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D M McKay

Publications and source records attributed to D M McKay.

At least 37 records · Page 2Linked to original sources
PubMed1999

Superantigen immune stimulation evokes epithelial monocyte chemoattractant protein 1 and RANTES production.

Bacterial superantigens (SAgs) have been implicated in inflammatory disease, and SAg-treated mice have increased jejunal T cells. Here we show that T84 cells (a human epithelial cell line) display increased MCP-1 and RANTES mRNA expression and protein production in response to conditioned medium from Staphylococcus aureus enterotoxin B (SEB; a model SAg)-activated immune cells. Also, MCP-1 and RANTES mRNAs were increased in jejunal enterocytes isolated from SEB-treated mice. We suggest that T-cell recruitment to the gut following SAg immune activation could be partially due to epithelium-derived chemokines.

Budesonide↗
PubMed1999

Characterization of enteric functional changes evoked by in vivo anti-CD3 T cell activation.

Specific in vivo T cell activation initiated by treatment with anti-CD3 antibodies leads to diarrhea and structural damage of the intestinal mucosa. In this study, the effect of T cell-induced mucosal damage on jejunal epithelial ion transport, muscle contractility, and neuronal ACh release was assessed in Ussing chambers, organ baths, and a specialized perfusion apparatus, respectively. Time-matched control mice received hamster serum containing irrelevant antibodies. Jejunal segments from anti-CD3-treated mice displayed a significantly elevated epithelial baseline short-circuit current (which indicates increased ion transport) and a concomitant reduction in responsiveness to prosecretory stimuli (nerve stimulation, carbachol, and forskolin). Longitudinal smooth muscle displayed altered spontaneous contractile activity, length-tension relationships, and carbachol-stimulated contraction in tissues excised from mice 20 and 40 h posttreatment. Anti-CD3 treatment did not affect stimulated ACh release from myenteric plexus neurons. We conclude that specific T cell activation via anti-CD3 antibody results in dramatic alterations in jejunal epithelial and smooth muscle function. Such T cell-induced changes in intestinal function may contribute to the symptomatology of T cell-mediated enteropathies, including graft-versus-host disease, celiac disease, and idiopathic inflammatory bowel disease.

Acetylcholine↗
PubMed1999

Immune-epithelial interactions in host defense.

Over the past 15 years, it has become very clear that the immune system can have profound effects on epithelial function. Acute immune-mediated changes in epithelial physiology are beneficial to host defense against enteric pathogens. For example, ion secretion washes out noxious luminal contents and increased permeability allows phagocytic cells and antibodies to enter the gut lumen. However, ongoing immune activation results in chronic effects that may be pathophysiologic. Responses are mediated by soluble immune mediators that act directly on the epithelium, or indirectly via nerves that also serve to amplify the epithelial response. Here, we will review some of the recent advances that have been made in the field of immunophysiology. The effect of mast cells on transport functions of the epithelium will be reviewed, with emphasis on the consequence of interactions between mast cells and nerves. The use of in vitro coculture systems has recently provided considerable information on the effects of neutrophils, eosinophils, monocytes, and lymphocytes on epithelial functions; the contribution of each immunocyte will be highlighted. Finally, we will describe evidence for the active participation of the epithelium in mucosal immune activation, including pathogen or cytokine induced epithelial cytokine synthesis or secretion and adhesion molecule expression.

Animals↗
PubMed1999

Improved effects of novel glucocorticosteroids on immune-induced epithelial pathophysiology.

Glucocorticosteroids are a mainstay therapy in inflammatory bowel disease and other chronic inflammatory conditions. However, severe systemic side effects are associated with their long-term use. The new generation of glucocorticosteroids have a high degree of topical activity with reduced systemic effects due to rapid metabolism. We previously described an in vitro model of inflammation in which monolayers of the human T84 colonic epithelial cell line displayed altered ion secretion and increased permeability after coculture with endotoxin-activated monocytes/macrophages (MPhi). Here, we tested the effects of budesonide and two novel analogs, D5519 and S1316, on MPhi-induced epithelial changes. Filter-grown T84 monolayers were cocultured with activated MPhi and single daily doses of drug were added to the luminal (physiological) side of the monolayer. Basal and stimulated epithelial ion transport [baseline short-circuit current (Isc) and DeltaIsc to forskolin, respectively] and barrier (transepithelial resistance) parameters were measured 48 h later in Ussing chambers. D5519, S1316, and budesonide (10(-7) to 10(-9) M) dose dependently inhibited the MPhi-induced epithelial abnormalities, restoring normal resistance, decreasing the elevated baseline Isc, and improving the reduced Isc response to forskolin. Of the drugs tested, D5519 was consistently the most potent and effective in inhibiting the MPhi-induced epithelial irregularities. Coupled with a further improvement in their rate of hepatic inactivation, our findings indicate that the novel steroids, particularly D5519, will be a valuable addition to current treatment strategies for inflammatory bowel disease and other chronic inflammatory conditions.

Budesonide↗
PubMed1998

Signal transduction pathways involved in enterohemorrhagic Escherichia coli-induced alterations in T84 epithelial permeability.

Enterohemorrhagic Escherichia coli (EHEC) infection is associated with watery diarrhea and can lead to complications, including hemorrhagic colitis and the hemolytic-uremic syndrome. The mechanisms by which these organisms produce diarrheal disease remain to be elucidated. Changes in T84 epithelial cell electrophysiology were examined following EHEC infection. T84 cell monolayers infected with EHEC O157:H7 displayed a time-dependent decrease in transepithelial resistance. Increases in the transepithelial flux of both [3H]mannitol and 51Cr-EDTA accompanied the EHEC-induced decreases in T84 resistance. Altered barrier function induced by EHEC occurred at the level of the tight junction since immunofluorescent staining of the tight-junction-associated protein ZO-1 was disrupted when examined by confocal microscopy. Decreased resistance induced by EHEC involved a protein kinase C (PKC)-dependent pathway as the highly specific PKC inhibitor, CGP41251, abrogated the EHEC-induced drop in resistance. PKC activity was also increased in T84 cells infected with EHEC. Calmodulin and myosin light chain kinase played a role in EHEC-induced resistance changes as inhibition of these effector molecules partially reversed the effects of EHEC on barrier function. These studies demonstrate that intracellular signal transduction pathways activated following EHEC infection link the increases in T84 epithelial permeability induced by this pathogen.

Calmodulin↗
PubMed1998

Changes in murine jejunal morphology evoked by the bacterial superantigen Staphylococcus aureus enterotoxin B are mediated by CD4+ T cells.

Bacterial superantigens (SAgs) are potent T-cell stimuli that have been implicated in the pathophysiology of autoimmune and inflammatory disease. We used Staphylococcus aureus enterotoxin B (SEB) as a model SAg to assess the effects of SAg exposure on gut form and cellularity. BALB/c, SCID (lacking T cells) and T-cell-reconstituted SCID mice were treated with SEB (5 or 100 microg intraperitoneally), and segments of the mid-jejunum were removed 4, 12, or 48 h later and processed for histochemical or immunocytochemical analysis of gut morphology and major histocompatibility complex class II (MHC II) expression and the enumeration of CD3+ T cells and goblet cells. Control mice received saline only. SEB treatment of BALB/c mice caused a time- and dose-dependent enteropathy that was characterized by reduced villus height, increased crypt depth, and a significant increase in MHC II expression. An increase in the number of CD3+ T cells was observed 48 h after exposure to 100 microg of SEB. Enteric structural alterations were not apparent in SEB-treated SCID mice compared to saline-treated SCID mice. In contrast, SEB challenge of SCID mice reconstituted with a mixed lymphocyte population or purified murine CD4+ T cells resulted in enteric histopathological changes reminiscent of those observed in SEB-treated BALB/c mice. These findings implicate CD4+ T cells in this SEB-induced enteropathy. Our results show that SAg immune activation causes significant changes in jejunal villus-crypt architecture and cellularity that are likely to impact on normal physiological processes. We speculate that the elevated MHC II expression and increased number of T cells could allow for enhanced immune responsiveness to other SAgs or environmental antigens.

Animals↗
PubMed1998

Monocyte/macrophages evoke epithelial dysfunction: indirect role of tumor necrosis factor-alpha.

We examined the ability of monocytes (MPhi) activated by bacterial products to alter epithelial physiology. Confluent monolayers of the T84 colonic epithelial cell line were grown on filter supports and then cocultured in the presence of human MPhi with or without the activating agents bacterial lipopolysaccharide and the bacterial tripeptide formyl-methionyl-leucyl-phenylalanine. After 24 or 48 h, monolayers were mounted in Ussing chambers where parameters of epithelial function were measured. Exposure to activated MPhi resulted in a significant increase (P < 0.05) in baseline short-circuit current (250% after 48 h) that was associated with enhanced secretion of Cl-. In addition, epithelial permeability was significantly increased as shown by reduced transepithelial resistance and increased flux of 51Cr-EDTA. Activated MPhi produced substantial amounts (approximately 3 ng/ml at 48 h) of tumor necrosis factor-alpha (TNF-alpha). TNF-alpha was identified as a key mediator acting via an autocrine mechanism to induce epithelial pathophysiology. Our data show that MPhi, when activated by common bacterial components, are potent effector cells capable of initiating significant changes in the transport and barrier properties of a model epithelium.

Adult↗
PubMed1998

CD4+ T cells mediate superantigen-induced abnormalities in murine jejunal ion transport.

The immunomodulatory properties of bacterial superantigens (SAgs) have been defined, yet comparatively little is known of how SAgs may affect enteric physiology. Staphylococcus aureus enterotoxin B (SEB) was used to examine the ability of SAgs to alter epithelial ion transport. BALB/c mice, severe combined immunodeficient (SCID, lack T cells) mice, or SCID mice reconstituted with lymphocytes or CD4+ T cells received SEB intraperitoneally, and jejunal segments were examined in Ussing chambers; controls received saline only. Baseline short-circuit current (Isc, indicates net ion transport) and Isc responses evoked by electrical nerve stimulation, histamine, carbachol, or forskolin were recorded. Serum levels of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) were measured. SEB-treated BALB/c mice showed elevated serum IL-2 and IFN-gamma levels, and jejunal segments displayed a time- and dose-dependent increase in baseline Isc compared with controls. Conversely, evoked ion secretion was selectively reduced in jejunum from SEB-treated mice. Elevated cytokine levels and changes in jejunal Isc were not observed in SEB-treated SCID mice. In contrast, SCID mice reconstituted with T cells were responsive to SEB challenge as shown by increased cytokine production and altered jejunal Isc responses that were similar to those observed in jejunum from SEB-treated BALB/c mice. We conclude that exposure to a model bacterial SAg causes distinct changes in epithelial physiology and that these events can be mediated by CD4+ T cells.

Animals↗
PubMed1998

Epithelial ion transport and barrier abnormalities evoked by superantigen-activated immune cells are inhibited by interleukin-10 but not interleukin-4.

Many studies have indicated an association between bacteria and the severity of enteric secretory or inflammatory disorders. We previously showed that monolayers of human T84 epithelial cells display altered ion transport and permeability after coculture with Staphylococcus aureus enterotoxin B (SEB, a model superantigen)-activated immune cells, where interferon-gamma and tumor necrosis factor-alpha were key mediators in the pathophysiology. Here we examined whether the regulatory Th2-type cytokines, interleukin (IL)-10 and IL-4, could prevent these epithelial irregularities. T84 monolayers were cocultured with human peripheral blood mononuclear cells (PBMC) or T cell-enriched, monocyte-depleted PBMC (T + B cells) +/- SEB for 20 hr in the presence or absence of IL-10 or IL-4. Subsequently, T84 monolayers were mounted in Ussing chambers and ion transport (short-circuit current (Isc) and DeltaIsc evoked by forskolin) and permeability (ion resistance and probe fluxes) were assessed. IL-10 dose-dependently inhibited the increased T84 permeability and the reduced responsiveness to forskolin that were evoked by coculture with SEB-activated PBMC or T + B cells. Similar changes in T84 function occurred in response to conditioned medium from SEB-activated immune cells; however, addition of IL-10 to the conditioned medium did not prevent the changes in epithelial function. In contrast, when PBMC were stimulated with SEB in the presence of IL-10, the subsequent conditioned medium was less effective in evoking altered epithelial function. These data suggest that the affect of IL-10 was due to effects on the immune cells and not directly on the epithelium. In contrast to IL-10, IL-4 did not ameliorate any of the immune-mediated changes in T84 function. We conclude that IL-10 can reduce the epithelial functional changes caused by SEB-activated immune cells and this data adds further support for IL-10 immunotherapy in the treatment of intestinal secretory or inflammatory disorders.

Cell Line↗
PubMed1997

Superantigen activation of immune cells evokes epithelial (T84) transport and barrier abnormalities via IFN-gamma and TNF alpha: inhibition of increased permeability, but not diminished secretory responses by TGF-beta2.

Superantigens (SAgs) are extremely potent stimulants of T cell activity that have been implicated in the etiopathophysiology of inflammatory disease. Here, we tested the hypothesis that Staphylococcus aureus enterotoxin B (SEB), a model SAg, can alter epithelial transport and/or barrier functions via immune stimulation. Confluent monolayers of the human colonic T84 epithelial cell line, grown on filter supports, were cocultured with SEB +/- PBMC. Subsequently, T84 transport (consisting of baseline short-circuit current (Isc, indicates net ion transport) and secretory responses to carbachol and forskolin) and barrier functions (consisting of transepithelial resistance and fluxes of 3H-labeled mannitol and 51Cr-EDTA) were examined in Ussing chambers. T84 monolayers cocultured with SEB-activated PBMC displayed a time- and dose-dependent decrease in secretory responses to carbachol and forskolin and a significant increase in permeability. These dramatic changes in epithelial function were not due to reduced epithelial viability. Neutralizing Abs to IFN-gamma partially prevented the transport abnormalities, and Abs to TNF-alpha inhibited the increase in epithelial permeability. Abs to IL-1beta and IL-6 did not modulate the SEB-activated PBMC-induced T84 pathophysiology. Addition of TGF-beta2 to conditioned medium from SEB-activated PBMC partially inhibited the increase in T84 permeability but did not affect the transport abnormalities. We conclude that SAgs can elicit epithelial irregularities characteristic of enteric inflammation and that IFN-gamma and TNF-alpha are key mediators in this coculture model of epithelial dysfunction. Additionally, we would highlight the role that TGF-beta2 may play in preventing prolonged increases in epithelial permeability.

Adult↗
PubMed1997

A role for the enteric nervous system in the response to helminth infections.

The enteric nervous system (ENS) in the gut contains a particularly high concentration of nerve cells, and effectively functions as an independent 'minibrain'. Interactions between nerve, endocrine, immune and other cell types allow the sophisticated regulation of normal gut physiology. They can also bring about a co-ordinated response to parasitic infection, possibly leading to expulsion of the parasite. In this review, Derek McKay and Ian Fairweather will consider, in brief, data pertaining to changes in the ENS following intestinal helminth infections and speculate on the role that these alterations may have in the expulsion of the parasite burden and the putative ability of the parasite to modulate these events.

Journal Article↗
PubMed1997

Review article: In vitro models in inflammatory bowel disease research--a critical review.

Research efforts in inflammatory bowel disease (IBD) have been directed towards the epithelium as it has become clear that epithelial cells play a critical role in inflammatory response. Most research involving IBD employs in vitro techniques. In vitro epithelial cell studies have played and are continuing to play a major role in providing specific information relevant to IBD. Thus, such studies have provided irrefutable evidence that epithelial responses can be induced by microbes/microbial products and by immune activation. Culture experiments have provided insights into the effects of individual cytokines and other inflammatory mediators on epithelial pathophysiology, injury and repair, apoptosis, necrosis, and other processes that may be involved in IBD. Activated epithelial cells can participate in and even orchestrate immune responses, by stimulating T cells (and possibly others) and by producing cytokines that recruit specific inflammatory cells. Physiological regulation of epithelial tight junctions has been demonstrated by in vitro studies; the implication of this information for treating IBD is just beginning to be explored. It is becoming increasingly clear that epithelial processing and presentation of antigens is critical to the outcome of the immune response.

Animals↗
PubMed1996

Nippostrongylus brasiliensis infection evokes neuronal abnormalities and alterations in neurally regulated electrolyte transport in rat jejunum.

Neuronal abnormalities have been described in the intestine of helminth-infected rats. However, the physiological ramifications of these changes have not been determined. Here, we examined epithelial ion secretion, indicated by increases in short-circuit current (Isc), evoked by electrical transmural stimulation (TS) of enteric nerves in Ussing-chambered jejunal tissues from Nippostrongylus brasiliensis-infected rats. Rats were examined at 10 and 35 days post-infection (p.i.); non-infected rats served as controls. TS resulted in significantly reduced ion secretion in jejunum from 10 day p.i. rats compared to controls or jejunum from 35 day p.i. rats. The TS response in tissue from infected rats had, unlike controls, no cholinergic component. Tissues from both non-infected and infected rats were equally responsive to the muscarinic agonist bethanechol, suggesting that the cholinergic defect was neuronal and not an inability of the epithelium to respond to cholinergic stimulation. However, increases in Isc evoked by exogenous substance P (SP) in tissue from rats 10 day p.i. were reduced in magnitude to approximately 25% of control values. Concomitant with these physiological changes, tissue from infected rats contained increased amounts of substance P immunoreactivity and intestinal sections displayed increased numbers of substance P-immunoreactive nerve fibre profiles at both 10 and 35 days p.i. Thus, following N. brasiliensis infection there is a shift in the enteric nervous system away from cholinergic to non-cholinergic regulation, associated with increased amounts of the pro-inflammatory neuropeptide, substance P. We speculate that changes in neuronal structure and function are intimately involved in the co-ordinated multicellular response to intestinal parasitic infection and subsequent gut recovery.

Animals↗
PubMed1996

T cell-monocyte interactions regulate epithelial physiology in a coculture model of inflammation.

We have examined the effect of T cell activation, with or without monocytes, on epithelial electrolyte transport and barrier functions. Confluent monolayers of human T84 epithelial cells were cocultured (1-3 days) with peripheral blood mononuclear cells (PBM) or T cells activated by anti-CD3 antibody. Monolayers were then mounted in Ussing chambers, and changes in ion transport (indicated by short-circuit current, Isc) and barrier (indicated by resistance and radiolabeled probe fluxes) functions were assessed. Coculture with activated PBM or conditioned medium from these cells altered the transport (decreased Isc responses to carbachol and forskolin) and barrier (decreased resistance and increased fluxes of [3H]mannitol and 51Cr-EDTA) properties of T84 monolayers. In contrast, coculture with equal numbers of T cells activated in the absence of monocytes did not significantly affect epithelial physiology. Monocytes treated with conditioned media from activated T cells evoked epithelial abnormalities similar to those caused by culture with activated PBM. Total correction of epithelial abnormalities was achieved only by treating T cell-conditioned medium with anti-interferon-gamma (IFN-gamma) before addition to monocytes, as well as addition of anti-tumor necrosis factor-alpha (TNF-alpha) to the coculture. Exogenous recombinant IFN-gamma and TNF-alpha added to T84 monolayers did not mimic the physiological changes induced by immune cells; addition of these cytokines to monocytes did reproduce the effects. We conclude that T cell-derived IFN-gamma activates monocytes to release TNF-alpha and other soluble mediators, resulting in epithelial dysfunction.

Actins↗
PubMed1996

Infection of T84 cells with enteropathogenic Escherichia coli alters barrier and transport functions.

The effect of enteropathogenic Escherichia coli (EPEC) infection on electrophysiology of T84 cell monolayers was examined. After 18 h of infection with EPEC (E2348), transepithelial electrical resistance was decreased (30 +/- 5% of uninfected values) compared with monolayers infected with a nonpathogenic E. coli strain (104 +/- 13%). Resistance of monolayers infected with EPEC mutant strain CVD206, deficient in attaching and effacing lesion formation, was partially reduced (66 +/- 10%). In addition, permeability of EPEC-infected T84 monolayers increased compared with uninfected cells. Associated with these changes was an altered distribution of the tight junction protein, ZO-1. Taken together, these findings suggest that the barrier defect induced by EPEC was at the level of the tight junction. Adenosine 3'5'-cyclic monophosphate-stimulated chloride secretion was also diminished in EPEC-infected cells, whereas Ca2+ -dependent chloride secretion was not different from uninfected cells. These findings indicate that EPEC infection alters intestinal epithelial barrier and transport functions. Furthermore, these results provide a possible mechanism for EPEC-induced diarrheal disease.

Actins↗
PubMed1996

Effects of neuropeptide Y and substance P on antigen-induced ion secretion in rat jejunum.

We previously described a model of intestinal hypersensitivity in which isolated gut segments from sensitized rats demonstrated a rapid epithelial secretory response to luminal antigen that was mediated by mucosal mast cells and capsaicin-sensitive nerves. In this study, we examined the ability of the inhibitory neuropeptide, neuropeptide Y (NPY), to diminish the antigen-induced secretory response. Rats were sensitized to egg albumin (EA), and 12-14 days later, jejunal tissue was excised and mounted in Ussing chambers. NPY inhibited the short-circuit current (Isc) increase and Cl- secretion evoked by addition of EA to the luminal side of the tissue; neural blockade with tetrodotoxin (TTX) had a similar inhibitory effect. In contrast, NPY was much less effective, and TTX was completely ineffective, on the response to serosal antigen. Additional experiments examined the cell target for NPY action. NPY and TTX almost abolished the Isc response to electrical transmural stimulation of enteric nerves, suggesting a possible neural site of action. In addition, NPY significantly reduced baseline Isc; this inhibition involved both TTX-dependent and TTX-independent components. Because nerves were previously shown to facilitate antigen uptake and substance P was implicated in the response to only luminal antigen, we postulated that NPY was inhibiting nerves that facilitate antigen transport from the lumen to effector cells in the lamina propria. We therefore examined the effect of exogenous substance P added after NPY inhibition. Substance P restored the luminal antigen-induced secretory response to pretreatment values. We conclude that the neuropeptides play a significant role in immunophysiology by acting at neural and epithelial sites in the intestinal mucosa.

Albumins↗
PubMed1996

Budesonide inhibits T cell-initiated epithelial pathophysiology in an in vitro model of inflammation.

Recognition of the therapeutic value of glucocorticosteroids in the treatment of inflammation has preceded awareness of the mechanism(s) of action of these drugs. We recently showed that coculture of human T84 epithelial monolayers for 2 days with anti-CD3 activated peripheral blood mononuclear cells (A-PBM) led to impaired ion transport responses and reduced barrier function. We tested the hypothesis that budesonide, as a member of the new generation of more topically selective steroids, could prevent these immune-mediated epithelial abnormalities. Budesonide added to the coculture system dose-dependently inhibited the following functional T84 abnormalities measured in Ussing chambers: reduced transport responses (decreased short-circuit current changes to carbachol (raises [Ca2+]i) and forskolin (raises cAMP, cyclic adenosine monophosphate(i)); and increased permeability (decreased resistance and increased fluxes of 3H-mannitol and 51CrEDTA). For the beneficial effects of budesonide to be observed, PBM pretreatment (> or = 3 hr) and daily addition (for 2 days) to the coculture system was necessary. Budesonide (10(-7) M) dramatically reduced A-PBM proliferation (measured by 3H-thymidine incorporation) and cytokine (IL-1beta, IL-2, IL-6, IFN-gamma, TNF-alpha) production, but was not cytotoxic to immune cells. Budesonide treatment of T84 epithelial cells alone did not directly affect epithelial physiology, nor did it prevent epithelial abnormalities evoked by subsequent exposure to A-PBM or conditioned media from immune cells. Our studies showed that budesonide prevents epithelial dysfunction in this model by inhibiting activation of both T cells and monocytes.

Adult↗