A gut bacterial containment system: Trillions of bacteria selectively inhabit our guts, but how do our bodies keep them contained? Spadoni et al. describe a “gut-vascular barrier” that prevents intestinal microbes from accessing the liver and the bloodstream in mice (see the Perspective by Bouziat and Jabri). Studies with human samples and in mice revealed that the cell biology of the gut-vascular barrier shares similarities with the blood-brain barrier of the central nervous system. Pathogenic bacteria such as Salmonella typhimurium could penetrate the gut-vascular barrier in mice, gaining access to the liver and bloodstream, in a manner dependent on the Salmonella pathogenicity island 2–type III secretion system. Science , this issue p. 830 ; see also p. 742

Crohn’s disease–related inflammation is characterized by reduced activity of the immunosuppressive cytokine transforming growth factor β1 (TGF-β1) due to high levels of SMAD7, an inhibitor of TGF-β1 signaling. Preclinical studies and a phase 1 study have shown that an oral SMAD7 antisense oligonucleotide, mongersen, targets ileal and colonic SMAD7. In a double-blind, placebo-controlled, phase 2 trial, we evaluated the efficacy of mongersen for the treatment of persons with active Crohn’s disease. Patients were randomly assigned to receive 10, 40, or 160 mg of mongersen or placebo per day for 2 weeks. The primary outcomes were clinical remission at day 15, defined as a Crohn’s Disease Activity Index (CDAI) score of less than 150, with maintenance of remission for at least 2 weeks, and the safety of mongersen treatment. A secondary outcome was clinical response (defined as a reduction of 100 points or more in the CDAI score) at day 28. The proportions of patients who reached the primary end point were 55% and 65% for the 40-mg and 160-mg mongersen groups, respectively, as compared with 10% for the placebo group (P<0.001). There was no significant difference in the percentage of participants reaching clinical remission between the 10-mg group (12%) and the placebo group. The rate of clinical response was significantly greater among patients receiving 10 mg (37%), 40 mg (58%), or 160 mg (72%) of mongersen than among those receiving placebo (17%) (P=0.04, P<0.001, and P<0.001, respectively). Most adverse events were related to complications and symptoms of Crohn’s disease. We found that study participants with Crohn’s disease who received mongersen had significantly higher rates of remission and clinical response than those who received placebo. (Funded by Giuliani; EudraCT number, 2011-002640-27.)

Objective: In mice, a subpopulation of gut dendritic cells (DCs) expressing CD103 drives the development of regulatory T (T _reg ) cells. Further, it was recently described that the cross-talk between human intestinal epithelial cells (IECs) and DCs helps in maintaining gut immune homeostasis via the induction of non-inflammatory DCs. In this study, an analysis was carried out to determine whether IECs could promote the differentiation of CD103 ⁺ tolerogenic DCs, and the function of primary CD103 ⁺ DCs isolated from human mesenteric lymph nodes (MLNs) was evaluated. Methods: Monocyte-derived DCs (MoDCs) and circulating CD1c ⁺ DCs were conditioned or not with supernatants from Caco-2 cells or IECs isolated from healthy donors or donors with Crohn’s disease and analysed for their ability to induce T _reg cell differentiation. In some cases, transforming growth factor β (TGFβ), retinoic acid (RA) or thymic stromal lymphopoietin (TSLP) were neutralised before conditioning. CD103 ⁺ and CD103 ⁻ DCs were sorted by fluorescence-activated cell sorting (FACS) from MLNs and used in T _reg cell differentiation experiments. Results: It was found that human IECs promoted the differentiation of tolerogenic DCs able to drive the development of adaptive Foxp3 ⁺ T _reg cells. This control was lost in patients with Crohn’s disease and paralleled a reduced expression of tolerogenic factors by primary IECs. MoDCs differentiated with RA or IEC supernatant upregulated the expression of CD103. Consistently, human primary CD103 ⁺ DCs isolated from MLNs were endowed with the ability to drive T _reg cell differentiation. This subset of DCs expressed CCR7 and probably represents a lamina propria-derived migratory population. Conclusions: A population of tolerogenic CD103 ⁺ DCs was identified in the human gut that probably differentiate in response to IEC-derived factors and drive T _reg cell development.

In ulcerative colitis [UC], mucosal damage occurs in areas that are infiltrated with neutrophils. The antimicrobial function of neutrophils relies in part on the formation of extracellular web-like structures, named neutrophil extracellular traps [NETs]. The formation and/or clearance of aberrant NETs have been associated with several immune diseases. Here we investigated the role of NETs in UC-related inflammation. The expression of NET-associated proteins was evaluated in colonic biopsies of patients with Crohn's disease [CD], UC and in normal controls [NC] by Western blotting, immunofluorescence and immunohistochemistry. Colonic biopsies of UC patients were analysed before and after anti-tumour necrosis factor α [anti-TNF-α] treatment. The capacity of neutrophils to produce NETs upon activation was tested in vitro. UC lamina propria mononuclear cells [LPMCs] were cultured with NETs in the presence or absence of an extracellular signal-regulated kinase-1/2 [ERK1/2] inhibitor and inflammatory cytokine induction was assessed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. We also characterized the contribution of NETs in dextran sodium sulfate [DSS]-induced colitis. NET-associated proteins were over-expressed in inflamed colon of UC patients as compared to CD patients and NC. Circulating neutrophils of UC patients produced NETs in response to TNF-α stimulation, and reduced expression of NET-related proteins and diminished NET formation were seen in patients receiving successful treatment with anti-TNF-α. Treatment of UC LPMCs with NETs activated ERK1/2, thus enhancing TNF-α and interleukin-1β [IL-1β] production. NETs were induced in mice with DSS-colitis and in vivo inhibition of NET release attenuated colitis. Our data show that NET release occurs in UC and suggest a role for NETs in sustaining mucosal inflammation in this disorder.

Background and aims: Probiotics and their metabolic products, here called postbiotics, have been proposed as food supplements for a healthier intestinal homeostasis, but also as therapeutic aids in inflammatory bowel disease (IBD) with, however, very little clinical benefit. This may be due to the lack of reliable preclinical models for testing the efficacy of different strains. Methods: The activity of three probiotic strains of Lactobacillus (or a postbiotic) was analysed and compared with a pathogenic strain of Salmonella on a novel organ culture system of human healthy and IBD intestinal mucosa developed in our laboratory. The system maintains an apical to basolateral polarity during stimulation due to the presence of a glued cave cylinder. The cylinder is detached at the end of the experiment and the tissue is processed for histology and immunohistochemistry. Cytokines released from the basolateral side are analysed. Results: The model system provides several physiological characteristics typical of a mucosal microenvironment including the presence of an organised mucus layer and an apical to basolateral polarity. Polarised administration of bacteria is critical to control the ensuing immune response as it mimics the physiological entrance of bacteria. The authors show that probiotics are not always beneficial for the healthy host and can also be detrimental in inflamed IBD. This study shows that a potent postbiotic can protect against the inflammatory properties of invasive Salmonella on healthy tissue and also downregulate ongoing inflammatory processes in IBD tissue. Conclusions: Probiotics can have inflammatory activities in both healthy and IBD tissue. Valid preclinical data on proper model systems should therefore be obtained before specific probiotic strains enter the clinics, especially if administered during acute inflammatory responses. Postbiotics may be a safe alternative for the treatment of patients with IBD in the acute inflammatory phase.

Objectives COVID-19 has rapidly become a major health emergency worldwide. Patients with IBD are at increased risk of infection, especially when they have active disease and are taking immunosuppressive therapy. The characteristics and outcomes of COVID-19 in patients with IBD remain unclear. Design This Italian prospective observational cohort study enrolled consecutive patients with an established IBD diagnosis and confirmed COVID-19. Data regarding age, sex, IBD (type, treatments and clinical activity), other comorbidities (Charlson Comorbidity Index (CCI)), signs and symptoms of COVID-19 and therapies were compared with COVID-19 outcomes (pneumonia, hospitalisation, respiratory therapy and death). Results Between 11 and 29 March 2020, 79 patients with IBD with COVID-19 were enrolled at 24 IBD referral units. Thirty-six patients had COVID-19-related pneumonia (46%), 22 (28%) were hospitalised, 7 (9%) required non-mechanical ventilation, 9 (11%) required continuous positive airway pressure therapy, 2 (3%) had endotracheal intubation and 6 (8%) died. Four patients (6%) were diagnosed with COVID-19 while they were being hospitalised for a severe flare of IBD. Age over 65 years (p=0.03), UC diagnosis (p=0.03), IBD activity (p=0.003) and a CCI score >1 (p=0.04) were significantly associated with COVID-19 pneumonia, whereas concomitant IBD treatments were not. Age over 65 years (p=0.002), active IBD (p=0.02) and higher CCI score were significantly associated with COVID-19-related death. Conclusions Active IBD, old age and comorbidities were associated with a negative COVID-19 outcome, whereas IBD treatments were not. Preventing acute IBD flares may avoid fatal COVID-19 in patients with IBD. Further research is needed.