Taming the mucosal immune response in Crohn's disease

A three-dimensional coculture of enterocytes, monocytes and dendritic cells to model inflamed intestinal mucosa in vitro

While epithelial cell culture models (e.g., Caco-2 cell line) are widely used to assess the absorption of drug molecules across healthy intestinal mucosa, there are no suitable in vitro models of the intestinal barrier in the state of inflammation. Thus development of novel drugs and formulations for the treatment of inflammatory bowel disease is largely bound to animal models. We here report on the development of a complex in vitro model of the inflamed intestinal mucosa, starting with the selection of suitable enterocyte cell line and proinflammatory stimulus and progressing to the setup and characterization of a three-dimensional coculture of human intestinal epithelial cells and immunocompetent macrophages and dendritic cells. In the 3D setup, controlled inflammation can be induced allowing the mimicking of pathophysiological changes occurring in vivo in the inflamed intestine. Different combinations of proinflammatory stimuli (lipopolysaccharides from Escherichia coli and Salmonella typhimurium, interleukin-1β, interferon-γ) and intestinal epithelial cell lines (Caco-2, HT-29, T84) were evaluated, and only Caco-2 cells were responsive to stimulation, with interleukin-1β being the strongest stimulator. Caco-2 cells responded to the proinflammatory stimulus with a moderate upregulation of proinflammatory markers and a slight, but significant, decrease (20%) of transepithelial electrical resistance (TEER) indicating changes in the epithelial barrier properties. Setting up the coculture model, macrophages and dendritic cells derived from periphery blood monocytes were embedded in a collagen layer on a Transwell filter insert and Caco-2 cells were seeded atop. Even in the presence of immunocompetent cells Caco-2 cells formed a tight monolayer. Addition of IL-1β increased inflammatory cytokine response more strongly compared to Caco-2 single culture and stimulated immunocompetent cells proved to be highly active in sampling apically applied nanoparticles. Thus the 3D coculture provides additional complexity and information compared to the stimulated single cell model. The coculture system may serve as a valuable tool for developing drugs and formulations for the treatment of inflammatory bowel diseases, as well as for studying the interaction of xenobiotics and nanoparticles with the intestinal epithelial barrier in the state of inflammation.

Exacerbated tissue destruction in DSS-induced acute colitis of OPN-null mice is associated with downregulation of TNF-alpha expression and non-programmed cell death

Osteopontin (OPN), a pro-inflammatory mediator, is constitutively expressed in normal gut and is upregulated in inflammatory colitis. To determine the significance of OPN in inflammatory bowel disease, we studied the development of acute, experimental colitis induced by dextran sulfate sodium (DSS) in OPN-null and wild-type (WT) mice. OPN expression was markedly increased in WT diseased colons, while a higher disease activity index, including spleen enlargement, bowel shortening, and mucosal destruction, was observed in OPN-null mice. Although peripheral blood neutrophil numbers were lower in DSS-treated OPN-null mice, tissue myeloperoxidase levels, reflecting enhanced neutrophil activity, were increased in the diseased colons. In comparison, lymphocyte numbers in peripheral blood were increased earlier than in DSS-treated WT mice. Despite a significantly greater spleen enlargement, flow cytometric analysis of splenocytes from the DSS-treated OPN-null mice revealed lower numbers of differentiated macrophages and (CD4+ and CD8alpha+) lymphocytes. Whereas pro-inflammatory cytokines, including G-CSF, RANTES, MIP1alpha, and TNF-alpha, were increased < 10-fold in DSS-treated WT splenocytes, expression of these cytokines was dramatically suppressed in the DSS-treated OPN-null splenocytes as well as gut tissues. The suppressed TNF-alpha response in OPN-null mice was reflected in a marked increase in non-apoptotic cell death in diseased colons. Collectively, these studies demonstrate that OPN is required for mucosal protection in acute inflammatory colitis.

New cytokine therapeutics for inflammatory bowel disease

Conventional therapy for inflammatory bowel diseases rely on corticosteroids and 5-aminosalicylates combined with immunosuppressive agents for maintenance. These drugs are not always effective and may inflict serious side effects. Other therapies are therefore awaited. Infliximab, a monoclonal antibody against the pro-inflammatory cytokine TNF-alpha has been successfully applied as a treatment for Crohn's disease. The mechanism of action of this drug extends beyond the level of TNF-alpha scavenging and includes induction of apoptosis of effector cells. Numerous anti-TNF antibodies have been developed and are currently evaluated in clinical trials. Other targets for monoclonal antibodies include integrins and cytokines involved in T-cell differentiation and activation. Likewise recombinant proteins that moderate TNF bioactivity and lymphocyte function have been developed. The therapeutic effect of recombinant interleukin-10 seems to be dependent on local delivery of the protein. Antisense therapy targeting lymphocyte migration has also been tested in IBD. Finally, the conventional drug thalidomide and possibly MAP-kinase inhibitors may become novel treatment entities for IBD.

Immune activation and nutritional status in adult Crohn's disease patients

BACKGROUND

Recent attention focused on the effect of inflammatory cytokines on intermediary metabolism contributing to the nutritional disturbances observed in acute or chronic inflammatory diseases.

AIMS

To examine the interactions between immune activation and nutritional parameters in adult Crohn's disease patients.

PATIENTS AND METHODS

We analysed anthropometric and biochemical nutritional parameters in 40 Crohn's disease patients and 26 healthy controls, and related them to inflammatory and immune markers.

RESULTS

Weight, body mass index, mid-arm circumference, triceps skinfold thickness, as well as albumin, transthyretin, retinol binding protein, insulin growth factor-I and Vitamin A were significantly decreased in Crohn's disease patients and negatively correlated to disease activity. By contrast, erythrocyte sedimentation rate, fibrinogen, C-reactive protein, alpha1-acylglycoprotein, soluble receptor of interleukin-2, blood neopterin, tumour necrosis factor-alpha and interleukin-1beta concentrations were significantly higher in patients and positively correlated to disease activity. Nutritional parameters and acute phase reactants were linked to tumour necrosis factor-alpha and interleukin-1beta concentrations, and markers of nutritional status were negatively correlated to positive acute phase reactants.

CONCLUSIONS

In Crohn's disease, inflammatory cytokines appear partly responsible for decreased nutritional status. Thus, nutritional intervention to correct nutritional (in particular protein) depletion, and/or therapeutic intervention reducing inflammation and therefore restoring adequate nutritional proteins synthesis, appears a major therapeutic goal in active Crohn's disease.

Pyostomatitis vegetans

Pyostomatitis vegetans is a rare oral disorder often associated with gastrointestinal and/or cutaneous diseases and sometimes with other disorders. The association of pyostomatitis vegetans with inflammatory bowel disease, particularly ulcerative colitis, is well known and in most cases bowel disease precedes the onset of oral lesions by months or years. A peripheral eosinophilia has been observed in most reported cases. Pyostomatitis vegetans is characterized by erythematous, thickened oral mucosa with multiple pustules and superficial erosions. Histopathologically, it is characterized by intraepithelial and/or subepithelial abscesses containing large numbers of eosinophils. The pathogenesis is as yet unknown although immunological and microbial factors have been suggested as possible aetiological factors. Management of pyostomatitis vegetans consists mainly of immunosuppression using topical or systemic corticosteroids with medical and/or surgical treatment of any underlying inflammatory bowel disease.

Interleukin-10-based therapy for inflammatory bowel disease

In recent years it has become clear that chronic inflammatory bowel disease (IBD), especially Crohn's disease (CD), is caused by a loss of tolerance against the autologous bacterial flora of the intestine. Tolerance against the indigenous flora requires optimal recognition of antigens by pattern recognition receptors and the presence of important regulatory cells and cytokines. Interleukin-10 (IL-10) has a major role in the regulatory network of cytokines controlling mucosal tolerance, and it is, therefore, not surprising that this cytokine is proposed as a potent anti-inflammatory biological therapy in chronic IBD. This review will discuss the characteristics of IL-10, its immunoregulatory properties in mice and humans, and the use of IL-10 as a treatment for CD. The review will summarise the clinical studies that have taken place and discuss the lessons learned from these trials. Finally, the advantages and disadvantages of promising new strategies of IL-10 treatment, including gene therapy and the use of genetically modified bacteria, will be discussed. Both novel therapies have been shown to be successful in animal models of disease, and clinical testing is currently underway. The future goal of IL-10 treatment should be focused on mucosal delivery and remission maintenance instead of remission induction. In conclusion, it can be said that despite the disappointing results of IL-10 therapy so far, there is still enough rationale for the use of IL-10 as an anti-inflammatory biological treatment in chronic IBD.