Interferon-γ regulates growth and controls Fcγ receptor expression and activation in human intestinal mast cells.

BACKGROUND: Development and function of tissue resident mast cells (MCs) is tightly controlled by various cytokines, most of which belong to the typical T helper (Th) 2-type cytokines such as IL-3 and IL-4. The effects of the Th1-type cytokine IFN-γ on human MCs is less clear. RESULTS: Here, we analyzed the effects of IFN-γ on tissue-derived, mature human MCs. We found that INF-γ decreases proliferation, without affecting apoptosis in human intestinal MCs cultured in the presence of optimal concentrations of stem cell factor (SCF) or SCF and IL-4. However, in the absence of growth factors or at suboptimal concentrations of SCF, INF-γ promotes survival through inhibition of MC apoptosis. Interestingly, we found that INF-γ has no effect on FcϵRI expression and FcϵRI-mediated release of histamine and leukotriene (LT)C4, while it has profound effects on FcγR expression and activation. We show that intestinal MCs express FcγRI, FcγRIIa, and FcγRIIc, whereas FcγRIIb expression was found in only 40% of the isolates and FcγRIII was never detectable. INF-γ strongly increases FcγRI and decreases FcγRIIa expression. INF-γ-naïve MCs produce LTC4 but fail to degranulate upon crosslinking of surface-bound monomeric IgG. In contrast, INF-γ-treated MCs rapidly release granule-stored histamine in addition to de novo-synthesized LTC4. CONCLUSION: In summary, we identify INF-γ as an important regulator of tissue-resident human MCs. IFN-γ displays a dual function by blocking extensive MC proliferation, while decreasing apoptosis in starving MCs and enhancing FcγRI expression and activation. These results emphasize the involvement of mucosal MCs in Th1-mediated disorders.

Central role of IL-6 and MMP-1 for cross talk between human intestinal mast cells and human intestinal fibroblasts.

Mast cells (MC) are key effector cells in allergic reactions but also involved in host defence, tissue remodeling, angiogenesis, and fibrogenesis. Here, we show that human intestinal fibroblasts (FB) suppress apoptosis in human intestinal MC dependent on IL-6. Intestinal FB produced IL-6 upon direct stimulation by intestinal MC in co-culture or by MC mediators such as TNF-α, IL-1ß, tryptase or histamine. MC incubated with IL-6 survived for up to 3 weeks similar to MC co-cultured with FB and MC survival could be blocked by neutralizing anti-IL-6 Abs. Moreover, FB stimulated by MC mediators upregulated their expression of matrix metalloproteinase-1 (MMP-1), a key fibrolytic enzyme. Noteworthy, FB co-cultured with MC or treated with MMP-1 lost confluence and showed increased numbers of apoptotic cells. Our data indicate an intimate cross talk between mucosal MC and FB resulting in MC survival and induction of a fibrolytic rather than a profibrotic state in FB.

Selective activation of human intestinal mast cells by Escherichia coli hemolysin.

Mast cells (MCs) are recognized to play an important role in bacterial host defense in the murine system. In this study, we studied the interaction of human MCs, isolated from the intestine and purified to homogeneity, with different Escherichia coli and Shigella flexneri strains. We show that alpha-hemolysin (Hly)-producing E. coli strains induce the release of histamine, leukotrienes, and proinflammatory cytokines in intestinal MCs. In contrast, MCs were virtually unresponsive to S. flexneri and several Hly-negative E. coli strains, including the isogenic Hly-deficient mutants of Hly(+) strains. Hly(+) E. coli but not Hly(-) E. coli caused an increase in intracellular Ca(2+) levels. Blocking of extracellular Ca(2+) and of the calmodulin/calcineurin pathway by cyclosporin A inhibited the response to Hly(+) E. coli. Furthermore, inhibition of MAPKs p38 and ERK reduces activation of MCs by Hly(+) E. coli. In addition, using an ex vivo system, we directly record the histamine release by MCs located in the lamina propria after infection with Hly(+) E. coli. Our data indicate that human intestinal mast cells interact with selected Gram-negative bacteria, establish E. coli Hly as a factor regulating MC effector functions, and argue further for a role of human MCs in innate immunity.

Antibiotics protect against fructose-induced hepatic lipid accumulation in mice: role of endotoxin.

BACKGROUND/AIMS: Consumption of refined carbohydrates in soft drinks has been postulated to be a key factor in the development of non-alcoholic fatty liver disease (NAFLD). The aim of the present study was to test the effects of ad libitum access to different sugars consumed in drinking water on hepatic fat accumulation. METHODS: For 8 weeks, C57BL/J6 mice had free access to solutions containing 30% glucose, fructose, sucrose, or water sweetened with artificial sweetener (AS) or plain water. Body weight, caloric intake, hepatic steatosis and lipid peroxidation were assessed. RESULTS: Total caloric intake and weight gain were highest in mice exposed to glucose. In contrast, hepatic lipid accumulation was significantly higher in mice consuming fructose compared to all other groups. Moreover, endotoxin levels in portal blood and lipid peroxidation as well as TNFalpha expression were significantly higher in fructose fed mice than in all other groups. Concomitant treatment of fructose fed mice with antibiotics (e.g., polymyxin B and neomycin) markedly reduced hepatic lipid accumulation in fructose fed mice. CONCLUSIONS: These data support the hypothesis that high fructose consumption may not only lead to liver damage through overfeeding but also may be directly pro-inflammatory by increasing intestinal translocation of endotoxin.

Effect of oral lactulose on clinical and immunohistochemical parameters in patients with inflammatory bowel disease: a pilot study.

BACKGROUND: The prebiotic potential of lactulose is well established and preclinical studies demonstrated a protective effect of lactulose in murine models of colitis. The aim of the present study was to investigate the clinical and histological efficacy of lactulose in patients with inflammatory bowel disease (IBD), for which probiotic therapy yielded promising results. METHODS: Patients were treated with standard medication alone or combined with 10 g lactulose daily as adjuvant therapy for 4 months. Clinical efficacy of treatment was assessed using clinical activity indices, a quality of life index (IBDQ), endoscopic scores, defecation frequency and monitoring corticosteroid medication. Orsomucoid, alpha1-antitrypsin and other laboratory parameters were determined. In addition, in some participants colonic biopsies were analyzed with haematoxylin-eosin staining or with antibodies against HLA-DR, CD68, IgA and CD3, and evaluated systematically. All measurements were performed both at enrollment and at the end of the trial. RESULTS: 14 patients presenting ulcerative colitis (UC) and 17 patients presenting Crohn's disease (CD), most of them in a clinically active state, were enrolled in this pilot study. After 4 month no significant improvement of clinical activity index, endoscopic score or immunohistochemical parameters was observed in CD or UC patients receiving lactulose in comparison to the control group. However, significant improvement of quality of life was observed in UC patients receiving lactulose compared to the control group (p = 0.04). CONCLUSION: The findings of the present pilot study indicate that oral lactulose has no beneficial effects in IBD patients in particular with regard to clinical activity, endoscopic score or immunohistochemical parameters. The importance of the beneficial effect of lactulose in UC patients regarding the quality of life needs further evaluation in larger controlled clinical trials.

Human mast cells, bacteria, and intestinal immunity.

Mast cells are versatile tissue regulator cells controlling major intestinal functions such as epithelial secretion, epithelial permeability, blood flow, neuroimmune interactions, and peristalsis. Most importantly, mast cells are key regulators of the integrity and function of the gastrointestinal barrier. At the same time, they can act as immunomodulatory cells by reacting to various exogenous signals from bacteria, viruses, and parasites through innate recognition receptors, such as Toll-like receptors (TLRs) or through receptors of the specific immune system, such as immunoglobulins (Igs) bound to their cell surface. This mast cell function is enhanced by an intensive cross talk of mast cells with other cells of the innate or adaptive immune systems. Finally, mast cells act as inflammatory cells mediating diseases such as allergy, once they become dysregulated because of excess of allergen, allergen-specific IgE and cytokines, or invading microbes. The present article focuses on the human mast cell functions in the intestine and compares the data with those derived from animal experiments. In particular, the role of bacteria and TLRs expression by mast cells for allergic reactions are discussed.