Ly6Chi Inflammatory Monocytes Research Articles

Antibiotic-induced gut dysbiosis leads to activation of microglia and impairment of cholinergic gamma oscillations in the hippocampus

Antibiotics are widely applied for the treatment of bacterial infections, but their long-term use may lead to gut flora dysbiosis and detrimental effects on brain physiology, behavior as well as cognitive performance. Still, a striking lack of knowledge exists concerning electrophysiological correlates of antibiotic-induced changes in gut microbiota and behavior. Here, we investigated changes in the synaptic transmission and plasticity together with behaviorally-relevant network activities from the hippocampus of antibiotic-treated mice. Prolonged antibiotic treatment led to a reduction of myeloid cell pools in bone marrow, circulation and those surveilling the brain. Circulating Ly6Chi inflammatory monocytes adopted a proinflammatory phenotype with increased expression of CD40 and MHC II. In the central nervous system, microglia displayed a subtle activated phenotype with elevated CD40 and MHC II expression, increased IL-6 and TNF production as well as with an increased number of Iba1 + cells in the hippocampal CA3 and CA1 subregions. Concomitantly, we detected a substantial reduction in the synaptic transmission in the hippocampal CA1 after antibiotic treatment. In line, carbachol-induced cholinergic gamma oscillation were reduced upon antibiotic treatment while the incidence of hippocampal sharp waves was elevated. These alterations were associated with the global changes in the expression of neurotrophin nerve growth factor and inducible nitric oxide synthase, both of which have been shown to influence cholinergic system in the hippocampus. Overall, our study demonstrates that antibiotic-induced dysbiosis of the gut microbiome and subsequent alteration of the immune cell function are associated with reduced synaptic transmission and gamma oscillations in the hippocampus, a brain region that is critically involved in mediation of innate and cognitive behavior.

Interferon-γ-Producing CD4+ T Cells Drive Monocyte Activation in the Bone Marrow During Experimental Leishmania donovani Infection.

Ly6Chi inflammatory monocytes develop in the bone marrow and migrate to the site of infection during inflammation. Upon recruitment, Ly6Chi monocytes can differentiate into dendritic cells or macrophages. According to the tissue environment they can also acquire different functions. Several studies have described pre-activation of Ly6Chi monocytes in the bone marrow during parasitic infection, but whether this process occurs during experimental visceral leishmaniasis and, if so, the mechanisms contributing to their activation are yet to be established. In wild type C57BL/6 (B6) mice infected with Leishmania donovani, the number of bone marrow Ly6Chi monocytes increased over time. Ly6Chi monocytes displayed a highly activated phenotype from 28 days to 5 months post infection (p.i), with >90% expressing MHCII and >20% expressing iNOS. In comparison, in B6.Rag2 -/- mice <10% of bone marrow monocytes were MHCII+ at day 28 p.i., an activation deficiency that was reversed by adoptive transfer of CD4+ T cells. Depletion of CD4+ T cells in B6 mice and the use of mixed bone marrow chimeras further indicated that monocyte activation was driven by IFNγ produced by CD4+ T cells. In B6.Il10 -/- mice, L. donovani infection induced a faster but transient activation of bone marrow monocytes, which correlated with the magnitude of CD4+ T cell production of IFNγ and resolution of the infection. Under all of the above conditions, monocyte activation was associated with greater control of parasite load in the bone marrow. Through reinfection studies in B6.Il10 -/- mice and drug (AmBisome®) treatment of B6 mice, we also show the dependence of monocyte activation on parasite load. In summary, these data demonstrate that during L. donovani infection, Ly6Chi monocytes are primed in the bone marrow in a process driven by CD4+ T cells and whereby IFNγ promotes and IL-10 limits monocyte activation and that the presence of parasites/parasite antigen plays a crucial role in maintaining bone marrow monocyte activation.

Basophils balance healing after myocardial infarction via IL-4/IL-13.

The inflammatory response after myocardial infarction (MI) is a precisely regulated process that greatly affects subsequent remodeling. Here, we show that basophil granulocytes infiltrated infarcted murine hearts, with a peak occurring between days 3 and 7. Antibody-mediated and genetic depletion of basophils deteriorated cardiac function and resulted in enhanced scar thinning after MI. Mechanistically, we found that basophil depletion was associated with a shift from reparative Ly6Clo macrophages toward increased numbers of inflammatory Ly6Chi monocytes in the infarcted myocardium. Restoration of basophils in basophil-deficient mice by adoptive transfer reversed this proinflammatory phenotype. Cellular alterations in the absence of basophils were accompanied by lower cardiac levels of IL-4 and IL-13, two major cytokines secreted by basophils. Mice with basophil-specific IL-4/IL-13 deficiency exhibited a similarly altered myeloid response with an increased fraction of Ly6Chi monocytes and aggravated cardiac function after MI. In contrast, IL-4 induction in basophils via administration of the glycoprotein IPSE/α-1 led to improved post-MI healing. These results in mice were corroborated by the finding that initially low counts of blood basophils in patients with acute MI were associated with a worse cardiac outcome after 1 year, characterized by a larger scar size. In conclusion, we show that basophils promoted tissue repair after MI by increasing cardiac IL-4 and IL-13 levels.

Ultra-selective carbon nanotubes for photoacoustic imaging of inflamed atherosclerotic plaques.

Disruption of vulnerable atherosclerotic plaques often leads to myocardial infarction and stroke, the leading causes of morbidity and mortality in the United States. A diagnostic method that detects high-risk atherosclerotic plaques at early stages could prevent these sequelae. The abundance of immune cells in the arterial wall, especially inflammatory Ly-6Chi monocytes and foamy macrophages, is indicative of plaque‎ inflammation, and may be associated with plaque vulnerability. Hence, we sought to develop a new method that specifically targets these immune cells to offer clinically-relevant diagnostic information about cardiovascular disease. We combine ultra-selective nanoparticle targeting of Ly-6Chi monocytes and foamy macrophages with clinically-viable photoacoustic imaging (PAI) in order to precisely and specifically image inflamed plaques ex vivo in a mouse model that mimics human vulnerable plaques histopathologically. Within the plaques, high-dimensional single-cell flow cytometry (13-parameter) showed that our nanoparticles were almost-exclusively taken up by the Ly-6Chi monocytes and foamy macrophages that heavily infiltrate plaques. PAI identified inflamed atherosclerotic plaques that display ~6-fold greater signal compared to controls (P<0.001) six hours after intravenous injection of ultra-selective carbon nanotubes, with in vivo corroboration via optical imaging. Our highly selective strategy may provide a targeted, non-invasive imaging strategy to accurately identify and diagnose inflamed atherosclerotic lesions.

The Immunomodulating Effect of Baicalin on Inflammation and Insulin Resistance in High-Fat-Diet-Induced Obese Mice.

Background Obesity is a chronic low-grade systemic inflammation state, which causes insulin resistance, diabetes, and other metabolic diseases. Baicalin is known to have anti-inflammatory and antiobesity effects. In this study, we investigated the cellular and molecular immunological effects of baicalin on obesity-induced inflammation. Methods Male C57BL/6 mice were assigned to four groups: the normal chow, high-fat diet (HFD), BC2 (HFD + baicalin 200 mg/kg), and BC4 (HFD + baicalin 400 mg/kg) group; the three groups except normal chow were fed with a high-fat diet for 8 weeks to induce obesity followed by baicalin treatment with two doses for 8 weeks. The body weight, epididymal fat weight, liver weight, food intake, oral glucose tolerance test (OGTT), oral fat tolerance test (OFTT), and serum lipids were measured. We evaluated insulin resistance by measuring the serum insulin level and homeostatic model assessment of insulin resistance (HOMA-IR). Also, the major obesity-associated immune cells including monocytes, macrophages, T lymphocytes, and dendritic cells in the blood, fat, and liver and the inflammatory and insulin signaling-related gene expressions in the fat and liver were evaluated. Results Baicalin significantly reduced the body weight and liver weight and improved serum fasting glucose, insulin, HOMA-IR, free fatty acid, HDL cholesterol, and the levels of glucose and triglyceride at each time point in the OGTT and OFTT. In the analysis of immune cells, baicalin significantly decreased inflammatory Ly6Chi monocytes, M1 adipose tissue macrophages (ATMs), and M1 Kupffer cells. On the contrary, baicalin increased anti-inflammatory M2 ATMs and liver CD4+ T cells and CD4/CD8 ratio. In the analysis of inflammatory and insulin signaling molecules, baicalin significantly downregulated the gene expression of tumor necrosis factor-α, F4/80, and C-C motif chemokine 2 while upregulated the insulin receptor mRNA expression. Conclusion From these results, baicalin can be a promising treatment option for obesity and its related metabolic diseases based on its anti-inflammatory property.

Pericardial macrophages and their role in myocardial infarction

Abstract Each year an estimated 790,000 people suffer a heart attack in the United States. With such a high incidence, it is important to understand the underlying cellular mechanisms at play during myocardial infarction. In this project we examined the role of pericardial macrophages in modulating the pathogenesis of myocardial infarction. We found that pericardial macrophages expressing the transcription factor GATA6 make up a majority of the cells in the healthy human’s pericardial fluid and have a regulatory function. However, patients with chronic ischemic cardiac disease had their GATA6+ macrophages replaced by inflammatory monocytes in the pericardial fluid. GATA6+ macrophages can be also isolated from murine pericardial fluid. We modeled myocardial infarction through permanent ligation of the left anterior descending artery in adult mice utilizing GATA6+ macrophage deficient LysCreGATA6fl/fl mice. LysCreGATA6fl/fl mice had worse fibrosis and more severe EKG abnormalities compared to control mice following myocardial infarction. Thrombi were also apparent in the hearts of LysCreGATA6fl/fl mice that were not present in control mice. In addition, mice lacking GATA6+ pericardial macrophages had a higher influx of inflammatory Ly6Chi monocytes to the myocardium during the early inflammatory phase of the disease, while pericardial macrophages did not traffic to the myocardium directly at any point. Therefore, we propose that pericardial macrophages inhibit late-stage cardiac remodeling following myocardial infarction by preventing the trafficking of inflammatory monocytes to the site of injury.

129 Stimulating the Cholinergic Anti-inflammatory Pathway Alters Inflammatory Cell Mobilization after Burn Injury

Abstract Introduction Severe burn injury causes a systemic inflammatory response (SIRS) that is characterized by mobilization of inflammatory cells into the circulation and is associated with distant organ injury that can lead to significant morbidity and mortality. The cholinergic anti-inflammatory pathway, mediated by the vagus nerve, regulates the anti-inflammatory response to injury and infection. We have previously shown in models of burn injury that stimulating the vagus nerve may be a potential therapy aimed at limiting SIRS. Here, we hypothesized that stimulating the vagus nerve (VNS) would limit the SIRS response by altering the mobilization and trafficking of inflammatory cells after burn injury. Methods Wild type 10–12-week-old C57BL/6 mice were injured with a 30% total body surface area steam burn. A separate cohort of animals was treated with electrical stimulation of the cervical vagus nerve for 10 minutes immediately post-burn. Bone marrow, blood and lung tissue were collected 24 hours after burn injury. Flow cytometry of bone marrow was performed to measure Lineage- c-kit± Sca-1+ (LSK) hematopoietic stem cells (HSC), then further analyzed to quantify changes in Long-term (LT) HSC, short-term (ST) HSC, and Multipotential Progenitor (MPP) compartments. Bone marrow, blood and perfused lung tissue were analyzed by flow cytometry using a panel of myeloid cell markers. Results Severe burn injury decreased bone marrow LSK expression by 50% compared to sham, with LT-HSC and MPP expression decreasing to a greater degree than ST-HSCs. VNS did not alter burn-induced changes in any bone marrow HSC cell type. Burn injury was associated with increased mobilization of CD45+CD11b+ monocytes and CD11b+Ly6Chi inflammatory monocytes into the peripheral blood and lung, while increased CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils was seen in the lung only. VNS significantly prevented the burn-induced increase in CD45+ inflammatory cells, CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils in the lung (see Figure), reducing their expression to sham levels, despite only modest changes to myeloid cell expression in the blood. Conclusions VNS attenuates myeloid cell cell trafficking to the lung after severe burn injury despite having no effect on emergency myelopoiesis in the bone marrow. Further studies are needed to define the mechanism by which the cholinergic anti-inflammatory pathway attenuates the SIRS response to burn.

Type 1 Innate Lymphoid Cells Regulate the Early Stage of Toxoplasma Gondii-Induced Neuroinflammation

Cerebral infections are restrained by a complex interplay of tissue-resident and recruited peripheral immune cells. Whether innate lymphoid cells (ILCs) are involved in the initiation of an orchestrated neuroinflammatory response is not fully understood. Here we demonstrate that ILCs accumulate in the cerebral parenchyma, the choroid plexus, and the meninges in the early stage of cerebralToxoplasma gondii infection. Longitudinal analyses revealed that NKp46+NK1.1+Eomes-CD49a+ ILC1-like cells surpass NKp46+NK1.1+Eomes+CD49a- conventional natural killer (cNK) cells in the course of infection. Antibody-mediated depletion of cNK and ILC1s cells resulted in diminished cytokine expression and increased cerebral parasite burden. Using cNK- and ILC1-deficient mouse models, we demonstrate that only the lack of ILC1s affected cerebral immune responses. In summary, our results provide evidence that ILC1-like cells are an early source of IFN‑γ and TNF in response to cerebral T. gondii infection, thereby inducing host defence factors as well as the recruitment of protective Ly6Chi inflammatory monocytes.

Non-neutralizing antibodies protect against chronic LCMV infection by promoting infection of inflammatory monocytes in mice.

Antibodies play an important role in host defense against microorganisms. Besides direct microbicidal activities, antibodies can also provide indirect protection via crosstalk to constituents of the adaptive immune system. Similar to many human chronic viral infections, persistence of Lymphocytic choriomeningitis virus (LCMV) is associated with compromised T‐ and B‐cell responses. The administration of virus‐specific non‐neutralizing antibodies (nnAbs) prior to LCMV infection protects against the establishment of chronic infection. Here, we show that LCMV‐specific nnAbs bind preferentially Ly6Chi inflammatory monocytes (IMs), promote their infection in an Fc‐receptor independent way, and support acquisition of APC properties. By constituting additional T‐cell priming opportunities, IMs promote early activation of virus‐specific CD8 T cells, eventually tipping the balance between T‐cell exhaustion and effector cell differentiation, preventing establishment of viral persistence without causing lethal immunopathology. These results document a beneficial role of IMs in avoiding T‐cell exhaustion and an Fc‐receptor independent protective mechanism provided by LCMV‐specific nnAbs against the establishment of chronic infection.

Differential and sequential immunomodulatory role of neutrophils and Ly6Chi inflammatory monocytes during antiviral antibody therapy

ABSTRACT Antiviral monoclonal antibodies (mAbs) can generate protective immunity through Fc-FcγRs interactions. We previously showed a role for immune complexes (ICs) in the enhancement of antiviral T-cell responses through FcγR-mediated activation of dendritic cells (DCs). Here we addressed how mAb therapy in retrovirus-infected mice affects the activation of neutrophils and inflammatory monocytes, two FcγR-expressing innate effector cells rapidly recruited to sites of infection. We found that both cell-types activated in vitro by viral ICs secreted chemokines able to recruit monocytes and neutrophils themselves. Moreover, inflammatory cytokines potentiated chemokines and cytokines release by IC-activated cells and induced FcγRIV upregulation. Similarly, infection and mAb-treatment upregulated FcγRIV on neutrophils and inflammatory monocytes and enhanced their cytokines/chemokines secretion. Notably, upon antibody therapy neutrophils and inflammatory monocytes displayed distinct functional activation states and sequentially modulated the antiviral immune response by secreting Th1-type polarizing cytokines and chemokines, which occurred in a FcγRIV-dependent manner. Consistently, FcγRIV- blocking in mAb-treated, infected mice led to reduced immune protection. Our work provides new findings on the immunomodulatory role of neutrophils and monocytes in the enhancement of immune responses upon antiviral mAb therapy.

MicroRNA-155 contributes to host immunity against Toxoplasma gondii.

Toxoplasma gondii is well known to infect almost all avian and mammalian species including humans, with worldwide distribution. This protozoan parasite can cause serious toxoplasmosis, posing with a risk to public health. The role of microRNAs in the pathogenesis of T. gondii has not been well described. The aim of the present study was to investigate the role of microRNA-155 (miR-155) in mediating innate and adaptive immune responses during T. gondii infection in mice models. The survival and parasite burden in T. gondii-infected miR-155−/− and wild-type (WT) C57BL6 mice were compared. In these two mouse models, ELISA tests were used for analysis of Th1-associated, Th2-associated, and Th17-associated cytokines, and flow cytometry was used for analysis of the subpopulations of NK, NKT, CD8+T, CD4+T cells and regulatory T cells (Tregs), as well as Ly6Chi inflammatory monocytes and dendritic cells. The lack of miR-155 led to increased parasite burden and decreased survival of infected mice in contrast to WT mice. Innate and adaptive immune responses were reduced in the absence of miR-155, along with decreased proinflammatory mediators, Th-1-associated and Th-2-associated cytokines and accumulation of lymphocyte subpopulations. Also, CD8+ T cell exhaustion was also worsened in the absence of miR-155 via targeting of SHIP-1 and SOCS1, showing as up-regulated recruitment of Tregs and expression of PD-1, and down-regulated expression of IFN-γ and TNF-α in CD8+ T cells. Our results show that miR-155 is a critical immune regulator for the control of T. gondii infection, suggesting that miR-155 can be explored as a potential molecular target for boosting immunity against T. gondii.

Myocarditis triggers inflammatory response in cardiac fibroblasts and profibrotic activation of myeloid and endothelial cells in mouse model of experimental autoimmune myocarditis

Abstract Background/Introduction Myocarditis, a heart-specific inflammation, is a common cause of pathological tissue remodeling and cardiac fibrosis resulting in stiffening of ventricles, functional impairment and heart failure. Immunization of susceptible mice with alpha myosin heavy chain (αMyHC) and complete Freund's adjuvant (CFA) induces CD4+ T cell-mediated experimental autoimmune myocarditis (EAM). In EAM model, resolution of acute cardiac inflammation is followed by a progressive dilated cardiomyopathy and systolic dysfunction. Purpose The aim of our study was to identify the role of resident cardiac fibroblasts, cardiac endothelial as well as inflammatory myeloid cells during the course of EAM. Methods EAM was induced by immunization with αMyHC/CFA in reporter BALB/c mice expressing EGFP under collagen type I promoter (Coll-EGFP) and RFP under a control of α-smooth muscle actin (αSMA) promoter (αSMA-RFP). Using flow cytometry analysis, cardiac cells were phenotyped and quantified at inflammatory (d19–21) and fibrotic (d40) stage of EAM. Sorted EGFP-positive cardiac fibroblasts obtained from healthy and myocarditis-positive mice (day 21 of EAM) were comparatively analyzed for the whole genome transcriptomics using the Next Generation Sequencing with read length 2x150bp and 20–30 million reads per sample. Results A massive infiltration of inflammatory CD45+CD11b+ myeloid cells (mainly CD11b+CD36+ macrophages, CD11b+CD36–Ly6GhiLy6chi neutrophils, CD11b+CD36–Ly6G–Ly6c– monocytes, CD11b+CD36–Ly6G–Ly6chi inflammatory monocytes) was observed at day 21 of EAM. Myeloid cells as well as endothelial cells showed increased production of type I collagen at day 21, which was further reduced at day 40 of EAM. At day 21, collagen-producing endothelial cells showed particularly elevated levels of adhesion molecules ICAM and VCAM. On the other hand, the total number of EGFP-positive cardiac fibroblasts remained unchanged during the course of EAM, as well as the percentage of cardiac fibroblasts positive for αSMA (myofibroblasts). Gene ontology analysis of transcripts differentially regulated in cardiac fibroblasts during acute myocarditis pointed mainly to activation of immune processes, response to stress, cytoskeletal and extracellular matrix organization. Specifically, in EAM at day 21 cardiac fibroblasts increased transcription of chemokines (Ccl6, Ccl9, Cxcl2, Cxcl3, Cxcl5, Cxcl9, Cxcl13), collagens (Col6a4, Col6a5, Col9a1, Col9a3, Col11a2, Col12a1, Col24a1, Col28a1), and genes involved in ECM biology (Bmp7, Kng2, Lgals3, Cthrc1, Cela1, Spn). Conclusions In EAM model, inflammatory myeloid and cardiac endothelial cells seem to contribute to excessive collagen type I production, whereas cardiac fibroblasts actively participate in inflammatory and profibrotic responses. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): The National Science Centre (Poland)

High-salt diet decreases mechanical thresholds in mice that is mediated by a CCR2-dependent mechanism

BackgroundThough it is well-known that a high-salt diet (HSD) is associated with many chronic diseases, the effects of long-term high-salt intake on physiological functions and homeostasis remain elusive. In this study, we investigated whether and how an HSD affects mouse nociceptive thresholds, and myeloid cell trafficking and activation.MethodsHealthy C57BL/6 male and female mice were fed an HSD (containing 4% NaCl in chow and 1% NaCl in water) from the time of weaning for 3 to 4 months. Circulating monocytes, nerve macrophages, spinal microglia, and associated inflammatory responses were scrutinized using flow cytometry, immunohistochemistry, and quantitative real-time polymerase chain reaction (qPCR) approaches. Mouse pain sensitivity to mechanical stimuli was monitored with von Frey tests along the experimental duration.ResultsMice on an HSD have reduced mechanical thresholds. They feel more pain than those on a normal diet (ND), e.g., regular laboratory chow (0.3% NaCl in chow). An HSD induced not only a remarkable expansion of circulating monocytes, CCR2+Ly6Chi inflammatory monocytes in particular, but also an accumulation of CD11b+F4/80+ macrophages in the peripheral nerves and an activation of Iba-1+ spinal microglia. Replacing an HSD with a ND was unable to reverse the HSD-induced mechanical hypersensitivity or rescue the altered immune responses. However, treating HSD-fed mice with a chemokine receptor CCR2 antagonist effectively normalized the pain thresholds and immune cell profile in the periphery and spinal cord. An HSD failed to alter pain thresholds and myeloid cell activation in CCR2-deficient mice. Spinal microglial activation is required for HSD-induced mechanical hypersensitivity in male, but not in female mice.ConclusionOverall, this study provides evidence that an HSD has a long-term impact on physiological function. CCR2-mediated cellular response, including myeloid cell trafficking and associated inflammation, plays pivotal roles in salt-dietary modulation of pain sensitivity.

S100A9 Links Inflammation and Repair in Myocardial Infarction.

The alarmin S100A9 has been identified as a potential therapeutic target in myocardial infarction. Short-term S100A9 blockade during the inflammatory phase post-myocardial infarction inhibits systemic and cardiac inflammation and improves cardiac function long term. To evaluate the impact of S100A9 blockade on postischemic cardiac repair. We assessed cardiac function, hematopoietic response, and myeloid phagocyte dynamics in WT (wild type) C57BL/6 mice with permanent coronary artery ligation, treated with the specific S100A9 blocker ABR-238901 for 7 or 21 days. In contrast to the beneficial effects of short-term therapy, extended S100A9 blockade led to progressive deterioration of cardiac function and left ventricle dilation. The treatment reduced the proliferation of Lin-Sca-1+c-Kit+ hematopoietic stem and progenitor cells in the bone marrow and the production of proreparatory CD150+CD48-CCR2+ hematopoietic stem cells. Monocyte trafficking from the spleen to the myocardium and subsequent phenotype switching to reparatory Ly6CloMerTKhi macrophages was also impaired, leading to inefficient efferocytosis, accumulation of apoptotic cardiomyocytes, and a larger myocardial scar. The transcription factor Nur77 (Nr4a1 [nuclear receptor subfamily 4 group A member 1]) mediates the transition from inflammatory Ly6Chi monocytes to reparatory Ly6Clo macrophages. S100A9 upregulated the levels and activity of Nur77 in monocytes and macrophages in vitro and in Ly6Chi/int monocytes in vivo, and S100A9 blockade antagonized these effects. Finally, the presence of reparatory macrophages in the myocardium was also impaired in S100A9-/- mice with permanent myocardial ischemia, leading to depressed cardiac function long term. We show that S100A9 plays an important role in both the inflammatory and the reparatory immune responses to myocardial infarction. Long-term S100A9 blockade negatively impacts cardiac recovery and counterbalances the beneficial effects of short-term therapy. These results define a therapeutic window targeting the inflammatory phase for optimal effects of S100A9 blockade as potential immunomodulatory treatment in acute myocardial infarction.

Immune Modulation of Monocytes Dampens the IL-17+ γδ T Cell Response and Associated Psoriasis Pathology in Mice

Psoriasis is a chronic inflammatory autoimmune skin condition that affects millions of people worldwide. It is driven by IL-17-producing CD4 and γδ T cells and targeted by current anti-IL-17 or anti-IL-23 mAb therapies. These treatments are expensive, increase the risk of opportunistic infections, and do not specifically target the inflammatory cascade. Other cells, including inflammatory monocytes, have been shown to migrate to psoriatic plaques in both human disease and the imiquimod-induced mouse model and could thus constitute potential alternative therapeutic targets. In the mouse, immune modifying particles (IMPs) specifically target Ly6Chi inflammatory monocytes migrating to the site of inflammation, sequestering them in the spleen. In this project, we determined whether IMPs could mitigate the development of imiquimod -induced psoriasis in mice. IMP treatment significantly reduced imiquimod-induced psoriasis severity, decreasing dermal infiltration of Ly6Chi monocytes as well as early-stage monocyte-derived dermal macrophages. This was associated with reduced levels of hallmark cytokines IL-23 and IL-1β as well as associated IL-17-producing γδ T cells. Our work highlights the crucial importance of inflammatory monocytes in the development of this disease as well as a therapeutic potential for IMP in psoriasis.

Nanomedicine-mediated prevention of inflammatory monocytes infiltration ameliorate ovalbumin-induced allergic rhinitis in mouse model

Th2 immune cells infiltration into nasal mucosa is one of the characters of allergic rhinitis (AR). We aimed to explore whether inhibition of Th2 immune cells infiltration would attenuate AR progression. AR mouse model was established by i.p. injection of ovalbumin (OVA). The infiltrated immune cells into nasal lavage fluid were detected by flow cytometry. Cytokine concentration in serum was determined by ELISA. AR mice symptoms were indicated by the number of sneezing and nasal rubbing events. In AR mice, CCL2 expression levels and CD45+CD11b+Ly6Chi inflammatory monocytes cells significantly increased as compared with control mice. CCL2 siRNA encapsulated nanoparticles (NPsiCCL2) prevent CCL2 expression and inflammatory monocytes infiltration in AR mice. NPsiCCL2 treatment dramatically decreased the number of sneezing and nasal rubbing events in AR mice. Moreover, NPsiCCL2 treatment attenuated serum OVA-specific IgE, OVA-specific IgG1 and histamine levels. Mechanically, NPsiCCL2 treatment attenuates AR symptoms via inhibiting Th2 cytokine (IL-4, IL-5 and IL-13) production. Nanomedicine-mediated prevention of inflammatory monocytes infiltration ameliorates ovalbumin-induced allergic rhinitis in mouse model.

Transcriptomic Analysis of Monocyte-Derived Non-Phagocytic Macrophages Favors a Role in Limiting Tissue Repair and Fibrosis.

Monocyte-derived macrophages are readily differentiating cells that adapt their gene expression profile to environmental cues and functional needs. During the resolution of inflammation, monocytes initially differentiate to reparative phagocytic macrophages and later to pro-resolving non-phagocytic macrophages that produce high levels of IFNβ to boost resolutive events. Here, we performed in-depth analysis of phagocytic and non-phagocytic myeloid cells to reveal their distinct features. Unexpectedly, our analysis revealed that the non-phagocytic compartment of resolution phase myeloid cells is composed of Ly6CmedF4/80− and Ly6ChiF4/80lo monocytic cells in addition to the previously described Ly6C−F4/80+ satiated macrophages. In addition, we found that both Ly6C+ monocytic cells differentiate to Ly6C−F4/80+macrophages, and their migration to the peritoneum is CCR2 dependent. Notably, satiated macrophages expressed high levels of IFNβ, whereas non-phagocytic monocytes of either phenotype did not. A transcriptomic comparison of phagocytic and non-phagocytic resolution phase F4/80+ macrophages showed that both subtypes express similar gene signatures that make them distinct from other myeloid cells. Moreover, we confirmed that these macrophages express closer transcriptomes to monocytes than to resident peritoneal macrophages (RPM) and resemble resolutive Ly6Clo macrophages and monocyte-derived macrophages more than their precursors, inflammatory Ly6Chi monocytes, recovered following liver injury and healing, and thioglycolate-induced peritonitis, respectively. A direct comparison of these subsets indicated that the non-phagocytic transcriptome is dominated by satiated macrophages and downregulate gene clusters associated with excessive tissue repair and fibrosis, ROS and NO synthesis, glycolysis, and blood vessel morphogenesis. On the other hand, non-phagocytic macrophages enhance the expression of genes associated with migration, oxidative phosphorylation, and mitochondrial fission as well as anti-viral responses when compared to phagocytic macrophages. Notably, conversion from phagocytic to satiated macrophages is associated with a reduction in the expression of extracellular matrix constituents that were demonstrated to be associated with idiopathic pulmonary fibrosis (IPF). Thus, macrophage satiation during the resolution of inflammation seems to bring about a transcriptomic transition that resists tissue fibrosis and oxidative damage while promoting the restoration of tissue homeostasis to complete the resolution of inflammation.

Haploinsufficient Rock1+/- and Rock2+/- Mice Are Not Protected from Cardiac Inflammation and Postinflammatory Fibrosis in Experimental Autoimmune Myocarditis.

Progressive cardiac fibrosis is a common cause of heart failure. Rho-associated, coiled-coil-containing protein kinases (ROCKs) have been shown to enhance fibrotic processes in the heart and in other organs. In this study, using wild-type, Rock1+/− and Rock2+/− haploinsufficient mice and mouse model of experimental autoimmune myocarditis (EAM) we addressed the role of ROCK1 and ROCK2 in development of myocarditis and postinflammatory fibrosis. We found that myocarditis severity was comparable in wild-type, Rock1+/− and Rock2+/− mice at day 21 of EAM. During the acute stage of the disease, hearts of Rock1+/− mice showed unaffected numbers of CD11b+CD36+ macrophages, CD11b+CD36–Ly6GhiLy6chi neutrophils, CD11b+CD36–Ly6G–Ly6chi inflammatory monocytes, CD11b+CD36–Ly6G–Ly6c– monocytes, CD11b+SiglecF+ eosinophils, CD11b+CD11c+ inflammatory dendritic cells and type I collagen-producing fibroblasts. Isolated Rock1+/− cardiac fibroblasts treated with transforming growth factor-beta (TGF-β) showed attenuated Smad2 and extracellular signal-regulated kinase (Erk) phosphorylations that were associated with impaired upregulation of smooth muscle actin alpha (αSMA) protein. In contrast to cardiac fibroblasts, expanded Rock1+/− heart inflammatory myeloid cells showed unaffected Smad2 activation but enhanced Erk phosphorylation following TGF-β treatment. Rock1+/− inflammatory cells responded to TGF-β by a reduced transcriptional profibrotic response and failed to upregulate αSMA and fibronectin at the protein levels. Unexpectedly, in the EAM model wild-type, Rock1+/− and Rock2+/− mice developed a similar extent of cardiac fibrosis at day 40. In addition, hearts of the wild-type and Rock1+/− mice showed comparable levels of cardiac vimentin, periostin and αSMA. In conclusion, despite the fact that ROCK1 regulates TGF-β-dependent profibrotic response, neither ROCK1 nor ROCK2 is critically involved in the development of postinflammatory fibrosis in the EAM model.

844 The alpha-7 Nicotinic Acetylcholine Receptor Mediates a Uniquely Human Response to Burn Injury

Abstract Introduction CHRFAM7A is a uniquely human gene that is a dominant negative inhibitor of the alpha-7 nicotinic acetylcholine receptor (a7nAchR). The relative balance of CHRFAM7A and a7nAchR expression may play an important role in mediating the human immune response to injury. We have previously shown that CHRFAM7A expression increased the hematopoietic stem cell reservoir in bone marrow and altered emergency myelopoiesis after injury. Here, we hypothesized that loss of the a7nAchR would produce a phenotype similar to CHRFAM7A overexpression, with an increased bone marrow reservoir of stem cells that would modulate myeloid cell mobilization after burn injury. Methods a7nAchR knockout (KO) mice (CHRNA7-/-) underwent 30% TBSA steam burn and were compared to age- and sex-matched wild-type mice. Bone marrow and blood were harvested 24 hours following burn injury for flow cytometry analysis. To measure bone marrow hematopoietic stem cells (HSC) we used flow cytometry to measure Lin−Sca1+c-Kit+ (LSK) cell expression. Bone marrow short term (ST) and long term (LT) HSCs were identified with CD48 and CD150. Immune cells were identified with myeloid markers including CD45, CD11b, Gr1, Ly6C, and Ly6G. Results a7nAchR KO mice have an increased bone marrow reservoir of LSK HSCs compared to WT. While bone marrow expression of ST-HSC and LT-HSC decreased after severe burn injury in WT mice, a7nAchR KO prevented the burn-induced depletion of ST-HSC and LT-HSC leaving a bone marrow HSC reservoir similar to sham. a7nAchR KO attenuated burn-induced mobilization of CD11b+ monocytes and CD11b+Ly6CHi inflammatory monocytes into the systemic circulation compared to WT. Conclusions Loss of the a7nAchR increases myeloid cell mobilization into the circulation after severe burn injury. There is significant variability in CHRFAM7A expression between individuals, suggesting that the relative balance of CHRFAM7A and a7nAchR expression may alter the host inflammatory response and influence human resilience after injury. Applicability of Research to Practice Understanding the factors that mediate the human response to burn injury could give important insights into variability in the inflammatory response between individuals and lead to therapeutics targeting the uniquely human response to burn injury.

Modulation of Monocyte-Driven Myositis in Alphavirus Infection Reveals a Role for CX3CR1+ Macrophages in Tissue Repair.

Arthritogenic alphaviruses such as Ross River and Chikungunya viruses cause debilitating muscle and joint pain and pose significant challenges in the light of recent outbreaks. How host immune responses are orchestrated after alphaviral infections and lead to musculoskeletal inflammation remains poorly understood. Here, we show that myositis induced by Ross River virus (RRV) infection is driven by CD11bhi Ly6Chi inflammatory monocytes and followed by the establishment of a CD11bhi Ly6Clo CX3CR1+ macrophage population in the muscle upon recovery. Selective modulation of CD11bhi Ly6Chi monocyte migration to infected muscle using immune-modifying microparticles (IMP) reduced disease score, tissue damage, and inflammation and promoted the accumulation of CX3CR1+ macrophages, enhancing recovery and resolution. Here, we detail the role of immune pathology, describing a poorly characterized muscle macrophage subset as part of the dynamics of alphavirus-induced myositis and tissue recovery and identify IMP as an effective immunomodulatory approach. Given the lack of specific treatments available for alphavirus-induced pathologies, this study highlights a therapeutic potential for simple immune modulation by IMP in infected individuals in the event of large alphavirus outbreaks.IMPORTANCE Arthritogenic alphaviruses cause debilitating inflammatory disease, and current therapies are restricted to palliative approaches. Here, we show that following monocyte-driven muscle inflammation, tissue recovery is associated with the accumulation of CX3CR1+ macrophages in the muscle. Modulating inflammatory monocyte infiltration using immune-modifying microparticles (IMP) reduced tissue damage and inflammation and enhanced the formation of tissue repair-associated CX3CR1+ macrophages in the muscle. This shows that modulating key effectors of viral inflammation using microparticles can alter the outcome of disease by facilitating the accumulation of macrophage subsets associated with tissue repair.