Antiviral instruction of bone marrow leukocytes during respiratory viral infections

SARS-CoV-2 infection modifies the transcriptome of the megakaryocytes in the bone marrow

ABSTRACT

Megakaryocytes (MKs), integral to platelet production, predominantly reside in the bone marrow (BM) and undergo regulated fragmentation within sinusoid vessels to release platelets into the bloodstream. Inflammatory states and infections influence MK transcription, potentially affecting platelet functionality. Notably, COVID-19 has been associated with altered platelet transcriptomes. In this study, we investigated the hypothesis that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection could affect the transcriptome of BM MKs. Using spatial transcriptomics to discriminate subpopulations of MKs based on proximity to BM sinusoids, we identified ∼19 000 genes in MKs. Machine learning techniques revealed that the transcriptome of healthy murine BM MKs exhibited minimal differences based on proximity to sinusoid vessels. Furthermore, at peak SARS-CoV-2 viremia, when the disease primarily affected the lungs, MKs were not significantly different from those from healthy mice. Conversely, a significant divergence in the MK transcriptome was observed during systemic inflammation, although SARS-CoV-2 RNA was never detected in the BM, and it was no longer detectable in the lungs. Under these conditions, the MK transcriptional landscape was enriched in pathways associated with histone modifications, MK differentiation, NETosis, and autoimmunity, which could not be explained by cell proximity to sinusoid vessels. Notably, the type I interferon signature and calprotectin (S100A8/A9) were not induced in MKs under any condition. However, inflammatory cytokines induced in the blood and lungs of COVID-19 mice were different from those found in the BM, suggesting a discriminating impact of inflammation on this specific subset of cells. Collectively, our data indicate that a new population of BM MKs may emerge through COVID-19-related pathogenesis.

SuperAgers and centenarians, dynamics of healthy ageing with cognitive resilience

Graceful healthy ageing and extended longevity is the most desired goal for human race. The process of ageing is inevitable and has a profound impact on the gradual deterioration of our physiology and health since it triggers the onset of many chronic conditions like dementia, osteoporosis, diabetes, arthritis, cancer, and cardiovascular disease. However, some people who lived/live more than 100 years called 'Centenarians" and how do they achieve their extended lifespans are not completely understood. Studying these unknown factors of longevity is important not only to establish a longer human lifespan but also to manage and treat people with shortened lifespans suffering from age-related morbidities. Furthermore, older adults who maintain strong cognitive function are referred to as "SuperAgers" and may be resistant to risk factors linked to cognitive decline. Investigating the mechanisms underlying their cognitive resilience may contribute to the development of therapeutic strategies that support the preservation of cognitive function as people age. The key to a long, physically, and cognitively healthy life has been a mystery to scientists for ages. Developments in the medical sciences helps us to a better understanding of human physiological function and greater access to medical care has led us to an increase in life expectancy. Moreover, inheriting favorable genetic traits and adopting a healthy lifestyle play pivotal roles in promoting longer and healthier lives. Engaging in regular physical activity, maintaining a balanced diet, and avoiding harmful habits such as smoking contribute to overall well-being. The synergy between positive lifestyle choices, access to education, socio-economic factors, environmental determinants and genetic supremacy enhances the potential for a longer and healthier life. Our article aims to examine the factors associated with healthy ageing, particularly focusing on cognitive health in centenarians. We will also be discussing different aspects of ageing including genomic instability, metabolic burden, oxidative stress and inflammation, mitochondrial dysfunction, cellular senescence, immunosenescence, and sarcopenia.

Association between bisphosphonate use and COVID-19 related outcomes

Background

Although there are several efficacious vaccines against COVID-19, vaccination rates in many regions around the world remain insufficient to prevent continued high disease burden and emergence of viral variants. Repurposing of existing therapeutics that prevent or mitigate severe COVID-19 could help to address these challenges. The objective of this study was to determine whether prior use of bisphosphonates is associated with reduced incidence and/or severity of COVID-19.

Methods

A retrospective cohort study utilizing payer-complete health insurance claims data from 8,239,790 patients with continuous medical and prescription insurance January 1, 2019 to June 30, 2020 was performed. The primary exposure of interest was use of any bisphosphonate from January 1, 2019 to February 29, 2020. Bisphosphonate users were identified as patients having at least one bisphosphonate claim during this period, who were then 1:1 propensity score-matched to bisphosphonate non-users by age, gender, insurance type, primary-care-provider visit in 2019, and comorbidity burden. Main outcomes of interest included: (a) any testing for SARS-CoV-2 infection; (b) COVID-19 diagnosis; and (c) hospitalization with a COVID-19 diagnosis between March 1, 2020 and June 30, 2020. Multiple sensitivity analyses were also performed to assess core study outcomes amongst more restrictive matches between BP users/non-users, as well as assessing the relationship between BP-use and other respiratory infections (pneumonia, acute bronchitis) both during the same study period as well as before the COVID outbreak.

Results

A total of 7,906,603 patients for whom continuous medical and prescription insurance information was available were selected. A total of 450,366 bisphosphonate users were identified and 1:1 propensity score-matched to bisphosphonate non-users. Bisphosphonate users had lower odds ratios (OR) of testing for SARS-CoV-2 infection (OR = 0.22; 95%CI:0.21-0.23; p<0.001), COVID-19 diagnosis (OR = 0.23; 95%CI:0.22-0.24; p<0.001), and COVID-19-related hospitalization (OR = 0.26; 95%CI:0.24-0.29; p<0.001). Sensitivity analyses yielded results consistent with the primary analysis. Bisphosphonate-use was also associated with decreased odds of acute bronchitis (OR = 0.23; 95%CI:0.22-0.23; p<0.001) or pneumonia (OR = 0.32; 95%CI:0.31-0.34; p<0.001) in 2019, suggesting that bisphosphonates may protect against respiratory infections by a variety of pathogens, including but not limited to SARS-CoV-2.

Conclusions

Prior bisphosphonate-use was associated with dramatically reduced odds of SARS-CoV-2 testing, COVID-19 diagnosis, and COVID-19-related hospitalizations. Prospective clinical trials will be required to establish a causal role for bisphosphonate-use in COVID-19-related outcomes.

Funding

This study was supported by NIH grants, AR068383 and AI155865, a grant from MassCPR (to UHvA) and a CRI Irvington postdoctoral fellowship, CRI2453 (to PH).

Type I Interferon Orchestrates Demand-Adapted Monopoiesis during Influenza A Virus Infection via STAT1-Mediated Upregulation of Macrophage Colony-Stimulating Factor Receptor Expression

Whether and how a local virus infection affects the hematopoietic system in the bone marrow is largely unknown, unlike with systemic infection. In this study, we showed that influenza A virus (IAV) infection leads to demand-adapted monopoiesis in the bone marrow. The beta interferon (IFN-β) promoter stimulator 1 (IPS-1)-type I IFN-IFN-α receptor 1 (IFNAR1) axis-mediated signaling was found to induce the emergency expansion of the granulocyte-monocyte progenitor (GMP) population and upregulate the expression of the macrophage colony-stimulating factor receptor (M-CSFR) on bipotent GMPs and monocyte progenitors via the signal transducer and activator of transcription 1 (STAT1), leading to a scaled-back proportion of granulocyte progenitors. To further address the influence of demand-adapted monopoiesis on IAV-induced secondary bacterial infection, IAV-infected wild-type (WT) and Stat1-/- mice were challenged with Streptococcus pneumoniae. Compared with WT mice, Stat1-/- mice did not demonstrate demand-adapted monopoiesis, had more infiltrating granulocytes, and were able to effectively eliminate the bacterial infection. IMPORTANCE Our findings show that influenza A virus infection induces type I interferon (IFN)-mediated emergency hematopoiesis to expand the GMP population in the bone marrow. The type I IFN-STAT1 axis was identified as being involved in mediating the viral-infection-driven demand-adapted monopoiesis by upregulating M-CSFR expression in the GMP population. As secondary bacterial infections often manifest during a viral infection and can lead to severe or even fatal clinical complications, we further assessed the impact of the observed monopoiesis on bacterial clearance. Our results suggest that the resulting decrease in the proportion of granulocytes may play a role in diminishing the IAV-infected host's ability to effectively clear secondary bacterial infection. Our findings not only provide a more complete picture of the modulatory functions of type I IFN but also highlight the need for a more comprehensive understanding of potential changes in hematopoiesis during local infections to better inform clinical interventions.

Antibody Production Remains Intact Despite Loss of Bone Marrow B cells in Murine Norovirus Infected Stat1-/- Mice

Murine norovirus (MNV), which can be used as a model system to study human noroviruses, can infect macrophages/monocytes, neutrophils, dendritic, intestinal epithelial, T and B cells, and is highly prevalent in laboratory mice. We previouslyshowed that MNV infection significantly reduces bone marrow B cell populations in a Stat1-dependent manner. We show here that while MNV-infected Stat1-/- mice have significant losses of bone marrow B cells, splenic B cells capable of mounting an antibody response to novel antigens retain the ability to expand. We also investigated whether increased granulopoiesis after MNV infection was causing B cell loss. We found that administration of anti-G-CSF antibody inhibits the pronounced bone marrow granulopoiesis induced by MNV infection of Stat1-/- mice, but this inhibition did not rescue bone marrow B cell losses. Therefore, MNV-infected Stat1-/- mice can still mount a robust humoral immune response despite decreased bone marrow B cells. This suggests that further investigation will be needed to identify other indirect factors or mechanisms that are responsible for the bone marrow B cell losses seen after MNV infection. In addition, this work contributes to our understanding of the potential physiologic effects of Stat1-related disruptions in research mouse colonies that may be endemically infected with MNV.

A recombinant protein containing influenza viral conserved epitopes and superantigen induces broad-spectrum protection

Influenza pandemics pose public health threats annually for lacking vaccine that provides cross-protection against novel and emerging influenza viruses. Combining conserved antigens that induce cross-protective antibody responses with epitopes that activate cross-protective T cell responses might be an attractive strategy for developing a universal vaccine. In this study, we constructed a recombinant protein named NMHC that consists of influenza viral conserved epitopes and a superantigen fragment. NMHC promoted the maturation of bone marrow-derived dendritic cells and induced CD4+ T cells to differentiate into Th1, Th2, and Th17 subtypes. Mice vaccinated with NMHC produced high levels of immunoglobulins that cross-bound to HA fragments from six influenza virus subtypes with high antibody titers. Anti-NMHC serum showed potent hemagglutinin inhibition effects to highly divergent group 1 (H1 subtype) and group 2 (H3 subtype) influenza virus strains. Furthermore, purified anti-NMHC antibodies bound to multiple HAs with high affinities. NMHC vaccination effectively protected mice from infection and lung damage when exposed to two subtypes of H1N1 influenza virus. Moreover, NMHC vaccination elicited CD4+ and CD8+ T cell responses that cleared the virus from infected tissues and prevented virus spread. In conclusion, this study provides proof of concept that NMHC vaccination triggers B and T cell immune responses against multiple influenza virus infections. Therefore, NMHC might be a candidate universal broad-spectrum vaccine for the prevention and treatment of multiple influenza viruses.

COVID-19 and orthopaedic surgery in a large trauma centre in India

Background:

We are in the midst of a pandemic caused by the novel SARS-Cov-2 virus. A large percentage of the patients are asymptomatic and hospitals around the world are struggling to restart routine services. We report the results of a universal testing protocol of all patients who underwent orthopaedic surgery in the month of July 2020 in a large orthopaedic speciality hospital in Bangalore, India.

Methods:

A retrospective study of all patients who underwent orthopaedic surgery in the month of July 2020 at a tertiary care orthopaedic speciality hospital in Bangalore, India. All patients underwent nasopharyngeal swab test before surgery. A questionnaire was used to assess the patient before the RT-PCR nasopharyngeal swab test. Data regarding imaging, investigations and follow up was recorded.

Results:

In the month of July 2020, 168 patients underwent routine nasopharyngeal RT-PCR swab test for COVID-19 prior to planned orthopaedic surgical procedure (Both trauma and elective cases). 16 of the RT-PCR tests were positive. However vascular cases and absolute emergencies were done without a RT-PCR test with PPE and all universal precautions. 11 patients underwent emergency surgery without a RT-PCR test. All 16 cases who were positive were asymptomatic. The asymptomatic positive rate was 9.52%. Of the 11 patients who underwent emergency surgery without a RT-PCR test, only one patient had a positive test post-operatively.

Conclusions:

Routine nasopharyngeal RT-PCR testing revealed a high rate of asymptomatic cases. If the RT-PCR test is positive, it is best to defer the case till the test returns negative. All precautions must be taken while performing emergency surgeries. Our algorithm in managing patients has proven to be effective and can be replicated with ease to continue operating and taking care of orthopaedic patients during this pandemic.

Teaching Old Dogs New Tricks? The Plasticity of Lung Alveolar Macrophage Subsets

Alveolar macrophages (AMs) are highly abundant lung cells with important roles in homeostasis and immunity. Their function influences the outcome of lung infections, lung cancer, and chronic inflammatory disease. Recent findings reveal functional heterogeneity of AMs. Following lung insult, resident AMs can either remain unchanged, acquire new functionality, or be replaced by monocyte-derived AMs. Evidence from mouse models correlates AM function with their embryonic or monocyte origin. We hypothesize that resident AMs are terminally differentiated cells with low responsiveness and limited plasticity, while recruited, monocyte-derived AMs are initially highly immunoreactive but more plastic, able to change their function in response to environmental cues. Understanding cell-intrinsic and -extrinsic mechanisms determining AM function may provide opportunities for intervention in lung disease.

Type I IFN is siloed in endosomes

Type I IFN (IFN-I) is thought to be rapidly internalized and degraded following binding to its receptor and initiation of signaling. However, many studies report the persistent effects mediated by IFN-I for days or even weeks, both ex vivo and in vivo. These long-lasting effects are attributed to downstream signaling molecules or induced effectors having a long half-life, particularly in specific cell types. Here, we describe a mechanism explaining the long-term effects of IFN-I. Following receptor binding, IFN-I is siloed into endosomal compartments. These intracellular “IFN silos” persist for days and can be visualized by fluorescence and electron microscopy. However, they are largely dormant functionally, due to IFN-I−induced negative regulators. By contrast, in individuals lacking these negative regulators, such as ISG15 or USP18, this siloed IFN-I can continue to signal from within the endosome. This mechanism may underlie the long-term effects of IFN-I therapy and may contribute to the pathophysiology of type I interferonopathies.

The Clinical Presentation and Immunology of Viral Pneumonia and Implications for Management of Coronavirus Disease 2019

This review will briefly examine the clinical presentation and important immunology of viral pneumonia with a focus on severe acute respiratory syndrome coronavirus 2 (coronavirus disease 2019).

ISRE-Reporter Mouse Reveals High Basal and Induced Type I IFN Responses in Inflammatory Monocytes

Type I and type III interferons (IFNs) are critical for controlling viral infections. However, the precise dynamics of the IFN response have been difficult to define in vivo. Signaling through type I IFN receptors leads to interferon-stimulated response element (ISRE)-dependent gene expression and an antiviral state. As an alternative to tracking IFN, we used an ISRE-dependent reporter mouse to define the cell types, localization, and kinetics of IFN responding cells during influenza virus infection. We find that measurable IFN responses are largely limited to hematopoietic cells, which show a high sensitivity to IFN. Inflammatory monocytes display high basal IFN responses, which are enhanced upon infection and correlate with infection of these cells. We find that inflammatory monocyte development is independent of IFN signaling; however, IFN is critical for chemokine production and recruitment following infection. The data reveal a role for inflammatory monocytes in both basal IFN responses and responses to infection.

Uccellini and García-Sastre create an ISRE reporter mouse and track interferon (IFN) responses in vivo in response to pathogen-associated molecular pattern (PAMP) stimulation and influenza infection. They find that IFN responses are highest in hematopoietic cells during infection. Specifically, Ly6C^hi inflammatory monocytes have high basal IFN responses that are further enhanced upon infection.

Decoding the Body Language of Immunity: Tackling the Immune System at the Organism Level

The immune system is a dynamic mesh of molecules, cells and tissues spanning the entire organism. Despite a wealth of knowledge about the components of the immune system, little is known about the general rules governing the organismal circuitry of immunity. Deciphering the immune system at the scale of the whole organism is crucial to understanding fundamental problems in immunobiology and physiology, and to manipulate immunity for maintaining health and preventing disease. Here I discuss the emerging principles of inter-organ communications during immune responses by focusing on three common themes that are the regulation of the (i) composition, (ii) condition and (iii) coordination of communicating organs by molecular and cellular factors. Based on these common principles, I emphasize fundamental gaps in our knowledge of organismal immune processes and the outlook to tackle immunity at the scale of the whole organism.

Circadian control of lung inflammation in influenza infection

Influenza is a leading cause of respiratory mortality and morbidity. While inflammation is essential for fighting infection, a balance of anti-viral defense and host tolerance is necessary for recovery. Circadian rhythms have been shown to modulate inflammation. However, the importance of diurnal variability in the timing of influenza infection is not well understood. Here we demonstrate that endogenous rhythms affect survival in influenza infection. Circadian control of influenza infection is mediated by enhanced inflammation as proven by increased cellularity in bronchoalveolar lavage (BAL), pulmonary transcriptomic profile and histology and is not attributable to viral burden. Better survival is associated with a time dependent preponderance of NK and NKT cells and lower proportion of inflammatory monocytes in the lung. Further, using a series of genetic mouse mutants, we elucidate cellular mechanisms underlying circadian gating of influenza infection.

Plasma cytokine profile on admission related to aetiology in community-acquired pneumonia

BACKGROUND

Potentially unnecessary antibiotic use for community-acquired pneumonia (CAP) contributes to selection of antibiotic-resistant pathogens. Cytokine expression at the time that treatment is started may assist in identifying patients not requiring antibiotics. We determined plasma cytokine patterns in patients retrospectively categorized as strict viral, pneumococcal or combined viral-bacterial CAP.

OBJECTIVE

To investigate whether cytokine-based prediction models can be used to differentiate strict viral CAP from other aetiologies at admission.

METHODS

From 344 hospitalized CAP patients, 104 patients were categorized as viral CAP (n = 17), pneumococcal CAP (n = 48) and combined bacterial-viral CAP (n = 39). IL-6, IL-10, IL-27, IFN-γ and C-reactive protein (CRP) were determined on admission in plasma. Prediction of strict viral aetiology was explored with two multivariate regression models and ROC curves.

RESULTS

Viral pneumonia was predicted by logistic regression using multiple cytokine levels (IL-6, IL-27 and CRP) with an AUC of 0.911 (95% CI: 0.852-0.971, P < .001). For the same patients the AUC of CRP was 0.813 (95% CI: 0.728-0.898, P < .001).

CONCLUSIONS

This study demonstrated differences in cytokine expression in selected CAP patients between viral and bacterial aetiology. Prospective validation studies are warranted.

Semiquantitative Proteomics Enables Mapping of Murine Neutrophil Dynamics following Lethal Influenza Virus Infection

Neutrophils are rapidly deployed innate immune cells, and excessive recruitment is causally associated with influenza-induced pathologic conditions. Despite this, the complete set of influenza lethality-associated neutrophil effector proteins is currently unknown. Whether the expression of these proteins is predetermined during bone marrow (BM) neutrophil maturation or further modulated by tissue compartment transitions has also not been comprehensively characterized at a proteome-wide scale. In this study, we used high-resolution mass spectrometry to map how the proteomes of murine neutrophils change comparatively across BM, blood, and the alveolar airspaces to deploy an influenza lethality-associated response. Following lethal influenza infection, mature neutrophils undergo two infection-dependent and one context-independent compartmental transitions. Translation of type I IFN-stimulated genes is first elevated in the BM, preceding the context-independent downregulation of ribosomal proteins observed in blood neutrophils. Following alveolar airspace infiltration, the bronchoalveolar lavage (BAL) neutrophil proteome is further characterized by a limited increase in type I IFN-stimulated and metal-sequestering proteins as well as a decrease in degranulation-associated proteins. An influenza-selective and dose-dependent increase in antiviral and lipid metabolism-associated proteins was also observed in BAL neutrophils, indicative of a modest capacity for pathogen response tuning. Altogether, our study provides new and comprehensive evidence that the BAL neutrophil proteome is shaped by BM neutrophil maturation as well as subsequent compartmental transitions following lethal influenza infection.

Peripheral and systemic antigens elicit an expandable pool of resident memory CD8+ T cells in the bone marrow

BM has been put forward as a major reservoir for memory CD8⁺  T cells. In order to fulfill that function, BM should "store" memory CD8⁺ T cells, which in biological terms would require these "stored" memory cells to be in disequilibrium with the circulatory pool. This issue is a matter of ongoing debate. Here, we unequivocally demonstrate that murine and human BM harbors a population of tissue-resident memory CD8⁺ T (T_RM ) cells. These cells develop against various pathogens, independently of BM infection or local antigen recognition. BM CD8⁺ T_RM cells share a transcriptional program with resident lymphoid cells in other tissues; they are polyfunctional cytokine producers and dependent on IL-15, Blimp-1, and Hobit. CD8⁺ T_RM cells reside in the BM parenchyma, but are in close contact with the circulation. Moreover, this pool of resident T cells is not size-restricted and expands upon peripheral antigenic re-challenge. This works extends the role of the BM in the maintenance of CD8⁺ T cell memory to include the preservation of an expandable reservoir of functional, non-recirculating memory CD8⁺ T cells, which develop in response to a large variety of peripheral antigens.

Molecular Adjuvants Based on Plasmids Encoding Protein Aggregation Domains Affect Bone Marrow Niche Homeostasis

Background:

During last years, DNA vaccine immunogenicity has been optimized by the employment of co-stimulatory molecules and molecular adjuvants. It has been reported that plasmid (pATRex), encompassing the DNA sequence for the von Willebrand A (vWA/A) domain of the An-thrax Toxin Receptor-1 (ANTXR-1, alias TEM8, Tumor Endothelial Marker 8), acts as strong immune adjuvant by inducing formation of insoluble intracellular aggregates. Markedly, we faced with upsetting findings regarding the safety of pATRex as adjuvant since the aggregosome formation prompted to os-teopenia in mice.

Objective:

The present study provides additional evidences about the proteinaceous adjuvants action within bone marrow and questioned regarding the self-aggregation protein adjuvants immunotoxicity on marrow niches.

Methods & Results:

Using histological, biochemical and proteomic assays we shed light on pATRex effects within bone marrow niche and specifically we evidenced an aplastic-like bone marrow with dis-rupted cytokine/chemokine production.

Conclusion:

The above findings provide compelling support to the thesis that adjuvants based on plas-mids encoding protein aggregation domains disrupt the physiological features of the bone marrow ele-ments.

The Different Tactics of Foot-and-Mouth Disease Virus to Evade Innate Immunity

Like all pathogens, foot-and-mouth disease virus (FMDV) is recognized by the immune system inducing a heightened immune response mainly mediated by type I and type III IFNs. To overcome the strong antiviral response induced by these cytokines, FMDV has evolved many strategies exploiting each region of its small RNA genome. These include: (a) inhibition of IFN induction at the transcriptional and translational level, (b) inhibition of protein trafficking; (c) blockage of specific post-translational modifications in proteins that regulate innate immune signaling; (d) modulation of autophagy; (e) inhibition of stress granule formation; and (f) in vivo modulation of immune cell function. Here, we summarize and discuss FMDV virulence factors and the host immune footprint that characterize infection in cell culture and in the natural hosts.

Alteration of Flt3-Ligand-dependent de novo generation of conventional dendritic cells during influenza infection contributes to respiratory bacterial superinfection

Secondary bacterial infections contribute to the excess morbidity and mortality of influenza A virus (IAV) infection. Disruption of lung integrity and impaired antibacterial immunity during IAV infection participate in colonization and dissemination of the bacteria out of the lungs. One key feature of IAV infection is the profound alteration of lung myeloid cells, characterized by the recruitment of deleterious inflammatory monocytes. We herein report that IAV infection causes a transient decrease of lung conventional dendritic cells (cDCs) (both cDC1 and cDC2) peaking at day 7 post-infection. While triggering emergency monopoiesis, IAV transiently altered the differentiation of cDCs in the bone marrow, the cDC1-biaised pre-DCs being particularly affected. The impaired cDC differentiation during IAV infection was independent of type I interferons (IFNs), IFN-γ, TNFα and IL-6 and was not due to an intrinsic dysfunction of cDC precursors. The alteration of cDC differentiation was associated with a drop of local and systemic production of Fms-like tyrosine kinase 3 ligand (Flt3-L), a critical cDC differentiation factor. Overexpression of Flt3-L during IAV infection boosted the cDC progenitors' production in the BM, replenished cDCs in the lungs, decreased inflammatory monocytes' infiltration and lowered lung damages. This was associated with partial protection against secondary pneumococcal infection, as reflected by reduced bacterial dissemination and prolonged survival. These findings highlight the impact of distal viral infection on cDC genesis in the BM and suggest that Flt3-L may have potential applications in the control of secondary infections.

Interferon priming is essential for human CD34+ cell-derived plasmacytoid dendritic cell maturation and function

Plasmacytoid dendritic cells (pDC) are essential for immune competence. Here we show that pDC precursor differentiated from human CD34+ hematopoietic stem and progenitor cells (HSPC) has low surface expression of pDC markers, and has limited induction of type I interferon (IFN) and IL-6 upon TLR7 and TLR9 agonists treatment; by contrast, cGAS or RIG-I agonists-mediated activation is not altered. Importantly, after priming with type I and II IFN, these precursor pDCs attain a phenotype and functional activity similar to that of peripheral blood-derived pDCs. Data from CRISPR/Cas9-mediated genome editing of HSPCs further show that HSPC-pDCs with genetic modifications can be obtained, and that expression of the IFN-α receptor is essential for the optimal function, but dispensable for the differentiation, of HSPC-pDC percursor. Our results thus demonstrate the biological effects of IFNs for regulating pDC function, and provide the means of generating of gene-modified human pDCs.

Adaptive Natural Killer Cells Integrate Interleukin-18 during Target-Cell Encounter

Human cytomegalovirus (HCMV) infection induces adaptations in the natural killer (NK)-cell compartment. Expanded subsets of adaptive NK cells display potent effector functions against cellular targets, despite their apparent unresponsiveness to stimulation with classical dendritic cell-derived cytokines interleukin (IL)-12 and IL-18. However, it remains unclear whether adaptive NK cells have completely lost their ability to sense inflammation via IL-12 and IL-18 or whether these pro-inflammatory signals can be functionally integrated into defined contexts. Here, we demonstrate that adaptive NKG2C⁺ NK cells can be costimulated by the presence of pro-inflammatory cytokines during target cell-induced activation. Cytokine costimulation of adaptive NK cells resulted in elevated interferon (IFN)-gamma and tumor necrosis factor (TNF) production, which promoted protein expression of HLA class I and adhesion molecules as well as transcription of genes involved in antigen processing and antiviral states in endothelial bystander cells in vitro. We further show that IL-18 drove costimulation in functional assays and was sufficient for elevated cytokine production in the absence of IL-12. Hence, adaptive NKG2C⁺ NK cells-although poorly responsive to IL-12 and IL-18 as an isolated stimulus-integrate IL-18 as a costimulatory signal during target-cell encounter.

Sendai Virus Propagation Using Chicken Eggs

Sendai virus is a member of the family Paramyxoviridae, and an enveloped virus with a negative-stranded RNA genome. Sendai virus is not pathogenic to humans, but for mice and can cause pneumonia in mice. Easy and efficient techniques for propagating Sendai virus are required for studying virus replication, virus-induced innate- and adaptive-immunity, Sendai-virus-based virotherapy and IgA nephropathy. Here, we describe a protocol for Sendai virus propagation using chicken eggs. This traditional protocol enables us to generate a large amount of virus enough for animal experiments as well as cell culture experiments in a relatively inexpensive way.

ILC1 Confer Early Host Protection at Initial Sites of Viral Infection

Infection is restrained by the concerted activation of tissue-resident and circulating immune cells. Whether tissue-resident lymphocytes confer early antiviral immunity at local sites of primary infection prior to the initiation of circulating responses is not well understood. Furthermore, the kinetics of initial antiviral responses at sites of infection remain unclear. Here, we show that tissue-resident type 1 innate lymphoid cells (ILC1) serve an essential early role in host immunity through rapid production of interferon (IFN)-γ following viral infection. Ablation of Zfp683-dependent liver ILC1 lead to increased viral load in the presence of intact adaptive and innate immune cells critical for mouse cytomegalovirus (MCMV) clearance. Swift production of interleukin (IL)-12 by tissue-resident XCR1⁺ conventional dendritic cells (cDC1) promoted ILC1 production of IFN-γ in a STAT4-dependent manner to limit early viral burden. Thus, ILC1 contribute an essential role in viral immunosurveillance at sites of initial infection in response to local cDC1-derived proinflammatory cytokines.

Organism-Level Analysis of Vaccination Reveals Networks of Protection across Tissues

A fundamental challenge in immunology is to decipher the principles governing immune responses at the whole-organism scale. Here, using a comparative infection model, we observe immune signal propagation within and between organs to obtain a dynamic map of immune processes at the organism level. We uncover two inter-organ mechanisms of protective immunity mediated by soluble and cellular factors. First, analyzing ligand-receptor connectivity across tissues reveals that type I IFNs trigger a whole-body antiviral state, protecting the host within hours after skin vaccination. Second, combining parabiosis, single-cell analyses, and gene knockouts, we uncover a multi-organ web of tissue-resident memory T cells that functionally adapt to their environment to stop viral spread across the organism. These results have implications for manipulating tissue-resident memory T cells through vaccination and open up new lines of inquiry for the analysis of immune responses at the organism level.

Type I Interferons as Regulators of Lung Inflammation

Immune responses to lung infections must be tightly regulated in order to permit pathogen eradication while maintaining organ function. Exuberant or dysregulated inflammation can impair gas exchange and underlies many instances of lung disease. An important driver of inflammation in the lung is the interferon (IFN) response. Type I IFNs are antiviral cytokines that induce a large range of proteins that impair viral replication in infected cells. This cell-intrinsic action plays a crucial role in protecting the lungs from spread of respiratory viruses. However, type I IFNs have also recently been found to be central to the initiation of lung inflammatory responses, by inducing recruitment and activation of immune cells. This helps control virus burden but can cause detrimental immunopathology and contribute to disease severity. Furthermore, there is now increasing evidence that type I IFNs are not only induced after viral infections but also after infection with bacteria and fungi. The pro-inflammatory function of type I IFNs in the lung opens up the possibility of immune modulation directed against this antiviral cytokine family. In this review, the initiation and signaling of type I IFNs as well as their role in driving and maintaining lung inflammation will be discussed.

Type I interferons in viral control and immune regulation

Type 1 interferons (IFN-I) exert pleiotropic biological effects during viral infections, all which contribute to balancing virus control and immune pathology. Despite extensive antiviral functions that subdue virus replication, recent studies demonstrate pathogenic and pro-viral roles for IFN-I signaling during acute and persistent virus infection. IFN-I signaling can promote morbidity and mortality through induction of aberrant inflammatory responses during acute viral infection. In contrast, IFN-I signaling during persistent viral infection supports immune suppression, lymphoid tissue disorganization and CD4 T cell dysfunction. Systematic characterization of the cellular populations and intricacies of IFN-I signaling that promote pathology or immune suppression during acute and persistent viral infections, respectively, should inform the development of treatments and modalities to control viral associated pathologies.

Autophagy Snuffs a Macrophage's Inner Fire

Autophagy is a well-known cell-intrinsic antiviral defense mechanism. Two new studies published in this issue of Cell Host & Microbe (Lu et al., 2016; Park et al., 2016) demonstrate that deletion of autophagy in myeloid cells leads paradoxically to better control of viral infection in vivo through enhanced inflammation, leading to antiviral resistance.

Functional Interplay between Type I and II Interferons Is Essential to Limit Influenza A Virus-Induced Tissue Inflammation

Host control of influenza A virus (IAV) is associated with exuberant pulmonary inflammation characterized by the influx of myeloid cells and production of proinflammatory cytokines including interferons (IFNs). It is unclear, however, how the immune system clears the virus without causing lethal immunopathology. Here, we demonstrate that in addition to its known anti-viral activity, STAT1 signaling coordinates host inflammation during IAV infection in mice. This regulatory mechanism is dependent on both type I IFN and IFN-γ receptor signaling and, importantly, requires the functional interplay between the two pathways. The protective function of type I IFNs is associated with not only the recruitment of classical inflammatory Ly6C^hi monocytes into IAV-infected lungs, but also the prevention of excessive monocyte activation by IFN-γ. Unexpectedly, type I IFNs preferentially regulate IFN-γ signaling in Ly6C^lo rather than inflammatory Ly6C^hi mononuclear cell populations. In the absence of type I IFN signaling, Ly6C^lo monocytes/macrophages, become phenotypically and functionally more proinflammatory than Ly6C^hi cells, revealing an unanticipated function of the Ly6C^lo mononuclear cell subset in tissue inflammation. In addition, we show that type I IFNs employ distinct mechanisms to regulate monocyte and neutrophil trafficking. Type I IFN signaling is necessary, but not sufficient, for preventing neutrophil recruitment into the lungs of IAV-infected mice. Instead, the cooperation of type I IFNs and lymphocyte-produced IFN-γ is required to regulate the tissue neutrophilic response to IAV. Our study demonstrates that IFN interplay links innate and adaptive anti-viral immunity to orchestrate tissue inflammation and reveals an additional level of complexity for IFN-dependent regulatory mechanisms that function to prevent excessive immunopathology while preserving anti-microbial functions.

Influenza A virus (IAV) is a leading cause of respiratory infection and induces a strong acute inflammation manifested by the recruitment of monocytes and neutrophils as well as the production of proinflammatory cytokines in infected lungs. The interferons (IFNs) are strongly induced by IAV and are known to mediate host resistance to the infection. However, in contrast to their well-studied inhibitory effect on viral replication, the effects of IFNs on host inflammatory responses are less well understood. In this manuscript, we demonstrate that anti-viral IFN signaling is also required for the orchestration of a tissue response associated with the protection against IAV infection in mice. Importantly, we identify that type I IFNs cross-regulate and cooperate with IFN-γ to inhibit monocyte activation and neutrophil infiltration, respectively. This study also demonstrates that Ly6C^lo monocytes/macrophages can potentially mediate influenza virus-induced inflammation, suggesting that IFNs dictate the homeostasis versus inflammatory function of mononuclear phagocytes in viral infection. Our study reveals a novel IFN-dependent regulatory mechanism designed to prevent the excessive immunopathology while preserving its anti-microbial functions. Moreover, these observations have particular relevance for understanding the mechanisms underlying the strong inflammatory response associated with lethal IAV strains and have implications for the development of new immunotherapies to treat influenza.

Pleiotropic Roles of Type 1 Interferons in Antiviral Immune Responses

Since Isaac's and Lindenmann's seminal experiments over 50 years ago demonstrating a soluble factor generated from heat killed virus-stimulated chicken embryos could inhibit live influenza virus replication, the term interferon has been synonymous with inhibition of virus replication. While the antiviral properties of type 1 interferon (IFN-I) are undeniable, recent studies have reported expanding and somewhat unexpected roles of IFN-I signaling during both acute and persistent viral infections. IFN-I signaling can promote morbidity and mortality through induction of aberrant inflammatory responses and recruitment of inflammatory innate immune cell populations during acute respiratory viral infections. During persistent viral infection, IFN-I signaling promotes containment of early viral replication/dissemination, however, also initiates and maintains immune suppression, lymphoid tissue disorganization, and CD4 T cell dysfunction through modulation of multiple immune cell populations. Finally, new data are emerging illuminating how specific IFN-I species regulate immune pathology and suppression during acute and persistent viral infections, respectively. Systematic characterization of the cellular populations that produce IFN-I, how the timing of IFN-I induction and intricacies of subtype specific IFN-I signaling promote pathology or immune suppression during acute and persistent viral infections should inform the development of treatments and modalities to control viral associated pathologies.

Control of adaptive immunity by the innate immune system

Microbial infections are recognized by the innate immune system both to elicit immediate defense and to generate long-lasting adaptive immunity. To detect and respond to vastly different groups of pathogens, the innate immune system uses several recognition systems that rely on sensing common structural and functional features associated with different classes of microorganisms. These recognition systems determine microbial location, viability, replication and pathogenicity. Detection of these features by recognition pathways of the innate immune system is translated into different classes of effector responses though specialized populations of dendritic cells. Multiple mechanisms for the induction of immune responses are variations on a common design principle wherein the cells that sense infections produce one set of cytokines to induce lymphocytes to produce another set of cytokines, which in turn activate effector responses. Here we discuss these emerging principles of innate control of adaptive immunity.

Disease-promoting effects of type I interferons in viral, bacterial, and coinfections

While type I interferons (IFNs) are universally acknowledged for their antiviral and immunostimulatory functions, there is increasing appreciation of the detrimental effects of inappropriate, excessive, or mistimed type I IFN responses in viral and bacterial infections. The underlying mechanisms by which type I IFNs promote susceptibility or severity include direct tissue damage by apoptosis induction or suppression of proliferation in tissue cells, immunopathology due to excessive inflammation, and cell death induced by TRAIL- and Fas-expressing immune cells, as well as immunosuppression through IL-10, IL-27, PD-L1, IL-1Ra, and other regulatory molecules that antagonize the induction or action of IL-1, IL-12, IL-17, IFN-γ, KC, and other effectors of the immune response. Bacterial superinfections following influenza infection are a prominent example of a situation where type I IFNs can misdirect the immune response. This review discusses current understanding of the parameters of signal strength, duration, timing, location, and cellular recipients that determine whether type I IFNs have beneficial or detrimental effects in infection.

The pathological effects of CCR2+ inflammatory monocytes are amplified by an IFNAR1-triggered chemokine feedback loop in highly pathogenic influenza infection

BACKGROUND

Highly pathogenic influenza viruses cause high levels of morbidity, including excessive infiltration of leukocytes into the lungs, high viral loads and a cytokine storm. However, the details of how these pathological features unfold in severe influenza infections remain unclear. Accumulation of Gr1 + CD11b + myeloid cells has been observed in highly pathogenic influenza infections but it is not clear how and why they accumulate in the severely inflamed lung. In this study, we selected this cell population as a target to investigate the extreme inflammatory response during severe influenza infection.

RESULTS

We established H1N1 IAV-infected mouse models using three viruses of varying pathogenicity and noted the accumulation of a defined Gr1 + CD11b + myeloid population correlating with the pathogenicity. Herein, we reported that CCR2+ inflammatory monocytes are the major cell compartments in this population. Of note, impaired clearance of the high pathogenicity virus prolonged IFN expression, leading to CCR2+ inflammatory monocytes amplifying their own recruitment via an interferon-α/β receptor 1 (IFNAR1)-triggered chemokine loop. Blockage of IFNAR1-triggered signaling or inhibition of viral replication by Oseltamivir significantly suppresses the expression of CCR2 ligands and reduced the influx of CCR2+ inflammatory monocytes. Furthermore, trafficking of CCR2+ inflammatory monocytes from the bone marrow to the lung was evidenced by a CCR2-dependent chemotaxis. Importantly, leukocyte infiltration, cytokine storm and expression of iNOS were significantly reduced in CCR2-/- mice lacking infiltrating CCR2+ inflammatory monocytes, enhancing the survival of the infected mice.

CONCLUSIONS

Our results indicated that uncontrolled viral replication leads to excessive production of inflammatory innate immune responses by accumulating CCR2+ inflammatory monocytes, which contribute to the fatal outcomes of high pathogenicity virus infections.

How specific is too specific? B-cell responses to viral infections reveal the importance of breadth over depth

Influenza virus infection induces robust and highly protective B-cell responses. Knowledge gained from the analysis of such protective humoral responses can provide important clues for the design of successful vaccines and vaccination approaches and also provides a window into the regulation of fundamental aspects of B-cell responses that may not be at play when responses to non-replicating agents are studied. Here, I review features of the B-cell response to viruses, with emphasis on influenza virus infection, a highly localized infection of respiratory tract epithelial cells, and a response that is directed against a virus that continuously undergoes genetic changes to its surface spike protein, a major target of neutralizing antibodies. Two aspects of the B-cell response to influenza are discussed here, namely polyreactive natural antibodies and the role and function of germinal center responses. Both these features of the B-cell response raise the question of how important antibody fine-specificity is for long-term protection from infection. As outlined, the pathogenesis of influenza virus and the nature of the antiviral B-cell response seem to emphasize repertoire diversity over affinity maturation as driving forces behind the influenza-specific B-cell immunity.

Tissue-resident memory T cells

Tissues such as the genital tract, skin, and lung act as barriers against invading pathogens. To protect the host, incoming microbes must be quickly and efficiently controlled by the immune system at the portal of entry. Memory is a hallmark of the adaptive immune system, which confers long-term protection and is the basis for efficacious vaccines. While the majority of existing vaccines rely on circulating antibody for protection, struggles to develop antibody-based vaccines against infections such as herpes simplex virus (HSV) and human immunodeficiency virus (HIV) have underscored the need to generate memory T cells for robust antiviral control. The circulating memory T-cell population is generally divided into two subsets: effector memory (TEM ) and central memory (TCM ). These two subsets can be distinguished by their localization, as TCM home to secondary lymphoid organs and TEM circulate through non-lymphoid tissues. More recently, studies have identified a third subset, called tissue-resident memory (TRM ) cells, based on its migratory properties. This subset is found in peripheral tissues that require expression of specific chemoattractants and homing receptors for T-cell recruitment and retention, including barrier sites such as the skin and genital tract. In this review, we categorize different tissues in the body based on patterns of memory T-cell migration and tissue residency. This review also describes the rules for TRM generation and the properties that distinguish them from circulating TEM and TCM cells. Finally, based on the failure of recent T-cell-based vaccines to provide optimal protection, we also discuss the potential role of TRM cells in vaccine design against microbes that invade through the peripheral tissues and highlight new vaccination strategies that take advantage of this newly described memory T-cell subset.

Infection-induced changes in hematopoiesis

The bone marrow (BM) is an important site for the interrelated processes of hematopoiesis, granulopoiesis, erythropoiesis, and lymphopoiesis. A wide variety of microbial challenges are associated with profound changes in this compartment that impact on hematopoietic differentiation and mobilization of a variety of cell types. This article reviews some of the key pathways that control BM homeostasis, the infectious and inflammatory processes that affect the BM, and how addressing the knowledge gaps in this area has the potential to widen our comprehension of immune homeostasis.

The role of cytokine responses during influenza virus pathogenesis and potential therapeutic options

Aberrant pulmonary immune responses are linked to the pathogenesis of multiple human respiratory viral infections. Elevated cytokine and chemokine production "cytokine storm" has been continuously associated with poor clinical outcome and pathogenesis during influenza virus infection in humans and animal models. Initial trials using global immune suppression with corticosteroids or targeted neutralization of single inflammatory mediators proved ineffective to ameliorate pathology during pathogenic influenza virus infection. Thus, it was believed that cytokine storm was either chemically intractable or not causal in the pathology observed. During this review, we will discuss the history of research assessing the roles various cytokines, chemokines, and innate immune cells play in promoting pathology or protection during influenza virus infection. Several promising new strategies modulating lipid signaling have been recently uncovered for global blunting, but not ablation, of innate immune responses following influenza virus infection. Importantly, modulating lipid signaling through various means has proven effective at curbing morbidity and mortality in animal models and may be useful for curbing influenza virus induced pathology in humans. Finally, we highlight future research directions for mechanistically dissecting how modulation of lipid signaling pathways results in favorable outcomes following influenza virus infection.

The early monocytic response to cytomegalovirus infection is MyD88 dependent but occurs independently of common inflammatory cytokine signals

Cytomegalovirus latently infects myeloid cells; however, the acute effects of the virus on this cell subset are poorly characterised. We demonstrate that systemic cytomegalovirus infection induced rapid activation of monocytes in the bone marrow, characterised by upregulation of CD69, CD11c, Ly6C and M-CSF receptor. Activated bone marrow monocytes were more sensitive to M-CSF and less sensitive to granulocyte-monocyte colony stimulating factor in vitro, resulting in the generation of more macrophages and fewer dendritic cells, respectively. Monocyte activation was also observed in the periphery and resulted in significant accumulation of monocytes in the spleen. MyD88 expression was required within the haematopoietic compartment to initiate monocyte activation and recruitment. However, monocytes lacking MyD88 were activated and recruited in the presence of MyD88-sufficient cells in mixed bone marrow chimeras, indicating that once initiated, the process was MyD88 independent. Interestingly, we found that monocyte activation occurred in the absence of the common inflammatory cytokines, namely type I interferons (IFNs), IL-6, TNF-α and IL-1 as well as the NLRP3 inflammasome adaptor protein, ASC. We also excluded a role for the chemokine-like protein MCK-2 (m131/129) expressed by murine CMV. Taken together, these results challenge the notion that a single inflammatory cytokine mediates activation and recruitment of monocytes in response to infection.

The influence of pregnancy on systemic immunity

Adaptations in maternal systemic immunity are presumed to be responsible for observed alterations in disease susceptibility and severity as pregnancy progresses. Epidemiological evidence as well as animal studies have shown that influenza infections are more severe during the second and third trimesters of pregnancy, resulting in greater morbidity and mortality, although the reason for this is still unclear. Our laboratory has taken advantage of 20 years of experience studying the murine immune response to respiratory viruses to address questions of altered immunity during pregnancy. With clinical studies and unique animal model systems, we are working to define the mechanisms responsible for altered immune responses to influenza infection during pregnancy and what roles hormones such as estrogen or progesterone play in these alterations.

The case for immunomodulatory approaches in treating HSV encephalitis

HSV encephalitis (HSE) is the most prevalent sporadic viral encephalitis. Although safe and effective antiviral therapies and greatly improved noninvasive diagnostic procedures have significantly improved outcomes, mortality (~20%) and debilitating neurological sequelae in survivors remain unacceptably high. An encouraging new development is that the focus is now shifting away from the virus exclusively, to include consideration of the host immune response to infection in the pathology underlying development of HSE. In this article, the authors discuss results from recent studies in experimental mouse models, as well as clinical reports that demonstrate a role for exaggerated host inflammatory responses in the brain in the development of HSE that is motivating researchers and clinicians to consider new therapeutic approaches for treating HSE. The authors also discuss results from a few studies that have shown that immunomodulatory drugs can be highly protective against HSE, which supports a role for deleterious host inflammatory responses in HSE. The impressive outcomes of some immunomodulatory approaches in mouse models of HSE emphasize the urgent need for clinical trials to rigorously evaluate combination antiviral and immunomodulatory therapy in comparison with standard antiviral therapy for treatment of HSE, and support for such an initiative is gaining momentum.

Coxsackievirus B3 infects the bone marrow and diminishes the restorative capacity of erythroid and lymphoid progenitors

Coxsackievirus B3 (CVB3) is known to infect stem cells in the neonatal central nervous system. Here, we evaluated the effects of CVB3 infection on the major source and repository of stem cells, the bone marrow (BM). Viral genome was detectable in BM within 24 h of infection, and productive infection of BM cells was evident, peaking at 48 h postinfection (p.i.), when ∼1 to 2% of BM cells produced infectious virus particles. Beginning at 2 to 3 days p.i., a dramatic and persistent loss of immature erythroid cells, B and T lymphocytes, and neutrophils was observed in BM and, by day 3 to 4 p.i., the femoral BM stroma was largely destroyed. Analysis of peripheral blood revealed a modest neutrophilia, a loss of reticulocytes, and a massive lymphopenia. The abundance of multipotent progenitor cells (Lin(-)/c-kit(+)/Flt3(+)) in BM declined ∼10-fold during CVB3 infection and, consistent with a deficiency of primitive hematopoietic progenitors, serum levels of the hematopoietic growth factor Flt3 ligand were dramatically elevated. Therefore, we analyzed the regenerative capacity of BM from CVB3-infected mice. Granulocyte/macrophage progenitors displayed a relatively normal proliferative ability, consistent with the fact that the peripheral blood level of neutrophils-which are very short-lived cells-remained high throughout infection. However, erythroid and lymphoid hematopoietic progenitors in BM from CVB3-infected mice showed a markedly reduced colony-forming capacity, consonant with the observed loss of both lymphocytes and immature erythroid cells/reticulocytes from the BM and peripheral blood. In summary, CVB3 infects the BM and exerts differential effects on the various hematopoietic progenitor populations.

Early sensing of Yersinia pestis airway infection by bone marrow cells

Bacterial infection of the lungs triggers a swift innate immune response that involves the production of cytokines and chemokines that promote recruitment of immune cells from the bone marrow (BM) into the infected tissue and limit the ability of the pathogen to replicate. Recent in vivo studies of pneumonic plague in animal models indicate that the pulmonary pro-inflammatory response to airway infection with Yersinia pestis is substantially delayed in comparison to other pathogens. Consequently, uncontrolled proliferation of the pathogen in the lungs is observed, followed by dissemination to internal organs and death. While the lack of an adequate early immune response in the lung is well described, the response of BM-derived cells is poorly understood. In this study, we show that intranasal (i.n.) infection of mice with a fully virulent Y. pestis strain is sensed early by the BM compartment, resulting in a reduction in CXCR4 levels on BM neutrophils and their subsequent release into the blood 12 hours (h) post infection. In addition, increased levels of BM-derived hematopoietic stem and progenitor cells (HSPC) were detected in the blood early after infection. Mobilization of both immature and mature cells was accompanied by the reduction of BM SDF-1 (CXCL-12) levels and the reciprocal elevation of SDF-1 in the blood 24 h post infection. RT-PCR analysis of RNA collected from total BM cells revealed an early induction of myeloid-associated genes, suggesting a prompt commitment to myeloid lineage differentiation. These findings indicate that lung infection by Y. pestis is sensed by BM cells early after infection, although bacterial colonization of the BM occurs at late disease stages, and point on a potential cross-talk between the lung and the BM at early stages of pneumonic plague.

Hematopoietic stem cells: interplay with immunity

Ample evidence indicated that hematopoietic stem cells (HSCs) receive signaling from infection or other immune responses to adjust their differentiation and self-renewal. More recent reports also suggested that, while the bone marrow microenvironment or niche may provide the immune privilege for HSCs, HSCs can present surface immune inhibitors per se to suppress innate immunity and adaptive immunity to evade potential immune surveillance and attack. These findings support the hypothesis that HSCs are capable of interacting with the immune system as signal "receivers" and signal "providers". On the one hand, HSCs are capable of directly sensing the signals from the immune system through their surface receptors to modulate their self-renewal and differentiation ("in" signaling); on the other hand, HSCs display surface immune inhibitory molecules to evade the attack from the innate and adaptive immune systems ("out" signaling). The continuing investigation of the interplay between HSCs and immunity may lead to the open-up of a new research filed - the immunology of stem cells.

Localized mucosal response to intranasal live attenuated influenza vaccine in adults

BACKGROUND

Influenza virus infection is a major public health burden worldwide. Available vaccines include the inactivated intramuscular trivalent vaccine and, more recently, an intranasal live attenuated influenza vaccine (LAIV). The measure of successful vaccination with the inactivated vaccine is a systemic rise in immunoglobulin G (IgG) level, but for the LAIV no such correlate has been established.

METHODS

Seventy-nine subjects were given the LAIV FluMist. Blood was collected prior to vaccination and 3 days and 30 days after vaccination. Nasal wash was collected 3 days and 30 days after vaccination. Responses were measured systemically and in mucosal secretions for cytokines, cell activation profiles, and antibody responses.

RESULTS

Only 9% of subjects who received LAIV seroconverted, while 33% of patients developed at least a 2-fold increase in influenza virus-specific immunoglobulin A (IgA) antibodies in nasal wash. LAIV induced a localized inflammation, as suggested by increased expression of interferon-response genes in mucosal RNA and increased granulocyte colony-stimulating factor (G-CSF) and IP-10 in nasal wash. Interestingly, patients who seroconverted had significantly lower serum levels of G-CSF before vaccination.

CONCLUSIONS

Protection by LAIV is likely provided through mucosal IgA and not by increases in systemic IgG. LAIV induces local inflammation. Seroconversion is achieved in a small fraction of subjects with a lower serum G-CSF level.

Type I interferon induction during influenza virus infection increases susceptibility to secondary Streptococcus pneumoniae infection by negative regulation of γδ T cells

The majority of deaths following influenza virus infection result from secondary bacterial superinfection, most commonly caused by Streptococcus pneumoniae. Several models have been proposed to explain how primary respiratory viral infections exacerbate secondary bacterial disease, but the mechanistic explanations have been contradictory. In this study, mice were infected with S. pneumoniae at different days after primary influenza A (X31) virus infection. Our findings show that the induction of type I interferons (IFNs) during a primary nonlethal influenza virus infection is sufficient to promote a deadly S. pneumoniae secondary infection. Moreover, mice deficient in type I interferon receptor (IFNAR knockout [KO] mice) effectively cleared the secondary bacterial infection from their lungs, increased the recruitment of neutrophils, and demonstrated an enhanced innate expression of interleukin-17 (IL-17) relative to wild-type (WT) mice. Lung γδ T cells were responsible for almost all IL-17 production, and their function is compromised during secondary S. pneumoniae infection of WT but not IFNAR KO mice. Adoptive transfer of γδ T cells from IFNAR KO mice reduced the susceptibility to secondary S. pneumoniae infection in the lung of WT mice. Altogether, our study highlights the importance of type I interferon as a key master regulator that is exploited by opportunistic pathogens such as S. pneumoniae. Our findings may be utilized to design effective preventive and therapeutic strategies that may be beneficial for coinfected patients during influenza epidemics.

Long-term persistence of limited HTLV-I Tax-specific cytotoxic T cell clones in a patient with adult T cell leukemia/lymphoma after allogeneic stem cell transplantation

PURPOSE

Adult T cell leukemia/lymphoma (ATL) is a highly aggressive malignancy of T cells caused by human T cell lymphotropic virus type 1 (HTLV-1). Recent clinical studies have suggested that allogeneic stem cell transplantation (HSCT) improves the clinical course of ATL by harnessing a graft-versus-ATL effect, and that donor-derived HTLV-1 Tax-specific CD8(+) cytotoxic T cells (CTLs) contribute to the graft-versus-ATL effect after HSCT. However, little is known about the immunological characteristics of Tax-specific CTLs in ATL patients who underwent HSCT.

METHODS

We serially analyzed frequencies, differentiation, functions and clonal dynamics of Tax-specific CTLs in paired samples of peripheral blood (PB) and bone marrow (BM) from an ATL patient after HSCT at the single-cell level. We used flowcytometric and single-cell T cell receptor (TCR) repertoire analysis methods without culture steps.

RESULTS

Donor-derived Tax-specific CTLs effectively suppressed HTLV-1 replication in both PB and BM at least during chronic graft-versus-host disease after HSCT. Furthermore, Tax-specific CTLs had comparable properties between BM and PB, except for preferential accumulation in BM rather than PB. Tax-specific CTLs persistently existed as less-differentiated CD45RA(-)CCR7(-) effector memory CTLs based on predominant phenotypes of CD27(+), CD28(+/-) and CD57(+/-). Our approach using single-cell TCR repertoire analysis method showed highly restricted oligoclonal responses of Tax-specific CTLs, and TCR BV7- or BV30- expressing two predominant CTL clones persistently existed and maintained strong cytotoxic activities against HTLV-1 in both PB and BM over three years after HSCT.

CONCLUSIONS

These findings about Tax-specific CTLs provide insights into future directions for studies on immunotherapy against ATL.

Estrogen mediates innate and adaptive immune alterations to influenza infection in pregnant mice

Pregnancy is a leading risk factor for severe complications during an influenza virus infection. Women infected during their second and third trimesters are at increased risk for severe cardiopulmonary complications, premature delivery, and death. Here, we establish a murine model of aerosolized influenza infection during pregnancy. We find significantly altered innate antiviral responses in pregnant mice, including decreased levels of IFN-β, IL-1α, and IFN-γ at early time points of infection. We also find reduced cytotoxic T cell activity and delayed viral clearance. We further demonstrate that pregnancy levels of the estrogen 17-β-estradiol are able to induce key anti-inflammatory phenotypes in immune responses to the virus independently of other hormones or pregnancy-related stressors. We conclude that elevated estrogen levels result in an attenuated anti-viral immune response, and that pregnancy-associated morbidities occur in the context of this anti-inflammatory phenotype.