Antimicrobial overproduction sustains intestinal inflammation by inhibiting Enterococcus colonization.

Loss of antimicrobial proteins such as REG3 family members compromises the integrity of the intestinal barrier. Here, we demonstrate that overproduction of REG3 proteins can also be detrimental by reducing a protective species in the microbiota. Patients with inflammatory bowel disease (IBD) experiencing flares displayed heightened levels of secreted REG3 proteins that mediated depletion of Enterococcus faecium (Efm) from the gut microbiota. Efm inoculation of mice ameliorated intestinal inflammation through activation of the innate immune receptor NOD2, which was associated with the bacterial DL-endopeptidase SagA that generates NOD2-stimulating muropeptides. NOD2 activation in myeloid cells induced interleukin-1ß (IL-1ß) secretion to increase the proportion of IL-22-producing CD4+ T helper cells and innate lymphoid cells that promote tissue repair. Finally, Efm was unable to protect mice carrying a NOD2 gene variant commonly found in IBD patients. Our findings demonstrate that inflammation self-perpetuates by causing aberrant antimicrobial activity that disrupts symbiotic relationships with gut microbes.

Antimicrobial overproduction sustains intestinal inflammation by inhibiting Enterococcus colonization.

Loss of antimicrobial proteins such as REG3 family members compromises the integrity of the intestinal barrier. Here, we demonstrate that overproduction of REG3 proteins can also be detrimental by reducing a protective species in the microbiota. Patients with inflammatory bowel disease (IBD) experiencing flares displayed heightened levels of secreted REG3 proteins that mediated depletion of Enterococcus faecium ( Efm ) from the gut microbiota. Efm inoculation of mice ameliorated intestinal inflammation through activation of the innate immune receptor NOD2, which was associated with the bacterial DL-endopeptidase SagA. Microbiota sensing by NOD2 in myeloid cells mediated IL-1ß secretion and increased the proportion of IL-22-producing CD4 + T helper cells and innate lymphoid cells. Finally, Efm was unable to protect mice carrying a NOD2 gene variant commonly found in IBD patients. Our findings demonstrate that inflammation self-perpetuates by causing aberrant antimicrobial activity that disrupts symbiotic relationships with gut microbes.

Enteric viruses evoke broad host immune responses resembling those elicited by the bacterial microbiome.

The contributions of the viral component of the microbiome-the virome-to the development of innate and adaptive immunity are largely unknown. Here, we systematically defined the host response in mice to a panel of eukaryotic enteric viruses representing six different families. Infections with most of these viruses were asymptomatic in the mice, the magnitude and duration of which was dependent on the microbiota. Flow cytometric and transcriptional profiling of mice mono-associated with these viruses unveiled general adaptations by the host, such as lymphocyte differentiation and IL-22 signatures in the intestine, as well as numerous viral-strain-specific responses that persisted. Comparison with a dataset derived from analogous bacterial mono-association in mice identified bacterial species that evoke an immune response comparable with the viruses we examined. These results expand an understanding of the immune space occupied by the enteric virome and underscore the importance of viral exposure events.

An intestinal organoid-based platform that recreates susceptibility to T-cell-mediated tissue injury.

A goal in precision medicine is to use patient-derived material to predict disease course and intervention outcomes. Here, we use mechanistic observations in a preclinical animal model to design an ex vivo platform that recreates genetic susceptibility to T-cell-mediated damage. Intestinal graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation. We found that intestinal GVHD in mice deficient in Atg16L1, an autophagy gene that is polymorphic in humans, is reversed by inhibiting necroptosis. We further show that cocultured allogeneic T cells kill Atg16L1-mutant intestinal organoids from mice, which was associated with an aberrant epithelial interferon signature. Using this information, we demonstrate that pharmacologically inhibiting necroptosis or interferon signaling protects human organoids derived from individuals harboring a common ATG16L1 variant from allogeneic T-cell attack. Our study provides a roadmap for applying findings in animal models to individualized therapy that targets affected tissues.

Cell kinetics of mechanically stimulated rat oral epithelia.

OBJECTIVE: To study cell kinetics of rat gingival (GE), sulcular (SE) and junctional (JE) epithelia in the steady-state and after application of mechanical pressure. DESIGN: Elastic bands were inserted between first and second maxillary molars of 8-week-old male rats, which were labelled with H(3) TdR and killed in groups of six to seven animals together with equal-sized groups of labelled control animals at intervals between 1 and 168 h. Autoradiographs were used to determine epithelial cell proliferation on the pressure side of M1 by calculating the percentage of (3)H TdR-labelled cells (PLC) in the basal (BL) and suprabasal (SL) layers of GE, SE and JE and to estimate median cell cycle (MCC) duration of BL cells by plotting mean and median grain counts against time. RESULTS: (3)H TdR-labelled cells were present in SL of SE and JE 1-12h after isotope injection suggesting that the BL might be not the only source of progenitor cells for JE as they might also be derived through migration from adjacent SE. Application of pressure significantly (ANOVA, P<0.05) reduced PLC in BL of GE, SE and JE indicating a decrease of cell proliferation after 1-12h in response to pressure. In steady-state, the MCC durations of BL cells of GE, SE and JE were 39, 14 and 9h, respectively. After application of pressure, they increased significantly (chi(2)-test, P<0.05) to 48, 44 and 34 h, respectively. CONCLUSIONS: Sustained pressure may lead to reduction of proliferative activity of these epithelia inducing slower progression of progenitor cells through the cell cycle.