Crohn's disease monocytes are primed for accentuated release of toxic oxygen metabolites

Research progress on the relationship between intestinal microecology and intestinal bowel disease

Intestinal microecology is the main component of human microecology. Intestinal microecology consists of intestinal microbiota, intestinal epithelial cells, and intestinal mucosal immune system. These components are interdependent and establish a complex interaction network that restricts each other. According to the impact on the human body, there are three categories of symbiotic bacteria, opportunistic pathogens, and pathogenic bacteria. The intestinal microecology participates in digestion and absorption, and material metabolism, and inhibits the growth of pathogenic microorganisms. It also acts as the body's natural immune barrier, regulates the innate immunity of the intestine, controls the mucosal barrier function, and also participates in the intestinal epithelial cells' physiological activities such as hyperplasia or apoptosis. When the steady‐state balance of the intestinal microecology is disturbed, the existing core intestinal microbiota network changes and leads to obesity, diabetes, and many other diseases, especially irritable bowel syndrome, inflammatory bowel disease (IBD), and colorectal malignancy. Intestinal diseases, including tumors, are particularly closely related to intestinal microecology. This article systematically discusses the research progress on the relationship between IBD and intestinal microecology from the pathogenesis, treatment methods of IBD, and the changes in intestinal microbiota.

Peripheral monocyte functions and activation in patients with quiescent Crohn's disease

Recent developments suggest a causal link between inflammation and impaired bacterial clearance in Crohn's disease (CD) due to alterations of intestinal macrophages. Studies suggest that excessive inflammation is the consequence of an underlying immunodeficiency rather than the primary cause of CD pathogenesis. We characterized phenotypic and functional features of peripheral blood monocytes of patients with quiescent CD (n = 18) and healthy controls (n = 19) by analyses of cell surface molecule expression, cell adherence, migration, chemotaxis, phagocytosis, oxidative burst, and cytokine expression and secretion with or without lipopolysaccharide (LPS) priming. Peripheral blood monocytes of patients with inactive CD showed normal expression of cell surface molecules (CD14, CD16, CD116), adherence to plastic surfaces, spontaneous migration, chemotaxis towards LTB4, phagocytosis of E. coli, and production of reactive oxygen species. Interestingly, peripheral blood monocytes of CD patients secreted higher levels of IL1β (p<.05). Upon LPS priming we found a decreased release of IL10 (p<.05) and higher levels of CCL2 (p<.001) and CCL5 (p<.05). The expression and release of TNFα, IFNγ, IL4, IL6, IL8, IL13, IL17, CXCL9, and CXCL10 were not altered compared to healthy controls. Based on our phenotypic and functional studies, peripheral blood monocytes from CD patients in clinical remission were not impaired compared to healthy controls. Our results highlight that defective innate immune mechanisms in CD seems to play a role in the (inflamed) intestinal mucosa rather than in peripheral blood.

Expression signatures, barriers and beyond: the role of oxidative stress in murine colitis and human inflammatory bowel disease revisited

(Table is included in full-text article). Inflammatory bowel disease is triggered by, as yet, unknown factors in the background of a polygenic susceptibility. Recent technological advances have made it possible to unravel genetic etiology and transcriptomal signature patterns of such complex diseases. Combining murine models with patient-derived data has proven a powerful approach to understand early events of etiopathogenesis and has pointed towards a primary deficiency of the innate immunological barrier function in this group of diseases. One of the emerging elements from transcriptomal studies is the imbalance of cellular programs involved in antioxidants with a resulting preponderance of reactive oxygen species in the inflamed intestinal tissue. The understanding of the complex genetic and genomic risk map of disease genes will not only further our understanding of inflammatory bowel disease etiopathogenesis, but may ultimately lead to therapeutic strategies aiming at the restoration of impaired intestinal barrier function.

NOD2 activity modulates the phenotype of LPS-stimulated dendritic cells to promote the development of T-helper type 2-like lymphocytes - Possible implications for NOD2-associated Crohn's disease

Sensing of commensal microorganisms via Toll-like receptors (TLR) in the gut is essential for maintaining intestinal homeostasis in healthy individuals. Conversely, Crohn's disease is characterised by an inappropriate T helper-type 1 (Th1)-mediated immune response towards these same microorganisms. NOD2 is expressed by dendritic cells (DC) and mediates responses to bacterial muramyl-dipeptides (MDP). Mutations in NOD2 (CARD15) have recently been associated with susceptibility to Crohn's disease although the underlying mechanisms have yet to be established. We investigated the functional outcome of NOD2 and TLR4-mediated activation in monocyte-derived DC from wild-type NOD2 healthy controls and NOD2 frame-shift mutation-carrying Crohn's disease patients. In wild-type DC, MDP acted synergistically with LPS to amplify inflammatory cytokine production, enhance co-stimulatory molecule expression, and produce DC that promoted the proliferation of naïve, allogeneic, CD4(+) T lymphocytes with a Th2-like cytokine profile. By contrast, DC carrying homozygous NOD2 mutations were unable to react to MDP, responded to LPS only, and promoted the development of Th1 cells. These results suggest activation of the NOD2 pathway in DC modulates their response to TLR agonists and regulates their ability to induce polarised Th1 responses. As a consequence, Crohn's disease patients with defective NOD2 may be predisposed to the generation of strongly polarised Th1 responses against common commensal microorganisms.

Infiltration of CD19+ plasma cells with frequent labeling of Ki-67 in corticosteroid-resistant active ulcerative colitis

Abnormalities in humoral immunity are implicated in the pathogenesis of ulcerative colitis. However, the detailed mechanisms of B-cell activation in the locale remain unaccounted for. We analyzed ulcerative colitis from the standpoint of lymphocytic expansion in the loco. Intestinal specimens obtained at surgery from 30 patients with ulcerative colitis treated with corticosteroids and 15 with Crohn's disease were analyzed by immunohistochemistry and flow cytometry. Ulcerative colitis was characterized by a diffuse distribution of Ki-67(+) small round cells particularly in the ulcer base (that were CD19(+) and CD20(-)), with a significant number of them also CD138(+). Immunoelectron microscopy for CD19 revealed an abundance of rough endoplasmic reticulum in the cytoplasm. These indicated that they are of immature plasma lineage cells. By contrast, plasma cells in Crohn's disease were negative for CD19, and the labeling for Ki-67 was infrequent, showing mature phenotype. Flow cytometry revealed an occurrence of CD19(+) and CD20(-) cells in ulcerative colitis but not in Crohn's disease. The labeling index of Ki-67 among CD19(+) plasma cells was positively correlated with the clinical activity of ulcerative colitis. High labeling of Ki-67 in CD19(+) plasma cells is specific for active ulcerative colitis that was resistant to medical treatment by corticosteroids.

Adenoviral transfer of the murine oncostatin M gene suppresses dextran-sodium sulfate-induced colitis

The use of biologics has promising potential in the treatment of inflammation. Studies with cultured cells and mouse models of disease have ascribed proinflammatory and anti-inflammatory functions to oncostatin M (OSM) and the related cytokine, interleukin-6 (IL-6). Here, we examined the effect of systemic administration of adenoviral (Ad) vectors encoding either murine OSM (AdMuOSM) or murine IL-6 (AdMuIL-6) in a mouse model of colitis. BALB/c mice were treated with a 5-day course of 4% dextran-sodium sulfate (DSS) water with or without administration of adenoviral vectors (i.p. or i.m. at 10(7) plaque-forming units [pfu]) given as a cotreatment or therapy. The deletion variant of the adenovirus served as a control for adenoviral infection. Colitis was assessed by (1) morphology (damage score, macrophage infiltration, apoptosis) and (2) function (myeloperoxidase activity and Ussing chamber analysis of epithelial ion transport). Infection with adenovirus alone did not affect colonic form or function. AdMuOSM (either i.p. or i.m.) significantly reduced the severity of the DSS-induced colitis. There was less damage, reduced macrophage infiltration, fewer apoptotic bodies, and a significant improvement in stimulated ion transport in colonic tissues from the treated mice. No benefit of AdMuIL-6 treatment was observed in this model system. Thus, systemic administration of AdMuOSM given as a cotreatment and to a lesser extent as a therapy was found to be of benefit in DSS-induced colitis, a murine model of inflammatory bowel disease (IBD).

The key role of macrophages in the immunopathogenesis of inflammatory bowel disease

Macrophages are important in the host's immunological and inflammatory responses. There is a large population of these cells in the normal intestinal mucosa where they represent the major antigen presenting cell population capable of determining the type of T cell responses that develop to luminal antigens. Studies suggest that the normal intestinal macrophages cannot be easily induced to mediate acute inflammatory responses. In active inflammatory bowel disease there is an increase in the mucosal macrophage population, derived from circulating monocytes. These recruited macrophages are phenotypically different from the resident population of cells and play a major role in mediating the chronic mucosal inflammation seen in patients with ulcerative colitis and Crohn's disease. They secrete many cytokines that are important in the proinflammatory responses, such as interleukin (IL)-1, IL-6, IL-8, IL-12, IL-18, and tumor necrosis factor-alpha. They also release reactive metabolites of oxygen and nitrogen and proteases that degrade the extracellular matrix. Macrophages also appear to be important during resolution of inflammation and repair of the intestinal mucosa that occurs during disease remission.

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.

Increased expression of costimulatory molecules on peripheral blood monocytes in patients with Crohn's disease

BACKGROUND

Activation of T lymphocytes and monocytes/macrophages has been implicated in the pathogenesis of Crohn's disease (CD). Costimulatory molecules play important roles in optimal T-cell activation.

METHODS

With flow cytometric analysis we have investigated the expression of the costimulatory molecules B7-1 (CD80), B7-2 (CD86), and CD18 and the intercellular adhesion molecule-1 (ICAM-1) on peripheral blood monocytes and the expression of the activation markers HLA-DR and IL-2R (CD25) on peripheral blood T lymphocytes from 31 CD patients, 17 ulcerative colitis (UC) patients, and 10 healthy controls.

RESULTS

In CD patients the percentage of activated T cells (CD3+ HLA-DR+ and CD3+ IL-2R+) was significantly increased compared with those of controls and UC patients (P < 0.05). Most monocytes from all three groups expressed B7-2, CD18, and ICAM-1 molecules (all > 79%), but only a few positive cells expressed B7-1 molecules (< 5%). No significant differences were detected in the percentage positivity of all costimulatory molecules tested among CD, UC, and controls. The mean fluorescence intensity (MFI) of B7-1 in all three groups was very weak and not significantly different. However, in CD patients there was a significantly increased MFI of B7-2, CD18, and ICAM-1 molecules compared with UC and controls (P < 0.05). On the other hand, both the percentage positivity and MFI of HLA-DR molecules on monocytes of UC patients were significantly lower than those of CD patients and controls (P < 0.05).

CONCLUSIONS

Expression of the costimulatory molecules B7-2, CD18, and ICAM-1 on peripheral blood monocytes of CD patients is increased. In CD patients activation of peripheral T lymphocytes may correlate with increased expression of these costimulatory molecules on peripheral blood monocytes.

Monocyte aggregation and multinucleated giant-cell formation in vitro in Crohn's disease. The effect of cell adhesion molecules

BACKGROUND

Multinucleated giant-cell (MGC) formation is a common histopathologic feature of various granulomatous diseases, including Crohn's disease (CD).

METHODS

We have investigated monocyte aggregation and subsequent MGC formation by in vitro culturing peripheral monocytes from 25 CD patients, 15 ulcerative colitis (UC) patients, and 10 healthy controls. The effect of cell adhesion molecules on the monocyte aggregation and MGC formation in CD patients was investigated by using anti-beta 2 integrin and anti-ICAM-1 antibodies.

RESULTS

The monocyte aggregation and MGC formation were significantly higher in CD than those seen in UC and controls (p < 0.05). In CD, antibody to beta 2 integrin could inhibit not only the monocyte aggregation but also the subsequent MGC formation. In contrast, the antibody to ICAM-1 could inhibit the monocyte aggregation; however, it could not inhibit the MGC formation.

CONCLUSIONS

Monocyte aggregation and MGC formation are increased in CD. beta 2 Integrin may play an important role in the monocyte aggregation and MGC formation of CD patients.

Circulating neutrophils from patients with ulcerative colitis have a normal respiratory burst

The hallmark of ulcerative colitis is a diffuse infiltration of neutrophils from the circulation into the colonic mucosa. The underlying mechanism for neutrophil tissue infiltration is unknown. One possible hypothesis is abnormal circulating neutrophils. This hypothesis has been previously tested with conflicting results. The aim of our study was to re-evaluate circulating neutrophil function in the absence of several possible confounding factors. To this end, we measured the respiratory burst of circulating neutrophils in response to two different stimuli by chemiluminescence in patients with active and inactive ulcerative colitis being off all medications. Our results show no significant difference between ulcerative colitis patients and controls in peak chemiluminescence, area-under-the-curve and time to peak comparisons. However, 27% of patients with active ulcerative colitis had an abnormally elevated chemiluminescence to stimuli. In addition, no correlations were seen between disease activity and peak chemiluminescence. Thus circulating neutrophils in the majority of patients with ulcerative colitis do not appear to be either "primed" or hyperactive. This may suggest the presence of local colonic factors that lead to neutrophil tissue infiltration and activation.

Immunoregulatory role of interleukin 10 in patients with inflammatory bowel disease

BACKGROUND/AIMS

Active inflammatory bowel disease (IBD) is associated with increased proinflammatory cytokines. Deficiency of interleukin (IL) 10, a contrainflammatory cytokine, leads to the development of colitis in IL-10 knockout mice. We characterized IL-10 regulation of proinflammatory cytokine (tumor necrosis factor [TNF] alpha and IL-1 beta) expression in IBD in vitro and in vivo.

METHODS

IL-10 regulation of IL-1 beta, TNF-alpha, and IL-1 receptor antagonist expression by peripheral monocytes or isolated lamina propria mononuclear cells (LPMNC), respectively, was studied by enzyme-linked immunosorbent assay (cytokine secretion) and by semiquantitative reverse-transcription polymerase chain reaction.

RESULTS

IL-10 down-regulates IL-1 beta and TNF-alpha secretion as well as messenger RNA levels in IBD peripheral monocytes and LPMNC in a dose-dependent manner. In parallel, IL-1 receptor antagonist secretion is induced, and IL-10 can restore diminished in vitro IL-1 receptor antagonist/IL-1 beta ratios in IBD to normal levels. Equal concentrations of IL-10 are detectable in both normal and IBD intestinal lamina propria biopsy homogenates. After topical IL-10 enema treatment of three steroid therapy-refractory patients with ulcerative colitis, in vitro release of proinflammatory cytokines from IBD peripheral monocytes as well as LPMNC is dramatically down-regulated.

CONCLUSIONS

IL-10 down-regulates the enhanced secretion as well as messenger RNA levels of proinflammatory cytokines by IBD mononuclear phagocytes in vitro. In vivo topical application of IL-10 induces down-regulation of proinflammatory cytokine secretion both systemically and locally.

Impaired response of activated mononuclear phagocytes to interleukin 4 in inflammatory bowel disease

BACKGROUND/AIMS

In inflammatory bowel disease (IBD), peripheral monocytes and intestinal macrophages show an increased state of priming and activation. The aim of this study was to test the hypothesis that the response of IBD mononuclear phagocytes to the contrainflammatory cytokine interleukin (IL) 4 may be altered.

METHODS

The in vitro secretion of proinflammatory cytokines (IL-1 beta, tumor necrosis factor alpha [TNF-alpha], and IL-1-receptor antagonist [IL-1ra]) by peripheral monocytes and by intestinal lamina propria mononuclear cells (LPMNCs) was assessed by enzyme-linked immunosorbent assay. In parallel, superoxide anion release, macrophage mannose receptor, and IL-4 receptor expression were investigated.

RESULTS

IBD peripheral monocytes and intestinal LPMNCs in vitro secrete increased amounts of proinflammatory cytokines (IL-1 beta and TNF-alpha) with decreased IL-1ra/IL-1 beta ratios. IL-4 down-regulates proinflammatory cytokine (IL-1 beta and TNF-alpha) and superoxide anion secretion in a dose-dependent manner. In contrast to normal and disease-specific controls, IBD peripheral monocytes and IBD intestinal LPMNCs show a diminished responsiveness to the inhibitory effect of IL-4. The IL-1ra/IL-1 beta ratios in normal monocytes are increased by IL-4, whereas in IBD monocytes low IL-1ra/IL-1 beta ratios persist after IL-4 treatment. IL-4-induced expression of macrophage mannose receptor, which is a molecule pivotal to macrophage-mediated host defense, again appeared to be impaired in IBD monocytes.

CONCLUSIONS

IL-4-mediated regulation of mononuclear phagocyte effector functions is disturbed in IBD.

Monocyte-chemoattractant protein 1 gene expression in intestinal epithelial cells and inflammatory bowel disease mucosa

BACKGROUND

Monocyte-chemoattractant protein 1 (MCP-1) activates macrophages and increases the migration of monocytes into tissue during inflammation. It was hypothesized that MCP-1 expression is involved in intestinal inflammation.

METHODS

MCP-1 protein was detected by immunohistochemistry and immunoprecipitation. Biological activity of MCP-1 was assessed using a chemotactic assay. MCP-1 messenger RNA (mRNA) levels were measured by quantitative reverse-transcription polymerase chain reaction.

RESULTS

In normal mucosa, MCP-1 was predominantly present in surface epithelium. In contrast, inflamed mucosa from patients with ulcerative colitis or Crohn's disease contained multiple cells immunoreactive for MCP-1, including spindle cells, mononuclear cells, and endothelial cells. Furthermore, MCP-1 mRNA expression was markedly increased in inflamed intestinal biopsy specimens from patients with inflammatory bowel disease. MCP-1 was detected in isolated intestinal epithelial cells and in conditioned media from Caco-2 cells. Caco-2 cell-conditioned media stimulated monocyte chemotaxis activity that was inhibited by anti-MCP-1 antibodies. Constituitive MCP-1 mRNA levels in Caco-2 cells were up-regulated by interleukin 1 beta and down-regulated by dexamethasone.

CONCLUSIONS

In addition to lamina propria macrophages, endothelial cells, and spindle cells, intestinal epithelial cells are able to produce MCP-1. MCP-1 is expressed constitutively in the intestinal colonic mucosa and is up-regulated during inflammation.