BackgroundInappropriate cross talk between mammals and their gut microbiota may trigger intestinal inflammation and drive extra-intestinal immune-mediated diseases. Epithelial cells constitute the interface between gut microbiota and host tissue, and may regulate host responses to commensal enteric bacteria. Gnotobiotic animals represent a powerful approach to study bacterial-host interaction but are not readily accessible to the wide scientific community. We aimed at refining a protocol that in a robust manner would deplete the cultivable intestinal microbiota of conventionally raised mice and that would prove to have significant biologic validity.Methodology/Principal FindingsPreviously published protocols for depleting mice of their intestinal microbiota by administering broad-spectrum antibiotics in drinking water were difficult to reproduce. We show that twice daily delivery of antibiotics by gavage depleted mice of their cultivable fecal microbiota and reduced the fecal bacterial DNA load by 400 fold while ensuring the animals' health. Mice subjected to the protocol for 17 days displayed enlarged ceca, reduced Peyer's patches and small spleens. Antibiotic treatment significantly reduced the expression of antimicrobial factors to a level similar to that of germ-free mice and altered the expression of 517 genes in total in the colonic epithelium. Genes involved in cell cycle were significantly altered concomitant with reduced epithelial proliferative activity in situ assessed by Ki-67 expression, suggesting that commensal microbiota drives cellular proliferation in colonic epithelium.ConclusionWe present a robust protocol for depleting conventionally raised mice of their cultivatable intestinal microbiota with antibiotics by gavage and show that the biological effect of this depletion phenocopies physiological characteristics of germ-free mice.

Background A high proportion of COVID‐19 patients have cardiac involvement, even those without known cardiac disease. Downregulation of angiotensin converting enzyme 2 (ACE2), a receptor for SARS‐CoV‐2 and the renin‐angiotensin system, as well as inflammatory mechanisms have been suggested to play a role. ACE2 is abundant in the gut and associated with gut microbiota composition. We hypothesized that gut leakage of microbial products, and subsequent inflammasome activation could contribute to cardiac involvement in COVID‐19 patients. Methods Plasma levels of a gut leakage marker (LPS‐binding protein, LBP), a marker of enterocyte damage (intestinal fatty acid binding protein, IFABP), a gut homing marker (CCL25, ligand for chemokine receptor CCR9) and markers of inflammasome activation (IL‐1β, IL‐18 and their regulatory proteins) were measured at three time points (day 1, 3‐5 and 7‐10) in 39 hospitalized COVID‐19 patients and related to cardiac involvement. Results Compared to controls, COVID‐19 patients had elevated plasma levels of LBP and CCL25 but not IFABP, suggesting impaired gut barrier function and accentuated gut homing of T cells without excessive enterocyte damage. Levels of LBP were twice as high at baseline in patients with elevated cardiac markers compared with those without and remained elevated during hospitalization. Also, markers of inflammasome activation were moderately elevated in patients with cardiac involvement. LBP was associated with higher NT‐pro‐BNP levels, whereas IL‐18, IL‐18BP and IL‐1Ra were associated with higher troponin levels. Conclusion Patients with cardiac involvement had elevated markers of gut leakage and inflammasome activation, suggestive of a potential gut‐heart axis in COVID‐19.

Between 2006 and 2014, the population aged and experienced an overall higher prevalence of non-AIDS comorbidities, including CKD and CVD. The increase in CVD could be explained by the aging population, and the increase in CKD by aging and changes in other factors. Treatment strategies balancing HIV outcomes with long-term management of comorbidities remain a priority.

Innate and adaptive mucosal defense mechanisms ensure a homeostatic relationship with the large and complex mutualistic gut microbiota. Dimeric IgA and pentameric IgM are transported across the intestinal epithelium via the epithelial polymeric Ig receptor (pIgR) and provide a significant portion of the first line of natural or adaptive antibodymediated immune defense of the intestinal mucosa. We found that colonic epithelial cells from pIgR KO mice differentially expressed (more than twofold change) more than 200 genes compared with cells from WT mice, and upregulated the expression of antimicrobial peptides in a commensal-dependent manner. Detailed profiling of microbial communities based on 16S rRNA genes revealed differences in the commensal microbiota between pIgR KO and WT mice. Furthermore, we found that pIgR KO mice showed increased susceptibility to dextran sulfate sodium-induced colitis, and that this was driven by their conventional intestinal microbiota. Thus, in the absence of pIgR, the stability of the commensal microbiota is disturbed, gut homeostasis is compromised, and the outcome of colitis is significantly worsened. Keywords: Antimicrobial peptide r Colitis r Polymeric Ig receptor Supporting Information available online IntroductionMucus membranes lining the gastrointestinal tract are constantly bombarded by an enormous number of foreign antigens derived Correspondence: Prof. Finn-Eirik Johansen e-mail: f.e.johansen@imbv.uio.no from dietary products and the commensal microbiota. The microbial load of the human colon (about 10 14 bacteria) is estimated to be more than ten times the number of eukaryotic cells in the body [1,2]. The commensal microbiota lives in a mutualistic relationship with their host and provides several benefits. These include * These authors contributed equally to this work. Eur. J. Immunol. 2012Immunol. . 42: 2959Immunol. -2970 the digestion of insoluble fibers and increased energy usage of foods, synthesis of vitamin K [3,4], and niche occupation that could otherwise be exploited by pathogens [5]. The aggregate gene pool of the microbiota, a.k.a. the metagenome, contains 150 times more genes than the human genome [6,7]. Although the human microbiome varies considerably between hosts, our core microbiome has been classified into only three types of communities termed enterotypes [8].A first line of immune defense mediated by nonspecific innate immune effector components has evolved to protect the epithelial barrier without causing inflammatory immune responses [9]. The primary effector component of the adaptive immune system at mucosal sites is secretory IgA (SIgA) [10]. These antibodies are generated by cooperation between dimeric IgA (dIgA)-producing plasma cells and mucosal epithelial cells (ECs), which actively transport dIgA antibodies to the lumen by polymeric Ig receptor (pIgR)-mediated transfer. During transcytosis, the extracellular domain of the pIgR, known as secretory component, becomes covalently coupled to the IgA molecule and final release of receptor-carg...

Mucosal numbers of Foxp3(+) Tregs and activated (CD25+) macrophages are elevated in both pediatric and adult ileal CD. The greater increase of ileal Foxp3+ Tregs in pediatric CD than in adult CD might contribute to the relatively less frequent phenotype of isolated ileal enteritis in CD children.

Background Human immunodeficiency virus (HIV)–infected immunological nonresponders (INRs) fail to reconstitute their CD4+ T-cell pool after initiation of antiretroviral therapy, and their prognosis is inferior to that of immunological responders (IRs). A prevailing hypothesis is that the INR phenotype is caused by a persistently disrupted mucosal barrier, but assessments of gut mucosal immunology in different anatomical compartments are scarce. Methods We investigated circulating markers of mucosal dysfunction, immune activation, mucosal Th17 and Th22 cells, and mucosa-adherent microbiota signatures in gut mucosal specimens from sigmoid colon and terminal ileum of 19 INRs and 20 IRs in addition to 20 HIV-negative individuals. Results INRs had higher blood levels of the enterocyte damage marker intestinal fatty acid–binding protein than IRs. In gut mucosal biopsies, INRs had lower fractions of CD4+ T cells, higher fractions of interleukin 22, and a tendency to higher fractions of interleukin 17–producing CD4+ T cells. These findings were all restricted to the colon and correlated to circulating markers of enterocyte damage. There were no observed differences in gut microbial composition between INRs and IRs. Conclusions Restricted to the colon, enterocyte damage and mucosal immune dysfunction play a role for insufficient immune reconstitution in HIV infection independent of the gut microbiota.

The association between pulmonary sequelae and markers of disease severity, as well as pro-fibrotic mediators, were studied in 108 patients 3 months after hospital admission for COVID-19. The COPD assessment test (CAT-score), spirometry, diffusion capacity of the lungs (DLCO), and chest-CT were performed at 23 Norwegian hospitals included in the NOR-SOLIDARITY trial, an open-labelled, randomised clinical trial, investigating the efficacy of remdesivir and hydroxychloroquine (HCQ). Thirty-eight percent had a CAT-score ≥ 10. DLCO was below the lower limit of normal in 29.6%. Ground-glass opacities were present in 39.8% on chest-CT, parenchymal bands were found in 41.7%. At admission, low pO2/FiO2 ratio, ICU treatment, high viral load, and low antibody levels, were predictors of a poorer pulmonary outcome after 3 months. High levels of matrix metalloproteinase (MMP)-9 during hospitalisation and at 3 months were associated with persistent CT-findings. Except for a negative effect of remdesivir on CAT-score, we found no effect of remdesivir or HCQ on long-term pulmonary outcomes. Three months after hospital admission for COVID-19, a high prevalence of respiratory symptoms, reduced DLCO, and persistent CT-findings was observed. Low pO2/FiO2 ratio, ICU-admission, high viral load, low antibody levels, and high levels of MMP-9 were associated with a worse pulmonary outcome.

Histologically normal colon mucosa contains fewer macrophages in children than in adults. However, in colon of children with untreated CD the mucosal macrophage density is increased. Activated mucosal macrophages are increased in untreated pediatric IBD regardless of inflammatory grade. Such upregulated innate mucosal immune activation may contribute to the colonic phenotype of childhood CD.