Innate Immune Protection Research Articles

Bruton's Tyrosine Kinase-Mediated Signaling in Myeloid Cells Is Required for Protective Innate Immunity During Pneumococcal Pneumonia.

Bruton’s tyrosine kinase (Btk) is a cytoplasmic kinase expressed in B cells and myeloid cells. It is essential for B cell development and natural antibody-mediated host defense against bacteria in humans and mice, but little is known about the role of Btk in innate host defense in vivo. Previous studies have indicated that lack of (natural) antibodies is paramount for impaired host defense against Streptococcus (S.) pneumoniae in patients and mice with a deficiency in functional Btk. In the present study, we re-examined the role of Btk in B cells and myeloid cells during pneumococcal pneumonia and sepsis in mice. The antibacterial defense of Btk-/- mice was severely impaired during pneumococcal pneumosepsis and restoration of natural antibody production in Btk-/- mice by transgenic expression of Btk specifically in B cells did not suffice to protect against infection. Btk-/- mice with reinforced Btk expression in MhcII+ cells, including B cells, dendritic cells and macrophages, showed improved antibacterial defense as compared to Btk-/- mice. Bacterial outgrowth in Lysmcre-Btkfl/Y mice was unaltered despite a reduced capacity of Btk-deficient alveolar macrophages to respond to pneumococci. Mrp8cre-Btkfl/Y mice with a neutrophil specific paucity in Btk expression, however, demonstrated impaired antibacterial defense. Neutrophils of Mrp8cre-Btkfl/Y mice displayed reduced release of granule content after pulmonary installation of lipoteichoic acid, a gram-positive bacterial cell wall component relevant for pneumococci. Moreover, Btk deficient neutrophils showed impaired degranulation and phagocytosis upon incubation with pneumococci ex vivo. Taken together, the results of our study indicate that besides regulating B cell-mediated immunity, Btk is critical for regulation of myeloid cell-mediated, and particularly neutrophil-mediated, innate host defense against S. pneumoniae in vivo.

Hypoxia-Inducible Factor-1α in Macrophages, but Not in Neutrophils, Is Important for Host Defense during Klebsiella pneumoniae-Induced Pneumosepsis.

Hypoxia-inducible factor- (HIF-) 1α has been implicated in the ability of cells to adapt to alterations in oxygen levels. Bacterial stimuli can induce HIF1α in immune cells, including those of myeloid origin. We here determined the role of myeloid cell HIF1α in the host response during pneumonia and sepsis caused by the common human pathogen Klebsiella pneumoniae. To this end, we generated mice deficient for HIF1α in myeloid cells (LysM-cre × Hif1αfl/fl) or neutrophils (Mrp8-cre × Hif1αfl/fl) and infected these with Klebsiella pneumoniae via the airways. Myeloid, but not neutrophil, HIF1α-deficient mice had increased bacterial loads in the lungs and distant organs after infection as compared to control mice, pointing at a role for HIF1α in macrophages. Myeloid HIF1α-deficient mice did not show increased bacterial growth after intravenous infection, suggesting that their phenotype during pneumonia was mediated by lung macrophages. Alveolar and lung interstitial macrophages from LysM-cre × Hif1αfl/fl mice produced lower amounts of the immune enhancing cytokine tumor necrosis factor upon stimulation with Klebsiella, while their capacity to phagocytose or to produce reactive oxygen species was unaltered. Alveolar macrophages did not upregulate glycolysis in response to lipopolysaccharide, irrespective of HIF1α presence. These data suggest a role for HIF1α expressed in lung macrophages in protective innate immunity during pneumonia caused by a common bacterial pathogen.

Association Between Bitter Taste Receptor Phenotype and Clinical Outcomes Among Patients With COVID-19

Bitter taste receptors (T2Rs) have been implicated in sinonasal innate immunity, and genetic variation conferred by allelic variants in T2R genes is associated with variation in upper respiratory tract pathogen susceptibility, symptoms, and outcomes. Bitter taste receptor phenotype appears to be associated with the clinical course and symptom duration of SARS-CoV-2 infection. To evaluate the association between T2R phenotype and patient clinical course after infection with SARS-CoV-2. A prospective cohort study was performed from July 1 through September 30, 2020, at a tertiary outpatient clinical practice and inpatient hospital in the United States among 1935 participants (patients and health care workers) with occupational exposure to SARS-CoV-2. Exposure to SARS-CoV-2. Participants underwent T2R38 phenotype taste testing to determine whether they were supertasters (those who experienced greater intensity of bitter tastes), tasters, or nontasters (those who experienced low intensity of bitter tastes or no bitter tastes) and underwent evaluation for lack of infection with SARS-CoV-2 via polymerase chain reaction (PCR) testing and IgM and IgG testing. A group of participants was randomly selected for genotype analysis to correlate phenotype. Participants were followed up until confirmation of infection with SARS-CoV-2 via PCR testing. Phenotype of T2R38 was retested after infection with SARS-CoV-2. The results were compared with clinical course. A total of 1935 individuals (1101 women [56.9%]; mean [SD] age, 45.5 [13.9] years) participated in the study. Results of phenotype taste testing showed that 508 (26.3%) were supertasters, 917 (47.4%) were tasters, and 510 (26.4%) were nontasters. A total of 266 participants (13.7%) had positive PCR test results for SARS-CoV-2. Of these, 55 (20.7%) required hospitalization. Symptom duration among patients with positive results ranged from 0 to 48 days. Nontasters were significantly more likely than tasters and supertasters to test positive for SARS-CoV-2 (odds ratio, 10.1 [95% CI, 5.8-17.8]; P < .001), to be hospitalized once infected (odds ratio, 3.9 [1.5-10.2]; P = .006), and to be symptomatic for a longer duration (mean [SE] duration, 23.7 [0.5] days vs 13.5 [0.4] days vs 5.0 [0.6] days; P < .001). A total of 47 of 55 patients (85.5%) with COVID-19 who required inpatient admission were nontasters. Conversely, 15 of 266 patients (5.6%) with positive PCR test results were supertasters. This cohort study suggests that T2R38 receptor allelic variants were associated with participants' innate immune response toward SARS-CoV-2. The T2R phenotype was associated with patients' clinical course after SARS-CoV-2 infection. Nontasters were more likely to be infected with SARS-CoV-2 than the other 2 groups, suggesting enhanced innate immune protection against SARS-CoV-2.

Old vaccines for new infections: Exploiting innate immunity to control COVID-19 and prevent future pandemics

The COVID-19 pandemic triggered an unparalleled pursuit of vaccines to induce specific adaptive immunity, based on virus-neutralizing antibodies and T cell responses. Although several vaccines have been developed just a year after SARS-CoV-2 emerged in late 2019, global deployment will take months or even years. Meanwhile, the virus continues to take a severe toll on human life and exact substantial economic costs. Innate immunity is fundamental to mammalian host defense capacity to combat infections. Innate immune responses, triggered by a family of pattern recognition receptors, induce interferons and other cytokines and activate both myeloid and lymphoid immune cells to provide protection against a wide range of pathogens. Epidemiological and biological evidence suggests that the live-attenuated vaccines (LAV) targeting tuberculosis, measles, and polio induce protective innate immunity by a newly described form of immunological memory termed “trained immunity.” An LAV designed to induce adaptive immunity targeting a particular pathogen may also induce innate immunity that mitigates other infectious diseases, including COVID-19, as well as future pandemic threats. Deployment of existing LAVs early in pandemics could complement the development of specific vaccines, bridging the protection gap until specific vaccines arrive. The broad protection induced by LAVs would not be compromised by potential antigenic drift (immune escape) that can render viruses resistant to specific vaccines. LAVs might offer an essential tool to “bend the pandemic curve,” averting the exhaustion of public health resources and preventing needless deaths and may also have therapeutic benefits if used for postexposure prophylaxis of disease.

The impact of aging on innate and adaptive immunity in the human female genital tract.

Mucosal tissues in the human female reproductive tract (FRT) are primary sites for both gynecological cancers and infections by a spectrum of sexually transmitted pathogens, including human immunodeficiency virus (HIV), that compromise women's health. While the regulation of innate and adaptive immune protection in the FRT by hormonal cyclic changes across the menstrual cycle and pregnancy are being intensely studied, little to nothing is known about the alterations in mucosal immune protection that occur throughout the FRT as women age following menopause. The immune system in the FRT has two key functions: defense against pathogens and reproduction. After menopause, natural reproductive function ends, and therefore, two overlapping processes contribute to alterations in immune protection in aging women: menopause and immunosenescence. The goal of this review is to summarize the multiple immune changes that occur in the FRT with aging, including the impact on the function of epithelial cells, immune cells, and stromal fibroblasts. These studies indicate that major aspects of innate and adaptive immunity in the FRT are compromised in a site‐specific manner in the FRT as women age. Further, at some FRT sites, immunological compensation occurs. Overall, alterations in mucosal immune protection contribute to the increased risk of sexually transmitted infections (STI), urogenital infections, and gynecological cancers. Further studies are essential to provide a foundation for the development of novel therapeutic interventions to restore immune protection and reverse conditions that threaten women's lives as they age.

HIV Pathogenesis in the Human Female Reproductive Tract.

Women remain disproportionately affected by the HIV/AIDS pandemic. The primary mechanism for HIV acquisition in women is sexual transmission, yet the immunobiological factors that contribute to HIV susceptibility remain poorly characterized. Here, we review current knowledge on HIV pathogenesis in women, focusing on infection and immune responses in the female reproductive tract (FRT). We describe recent findings on innate immune protection and HIV target cell distribution in the FRT. We also review multiple factors that modify susceptibility to infection, including sex hormones, microbiome, trauma, and how HIV risk changes during women's life cycle. Finally, we review current strategies for HIV prevention and identify barriers for research in HIV infection and pathogenesis in women. A complex network of interrelated biological and sociocultural factors contributes to HIV risk in women and impairs prevention and cure strategies. Understanding how HIV establishes infection in the FRT can provide clues to develop novel interventions to prevent HIV acquisition in women.

The interplay between the immune system and viruses.

The human immune response can be divided into two arms: innate and adaptive immunity. The innate immune system consists of "hard-wired" responses encoded by host germline genes. In contrast, the adaptive response consists of gene elements that are somatically rearranged to assemble antigen-binding molecules with specificity for individual foreign structures. In contrast to the adaptive immune system, which depends upon T and B lymphocytes, innate immune protection is a task performed by cells of both hematopoietic and non-hematopoietic origin. Hematopoietic cells involved in innate immune responses include macrophages, dendritic cells, mast cell, neutrophils, eosinophils, natural killer (NK) cells and natural killer T cells. The induction of an adaptive immune response begins when a pathogen is ingested by an Antigen Presenting Cell (APC), such as the Dendritic cell (DC), in the infected tissue. DCs bridge the gap between first line innate responses and powerful adaptive immune responses, by internalizing, processing and presenting antigens on Major Histocompatibility Complex (MHC) and MHC-like molecules to the adaptive immune cells In addition to DCs, macrophages and B cells are deemed antigen presenting cells (Llewelyn & Cohen, 2002).

The downregulation of IL-18R defines bona fide kidney-resident CD8+ Tcells.

SummaryStepwise induction of CD69 and CD103 marks distinct differentiation stages of mucosal Trms. But the majority of non-mucosal Trm lacks CD103 expression. The expression of CD69 alone cannot faithfully define Trm cells in heavily vascularized non-mucosal tissues, such as the kidney. Here, we found that a subset of kidney Trms downregulated IL-18 receptor during differentiation. Via global transcriptional analysis and parabiosis experiments, we have discovered that the downregulation of interleukin-18 receptor (IL-18R) is associated with the establishment of tissue residency. Together with the expression of CD69, IL-18Rlo exclusively identify tissue-resident cells whereas IL-18Rhi population contains both tissue-resident and migratory ones. Local cytokines including transforming growth factor β (TGF-β) and interferon α (IFN-α)/β as well as TGF-β-dependent suppression of transcription factor Tcf-1 are essential for IL-18R downregulation during kidney Trm differentiation. Together, we identified a convenient surface marker to distinguish bona fide kidney-resident CD8+ T cells as well as underlying molecular mechanisms controlling this differentiation process.

The Cutaneous Wound Innate Immunological Microenvironment.

The skin represents the first line of defense and innate immune protection against pathogens. Skin normally provides a physical barrier to prevent infection by pathogens; however, wounds, microinjuries, and minor barrier impediments can present open avenues for invasion through the skin. Accordingly, wound repair and protection from invading pathogens are essential processes in successful skin barrier regeneration. To repair and protect wounds, skin promotes the development of a specific and complex immunological microenvironment within and surrounding the disrupted tissue. This immune microenvironment includes both innate and adaptive processes, including immune cell recruitment to the wound and secretion of extracellular factors that can act directly to promote wound closure and wound antimicrobial defense. Recent work has shown that this immune microenvironment also varies according to the specific context of the wound: the microbiome, neuroimmune signaling, environmental effects, and age play roles in altering the innate immune response to wounding. This review will focus on the role of these factors in shaping the cutaneous microenvironment and how this ultimately impacts the immune response to wounding.

Airway Macrophages Mediate Mucosal Vaccine-Induced Trained Innate Immunity against Mycobacterium tuberculosis in Early Stages of Infection.

Mycobacterium tuberculosis, the causative agent of pulmonary tuberculosis (TB), is responsible for millions of infections and deaths annually. Decades of TB vaccine development have focused on adaptive T cell immunity, whereas the importance of innate immune contributions toward vaccine efficacy has only recently been recognized. Airway macrophages (AwM) are the predominant host cell during early pulmonary M. tuberculosis infection and, therefore, represent attractive targets for vaccine-mediated immunity. We have demonstrated that respiratory mucosal immunization with a viral-vectored vaccine imprints AwM, conferring enhanced protection against heterologous bacterial challenge. However, it is unknown if innate immune memory also protects against M. tuberculosis In this study, by using a murine model, we detail whether respiratory mucosal TB vaccination profoundly alters the airway innate immune landscape associated with AwM prior to M. tuberculosis exposure and whether such AwM play a critical role in host defense against M. tuberculosis infection. Our study reveals an important role of AwM in innate immune protection in early stages of M. tuberculosis infection in the lung.

Antiviral efficacy of orally delivered neoagarohexaose, a nonconventional TLR4 agonist, against norovirus infection in mice

The neoagarohexaose (NA6) is an oligosaccharide that is derived from agarose, the major component of red algae cell walls, by enzymatic hydrolysis. Here we show that NA6 is a noncanonical Toll-like receptor 4 (TLR4) agonist with antiviral activity against norovirus. Its TLR4 activation was dependent on myeloid differentiation factor 2 (MD2) and cluster of differentiation 14 (CD14), leading to interferon-β (IFN-β) and tumor necrosis factor-α (TNF-α) production. This effect was abolished by TLR4 knockdown or knockout in murine macrophages. NA6 inhibited murine norovirus (MNV) replication with an EC50 of 1.5 μM in RAW264.7 cells. It also lowered viral RNA titer in a human hepatocellular carcinoma Huh7-derived cell line harboring a human norovirus subgenomic replicon. The antiviral activity of NA6 was mainly attributed to IFN-β produced through the TLR4-TRIF signaling pathway. NA6-induced TNF-α, which had little effect on norovirus replication per se, primed macrophages to mount greater antiviral innate immune responses when IFN signaling was activated. NA6 boosted the induction of IFN-β in MNV-infected RAW264.7 cells and upregulated IFN-regulatory factor-1, an IFN-stimulated gene. NA6 induced IFN-β expression in the distal ileum with Peyer's patches and oral administration of NA6 reduced MNV loads through activation of TLR4 signaling, highlighting its potential contribution to protective antiviral innate immunity against norovirus.

Fish lysozyme gene family evolution and divergent function in early development

Lysozymes are an ancient group of antimicrobial enzymes of the innate immune system. Here we provide a comparative analysis of the evolution and function of lysozymes during early development in fish, the most speciose vertebrate group. In fishes, lineage and species-specific evolution of both C-type (chicken or conventional) and G-type (goose type) genes occurred. Phylogenetic analysis revealed that the teleost lysozyme G-type members group with the tetrapod homologues but the teleost C-type form three different clusters with the tetrapods. Most of the teleost C-type cluster with tetrapod Lyz but there are some that group with the mammalian Lyzl1/2 and LALBA. This suggests that early in gnathostome evolution these genes already existed and that lyzl1/2 and lalba genes are present in fish and tetrapods. Gene synteny analysis to confirm sequence orthologies failed to identify conserved genome regions between teleosts and other vertebrates lysozyme gene regions suggesting that in the ancestral bony fish genome lyz, lyzl1/2, lalba and lyg precursor genes were transposed to different chromosome regions. The homologue of the mammalian lactalbumin (LALBA) gene was identified for the first time in teleosts and was expressed in skin and during egg and larval development. Lysozyme activity was detected in teleost eggs and varied between species and in the gilthead sea bream lyg and lalba transcript abundance differed in eggs and larvae from different brood stock suggesting differences exist in maternal innate immune protection.

Does High Cardiorespiratory Fitness Confer Some Protection Against Proinflammatory Responses After Infection by SARS-CoV-2?

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) originated in China in late 2019 and has since spread rapidly to every continent in the world. This pandemic continues to cause widespread personal suffering, along with severe pressure on medical and health care providers. The symptoms of SARS‐CoV‐2 and the subsequent prognosis are worsened in individuals who have preexisting comorbidities prior to infection by the virus. Individuals with obesity or overweight, insulin resistance, and diabetes typically have chronic low‐grade inflammation characterized by increased levels of several proinflammatory cytokines and the inflammasome; this state predisposes to greater risk for infection along with more adverse outcomes. Here, we consider whether a high level of cardiorespiratory fitness induced by prior exercise training may confer some innate immune protection against COVID‐19 by attenuating the “cytokine storm syndrome” often experienced by “at risk” individuals.

Protect Pregnant and Lactating Women with COVID-19 Through Research, Not from Research.

Protect Pregnant and Lactating Women with COVID-19 Through Research, Not from Research.

Probiotics, Prebiotics and Synbiotics for Nile tilapia: Growth performance and protection against Aeromonas hydrophila infection

The use of probiotics, prebiotics and synbiotics provides better growth rates, improves the innate immune system and protection against several bacterial pathogens. The species Aeromonas hydrophila causes high mortality rate and production loss, provoking an antimicrobial overuse. This study aimed to prove the capacity of commercial probiotic DBA® (Bifidobacterium sp, Lactobacillus acidophilus and Enterococcus faecium), prebiotics MOS and chitosan, combined as synbiotics or not to promote Nile tilapia growth performance, innate immune system modulation and protection against A. hydrophila. One experiment with 24 units, duration of 63 days, and another experiment infection assay with A. hydrophila (18 experimental units, individual recirculation system, duration of 15 days) were performed. The treatments were: control, probiotic DBA (PRO), the prebiotics mannan oligosaccharides (Actigen®) (MOS) and chitosan (CHI), and the synbiotics composed of probiotic and MOS (Actigen®) (PRO + MOS), probiotic and chitosan (PRO + CHI). Growth performance, hematology, intestinal histology and immunology, and relative protection level against A. hydrophila were analyzed. Significant differences were observed in the final biomass for the treatments PRO + CHI and CHI when compared with PRO + MOS, and greater individual weight gain in group PRO + CHI in relation to group PRO + MOS. High concentrations of Lactobacillus spp. in intestinal tract of probiotics, prebiotics and symbiotics groups were observed. The treatments PRO + MOS, PRO + CHI and PRO promoted apparent preservation of the intestinal epithelium and stimulated an increase in goblet cells, blood vessels and mast cells, associated to immune system. The symbiotics MOS and DBA® promoted better relative protection level with percentage of 40%. This study recommends the use of probiotics, prebiotics and synbiotics to improve the protection against A. hydrophila infection without growth reduction. Inclusion of feed additives may reduce the application of antimicrobials in fish farming.

Should Infants Be Separated from Mothers with COVID-19? First, Do No Harm.

Should Infants Be Separated from Mothers with COVID-19? First, Do No Harm.

Feeding-dependent VIP neuron-ILC3 circuit regulates the intestinal barrier.

The intestinal mucosa serves as both a conduit for uptake of food-derived nutrients and microbiome-derived metabolites and as a barrier that prevents tissue invasion by microbes and tempers inflammatory responses to the myriad contents of the lumen. How the intestine coordinates physiological and immune responses to food consumption to optimize nutrient uptake while maintaining barrier functions remains unclear. Here we show in mice how a gut neuronal signal triggered by food intake is integrated with intestinal antimicrobial and metabolic responses controlled by type 3 innate lymphoid cells (ILC3)1–3. Food consumption rapidly activates a population of enteric neurons that express vasoactive intestinal peptide (VIP)4. Projections of VIP-producing neurons (VIPergic neurons) in the lamina propria are in close proximity to clusters of ILC3 that selectively express VIP receptor type 2 (VIPR2; also known as VPAC2). Production of interleukin (IL)-22 by ILC3, which is up-regulated by commensal microbes such as segmented filamentous bacteria (SFB)5–7, is inhibited upon engagement of VIPR2. As a consequence, there is a reduction in epithelial cell-derived antimicrobial peptide, but enhanced expression of lipid-binding proteins and transporters8. During food consumption, activation of VIPergic neurons thus enhances growth of epithelial-associated SFB and increases lipid absorption. Our results reveal a feeding- and circadian-regulated dynamic intestinal neuro-immune circuit that promotes a trade-off between IL-22-mediated innate immune protection and efficiency of nutrient absorption. Modulation of this pathway may hence be effective for enhancing resistance to enteropathogen2,3,9 and for treatment of metabolic diseases.

MGL1 Receptor Plays a Key Role in the Control of T. cruzi Infection by Increasing Macrophage Activation through Modulation of ERK1/2, c-Jun, NF-κB and NLRP3 Pathways.

Macrophage galactose-C type lectin (MGL)1 receptor is involved in the recognition of Trypanosoma cruzi (T. cruzi) parasites and is important for the modulation of the innate and adaptive immune responses. However, the mechanism by which MGL1 promotes resistance to T. cruzi remains unclear. Here, we show that MGL1 knockout macrophages (MGL1−/− Mφ) infected in vitro with T. cruzi were heavily parasitized and showed decreased levels of reactive oxygen species (ROS), nitric oxide (NO), IL-12 and TNF-α compared to wild-type macrophages (WT Mφ). MGL1−/− Mφ stimulated in vitro with T. cruzi antigen (TcAg) showed low expression of TLR-2, TLR-4 and MHC-II, which resulted in deficient splenic cell activation compared with similar co-cultured WT Mφ. Importantly, the activation of p-ERK1/2, p-c-Jun and p-NF-κB p65 were significantly reduced in MGL1−/− Mφ exposed to TcAg. Similarly, procaspase 1, caspase 1 and NLRP3 inflammasome also displayed a reduced expression that was associated with low IL-β production. Our data reveal a previously unappreciated role for MGL1 in Mφ activation through the modulation of ERK1/2, c-Jun, NF-κB and NLRP3 signaling pathways, and to the development of protective innate immunity against experimental T. cruzi infection.

Infectious Bronchitis Virus Population Structure Defines Immune Response and Protection.

A commercial Arkansas (Ark) Delmarva Poultry Industry (DPI)-type vaccine and a more homogeneous population of that vaccine obtained previously through adaptation to chicken embryo kidney (CEK) cells (CEK-ArkDPI) were used as a model to further understand the impact of population genetic structure on generation of immune responses and protection. In a first experiment, vaccinated chickens were challenged with an IBV Ark99-type virulent strain (AL/4614/98). Despite extensive sequence similarity between the vaccines, the more heterogeneous commercial ArkDPI was more efficient at reducing viral loads in challenged chickens, while respiratory signs and tracheal lesions were reduced similarly by either vaccine. A distinct subpopulation of the Ark challenge virus showing asparagine at S1 position 56 was consistently negatively selected by immune pressure originating from vaccination with either vaccine. Antibody levels and antibody avidity to Ark-type S1 protein were greater in CEK-ArkDPI-vaccinated chickens compared to chickens vaccinated with the more diverse commercial ArkDPI vaccine. Synchronous replication of a homogeneous virus population likely elicits clonal expansion and affinity maturation of a greater number of responding B cells compared to a diverse virus population continuously changing its proportion of phenotypes during replication. The results of a second experiment showed that during initial vaccine virus replication (24 and 48 hr postvaccination), the virus population showing increased diversity (commercial ArkDPI) achieved higher concentrations of IBV RNA in the trachea compared to the more homogenous virus. mRNA expression of genes associated with innate immune responses in the trachea 48 hr postvaccination generally showed greater upregulation in chickens vaccinated with the heterogeneous commercial ArkDPI vaccine compared to the CEK-adapted virus. The greater upregulation of these genes is likely associated with higher virus replication achieved by the heterogeneous commercial vaccine. Thus, while the adaptive antibody response was favored by the more homogenous structure of the CEK-ArkDPI vaccine population (higher antibody levels and antibody avidity), the innate immune response was favored by the more diverse viral population of the commercial ArkDPI. We confirmed previous results that distinct subpopulations in wild Ark challenge virus become selected by immune pressure originating from vaccination, and we concluded that the population structure of IBV vaccines impacts innate immune response, antibody avidity, and protection.

Prekallikrein inhibits innate immune signaling in the lung and impairs host defense during pneumosepsis in mice.

Prekallikrein (PKK, also known as Fletcher factor and encoded by the gene KLKB1 in humans) is a component of the contact system. Activation of the contact system has been implicated in lethality in fulminant sepsis models. Pneumonia is the most frequent cause of sepsis. We sought to determine the role of PKK in host defense during pneumosepsis. To this end, mice were infected with the common human pathogen Klebsiella pneumoniae via the airways, causing an initially localized infection of the lungs with subsequent bacterial dissemination and sepsis. Mice were treated with a selective PKK‐directed antisense oligonucleotide (ASO) or a scrambled control ASO for 3 weeks prior to infection. Host response readouts were determined at 12 or 36 h post‐infection, including genome‐wide messenger RNA profiling of lungs, or mice were followed for survival. PKK ASO treatment inhibited constitutive hepatic Klkb1 mRNA expression by >80% and almost completely abolished plasma PKK activity. Klkb1 mRNA could not be detected in lungs. Pneumonia was associated with a progressive decline in PKK expression in mice treated with control ASO. PKK ASO administration was associated with a delayed mortality, reduced bacterial burdens, and diminished distant organ injury. While PKK depletion did not influence lung pathology or neutrophil recruitment, it was associated with an upregulation of multiple innate immune signaling pathways in the lungs already prior to infection. Activation of the contact system could not be detected, either during infection in vivo or at the surface of Klebsiella in vitro. These data suggest that circulating PKK confines pro‐inflammatory signaling in the lung by a mechanism that does not involve contact system activation, which in the case of respiratory tract infection may impede early protective innate immunity. © 2019 Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.