Interleukin (IL)-11 is a member of the IL-6 family of cytokines and is involved in multiple cellular responses, including tumor development. However, the origin and functions of IL-11-producing ...(IL-11
) cells are not fully understood. To characterize IL-11
cells in vivo, we generate Il11 reporter mice. IL-11
cells appear in the colon in murine tumor and acute colitis models. Il11ra1 or Il11 deletion attenuates the development of colitis-associated colorectal cancer. IL-11
cells express fibroblast markers and genes associated with cell proliferation and tissue repair. IL-11 induces the activation of colonic fibroblasts and epithelial cells through phosphorylation of STAT3. Human cancer database analysis reveals that the expression of genes enriched in IL-11
fibroblasts is elevated in human colorectal cancer and correlated with reduced recurrence-free survival. IL-11
fibroblasts activate both tumor cells and fibroblasts via secretion of IL-11, thereby constituting a feed-forward loop between tumor cells and fibroblasts in the tumor microenvironment.
The benefits of commensal bacteria to the health of the host have been well documented, such as providing stimulation to potentiate host immune responses, generation of useful metabolites, and direct ...competition with pathogens. However, the ability of the host immune system to control the microbiota remains less well understood. Recent microbiota analyses in mouse models have revealed detailed structures and diversities of microbiota at different sites of the digestive tract in mouse populations. The contradictory findings of previous studies on the role of host immune responses in overall microbiota composition are likely attributable to the high β-diversity in mouse populations as well as technical limitations of the methods to analyze microbiota. The host employs multiple systems to strictly regulate their interactions with the microbiota. A spatial segregation between the host and microbiota is achieved with the mucosal epithelium, which is further fortified with a mucus layer on the luminal side and Paneth cells that produce antimicrobial peptides. When commensal bacteria or pathogens breach the epithelial barrier and translocate to peripheral tissues, the host immune system is activated to eliminate them. Defective segregation and tissue elimination of commensals result in exaggerated inflammatory responses and possibly death of the host. In this review, we discuss the current understanding of mouse microbiota, its common features with human microbiota, the technologies utilized to analyze microbiota, and finally the challenges faced to delineate the role of host immune responses in the composition of the luminal microbiota.
Pathobionts play a critical role in disease development, but the immune mechanisms against pathobionts remain poorly understood. Here, we report a critical role for interleukin-22 (IL-22) in systemic ...protection against bacterial pathobionts that translocate into the circulation after infection with the pathogen Clostridium difficile. Infection with C. difficile induced IL-22, and infected Il22−/− mice harbored high numbers of pathobionts in extraintestinal organs despite comparable pathogen load and intestinal damage in mutant and wild-type mice. Pathobionts exhibited increased resistant against complement-mediated phagocytosis, and their intravenous administration resulted in high animal mortality. Selective removal of translocated commensals rescued Il22−/− mice, and IL-22 administration enhanced the elimination of pathobionts. Mechanistically, IL-22 augmented bacterial phagocytosis by increasing the expression and bacterial binding of complement C3. Our study demonstrates an unexpected role for IL-22 in controlling the elimination of pathobionts that enter the systemic circulation through the regulation of the complement system.
•An enteropathogen induces translocation of pathobionts to extraintestinal organs•IL-22 is critical for systemic elimination of translocated pathobionts•Complement-resistant enterobacterial pathobionts induce host complication•IL-22 augments expression and binding of C3 to enterobacterial pathobionts
Although interleukin-22 (IL-22) has been reported to provide protection to intestinal pathogens such as C. rodentium, its function in the periphery is less clear. Hasegawa et al. demonstrate a critical role for IL-22 in systemic protection against bacterial pathobionts that translocate into the circulation after infection with the pathogen C. difficile.
Clostridium difficile is a Gram-positive obligate anaerobic pathogen that causes pseudomembranous colitis in antibiotics-treated individuals. However, host immune protective mechanisms against C. ...difficile are largely unknown. In this study, we show that C. difficile possesses potent stimulatory activity for nucleotide-binding oligomerization domain 1 (Nod1), an intracellular pattern recognition molecule that senses bacterial peptidoglycan-related molecules. Nod1(-/-), but not Nod2(-/-), mice exhibited increased lethality in response to C. difficile intestinal infection despite comparable levels of intestinal damage and epithelial permeability in Nod1(-/-) and control mice. The enhanced lethality was accompanied by impaired C. difficile clearance, increased bacterial translocation, and elevated levels of endotoxin and IL-1β in the serum of Nod1(-/-) mice. Histological and flow cytometric analyses revealed that Nod1(-/-) mice had defective recruitment of neutrophils, but not macrophages, to the intestine after C. difficile infection. The reduced recruitment of neutrophils correlated with impaired production of CXCL1, but not CCL2, XCL1, and other cytokines/chemokines, in infected Nod1(-/-) mice. The influx of neutrophils also was reduced when C. difficile was administered i.p., suggesting that Nod1 directly recognizes C. difficile to induce the recruitment of neutrophils to the infected site. These results indicate that Nod1 regulates host susceptibility to C. difficile and suggest that Nod1-mediated neutrophil recruitment is an important immune response against the enteric pathogen.
Gut dysbiosis associated with intestinal inflammation is characterized by the blooming of particular bacteria such as adherent-invasive E. coli (AIEC). However, the precise mechanisms by which AIEC ...impact on colitis remain largely unknown. Here we show that antibiotic-induced dysbiosis worsened chemically-induced colitis in IL-22-deficient mice, but not in wild-type mice. The increase in intestinal inflammation was associated with the expansion of E. coli strains with genetic and functional features of AIEC. These E. coli isolates exhibited high ability to out compete related bacteria via colicins and resistance to the host complement system in vitro. Mutation of wzy, the lipopolysaccharide O polymerase gene, rendered AIEC more sensitive to the complement system and more susceptible to engulfment and killing by phagocytes while retaining its ability to outcompete related bacteria in vitro. The wzy AIEC mutant showed impaired fitness to colonize the intestine under colitic conditions, but protected mice from chemically-induced colitis. Importantly, the ability of the wzy mutant to protect from colitis was blocked by depletion of complement C3 which was associated with impaired intestinal eradication of AIEC in colitic mice. These studies link surface lipopolysaccharide O-antigen structure to the regulation of colitic activity in commensal AIEC via interactions with the complement system.
Periodontitis is a common disease that is characterized by resorption of the alveolar bone and mediated by commensal bacteria that trigger host immune responses and bone destruction through ...unidentified mechanisms. We report that Nod1, an innate intracellular host receptor for bacterial peptidoglycan-related molecules, is critical for commensal-induced periodontitis in a mouse model. Mice lacking Nod1 exhibit reduced bone resorption as well as impaired recruitment of neutrophils to gingival tissues and osteoclasts to the alveolar bone, which mediate tissue and bone destruction. Further analysis showed that accumulation of a Nod1-stimulating commensal bacterium, NI1060, at gingival sites was sufficient to induce neutrophil recruitment and bone resorption. Genomic sequencing revealed that NI1060 is a mouse-specific bacterium that is related to bacteria associated with the development of aggressive periodontitis in humans. These findings provide insight into commensal-host interactions contributing to periodontitis and identify a potential target for preventing this common oral disease.
•Nod1 is critical for immune responses resulting in commensal-induced oral bone resorption•A Nod1-stimulating commensal, NI1060, accumulates at damaged gingival sites•NI1060 is related to a human aggressive periodontitis-associated bacterium•Nod1 stimulation by NI1060 is important to induce bone resorption
Strain NI1060 is an oral bacterium responsible for periodontitis in a murine ligature-induced disease model. To better understand its pathogenicity, we have determined the complete sequence of its ...2,553,982 bp genome. Although closely related to Pasteurella pneumotropica, a pneumonia-associated rodent commensal based on its 16S rRNA, the NI1060 genomic content suggests that they are different species thriving on different energy sources via alternative metabolic pathways. Genomic and phylogenetic analyses showed that strain NI1060 is distinct from the genera currently described in the family Pasteurellaceae, and is likely to represent a novel species. In addition, we found putative virulence genes involved in lipooligosaccharide synthesis, adhesins and bacteriotoxic proteins. These genes are potentially important for host adaption and for the induction of dysbiosis through bacterial competition and pathogenicity. Importantly, strain NI1060 strongly stimulates Nod1, an innate immune receptor, but is defective in two peptidoglycan recycling genes due to a frameshift mutation. The in-depth analysis of its genome thus provides critical insights for the development of NI1060 as a prime model system for infectious disease.
Nod1 and Nod2 are intracellular proteins that are involved in recognition of bacterial molecules and their genetic variations have been linked to several inflammatory diseases that are strongly ...affected by environmental factors. However, the distribution of Nod1- and Nod2-stimulatory molecules in different bacterial species and environments is unknown. Here we established a quantitative bioassay to screen and characterize Nod1- and Nod2-stimulatory activities in different environmental sites and bacterial species. Using this system, we found that common environments including foods and soils contain high levels of Nod1- and Nod2-stimulatory activities. Several Bacillus species were identified to possess the highest Nod1-stimulatory activity among soil bacteria. Unlike other immunostimulatory molecules, the higher level of Nod1-stimulatory activity was found in the culture supernatant and not in extracts from whole cell bacteria. Nod1-stimulatory molecules were highly stable at extreme pH and boiling conditions and were synthesized in an amidase- and sltY-independent manner. These results suggest a novel mechanism by which bacteria present in the environment stimulate the host immune system through Nod1.
Human histone H2AX is rapidly phosphorylated on serine 139 in response to DNA double-strand breaks and plays a crucial role in tethering the factors involved in DNA repair and damage signaling. ...Replication stress caused by hydroxyurea or UV also initiates H2AX phosphorylation in S-phase cells, although UV-induced H2AX phosphorylation in non-cycling cells has recently been observed. Here we study the UV-induced H2AX phosphorylation in human primary fibroblasts under growth-arrested conditions. This reaction absolutely depends on nucleotide excision repair (NER) and is mechanistically distinct from the replication stress-induced phosphorylation. The treatment of cytosine-beta-D-arabinofuranoside strikingly enhances the NER-dependent H2AX phosphorylation and induces the accumulation of replication protein A (RPA) and ATR-interacting protein (ATRIP) at locally UV-damaged subnuclear regions. Consistently, the phosphorylation appears to be mainly mediated by ataxia-telangiectasia mutated and Rad3-related (ATR), although Chk1 (Ser345) is not phosphorylated by the activated ATR. The cellular levels of DNA polymerases delta and epsilon and proliferating cell nuclear antigen are markedly reduced in quiescent cells. We propose a model that perturbed gap-filling synthesis following dual incision in NER generates single-strand DNA gaps and hence initiates H2AX phosphorylation by ATR with the aid of RPA and ATRIP.
Nod1 is a member of family of intracellular proteins that mediate host recognition of bacterial peptidoglycan. To characterize immune responses mediated by Nod1, synthetic ligand compounds possessing ...enhanced ability to stimulate Nod1 were developed to study the function of Nod1. Stimulation of epithelial cells with Nod1 stimulatory molecules induced chemokines and other proinflammatory molecules that are important for innate immune responses and recruitment of acute inflammatory cells. Administration of Nod1 ligands into mice induced chemokines and recruitment of acute inflammatory cells, an activity that was abolished in Nod1-null mice. Microarray analysis revealed that Nod1 stimulation induces a restricted number of genes in intestinal epithelial cells compared with that induced by tumor necrosis factor (TNF) alpha. Nod1 stimulation did not induce TNFalpha, interleukin 12, and interferon gamma, suggesting that the primary role of Nod1 is to induce the recruitment of immune cells. These results indicate that Nod1 functions as a pathogen recognition molecule to induce expression of molecules involved in the early stages of the innate immune response.
PDF
