Enzymatic Activity of HPGD in Treg Cells Suppresses Tconv Cells to Maintain Adipose Tissue Homeostasis and Prevent Metabolic Dysfunction.

Regulatory T cells (Treg cells) are important for preventing autoimmunity and maintaining tissue homeostasis, but whether Treg cells can adopt tissue- or immune-context-specific suppressive mechanisms is unclear. Here, we found that the enzyme hydroxyprostaglandin dehydrogenase (HPGD), which catabolizes prostaglandin E2 (PGE2) into the metabolite 15-keto PGE2, was highly expressed in Treg cells, particularly those in visceral adipose tissue (VAT). Nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ)-induced HPGD expression in VAT Treg cells, and consequential Treg-cell-mediated generation of 15-keto PGE2 suppressed conventional T cell activation and proliferation. Conditional deletion of Hpgd in mouse Treg cells resulted in the accumulation of functionally impaired Treg cells specifically in VAT, causing local inflammation and systemic insulin resistance. Consistent with this mechanism, humans with type 2 diabetes showed decreased HPGD expression in Treg cells. These data indicate that HPGD-mediated suppression is a tissue- and context-dependent suppressive mechanism used by Treg cells to maintain adipose tissue homeostasis.

Dysregulation of stress erythropoiesis and enhanced susceptibility to Salmonella Typhimurium infection in AhR-deficient mice.

BACKGROUND: By acting as an environmental sensor, the ligand-induced transcription factor aryl hydrocarbon receptor (AhR) regulates acute innate and adaptive immune responses against pathogens. Here, we analyzed the function of AhR in a model for chronic systemic infection with attenuated Salmonella Typhimurium (STM). METHODS: WT and AhR-deficient mice were infected with the attenuated STM strain TAS2010 and analyzed for bacterial burden, host defense functions and inflammatory stress erythropoiesis. RESULTS: AhR-deficient mice were highly susceptible to TAS2010 infection compared with WT mice demonstrated by reduced bacterial clearance and increased mortality. STM infection resulted in macrocytic anemia and enhanced splenomegaly along with destruction of the splenic architecture in AhR-deficient mice. In addition, AhR-deficient mice displayed a major expansion of splenic immature red blood cells, indicative of infection-induced stress erythropoiesis. Elevated serum levels of erythropoietin and interleukin-6 upon infection as well as increased numbers of splenic stress erythroid progenitors already in steady state probably drive this effect and might cause the alterations in splenic immune cell compartments, thereby preventing an effective host defense against STM in AhR-deficient mice. CONCLUSIONS: AhR-deficient mice fail to clear chronic TAS2010 infection due to enhanced stress erythropoiesis in the spleen and accompanying destruction of the splenic architecture.

CCL17 Aggravates Myocardial Injury by Suppressing Recruitment of Regulatory T Cells.

BACKGROUND: Recent studies have established that CCR2 (C-C chemokine receptor type 2) marks proinflammatory subsets of monocytes, macrophages, and dendritic cells that contribute to adverse left ventricle (LV) remodeling and heart failure progression. Elucidation of the effector mechanisms that mediate adverse effects of CCR2+ monocytes, macrophages, and dendritic cells will yield important insights into therapeutic strategies to suppress myocardial inflammation. METHODS: We used mouse models of reperfused myocardial infarction, angiotensin II and phenylephrine infusion, and diphtheria toxin cardiomyocyte ablation to investigate CCL17 (C-C chemokine ligand 17). We used Ccl17 knockout mice, flow cytometry, RNA sequencing, biochemical assays, cell trafficking studies, and in vivo cell depletion to identify the cell types that generate CCL17, define signaling pathways that controlled its expression, delineate the functional importance of CCL17 in adverse LV remodeling and heart failure progression, and determine the mechanistic basis by which CCL17 exerts its effects. RESULTS: We demonstrated that CCL17 is expressed in CCR2+ macrophages and cluster of differentiation 11b+ conventional dendritic cells after myocardial infarction, angiotensin II and phenylephrine infusion, and diphtheria toxin cardiomyocyte ablation. We clarified the transcriptional signature of CCL17+ macrophages and dendritic cells and identified granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling as a key regulator of CCL17 expression through cooperative activation of STAT5 (signal transducer and activator of transcription 5) and canonical NF-κB (nuclear factor κ-light-chain-enhancer of activated B cells) signaling. Ccl17 deletion resulted in reduced LV remodeling, decreased myocardial fibrosis and cardiomyocyte hypertrophy, and improved LV systolic function after myocardial infarction and angiotensin II and phenylephrine infusion. We observed increased abundance of regulatory T cells (Tregs) in the myocardium of injured Ccl17 knockout mice. CCL17 inhibited Treg recruitment through biased activation of CCR4. CCL17 activated Gq signaling and CCL22 (C-C chemokine ligand 22) activated both Gq and ARRB (ß-arrestin) signaling downstream of CCR4. CCL17 competitively inhibited CCL22 stimulated ARRB signaling and Treg migration. We provide evidence that Tregs mediated the protective effects of Ccl17 deletion on myocardial inflammation and adverse LV remodeling. CONCLUSIONS: These findings identify CCL17 as a proinflammatory mediator of CCR2+ macrophages and dendritic cells and suggest that inhibition of CCL17 may serve as an effective strategy to promote Treg recruitment and suppress myocardial inflammation.

CD4+ T cell immunity to Salmonella is transient in the circulation.

While Salmonella enterica is seen as an archetypal facultative intracellular bacterial pathogen where protection is mediated by CD4+ T cells, identifying circulating protective cells has proved very difficult, inhibiting steps to identify key antigen specificities. Exploiting a mouse model of vaccination, we show that the spleens of C57BL/6 mice vaccinated with live-attenuated Salmonella serovar Typhimurium (S. Typhimurium) strains carried a pool of IFN-γ+ CD4+ T cells that could adoptively transfer protection, but only transiently. Circulating Salmonella-reactive CD4+ T cells expressed the liver-homing chemokine receptor CXCR6, accumulated over time in the liver and assumed phenotypic characteristics associated with tissue-associated T cells. Liver memory CD4+ T cells showed TCR selection bias and their accumulation in the liver could be inhibited by blocking CXCL16. These data showed that the circulation of CD4+ T cells mediating immunity to Salmonella is limited to a brief window after which Salmonella-specific CD4+ T cells migrate to peripheral tissues. Our observations highlight the importance of triggering tissue-specific immunity against systemic infections.

The GM-CSF/CCL17 pathway in obesity-associated osteoarthritic pain and disease in mice.

OBJECTIVES: We have previously identified a granulocyte macrophage-colony stimulating factor (GM-CSF)/C-C motif ligand 17 (CCL17) pathway in monocytes/macrophages, in which GM-CSF regulates the formation of CCL17, and it is important for an experimental osteoarthritis (OA) model. We explore here additional OA models, including in the presence of obesity, such as a requirement for this pathway. DESIGN: The roles of GM-CSF, CCL17, CCR4, and CCL22 in various experimental OA models, including those incorporating obesity (eight-week high-fat diet), were investigated using gene-deficient male mice. Pain-like behavior and arthritis were assessed by relative static weight distribution and histology, respectively. Cell populations (flow cytometry) and cytokine messenger RNA (mRNA) expression (qPCR) in knee infrapatellar fat pad were analyzed. Human OA sera were collected for circulating CCL17 levels (ELISA) and OA knee synovial tissue for gene expression (qPCR). RESULTS: We present evidence that: i) GM-CSF, CCL17, and CCR4, but not CCL22, are required for the development of pain-like behavior and optimal disease in three experimental OA models, as well as for exacerbated OA development due to obesity, ii) obesity alone leads to spontaneous knee joint damage in a GM-CSF- and CCL17-dependent manner, and iii) in knee OA patients, early indications are that BMI correlates with a lower Oxford Knee Score (r = -0.458 and p = 0.0096), with elevated circulating CCL17 levels (r = 0.2108 and p = 0.0153) and with elevated GM-CSF and CCL17 gene expression in OA synovial tissue. CONCLUSIONS: The above findings indicate that GM-CSF, CCL17, and CCR4 are involved in obesity-associated OA development, broadening their potential as targets for possible treatments for OA.

Alternative cross-priming through CCL17-CCR4-mediated attraction of CTLs toward NKT cell-licensed DCs.

Cross-priming allows dendritic cells (DCs) to induce cytotoxic T cell (CTL) responses to extracellular antigens. DCs require cognate 'licensing' for cross-priming, classically by helper T cells. Here we demonstrate an alternative mechanism for cognate licensing by natural killer T (NKT) cells recognizing microbial or synthetic glycolipid antigens. Such licensing caused cross-priming CD8alpha(+) DCs to produce the chemokine CCL17, which attracted naive CTLs expressing the chemokine receptor CCR4. In contrast, DCs licensed by helper T cells recruited CTLs using CCR5 ligands. Thus, depending on the type of antigen they encounter, DCs can be licensed for cross-priming by NKT cells or helper T cells and use at least two independent chemokine pathways to attract naive CTLs. Because these chemokines acted synergistically, this can potentially be exploited to improve vaccinations.

Herpes simplex virus 1 proteins can induce skin inflammation in an atopic dermatitis-like mouse model.

Herpes simplex virus type 1 (HSV-1) can induce in certain individuals with atopic dermatitis (AD) severe cutaneous infections that can spread throughout the entire body, a condition named as AD complicated by eczema herpeticum (ADEH). It has been recently found that ADEH patients can produce specific IgE against HSV-1 proteins, which may contribute to lower protection against HSV-1. However, little is known about the capacity of these HSV-1 proteins to produce an inflammatory response at the skin level. In this study, using a mouse model of AD-like dermatitis, three HSV-1 proteins (glycoprotein D -gD-, glycoprotein B -gB- and VP22) were applied on tape-stripped back skin mice in three exposures periods. Ovalbumin (OVA) and 0.9% NaCl were used as positive and negative controls, respectively. Skin samples were obtained for analysis of specific cell components of skin infiltration. The results showed that the viral protein gD induced a statistically significant increase in the number of dermal infiltrating CD3+, CD4+ cells and mast cells compared with the negative control group. gD was also able to induce epidermal thickening and epidermal infiltration of T cells closely related to the one produced in mice sensitized with OVA. However, VP22 and gB contributed to a lesser extent to skin inflammation. These results showed that proteins from HSV-1, especially gD, can have per se an important T cell and mast cell-driven inflammatory potential at the skin level.

Foxp1 controls mature B cell survival and the development of follicular and B-1 B cells.

The transcription factor Foxp1 is critical for early B cell development. Despite frequent deregulation of Foxp1 in B cell lymphoma, the physiological functions of Foxp1 in mature B cells remain unknown. Here, we used conditional gene targeting in the B cell lineage and report that Foxp1 disruption in developing and mature B cells results in reduced numbers and frequencies of follicular and B-1 B cells and in impaired antibody production upon T cell-independent immunization in vivo. Moreover, Foxp1-deficient B cells are impaired in survival even though they exhibit an increased capacity to proliferate. Transcriptional analysis identified defective expression of the prosurvival Bcl-2 family gene Bcl2l1 encoding Bcl-xl in Foxp1-deficient B cells, and we identified Foxp1 binding in the regulatory region of Bcl2l1 Transgenic overexpression of Bcl2 rescued the survival defect in Foxp1-deficient mature B cells in vivo and restored peripheral B cell numbers. Thus, our results identify Foxp1 as a physiological regulator of mature B cell survival mediated in part via the control of Bcl-xl expression and imply that this pathway might contribute to the pathogenic function of aberrant Foxp1 expression in lymphoma.

Innate and adaptive stimulation of murine diverse NKT cells result in distinct cellular responses.

Natural killer T (NKT) cells recognize glycolipids presented on CD1d. They share features of adaptive T lymphocytes and innate NK cells, and mediate immunoregulatory functions via rapid production of cytokines. Invariant (iNKT) and diverse (dNKT) NKT cell subsets are defined by their TCR. The immunological role of dNKT cells, that do not express the invariant TCRα-chain used by iNKT cells, is less well explored than that of iNKT cells. Here, we investigated signals driving Toll-like receptor (TLR) ligand activation of TCR-transgenic murine dNKT cells. IFN-γ production by dNKT cells required dendritic cells (DC), cell-to-cell contact and presence of TLR ligands. TLR-stimulated DC activated dNKT cells to secrete IFN-γ in a CD1d-, CD80/86- and type I IFN-independent manner. In contrast, a requirement for IL-12p40, and a TLR ligand-selective dependence on IL-18 or IL-15 was observed. TLR ligand/DC stimulation provoked early secretion of pro-inflammatory cytokines by both CD62L+ and CD62L- dNKT cells. However, proliferation was limited. In contrast, TCR/co-receptor-mediated activation resulted in proliferation and delayed production of a broader cytokine spectrum preferentially in CD62L- dNKT cells. Thus, innate (TLR ligand/DC) and adaptive (TCR/co-receptor) stimulation of dNKT cells resulted in distinct cellular responses that may contribute differently to the formation of immune memory.

Type I interferon inhibits interleukin-1 production and inflammasome activation.

Type I interferon (IFN) is a common therapy for autoimmune and inflammatory disorders, yet the mechanisms of action are largely unknown. Here we showed that type I IFN inhibited interleukin-1 (IL-1) production through two distinct mechanisms. Type I IFN signaling, via the STAT1 transcription factor, repressed the activity of the NLRP1 and NLRP3 inflammasomes, thereby suppressing caspase-1-dependent IL-1ß maturation. In addition, type I IFN induced IL-10 in a STAT1-dependent manner; autocrine IL-10 then signaled via STAT3 to reduce the abundance of pro-IL-1α and pro-IL-1ß. In vivo, poly(I:C)-induced type I IFN diminished IL-1ß production in response to alum and Candida albicans, thus increasing susceptibility to this fungal pathogen. Importantly, monocytes from multiple sclerosis patients undergoing IFN-ß treatment produced substantially less IL-1ß than monocytes derived from healthy donors. Our findings may thus explain the effectiveness of type I IFN in the treatment of inflammatory diseases but also the observed "weakening" of the immune system after viral infection.

CSF-1 in Inflammatory and Arthritic Pain Development.

Pain is one of the most debilitating symptoms in many diseases for which there is inadequate management and understanding. CSF-1, also known as M-CSF, acts via its receptor (CSF-1R, c-Fms) to regulate the development of the monocyte/macrophage lineage and to act locally in tissues to control macrophage numbers and function. It has been implicated in the control of neuropathic pain via a central action on microglia. We report in this study that systemic administration of a neutralizing anti-CSF-1R or CSF-1 mAb inhibits the development of inflammatory pain induced by zymosan, GM-CSF, and TNF in mice. This approach also prevented but did not ameliorate the development of arthritic pain and optimal disease driven by the three stimuli in mice, suggesting that CSF-1 may only be relevant when the driving inflammatory insults in tissues are acute and/or periodic. Systemic CSF-1 administration rapidly induced pain and enhanced the arthritis in an inflamed mouse joint, albeit via a different pathway(s) from that used by systemic GM-CSF and TNF. It is concluded that CSF-1 can function peripherally during the generation of inflammatory pain and hence may be a target for such pain and associated disease, including when the clinically important cytokines, TNF and GM-CSF, are involved. Our findings have ramifications for the selection and design of anti-CSF-1R/CSF-1 trials.

Ultraviolet-radiation-induced inflammation promotes angiotropism and metastasis in melanoma.

Intermittent intense ultraviolet (UV) exposure represents an important aetiological factor in the development of malignant melanoma. The ability of UV radiation to cause tumour-initiating DNA mutations in melanocytes is now firmly established, but how the microenvironmental effects of UV radiation influence melanoma pathogenesis is not fully understood. Here we report that repetitive UV exposure of primary cutaneous melanomas in a genetically engineered mouse model promotes metastatic progression, independent of its tumour-initiating effects. UV irradiation enhanced the expansion of tumour cells along abluminal blood vessel surfaces and increased the number of lung metastases. This effect depended on the recruitment and activation of neutrophils, initiated by the release of high mobility group box 1 (HMGB1) from UV-damaged epidermal keratinocytes and driven by Toll-like receptor 4 (TLR4). The UV-induced neutrophilic inflammatory response stimulated angiogenesis and promoted the ability of melanoma cells to migrate towards endothelial cells and use selective motility cues on their surfaces. Our results not only reveal how UV irradiation of epidermal keratinocytes is sensed by the innate immune system, but also show that the resulting inflammatory response catalyses reciprocal melanoma-endothelial cell interactions leading to perivascular invasion, a phenomenon originally described as angiotropism in human melanomas by histopathologists. Angiotropism represents a hitherto underappreciated mechanism of metastasis that also increases the likelihood of intravasation and haematogenous dissemination. Consistent with our findings, ulcerated primary human melanomas with abundant neutrophils and reactive angiogenesis frequently show angiotropism and a high risk for metastases. Our work indicates that targeting the inflammation-induced phenotypic plasticity of melanoma cells and their association with endothelial cells represent rational strategies to specifically interfere with metastatic progression.

Dietary AhR Ligands Regulate AhRR Expression in Intestinal Immune Cells and Intestinal Microbiota Composition.

A diet rich in vegetables and fruit is generally considered healthy because of a high content of phytochemicals, vitamins, and fiber. The phytochemical indole-3-carbinol (I3C), a derivative of glucobrassicin, is sold as a dietary supplement promising diverse health benefits. I3C metabolites act as ligands of the aryl hydrocarbon receptor (AhR), an important sensor for environmental polyaromatic chemicals. Here, we investigated how dietary AhR ligand supplementation influences AhR target gene expression and intestinal microbiota composition. For this, we used AhR repressor (AhRR)-reporter mice as a tool to study AhR activation in the intestine following dietary I3C-supplementation in comparison with AhR ligand-deprived diets, including a high fat diet. AhRR expression in intestinal immune cells was mainly driven by dietary AhR ligands and was independent of microbial metabolites. A lack of dietary AhR ligands caused enhanced susceptibility to dextran sodium sulfate (DSS)-induced colitis and correlated with the expansion of Enterobacteriaceae, whereas Clostridiales, Muribaculaceae, and Rikenellaceae were strongly reduced. I3C supplementation largely reverted this effect. Comparison of I3C-induced changes in microbiota composition using wild-type (WT), AhRR-deficient, and AhR-deficient mice revealed both AhR-dependent and -independent alterations in the microbiome. Overall, our study demonstrates that dietary AhR ligand supplementation has a profound influence on Ahrr expression in intestinal immune cells as well as microbiota composition.

AHR Signaling Dampens Inflammatory Signature in Neonatal Skin γδ T Cells.

Background Aryl hydrocarbon receptor (AHR)-deficient mice do not support the expansion of dendritic epidermal T cells (DETC), a resident immune cell population in the murine epidermis, which immigrates from the fetal thymus to the skin around birth. Material and Methods In order to identify the gene expression changes underlying the DETC disappearance in AHR-deficient mice, we analyzed microarray RNA-profiles of DETC, sorted from the skin of two-week-old AHR-deficient mice and their heterozygous littermates. In vitro studies were done for verification, and IL-10, AHR repressor (AHRR), and c-Kit deficient mice analyzed for DETC frequency. Results We identified 434 annotated differentially expressed genes. Gene set enrichment analysis demonstrated that the expression of genes related to proliferation, ion homeostasis and morphology differed between the two mouse genotypes. Importantly, with 1767 pathways the cluster-group "inflammation" contained the majority of AHR-dependently regulated pathways. The most abundant cluster of differentially expressed genes was "inflammation." DETC of AHR-deficient mice were inflammatory active and had altered calcium and F-actin levels. Extending the study to the AHRR, an enigmatic modulator of AHR-activity, we found approximately 50% less DETC in AHRR-deficient mice than in wild-type-littermates. Conclusion AHR-signaling in DETC dampens their inflammatory default potential and supports their homeostasis in the skin.

RNA Aptamers Recognizing Murine CCL17 Inhibit T Cell Chemotaxis and Reduce Contact Hypersensitivity In Vivo.

The chemokine CCL17, mainly produced by dendritic cells (DCs) in the immune system, is involved in the pathogenesis of various inflammatory diseases. As a ligand of CCR4, CCL17 induces chemotaxis and facilitates T cell-DC interactions. We report the identification of two novel RNA aptamers, which were validated in vitro and in vivo for their capability to neutralize CCL17. Both aptamers efficiently inhibited the directed migration of the CCR4+ lymphoma line BW5147.3 toward CCL17 in a dose-dependent manner. To study the effect of these aptamers in vivo, we used a murine model of contact hypersensitivity. Systemic application of the aptamers significantly prevented ear swelling and T cell infiltration into the ears of sensitized mice after challenge with the contact sensitizer. The results of this proof-of-principle study establish aptamers as potent inhibitors of CCL17-mediated chemotaxis. Potentially, CCL17-specific aptamers may be used therapeutically in humans to treat or prevent allergic and inflammatory diseases.

Mannose receptor induces T-cell tolerance via inhibition of CD45 and up-regulation of CTLA-4.

The mannose receptor (MR) is an endocytic receptor involved in serum homeostasis and antigen presentation. Here, we identify the MR as a direct regulator of CD8(+) T-cell activity. We demonstrate that MR expression on dendritic cells (DCs) impaired T-cell cytotoxicity in vitro and in vivo. This regulatory effect of the MR was mediated by a direct interaction with CD45 on the T cell, inhibiting its phosphatase activity, which resulted in up-regulation of cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4) and the induction of T-cell tolerance. Inhibition of CD45 prevented expression of B-cell lymphoma 6 (Bcl-6), a transcriptional inhibitor that directly bound the CTLA-4 promoter and regulated its activity. These data demonstrate that endocytic receptors expressed on DCs contribute to the regulation of T-cell functionality.

CCL17 exerts a neuroimmune modulatory function and is expressed in hippocampal neurons.

Chemokines are important signaling molecules in the immune and nervous system. Using a fluorescence reporter mouse model, we demonstrate that the chemokine CCL17, a ligand of the chemokine receptor CCR4, is produced in the murine brain, particularly in a subset of hippocampal CA1 neurons. We found that basal expression of Ccl17 in hippocampal neurons was strongly enhanced by peripheral challenge with lipopolysaccharide (LPS). LPS-mediated induction of Ccl17 in the hippocampus was dependent on local tumor necrosis factor (TNF) signaling, whereas upregulation of Ccl22 required granulocyte-macrophage colony-stimulating factor (GM-CSF). CCL17 deficiency resulted in a diminished microglia density under homeostatic and inflammatory conditions. Further, microglia from naïve Ccl17-deficient mice possessed a reduced cellular volume and a more polarized process tree as assessed by computer-assisted imaging analysis. Regarding the overall branching, cell surface area, and total tree length, the morphology of microglia from naïve Ccl17-deficient mice resembled that of microglia from wild-type mice after LPS stimulation. In line, electrophysiological recordings indicated that CCL17 downmodulates basal synaptic transmission at CA3-CA1 Schaffer collaterals in acute slices from naïve but not LPS-treated animals. Taken together, our data identify CCL17 as a homeostatic and inducible neuromodulatory chemokine affecting the presence and morphology of microglia and synaptic transmission in the hippocampus.

Gut microbial translocation corrupts myeloid cell function to control bacterial infection during liver cirrhosis.

OBJECTIVE: Patients with liver cirrhosis suffer from increased susceptibility to life-threatening bacterial infections that cause substantial morbidity. METHODS: Experimental liver fibrosis in mice induced by bile duct ligation or CCl4 application was used to characterise the mechanisms determining failure of innate immunity to control bacterial infections. RESULTS: In murine liver fibrosis, translocation of gut microbiota induced tonic type I interferon (IFN) expression in the liver. Such tonic IFN expression conditioned liver myeloid cells to produce high concentrations of IFN upon intracellular infection with Listeria that activate cytosolic pattern recognition receptors. Such IFN-receptor signalling caused myeloid cell interleukin (IL)-10 production that corrupted antibacterial immunity, leading to loss of infection-control and to infection-associated mortality. In patients with liver cirrhosis, we also found a prominent liver IFN signature and myeloid cells showed increased IL-10 production after bacterial infection. Thus, myeloid cells are both source and target of IFN-induced and IL-10-mediated immune dysfunction. Antibody-mediated blockade of IFN-receptor or IL-10-receptor signalling reconstituted antibacterial immunity and prevented infection-associated mortality in mice with liver fibrosis. CONCLUSIONS: In severe liver fibrosis and cirrhosis, failure to control bacterial infection is caused by augmented IFN and IL-10 expression that incapacitates antibacterial immunity of myeloid cells. Targeted interference with the immune regulatory host factors IL-10 and IFN reconstitutes antibacterial immunity and may be used as therapeutic strategy to control bacterial infections in patients with liver cirrhosis.

Cannabinoid Receptor 2 Modulates Susceptibility to Experimental Cerebral Malaria through a CCL17-dependent Mechanism.

Cerebral malaria is a severe and often fatal complication of Plasmodium falciparum infection. It is characterized by parasite sequestration, a breakdown of the blood-brain barrier, and a strong inflammation in the brain. We investigated the role of the cannabinoid receptor 2 (CB2), an important modulator of neuroinflammatory responses, in experimental cerebral malaria (ECM). Strikingly, mice with a deletion of the CB2-encoding gene (Cnr2(-/-)) inoculated with Plasmodium berghei ANKA erythrocytes exhibited enhanced survival and a diminished blood-brain barrier disruption. Therapeutic application of a specific CB2 antagonist also conferred increased ECM resistance in wild type mice. Hematopoietic derived immune cells were responsible for the enhanced protection in bone marrow (BM) chimeric Cnr2(-/-) mice. Mixed BM chimeras further revealed that CB2-expressing cells contributed to ECM development. A heterogeneous CD11b(+) cell population, containing macrophages and neutrophils, expanded in the Cnr2(-/-) spleen after infection and expressed macrophage mannose receptors, arginase-1 activity, and IL-10. Also in the Cnr2(-/-) brain, CD11b(+) cells that expressed selected anti-inflammatory markers accumulated, and expression of inflammatory mediators IFN-γ and TNF-α was reduced. Finally, the M2 macrophage chemokine CCL17 was identified as an essential factor for enhanced survival in the absence of CB2, because CCL17 × Cnr2 double-deficient mice were fully susceptible to ECM. Thus, targeting CB2 may be promising for the development of alternative treatment regimes of ECM.

Requirement of MyD88 signaling in keratinocytes for Langerhans cell migration and initiation of atopic dermatitis-like symptoms in mice.

Atopic dermatitis (AD) is a chronic inflammatory disease controlled by the innate and adaptive immune system. To elucidate the impact of innate immune signaling in AD, we analyzed MyD88-deficient mice in a murine model of AD-like dermatitis by epicutaneous sensitization with ovalbumin (OVA). Global MyD88 deficiency led to reduced epidermal thickening and diminished accumulation of macrophages within the inflamed skin. In addition, we observed impaired emigration of Langerhans cells (LCs) out of the epidermis of MyD88-deficient mice. These findings indicate that MyD88 deficiency affects various skin-resident cell types in the AD model. Moreover, production of IFN-g, IL-17, and CCL17 was reduced in skin draining lymph node cells and OVA-specific immunoglobulin levels were lower in MyD88-deficient mice. We further investigated the role of MyD88 in keratinocytes, as keratinocytes contribute to AD pathology. Exclusive expression of MyD88 in epidermal keratinocytes partially restored LC emigration after AD induction and expression of CCL17 in skin draining lymph nodes (LNs), but did not promote epidermal thickening nor production of IL-17. Altogether, these data demonstrate that MyD88 signaling in keratinocytes is able to restore LC migration in an otherwise MyD88-deficient background, and significantly contributes to the development of AD-like dermatitis.