•Distinct populations of intestinal macrophages segregated both transcriptionally and anatomically, exist in the mouse and human.•The intestine hosts long-lived macrophage populations, that are not ...replenished by circulating monocytes in the steady state.•Macrophages in the intestinal lamina propria are critical mediators of tissue tolerance under steady state and inflammatory conditions.•Macrophages in the intestinal muscularis are specialized to interact with the enteric-associated nervous system.•Intestinal macrophages have co-opted further roles in tissue physiology, including vascular integrity and smooth muscle contraction.
The mammalian gastrointestinal tract harbors a large reservoir of tissue macrophages, which, in concert with other immune cells, help to maintain a delicate balance between tolerance to commensal microbes and food antigens, and resistance to potentially harmful microbes or toxins. Beyond their roles in resistance and tolerance, recent studies have uncovered novel roles played by tissue-resident, including intestinal-resident macrophages in organ physiology. Here, we will discuss recent advances in the understanding of the origin, phenotype and function of macrophages residing in the different layers of the intestine during homeostasis and under pathological conditions.
The gut microbiota affects tissue physiology, metabolism, and function of both the immune and nervous systems. We found that intrinsic enteric-associated neurons (iEANs) in mice are functionally ...adapted to the intestinal segment they occupy; ileal and colonic neurons are more responsive to microbial colonization than duodenal neurons. Specifically, a microbially responsive subset of viscerofugal CART
neurons, enriched in the ileum and colon, modulated feeding and glucose metabolism. These CART
neurons send axons to the prevertebral ganglia and are polysynaptically connected to the liver and pancreas. Microbiota depletion led to NLRP6- and caspase 11-dependent loss of CART
neurons and impaired glucose regulation. Hence, iEAN subsets appear to be capable of regulating blood glucose levels independently from the central nervous system.
Connections between the gut and brain monitor the intestinal tissue and its microbial and dietary content
, regulating both physiological intestinal functions such as nutrient absorption and motility
..., and brain-wired feeding behaviour
. It is therefore plausible that circuits exist to detect gut microorganisms and relay this information to areas of the central nervous system that, in turn, regulate gut physiology
. Here we characterize the influence of the microbiota on enteric-associated neurons by combining gnotobiotic mouse models with transcriptomics, circuit-tracing methods and functional manipulations. We find that the gut microbiome modulates gut-extrinsic sympathetic neurons: microbiota depletion leads to increased expression of the neuronal transcription factor cFos, and colonization of germ-free mice with bacteria that produce short-chain fatty acids suppresses cFos expression in the gut sympathetic ganglia. Chemogenetic manipulations, translational profiling and anterograde tracing identify a subset of distal intestine-projecting vagal neurons that are positioned to have an afferent role in microbiota-mediated modulation of gut sympathetic neurons. Retrograde polysynaptic neuronal tracing from the intestinal wall identifies brainstem sensory nuclei that are activated during microbial depletion, as well as efferent sympathetic premotor glutamatergic neurons that regulate gastrointestinal transit. These results reveal microbiota-dependent control of gut-extrinsic sympathetic activation through a gut-brain circuit.
The enteric nervous system (ENS) controls several intestinal functions including motility and nutrient handling, which can be disrupted by infection-induced neuropathies or neuronal cell death. We ...investigated possible tolerance mechanisms preventing neuronal loss and disruption in gut motility after pathogen exposure. We found that following enteric infections, muscularis macrophages (MMs) acquire a tissue-protective phenotype that prevents neuronal loss, dysmotility, and maintains energy balance during subsequent challenge with unrelated pathogens. Bacteria-induced neuroprotection relied on activation of gut-projecting sympathetic neurons and signaling via β2-adrenergic receptors (β2AR) on MMs. In contrast, helminth-mediated neuroprotection was dependent on T cells and systemic production of interleukin (IL)-4 and IL-13 by eosinophils, which induced arginase-expressing MMs that prevented neuronal loss from an unrelated infection located in a different intestinal region. Collectively, these data suggest that distinct enteric pathogens trigger a state of disease or tissue tolerance that preserves ENS number and functionality.
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•Bacteria-induced neuroprotection is mediated by β-2AR signaling in macrophages•Helminth-induced neuroprotection relies on eosinophil-derived IL-4 and IL-13•Pet store mice display similar neuroprotection as previously infected SPF mice•Post-infectious bone marrow and tissue environment maintain long-term neuroprotection
Bacterial and helminth pathogens in the intestine induce distinct pathways converging on tissue macrophages that mediate enteric neuronal protection, aiding host fitness via intestinal motility and energy balance during subsequent infections.
Enteric-associated neurons (EANs) are closely associated with immune cells and continuously monitor and modulate homeostatic intestinal functions, including motility and nutrient sensing. ...Bidirectional interactions between neuronal and immune cells are altered during disease processes such as neurodegeneration or irritable bowel syndrome. We investigated the effects of infection-induced inflammation on intrinsic EANs (iEANs) and the role of intestinal muscularis macrophages (MMs) in this context. Using murine models of enteric infections, we observed long-term gastrointestinal symptoms, including reduced motility and loss of excitatory iEANs, which was mediated by a Nlrp6- and Casp11-dependent mechanism, depended on infection history, and could be reversed by manipulation of the microbiota. MMs responded to luminal infection by upregulating a neuroprotective program via β2-adrenergic receptor (β2-AR) signaling and mediated neuronal protection through an arginase 1-polyamine axis. Our results identify a mechanism of neuronal death post-infection and point to a role for tissue-resident MMs in limiting neuronal damage.
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•Enteric pathogens trigger reversible neuronal loss and long-term GI symptoms•Enteric infection-triggered neuronal loss is Nlrp6- and caspase 11-dependent•Intestinal muscularis macrophages (MMs) rapidly respond to enteric pathogens•Neuronal death is limited by a MM-β2-adrenergic-arginase 1-polyamine axis
Bacterial enteric infections lead to lasting inflammatory changes in the intestine with concomitant reduction in the myenteric neuron number caused by Nlrp6- and caspase 11-mediated cell death, which can be opposed by β2-adrenergic-arginase 1-polyamine axis signaling in muscularis macrophages.
The mammalian gut microbiota provides essential metabolites to the host and promotes the differentiation and accumulation of extrathymically generated regulatory T (pTreg) cells. To explore the ...impact of these cells on intestinal microbial communities, we assessed the composition of the microbiota in pTreg cell-deficient and -sufficient mice. pTreg cell deficiency led to heightened type 2 immune responses triggered by microbial exposure, which disrupted the niche of border-dwelling bacteria early during colonization. Moreover, impaired pTreg cell generation led to pervasive changes in metabolite profiles, altered features of the intestinal epithelium, and reduced body weight in the presence of commensal microbes. Absence of a single species of bacteria depleted in pTreg cell-deficient animals, Mucispirillum schaedleri, partially accounted for the sequelae of pTreg cell deficiency. These observations suggest that pTreg cells modulate the metabolic function of the intestinal microbiota by restraining immune defense mechanisms that may disrupt a particular bacterial niche.
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•pTreg cells affect the intestinal microbiota composition in healthy mice•pTreg cells suppress type 2 responses and preserve a niche for border-dwelling bacteria•pTreg cell-dependent border-dwelling bacteria affect the host metabolome•pTreg cells promote organismal homeostasis in the presence of commensal bacteria
Extrathymically generated regulatory (pTreg) cells are induced by bacterial products at mucosal sites. In this issue, Campbell et al. show that pTreg cell deficiency impedes the establishment of a subset of intestinal bacteria due to heightened immune responses, with significant effects on host metabolites and fitness.
Bifunctional siRNAs for tumor therapy Matheis, Fanny; Besch, Robert
Methods in molecular biology (Clifton, N.J.),
2014, Letnik:
1169
Journal Article
Double-stranded RNA molecules carrying a triphosphate moiety represent a molecular structure by which the host recognizes viral infections. Such RNA molecules can be generated synthetically by ...chemical synthesis or by in vitro transcription (see Chapter 2, Hornung et al.). Similar to viruses, they initiate an antiviral immune response, e.g., by stimulation of the immune system. Short, double-stranded RNA in the cytosol can also trigger the RNA interference mechanism, which also has been considered as an antiviral response. Notably, synthetic RNAs that are designed to be specific for a certain host mRNA inhibit expression of the respective gene, leading to specific gene silencing. Both effects-gene silencing and immunostimulation-are interesting from a therapeutic perspective, e.g., for cancer therapy. Notably, both effects can be activated by a single molecule, an siRNA carrying a triphosphate moiety. This chapter provides information how to design such compounds with respect to the associated signaling pathways and the techniques to evaluate bifunctional RNAs in the context of tumor therapy.
Regulatory T (Treg) cells expressing the transcription factor Foxp3 are an essential suppressive T cell lineage of dual origin: Foxp3 induction in thymocytes and mature CD4+ T cells gives rise to ...thymic (tTreg) and peripheral (pTreg) Treg cells, respectively. While tTreg cells suppress autoimmunity, pTreg cells enforce tolerance to food and commensal microbiota. However, the role of Foxp3 in pTreg cells and the mechanisms supporting their differentiation remain poorly understood. Here, we used genetic tracing to identify microbiota-induced pTreg cells and found that many of their distinguishing features were Foxp3 independent. Lineage-committed, microbiota-dependent pTreg-like cells persisted in the colon in the absence of Foxp3. While Foxp3 was critical for the suppression of a Th17 cell program, colitis, and mastocytosis, pTreg cells suppressed colonic effector T cell expansion in a Foxp3-independent manner. Thus, Foxp3 and the tolerogenic signals that precede and promote its expression independently confer distinct facets of pTreg functionality.
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•Developed a strategy for genetic labeling of peripherally induced Treg (pTreg) cells•Expression of a pTreg transcriptional program is Foxp3-independent•Foxp3 is dispensable for commitment and fitness of microbiota-dependent pTreg cells•Foxp3-deficient Treg cells can suppress colonic T cell expansion
Foxp3 induction in mature CD4+ T cells gives rise to peripheral Treg (pTreg) cells that enforce tolerance to food and commensal microbes. However, the role of Foxp3 in pTreg cells and the mechanisms supporting their differentiation remain unclear. Van der Veeken et al. use genetic tracing to identify microbiota-induced pTreg cells and find that they have Foxp3-dependent and Foxp3-independent features.
Regulatory T (Treg) cells expressing the transcription factor Foxp3 are an essential suppressive T cell lineage of dual origin: Foxp3 induction in thymocytes and mature CD4
+
T cells gives rise to ...thymic (tTreg) and peripheral (pTreg) Treg cells, respectively. While tTreg cells suppress autoimmunity, pTreg cells enforce tolerance to food and commensal microbiota. However, the role of Foxp3 in pTreg cells and the mechanisms supporting their differentiation remain poorly understood. Here, we used genetic tracing to identify microbiota-induced pTreg cells and found that many of their distinguishing features were Foxp3-independent. Lineage-committed, microbiota-dependent pTreg-like cells persisted in the colon in the absence of Foxp3. While Foxp3 was critical for the suppression of a Th17 cell program, colitis and mastocytosis, pTreg cells suppressed colonic effector T cell expansion in a Foxp3-independent manner. Thus, Foxp3 and the tolerogenic signals that precede and promote its expression independently confer distinct facets of pTreg functionality.
Growing evidence suggests that concurrent loco-regional and systemic treatment modalities may lead to synergistic anti-tumor effects in advanced melanoma. In this retrospective multicenter study, we ...evaluate the use of electrochemotherapy (ECT) combined with ipilimumab or PD-1 inhibition. We investigated patients with unresectable or metastatic melanoma who received the combination of ECT and immune checkpoint blockade for distant or cutaneous metastases within 4 weeks. Clinical and laboratory data were collected and analyzed with respect to safety and efficacy. A total of 33 patients from 13 centers were identified with a median follow-up time of 9 months. Twenty-eight patients received ipilimumab, while five patients were treated with a PD-1 inhibitor (pembrolizumab
n
= 3, nivolumab
n
= 2). The local overall response rate (ORR) was 66.7 %. The systemic ORR was 19.2 and 40.0 % in the ipilimumab and PD-1 cohort, respectively. The median duration of response was not reached in either group. The median time to disease progression was 2.5 months for the entire population with 2 months for ipilimumab and 5 months for PD-1 blockade. The median overall survival was not reached in patients with ipilimumab and 15 months in the PD-1 group. Severe systemic adverse events were detected in 25.0 % in the ipilimumab group. No treatment-related deaths were observed. This is the first reported evaluation of ECT and simultaneous PD-1 inhibition and the largest published dataset on ECT with concurrent ipilimumab. The local response was lower than reported for ECT only. Ipilimumab combined with ECT was feasible, tolerable and showed a high systemic response rate.