Reprogramming of murine macrophages through TLR2 confers viral resistance via TRAF3-mediated, enhanced interferon production

TRAF3/STAT6 axis regulates macrophage polarization and tumor progression

Converting tumor-associated macrophages (TAMs) from the M2 to the M1 phenotype is considered an effective strategy for cancer therapy. TRAF3 is known to regulate NF-κB signaling. However, the role of TRAF3 in TAM polarization has not yet been completely elucidated. Here, we found that ablation of TRAF3 increased M1 markers, iNOS, FGR and SLC4A7, while down-regulated M2 markers, CD206, CD36 and ABCC3, expression levels in macrophages. Moreover, TRAF3 deficiency enhanced LPS-induced M1 and abolished IL-4-induced macrophage polarization. Next, quantitative ubiquitomics assays demonstrated that among the quantitative 7618 ubiquitination modification sites on 2598 proteins, ubiquitination modification of IL-4 responding proteins was the most prominently reduced according to enrichment analysis. STAT6, a key factor of IL-4 responding protein, K450 and K129 residue ubiquitination levels were dramatically decreased in TRAF3-deficient macrophages. Ubiquitination assay and luciferase assay demonstrated that TRAF3 promotes STAT6 ubiquitination and transcriptional activity. Site mutation analysis revealed STAT6 K450 site ubiquitination played a vital role in TRAF3-mediated STAT6 activation. Finally, B16 melanoma mouse model demonstrated that myeloid TRAF3 deficiency suppressed tumor growth and lung metastasis in vivo. Taken together, TRAF3 plays a vital role in M2 polarization via regulating STAT6 K450 ubiquitination in macrophages.

Poxviruses and the immune system: Implications for monkeypox virus

Poxviruses (PXVs) are mostly known for the variola virus, being the cause of smallpox; however, re-emerging PXVs have also shown a great capacity to develop outbreaks of pox-like infections in humans. The situation is alarming; PXV outbreaks have been involving both endemic and non-endemic areas in recent decades. Stopped smallpox vaccination is a reason offered mainly for this changing epidemiology that implies the protective role of immunity in the pathology of PXV infections. The immune system recognizes PXVs and elicits responses, but PXVs can antagonize these responses. Here, we briefly review the immunology of PXV infections, with emphasis on the role of pattern-recognition receptors, macrophages, and natural killer cells in the early response to PXV infections and PXVs’ strategies influencing these responses, as well as taking a glance at other immune cells, which discussion over them mainly occurs in association with PXV immunization rather than PXV infection. Throughout the review, numerous evasion mechanisms are highlighted, which might have implications for designing specific immunotherapies for PXV in the future.

Extracellular fibrinogen-binding protein released by intracellular Staphylococcus aureus suppresses host immunity by targeting TRAF3

Many pathogens secrete effectors to hijack intracellular signaling regulators in host immune cells to promote pathogenesis. However, the pathogenesis of Staphylococcus aureus secretory effectors within host cells is unclear. Here, we report that Staphylococcus aureus secretes extracellular fibrinogen-binding protein (Efb) into the cytoplasm of macrophages to suppress host immunity. Mechanistically, RING finger protein 114, a host E3 ligase, mediates K27-linked ubiquitination of Efb at lysine 71, which facilitates the recruitment of tumor necrosis factor receptor associated factor (TRAF) 3. The binding of Efb to TRAF3 disrupts the formation of the TRAF3/TRAF2/cIAP1 (cellular-inhibitor-of-apoptosis-1) complex, which mediates K48-ubiquitination of TRAF3 to promote degradation, resulting in suppression of the inflammatory signaling cascade. Additionally, the Efb K71R mutant loses the ability to inhibit inflammation and exhibits decreased pathogenicity. Therefore, our findings identify an unrecognized mechanism of Staphylococcus aureus to suppress host defense, which may be a promising target for developing effective anti-Staphylococcus aureus immunomodulators.

Staphylococcus aureus secrete numerous effectors to evade or inhibit the host immune response, yet the mechanism underlying the effectors ability to manipulate the signalling pathways of macrophages remain unclear. Authors utilise in vitro and in vivo models to explore the role of extracellular fibrinogen-binding protein (Efb) in immune response modulation and pathogenicity.

Bifurcation of signalling in human innate immune pathways to NF-kB and IRF family activation

The human innate immune response can be activated through a wide range of stimuli. This multi-faceted system can be triggered by a range of immunostimulants including pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These stimuli drive intracellular signalling pathways that branch off downstream to activate several distinct transcription factors. The two most impactful of which in innate immune outcomes are the NF-κB and the IRF family members. Both transcription factor families play defining roles in driving inflammation as well as the antiviral response. Pathways leading to their simultaneous activation share common upstream components but eventually distinct regulators which directly facilitate their activation. This review will discuss the current state of knowledge about what is known about how these pathways bifurcate to activate NF-κB and IRF family members.

Interferon-β regulates proresolving lipids to promote the resolution of acute airway inflammation

Acute respiratory distress syndrome is characterized by aberrant inflammatory responses, including polymorphonuclear neutrophil granulocyte dysfunction and hyperactive Toll-like receptor signaling. Timely resolution of bacterial infections depends on efficient removal of neutrophils from the inflamed tissue. Here we show that the antiviral cytokine interferon-β is essential for the resolution of neutrophil-driven airway inflammation by countering Toll-like receptor 9–mediated suppression of phagocytosis, neutrophil apoptosis, and uptake by macrophages. We also report that the beneficial effects of interferon-β are, in part, mediated by production of proresolving lipid mediators, such as 15-epi-lipoxin A₄ and resolvin D1, which act through the lipoxin receptor ALX/FPR2. These findings uncover an interferon-β–initiated ALX/FPR2-centered resolution program as a potential target for facilitating the resolution of airway inflammation.

Aberrant immune responses, including hyperresponsiveness to Toll-like receptor (TLR) ligands, underlie acute respiratory distress syndrome (ARDS). Type I interferons confer antiviral activities and could also regulate the inflammatory response, whereas little is known about their actions to resolve aberrant inflammation. Here we report that interferon-β (IFN-β) exerts partially overlapping, but also cooperative actions with aspirin-triggered 15-epi-lipoxin A₄ (15-epi-LXA₄) and 17-epi-resolvin D1 to counter TLR9-generated cues to regulate neutrophil apoptosis and phagocytosis in human neutrophils. In mice, TLR9 activation impairs bacterial clearance, prolongs Escherichia coli–evoked lung injury, and suppresses production of IFN-β and the proresolving lipid mediators 15-epi-LXA₄ and resolvin D1 (RvD1) in the lung. Neutralization of endogenous IFN-β delays pulmonary clearance of E. coli and aggravates mucosal injury. Conversely, treatment of mice with IFN-β accelerates clearance of bacteria, restores neutrophil phagocytosis, promotes neutrophil apoptosis and efferocytosis, and accelerates resolution of airway inflammation with concomitant increases in 15-epi-LXA₄ and RvD1 production in the lungs. Pharmacological blockade of the lipoxin receptor ALX/FPR2 partially prevents IFN-β–mediated resolution. These findings point to a pivotal role of IFN-β in orchestrating timely resolution of neutrophil and TLR9 activation–driven airway inflammation and uncover an IFN-β–initiated resolution program, activation of an ALX/FPR2-centered, proresolving lipids-mediated circuit, for ARDS.

Streptococcus pneumoniae colonization associates with impaired adaptive immune responses against SARS-CoV-2

Background

Although recent epidemiological data suggest that pneumococci may contribute to the risk of SARS-CoV-2 disease, cases of coinfection with Streptococcus pneumoniae in patients with coronavirus disease 2019 (COVID-19) during hospitalization have been reported infrequently. This apparent contradiction may be explained by interactions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and pneumococci in the upper airway, resulting in the escape of SARS-CoV-2 from protective host immune responses.

Methods

Here, we investigated the relationship of these 2 respiratory pathogens in 2 distinct cohorts of health care workers with asymptomatic or mildly symptomatic SARS-CoV-2 infection identified by systematic screening and patients with moderate to severe disease who presented to the hospital. We assessed the effect of coinfection on host antibody, cellular, and inflammatory responses to the virus.

Results

In both cohorts, pneumococcal colonization was associated with diminished antiviral immune responses, which primarily affected mucosal IgA levels among individuals with mild or asymptomatic infection and cellular memory responses in infected patients.

Conclusion

Our findings suggest that S. pneumoniae impair host immunity to SARS-CoV-2 and raise the question of whether pneumococcal carriage also enables immune escape of other respiratory viruses and facilitates reinfection.

Trial registration

ISRCTN89159899 (FASTER study) and ClinicalTrials.gov NCT03502291 (LAIV study).

ACKR2 limits skin fibrosis and hair loss through IFN-β

The resolution of inflammation facilitates proper wound healing and limits tissue repair short of exaggerated fibrotic scarring. The atypical chemokine receptor (ACKR)2/D6 scavenges inflammatory chemokines, while IFN-β is a recently unveiled pro-resolving cytokine. Both effector molecules limit acute inflammatory episodes and promote their resolution in various organs. Here, we found fibrotic skin lesions from ACKR2^-/- mice presented increased epidermal and dermal thickening, atrophy of the subcutaneous adipose tissue, augmented disorientation of collagen deposition, and enhanced deformation and loss of hair follicles compared to WT counterparts. In addition, affected skin sections from ACKR2^-/- mice contained reduced levels of the pro-resolving mediators IFN-β and IL-10, but increased levels of the pro-inflammatory chemokines CCL2 and 3, the pro-fibrotic cytokine TGF-β, and the immune-stimulating cytokine IL-12. Notably, treatment with exogenous IFN-β rescued, at least in part, all the pro-fibrotic outcomes and lesion size in ACKR2^-/- mice and promoted expression of the pro-resolving enzyme 12/15-lipoxygenase (LO) in both ACKR2^-/- and WT mice. Moreover, Ifnb^-/- mice displayed enhanced pro-fibrotic indices upon exposure to bleomycin. These findings suggest ACKR2 is an important mediator in limiting inflammatory skin fibrosis and acts via IFN-β production to promote the resolution of inflammation and minimize tissue scaring.

Macrophage Immune Memory Controls Endometriosis in Mice and Humans

Endometriosis is a frequent, chronic, inflammatory gynecological disease characterized by the presence of ectopic endometrial tissue causing pain and infertility. Macrophages have a central role in lesion establishment and maintenance by driving chronic inflammation and tissue remodeling. Macrophages can be reprogrammed to acquire memory-like characteristics after antigenic challenge to reinforce or inhibit a subsequent immune response, a phenomenon termed "trained immunity." Here, whereas bacille Calmette-Guérin (BCG) training enhances the lesion growth in a mice model of endometriosis, tolerization with repeated low doses of lipopolysaccharide (LPS^low) or adoptive transfer of LPS^low-tolerized macrophages elicits a suppressor effect. LPS^low-tolerized human macrophages mitigate the fibro-inflammatory phenotype of endometriotic cells in an interleukin-10 (IL-10)-dependent manner. A history of severe Gram-negative infection is associated with reduced infertility duration and alleviated symptoms, in contrast to patients with Gram-positive infection history. Thus, the manipulation of innate immune memory may be effective in dampening hyper-inflammatory conditions, opening the way to promising therapeutic approaches.

MicroRNA-1226-3p has a tumor-promoting role in osteosarcoma

Osteosarcoma is a malignant bone tumor that commonly occurs in young individuals. It accounts for 10% of solid tumors in those who are 15–19 years old. MicroRNA (miRNA/miR) dysregulation serves a crucial role in the molecular mechanism of osteosarcoma. The present study reported a novel miRNA (miR-1226-3p) and investigated its function in osteosarcoma. miR-1226-3p mimics and miR-1226-3p antisense oligonucleotides were transfected into human osteosarcoma SaOS-2 cells to alter miR-1226-3 expression, while the hFOB 1.19 cell line was used as the control. The apoptosis rate was analyzed using a dead cell apoptosis kit. TNF receptor-associated factor 3 (TRAF3) protein expression was assayed by western blotting. The results of bioinformatics and clinical specimen analyses revealed that higher expression levels of miR-1226-3p were associated with lower survival rates. Additionally, the results of experiments on cultured cells revealed that miR-1226-3p promoted the proliferation of SaOS-2 cells, while miR-1226-3p inhibition decreased cell proliferation and increased apoptosis. Furthermore, it was revealed that miR-1226-3p targeted TRAF3 in SaOS-2 cells. In conclusion, the present study suggested that miR-1226-3p promoted the proliferation of osteosarcoma cells.

Pneumococcal colonization impairs mucosal immune responses to live attenuated influenza vaccine

Influenza virus infections affect millions of people annually, and current available vaccines provide varying rates of protection. However, the way in which the nasal microbiota, particularly established pneumococcal colonization, shape the response to influenza vaccination is not yet fully understood. In this study, we inoculated healthy adults with live Streptococcuspneumoniae and vaccinated them 3 days later with either tetravalent-inactivated influenza vaccine (TIV) or live attenuated influenza vaccine (LAIV). Vaccine-induced immune responses were assessed in nose, blood, and lung. Nasal pneumococcal colonization had no impact upon TIV-induced antibody responses to influenza, which manifested in all compartments. However, experimentally induced pneumococcal colonization dampened LAIV-mediated mucosal antibody responses, primarily IgA in the nose and IgG in the lung. Pulmonary influenza-specific cellular responses were more apparent in the LAIV group compared with either the TIV or an unvaccinated group. These results indicate that TIV and LAIV elicit differential immunity to adults and that LAIV immunogenicity is diminished by the nasal presence of S. pneumoniae. Therefore, nasopharyngeal pneumococcal colonization may affect LAIV efficacy.

Innate immune responses in RNA viral infection

RNA viruses cause a multitude of human diseases, including several pandemic events in the past century. Upon viral invasion, the innate immune system responds rapidly and plays a key role in activating the adaptive immune system. In the innate immune system, the interactions between pathogen-associated molecular patterns and host pattern recognition receptors activate multiple signaling pathways in immune cells and induce the production of pro-inflammatory cytokines and interferons to elicit antiviral responses. Macrophages, dendritic cells, and natural killer cells are the principal innate immune components that exert antiviral activities. In this review, the current understanding of innate immunity contributing to the restriction of RNA viral infections was briefly summarized. Besides the main role of immune cells in combating viral infection, the intercellular transfer of pathogen and host-derived materials and their epigenetic and metabolic interactions associated with innate immunity was discussed. This knowledge provides an enhanced understanding of the innate immune response to RNA viral infections in general and aids in the preparation for the existing and next emerging viral infections.

Development and Characterization of an Avirulent Leishmania major Strain

Leishmania major causes cutaneous leishmaniasis. An antileishmanial vaccine for humans is unavailable. In this study, we report development of two attenuated L. major strains-5ASKH-HP and LV39-HP-by continuous culture (high passage) of the corresponding virulent strains (low passage). Both avirulent strains showed similar changes in proteome profiles when analyzed by surface-enhanced laser desorption ionization mass spectrometry. Liquid chromatography-mass spectrometry and microarray characterization of 5ASKH strains revealed substantially altered gene and protein expression profiles, respectively. Both virulent and avirulent L. major strains grew comparably in culture, but the avirulent strain survived significantly less in BALB/c-derived peritoneal macrophages. Both attenuated strains failed to infect BALB/c mice and elicited IFN-γ, but not IL-4 and IL-10, responses. 5ASKH-HP parasites failed to induce significant infection even in severely immunocompromised- SCID or inducible NO synthase-, CD40-, or IL-12-deficient mice, indicating attenuation. The avirulent strain induced less IL-10, but higher IL-12, in macrophages. The avirulent strain failed to reduce CD40 relocation to the detergent-resistant membrane domain and to inhibit CD40-induced phosphorylation of the kinases Lyn and protein kinase C-β and MAPKs MKK-3/6 and p38MAPK or to upregulate MEK-1/2 and ERK-1/2 in BALB/c-derived peritoneal macrophages. The virulent and the avirulent strains reciprocally modulated CD40-induced Ras-mediated signaling through PI-3K and Raf-1. Avirulent 5ASKH-primed BALB/c mice were protected against virulent L. major challenge infection. The loss of virulence accompanied by substantially altered proteome profiles and the elicitation of host-protective immune responses indicate plausibly irreversible attenuation of the L. major strain and its potential use as a vaccine strain.

Common innate pathways to autoimmune disease

Until recently, autoimmune disease research has primarily been focused on elucidating the role of the adaptive immune system. In the past decade or so, the role of the innate immune system in the pathogenesis of autoimmunity has increasingly been realized. Recent findings have elucidated paradigm-shifting concepts, for example, the implications of "trained immunity" and a dysbiotic microbiome in the susceptibility of predisposed individuals to clinical autoimmunity. In addition, the application of modern technologies such as the quantum dot (Qdot) system and 'Omics' (e.g., genomics, proteomics, and metabolomics) data-processing tools has proven fruitful in revisiting mechanisms underlying autoimmune pathogenesis and in identifying novel therapeutic targets. This review highlights recent findings discussed at the American Autoimmune Related Disease Association (AARDA) 2019 colloquium. The findings covering autoimmune diseases and autoinflammatory diseases illustrate how new developments in common innate immune pathways can contribute to the better understanding and management of these immune-mediated disorders.

Rhinovirus-Induced SIRT-1 via TLR2 Regulates Subsequent Type I and Type III IFN Responses in Airway Epithelial Cells

IFN responses to viral infection are necessary to establish intrinsic antiviral state, but if unchecked can lead to heightened inflammation. Recently, we showed that TLR2 activation contributes to limitation of rhinovirus (RV)-induced IFN response in the airway epithelial cells. We also demonstrated that compared with normal airway epithelial cells, those from patients with chronic obstructive pulmonary disease (COPD) show higher IFN responses to RV, but the underlying mechanisms are not known. Initially, RV-induced IFN responses depend on dsRNA receptor activation and then are amplified via IFN-stimulated activation of JAK/STAT signaling. In this study, we show that in normal cells, TLR2 limits RV-induced IFN responses by attenuating STAT1 and STAT2 phosphorylation and this was associated with TLR2-dependent SIRT-1 expression. Further, inhibition of SIRT-1 enhanced RV-induced IFN responses, and this was accompanied by increased STAT1/STAT2 phosphorylation, indicating that TLR2 may limit RV-induced IFN responses via SIRT-1. COPD airway epithelial cells showed attenuated IL-8 responses to TLR2 agonist despite expressing TLR2 similar to normal, indicating dysregulation in TLR2 signaling pathway. Unlike normal, COPD cells failed to show RV-induced TLR2-dependent SIRT-1 expression. Pretreatment with quercetin, which increases SIRT-1 expression, normalized RV-induced IFN levels in COPD airway epithelial cells. Inhibition of SIRT-1 in quercetin-pretreated COPD cells abolished the normalizing effects of quercetin on RV-induced IFN expression in these cells, confirming that quercetin exerts its effect via SIRT-1. In summary, we show that TLR2 is required for limiting RV-induced IFNs, and this pathway is dysregulated in COPD airway epithelial cells, leading to exaggerated IFN production.

IFN-β is a macrophage-derived effector cytokine facilitating the resolution of bacterial inflammation

The uptake of apoptotic polymorphonuclear cells (PMN) by macrophages is critical for timely resolution of inflammation. High-burden uptake of apoptotic cells is associated with loss of phagocytosis in resolution phase macrophages. Here, using a transcriptomic analysis of macrophage subsets, we show that non-phagocytic resolution phase macrophages express a distinct IFN-β-related gene signature in mice. We also report elevated levels of IFN-β in peritoneal and broncho-alveolar exudates in mice during the resolution of peritonitis and pneumonia, respectively. Elimination of endogenous IFN-β impairs, whereas treatment with exogenous IFN-β enhances, bacterial clearance, PMN apoptosis, efferocytosis and macrophage reprogramming. STAT3 signalling in response to IFN-β promotes apoptosis of human PMNs. Finally, uptake of apoptotic cells promotes loss of phagocytic capacity in macrophages alongside decreased surface expression of efferocytic receptors in vivo. Collectively, these results identify IFN-β produced by resolution phase macrophages as an effector cytokine in resolving bacterial inflammation.

Multiple sclerosis and faecal microbiome transplantation: are you going to eat that?

Gut microbiome interaction goes beyond commensal function as vitamin production or support nutrients digestion. It also interplays with the host immune system and may be related to the development of immune-mediated diseases. Multiple sclerosis patients have dysbiosis compared to healthy individuals. But how this relates to disease development and severity is still uncertain. Dietary change including probiotic mixtures or ketogenic regimen has proven to change microbiome in multiple sclerosis (MS) subjects to one similar to healthy controls. However, proof of clinical benefits is lacking. We dissert on current knowledge about immune system and gut bacteria interactions. We discuss faecal microbial transplantation as a potential intervention to ameliorate gut dysbiosis in MS as well as the caveats of a clinical trial design.

TRAF3 as a Multifaceted Regulator of B Lymphocyte Survival and Activation

The adaptor protein TNF receptor-associated factor 3 (TRAF3) serves as a powerful negative regulator in multiple aspects of B cell biology. Early in vitro studies in transformed cell lines suggested the potential of TRAF3 to inhibit signaling by its first identified binding receptor, CD40. However, because the canonical TRAF3 binding site on many receptors also mediates binding of other TRAFs, and whole-mouse TRAF3 deficiency is neonatally lethal, an accurate understanding of TRAF3's specific functions was delayed until conditional TRAF3-deficient mice were produced. Studies of B cell-specific TRAF3-deficient mice, complemented by investigations in normal and malignant mouse and human B cells, reveal that TRAF3 has powerful regulatory roles that are unique to this TRAF, as well as functions context-specific to the B cell. This review summarizes the current state of knowledge of these roles and functions. These include inhibition of signaling by plasma membrane receptors, negative regulation of intracellular receptors, and restraint of cytoplasmic NF- κB pathways. TRAF3 is also now known to function as a resident nuclear protein, and to impact B cell metabolism. Through these and additional mechanisms TRAF3 exerts powerful restraint upon B cell survival and activation. It is thus perhaps not surprising that TRAF3 has been revealed as an important tumor suppressor in B cells. The many and varied functions of TRAF3 in B cells, and new directions to pursue in future studies, are summarized and discussed here.

Differential outcomes of TLR2 engagement in inflammation-induced preterm birth

Preterm birth (PTB) is the leading cause of neonatal mortality worldwide. Infection and inflammation are considered main causes of PTB. Among multiple pathogens, Gram‐positive bacteria are commonly linked with induction of PTB. Although activation of innate immune responses, via TLR2 engagement, by Gram‐positive bacteria is a likely cause, whether induction of PTB depends on the potency of specific microbial components to induce Toll‐like receptor (TLR)2‐driven inflammation has not been elucidated. Here, we show that TLR2 activation by synthetic lipopeptides, Pam2Cys, and Pam3Cys specifically, variably influenced inflammation and subsequent induction of PTB. Pam2Cys challenge, compared to Pam3Cys, induced PTB and promoted significantly higher expression of inflammatory cytokines, specifically IL‐6 and IFN‐β, both in vivo and in vitro. Notably, antibody‐mediated neutralization of IL‐6 or genetic deletion of type I IFN receptor (IFNAR) was sufficient to protect from Pam2Cys‐driven PTB and to temper excessive proinflammatory cytokine production. Conversely, IFN‐β or IL‐6 was not sufficient to promote induction of PTB by Pam3Cys. In summary, our data implies a divergent function of TLR2‐activating lipopeptides in the magnitude and type of ligand‐driven inflammatory vigor in induction of PTB.

Activating Peripheral Innate Immunity Enables Safe and Effective Oncolytic Virotherapy in the Brain

The oncolytic mutant vesicular stomatitis virus VSVΔ51 achieves robust efficacy in multiple extracranial tumor models. Yet for malignancies of the brain, direct intratumoral infusion of VSVΔ51 causes lethal virus-induced neuropathology. Here, we have developed a novel therapeutic regime that uses peripheral immunization with a single sub-lethal dose of VSVΔ51 to establish an acute anti-viral state that enables the safe intracranial (IC) infusion of an otherwise lethal dose of VSVΔ51 within just 6 hr. Although type I interferons alone appeared insufficient to explain this protective phenotype, serum isolated at early time points from primed animals conferred protection against an IC dose of virus. Adaptive immune populations had minimal contributions. Finally, the therapeutic utility of this novel strategy was demonstrated by peripherally priming and intracranially treating mice bearing aggressive CT2A syngeneic astrocytomas with VSVΔ51. Approximately 25% of animals achieved complete regression of established tumors, with no signs of virus-induced neurological impairment. This approach may harness an early warning system in the brain that has evolved to protect the host against otherwise lethal neurotropic viral infections. We have exploited this protective mechanism to safely and efficaciously treat brain tumors with an otherwise neurotoxic virus, potentially widening the available treatment options for oncolytic virotherapy in the brain.

The θ-defensin retrocyclin 101 inhibits TLR4- and TLR2-dependent signaling and protects mice against influenza infection

A member of the θ‐defensin family protects mice during infection with influenza, suggesting a new strategy for viral therapy in humans.

Despite widespread use of annual influenza vaccines, seasonal influenza‐associated deaths number in the thousands each year, in part because of exacerbating bacterial superinfections. Therefore, discovering additional therapeutic options would be a valuable aid to public health. Recently, TLR4 inhibition has emerged as a possible mechanism for protection against influenza‐associated lethality and acute lung injury. Based on recent data showing that rhesus macaque θ‐defensins could inhibit TLR4‐dependent gene expression, we tested the hypothesis that a novel θ‐defensin, retrocyclin (RC)‐101, could disrupt TLR4‐dependent signaling and protect against viral infection. In this study, RC‐101, a variant of the humanized θ‐defensin RC‐1, blocked TLR4‐mediated gene expression in mouse and human macrophages in response to LPS, targeting both MyD88‐ and TRIF‐dependent pathways. In a cell‐free assay, RC‐101 neutralized the biologic activity of LPS at doses ranging from 0.5 to 50 EU/ml, consistent with data showing that RC‐101 binds biotinylated LPS. The action of RC‐101 was not limited to the TLR4 pathway because RC‐101 treatment of macrophages also inhibited gene expression in response to a TLR2 agonist, Pam3CSK4, but failed to bind that biotinylated agonist. Mouse macrophages infected in vitro with mouse‐adapted A/PR/8/34 influenza A virus (PR8) also produced lower levels of proinflammatory cytokine gene products in a TLR4‐independent fashion when treated with RC‐101. Finally, RC‐101 decreased both the lethality and clinical severity associated with PR8 infection in mice. Cumulatively, our data demonstrate that RC‐101 exhibits therapeutic potential for the mitigation of influenza‐related morbidity and mortality, potentially acting through TLR‐dependent and TLR‐independent mechanisms.

The p90 ribosomal S6 kinase-UBR5 pathway controls Toll-like receptor signaling via miRNA-induced translational inhibition of tumor necrosis factor receptor-associated factor 3

MicroRNAs (miRNAs) are small, noncoding RNAs that post-transcriptionally regulate gene expression. For example, miRNAs repress gene expression by recruiting the miRNA-induced silencing complex (miRISC), a ribonucleoprotein complex that contains miRNA-engaged Argonaute (Ago) and the scaffold protein GW182. Recently, ubiquitin-protein ligase E3 component N-recognin 5 (UBR5) has been identified as a component of miRISC. UBR5 directly interacts with GW182 proteins and participates in miRNA silencing by recruiting downstream effectors, such as the translation regulator DEAD-box helicase 6 (DDX6) and transducer of ERBB2,1/2,2 (Tob1/2), to the Ago-GW182 complex. However, the regulation of miRISC-associated UBR5 remains largely elusive. In the present study, we showed that UBR5 down-regulates the levels of TNF receptor-associated factor 3 (TRAF3), a key component of Toll-like receptor signaling, via the miRNA pathway. We further demonstrated that p90 ribosomal S6 kinase (p90RSK) is an upstream regulator of UBR5. p90RSK phosphorylates UBR5 at Thr⁶³⁷, Ser¹²²⁷, and Ser²⁴⁸³, and this phosphorylation is required for the translational repression of TRAF3 mRNA. Phosphorylated UBR5 co-localized with GW182 and Ago2 in cytoplasmic speckles, which implies that miRISC is affected by phospho-UBR5. Collectively, these results indicated that the p90RSK-UBR5 pathway stimulates miRNA-mediated translational repression of TRAF3. Our work has added another layer to the regulation of miRISC.

Breaking down the gut microbiome composition in multiple sclerosis

BACKGROUND

The gut microbiome, which consists of a highly diverse ecologic community of micro-organisms, has increasingly been studied regarding its role in multiple sclerosis (MS) immunopathogenesis. This review critically examines the literature investigating the gut microbiome in MS.

METHODS

A comprehensive search was performed of PubMed databases and ECTRIMS meeting abstracts for literature relating to the gut microbiome in MS. Controlled studies examining the gut microbiome in patients with MS were included for review.

RESULTS

Identified studies were predominantly case-control in their design and consistently found differences in the gut microbiome of MS patients compared to controls. We examine plausible mechanistic links between these differences and MS immunopathogenesis, and discuss the therapeutic implications of these findings.

CONCLUSIONS

Review of the available literature reveals potential immunopathogenic links between the gut microbiome and MS, identifies avenues for therapeutic advancement, and emphasizes the need for further systematic study in this emerging field.

Single Cell Bottlenecks in the Pathogenesis of Streptococcus pneumoniae

Herein, we studied a virulent isolate of the leading bacterial pathogen Streptococcus pneumoniae in an infant mouse model of colonization, disease and transmission, both with and without influenza A (IAV) co-infection. To identify vulnerable points in the multiple steps involved in pneumococcal pathogenesis, this model was utilized for a comprehensive analysis of population bottlenecks. Our findings reveal that in the setting of IAV co-infection the organism must pass through single cell bottlenecks during bloodstream invasion from the nasopharynx within the host and in transmission between hosts. Passage through these bottlenecks was not associated with genetic adaptation by the pathogen. The bottleneck in transmission occurred between bacterial exit from one host and establishment in another explaining why the number of shed organisms in secretions is critical to overcoming it. These observations demonstrate how viral infection, and TLR-dependent innate immune responses it stimulates and that are required to control it, drive bacterial contagion.

Many discrete steps are involved in the progression of infectious diseases. Bottlenecks represent key points where the population size/genetic diversity is at a minimum and the pathogen is most vulnerable to intervention strategies. Our study used an infant mouse model for a comprehensive analysis of bottlenecks in infection by the major pathogen Streptococcus pneumoniae. In our model, we also considered influenza A virus, a clinically important and common co-infection. The main findings reveal i) a single cell bottleneck during host-to-host transmission and ii) the bottleneck in transmission occurs during events between bacterial exit from one host and establishment in another host. We manipulated innate immune responses involved in viral control and inflammation to show that viral co-infection allows the bottleneck in transmission to be overcome by increasing bacterial exit. Finally, we demonstrate that a specific host response stimulated by influenza A is sufficient to recapitulate effects of viral co-infection. Thus, our study identifies key vulnerable stages during S. pneumoniae infection and provides mechanistic understanding for how viral infection promotes bacterial contagion.

The Prostaglandin E2-EP3 Receptor Axis Regulates Anaplasma phagocytophilum-Mediated NLRC4 Inflammasome Activation

Rickettsial agents are sensed by pattern recognition receptors but lack pathogen-associated molecular patterns commonly observed in facultative intracellular bacteria. Due to these molecular features, the order Rickettsiales can be used to uncover broader principles of bacterial immunity. Here, we used the bacterium Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis, to reveal a novel microbial surveillance system. Mechanistically, we discovered that upon A. phagocytophilum infection, cytosolic phospholipase A2 cleaves arachidonic acid from phospholipids, which is converted to the eicosanoid prostaglandin E2 (PGE2) via cyclooxygenase 2 (COX2) and the membrane associated prostaglandin E synthase-1 (mPGES-1). PGE2-EP3 receptor signaling leads to activation of the NLRC4 inflammasome and secretion of interleukin (IL)-1β and IL-18. Importantly, the receptor-interacting serine/threonine-protein kinase 2 (RIPK2) was identified as a major regulator of the immune response against A. phagocytophilum. Accordingly, mice lacking COX2 were more susceptible to A. phagocytophilum, had a defect in IL-18 secretion and exhibited splenomegaly and damage to the splenic architecture. Remarkably, Salmonella-induced NLRC4 inflammasome activation was not affected by either chemical inhibition or genetic ablation of genes associated with PGE2 biosynthesis and signaling. This divergence in immune circuitry was due to reduced levels of the PGE2-EP3 receptor during Salmonella infection when compared to A. phagocytophilum. Collectively, we reveal the existence of a functionally distinct NLRC4 inflammasome illustrated by the rickettsial agent A. phagocytophilum.

TRAF3, ubiquitination, and B-lymphocyte regulation

The signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is both modified by and contributes to several types of ubiquitination events. TRAF3 plays a variety of context-dependent regulatory roles in all types of immune cells. In B lymphocytes, TRAF3 contributes to regulation of signaling by members of both the TNFR superfamily and innate immune receptors. TRAF3 also plays a unique cell type-specific and critical role in the restraint of B-cell homeostatic survival, a role with important implications for both B-cell differentiation and the pathogenesis of B-cell malignancies. This review focuses upon the relationship between ubiquitin and TRAF3, and how this contributes to multiple functions of TRAF3 in the regulation of signal transduction, transcriptional activation, and effector functions of B lymphocytes.

TRAF3 as a powerful and multitalented regulator of lymphocyte functions

This review summarizes the current state of knowledge regarding the roles of the signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 in regulating the functions of B and T lymphocytes. In B lymphocytes, TNFR-associated factor 3 inhibits signaling by TNFR superfamily receptors, Toll-like receptors, and interleukin-6R. In contrast, signaling to B cells by the virally encoded oncogenic protein latent membrane protein 1 is promoted by TNFR-associated factor 3. An important B cell-specific role for TNFR-associated factor 3 is the inhibition of homeostatic survival, directly relevant to the common occurrence of TNFR-associated factor 3 mutations in human B cell malignancies. TNFR-associated factor 3 was recently found to be a resident nuclear protein in B cells, where it interacts with and inhibits gene expression mediated by the cAMP response element-binding protein transcription complex, including expression of the prosurvival protein myeloid leukemia cell differentiation protein 1. In T lymphocytes, TNFR-associated factor 3 is required for normal signaling by the T cell antigen receptor, while inhibiting signaling by the interleukin-2 receptor. Cytoplasmic TNFR -associated factor 3 restrains nuclear factor-κB2 activation in both T and B cells. Clinical implications and future directions for the study of this context-dependent signaling regulator are discussed.

TRAF3: a novel tumor suppressor gene in macrophages

Tumor necrosis factor receptor-associated factor 3 (TRAF3), a member of the TRAF family of cytoplasmic adaptor proteins with E3 ligase activity, is ubiquitously expressed in various cell types of the immune system. It is shared for signaling by a variety of adaptive and innate immune receptors as well as cytokine receptors. Previous studies examining conditional TRAF3-deficient mouse models that have the Traf3 gene specifically deleted in B lymphocytes or T lymphocytes have revealed the diverse and critical in vivo functions of TRAF3 in adaptive immunity. Although in vitro evidence points to a pivotal and indispensable role for TRAF3 in type I interferon production induced by pattern recognition receptors in macrophages and dendritic cells, the in vivo functions of TRAF3 in the innate immune system had long remained unclear. Three laboratories have recently addressed this gap in knowledge by investigating myeloid cell-specific TRAF3-deficient (genotype: TRAF3^flox/floxLysM^+/Cre) mice. The new evidence together demonstrates that specific ablation of TRAF3 in myeloid cells leads to inflammatory diseases, altered progression of diabetes, and spontaneous development of different types of tumors and infections in mice. These new findings indicate that TRAF3 acts as an anti-inflammatory factor and is required for optimal innate immunity in myeloid cells. Strikingly, the new evidence also identifies TRAF3 as a novel tumor suppressor gene in macrophages and other myeloid cells. In this review, we discuss and summarize the new findings and current knowledge about the multi-faceted regulatory roles and complex signaling mechanisms of myeloid cell TRAF3 in inflammation, innate immunity, and tumor development.

TLR and RLR Signaling Are Reprogrammed in Opposite Directions after Detection of Viral Infection

Innate immune recognition of RNA is key for the initiation of immunity in response to viral infection. Although the factors controlling the detection of viral RNA by innate immune receptors in host cells are increasingly well understood, little is known about the dynamic changes in signaling after the initial triggering of these receptors. In this study, we report that preconditioning with the synthetic dsRNA polyinosinic-polycytidylic acid [poly(I:C)], a mimetic of viral RNA, rapidly reprograms murine APCs by simultaneously augmenting sensitivity of endosomal TLRs and inhibiting activation of RIG-I-like receptors (RLRs) in an IFN-β-dependent manner. These changes in receptor sensitivity were also seen in vivo after treatment of mice with poly(I:C). Mechanistically, the increased sensitivity of the TLR pathway was associated with elevated MAPK and NF-κB activity. The RLR response was inhibited downstream of TANK-binding kinase-1, resulting in decreased IFN regulatory factor 3 phosphorylation. Reprogramming of pattern-recognition receptor signaling also occurred after viral infection, because infection of host cells with Sendai virus or their exposure to supernatant from virus-infected cells induced the same changes in TLR and RLR sensitivity as poly(I:C). Thus, innate recognition of viral infection critically modifies responses to pattern-recognition receptor stimulation. These dynamic adaptations to infection may reinforce antiviral immunity and at the same time serve to limit pathological inflammation.

Mapping the pulmonary environment of animals protected from virulent H1N1 influenza infection using the TLR-2 agonist Pam₂Cys

We have previously shown that intranasal administration of the Toll-like receptor-2 agonist, S-(2,3-bis(palmitoyloxy)propyl) cysteine (Pam2Cys), provides immediate and antigen independent protection against challenge with influenza virus. Here we characterize the cellular pulmonary environments of mice which had either been treated with Pam2Cys or placebo and then challenged with influenza virus. We show that Pam2Cys treatment results in the influx of innate immune cells into the lungs and that depletion of phagocytic cells from this influx using clodronate-loaded liposomes caused a reduction in the number of interstitial macrophages and monocytes. This resulted in abolition of the protective effect indicating the importance of this cellular subset in Pam2Cys-mediated protection.

TLR2 and TLR4 in autoimmune diseases: a comprehensive review

Autoimmune diseases are immune disorders characterized by T cell hyperactivity and B cell overstimulation leading to overproduction of autoantibodies. Although the pathogenesis of various autoimmune diseases remains to be elucidated, environmental factors have been thought to contribute to the initiation and maintenance of auto-respond inflammation. Toll-like receptors (TLRs) are pattern recognition receptors belonging to innate immunity that recognize and defend invading microorganisms. Besides these exogenous pathogen-associated molecular patterns, TLRs can also bind with damage-associated molecular patterns produced under strike or by tissue damage or cells apoptosis. It is believed that TLRs build a bridge between innate immunity and autoimmunity. There are five adaptors to TLRs including MyD88, TRIF, TIRAP/MAL, TRAM, and SARM. Upon activation, TLRs recruit specific adaptors to initiate the downstream signaling pathways leading to the production of inflammatory cytokines and chemokines. Under certain circumstances, ligation of TLRs drives to aberrant activation and unrestricted inflammatory responses, thereby contributing to the perpetuation of inflammation in autoimmune diseases. In the past, most studies focused on the intracellular TLRs, such as TLR3, TLR7, and TLR9, but recent studies reveal that cell surface TLRs, especially TLR2 and TLR4, also play an essential role in the development of autoimmune diseases and afford multiple therapeutic targets. In this review, we summarized the biological characteristics, signaling mechanisms of TLR2/4, the negative regulators of TLR2/4 pathway, and the pivotal function of TLR2/4 in the pathogenesis of autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, Sjogren's syndrome, psoriasis, multiple sclerosis, and autoimmune diabetes.

Glycogen synthase kinase 3β ubiquitination by TRAF6 regulates TLR3-mediated pro-inflammatory cytokine production

TRAF6 is critical for the production of inflammatory cytokines in various TLR-mediated signalling pathways. However, it is poorly understood how TRAF6 regulates TLR3 responses. Here we demonstrate that GSK3β interacts with TRAF6 and positively regulates the TLR3-mediated signalling. Suppression of GSK3β expression or its kinase activity drastically reduces the production of inflammatory cytokines and the induction of c-Fos by decreasing ERK and p38 phosphorylation. GSK3β physically associates with TRAF6 in a TLR3 ligand poly I:C-dependent manner. TRAF6 is determined to be a direct E3 ligase for GSK3β, and TRAF6-mediated GSK3β ubiquitination is essential for poly I:C-dependent cytokine production by promoting the TLR3 adaptor protein TRIF-assembled signalling complex.

GSK3β is a molecular hub implicated in regulation of cell metabolism, migration, proliferation and survival. Here the authors show that GSK3β regulates inflammatory cytokine production by promoting the assembly of a signalling platform downstream of TLR3, a sensor of viral infection.

Space and time: New considerations about the relationship between Toll-like receptors (TLRs) and type I interferons (IFNs)

The Toll like receptors (TLRs) and the type I interferons have critical roles to play in innate immunity. In this review we will discuss new developments relating to the important area of TLR/IFN cross regulation.

Macrophage Polarization in Virus-Host Interactions

Macrophage involvement in viral infections and antiviral states is common. However, this involvement has not been well-studied in the paradigm of macrophage polarization, which typically has been categorized by the dichotomy of classical (M1) and alternative (M2) statuses. Recent studies have revealed the complexity of macrophage polarization in response to various cellular mediators and exogenous stimuli by adopting a multipolar view to revisit the differential process of macrophages, especially those re-polarized during viral infections. Here, through examination of viral infections targeting macrophages/monocytic cells, we focus on the direct involvement of macrophage polarization during viral infections. Type I and type III interferons (IFNs) are critical in regulation of viral pathogenesis and host antiviral infection; thus, we propose to incorporate IFN-mediated antiviral states into the framework of macrophage polarization. This view is supported by the multifunctional properties of type I IFNs, which potentially elicit and regulate both M1- and M2-polarization in addition to inducing the antiviral state, and by the discoveries of viral mechanisms to adapt and modulate macrophage polarization. Indeed, several recent studies have demonstrated effective prevention of viral diseases through manipulation of macrophage immune statuses.

Myeloid cell TRAF3 regulates immune responses and inhibits inflammation and tumor development in mice

Myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells, are crucial players in innate immunity and inflammation. These cells constitutively or inducibly express a number of receptors of the TNFR and TLR families, whose signals are transduced by TNFR-associated factor (TRAF) molecules. In vitro studies showed that TRAF3 is required for TLR-induced type I IFN production, but the in vivo function of TRAF3 in myeloid cells remains unknown. In this article, we report the generation and characterization of myeloid cell-specific TRAF3-deficient (M-TRAF3(-/-)) mice, which allowed us to gain insights into the in vivo functions of TRAF3 in myeloid cells. We found that TRAF3 ablation did not affect the maturation or homeostasis of myeloid cells in young adult mice, even though TRAF3-deficient macrophages and neutrophils exhibited constitutive NF-κB2 activation. However, in response to injections with LPS (a bacterial mimic) or polyinosinic-polycytidylic acid (a viral mimic), M-TRAF3(-/-) mice exhibited an altered profile of cytokine production. M-TRAF3(-/-) mice immunized with T cell-independent and -dependent Ags displayed elevated T cell-independent IgG3 and T cell-dependent IgG2b responses. Interestingly, 15- to 22-mo-old M-TRAF3(-/-) mice spontaneously developed chronic inflammation or tumors, often affecting multiple organs. Taken together, our findings indicate that TRAF3 expressed in myeloid cells regulates immune responses in myeloid cells and acts to inhibit inflammation and tumor development in mice.

Comparative functional genomics and the bovine macrophage response to strains of the mycobacterium genus

Mycobacterial infections are major causes of morbidity and mortality in cattle and are also potential zoonotic agents with implications for human health. Despite the implementation of comprehensive animal surveillance programs, many mycobacterial diseases have remained recalcitrant to eradication in several industrialized countries. Two major mycobacterial pathogens of cattle are Mycobacterium bovis and Mycobacterium avium subspecies paratuberculosis (MAP), the causative agents of bovine tuberculosis (BTB) and Johne's disease (JD), respectively. BTB is a chronic, granulomatous disease of the respiratory tract that is spread via aerosol transmission, while JD is a chronic granulomatous disease of the intestines that is transmitted via the fecal-oral route. Although these diseases exhibit differential tissue tropism and distinct complex etiologies, both M. bovis and MAP infect, reside, and replicate in host macrophages - the key host innate immune cell that encounters mycobacterial pathogens after initial exposure and mediates the subsequent immune response. The persistence of M. bovis and MAP in macrophages relies on a diverse series of immunomodulatory mechanisms, including the inhibition of phagosome maturation and apoptosis, generation of cytokine-induced necrosis enabling dissemination of infection through the host, local pathology, and ultimately shedding of the pathogen. Here, we review the bovine macrophage response to infection with M. bovis and MAP. In particular, we describe how recent advances in functional genomics are shedding light on the host macrophage-pathogen interactions that underlie different mycobacterial diseases. To illustrate this, we present new analyses of previously published bovine macrophage transcriptomics data following in vitro infection with virulent M. bovis, the attenuated vaccine strain M. bovis BCG, and MAP, and discuss our findings with respect to the differing etiologies of BTB and JD.

TLR2 signaling decreases transmission of Streptococcus pneumoniae by limiting bacterial shedding in an infant mouse Influenza A co-infection model

While the importance of transmission of pathogens is widely accepted, there is currently little mechanistic understanding of this process. Nasal carriage of Streptococcus pneumoniae (the pneumococcus) is common in humans, especially in early childhood, and is a prerequisite for the development of disease and transmission among hosts. In this study, we adapted an infant mouse model to elucidate host determinants of transmission of S. pneumoniae from inoculated index mice to uninfected contact mice. In the context of co-infection with influenza A virus, the pneumococcus was transmitted among wildtype littermates, with approximately half of the contact mice acquiring colonization. Mice deficient for TLR2 were colonized to a similar density but transmitted S. pneumoniae more efficiently (100% transmission) than wildtype animals and showed decreased expression of interferon α and higher viral titers. The greater viral burden in tlr2-/- mice correlated with heightened inflammation, and was responsible for an increase in bacterial shedding from the mouse nose. The role of TLR2 signaling was confirmed by intranasal treatment of wildtype mice with the agonist Pam3Cys, which decreased inflammation and reduced bacterial shedding and transmission. Taken together, these results suggest that the innate immune response to influenza virus promotes bacterial shedding, allowing the bacteria to transit from host to host. These findings provide insight into the role of host factors in the increased pneumococcal carriage rates seen during flu season and contribute to our overall understanding of pathogen transmission.

Roles for TNF-receptor associated factor 3 (TRAF3) in lymphocyte functions

TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors, located both inside the cell and at the plasma membrane. These include members of the TNF receptor superfamily (TNFR-SF), toll-like receptors (TLR), and cytokine receptors. It has become increasingly evident that the roles and functions of TRAF3 are highly context-dependent. TRAF3 can serve distinct roles for different receptors in the same cell, and also has highly cell-type-dependent functions. This review focuses upon the current state of knowledge regarding how TRAF3 regulates the biology and effector functions of B and T lymphocytes, two major cell types of the adaptive immune response in which TRAF3 has markedly distinct roles.

Bacterial lipodipeptide, Lipid 654, is a microbiome-associated biomarker for multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of unknown etiology. Infectious agents have been suggested to have a role as environmental factors in MS, but this concept remains controversial. Recently, gastrointestinal commensal bacteria have been implicated in the pathogenesis of autoimmune diseases, but mechanisms underlying the relationship of human systemic autoimmunity with the commensal microbiome have yet to be identified. Consistent with the lack of understanding of pathogenic mechanisms and relevant environmental factors in MS, no blood biomarkers have been identified that distinguish MS patients from healthy individuals. We recently identified a unique gastrointestinal and oral bacteria-derived lipodipeptide, Lipid 654, which is produced by commensal bacteria and functions as a human and mouse Toll-like receptor 2 ligand. Using multiple-reaction-monitoring mass spectrometry, a critical approach in targeted lipidomics, we now report that Lipid 654 can be recovered in the serum of healthy individuals. Most interestingly, we find that Lipid 654 is expressed at significantly lower levels in the serum of patients with MS compared with both healthy individuals and patients with Alzheimer's disease. These results thus identify for the first time a potential mechanism relating the gastrointestinal and oral commensal microbiome to a human systemic autoimmune disease. In addition, these results also identify a potential etiologic environmental factor and novel clinically relevant serum biomarker for MS.