Crosstalk between type I and II interferons in regulation of myeloid cell responses during bacterial infection

Early cellular mechanisms of type I interferon-driven susceptibility to tuberculosis

Mycobacterium tuberculosis (Mtb) causes 1.6 million deaths annually. Active tuberculosis correlates with a neutrophil-driven type I interferon (IFN) signature, but the cellular mechanisms underlying tuberculosis pathogenesis remain poorly understood. We found that interstitial macrophages (IMs) and plasmacytoid dendritic cells (pDCs) are dominant producers of type I IFN during Mtb infection in mice and non-human primates, and pDCs localize near human Mtb granulomas. Depletion of pDCs reduces Mtb burdens, implicating pDCs in tuberculosis pathogenesis. During IFN-driven disease, we observe abundant DNA-containing neutrophil extracellular traps (NETs) described to activate pDCs. Cell-type-specific disruption of the type I IFN receptor suggests that IFNs act on IMs to inhibit Mtb control. Single-cell RNA sequencing (scRNA-seq) indicates that type I IFN-responsive cells are defective in their response to IFNγ, a cytokine critical for Mtb control. We propose that pDC-derived type I IFNs act on IMs to permit bacterial replication, driving further neutrophil recruitment and active tuberculosis disease.

Deadly interactions: Synergistic manipulations of concurrent pathogen infections potentially enabling future pandemics

Certain mono-infections of influenza viruses and novel coronaviruses, including severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) are significant threats to human health. Concurrent infections by influenza viruses and coronaviruses increases their danger. Influenza viruses have eight manipulations capable of assisting SARS-CoV-2 and other coronaviruses, and several of these manipulations, which are not specific to viruses, can also directly or indirectly boost dangerous secondary bacterial pneumonias. The influenza virus manipulations include: inhibiting transcription factors and cytokine expression; impairing defensive protein expression; increasing RNA viral replication; inhibiting defenses by manipulating cellular sensors and signaling pathways; inhibiting defenses by secreting exosomes; stimulating cholesterol production to increase synthesized virion infectivities; increasing cellular autophagy to assist viral replication; and stimulating glucocorticoid synthesis to suppress innate and adaptive immune defenses by inhibiting cytokine, chemokine, and adhesion molecule production. Teaser: Rapidly spreading multidrug-resistant respiratory bacteria, combined with influenza virus's far-reaching cellular defense manipulations benefiting evolving SARS-CoV-2 or other coronaviruses and/or respiratory bacteria, can enable more severe pandemics or co-pandemics.

The Role of Cytokines in Cholesterol Accumulation in Cells and Atherosclerosis Progression

Atherosclerosis is the most common cardiovascular disease and is the number one cause of death worldwide. Today, atherosclerosis is a multifactorial chronic inflammatory disease with an autoimmune component, accompanied by the accumulation of cholesterol in the vessel wall and the formation of atherosclerotic plaques, endothelial dysfunction, and chronic inflammation. In the process of accumulation of atherogenic lipids, cells of the immune system, such as monocytes, macrophages, dendritic cells, etc., play an important role, producing and/or activating the production of various cytokines—interferons, interleukins, chemokines. In this review, we have tried to summarize the most important cytokines involved in the processes of atherogenesis.

SRSF1 acts as an IFN-I-regulated cellular dependency factor decisively affecting HIV-1 post-integration steps

Efficient HIV-1 replication depends on balanced levels of host cell components including cellular splicing factors as the family of serine/arginine-rich splicing factors (SRSF, 1-10). Type I interferons (IFN-I) play a crucial role in the innate immunity against HIV-1 by inducing the expression of IFN-stimulated genes (ISGs) including potent host restriction factors. The less well known IFN-repressed genes (IRepGs) might additionally affect viral replication by downregulating host dependency factors that are essential for the viral life cycle; however, so far, the knowledge about IRepGs involved in HIV-1 infection is very limited. In this work, we could demonstrate that HIV-1 infection and the associated ISG induction correlated with low SRSF1 levels in intestinal lamina propria mononuclear cells (LPMCs) and peripheral blood mononuclear cells (PBMCs) during acute and chronic HIV-1 infection. In HIV-1-susceptible cell lines as well as primary monocyte-derived macrophages (MDMs), expression levels of SRSF1 were transiently repressed upon treatment with specific IFNα subtypes in vitro. Mechanically, 4sU labeling of newly transcribed mRNAs revealed that IFN-mediated SRSF1 repression is regulated on early RNA level. SRSF1 knockdown led to an increase in total viral RNA levels, but the relative proportion of the HIV-1 viral infectivity factor (Vif) coding transcripts, which is essential to counteract APOBEC3G-mediated host restriction, was significantly reduced. In the presence of high APOBEC3G levels, however, increased LTR activity upon SRSF1 knockdown facilitated the overall replication, despite decreased vif mRNA levels. In contrast, SRSF1 overexpression significantly impaired HIV-1 post-integration steps including LTR transcription, alternative splice site usage, and virus particle production. Since balanced SRSF1 levels are crucial for efficient viral replication, our data highlight the so far undescribed role of SRSF1 acting as an IFN-modulated cellular dependency factor decisively regulating HIV-1 post-integration steps.

Malaria abrogates O'nyong-nyong virus pathologies by restricting virus infection in nonimmune cells

O'nyongnyong virus (ONNV) is a re-emerging alphavirus previously known to be transmitted by main malaria vectors, thus suggesting the possibility of coinfections with arboviruses in co-endemic areas. However, the pathological outcomes of such infections remain unknown. Using murine coinfection models, we demonstrated that a preexisting blood-stage Plasmodium infection suppresses ONNV-induced pathologies. We further showed that suppression of viremia and virus dissemination are dependent on Plasmodium-induced IFNγ and are associated with reduced infection of CD45- cells at the site of virus inoculation. We further proved that treatment with IFNγ or plasma samples from Plasmodium vivax-infected patients containing IFNγ are able to restrict ONNV infection in human fibroblast, synoviocyte, skeletal muscle, and endothelial cell lines. Mechanistically, the role of IFNγ in restricting ONNV infection was confirmed in in vitro infection assays through the generation of an IFNγ receptor 1 α chain (IFNγR1)-deficient cell line.

The Unitary Micro-Immunotherapy Medicine Interferon-γ (4 CH) Displays Similar Immunostimulatory and Immunomodulatory Effects than Those of Biologically Active Human Interferon-γ on Various Cell Types

As a cytokine, gamma-interferon (IFN-γ) is considered a key player in the fine-tuned orchestration of immune responses. The extreme cellular sensitivity to cytokines is attested by the fact that very few of these bioactive molecules per cell are enough to trigger cellular functions. These findings can, at least partially, explain how/why homeopathically-prepared cytokines, and especially micro-immunotherapy (MI) medicines, are able to drive cellular responses. We focused our fundamental research on a unitary MI preparation of IFN-γ, specifically employed at 4 CH, manufactured and impregnated onto sucrose-lactose pillules as all other MI medicines. We assessed the IFN-γ concentration in the medium after dilution of the IFN-γ (4 CH)-bearing pillules and we evaluated in vitro drug responses in a wide range of immune cells, and in endothelial cells. Our results showed that IFN-γ (4 CH) stimulated the proliferation, the activation and the phagocytic capabilities of primary immune cells, as well as modulated their cytokine-secretion and immunity-related markers’ expression in a trend that is quite comparable with the well-recognized biological effects induced by IFN-γ. Altogether, these data provide novel and additional evidences on MI medicines, and specifically when active substances are prepared at 4 CH, thus suggesting the need for more investigations.

NF-κB-dependent IRF1 activation programs cDC1 dendritic cells to drive antitumor immunity

Conventional type 1 dendritic cells (cDC1s) are critical for antitumor immunity. They acquire antigens from dying tumor cells and cross-present them to CD8⁺ T cells, promoting the expansion of tumor-specific cytotoxic T cells. However, the signaling pathways that govern the antitumor functions of cDC1s in immunogenic tumors are poorly understood. Using single-cell transcriptomics to examine the molecular pathways regulating intratumoral cDC1 maturation, we found nuclear factor κB (NF-κB) and interferon (IFN) pathways to be highly enriched in a subset of functionally mature cDC1s. We identified an NF-κB-dependent and IFN-γ-regulated gene network in cDC1s, including cytokines and chemokines specialized in the recruitment and activation of cytotoxic T cells. By mapping the trajectory of intratumoral cDC1 maturation, we demonstrated the dynamic reprogramming of tumor-infiltrating cDC1s by NF-κB and IFN signaling pathways. This maturation process was perturbed by specific inactivation of either NF-κB or IFN regulatory factor 1 (IRF1) in cDC1s, resulting in impaired expression of IFN-γ-responsive genes and consequently a failure to efficiently recruit and activate antitumoral CD8⁺ T cells. Last, we demonstrate the relevance of these findings to patients with melanoma, showing that activation of the NF-κB/IRF1 axis in association with cDC1s is linked with improved clinical outcome. The NF-κB/IRF1 axis in cDC1s may therefore represent an important focal point for the development of new diagnostic and therapeutic approaches to improve cancer immunotherapy.

Role of the transcriptional regulator SP140 in resistance to bacterial infections via repression of type I interferons

Type I interferons (IFNs) are essential for anti-viral immunity, but often impair protective immune responses during bacterial infections. An important question is how type I IFNs are strongly induced during viral infections, and yet are appropriately restrained during bacterial infections. The Super susceptibility to tuberculosis 1 (Sst1) locus in mice confers resistance to diverse bacterial infections. Here we provide evidence that Sp140 is a gene encoded within the Sst1 locus that represses type I IFN transcription during bacterial infections. We generated Sp140^–/– mice and found that they are susceptible to infection by Legionella pneumophila and Mycobacterium tuberculosis. Susceptibility of Sp140^–/– mice to bacterial infection was rescued by crosses to mice lacking the type I IFN receptor (Ifnar^–/–). Our results implicate Sp140 as an important negative regulator of type I IFNs that is essential for resistance to bacterial infections.

IFNs Reset the Differential Capacity of Human Monocyte Subsets to Produce IL-12 in Response to Microbial Stimulation

Human primary monocytes are composed of a minor, more mature CD16+(CD14low/neg) population and a major CD16neg(CD14+) subset. The specific functions of CD16+ versus CD16neg monocytes in steady state or inflammation remain poorly understood. In previous work, we found that IL-12 is selectively produced by the CD16+ subset in response to the protozoan pathogen, Toxoplasma gondii In this study, we demonstrated that this differential responsiveness correlates with the presence of an IFN-induced transcriptional signature in CD16+ monocytes already at baseline. Consistent with this observation, we found that in vitro IFN-γ priming overcomes the defect in the IL-12 response of the CD16neg subset. In contrast, pretreatment with IFN-γ had only a minor effect on IL-12p40 secretion by the CD16+ population. Moreover, inhibition of the mTOR pathway also selectively increased the IL-12 response in CD16neg but not in CD16+ monocytes. We further demonstrate that in contrast to IFN-γ, IFN-α fails to promote IL-12 production by the CD16neg subset and blocks the effect of IFN-γ priming. Based on these observations, we propose that the acquisition of IL-12 responsiveness by peripheral blood monocyte subsets depends on extrinsic signals experienced during their developmental progression in vivo. This process can be overridden during inflammation by the opposing regulatory effects of type I and II IFN as well as the mTOR inhibition.

Pathogenic Biohacking: Induction, Modulation and Subversion of Host Transcriptional Responses by Listeria monocytogenes

During infection, the foodborne bacterial pathogen Listeria monocytogenes dynamically influences the gene expression profile of host cells. Infection-induced transcriptional changes are a typical feature of the host-response to bacteria and contribute to the activation of protective genes such as inflammatory cytokines. However, by using specialized virulence factors, bacterial pathogens can target signaling pathways, transcription factors, and epigenetic mechanisms to alter host gene expression, thereby reprogramming the response to infection. Therefore, the transcriptional profile that is established in the host is delicately balanced between antibacterial responses and pathogenesis, where any change in host gene expression might significantly influence the outcome of infection. In this review, we discuss the known transcriptional and epigenetic processes that are engaged during Listeria monocytogenes infection, the virulence factors that can remodel them, and the impact these processes have on the outcome of infection.

Function and Modulation of Type I Interferons during Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory infections in infants and young children, accounting for an estimated 3 million hospitalizations annually worldwide. Despite the major health burden, there is currently no licensed RSV vaccine. RSV is recognized by a range of cellular receptors including both toll-like receptors (TLR) and retinoic acid-inducible gene-I-like receptors (RIG-I). This interaction initiates signaling through mitochondrial antiviral signaling (MAVS) and interferon regulatory factor (IRF) proteins, resulting in the induction of type I interferons (IFN). Early viral control is mediated by either IFN-α or IFN-β signaling through the IFN receptor (IFNAR), inducing the production of antiviral interferon-stimulating genes (ISGs). Type I IFNs also initiate the early production of proinflammatory cytokines including interleukin 6 (IL-6), tumor necrosis factor (TNF), and IFN-γ. Type I IFN levels correlate with age, and inadequate production may be a critical factor in facilitating the increased RSV disease severity observed in infants. Here, we review the current literature on the function of type I IFNs in RSV pathogenesis, as well as their involvement in the differential immune responses observed in infants and adults.

Myeloid cell responsiveness to interferon-gamma is sufficient for initial resistance to Listeria monocytogenes

The type II interferon (IFNγ) promotes resistance to intracellular pathogens. Most immune and somatic cells also express the IFNγ receptor (IFNGR) and respond to IFNγ. While myeloid cell have been implicated as important targets of IFNγ, it remains unknown if IFNγ signaling to myeloid cell types suffices for resistance to infection. Here, we addressed this question by generating mice in which IFNGR1 is selectively expressed by myeloid cells. These “MSGR1” (myeloid selective IFNGR1) mice express an epitope-tagged Ifngr1 transgene (fGR1) from the myeloid-specific c-fms promoter in a background lacking endogenous Ifngr1. IFNGR staining was selectively observed on myeloid cells in the MSGR1 mice and correlated with responsiveness of these cells to IFNγ. During systemic infection by the bacterium Listeria monocytogenes, activation marker staining was comparable on monocytes from MSGR1 and control B6 mice. Bacterial burdens and survival were also equivalent in MSGR1 and wildtype B6 animals at a timepoint when B6.Ifngr1^−/− mice began to succumb. These data confirm that activation of inflammatory monocytes and neutrophils is a key mechanism by which IFNγ promotes innate anti-bacterial immunity and suggest that IFNγ targeting of myeloid cells is largely sufficient to mediate protection against systemic L. monocytogenes.

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Expression of IFNGR1 is restricted to monocytes and neutrophils in “MSGR1” (myeloid selective IFNGR1) mice.

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Myeloid cells from MSGR1 mice are responsive to IFNγ and show elevated activation compared to cells from B6.Ifngr1^−/− mice.

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MSGR1 myeloid cells respond to Listeria monocytogenes infection and promote early resistance.

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IFNγ stimulation of myeloid cells can thus protect against infection independent of effects on other hematopoietic and non-hematopoietic cell populations.

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Particularly in female mice, IFNγ stimulation of non-myeloid cells may also contribute to improved survival.

Inflammation as a Modulator of Host Susceptibility to Pulmonary Influenza, Pneumococcal, and Co-Infections

Bacterial and viral pathogens are predominant causes of pulmonary infections and complications. Morbidity and mortality from these infections is increased in populations that include the elderly, infants, and individuals with genetic disorders such as Down syndrome. Immune senescence, concurrent infections, and other immune alterations occur in these susceptible populations, but the underlying mechanisms that dictate increased susceptibility to lung infections are not fully defined. Here, we review unique features of the lung as a mucosal epithelial tissue and aspects of inflammatory and immune responses in model pulmonary infections and co-infections by influenza virus and Streptococcus pneumoniae. In these models, lung inflammatory responses are a double-edged sword: recruitment of immune effectors is essential to eliminate bacteria and virus-infected cells, but inflammatory cytokines drive changes in the lung conducive to increased pathogen replication. Excessive accumulation of inflammatory cells also hinders lung function, possibly causing death of the host. Some animal studies have found that targeting host modulators of lung inflammatory responses has therapeutic or prophylactic effects in these infection and co-infection models. However, conflicting results from other studies suggest microbiota, sequence of colonization, or other unappreciated aspects of lung biology also play important roles in the outcome of infections. Regardless, a predisposition to excessive or aberrant inflammatory responses occurs in susceptible human populations. Hence, in appropriate contexts, modulation of inflammatory responses may prove effective for reducing the frequency or severity of pulmonary infections. However, there remain limitations in our understanding of how this might best be achieved—particularly in diverse human populations.

Ligand-induced IFNGR1 down-regulation calibrates myeloid cell IFNγ responsiveness

The type II IFN (IFNγ) enhances antimicrobial activity yet also drives expression of genes that amplify inflammatory responses. Hence, excessive IFNγ stimulation can be pathogenic. Here, we describe a previously unappreciated mechanism whereby IFNγ itself dampens myeloid cell activation. Staining of monocytes from Listeria monocytogenes-infected mice provided evidence of type I IFN-independent reductions in IFNGR1. IFNγ was subsequently found to reduce surface IFNGR1 on cultured murine myeloid cells and human CD14+ peripheral blood mononuclear cells. IFNγ-driven reductions in IFNGR1 were not explained by ligand-induced receptor internalization. Rather, IFNγ reduced macrophage Ifngr1 transcription by altering chromatin structure at putative Ifngr1 enhancer sites. This is a distinct mechanism from that used by type I IFNs. Ligand-induced reductions in IFNGR1 altered myeloid cell sensitivity to IFNγ, blunting activation of STAT1 and 3. Our data, thus, reveal a mechanism by which IFNGR1 abundance and myeloid cell sensitivity to IFNγ can be modulated in the absence of type I IFNs. Multiple mechanisms, thus, exist to calibrate macrophage IFNGR1 abundance, likely permitting the fine tuning of macrophage activation and inflammation.

Role of Type I Interferon (IFN) in the Respiratory Syncytial Virus (RSV) Immune Response and Disease Severity

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in children <2 years of age. Increased morbidity and mortality have been reported in high-risk patients, such as premature infants, patients with cardiac disease, and severely immune compromised patients. Severe disease is associated with the virulence of the virus as well as host factors specifically including the innate immune response. The role of type I interferons (IFNs) in the response to RSV infection is important in regulating the rate of virus clearance and in directing the character of the immune response, which is normally associated with protection and less severe disease. Two RSV non-structural proteins, NS1 and NS2, as well as the envelope G glycoprotein are known to suppress type I IFN production and a robust type I IFN response to RSV does not occur in human infants or neonatal mouse models of RSV infection. Additionally, presence of type I IFNs are associated with mild symptoms in infants and administration of IFN-α prior to infection of neonatal mice with RSV reduces immunopathology. This evidence has driven RSV prophylaxis and therapeutic efforts to consider strategies for enhancing type I IFN production.