Endogenously produced catecholamines improve the regulatory function of TLR9-activated B cells.

The sympathetic nervous system (SNS) contributes to immune balance by promoting anti-inflammatory B cells. However, whether B cells possess a self-regulating mechanism by which they modulate regulatory B cell (Breg) function is not well understood. In this study, we investigated the ability of B cells to synthesize their own catecholamines upon stimulation with different B cell activators and found that expression of the enzyme tyrosine hydroxylase (TH), required to generate catecholamines, is up-regulated by Toll-like receptor (TLR)9. This TLR9-dependent expression of TH correlated with up-regulation of adrenergic receptors (ADRs), enhanced interleukin (IL)-10 production, and overexpression of the co-inhibitory ligands programmed death ligand 1 (PD-L1) and Fas ligand (FasL). Moreover, concomitant stimulation of ß1-3-ADRs together with a B cell receptor (BCR)/TLR9 stimulus clearly enhances the anti-inflammatory potential of Bregs to suppress CD4 T cells, a crucial population in the pathogenesis of autoimmune diseases, like rheumatoid arthritis (RA). Furthermore, TH up-regulation was also demonstrated in B cells during the course of collagen-induced arthritis (CIA), a mouse model for the investigation of RA. In conclusion, our data show that B cells possess an autonomous mechanism to modulate their regulatory function in an autocrine and/or paracrine manner. These findings help to better understand the function of B cells in the regulation of autoimmune diseases and the interplay of SNS.

Enforced viral replication activates adaptive immunity and is essential for the control of a cytopathic virus.

The innate immune system limits viral replication via type I interferon and also induces the presentation of viral antigens to cells of the adaptive immune response. Using infection of mice with vesicular stomatitis virus, we analyzed how the innate immune system inhibits viral propagation but still allows the presentation of antigen to cells of the adaptive immune response. We found that expression of the gene encoding the inhibitory protein Usp18 in metallophilic macrophages led to lower type I interferon responsiveness, thereby allowing locally restricted replication of virus. This was essential for the induction of adaptive antiviral immune responses and, therefore, for preventing the fatal outcome of infection. In conclusion, we found that enforced viral replication in marginal zone macrophages was an immunological mechanism that ensured the production of sufficient antigen for effective activation of the adaptive immune response.

Combination immunotherapy with anti-PD-L1 antibody and depletion of regulatory T cells during acute viral infections results in improved virus control but lethal immunopathology.

Combination immunotherapy (CIT) is currently applied as a treatment for different cancers and is proposed as a cure strategy for chronic viral infections. Whether such therapies are efficient during an acute infection remains elusive. To address this, inhibitory receptors were blocked and regulatory T cells depleted in acutely Friend retrovirus-infected mice. CIT resulted in a dramatic expansion of cytotoxic CD4+ and CD8+ T cells and a subsequent reduction in viral loads. Despite limited viral replication, mice developed fatal immunopathology after CIT. The pathology was most severe in the gastrointestinal tract and was mediated by granzyme B producing CD4+ and CD8+ T cells. A similar post-CIT pathology during acute Influenza virus infection of mice was observed, which could be prevented by vaccination. Melanoma patients who developed immune-related adverse events under immune checkpoint CIT also presented with expanded granzyme-expressing CD4+ and CD8+ T cell populations. Our data suggest that acute infections may induce immunopathology in patients treated with CIT, and that effective measures for infection prevention should be applied.

IFN-ß, but not IFN-α, is Responsible for the Pro-Bacterial Effect of Type I Interferon.

BACKGROUND/AIMS: During an immune response, type I interferon (IFN-I) signaling induces a wide range of changes, including those which are required to overcome viral infection and those which suppress cytotoxic T cells to avoid immunopathology. During certain bacterial infections, IFN-I signaling exerts largely detrimental effects. Although the IFN-I family of proteins all share one common receptor, biologic responses to signaling vary depending on IFN-I subtype. Here, we asked if one IFN-I subtype dominates the pro-bacterial effect of IFN-I signaling and found that control of Listeria monocytogenes (L.m.) infection is more strongly suppressed by IFN-ß than IFN-α. METHODS: To study this, we measured bacterial titers in IFNAR-/-, IFN-ß­/­, Stat2-/-, Usp18fl/fl and Usp18fl/fl x CD11c-Cre mice models in addition to IFN-I blocking antibodies. Moreover, we measured interferon stimulated genes in bone marrow derived dendritic cells after treatment with IFN-α4 and IFN-ß. RESULTS: Specifically, we show that genetic deletion of IFN-ß or antibody-mediated IFN-ß neutralization was sufficient to reduce bacterial titers to levels similar to those observed in mice that completely lack IFN-I signaling (IFNAR-/- mice). However, IFN-α blockade failed to significantly reduce L.m. titers, suggesting that IFN-ß is the dominant IFN-I subtype responsible for the pro-bacterial effect of IFN-I. Mechanistically, when focusing on IFN-I signals to dendritic cells, we found that IFN-ß induces ISGs more robustly than IFN-α, including USP18, the protein we previously identified as driving the pro-bacterial effects of IFN-I. Further, we found that this induction was STAT1/STAT2 heterodimer- or STAT2/STAT2 homodimer-dependent, as STAT2-deficient mice were more resistant to L.m. infection. CONCLUSION: In conclusion, IFN-Β is the principal member of the IFN-I family responsible for driving the pro-bacterial effect of IFN-I.

Tumor Necrosis Factor-Mediated Survival of CD169+ Cells Promotes Immune Activation during Vesicular Stomatitis Virus Infection.

Innate immune activation is essential to mount an effective antiviral response and to prime adaptive immunity. Although a crucial role of CD169+ cells during vesicular stomatitis virus (VSV) infections is increasingly recognized, factors regulating CD169+ cells during viral infections remain unclear. Here, we show that tumor necrosis factor is produced by CD11b+ Ly6C+ Ly6G+ cells following infection with VSV. The absence of TNF or TNF receptor 1 (TNFR1) resulted in reduced numbers of CD169+ cells and in reduced type I interferon (IFN-I) production during VSV infection, with a severe disease outcome. Specifically, TNF triggered RelA translocation into the nuclei of CD169+ cells; this translocation was inhibited when the paracaspase MALT-1 was absent. Consequently, MALT1 deficiency resulted in reduced VSV replication, defective innate immune activation, and development of severe disease. These findings indicate that TNF mediates the maintenance of CD169+ cells and innate and adaptive immune activation during VSV infection.IMPORTANCE Over the last decade, strategically placed CD169+ metallophilic macrophages in the marginal zone of the murine spleen and lymph nodes (LN) have been shown to play a very important role in host defense against viral pathogens. CD169+ macrophages have been shown to activate innate and adaptive immunity via "enforced virus replication," a controlled amplification of virus particles. However, the factors regulating the CD169+ macrophages remain to be studied. In this paper, we show that after vesicular stomatitis virus infection, phagocytes produce tumor necrosis factor (TNF), which signals via TNFR1, and promote enforced virus replication in CD169+ macrophages. Consequently, lack of TNF or TNFR1 resulted in defective immune activation and VSV clearance.

Immunoactivation induced by chronic viral infection inhibits viral replication and drives immunosuppression through sustained IFN-I responses.

Acute or chronic viral infections can lead to generalized immunosuppression. Several mechanisms, such as immunopathology of CD8(+) T cells, inhibitory receptors, or regulatory T (Treg) cells, contribute to immune dysfunction. Moreover, patients with chronic viral infections usually do not respond to vaccination, a finding that has not been previously explained. Recently, we reported that CD169(+) macrophages enforce viral replication, which is essential for guaranteeing antigen synthesis and efficient adaptive immune responses. In the present study, we used a chronic lymphocytic choriomeningitis virus infection mouse model to determine whether this mechanism is affected by chronic viral infection, which may impair the activation of adaptive immunity. We found that enforced viral replication of a superinfecting virus is completely blunted in chronically infected mice. This absence of enforced viral replication in CD169(+) macrophages is not explained by CD8(+) T-cell-mediated immunopathology but rather by prolonged IFN-I responses. Consequently, the absence of viral replication impairs both antigen production and the adaptive immune response against the superinfecting virus. These findings indicate that chronic infection leads to sustained IFN-I action, which is responsible for the absence of an antiviral immune response against a secondary viral infection.

Farnesoid X Receptor in Mice Prevents Severe Liver Immunopathology During Lymphocytic Choriomeningitis Virus Infection.

BACKGROUND: Bile acids (BAs) are steroid molecules that are synthesized in the liver. In addition to their important role as a surfactant in solubilizing lipids and promoting the absorption of lipids in the gastrointestinal tract, they act as inflammagens. The role of BAs and their receptor farnesoid X receptor (FXR) during viral infection has not been studied in detail. METHODS: By using FXR-deficient mice, we investigated the role of bile acid receptor FXR during infection with lymphocytic choriomeningitis virus (LCMV). The importance of FXR in inducing IFN-I and monocytes proliferation were investigated and viral titers and T cell exhaustion were analyzed at different time points. RESULTS: This study shows that controlled levels of BAs activate FXR in hepatocytes and FXR in response upregulates the production of type I interferon. In turn, FXR maintains BAs within a balanced range to inhibit their toxic effects. The absence of FXR results in high levels of BAs, which inhibit the proliferation of monocytes and result in a defect in viral elimination, consequently leading to T cell exhaustion. CONCLUSION: We found that FXR contributes to IFN-I production in hepatocytes and balances BA levels to inhibit their toxic effects on monocytes.

IL-10 Induces T Cell Exhaustion During Transplantation of Virus Infected Hearts.

BACKGROUND/AIMS: Unexpected transmissions of viral pathogens during solid organ transplantation (SOT) can result in severe, life-threatening diseases in transplant recipients. Immune activation contributes to disease onset. However mechanisms balancing the immune response against transmitted viral infection through organ transplantation remain unknown. Methods & RESULTS: Here we found, using lymphocytic choriomeningitis virus (LCMV), that transplantation of LCMV infected hearts led to exhaustion of virus specific CD8+ T cells, viral persistence in organs and survival of graft and recipient. Genetic depletion of Interleukin-10 (IL-10) resulted in strong immune activation, graft dysfunction and death of mice, suggesting that IL-10 was a major regulator of CD8+ T cell exhaustion during SOT. In the presence of memory CD8+ T cells, virus could be controlled. However sufficient antiviral immune response resulted in acute rejection of transplanted heart. CONCLUSION: We found that virus transmitted via SOT could not be controlled by naïve mice recipients due to IL-10 mediated CD8+ T cell exhaustion which thereby prevented immunopathology and graft failure whereas memory mice recipients were able to control the virus and induced graft failure.

High Frequencies of Anti-Host Reactive CD8+ T Cells Ignore Non-Hematopoietic Antigen after Bone Marrow Transplantation in a Murine Model.

BACKGROUND: Graft versus host disease (GvHD) occurs in 20% of cases with patients having an MHC I matched bone marrow transplantation (BMT). Mechanisms causing this disease remain to be studied. METHODS: Here we used a CD8+ T cell transgenic mouse line (P14/CD45.1+) and transgenic DEE mice bearing ubiquitously the glycoprotein 33-41 (GP33) antigen derived from the major lymphocytic choriomeningitis virus (LCMV) epitope to study mechanisms of tolerance in anti-host reactive CD8+ T cells after BMT. RESULTS: We found that anti-host reactive CD8+ T cells (P14 T cells) were not negatively selected in the thymus and that they were present in wild type (WT) recipient mice as well as in DEE recipient mice. Anti-host reactive CD8+ T cells ignored the GP33 antigen expressed ubiquitously by host cells but they could be activated ex vivo via LCMV-infection. Lipopolysaccharides (LPS) induced transient cell damage in DEE mice bearing anti-host reactive CD8+ T cells after BMT, suggesting that induction of host inflammatory response could break antigen ignorance. Introducing the GP33 antigen into BM cells led to deletion of anti-host reactive CD8+ T cells. CONCLUSION: We found that after BMT anti-host reactive CD8+ T cells ignored host antigen in recipients and that they were only deleted when host antigen was present in hematopoietic cells. Moreover, LPS-induced immune activation contributed to induction of alloreactivity of anti-host reactive CD8+ T cells after BMT.

Two separate mechanisms of enforced viral replication balance innate and adaptive immune activation.

The induction of innate and adaptive immunity is essential for controlling viral infections. Limited or overwhelming innate immunity can negatively impair the adaptive immune response. Therefore, balancing innate immunity separately from activating the adaptive immune response would result in a better antiviral immune response. Recently, we demonstrated that Usp18-dependent replication of virus in secondary lymphatic organs contributes to activation of the innate and adaptive immune responses. Whether specific mechanisms can balance innate and adaptive immunity separately remains unknown. In this study, using lymphocytic choriomeningitis virus (LCMV) and replication-deficient single-cycle LCMV vectors, we found that viral replication of the initial inoculum is essential for activating virus-specific CD8(+) T cells. In contrast, extracellular distribution of virus along the splenic conduits is necessary for inducing systemic levels of type I interferon (IFN-I). Although enforced virus replication is driven primarily by Usp18, B cell-derived lymphotoxin beta contributes to the extracellular distribution of virus along the splenic conduits. Therefore, lymphotoxin beta regulates IFN-I induction independently of CD8(+) T-cell activity. We found that two separate mechanisms act together in the spleen to guarantee amplification of virus during infection, thereby balancing the activation of the innate and adaptive immune system.

Involvement of Toso in activation of monocytes, macrophages, and granulocytes.

Rapid activation of immune responses is necessary for antibacterial defense, but excessive immune activation can result in life-threatening septic shock. Understanding how these processes are balanced may provide novel therapeutic potential in treating inflammatory disease. Fc receptors are crucial for innate immune activation. However, the role of the putative Fc receptor for IgM, known as Toso/Faim3, has to this point been unclear. In this study, we generated Toso-deficient mice and used them to uncover a critical regulatory function of Toso in innate immune activation. Development of innate immune cells was intact in the absence of Toso, but Toso-deficient neutrophils exhibited more reactive oxygen species production and reduced phagocytosis of pathogens compared with controls. Cytokine production was also decreased in Toso(-/-) mice compared with WT animals, rendering them resistant to septic shock induced by lipopolysaccharide. However, Toso(-/-) mice also displayed limited cytokine production after infection with the bacterium Listeria monocytogenes that was correlated with elevated presence of Listeria throughout the body. Accordingly, Toso(-/-) mice succumbed to infections of L. monocytogenes, whereas WT mice successfully eliminated the infection. Taken together, our data reveal Toso to be a unique regulator of innate immune responses during bacterial infection and septic shock.

Virus-Induced Type I Interferon Deteriorates Control of Systemic Pseudomonas Aeruginosa Infection.

BACKGROUND: Type I interferon (IFN-I) predisposes to bacterial superinfections, an important problem during viral infection or treatment with interferon-alpha (IFN-α). IFN-I-induced neutropenia is one reason for the impaired bacterial control; however there is evidence that more frequent bacterial infections during IFN-α-treatment occur independently of neutropenia. METHODS: We analyzed in a mouse model, whether Pseudomonas aeruginosa control is influenced by co-infection with the lymphocytic choriomeningitis virus (LCMV). Bacterial titers, numbers of neutrophils and the gene-expression of liver-lysozyme-2 were determined during a 24 hours systemic infection with P. aeruginosa in wild-type and Ifnar(-/-) mice under the influence of LCMV or poly(I:C). RESULTS: Virus-induced IFN-I impaired the control of Pseudomonas aeruginosa. This was associated with neutropenia and loss of lysozyme-2-expression in the liver, which had captured P. aeruginosa. A lower release of IFN-I by poly(I:C)-injection also impaired the bacterial control in the liver and reduced the expression of liver-lysozyme-2. Low concentration of IFN-I after infection with a virulent strain of P. aeruginosa alone impaired the bacterial control and reduced lysozyme-2-expression in the liver as well. CONCLUSION: We found that during systemic infection with P. aeruginosa Kupffer cells quickly controlled the bacteria in cooperation with neutrophils. Upon LCMV-infection this cooperation was disturbed.

Usp18 driven enforced viral replication in dendritic cells contributes to break of immunological tolerance in autoimmune diabetes.

Infection with viruses carrying cross-reactive antigens is associated with break of immunological tolerance and induction of autoimmune disease. Dendritic cells play an important role in this process. However, it remains unclear why autoimmune-tolerance is broken during virus infection, but usually not during exposure to non-replicating cross-reactive antigens. Here we show that antigen derived from replicating virus but not from non-replicating sources undergoes a multiplication process in dendritic cells in spleen and lymph nodes. This enforced viral replication was dependent on Usp18 and was essential for expansion of autoreactive CD8⁺ T cells. Preventing enforced virus replication by depletion of CD11c⁺ cells, genetically deleting Usp18, or pharmacologically inhibiting of viral replication blunted the expansion of autoreactive CD8⁺ T cells and prevented autoimmune diabetes. In conclusion, Usp18-driven enforced viral replication in dendritic cells can break immunological tolerance and critically influences induction of autoimmunity.

IFN-γ licenses CD11b(+) cells to induce progression of systemic lupus erythematosus.

Autoantibodies are a hallmark of autoimmune diseases, such as rheumatoid arthritis, autoimmune hepatitis, and systemic lupus erythematosus (SLE). High titers of anti-nuclear antibodies are used as surrogate marker for SLE, however their contribution to pathogenesis remains unclear. Using murine model of SLE and human samples, we studied the effect of immune stimulation on relapsing of SLE. Although autoantibodies bound to target cells in vivo, only additional activation of CD8(+) T cells converted this silent autoimmunity into overt disease. In mice as well as in humans CD8(+) T cells derived IFN-γ enhanced expression of Fc-receptors on CD11b(+) cells. High expression of Fc-receptors allowed CD11b(+) cells to bind to antibody covered target cells and to destroy them in vivo. We found that autoantibodies induce clinically relevant disease when adaptive immunity, specific for disease non-related antigen, is activated.

B cell-intrinsic deficiency of the Wiskott-Aldrich syndrome protein (WASp) causes severe abnormalities of the peripheral B-cell compartment in mice.

Wiskott Aldrich syndrome (WAS) is caused by mutations in the WAS gene that encodes for a protein (WASp) involved in cytoskeleton organization in hematopoietic cells. Several distinctive abnormalities of T, B, and natural killer lymphocytes; dendritic cells; and phagocytes have been found in WASp-deficient patients and mice; however, the in vivo consequence of WASp deficiency within individual blood cell lineages has not been definitively evaluated. By conditional gene deletion we have generated mice with selective deficiency of WASp in the B-cell lineage (B/WcKO mice). We show that this is sufficient to cause a severe reduction of marginal zone B cells and inability to respond to type II T-independent Ags, thereby recapitulating phenotypic features of complete WASp deficiency. In addition, B/WcKO mice showed prominent signs of B-cell dysregulation, as indicated by an increase in serum IgM levels, expansion of germinal center B cells and plasma cells, and elevated autoantibody production. These findings are accompanied by hyperproliferation of WASp-deficient follicular and germinal center B cells in heterozygous B/WcKO mice in vivo and excessive differentiation of WASp-deficient B cells into class-switched plasmablasts in vitro, suggesting that WASp-dependent B cell-intrinsic mechanisms critically contribute to WAS-associated autoimmunity.

Reduced type I interferon production by dendritic cells and weakened antiviral immunity in patients with Wiskott-Aldrich syndrome protein deficiency.

BACKGROUND: Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency caused by absence of Wiskott-Aldrich syndrome protein (WASP) expression, resulting in defective function of many immune cell lineages and susceptibility to severe bacterial, viral, and fungal infections. Despite a significant proportion of patients with WAS having recurrent viral infections, surprisingly little is known about the effects of WASP deficiency on antiviral immunity. OBJECTIVE: We sought to evaluate the antiviral immune response in patients with WASP deficiency in vivo. METHODS: Viral clearance and associated immunopathology were measured after infection of WASP-deficient (WAS KO) mice with lymphocytic choriomeningitis virus (LCMV). Induction of antiviral CD8(+) T-cell immunity and cytotoxicity was documented in WAS KO mice by means of temporal enumeration of total and antigen-specific T-cell numbers. Type I interferon (IFN-I) production was measured in serum in response to LCMV challenge and characterized in vivo by using IFN-I reporter mice crossed with WAS KO mice. RESULTS: WAS KO mice showed reduced viral clearance and enhanced immunopathology during LCMV infection. This was attributed to both an intrinsic CD8(+) T-cell defect and defective priming of CD8(+) T cells by dendritic cells (DCs). IFN-I production by WAS KO DCs was reduced both in vivo and in vitro. CONCLUSIONS: These studies use a well-characterized model of persistence-prone viral infection to reveal a critical deficiency of CD8(+) T-cell responses in murine WASP deficiency, in which abrogated production of IFN-I by DCs might play an important contributory role. These findings might help us to understand the immunodeficiency of WAS.

Components of the sympathetic nervous system as targets to modulate inflammation - rheumatoid arthritis synovial fibroblasts as neuron-like cells?

BACKGROUND: Catecholamines are major neurotransmitters of the sympathetic nervous system (SNS) and they are of pivotal importance in regulating numerous physiological and pathological processes. Rheumatoid arthritis (RA) is influenced by the activity of the SNS and its neurotransmitters norepinephrine (NE) and dopamine (DA) and early sympathectomy alleviates experimental arthritis in mice. In contrast, late sympathectomy aggravates RA, since this procedure eliminates anti-inflammatory, tyrosine hydroxylase (TH) positive cells that appear in the course of RA. While it has been shown that B cells can take up, degrade and synthesize catecholamines it is still unclear whether this also applies to synovial fibroblasts, a mesenchymal cell that is actively engaged in propagating inflammation and cartilage destruction in RA. Therefore, this study aims to present a detailed description of the catecholamine pathway and its influence on human RA synovial fibroblasts (RASFs). RESULTS: RASFs express all catecholamine-related targets including the synthesizing enzymes TH, DOPA decarboxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase. Furthermore, vesicular monoamine transporters 1/2 (VMAT1/2), dopamine transporter (DAT) and norepinephrine transporter (NET) were detected. RASFs are also able to degrade catecholamines as they express monoaminoxidase A and B (MAO-A/MAO-B) and catechol-O-methyltransferase (COMT). TNF upregulated VMAT2, MAO-B and NET levels in RASFs. DA, NE and epinephrine (EPI) were produced by RASFs and extracellular levels were augmented by either MAO, COMT, VMAT or DAT/NET inhibition but also by tumor necrosis factor (TNF) stimulation. While exogenous DA decreased interleukin-6 (IL-6) production and cell viability at the highest concentration (100 µM), NE above 1 µM increased IL-6 levels with a concomitant decrease in cell viability. MAO-A and MAO-B inhibition had differential effects on unstimulated and TNF treated RASFs. The MAO-A inhibitor clorgyline fostered IL-6 production in unstimulated but not TNF stimulated RASFs (10 nM-1 µM) while reducing IL-6 at 100 µM with a dose-dependent decrease in cell viability in both groups. The MAO-B inhibitor lazabemide hydrochloride did only modestly decrease cell viability at 100 µM while enhancing IL-6 production in unstimulated RASFs and decreasing IL-6 in TNF stimulated cells. CONCLUSIONS: RASFs possess a complete and functional catecholamine machinery whose function is altered under inflammatory conditions. Results from this study shed further light on the involvement of sympathetic neurotransmitters in RA pathology and might open therapeutic avenues to counteract inflammation with the MAO enzymes being key candidates.

Tunicamycin inhibits diabetes.

BACKGROUND: Autoimmune diseases are characterized by a breakdown of immunologic tolerance, and this breakdown can lead to life-threatening or lifelong disorders. Moreover; drugs that are used to treat these diseases are few in number and are associated with many serious adverse effects. METHODS: We used the rat insulin promoter-glycoprotein mouse model to analyze the role of tunicamycin in the process of autoimmune diabetes; the P14 mouse model to analyze the effect of tunicamycin on CD8(+) T cells; chop knockout mice to analyze the role of tunicamycin on an endoplasmic reticulum stress model; and fluorescence-activated cell sorting, quantitative real-time polymerase chain reaction, and histologic methods. RESULTS: We found that a single dose of tunicamycin reduced the activation and pancreatic infiltration of CD8(+) T cells. This activity delayed the incidence of virus-induced diabetes and improved survival rates. CONCLUSION: Tunicamycin may offer therapeutic opportunities for T cell-mediated autoimmune diseases such as diabetes.

ß2-Adrenergic Receptor Expression and Intracellular Signaling in B Cells Are Highly Dynamic during Collagen-Induced Arthritis.

The sympathetic nervous system (SNS) has either a pro-inflammatory or anti-inflammatory effect, depending on the stage of arthritis. In the past, treatment of arthritic B cells with a ß2-adrenergic receptor (ß2-ADR) agonist has been shown to attenuate arthritis. In this study, the expression and signaling of ß2-ADR in B cells during collagen-induced arthritis (CIA) were investigated to provide an explanation of why only B cells from arthritic mice are able to improve CIA. Splenic B cells were isolated via magnetic-activated cell sorting (MACS). Adrenergic receptors on B cells and intracellular ß2-ADR downstream molecules (G protein-coupled receptor kinase 2 (GRK-2), ß-Arrestin 2, p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB)) were analyzed at different time points in naïve and arthritic B cells with and without stimulation of ß2-ADR agonist terbutaline by flow cytometry. ß2-ADR-expressing B cells increase during CIA without a change in receptor density. Moreover, we observed a profound downregulation of GRK-2 shortly after induction of arthritis and an increase in ß-Arrestin 2 only at late stage of arthritis. The second messengers studied (p38, ERK1/2 and CREB) followed a biphasic course, characterized by a reduction at onset and an increase in established arthritis. Stimulation of CIA B cells with the ß-ADR agonist terbutaline increased pp38 MAPK independent of the timepoint, while pERK1/2 and pCREB were enhanced only in the late phase of arthritis. The phosphorylation of p38 MAPK, ERK1/2 and CREB in the late phase of arthritis was associated with increased IL-10 produced by B10 cells. The change of ß2-ADR expression and signaling during sustained inflammation might be an integral part of the switch from pro- to anti-inflammatory action of sympathetic mechanisms in late arthritis.

Tissue macrophages suppress viral replication and prevent severe immunopathology in an interferon-I-dependent manner in mice.

UNLABELLED: The innate immune response plays an essential role in the prevention of early viral dissemination. We used the lymphocytic choriomeningitis virus model system to analyze the role of tissue macrophages/Kupffer cells in this process. Our findings demonstrated that Kupffer cells are essential for the efficient capture of infectious virus and for preventing viral replication. The latter process involved activation of Kupffer cells by interferon (IFN)-I and prevented viral spread to neighboring hepatocytes. In the absence of Kupffer cells, hepatocytes were not able to suppress virus replication, even in the presence of IFN-I, leading to prolonged viral replication and severe T cell-dependent immunopathology. CONCLUSION: Tissue-resident macrophages play a crucial role in early viral capture and represent the major liver cell type exhibiting responsiveness to IFN-I and providing control of viral replication.