The restoration of blood flow, i.e., reperfusion, is the treatment of choice to save viable tissue following acute ischemia of a vascular territory. Nevertheless, reperfusion can be accompanied by significant inflammatory events that limit the beneficial effects of blood flow restoration. To evaluate the potential role of the intestinal microbiota in facilitating the development of tissue injury and systemic inflammation, germ-free and conventional mice were compared in their ability to respond to ischemia and reperfusion injury. In conventional mice, there was marked local (intestine) and remote (lung) edema formation, neutrophil influx, hemorrhage, and production of TNF-α, KC, MIP-2, and MCP-1. Moreover, there was an increase in the concentration of serum TNF-α and 100% lethality. In germ-free mice, there was no local, remote, or systemic inflammatory response or lethality after intestinal ischemia and reperfusion and, in contrast to conventional mice, germ-free animals produced greater amounts of IL-10. Similar results were obtained after administration of LPS, i.e., little production of TNF-α or lethality and production of IL-10 after LPS in germ-free mice. Blockade of IL-10 with Abs induced marked inflammation and lethality in germ-free mice after ischemia and reperfusion or LPS administration, demonstrating that the ability of these mice to produce IL-10 was largely responsible for their “no inflammation” phenotype. This was consistent with the prevention of reperfusion-associated injury by the exogenous administration of IL-10 to conventional mice. Thus, the lack of intestinal microbiota is accompanied by a state of active IL-10-mediated inflammatory hyporesponsiveness.

Objective Host–microbial interactions are central in health and disease. Monosodium urate monohydrate (MSU) crystals cause gout by activating the NLRP3 inflammasome, leading to interleukin‐1β (IL‐1β) production and neutrophil recruitment. This study was undertaken to investigate the relevance of gut microbiota, acetate, and the metabolite‐sensing receptor GPR43 in regulating inflammation in a murine model of gout. Methods Gout was induced by the injection of MSU crystals into the knee joints of mice. Macrophages from the various animals were stimulated to determine inflammasome activation and production of reactive oxygen species (ROS). Results Injection of MSU crystals caused joint inflammation, as seen by neutrophil influx, hypernociception, and production of IL‐1β and CXCL1. These parameters were greatly decreased in germ‐free mice, mice treated with antibiotics, and GPR‐43–deficient mice. Recolonization or administration of acetate to germ‐free mice restored inflammation in response to injection of MSU crystals. In vitro, macrophages produced ROS and assembled the inflammasome when stimulated with MSU. Macrophages from germ‐free animals produced little ROS, and there was little inflammasome assembly. Similar results were observed in macrophages from GPR‐43–deficient mice. Treatment of germ‐free mice with acetate restored in vitro responsiveness of macrophages to MSU crystals. Conclusion In the absence of microbiota, there is decreased production of short‐chain fatty acids that are necessary for adequate inflammasome assembly and IL‐1β production in a manner that is at least partially dependent on GPR43. These results clearly show that the commensal microbiota shapes the host's ability to respond to an inflammasome‐dependent acute inflammatory stimulus outside the gut.

The ability of an individual to sense pain is fundamental for its capacity to adapt to its environment and to avoid damage. The sensation of pain can be enhanced by acute or chronic inflammation. In the present study, we have investigated whether inflammatory pain, as measured by hypernociceptive responses, was modified in the absence of the microbiota. To this end, we evaluated mechanical nociceptive responses induced by a range of inflammatory stimuli in germ-free and conventional mice. Our experiments show that inflammatory hypernociception induced by carrageenan, lipopolysaccharide, TNF-␣, IL-1␤, and the chemokine CXCL1 was reduced in germfree mice. In contrast, hypernociception induced by prostaglandins and dopamine was similar in germ-free or conventional mice. Reduction of hypernociception induced by carrageenan was associated with reduced tissue inflammation and could be reversed by reposition of the microbiota or systemic administration of lipopolysaccharide. Significantly, decreased hypernociception in germ-free mice was accompanied by enhanced IL-10 expression upon stimulation and could be reversed by treatment with an anti-IL-10 antibody. Therefore, these results show that contact with commensal microbiota is necessary for mice to develop inflammatory hypernociception. These findings implicate an important role of the interaction between the commensal microbiota and the host in favoring adaptation to environmental stresses, including those that cause pain.cytokines ͉ germ-free mice ͉ hyperalgesia ͉ nociception

Mammals are colonized by an astronomical number of commensal microorganisms on their environmental exposed surfaces. These symbiotic species build up a complex community that aids their hosts in several physiological activities. We have shown that lack of intestinal microbiota is accompanied by a state of active IL-10–mediated inflammatory hyporesponsiveness. The present study investigated whether the germfree state and its hyporesponsive phenotype alter host resistance to an infectious bacterial insult. Experiments performed in germfree mice infected with Klebsiella pneumoniae showed that these animals are drastically susceptible to bacterial infection in an IL-10–dependent manner. In germfree mice, IL-10 restrains proinflammatory mediator production and neutrophil recruitment and favors pathogen growth and dissemination. Germfree mice were resistant to LPS treatment. However, priming of these animals with several TLR agonists recovered their inflammatory responsiveness to sterile injury. LPS pretreatment also rendered germfree mice resistant to pulmonary K. pneumoniae infection, abrogated IL-10 production, and restored TNF-α and CXCL1 production and neutrophil mobilization into lungs of infected germfree mice. This effective inflammatory response mounted by LPS-treated germfree mice resulted in bacterial clearance and enhanced survival upon infection. Therefore, host colonization by indigenous microbiota alters the way the host reacts to environmental infectious stimuli, probably through activation of TLR-dependent pathways. Symbiotic gut colonization enables proper inflammatory response to harmful insults to the host, and increases resilience of the entire mammal-microbiota consortium to environmental pressures.

In this paper, comparative molecular studies between authentic Saccharomyces cerevisiae strains, related species, and the strain described as Saccharomyces boulardii were performed. The response of a S. boulardii strain and a S. cerevisiae strain (W303) to different stress conditions was also evaluated. The results obtained in this study show that S. boulardii is genetically very close or nearly identical to S. cerevisiae. Metabolically and physiologically, however, it shows a very different behavior, particularly in relation to growth yield and resistance to temperature and acidic stresses, which are important characteristics for a microorganism to be used as a probiotic.

The effect of Saccharomyces boulardii on the immune system was evaluated, comparing germ‐free Swiss/NIH mice monoassociated with the probiotic with germ‐free mice. Saccharomyces boulardii colonized the gut of germ‐free mice and survived the gastrointestinal conditions. An increase in sIgA production, both total and anti‐S. boulardii, was observed in the intestinal contents of monoassociated mice when compared with germ‐free controls. The number of Küpffer cells was significantly higher in monoassociated mice than in germ‐free controls. In S. boulardii‐monoassociated mice, clearance of Escherichia coli B41 was higher than in germ‐free controls. TNF‐α, IFN‐γ and IL‐12 serum levels were higher at earlier time points in monoassociated mice when compared with germ‐free mice. These results show that the yeast S. boulardii modulates the host immune responses. This effect may be of interest for improving the resistance to enteropathogenic bacterial infections.

The appropriate development of an inflammatory response is central for the ability of a host to deal with any infectious insult. However, excessive, misplaced, or uncontrolled inflammation may lead to acute or chronic diseases. The microbiota plays an important role in the control of inflammatory responsiveness. In this study, we investigated the role of lipoxin A4 and annexin-1 for the IL-10-dependent inflammatory hyporesponsiveness observed in germfree mice. Administration of a 15-epi-lipoxin A4 analog or an annexin-1-derived peptide to conventional mice prevented tissue injury, TNF-α production, and lethality after intestinal ischemia/reperfusion. This was associated with enhanced IL-10 production. Lipoxin A4 and annexin-1 failed to prevent reperfusion injury in IL-10-deficient mice. In germfree mice, there was enhanced expression of both lipoxin A4 and annexin-1. Blockade of lipoxin A4 synthesis with a 5-lipoxygenase inhibitor or Abs against annexin-1 partially prevented IL-10 production and this was accompanied by partial reversion of inflammatory hyporesponsiveness in germfree mice. Administration of BOC-1, an antagonist of ALX receptors (at which both lipoxin A4 and annexin-1 act), or simultaneous administration of 5-lipoxygenase inhibitor and anti-annexin-1 Abs, was associated with tissue injury, TNF-α production, and lethality similar to that found in conventional mice. Thus, our data demonstrate that inflammatory responsiveness is tightly controlled by the presence of the microbiota and that the innate capacity of germfree mice to produce IL-10 is secondary to their endogenous greater ability to produce lipoxin A4 and annexin-1.

The commensal microbiota has a high impact on health and disease by modulating the development and homeostasis of host immune system. Immune cells are involved in virtually every aspect of the wound repair process; however, the impact of commensal microbiota on skin wound healing is largely unknown. In this study, we evaluated the influence of commensal microbiota on tissue repair of excisional skin wounds by using germ-free (GF) Swiss mice. We observed that macroscopic wound closure rate is accelerated in the absence of commensal microbiota. Accordantly, histologically assessed wound epithelization was accelerated in GF in comparison with conventional (CV) Swiss mice. The wounds of GF mice presented a significant decrease in neutrophil accumulation and an increase in mast cell and macrophage infiltration into wounds. Interestingly, alternatively activated healing macrophage-related genes were highly expressed in the wound tissue of GF mice. Moreover, levels of the anti-inflammatory cytokine IL-10, the angiogenic growth factor VEGF and angiogenesis were higher in the wound tissue of those mice. Conversely, scarring and levels of the profibrogenic factor TGF-β1 were greatly reduced in GF mice wounded skin when compared with CV mice. Of note, conventionalization of GF mice with CV microbiota restored wound closure rate, neutrophil and macrophage accumulation, cytokine production, and scarring to the same extent as CV mice. Overall, our findings suggest that, in the absence of any contact with microbiota, skin wound healing is accelerated and scarless, partially because of reduced accumulation of neutrophils, increased accumulation of alternatively activated healing macrophages, and better angiogenesis at wound sites.