Uptake through glycoprotein 2 of FimH(+) bacteria by M cells initiates mucosal immune response.

The mucosal immune system forms the largest part of the entire immune system, containing about three-quarters of all lymphocytes and producing grams of secretory IgA daily to protect the mucosal surface from pathogens. To evoke the mucosal immune response, antigens on the mucosal surface must be transported across the epithelial barrier into organized lymphoid structures such as Peyer's patches. This function, called antigen transcytosis, is mediated by specialized epithelial M cells. The molecular mechanisms promoting this antigen uptake, however, are largely unknown. Here we report that glycoprotein 2 (GP2), specifically expressed on the apical plasma membrane of M cells among enterocytes, serves as a transcytotic receptor for mucosal antigens. Recombinant GP2 protein selectively bound a subset of commensal and pathogenic enterobacteria, including Escherichia coli and Salmonella enterica serovar Typhimurium (S. Typhimurium), by recognizing FimH, a component of type I pili on the bacterial outer membrane. Consistently, these bacteria were colocalized with endogenous GP2 on the apical plasma membrane as well as in cytoplasmic vesicles in M cells. Moreover, deficiency of bacterial FimH or host GP2 led to defects in transcytosis of type-I-piliated bacteria through M cells, resulting in an attenuation of antigen-specific immune responses in Peyer's patches. GP2 is therefore a previously unrecognized transcytotic receptor on M cells for type-I-piliated bacteria and is a prerequisite for the mucosal immune response to these bacteria. Given that M cells are considered a promising target for oral vaccination against various infectious diseases, the GP2-dependent transcytotic pathway could provide a new target for the development of M-cell-targeted mucosal vaccines.

IL-6-dependent mucosal protection prevents establishment of a microbial niche for attaching/effacing lesion-forming enteric bacterial pathogens.

Enteric infections with attaching/effacing lesion-inducing bacterial pathogens are a worldwide health problem. A murine infection model with one such pathogen, Citrobacter rodentium, was used to elucidate the importance of the pleiotropic immune regulator, IL-6, in the pathogenesis of infection. IL-6 was strongly induced in colonic epithelial cells and macrophages upon C. rodentium infection and was required for effective host defense, because mice lacking IL-6 failed to control bacterial numbers 2-3 wk after infection and exhibited increased mortality. IL-6 was not needed for mounting effective T and B cell responses to the pathogens, nor was it important for induction of IFN-gamma or TNF-alpha, cytokines involved in host defense against the bacteria, or the antibacterial effector, NO. Instead, IL-6 played a key role in mucosal protection, since its absence was associated with marked infection-induced apoptosis in the colonic epithelium and subsequent ulcerations. Cell culture studies confirmed that IL-6 protected colon epithelial cells directly against inducible apoptosis, which was accompanied by increased expression of an array of genes encoding antiapoptotic proteins, including Bcl-x(L), Mcl-1, cIAP-2, and Bcl-3. Ulcerations appeared to be pathogenetically important, because bacteria localized preferentially to those regions, and chemically induced colonic ulcerations promoted bacterial colonization. Furthermore, blood components likely present in ulcer exudates, particularly alanine, asparagine, and glycine, promoted bacterial growth. Thus, IL-6 is an important regulator of host defense against C. rodentium by protecting the mucosa against ulcerations which can act as a microbial niche for the bacteria.

[A case of Turner syndrome complicated with Crohn's disease, erythema nodosum and Hashimoto disease].

A 26-year-old woman, who had had Turner syndrome from age 10 years old, had diarrhea, fever, joint pain, and erythema in the lower left leg. She was given a diagnosis of Crohn's disease, erythema nodosum, and Hashimoto disease. Systemic steroid therapy was very effective for both intestinal and skin lesions. It has been reported that half of inflammatory bowel disease patients with Turner syndrome have 46XiX (q) type chromosome abnormality, and this case also has this type of abnormality.

Role of Shiga toxin versus H7 flagellin in enterohaemorrhagic Escherichia coli signalling of human colon epithelium in vivo.

Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) is a clinically important foodborne pathogen that colonizes human colon epithelium and induces acute colonic inflammation, but does not invade the epithelial cells. Whereas Shiga toxin (Stx) and bacterial flagellin have been studied for their ability to upregulate the production of proinflammatory chemokines by cultured human colon cancer cell lines, the relevance of studies in colon cancer cell lines to the production of proinflammatory signals by normal epithelial cells in EHEC-infected human colon is not known. We show herein that Stx does not bind to human colon epithelium in vivo. Moreover, globotriaosylceramide (Gb3/CD77) synthase, the enzyme required for synthesis of the Gb3/CD77 receptor for Stx, was not expressed by normal or inflamed human colon epithelium in vivo. In contrast, Toll-like receptor (TLR) 5, the receptor for bacterial flagellin, was expressed by normal human colon epithelium and by colon epithelium in human intestinal xenografts. EHEC H7 flagellin instilled in the lumen of human colon xenografts that contain an intact human epithelium upregulated the expression of epithelial cell proinflammatory chemokines, which was accompanied by a subepithelial influx of neutrophils. Isogenic mutants of EHEC that lacked flagellin did not significantly upregulate prototypic neutrophil and dendritic cell chemoattractants by model human colon epithelia, irrespective of Stx production. We conclude that EHEC H7 flagellin and not Stx is the major EHEC factor that directly upregulates proinflammatory chemokine production by human colon epithelium in vivo.

Nod2 mutation in Crohn's disease potentiates NF-kappaB activity and IL-1beta processing.

Variants of NOD2, an intracellular sensor of bacteria-derived muramyl dipeptide (MDP), increase susceptibility to Crohn's disease (CD). These variants are thought to be defective in activation of nuclear factor kappaB (NF-kappaB) and antibacterial defenses, but CD clinical specimens display elevated NF-kappaB activity. To illuminate the pathophysiological function of NOD2, we introduced such a variant to the mouse Nod2 locus. Mutant mice exhibited elevated NF-kappaB activation in response to MDP and more efficient processing and secretion of the cytokine interleukin-1beta (IL-1beta). These effects are linked to increased susceptibility to bacterial-induced intestinal inflammation and identify NOD2 as a positive regulator of NF-kappaB activation and IL-1beta secretion.

Expression of LL-37 by human gastric epithelial cells as a potential host defense mechanism against Helicobacter pylori.

BACKGROUND & AIMS: LL-37/human cationic antimicrobial peptide 18 (hCAP18) is a human cathelicidin with broad-spectrum antimicrobial, lipopolysaccharide binding, and chemotactic activities. This study examined the role of LL-37/hCAP18 in gastric innate immune defense by characterizing its constitutive and regulated expression by human gastric mucosa and its bactericidal activity against the gastric pathogen Helicobacter pylori. METHODS: LL-37/hCAP18 messenger RNA expression in normal and H. pylori -infected gastric mucosa and gastric epithelial cells was determined by in situ hybridization, real-time polymerase chain reaction, immunostaining, and immunoblot analysis. Bactericidal activity was measured by using a colony-forming unit assay. RESULTS: LL-37/hCAP18 messenger RNA and protein were expressed in a distinct distribution by surface epithelial cells as well as chief and parietal cells in the fundic glands of normal gastric mucosa. LL-37/hCAP18 was significantly increased in the epithelium and gastric secretions of H. pylori -infected patients, but not in individuals with non-H. pylori -induced gastric inflammation. Infection of cultured gastric epithelial cells with a wild-type but not an isogenic Delta cagE mutant strain of H. pylori increased LL-37/hCAP18 expression, indicating that H. pylori -induced regulation of LL-37/hCAP18 production required an intact type IV secretion system. LL-37, the C-terminal peptide of LL-37/hCAP18, alone or in synergy with human beta-defensin 1, was bactericidal for several H. pylori strains. CONCLUSIONS: These data indicate that H. pylori up-regulates production of LL-37/hCAP18 by gastric epithelium and suggest this cathelicidin contributes to determining the balance between host mucosal defense and H. pylori survival mechanisms that govern chronic infection with this gastric pathogen.

Cytokine profile in colonic mucosa of ulcerative colitis correlates with disease activity and response to granulocytapheresis.

OBJECTIVE: The aim of this study was to clarify the correlation between cytokine profile in colonic mucosa with disease activity and response to granulocytapheresis (GCAP) in patients with ulcerative colitis (UC), using a reliable, reproducible quantitative method. METHODS: Colonoscopic biopsies of inflamed colonic mucosa (16 patients, 21 cases) and uninflamed colonic mucosa (25 patients, 33 cases) were obtained from UC patients. Messenger (m)RNA was extracted and subjected to realtime polymerase chain reaction for quantitative measurement of interleukin (IL)-12, interferon-gamma, tumor necrosis factor-alpha, IL-4, IL-8, and IL-18 mRNAs. In seven patients with high disease activity despite prednisolone (PSL) treatment (> or = 20 mg/day), one course of GCAP was conducted, and pre- and post-GCAP cytokine profiles were determined. RESULTS: In inflamed colonic mucosa of UC patients, three cytokine profiles were observed: 1) high expression of interferon-gamma, tumor necrosis factor-alpha, and IL-4 mRNAs but low expression of IL-8 mRNA; 2) high expression of IL-8 mRNA and low expression of others; and 3) low expression of all cytokines examined. Inflamed colonic mucosa of patients with high disease activity showed the second pattern. Inflamed colonic mucosa of patients who were not treated with PSL and who had low disease activity showed the first pattern, whereas those on high-dose PSL exhibited the second pattern. IL-8 mRNA was significantly higher in inflamed UC samples than in uninflamed samples. GCAP was effective in five of seven PSL-resistant patients (71.4%). IL-8 was the only cytokine that correlated with effectiveness of GCAP. Compared with GCAP nonresponders, responders had significantly higher IL-8 mRNA before GCAP and showed marked reduction of IL-8 mRNA after GCAP. CONCLUSIONS: IL-8 mRNA was significantly increased in inflamed mucosa of UC. Patients with high IL-8 mRNA expression in colonic mucosa despite PSL treatment were responsive to GCAP. Therefore, quantitative measurement of mucosal IL-8 mRNA may be useful in predicting the response to GCAP.