Contribution of Interferon-β to the Murine Macrophage Response to the Toll-like Receptor 4 Agonist, Lipopolysaccharide

Sebacic acid, a royal jelly-containing fatty acid, decreases LPS-induced IL-6 mRNA expression in differentiated human THP-1 macrophage-like cells

Macrophages produce many inflammatory mediators, such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), in innate immune responses. However, excess production of these mediators by activated macrophages triggers deleterious effects, leading to disorders associated with inflammation. Royal jelly (RJ), a milky-white substance secreted by worker bees, contains unique fatty acids, including 10-hydroxy-2-decenoic acid (10H2DA) and sebacic acid (SA). 10H2DA has been reported to have various biological functions, such as anti-inflammation. However, the anti-inflammatory effect of SA is not fully understood. In this study, we investigated the effects of SA on lipopolysaccharide (LPS)-induced cytokine expression using differentiated human THP-1 macrophage-like cells. SA dose-dependently decreased LPS-induced mRNA expression of IL-6, but not TNF-α and IL-1β. SA suppressed the phosphorylation of signal transducers and activators of transcription 1 (STAT1) and STAT3, but hardly affected the activation of JNK, p38, or NF-κB. In addition, SA decreased LPS-induced interferon-β (IFN-β) expression, and the addition of IFN-β restored the inhibition by SA of LPS-induced STAT activation and IL-6 expression. Furthermore, SA suppressed LPS-induced nuclear translocation of interferon regulatory factor 3 (IRF3), a transcription factor responsible for IFN-β expression. Taken together, we conclude that SA selectively decreases LPS-induced expression of IL-6 mRNA through inhibition of the IRF3/IFN-β/STAT axis.

Dexamethasone impairs the expression of antimicrobial mediators in lipopolysaccharide-activated primary macrophages by inhibiting both expression and function of interferon β

Glucocorticoids potently inhibit expression of many inflammatory mediators, and have been widely used to treat both acute and chronic inflammatory diseases for more than seventy years. However, they can have several unwanted effects, amongst which immunosuppression is one of the most common. Here we used microarrays and proteomic approaches to characterise the effect of dexamethasone (a synthetic glucocorticoid) on the responses of primary mouse macrophages to a potent pro-inflammatory agonist, lipopolysaccharide (LPS). Gene ontology analysis revealed that dexamethasone strongly impaired the lipopolysaccharide-induced antimicrobial response, which is thought to be driven by an autocrine feedback loop involving the type I interferon IFNβ. Indeed, dexamethasone strongly and dose-dependently inhibited the expression of IFNβ by LPS-activated macrophages. Unbiased proteomic data also revealed an inhibitory effect of dexamethasone on the IFNβ-dependent program of gene expression, with strong down-regulation of several interferon-induced antimicrobial factors. Surprisingly, dexamethasone also inhibited the expression of several antimicrobial genes in response to direct stimulation of macrophages with IFNβ. We tested a number of hypotheses based on previous publications, but found that no single mechanism could account for more than a small fraction of the broad suppressive impact of dexamethasone on macrophage type I interferon signaling, underlining the complexity of this pathway. Preliminary experiments indicated that dexamethasone exerted similar inhibitory effects on primary human monocyte-derived or alveolar macrophages.

Requirement of scavenger receptors for activation of the IRF-3/IFN-β/STAT-1 pathway in TLR4-mediated production of NO by LPS-activated macrophages

Production of nitric oxide (NO) by LPS-activated macrophages is due to a complex cellular signaling initiated by TLR4 that leads to the transcription of IFN-β, which activates IRF-1 and STAT-1, as well as to the activation of NF-κB, required for iNOS transcription. High concentrations of LPS can also be uptaken by scavenger receptors (SRs), which, in concert with TLR4, leads to inflammatory responses. The mechanisms by which TLR4 and SRs interact, and the pathways activated by this interaction in macrophages are not elucidated. Therefore, our main goal was to evaluate the role of SRs, particularly SR-A, in LPS-stimulated macrophages for NO production. We first showed that, surprisingly, LPS can induce the expression of iNOS and the production of NO in TLR4^-/- mice, provided exogenous IFN-β is supplied. These results indicate that LPS stimulate receptors other than TLR4. The inhibition of SR-A using DSS or neutralizing antibody to SR-AI showed that SR-A is essential for the expression of iNOS and NO production in stimulation of TLR4 by LPS. The restoration of the ability to express iNOS and produce NO by addition of rIFN-β to inhibited SR-A cells indicated that the role of SR-AI in LPS-induced NO production is to provide IFN-β, probably by mediating the internalization of LPS/TLR4, and the differential inhibition by DSS and neutralizing antibody to SR-AI suggested that other SRs are also involved. Our results reinforce that TLR4 and SR-A act in concert in LPS activation and demonstrated that, for the production of NO, it does mainly by synthesizing IRF-3 and also by activating the TRIF/IRF-3 pathway for IFN-β production, essential for LPS-mediated transcription of iNOS. Consequently STAT-1 is activated, and IRF-1 is expressed, which together with NF-κB from TLR4/MyD88/TIRAP, induce iNOS synthesis and NO production. SUMMARY SENTENCE: TLR4 and SRs act in concert activating IRF-3 to transcribe IFN-β and activate STAT-1 to produce NO by LPS-activated macrophages.

SRSF6 balances mitochondrial-driven innate immune outcomes through alternative splicing of BAX

To mount a protective response to infection while preventing hyperinflammation, gene expression in innate immune cells must be tightly regulated. Despite the importance of pre-mRNA splicing in shaping the proteome, its role in balancing immune outcomes remains understudied. Transcriptomic analysis of murine macrophage cell lines identified Serine/Arginine Rich Splicing factor 6 (SRSF6) as a gatekeeper of mitochondrial homeostasis. SRSF6-dependent orchestration of mitochondrial health is directed in large part by alternative splicing of the pro-apoptosis pore-forming protein BAX. Loss of SRSF6 promotes accumulation of BAX-κ, a variant that sensitizes macrophages to undergo cell death and triggers upregulation of interferon stimulated genes through cGAS sensing of cytosolic mitochondrial DNA. Upon pathogen sensing, macrophages regulate SRSF6 expression to control the liberation of immunogenic mtDNA and adjust the threshold for entry into programmed cell death. This work defines BAX alternative splicing by SRSF6 as a critical node not only in mitochondrial homeostasis but also in the macrophage's response to pathogens.

Tannerella forsythia strains differentially induce interferon gamma-induced protein 10 (IP-10) expression in macrophages due to lipopolysaccharide heterogeneity

Tannerella forsythia is strongly implicated in the development of periodontitis, an inflammatory disease that destroys the bone and soft tissues supporting the tooth.  To date, the knowledge of the virulence attributes of T. forsythia species has mainly come from studies with a laboratory adapted strain (ATCC 43 037). In this study, we focused on two T. forsythia clinical isolates, UB4 and UB20, in relation to their ability to activate macrophages. We found that these clinical isolates differentially induced proinflammatory cytokine expression in macrophages. Prominently, the expression of the chemokine protein IP-10 (CXCL10) was highly induced by UB20 as compared to UB4 and the laboratory strain ATCC 43 037. Our study focused on the lipopolysaccharide component (LPS) of these strains and found that UB20 expressed a smooth-type LPS, unlike UB4 and ATCC 43 037 each of which expressed a rough-type LPS. The LPS from UB20, via activation of TLR4, was found to be a highly potent inducer of IP-10 expression via signaling through STAT1 (signal transducer and activator of transcription-1). These data suggest that pathogenicity of T. forsythia species could be strain dependent and the LPS heterogeneity associated with the clinical strains might be responsible for their pathogenic potential and severity of periodontitis.

Immunoregulation by type I interferons in the peritoneal cavity

The peritoneal cavity, a fluid-containing potential space surrounding the abdominal and pelvic organs, is home to a rich network of immune cells that maintain tissue homeostasis and provide protection against infection. However, under pathological conditions such as peritonitis, endometriosis, and peritoneal carcinomatosis, the peritoneal immune system can become dysregulated, resulting in nonresolving inflammation and disease progression. An enhanced understanding of the factors that regulate peritoneal immune cells under both homeostatic conditions and in disease contexts is therefore required to identify new treatment strategies for these often life-limiting peritoneal pathologies. Type I interferons (T1IFNs) are a family of cytokines with broad immunoregulatory functions, which provide defense against viruses, bacteria, and cancer. There have been numerous reports of immunoregulation by T1IFNs within the peritoneal cavity, which can contribute to both the resolution or propagation of peritoneal disease states, depending on the specifics of the disease setting and local environment. In this review, we provide an overview of the major immune cell populations that reside in the peritoneal cavity (or infiltrate it under inflammatory conditions) and highlight their contribution to the initiation, progression, or resolution of peritoneal diseases. Additionally, we will discuss the role of T1IFNs in the regulation of peritoneal immune cells, and summarize the results of laboratory studies and clinical trials which have investigated T1IFNs in peritonitis/sepsis, endometriosis, and peritoneal carcinomatosis.

Type I IFNs facilitate innate immune control of the opportunistic bacteria Burkholderia cenocepacia in the macrophage cytosol

The mammalian immune system is constantly challenged by signals from both pathogenic and non-pathogenic microbes. Many of these non-pathogenic microbes have pathogenic potential if the immune system is compromised. The importance of type I interferons (IFNs) in orchestrating innate immune responses to pathogenic microbes has become clear in recent years. However, the control of opportunistic pathogens-and especially intracellular bacteria-by type I IFNs remains less appreciated. In this study, we use the opportunistic, Gram-negative bacterial pathogen Burkholderia cenocepacia (Bc) to show that type I IFNs are capable of limiting bacterial replication in macrophages, preventing illness in immunocompetent mice. Sustained type I IFN signaling through cytosolic receptors allows for increased expression of autophagy and linear ubiquitination mediators, which slows bacterial replication. Transcriptomic analyses and in vivo studies also show that LPS stimulation does not replicate the conditions of intracellular Gram-negative bacterial infection as it pertains to type I IFN stimulation or signaling. This study highlights the importance of type I IFNs in protection against opportunistic pathogens through innate immunity, without the need for damaging inflammatory responses.

Combined IFN-β and PLT Detection Can Identify Kawasaki Disease Efficiently

Objective: To evaluate the value of combined interferon β (IFN-β) and platelet (PLT) detection for Kawasaki disease (KD) identification. Methods: Forty-four children who were newly diagnosed with KD were selected as the KD group. They were divided into acute phase of KD and subacute phase of KD. They were also separated into groups with and without coronary artery disease (CAD) (CAD+ and CAD-, respectively). Meanwhile, 44 children hospitalized with febrile disease and 44 healthy children were selected as a febrile control group and normal control group, whom were attended to at Children's Hospital of Soochow University at the same time. We detected the concentration of IFN-β and PLT of peripheral blood serum for all three groups and analyzed the difference. Results: At acute and subacute phases of KD, both IFN-β and PLT are higher than both the febrile control group and healthy control group, especially at subacute phase; the difference between groups was statistically significant, P < 0.05. Receiver operating characteristic (ROC) curve showed that the areas under the ROC curve (AUCs) of IFN-β and PLT at acute phase of KD were 0.81 and 0.72, respectively; the sensitivity and specificity were 97.22 and 63.64%, and 57.89 and 73.86%, respectively. The AUCs of combined IFN-β and PLT were 0.81 at acute phase and 0.96 at subacute phase of KD, with sensitivity and specificity of 97.22 and 55.26%, and 86.36 and 100%, respectively. The cutoff value of combined IFN-β and PLT detection was IFN-β = 3.51 pg/ml and PLT = 303 × 10⁹/L at acute phase of KD, IFN-β = 4.21 pg/ml and PLT = 368 × 10⁹/L at subacute phase from plot vs. criterion values. However, there are no significant differences between the CAD- group and the CAD+ group for combined IFN-β and PLT, both P > 0.5, neither at acute nor at subacute phase of KD. Conclusion: Combined IFN-β and PLT detection is an efficient biomarker for KD identification. The cutoff values are IFN-β = 3.51 pg/ml and PLT = 303 × 10⁹/L at acute phase of KD and IFN-β = 4.21 pg/ml and PLT = 368 × 10⁹/L at subacute phase.

Protective Potentials of Type III Interferons in COVID-19 Patients: Lessons from Differential Properties of Type I- and III Interferons

While an appropriately regulated production of interferons (IFNs) performs a fundamental role in the defense against coronaviruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), dysregulated overproduction of inflammatory mediators can play an important role in the development of SARS-CoV-2 infection-related complications, such as acute respiratory distress syndrome. As the principal constituents of innate immunity, both type I and III IFNs share antiviral features. However, important properties, including preferential expression at mucosal barriers (such as respiratory tract), local influences, lower receptor distribution, smaller target cell types, noninflammatory effects, and immunomodulatory impacts, were attributed only to type III IFNs. Accordingly, type III IFNs can establish an optimal effective antiviral response, without triggering exaggerated systemic inflammation that is generally attributed to the type I IFNs. However, some harmful effects were attributed to the III IFNs and there are also major differences between human and mouse concerning the immunomodulatory effects of III IFNs. Here, we describe the differential properties of type I and type III IFNs and present a model of IFN response during SARS-COV-2 infection, while highlighting the superior potential of type III IFNs in COVID-19.

Dissociation of TRIF bias and adjuvanticity

Toll-like receptors (TLRs), a family of "pattern recognition receptors," bind microbial and host-derived molecules, leading to intracellular signaling and proinflammatory gene expression. TLR4 is unique in that ligand-mediated activation requires the co-receptor myeloid differentiation 2 (MD2) to initiate two signaling cascades: the MyD88-dependent pathway is initiated at the cell membrane, and elicits rapid MAP kinase and NF-κB activation, while the TIR-domain containing adaptor inducing interferon-β (TRIF)-dependent pathway is initiated from TLR4-containing endosomes and results in IRF3 activation. Previous studies associated inflammation with the MyD88 pathway and adjuvanticity with the TRIF pathway. Gram-negative lipopolysaccharide (LPS) is a potent TLR4 agonist, and structurally related molecules signal through TLR4 to differing extents. Herein, we compared monophosphoryl lipid A (sMPL) and E6020, two synthetic, non-toxic LPS lipid A analogs used as vaccine adjuvants, for their capacities to activate TLR4-mediated innate immune responses and to enhance antibody production. In mouse macrophages, high dose sMPL activates MyD88-dependent signaling equivalently to E6020, while E6020 exhibits significantly more activation of the TRIF pathway (a "TRIF bias") than sMPL. Eritoran, a TLR4/MD2 antagonist, competitively inhibited sMPL more strongly than E6020. Despite these differences, sMPL and E6020 adjuvants enhanced antibody responses to comparable extents, with balanced immunoglobulin (Ig) isotypes in two immunization models. These data indicate that a TRIF bias is not necessarily predictive of superior adjuvanticity.

Anti-interferon-α receptor 1 antibodies attenuate inflammation and organ injury following hemorrhagic shock

BACKGROUND

Hemorrhagic shock (HS) is a life-threatening condition resulting from rapid and significant loss of intravascular volume, leading to hemodynamic instability and death. Inflammation contributes to the multiple organ injury in HS. Type I interferons (IFNs), such as IFN-α and IFN-β, are a family of cytokines that regulate the inflammatory response through binding to IFN-α receptor (IFNAR) which consists of IFNAR1 and IFNAR2 chains. We hypothesized that type I IFNs provoke inflammation and worsen organ injury in HS.

METHODS

Male C57BL/6 mice (20-25 g) underwent hemorrhage by controlled bleeding via the femoral artery to maintain a mean arterial pressure of 27 ± 2.5 mm Hg for 90 minutes, followed by resuscitation for 30 minutes with two times shed blood volume of Ringer's lactate solution containing 1 mg/kg body weight of anti-IFNAR1 antibody (Ab) or control isotype-matched IgG (IgG). Blood and tissue samples were collected at 20 hours after the resuscitation for various analyses.

RESULTS

The expression of IFN-α and IFN-β mRNAs was significantly elevated in lungs and liver of the mice after HS. The IFNAR1-Ab treatment significantly decreased serum levels of organ injury markers lactate dehydrogenase and aspartate aminotransferase, as well as improved the integrity of lung and liver morphology, compared to the IgG control. The protein levels of proinflammatory cytokines TNF-α and IL-6, and mRNA expression of proinflammatory chemokines monocyte chemoattractant protein (MCP)-1, MCP-2, macrophage inflammatory protein 2 (MIP-2), and keratinocyte cytokine (KC) in the lungs of the HS mice were significantly decreased after treated with IFNAR1-Ab. Moreover, the myeloperoxidase activity and number of apoptotic cells in the lungs of HS mice treated with IFNAR1-Ab were decreased in comparison to the IgG control.

CONCLUSION

Administration of IFNAR1-Ab reduces inflammation and tissue injury. Thus, type I IFN signaling may be a potential therapeutic target for mitigating organ dysfunction in patients suffering from HS.

STUDY TYPE

Translational animal model.

IRF-7 Mediates Type I IFN Responses in Endotoxin-Challenged Mice

IRF-7 mediates robust production of type I IFN via MyD88 of the TLR9 pathway in plasmacytoid dendritic cells (pDCs). Previous in vitro studies using bone marrow-derived dendritic cells lacking either Irf7 or Irf3 have demonstrated that only IRF-3 is required for IFN-β production in the TLR4 pathway. Here, we show that IRF-7 is essential for both type I IFN induction and IL-1β responses via TLR4 in mice. Mice lacking Irf7 were defective in production of both IFN-β and IL-1β, an IFN-β-induced pro-inflammatory cytokine, after LPS challenge. IFN-β production in response to LPS was impaired in IRF-7-deficient macrophages, but not dendritic cells. Unlike pDCs, IRF-7 is activated by the TRIF-, but not MyD88-, dependent pathway via TBK-1 in macrophages after LPS stimulation. Like pDCs, resting macrophages constitutively expressed IRF-7 protein. This basal IRF-7 protein was completely abolished in either Ifnar1 ^-/- or Stat1 ^-/- macrophages, which corresponded with the loss of LPS-stimulated IFN-β induction in these macrophages. These findings demonstrate that macrophage IRF-7 is critical for LPS-induced type I IFN responses, which in turn facilitate IL-1β production in mice.

IFN- signalling regulates RAW 264.7 macrophage activation, cytokine production, and killing activity

Type I IFN holds a critical role in host defence, providing protection against pathogenic organisms through coordinating a pro-inflammatory response. Type I IFN provides additional protection through mitigating this inflammatory response, preventing immunopathology. Within the context of viral infections, type I IFN signalling commonly results in successful viral clearance. Conversely, during bacterial infections, the role of type I IFN is less predictable, leading to either detrimental or beneficial outcomes. The factors responsible for the variability in the role of type I IFN remain unclear. Here, we aimed to elucidate differences in the effect of type I IFN signalling on macrophage functioning in the context of TLR activation. Using RAW 264.7 macrophages, we observed the influence of type I IFN to be dependent on the type of TLR ligand, length of TLR exposure and the timing of IFN-β signalling. However, in all conditions, IFN-β increased the production of the anti-inflammatory cytokine IL-10. Examination of RAW 264.7 macrophage function showed type I IFN to induce an activated phenotype by up-regulating MHC II expression and enhancing killing activity. Our results support a context-dependent role for type I IFN in regulating RAW 264.7 macrophage activity.

Noncanonical STAT1 phosphorylation expands its transcriptional activity into promoting LPS-induced IL-6 and IL-12p40 production

The lipopolysaccharide (LPS)–induced endocytosis of Toll-like receptor 4 (TLR4) is an essential step in the production of interferon-β (IFN-β), which activates the transcription of antiviral response genes by STAT1 phosphorylated at Tyr701. Here, we showed that STAT1 regulated proinflammatory cytokine production downstream of TLR4 endocytosis independently of IFN-β signaling and the key proinflammatory regulator NF-κB. In human macrophages, TLR4 endocytosis activated a noncanonical phosphorylation of STAT1 at Thr749, which subsequently promoted the production of interleukin-6 (IL-6) and IL-12p40 through distinct mechanisms. STAT1 phosphorylated at Thr749activated the expression of the gene encoding ARID5A, which stabilizesIL6mRNA. Moreover, STAT1 phosphorylated at Thr749directly enhanced transcription of the gene encoding IL-12p40 (IL12B). Instead of affecting STAT1 nuclear translocation, phosphorylation of Thr749facilitated the binding of STAT1 to a noncanonical DNA motif (5′-TTTGANNC-3′) in the promoter regions ofARID5AandIL12B. The endocytosis of TLR4 induced the formation of a complex between the kinases TBK1 and IKKβ, which mediated the phosphorylation of STAT1 at Thr749. Our data suggest that noncanonical phosphorylation in response to LPS confers STAT1 with distinct DNA binding and gene-regulatory properties that promote bothIL12Bexpression andIL6mRNA stabilization. Thus, our study provides a potential mechanism for how TLR4 endocytosis might regulate proinflammatory cytokine production.

Type I IFN, Ly6C+ cells, and Phagocytes Support Suppression of Peritoneal Carcinomatosis Elicited by a TLR and CLR Agonist Combination

Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Our previous study demonstrated a Toll-like receptor and C-type lectin receptor agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6'-dicorynomycolate (TDCM) effectively inhibits tumor growth and ascites development following TA3-Ha and EL4 challenge through a mechanism dependent on B-1a cell-produced natural IgM and complement. In this study, we investigated additional players in the MPL/TDCM-elicited response. MPL/TDCM treatment rapidly increased type I IFN levels in the peritoneal cavity along with myeloid cell numbers, including macrophages and Ly6C^hi monocytes. Type I IFN receptor (IFNAR1^-/-) mice produced tumor-reactive IgM following MPL/TDCM treatment, but failed to recruit Ly6C⁺ monocytes and were not afforded protection during tumor challenges. Clodronate liposome depletion of phagocytic cells, as well as targeted depletion of Ly6C⁺ cells, also ablated MPL/TDCM-induced protection. Cytotoxic mediators known to be produced by these cells were required for effects. TNFα was required for effective TA3-Ha killing and nitric oxide was required for EL4 killing. Collectively, these data reveal a model whereby MPL/TDCM-elicited antitumor effects strongly depend on innate cell responses, with B-1a cell-produced tumor-reactive IgM and complement pairing with myeloid cell-produced cytotoxic mediators to effectively eradicate tumors in the peritoneal cavity.

An Essential Role for Perforin-2 in Type I IFN Signaling

Type I IFNs play a complex role in determining the fate of microbial pathogens and may also be deleterious to the host during bacterial and viral infections. Upon ligand binding, a receptor proximal complex consisting of IFN-α and -β receptors 1 and 2 (IFNAR1, IFNAR2, respectively), tyrosine kinase 2 (Tyk2), Jak1, and STAT2 are assembled and promote the phosphorylation of STAT1 and STAT2. However, how the IFNARs proximal complex is assembled upon binding to IFN is poorly understood. In this study, we show that the membrane-associated pore-forming protein Perforin-2 (P2) is critical for LPS-induced endotoxic shock in wild-type mice. Type I IFN-mediated JAK-STAT signaling is severely impaired, and activation of MAPKs and PI3K signaling pathways are delayed in P2-deficient mouse bone marrow-derived macrophages, mouse embryonic fibroblasts (MEFs), and human HeLa cells upon IFN stimulation. The P2 N-glycosylated extracellular membrane attack complex/perforin domain and the P2 domain independently associate with the extracellular regions of IFNAR1 and IFNAR2, respectively, in resting MEFs. In addition, the P2 cytoplasmic tail domain mediated the constitutive interaction between STAT2 and IFNAR2 in resting MEFs, an interaction that is dependent on the association of the extracellular regions of P2 and IFNAR2. Finally, the constitutive association of P2 with both receptors and STAT2 is critical for the receptor proximal complex assembly and reciprocal transphosphorylation of Jak1 and Tyk2 as well as the phosphorylation and activation of STAT1 and STAT2 upon IFN-β stimulation.

Interferon-β Plays a Detrimental Role in Experimental Traumatic Brain Injury by Enhancing Neuroinflammation That Drives Chronic Neurodegeneration

DNA damage and type I interferons (IFNs) contribute to inflammatory responses after traumatic brain injury (TBI). TBI-induced activation of microglia and peripherally-derived inflammatory macrophages may lead to tissue damage and neurological deficits. Here, we investigated the role of IFN-β in secondary injury after TBI using a controlled cortical impact model in adult male IFN-β-deficient (IFN-β^-/-) mice and assessed post-traumatic neuroinflammatory responses, neuropathology, and long-term functional recovery. TBI increased expression of DNA sensors cyclic GMP-AMP synthase and stimulator of interferon genes in wild-type (WT) mice. IFN-β and other IFN-related and neuroinflammatory genes were also upregulated early and persistently after TBI. TBI increased expression of proinflammatory mediators in the cortex and hippocampus of WT mice, whereas levels were mitigated in IFN-β^-/- mice. Moreover, long-term microglia activation, motor, and cognitive function impairments were decreased in IFN-β^-/- TBI mice compared with their injured WT counterparts; improved neurological recovery was associated with reduced lesion volume and hippocampal neurodegeneration in IFN-β^-/- mice. Continuous central administration of a neutralizing antibody to the IFN-α/β receptor (IFNAR) for 3 d, beginning 30 min post-injury, reversed early cognitive impairments in TBI mice and led to transient improvements in motor function. However, anti-IFNAR treatment did not improve long-term functional recovery or decrease TBI neuropathology at 28 d post-injury. In summary, TBI induces a robust neuroinflammatory response that is associated with increased expression of IFN-β and other IFN-related genes. Inhibition of IFN-β reduces post-traumatic neuroinflammation and neurodegeneration, resulting in improved neurological recovery. Thus, IFN-β may be a potential therapeutic target for TBI.SIGNIFICANCE STATEMENT TBI frequently causes long-term neurological and psychiatric changes in head injury patients. TBI-induced secondary injury processes including persistent neuroinflammation evolve over time and can contribute to chronic neurological impairments. The present study demonstrates that TBI is followed by robust activation of type I IFN pathways, which have been implicated in microglial-associated neuroinflammation and chronic neurodegeneration. We examined the effects of genetic or pharmacological inhibition of IFN-β, a key component of type I IFN mechanisms to address its role in TBI pathophysiology. Inhibition of IFN-β signaling resulted in reduced neuroinflammation, attenuated neurobehavioral deficits, and limited tissue loss long after TBI. These preclinical findings suggest that IFN-β may be a potential therapeutic target for TBI.

Toll-like Receptors from the Perspective of Cancer Treatment

Toll-like receptors (TLRs) represent a family of pattern recognition receptors that recognize certain pathogen-associated molecular patterns and damage-associated molecular patterns. TLRs are highly interesting to researchers including immunologists because of the involvement in various diseases including cancers, allergies, autoimmunity, infections, and inflammation. After ligand engagement, TLRs trigger multiple signaling pathways involving nuclear factor-κB (NF-κB), interferon-regulatory factors (IRFs), and mitogen-activated protein kinases (MAPKs) for the production of various cytokines that play an important role in diseases like cancer. TLR activation in immune as well as cancer cells may prevent the formation and growth of a tumor. Nonetheless, under certain conditions, either hyperactivation or hypoactivation of TLRs supports the survival and metastasis of a tumor. Therefore, the design of TLR-targeting agonists as well as antagonists is a promising immunotherapeutic approach to cancer. In this review, we mainly describe TLRs, their involvement in cancer, and their promising properties for anticancer drug discovery.

Labelled regulatory elements are pervasive features of the macrophage genome and are dynamically utilized by classical and alternative polarization signals

The concept of tissue-specific gene expression posits that lineage-determining transcription factors (LDTFs) determine the open chromatin profile of a cell via collaborative binding, providing molecular beacons to signal-dependent transcription factors (SDTFs). However, the guiding principles of LDTF binding, chromatin accessibility and enhancer activity have not yet been systematically evaluated. We sought to study these features of the macrophage genome by the combination of experimental (ChIP-seq, ATAC-seq and GRO-seq) and computational approaches. We show that Random Forest and Support Vector Regression machine learning methods can accurately predict chromatin accessibility using the binding patterns of the LDTF PU.1 and four other key TFs of macrophages (IRF8, JUNB, CEBPA and RUNX1). Any of these TFs alone were not sufficient to predict open chromatin, indicating that TF binding is widespread at closed or weakly opened chromatin regions. Analysis of the PU.1 cistrome revealed that two-thirds of PU.1 binding occurs at low accessible chromatin. We termed these sites labelled regulatory elements (LREs), which may represent a dormant state of a future enhancer and contribute to macrophage cellular plasticity. Collectively, our work demonstrates the existence of LREs occupied by various key TFs, regulating specific gene expression programs triggered by divergent macrophage polarizing stimuli.

Global virus outbreaks: Interferons as 1st responders

Outbreaks of severe virus infections with the potential to cause global pandemics are increasing. In many instances these outbreaks have been newly emerging (SARS coronavirus), re-emerging (Ebola virus, Zika virus) or zoonotic (avian influenza H5N1) virus infections. In the absence of a targeted vaccine or a pathogen-specific antiviral, broad-spectrum antivirals would function to limit virus spread. Given the direct antiviral effects of type I interferons (IFNs) in inhibiting the replication of both DNA and RNA viruses at different stages of their replicative cycles, and the effects of type I IFNs on activating immune cell populations to clear virus infections, IFNs-α/β present as ideal candidate broad-spectrum antivirals.

Inflammation and Immunity: From an Adipocyte's Perspective

Comprehension of adipocyte function has evolved beyond a long-held belief of their inert nature, as simple energy storing and releasing cells. Adipocytes, including white, brown, and beige, are capable mediators of global metabolic health, but their intersection with inflammation is a budding field of exploration. Evidence hints at a reciprocal relationship adipocytes share with immune cells. Adipocyte's capacity to behave in an "immune-like" manner and ability to sense inflammatory cues that subsequently alter core adipocyte function might play an important role in shaping immune responses. Clarifying this intricate relationship could uncover previously underappreciated contribution of adipocytes to inflammation-driven human health and disease. In this review, we highlight the potential of largely underappreciated adipocyte "immune-like" function and how it may contribute to inflammation, immunity, and pathology of various diseases.

Specific sequences of infectious challenge lead to secondary hemophagocytic lymphohistiocytosis-like disease in mice

Secondary hemophagocytic lymphohistiocytosis (sHLH) is a highly mortal complication associated with sepsis. In adults, it is often seen in the setting of infections, especially viral infections, but the mechanisms that underlie pathogenesis are unknown. sHLH is characterized by a hyperinflammatory state and the presence hemophagocytosis. We found that sequential challenging of mice with a nonlethal dose of viral toll-like receptor (TLR) agonist followed by a nonlethal dose of TLR4 agonist, but not other permutations, produced a highly lethal state that recapitulates many aspects of human HLH. We found that this hyperinflammatory response could be recapitulated in vitro in bone marrow-derived macrophages. RNA sequencing analyses revealed dramatic up-regulation of the red-pulp macrophage lineage-defining transcription factor SpiC and its associated transcriptional program, which was also present in bone marrow macrophages sorted from patients with sHLH. Transcriptional profiling also revealed a unique metabolic transcriptional profile in these macrophages, and immunometabolic phenotyping revealed impaired mitochondrial function and oxidative metabolism and a reliance on glycolytic metabolism. Subsequently, we show that therapeutic administration of the glycolysis inhibitor 2-deoxyglucose was sufficient to rescue animals from HLH. Together, these data identify a potential mechanism for the pathogenesis of sHLH and a potentially useful therapeutic strategy for its treatment.

Peritoneal macrophages have an impaired immune response in obesity which can be reversed by subsequent weight loss

INTRODUCTION

Obesity is recognized as a risk factor for various microbial infections. The immune system, which is affected by obesity, plays an important role in the pathophysiology of these infections and other obesity-related comorbidities. Weight loss is considered the most obvious treatment for obesity. However, multiple studies suggest that the comorbidities of obesity may persist after weight loss. Deregulation of immune cells including adipose tissue macrophages of obese individuals has been extensively studied, but how obesity and subsequent weight loss affect immune cell function outside adipose tissue is not well defined.

RESEARCH DESIGN AND METHODS

Here we investigated the phenotype of non-adipose tissue macrophages by transcriptional characterization of thioglycollate-elicited peritoneal macrophages (PM) from mice with diet-induced obesity and type 2 diabetes (T2D). Subsequently, we defined the characteristics of PMs after weight loss and mimicked a bacterial infection by exposing PMs to lipopolysaccharide.

RESULTS AND CONCLUSIONS

In contrast to the proinflammatory phenotype of adipose tissue macrophages in obesity and T2D, we found a deactivated state of PMs in obesity and T2D. Weight loss could reverse this deactivated macrophage phenotype. Anti-inflammatory characteristics of these non-adipose macrophages may explain why patients with obesity and T2D have an impaired immune response against pathogens. Our data also suggest that losing weight restores macrophage function and thus contributes to the reduction of immune-related comorbidities in patients.

The role of type I interferons (IFNs) in the regulation of chicken macrophage inflammatory response to bacterial challenge

Mammalian type I interferons (IFNα/β) are known to modulate inflammatory processes in addition to their antiviral properties. Indeed, virus-induced type I interferons regulate the mammalian phagocyte immune response to bacteria during superinfections. However, it remains unresolved whether type I IFNs similarly impact the chicken macrophage immune response. We first evidenced that IFNα and IFNβ act differently in terms of gene expression stimulation and activation of intracellular signaling pathways in chicken macrophages. Next, we showed that priming of chicken macrophages with IFNα increased bacteria uptake, boosted bacterial-induced ROS/NO production and led to an increased transcriptional expression or production of NOS2/NO, IL1B/IL-1β and notably IFNB/IFNβ. Neutralization of IFNβ during bacterial challenge limited IFNα-induced augmentation of the pro-inflammatory response. In conclusion, we demonstrated that type I IFNs differently regulate chicken macrophage functions and drive a pro-inflammatory response to bacterial challenge. These findings shed light on the diverse functions of type I IFNs in chicken macrophages.

Bradyrhizobium Lipid A: Immunological Properties and Molecular Basis of Its Binding to the Myeloid Differentiation Protein-2/Toll-Like Receptor 4 Complex

Lipopolysaccharides (LPS) are potent activator of the innate immune response through the binding to the myeloid differentiation protein-2 (MD-2)/toll-like receptor 4 (TLR4) receptor complexes. Although a variety of LPSs have been characterized so far, a detailed molecular description of the structure–activity relationship of the lipid A part has yet to be clarified. Photosynthetic Bradyrhizobium strains, symbiont of Aeschynomene legumes, express distinctive LPSs bearing very long-chain fatty acids with a hopanoid moiety covalently linked to the lipid A region. Here, we investigated the immunological properties of LPSs isolated from Bradyrhizobium strains on both murine and human immune systems. We found that they exhibit a weak agonistic activity and, more interestingly, a potent inhibitory effect on MD-2/TLR4 activation exerted by toxic enterobacterial LPSs. By applying computational modeling techniques, we also furnished a plausible explanation for the Bradyrhizobium LPS inhibitory activity at atomic level, revealing that its uncommon lipid A chemical features could impair the proper formation of the receptorial complex, and/or has a destabilizing effect on the pre-assembled complex itself.

IFN-β Improves Sepsis-related Alveolar Macrophage Dysfunction and Postseptic Acute Respiratory Distress Syndrome-related Mortality

IFN-β is reported to improve survival in patients with acute respiratory distress syndrome (ARDS), possibly by preventing sepsis-induced immunosuppression, but its therapeutic nature in ARDS pathogenesis is poorly understood. We investigated the therapeutic effects of IFN-β for postseptic ARDS to better understand its pathogenesis in mice. Postseptic ARDS was reproduced in mice by cecal ligation and puncture to induce sepsis, followed 4 days later by intratracheal instillation of Pseudomonas aeruginosa to cause pneumonia with or without subcutaneous administration of IFN-β 1 day earlier. Sepsis induced prolonged increases in alveolar TNF-α and IL-10 concentrations and innate immune reprogramming; specifically, it reduced alveolar macrophage (AM) phagocytosis and KC (CXCL1) secretion. Ex vivo AM exposure to TNF-α or IL-10 duplicated cytokine release impairment. Compared with sepsis or pneumonia alone, pneumonia after sepsis was associated with blunted alveolar KC responses and reduced neutrophil recruitment into alveoli despite increased neutrophil burden in lungs (i.e., "incomplete alveolar neutrophil recruitment"), reduced bacterial clearance, increased lung injury, and markedly increased mortality. Importantly, IFN-β reversed the TNF-α/IL-10-mediated impairment of AM cytokine secretion in vitro, restored alveolar innate immune responsiveness in vivo, improved alveolar neutrophil recruitment and bacterial clearance, and consequently reduced the odds ratio for 7-day mortality by 85% (odds ratio, 0.15; 95% confidence interval, 0.03-0.82; P = 0.045). This mouse model of sequential sepsis → pneumonia infection revealed incomplete alveolar neutrophil recruitment as a novel pathogenic mechanism for postseptic ARDS, and systemic IFN-β improved survival by restoring the impaired function of AMs, mainly by recruiting neutrophils to alveoli.

The cGAS/STING Pathway Is Important for Dendritic Cell Activation but Is Not Essential to Induce Protective Immunity against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) infection remains a major public health concern. The STING (stimulator of interferon genes) pathway contributes to the cytosolic surveillance of host cells. Most studies on the role of STING activation in Mtb infection have focused on macrophages. Moreover, a detailed investigation of the role of STING during Mtb infection in vivo is required. Here, we deciphered the involvement of STING in the activation of dendritic cells (DCs) and the host response to Mtb infection in vivo. In DCs, this adaptor molecule was important for Ifn-β expression and IL-12 production as well as for the surface expression of the activation markers CD40 and CD86. We also documented that Mtb DNA induces STING activation in murine fibroblasts. In vivo Mtb aerogenic infection induced the upregulation of the STING and cGAS (cyclic GMP-AMP synthase) genes, and Ifn-β pulmonary expression was dependent on both sensors. However, mice deficient for STING or cGAS presented a similar outcome to wild-type controls, with no major alterations in body weight gain, bacterial burden, or survival. Lung inflammation, proinflammatory cytokine production, and inflammatory cell recruitment were similar in STING- and cGAS-deficient mice compared to wild-type controls. In summary, although the STING pathway seems to be crucial for DC activation during Mtb infection, it is dispensable for host protection in vivo.

Kudzu Leaf Extract Suppresses the Production of Inducible Nitric Oxide Synthase, Cyclooxygenase-2, Tumor Necrosis Factor-Alpha, and Interleukin-6 via Inhibition of JNK, TBK1 and STAT1 in Inflammatory Macrophages

Kudzu (Pueraria montana var. lobata (Willd.) Sanjappa & Pradeep) is a perennial leguminous vine, and its root and flower have been used for herbal medicine in Asia for a long time. Most dietary flavonoids are reported to be concentrated in its root, not in its aerial parts including leaves. In this study, we investigated whether kudzu leaf and its major constituent, robinin (kaempferol-3-O-robinoside-7-O-rhanmoside) possessed anti-inflammatory activity. To test this hypothesis, we used peritoneal macrophages isolated from BALB/c mice and stimulated the cells with lipopolysaccharide (LPS) or LPS plus interferon (IFN)-γ. Compared with kudzu root extract, its leaf extract was more potent in inhibiting the production of inducible nitric oxide synthase (iNOS), cyclooxygenase-2, tumor necrosis factor-α, and interleukin-6. Kudzu leaf extract decreased LPS-induced activation of c-Jun N-terminal kinase (JNK) and TANK-binding kinase 1(TBK1) with no effects on nuclear factor-κB and activator protein 1 transcriptional activity. Also, kudzu leaf extract inhibited LPS/IFN-γ-induced signal transducer and activator of transcription 1 (STAT1) activation partly via an altered level of STAT1 expression. Robinin, being present in 0.46% of dry weight of leaf extract, but almost undetected in the root, decreased iNOS protein involving modulation of JNK and STAT1 activation. However, robinin showed no impact on other inflammatory markers. Our data provide evidence that kudzu leaf is an excellent food source of as yet unknown anti-inflammatory constituents.

Lanosterol Modulates TLR4-Mediated Innate Immune Responses in Macrophages

Macrophages perform critical functions in both innate immunity and cholesterol metabolism. Here, we report that activation of Toll-like receptor 4 (TLR4) in macrophages causes lanosterol, the first sterol intermediate in the cholesterol biosynthetic pathway, to accumulate. This effect is due to type I interferon (IFN)-dependent histone deacetylase 1 (HDAC1) transcriptional repression of lanosterol-14α-demethylase, the gene product of Cyp51A1. Lanosterol accumulation in macrophages, because of either treatment with ketoconazole or induced conditional disruption of Cyp51A1 in mouse macrophages in vitro, decreases IFNβ-mediated signal transducer and activator of transcription (STAT)1-STAT2 activation and IFNβ-stimulated gene expression. These effects translate into increased survival to endotoxemic shock by reducing cytokine secretion. In addition, lanosterol accumulation increases membrane fluidity and ROS production, thus potentiating phagocytosis and the ability to kill bacteria. This improves resistance of mice to Listeria monocytogenes infection by increasing bacterial clearance in the spleen and liver. Overall, our data indicate that lanosterol is an endogenous selective regulator of macrophage immunity.

Regulation of Osteoclast Differentiation by Cytokine Networks

Cytokines play a pivotal role in maintaining bone homeostasis. Osteoclasts (OCs), the sole bone resorbing cells, are regulated by numerous cytokines. Macrophage colony-stimulating factor and receptor activator of NF-κB ligand play a central role in OC differentiation, which is also termed osteoclastogenesis. Osteoclastogenic cytokines, including tumor necrosis factor-α, IL-1, IL-6, IL-7, IL-8, IL-11, IL-15, IL-17, IL-23, and IL-34, promote OC differentiation, whereas anti-osteoclastogenic cytokines, including interferon (IFN)-α, IFN-β, IFN-γ, IL-3, IL-4, IL-10, IL-12, IL-27, and IL-33, downregulate OC differentiation. Therefore, dynamic regulation of osteoclastogenic and anti-osteoclastogenic cytokines is important in maintaining the balance between bone-resorbing OCs and bone-forming osteoblasts (OBs), which eventually affects bone integrity. This review outlines the osteoclastogenic and anti-osteoclastogenic properties of cytokines with regard to osteoimmunology, and summarizes our current understanding of the roles these cytokines play in osteoclastogenesis.

Rotavirus Degrades Multiple Interferon (IFN) Type Receptors To Inhibit IFN Signaling and Protects against Mortality from Endotoxin in Suckling Mice

STAT1 phosphorylation in response to exogenous interferon (IFN) administration can be inhibited by rotaviral replication both in vitro and in vivo In addition many rotavirus strains are resistant to the actions of different IFN types. The regulation by rotaviruses (RVs) of antiviral pathways mediated by multiple IFN types is not well understood. In this study, we find that during infection in vitro and in vivo, RVs significantly deplete IFN type I, II, and III receptors (IFNRs). Regulation of IFNRs occurred exclusively within RV-infected cells and could be abrogated by inhibiting the lysosomal-endosomal degradation pathway. In vitro, IFNR degradation was conserved across multiple RV strains that differ in their modes of regulating IFN induction. In suckling mice, exogenously administered type I, II, or III IFN induced phosphorylation of STAT1-Y701 within intestinal epithelial cells (IECs) of suckling mice. Murine EW strain RV infection transiently activated intestinal STAT1 at 1 day postinfection (dpi) but not subsequently at 2 to 3 dpi. In response to injection of purified IFN-α/β or -λ, IECs in EW-infected mice exhibited impaired STAT1-Y701 phosphorylation, correlating with depletion of different intestinal IFNRs and impaired IFN-mediated transcription. The ability of EW murine RV to inhibit multiple IFN types led us to test protection of suckling mice from endotoxin-mediated shock, an outcome that is dependent on the host IFN response. Compared to mortality in controls, mice infected with EW murine RV were substantially protected against mortality following parenteral endotoxin administration. These studies identify a novel mechanism of IFN subversion by RV and reveal an unexpected protective effect of RV infection on endotoxin-mediated shock in suckling mice.IMPORTANCE Antiviral functions of types I, II, and III IFNs are mediated by receptor-dependent activation of STAT1. Here, we find that RV degrades the types I, II, and III IFN receptors (IFNRs) in vitro In a suckling mouse model, RV effectively blocked STAT1 activation and transcription following injection of different purified IFNs. This correlated with significantly decreased protein expression of intestinal types I and II IFNRs. Recent studies demonstrate that in mice lipopolysaccharide (LPS)-induced lethality is prevented by genetic ablation of IFN signaling genes such as IFNAR1 and STAT1. When suckling mice were infected with RV, they were substantially protected from lethal exposure to endotoxin. These findings provide novel insights into the mechanisms underlying rotavirus regulation of different interferons and are likely to stimulate new research into both rotavirus pathogenesis and endotoxemia.

Type I interferons drive inflammasome-independent emergency monocytopoiesis during endotoxemia

Emergency monocytopoiesis is an inflammation-driven hematological process that supplies the periphery with monocytes and subsequently with macrophages and monocyte-derived dendritic cells. Yet, the regulatory mechanisms by which early bone marrow myeloid progenitors commit to monocyte-derived phagocytes during endotoxemia remains elusive. Herein, we show that type I interferons signaling promotes the differentiation of monocyte-derived phagocytes at the level of their progenitors during a mouse model of endotoxemia. In this model, we characterized early changes in the numbers of conventional dendritic cells, monocyte-derived antigen-presenting cells and their respective precursors. While loss of caspase-1/11 failed to impair a shift toward monocytopoiesis, we observed sustained type-I-IFN-dependent monocyte progenitors differentiation in the bone marrow correlated to an accumulation of Mo-APCs in the spleen. Importantly, IFN-alpha and -beta were found to efficiently generate the development of monocyte-derived antigen-presenting cells while having no impact on the precursor activity of conventional dendritic cells. Consistently, the LPS-driven decrease of conventional dendritic cells and their direct precursor occurred independently of type-I-IFN signaling in vivo. Our characterization of early changes in mononuclear phagocytes and their dependency on type I IFN signaling during sepsis opens the way to the development of treatments for limiting the immunosuppressive state associated with sepsis.

Repression of interferon β-regulated cytokines by the JAK1/2 inhibitor ruxolitinib in inflammatory human macrophages

Ruxolitinib is a Janus kinase (JAK) 1/2 inhibitor, currently used in the treatment of myeloproliferative neoplasms. It exerts potent anti-inflammatory activity, but the involved molecular and cellular mechanisms remain poorly understood. In order to gain insights about this point, ruxolitinib effects towards expression of main inflammatory cytokines were studied in human macrophages, which constitute a key-cell type implicated in inflammation. Analysis of mRNA expression of cytokines (n=84) by PCR array indicated that, among those induced by the pro-inflammatory stimulus lipopolysaccharide (LPS) (n=44), 61.4% (n=27) were repressed by 5μM ruxolitinib. The major inflammatory cytokines, interleukin (IL) 6 and tumor necrosis factor α, were notably down-regulated by ruxolitinib at both the mRNA and protein level. Other repressed cytokines included IL27 and the chemokines CCL2, CXCL9, CXCL10 and CXCL11, but not IL1β. The interferon (IFN) β/JAK/signal transducer and activator of transcription (STAT) pathway, well-activated by LPS in human macrophages as demonstrated by increased secretion of IFNβ, STAT1 phosphorylation, and up-regulation of reference IFNβ-responsive genes, was concomitantly blocked by the JAK inhibitor. Most of cytokines targeted by ruxolitinib were shown to be regulated by IFNβ in a JAK-sensitive manner. In addition, counteracting the IFNβ/JAK/STAT cascade using a blocking monoclonal antibody directed against IFNβ receptor resulted in a similar profile of cytokine repression to that observed in response to the JAK inhibitor. Overall, these data provide evidence for ruxolitinib-mediated repression of inflammatory cytokines in human macrophages through inhibition of the LPS/IFNβ/JAK/STAT signalling pathway, which probably contributes to the anti-inflammatory effects of the JAK inhibitor.

Interferon-β regulates dendritic cell activation and migration in experimental autoimmune encephalomyelitis

CD11c⁺ dendritic cells (DCs) exert a critical role as antigen-presenting cells in regulating pathogenic T cells in multiple sclerosis (MS). To determine whether the therapeutic benefit of interferon-β (IFN-β) treatment for MS is in part influenced by IFN regulation of DC function, we examined the immunophenotype of DCs derived from IFN-β^+/+ and IFN-β^-/- mice using a myelin oligodendrocyte glycoprotein (MOG) peptide-induced mouse model of MS, experimental autoimmune encephalomyelitis (EAE). Our earlier work identified that IFN-β^-/- mice exhibit earlier onset and more rapid progression of neurological impairment compared with IFN-β^+/+ mice. In this study we show that lipopolysaccharide-/MOG peptide-stimulated IFN-β^-/- DCs secrete cytokines associated with pathological T helper type 17 rather than regulatory T-cell polarization and exhibit increased CD80 and MHCII expression when compared with stimulated IFN-β^+/+ DCs. IFN-β^-/- DCs from mice immunized to develop EAE induce greater proliferation of MOG-transgenic CD4⁺ T cells and promote interleukin-17 production by these T cells. Adoptive transfer of MOG peptide-primed IFN-β^-/- DCs into IFN-β^+/+ and IFN-β^-/- mice immunized to develop EAE resulted in their rapid migration into the central nervous system of recipient mice, before onset of disease, which we attribute to failed signal transducer and activator of transcription 1-mediated inhibition of CCR7. Taken together, our data support immunoregulatory roles for IFN-β in the activation and migration of DCs during EAE.

NOX2 deficiency alters macrophage phenotype through an IL-10/STAT3 dependent mechanism: implications for traumatic brain injury

BACKGROUND

NADPH oxidase (NOX2) is an enzyme system that generates reactive oxygen species (ROS) in microglia and macrophages. Excessive ROS production is linked with neuroinflammation and chronic neurodegeneration following traumatic brain injury (TBI). Redox signaling regulates macrophage/microglial phenotypic responses (pro-inflammatory versus anti-inflammatory), and NOX2 inhibition following moderate-to-severe TBI markedly reduces pro-inflammatory activation of macrophages/microglia resulting in concomitant increases in anti-inflammatory responses. Here, we report the signaling pathways that regulate NOX2-dependent macrophage/microglial phenotype switching in the TBI brain.

METHODS

Bone marrow-derived macrophages (BMDMs) prepared from wildtype (C57Bl/6) and NOX2 deficient (NOX2^-/-) mice were treated with lipopolysaccharide (LPS; 10 ng/ml), interleukin-4 (IL-4; 10 ng/ml), or combined LPS/IL-4 to investigate signal transduction pathways associated with macrophage activation using western immunoblotting and qPCR analyses. Signaling pathways and activation markers were evaluated in ipsilateral cortical tissue obtained from adult male wildtype and NOX2^-/- mice that received moderate-level controlled cortical impact (CCI). A neutralizing anti-IL-10 approach was used to determine the effects of IL-10 on NOX2-dependent transitions from pro- to anti-inflammatory activation states.

RESULTS

Using an LPS/IL-4-stimulated BMDM model that mimics the mixed pro- and anti-inflammatory responses observed in the injured cortex, we show that NOX2^-/- significantly reduces STAT1 signaling and markers of pro-inflammatory activation. In addition, NOX2^-/- BMDMs significantly increase anti-inflammatory marker expression; IL-10-mediated STAT3 signaling, but not STAT6 signaling, appears to be critical in regulating this anti-inflammatory response. Following moderate-level CCI, IL-10 is significantly increased in microglia/macrophages in the injured cortex of NOX2^-/- mice. These changes are associated with increased STAT3 activation, but not STAT6 activation, and a robust anti-inflammatory response. Neutralization of IL-10 in NOX2^-/- BMDMs or CCI mice blocks STAT3 activation and the anti-inflammatory response, thereby demonstrating a critical role for IL-10 in regulating NOX2-dependent transitions between pro- and anti-inflammatory activation states.

CONCLUSIONS

These studies indicate that following TBI NOX2 inhibition promotes a robust anti-inflammatory response in macrophages/microglia that is mediated by the IL-10/STAT3 signaling pathway. Thus, therapeutic interventions that inhibit macrophage/microglial NOX2 activity may improve TBI outcomes by not only limiting pro-inflammatory neurotoxic responses, but also enhancing IL-10-mediated anti-inflammatory responses that are neuroprotective.

Type I interferons regulate susceptibility to inflammation-induced preterm birth

Preterm birth (PTB) is a leading worldwide cause of morbidity and mortality in infants. Maternal inflammation induced by microbial infection is a critical predisposing factor for PTB. However, biological processes associated with competency of pathogens, including viruses, to induce PTB or sensitize for secondary bacterial infection-driven PTB are unknown. We show that pathogen/pathogen-associated molecular pattern-driven activation of type I IFN/IFN receptor (IFNAR) was sufficient to prime for systemic and uterine proinflammatory chemokine and cytokine production and induction of PTB. Similarly, treatment with recombinant type I IFNs recapitulated such effects by exacerbating proinflammatory cytokine production and reducing the dose of secondary inflammatory challenge required for induction of PTB. Inflammatory challenge-driven induction of PTB was eliminated by defects in type I IFN, TLR, or IL-6 responsiveness, whereas the sequence of type I IFN sensing by IFNAR on hematopoietic cells was essential for regulation of proinflammatory cytokine production. Importantly, we also show that type I IFN priming effects are conserved from mice to nonhuman primates and humans, and expression of both type I IFNs and proinflammatory cytokines is upregulated in human PTB. Thus, activation of the type I IFN/IFNAR axis in pregnancy primes for inflammation-driven PTB and provides an actionable biomarker and therapeutic target for mitigating PTB risk.

Constitutive overexpressed type I interferon induced downregulation of antiviral activity in medaka fish (Oryzias latipes)

In fish, as well as vertebrates, type I interferons (IFNs) are important cytokines that help to provide innate, antiviral immunity. Although low amounts of IFN are constitutively secreted under normal physiological conditions, long-term and excessive IFN stimulation leads to reduced sensitivity to the IFN signal. This provides a negative feedback mechanism that prevents inappropriate responses and autoimmunity. At present, however, neither IFN desensitization nor the normal physiological role of constitutive IFN are well characterized in fish. The objective here was therefore to produce and characterize a transgenic medaka fish (Oryzias latipes), designated IFNd-Tg, that constitutively overexpressed the IFNd gene. A dual promoter expression vector was constructed for overexpression of IFNd under an EF1α promoter and a DsRed reporter gene under control of a γF-crystaline promoter. The phenotype of the IFNd-Tg fish had a lower response to poly(I:C) and increased susceptibility to nervous necrosis virus (NNV) infection compared to wild-type (WT). Furthermore, transduction of IFN signals for STAT1b, STAT2 and IRF9 were down-regulated in the IFNd-Tg fish, and expression levels of RLR signal molecules (MDA5, MITA, IRF1 and IRF3) were lower than in WT. The constitutive overexpression of IFNd resulted in desensitization of IFN-stimulation, apparently due to downregulation of IFN signal transduction, and this caused increased susceptibility to NNV.

Beta Interferon Production Is Regulated by p38 Mitogen-Activated Protein Kinase in Macrophages via both MSK1/2- and Tristetraprolin-Dependent Pathways

Autocrine or paracrine signaling by beta interferon (IFN-β) is essential for many of the responses of macrophages to pathogen-associated molecular patterns. This feedback loop contributes to pathological responses to infectious agents and is therefore tightly regulated. We demonstrate here that macrophage expression of IFN-β is negatively regulated by mitogen- and stress-activated kinases 1 and 2 (MSK1/2). Lipopolysaccharide (LPS)-induced expression of IFN-β was elevated in both MSK1/2 knockout mice and macrophages. Although MSK1 and -2 promote the expression of the anti-inflammatory cytokine interleukin 10, it did not strongly contribute to the ability of MSKs to regulate IFN-β expression. Instead, MSK1 and -2 inhibit IFN-β expression via the induction of dual-specificity phosphatase 1 (DUSP1), which dephosphorylates and inactivates the mitogen-activated protein kinases p38 and Jun N-terminal protein kinase (JNK). Prolonged LPS-induced activation of p38 and JNK, phosphorylation of downstream transcription factors, and overexpression of IFN-β mRNA and protein were similar in MSK1/2 and DUSP1 knockout macrophages. Two distinct mechanisms were implicated in the overexpression of IFN-β: first, JNK-mediated activation of c-jun, which binds to the IFN-β promoter, and second, p38-mediated inactivation of the mRNA-destabilizing factor tristetraprolin, which we show is able to target the IFN-β mRNA.

Macrophage-based cell therapies: The long and winding road

In the quest for better medicines, attention is increasingly turning to cell-based therapies. The rationale is that infused cells can provide a targeted therapy to precisely correct a complex disease phenotype. Between 1987 and 2010, autologous macrophages (MΦs) were used in clinical trials to treat a variety of human tumors; this approach provided a modest therapeutic benefit in some patients but no lasting remissions. These trials were initiated prior to an understanding of: the complexity of MΦ phenotypes, their ability to alter their phenotype in response to various cytokines and/or the environment, and the extent of survival of the re-infused MΦs. It is now known that while inflammatory MΦs can kill tumor cells, the tumor environment is able to reprogram MΦs into a tumorigenic phenotype; inducing blood vessel formation and contributing to a cancer cell growth-promoting milieu. We review how new information enables the development of large numbers of ex vivo generated MΦs, and how conditioning and gene engineering strategies are used to restrict the MΦ to an appropriate phenotype or to enable production of therapeutic proteins. We survey applications in which the MΦ is loaded with nanomedicines, such as liposomes ex vivo, so when the drug-loaded MΦs are infused into an animal, the drug is released at the disease site. Finally, we also review the current status of MΦ biodistribution and survival after transplantation into an animal. The combination of these recent advances opens the way for improved MΦ cell therapies.

A reverse-phase protein microarray-based screen identifies host signaling dynamics upon Burkholderia spp. infection

Burkholderia is a diverse genus of gram-negative bacteria that causes high mortality rate in humans, equines and cattle. The lack of effective therapeutic treatments poses serious public health threats. Developing insights toward host-Burkholderia spp. interaction is critical for understanding the pathogenesis of infection as well as identifying therapeutic targets for drug development. Reverse-phase protein microarray technology was previously proven to identify and characterize novel biomarkers and molecular signatures associated with infectious disease and cancer. In the present study, this technology was utilized to interrogate changes in host protein expression and phosphorylation events in macrophages infected with a collection of geographically diverse strains of Burkholderia spp. The expression or phosphorylation state of 25 proteins was altered during Burkholderia spp. infections of which eight proteins were selected for further characterization by immunoblotting. Increased phosphorylation of AMPK-α1, Src, and GSK3β suggested the importance of their roles in regulating Burkholderia spp. mediated innate immune response. Modulating the inflammatory response by perturbing their activities may provide therapeutic routes for future treatments.

Salmonella Typhimurium Co-Opts the Host Type I IFN System To Restrict Macrophage Innate Immune Transcriptional Responses Selectively

Innate immune inflammatory responses are subject to complex layers of negative regulation at intestinal mucosal surfaces. Although the type I IFN system is critical for amplifying antiviral immunity, it has been shown to play a homeostatic role in some models of autoimmune inflammation. Type I IFN is triggered in the gut by select bacterial pathogens, but whether and how the type I IFN might regulate innate immunity in the intestinal environment have not been investigated in the context of Salmonella enterica serovar Typhimurium (ST). ST infection of human or murine macrophages reveals that IFN-β selectively restricts the transcriptional responses mediated by both the TLRs and the NOD-like receptors. Specifically, IFN-β potently represses ST-dependent innate induction of IL-1 family cytokines and neutrophil chemokines. This IFN-β-mediated transcriptional repression was independent of the effects of IFN-β on ST-induced macrophage cell death, but significantly dependent on IL-10 regulation. We further evaluated ST pathogenesis in vivo following oral inoculation of mice lacking IFN-β. We show that IFN-β(-/-) mice exhibit greater resistance to oral ST infection and a slower spread of ST to distal sterile sites. This work provides mechanistic insight into the relationship between ST and type I IFN, and demonstrates an additional mechanism by which IFN-β may promote spread of enteric pathogens.

Salt-inducible kinase 3 deficiency exacerbates lipopolysaccharide-induced endotoxin shock accompanied by increased levels of pro-inflammatory molecules in mice

Macrophages play important roles in the innate immune system during infection and systemic inflammation. When bacterial lipopolysaccharide (LPS) binds to Toll-like receptor 4 on macrophages, several signalling cascades co-operatively up-regulate gene expression of inflammatory molecules. The present study aimed to examine whether salt-inducible kinase [SIK, a member of the AMP-activated protein kinase (AMPK) family] could contribute to the regulation of immune signal not only in cultured macrophages, but also in vivo. LPS up-regulated SIK3 expression in murine RAW264.7 macrophages and exogenously over-expressed SIK3 negatively regulated the expression of inflammatory molecules [interleukin-6 (IL-6), nitric oxide (NO) and IL-12p40] in RAW264.7 macrophages. Conversely, these inflammatory molecule levels were up-regulated in SIK3-deficient thioglycollate-elicited peritoneal macrophages (TEPM), despite no impairment of the classical signalling cascades. Forced expression of SIK3 in SIK3-deficient TEPM suppressed the levels of the above-mentioned inflammatory molecules. LPS injection (10 mg/kg) led to the death of all SIK3-knockout (KO) mice within 48 hr after treatment, whereas only one mouse died in the SIK1-KO (n = 8), SIK2-KO (n = 9) and wild-type (n = 8 or 9) groups. In addition, SIK3-KO bone marrow transplantation increased LPS sensitivity of the recipient wild-type mice, which was accompanied by an increased level of circulating IL-6. These results suggest that SIK3 is a unique negative regulator that suppresses inflammatory molecule gene expression in LPS-stimulated macrophages.

Interferon-β Mediates Signaling Pathways Uniquely Regulated in Hepatic Stellate Cells and Attenuates the Progression of Hepatic Fibrosis in a Dietary Mouse Model

The results of clinical and experimental studies suggest that type I interferons (IFNs) may have direct antifibrotic activity in addition to their antiviral properties. However, the mechanisms are still unclear; in particular, little is known about the antifibrotic activity of IFN-β and how its activity is distinct from that of IFN-α. Using DNA microarrays, we demonstrated that gene expression in TWNT-4 cells, an activated human hepatic stellate cell line, was remarkably altered by IFN-β more than by IFN-α. Integrated pathway enrichment analyses revealed that a variety of IFN-β-mediated signaling pathways are uniquely regulated in TWNT-4 cells, including those related to cell cycle and Toll-like receptor 4 (TLR4) signaling. To investigate the antifibrotic activity of IFN-β and the involvement of TLR4 signaling in vivo, we used mice fed a choline-deficient l-amino acid-defined diet as a model of nonalcoholic steatohepatitis-related hepatic fibrosis. In this model, the administration of IFN-β significantly attenuated augmentation of the area of liver fibrosis, with accompanying transcriptional downregulation of the TLR4 adaptor molecule MyD88. Our results provide important clues for understanding the mechanisms of the preferential antifibrotic activity of IFN-β and suggest that IFN-β itself, as well as being a modulator of its unique signaling pathway, may be a potential treatment for patients with hepatic fibrosis in a pathogenesis-independent manner.

Interferons and viruses: an evolutionary arms race of molecular interactions

Over half a century has passed since interferons (IFNs) were discovered and shown to inhibit virus infection in cultured cells. Since then, researchers have steadily brought to light the molecular details of IFN signaling, catalogued their pleiotropic effects on cells, and harnessed their therapeutic potential for a variety of maladies. While advances have been plentiful, several fundamental questions have yet to be answered and much complexity remains to be unraveled. We explore the current knowledge surrounding four main questions: are type I IFN subtypes differentially produced in response to distinct pathogens? How are IFN subtypes distinguished by cells? What are the mechanisms and consequences of viral antagonism? Lastly, how can the IFN response be harnessed to improve vaccine efficacy?

A dual cis-regulatory code links IRF8 to constitutive and inducible gene expression in macrophages

The transcription factor IRF8 controls both developmental and inflammatory stimulus-inducible genes in macrophages. Mancino et al. found that IRF8 is recruited to distinct sets of DNA consensus sequences before and after lipopolysaccharide (LPS) stimulation. While constitutively expressed IRF8-dependent genes contained only sites mediating basal IRF8/PU.1 recruitment, inducible IRF8-dependent genes contained variable combinations of constitutive and inducible sites.

The transcription factor (TF) interferon regulatory factor 8 (IRF8) controls both developmental and inflammatory stimulus-inducible genes in macrophages, but the mechanisms underlying these two different functions are largely unknown. One possibility is that these different roles are linked to the ability of IRF8 to bind alternative DNA sequences. We found that IRF8 is recruited to distinct sets of DNA consensus sequences before and after lipopolysaccharide (LPS) stimulation. In resting cells, IRF8 was mainly bound to composite sites together with the master regulator of myeloid development PU.1. Basal IRF8–PU.1 binding maintained the expression of a broad panel of genes essential for macrophage functions (such as microbial recognition and response to purines) and contributed to basal expression of many LPS-inducible genes. After LPS stimulation, increased expression of IRF8, other IRFs, and AP-1 family TFs enabled IRF8 binding to thousands of additional regions containing low-affinity multimerized IRF sites and composite IRF–AP-1 sites, which were not premarked by PU.1 and did not contribute to the basal IRF8 cistrome. While constitutively expressed IRF8-dependent genes contained only sites mediating basal IRF8/PU.1 recruitment, inducible IRF8-dependent genes contained variable combinations of constitutive and inducible sites. Overall, these data show at the genome scale how the same TF can be linked to constitutive and inducible gene regulation via distinct combinations of alternative DNA-binding sites.

Innate immune pattern recognition: a cell biological perspective

Receptors of the innate immune system detect conserved determinants of microbial and viral origin. Activation of these receptors initiates signaling events that culminate in an effective immune response. Recently, the view that innate immune signaling events rely on and operate within a complex cellular infrastructure has become an important framework for understanding the regulation of innate immunity. Compartmentalization within this infrastructure provides the cell with the ability to assign spatial information to microbial detection and regulate immune responses. Several cell biological processes play a role in the regulation of innate signaling responses; at the same time, innate signaling can engage cellular processes as a form of defense or to promote immunological memory. In this review, we highlight these aspects of cell biology in pattern-recognition receptor signaling by focusing on signals that originate from the cell surface, from endosomal compartments, and from within the cytosol.

Type I interferon signaling contributes to the bias that Toll-like receptor 4 exhibits for signaling mediated by the adaptor protein TRIF

Signaling by Toll-like receptor 4 (TLR4) is mediated by either of two adaptor proteins: myeloid differentiation marker 88 (MyD88) or Toll-interleukin-1 (IL-1) receptor (TIR) domain-containing adaptor inducing interferon-β (TRIF). Whereas MyD88-mediated signaling leads to proinflammatory responses, TRIF-mediated signaling leads to less toxic immunostimulatory responses that are beneficial in boosting vaccine responses. The hypothesis that monophosphorylated lipid A structures act as TRIF-biased agonists of TLR4 offered a potential mechanism to explain their clinical value as vaccine adjuvants, but studies of TRIF-biased agonists have been contradictory. In experiments with mouse dendritic cells, we found that irrespective of the agonist used, TLR4 functioned as a TRIF-biased signaling system through a mechanism that depended on the autocrine and paracrine effects of type I interferons. The TLR4 agonist synthetic lipid A induced expression of TRIF-dependent genes at lower concentrations than were necessary to induce the expression of genes that depend on MyD88-mediated signaling. Blockade of type I interferon signaling selectively decreased the potency of lipid A (increased the concentration required) in inducing the expression of TRIF-dependent genes, thereby eliminating adaptor bias. These data may explain how high-potency TLR4 agonists can act as clinically useful vaccine adjuvants by selectively activating TRIF-dependent signaling events required for immunostimulation, without or only weakly activating potentially harmful MyD88-dependent inflammatory responses.