HC diet reduced autoimmune diabetes by 50% in DP-BB rats. In DP-BB rats, prediabetic gut permeability negatively correlated with the moment of autoimmune diabetes onset. The improved intestinal barrier function that was induced by HC diet in DP-BB rats was visualised by decreasing lactulose:mannitol ratio, decreasing serum zonulin levels and increasing ileal TEER. The HC diet modified ileal mRNA expression of Myo9b, and Cldn1 and Cldn2, but left Ocln expression unaltered.

Conclusions/interpretation

Improved intestinal barrier function might be an important intermediate in the prevention of autoimmune diabetes by the HC diet in DP-BB rats. Effects on tight junctions, ileal cytokines and zonulin production might be important mechanisms for this effect.     

Calcium glycerophosphate preserves transepithelial integrity in the Caco-2 model of intestinal transport

AIM:To assess the direct effects of ischemia on intestinal epithelial integrity. Furthermore,clinical efforts at mitigating the effect of hypoperfusion on gut permeability have focused on restoring gut vascular function. METHODS:We report that,in the Caco-2 cell model of transepithelial transport,calcium glycerophosphate(CGP),an inhibitor of intestinal alkaline phosphatase F3,has a significant effect to preserve transepithelial electrical resistance(TEER) and to attenuate increases in mannitol flux rates during hypoxia or cytokine stimulation. RESULTS:The effect was observable even at concentrations as low as 1 μmol/L. As celiac disease is also marked by a loss of gut epithelial integrity,the effect of CGP to attenuate the effect of the α-gliadin peptide 31-55 was also examined. In this instance,CGP exerted little effect of preservation of TEER,but significantly attenuated peptide induced increase in mannitol flux. CONCLUSION:It appears that CGP treatment might synergize with other therapies to preserve gut epithelial integrity.     

Effect of alcohol on miR-212 expression in intestinal epithelial cells and its potential role in alcoholic liver disease

Background and Aims:  Alcohol-induced gut leakiness is a key factor in alcoholic liver disease (ALD); it allows endotoxin to enter the circulation and initiate liver damage. Zonula occludens 1 (ZO-1) protein is a major component of tight junctions that regulates intestinal permeability. microRNAs (miRNAs) are recently discovered regulatory molecules that inhibit expression of their target genes. The aims of our study were: (i) to investigate the effect of alcohol on miRNA-212 (miR-212) and on expression of its predicted target gene, ZO-1, (ii) to study the potential role of miR-212 in the pathophysiology of ALD in man.
Methods:  Using a TaqMan miRNA assay system, we measured miR-212 expression levels in colon biopsy samples from patients with ALD and in Caco-2 cells (a human intestinal epithelial cell line) treated with or without EtOH. We measured ZO-1 protein levels using western blots. ZO-1 mRNA was assayed using real-time PCR. Intestinal barrier integrity was measured using fluorescein sulfonic acid clearance and immunofluorescent staining for ZO-1.
Results:  Ethanol increased miR-212 expression, decreased ZO-1 protein levels, disrupted tight junctions, and increased the permeability of monolayers of Caco-2 cells. An miR-212 over-expression is correlated with hyperpermeability of the monolayer barrier. miR-212 levels were higher in colon biopsy samples in patients with ALD than in healthy controls; ZO-1 protein levels were lower.
Conclusion:  These data suggest a novel mechanism for alcohol-induced gut leakiness, one in which EtOH induces miR-212 over-expression which causes gut leakiness by down-regulating ZO-1 translation. This mechanism is a potential therapeutic target for leaky gut in patients with or at risk for ALD.     

Reproductive age-related changes in the blood brain barrier: Expression of IgG and tight junction proteins

We previously demonstrated that there is a significantly greater transfer of intravenously-injected Evan's blue dye into the forebrain of acyclic (reproductive senescent) females compared to young adult females, indicating that blood brain barrier permeability is compromised in the reproductive senescent forebrain. The present study examined brain IgG expression and microvessel tight junction proteins to assess ovarian age-related changes in microvascular permeability, and further compared young and senescent females with age-matched males to distinguish changes attributable to age and reproductive senescence. Blood brain barrier breakdown are often associated with increased extravasation of plasma proteins and high levels of immunoglobulin G (IgG) in brain. In the present study, IgG expression was dramatically increased in the hippocampus and thalamus, but not the hypothalamus of reproductive senescent females compared to young adult females. In males, IgG expression was increased in all these regions in middle-aged animals (aged-matched to senescent females) as compared to young males (age-matched to the young adult females). Furthermore, the proportion of hippocampal microvessels with perivascular IgG immunoreactivity was significantly greater in reproductive senescent females as compared to young adult females, while middle-aged males and young adult males did not differ. The tight junctions between adjacent microvascular endothelial cells regulated by transmembrane proteins such as claudin-5 and occludin play a critical role in maintaining the blood brain barrier integrity. Increased hippocampal IgG expression in senescent females was paralleled by poor junctional localization of the tight junction protein claudin-5 in hippocampal microvessels. However, there was no difference in hippocampal claudin-5 localization between young adult and middle-aged males, indicating that dysregulation of this junctional protein was associated with ovarian aging. Parallel studies in human brain microvessels also revealed age-dependent disruption in claudin-5 distribution in post-menopausal women compared to pre-menopausal women. Collectively, these data support the hypothesis that constitutive loss of barrier integrity in the forebrain during reproductive senescence may be due, in part, to the selective loss of tight junction proteins in endothelial junctions.     

Structure and function of tight junctions. Role in intestinal barrier

The tight junctions are narrow belts that circumferentially surround the upper part of the lateral surfaces of the adjacent epithelial cells to create fusion points or "kisses". They are involved in maintaining the cellular polarity and in the establishment of compositionally distinct fluid compartments in the body. Tight junctions are formed by many specific proteins and are connected with the cytoskeleton. In contrast to what might be expected, the intestinal tight junctions are highly dynamic areas and their permeability can change in response to both external and intracellular stimuli. In fact, the tight junctions play an important role in the regulation of the passive transepithelial movement of molecules. A number of signalling molecules have been implicated in the regulation of tight junction function, including Ca++, protein kinase C, G proteins, phospholipase A2 and C. In many intestinal and systemic diseases, changes in intestinal permeability are related to alteration of tight junctions as an expression of intestinal barrier damage. Moreover, permeability of the tight junctions can be modified by bacterial toxins, cytokines, hormones and drugs. A better understanding of tight junction structure, biogenesis and regulation mechanisms should throw further light on the intestinal barrier functions and suggest innovative therapeutic strategies.     

Combined probiotic bacteria promotes intestinal epithelial barrier function in interleukin-10-gene-deficient mice

AIM:To investigate the protective effects of combinations of probiotic(Bifico)on interleukin(IL)-10-genedeficient(IL-10 KO)mice and Caco-2 cell monolayers.METHODS:IL-10 KO mice were used to assess the benefits of Bifico in vivo.IL-10 KO and control mice received approximately 1.5×108 cfu/d of Bifico for 4 wk.Colons were then removed and analyzed for epithelial barrier function by Ussing Chamber,while an ELISA was used to evaluate proinflammatory cytokines.The colon epithelial cell line,Caco-2,was used to test the benefit of Bifico in vitro.Enteroinvasive Escherichia coli(EIEC)and the probiotic mixture Bifico,or single probiotic strains,were applied to cultured Caco-2 monolayers.Barrier function was determined by measuring transepithelial electrical resistance and tight junction protein expression.RESULTS:Treatment of IL-10 KO mice with Bifico partially restored body weight,colon length,and epithelial barrier integrity to wild-type levels.In addition,IL-10 KO mice receiving Bifico treatment had reduced mucosal secretion of tumor necrosis factor-αand interferon-γ,and attenuated colonic disease.Moreover,treatment of Caco-2 monolayers with Bifico or singlestrain probiotics in vitro inhibited EIEC invasion and reduced the secretion of proinflammatory cytokines.CONCLUSION:Bifico reduced colon inflammation in IL-10 KO mice,and promoted and improved epithelialbarrier function,enhanced resistance to EIEC invasion,and decreased proinflammatory cytokine secretion.     

肠致病性大肠杆菌改变肠道上皮细胞极性的研究进展

上皮细胞构成了宿主阻止病原微生物入侵机体的生理屏障。细胞间连接,主要是紧密连接,将上皮细胞特殊的顶端和基底外侧膜位点分开,形成极化的上皮细胞,用于维持顶端-基底极性。肠致病性大肠杆菌通过破坏感染位点多种因素导致顶端-基底极性消失,包括上皮细胞屏障结构、黏附和极性蛋白的分布,以及极性复合物。本文主要阐述了紧密连接在维持上皮细胞极性中的作用、肠致病性大肠杆菌对紧密连接的破坏作用、肠致病性大肠杆菌对上皮细胞极性的影响及其作用机制,为肠致病性大肠杆菌作用机制的研究和防御措施提供参考。