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Scarring after severe burn is a result of changes in collagen deposition and fibroblast activity that result in repaired but not regenerated tissue. Re-epithelialisation of wounds and dermal cell repopulation has been thought to be driven by cells in the periphery of the wound. However, recent research demonstrated that cells originating from the bone marrow contribute to healing wounds in other tissues and also after incisional injury. We investigated the contribution of bone marrow-derived cells to long-term cell populations in scar tissue (primarily fibroblasts and keratinocytes) after severe burn. Wild-type mice were lethally irradiated and then the bone marrow reconstituted by injection of chimeric bone marrow cells expressing EGFP marker protein. Mice with chimeric bone marrow were then given a burn, either an 1-cm diameter injury (to mimic minor injury) or 2-cm diameter (to mimic moderate injury). Wounds were analysed at days 1, 3, 7, 14, 21, 28, 56 and 120 using FACS and immunohistochemistry to identify the percentage and cell type within the wound originating from the bone marrow. The inflammatory cell infiltrate at the early time-points was bone marrow in origin. At later time-points, we noted that over half of the fibroblast population was bone marrow-derived; we also observed that a small percentage of keratinocytes appeared to be bone marrow in origin. These findings support the theory that the bone marrow plays an important role in providing cells not only for inflammation but also dermal and epidermal cells during burn wound healing. This increases our understanding of cell origins in the healing wound, and has the potential to impact on clinical practice providing a potential mechanism for intervention away from conventional topical treatments and directed instead to systemic treatments affecting the bone marrow response. [ABSTRACT FROM AUTHOR]

Background: Despite vaccination, influenza and otitis media (OM) remain leading causes of illness. We previously found that the human respiratory commensal Haemophilus haemolyticus prevents bacterial infection in vitro and that the related murine commensal Muribacter muris delays OM development in mice. The observation that M muris pretreatment reduced lung influenza titer and inflammation suggests that these bacteria could be exploited for protection against influenza/OM., Methods: Safety and efficacy of intranasal H haemolyticus at 5 × 107 colony-forming units (CFU) was tested in female BALB/cARC mice using an influenza model and influenza-driven nontypeable Haemophilus influenzae (NTHi) OM model. Weight, symptoms, viral/bacterial levels, and immune responses were measured., Results: Intranasal delivery of H haemolyticus was safe and reduced severity of influenza, with quicker recovery, reduced inflammation, and lower lung influenza virus titers (up to 8-fold decrease vs placebo; P ≤ .01). Haemophilus haemolyticus reduced NTHi colonization density (day 5 median NTHi CFU/mL = 1.79 × 103 in treatment group vs 4.04 × 104 in placebo, P = .041; day 7 median NTHi CFU/mL = 28.18 vs 1.03 × 104; P = .028) and prevented OM (17% OM in treatment group, 83% in placebo group; P = .015)., Conclusions: Haemophilus haemolyticus has potential as a live biotherapeutic for prevention or early treatment of influenza and influenza-driven NTHi OM. Additional studies will deem whether these findings translate to humans and other respiratory infections., Competing Interests: Potential conflicts of interest. P. C. R. has served on vaccine scientific advisory boards and together with L. S. K. has received institutional funding for investigator-initiated grants from GlaxoSmithKline, Pfizer, and MSD that are unrelated to this work. L. S. K., P. C. R., and C. M. G. are coinventors on patents filed in 2020 for using Pasteurellaceae species, including H haemolyticus, for prevention of respiratory infections: United States Patent and Trademark Office Application number: 17/337052 and Australian Patent Office Application number: 2020203634 (“Treating or preventing respiratory infection”; priority date: 2 June 2020; inventors: L. S. K., P. C. R., C. M. G.). K. R. S. is a consultant for Sanofi, Roche, and Novo Nordisk. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The bone marrow is a specialized niche responsible for the maintenance of hematopoietic stem and progenitor cells during homeostasis and inflammation. Recent studies, however, have extended this essential role to the extramedullary and extravascular lung microenvironment. Here, we provide further evidence for a reservoir of hematopoietic stem and progenitor cells within the lung from Embryonic Day 18.5 until adulthood. These lung progenitors display distinct microenvironment-specific developmental kinetics compared with their bone marrow counterparts, exemplified by a rapid shift from a common myeloid to a megakaryocyte-erythrocyte progenitor-dominated niche with increasing age. In adult mice, influenza A viral infection results in a transient reduction in multipotent progenitors within the lungs, with a parallel increase in downstream granulocyte-monocyte progenitors and dendritic cell populations associated with acute viral infections. Our findings suggest that lung hematopoietic progenitors play a role in reestablishing immunological homeostasis in the respiratory mucosa, which may have significant clinical implications for maintaining pulmonary health after inflammatory perturbation.

Background: Impaired interferon response and allergic sensitization may contribute to virus-induced wheeze and asthma development in young children. Plasmacytoid dendritic cells (pDCs) play a key role in antiviral immunity as critical producers of type I interferons. pDCs also express the high-affinity IgE receptor through which type I interferon production may be negatively regulated. Whether antiviral function of pDCs is associated with recurrent episodes of wheeze in young children is not well understood., Objective: We sought to evaluate the phenotype and function of circulating pDCs in children with a longitudinally defined wheezing phenotype., Methods: We performed multiparameter flow cytometry on PBMCs from 38 children presenting to the emergency department with an acute episode of respiratory wheeze and 19 controls. RNA sequencing on isolated pDCs from the same individuals was also performed. For each subject, their longitudinal exacerbation phenotype was determined using the Western Australia public hospital database., Results: We observed a significant depletion of circulating pDCs in young children with a persistent phenotype of wheeze. The same individuals also displayed upregulation of the FcεRI on their pDCs. Based on transcriptomic analysis, pDCs from these individuals did not mount a robust systemic antiviral response as observed in children who displayed a nonrecurrent wheezing phenotype., Conclusions: Our data suggest that circulating pDC phenotype and function are altered in young children with a persistent longitudinal exacerbation phenotype. Expression of high-affinity IgE receptor is increased and their function as major interferon producers is impaired during acute exacerbations of wheeze., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Human perinatal life is characterized by a period of extraordinary change during which newborns encounter abundant environmental stimuli and exposure to potential pathogens. To meet such challenges, the neonatal immune system is equipped with unique functional characteristics that adapt to changing conditions as development progresses across the early years of life, but the molecular characteristics of such adaptations remain poorly understood. The application of single cell genomics to birth cohorts provides an opportunity to investigate changes in gene expression programs elicited downstream of innate immune activation across early life at unprecedented resolution., Methods: In this study, we performed single cell RNA-sequencing of mononuclear cells collected from matched birth cord blood and 5-year peripheral blood samples following stimulation (18hrs) with two well-characterized innate stimuli; lipopolysaccharide (LPS) and Polyinosinic:polycytidylic acid (Poly(I:C))., Results: We found that the transcriptional response to LPS was constrained at birth and predominantly partitioned into classical proinflammatory gene upregulation primarily by monocytes and Interferon (IFN)-signaling gene upregulation by lymphocytes. Moreover, these responses featured substantial cell-to-cell communication which appeared markedly strengthened between birth and 5 years. In contrast, stimulation with Poly(I:C) induced a robust IFN-signalling response across all cell types identified at birth and 5 years. Analysis of gene regulatory networks revealed IRF1 and STAT1 were key drivers of the LPS-induced IFN-signaling response in lymphocytes with a potential developmental role for IRF7 regulation., Conclusion: Additionally, we observed distinct activation trajectory endpoints for monocytes derived from LPS-treated cord and 5-year blood, which was not apparent among Poly(I:C)-induced monocytes. Taken together, our findings provide new insight into the gene regulatory landscape of immune cell function between birth and 5 years and point to regulatory mechanisms relevant to future investigation of infection susceptibility in early life., Competing Interests: JFR and AB are co-inventors on a patent application that is related to this work. JFR and AB are co-founders, equity holders, and directors of the startup company Respiradigm Pty Ltd and subsidiary First Breath Health Pty Ltd that are related to this work. AB is the founder of the startup company INSiGENe Pty Ltd that is unrelated to this work. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Read, Serralha, Armitage, Iqbal, Cruickshank, Saxena, Strickland, Waithman, Holt and Bosco.)

Asthma exacerbations in children are associated with respiratory viral infection and atopy, resulting in systemic immune activation and infiltration of immune cells into the airways. The gene networks driving the immune activation and subsequent migration of immune cells into the airways remains incompletely understood. Cellular and molecular profiling of PBMC was employed on paired samples obtained from atopic asthmatic children (n = 19) during acute virus-associated exacerbations and later during convalescence. Systems level analyses were employed to identify coexpression networks and infer the drivers of these networks, and validation was subsequently obtained via independent samples from asthmatic children. During exacerbations, PBMC exhibited significant changes in immune cell abundance and upregulation of complex interlinked networks of coexpressed genes. These were associated with priming of innate immunity, inflammatory and remodelling functions. We identified activation signatures downstream of bacterial LPS, glucocorticoids and TGFB1. We also confirmed that LPS binding protein was upregulated at the protein-level in plasma. Multiple gene networks known to be involved positively or negatively in asthma pathogenesis, are upregulated in circulating PBMC during acute exacerbations, supporting the hypothesis that systemic pre-programming of potentially pathogenic as well as protective functions of circulating immune cells preceeds migration into the airways. Enhanced sensitivity to LPS is likely to modulate the severity of acute asthma exacerbations through exposure to environmental LPS., (© 2023. The Author(s).)

There are well-described sex-based differences in how the immune system operates. In particular, cisgender (cis) females have a more easily activated immune system; associated with an increased prevalence of autoimmune diseases and adverse events following vaccinations. Conversely, cis males have a higher threshold for immune activation, and are more prone to certain infectious diseases, such as coronavirus disease (COVID-19). Oestrogen and testosterone have immune-modulatory properties, and it is likely that these contribute to the sexual dimorphism of the immune system. There are also important immune-related genes located on the X chromosome, such as toll-like receptor (TLR) 7/8; and the mosaic bi-allelic expression of such genes may contribute to the state of immune hyperactivation in cis females. The scientific literature strongly suggests that sex-based differences in the functioning of the immune system are related to both X-linked genes and immune modulation by sex hormones. However, it is currently not clear how this impacts transgender (trans) people receiving gender-affirming hormonal therapy. Moreover, it is estimated that in Australia, at least 2.3% of adolescents identify as trans and/or gender diverse, and referrals to specialist gender-affirming care are increasing each year. Despite the improving social awareness of trans people, they remain chronically underrepresented in the scientific literature. In addition, a small number of case studies describe new onset autoimmune disorders in adult trans females following oestrogen use. However, there is currently minimal long-term research with an immunological focus on trans people. Therefore, to ensure the positive health outcomes of trans people, it is crucial that the role of sex hormones in immune modulation is investigated further., Competing Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s), 2022.)

Appropriate innate immune function is essential to limit pathogenesis and severity of severe lower respiratory infections (sLRI) during infancy, a leading cause of hospitalization and risk factor for subsequent asthma in this age group. Employing a systems biology approach to analysis of multi-omic profiles generated from a high-risk cohort (n=50), we found that the intensity of activation of an LPS-induced interferon gene network at birth was predictive of sLRI risk in infancy (AUC=0.724). Connectivity patterns within this network were stronger among susceptible individuals, and a systems biology approach identified IRF1 as a putative master regulator of this response. These findings were specific to the LPS-induced interferon response and were not observed following activation of viral nucleic acid sensing pathways. Comparison of responses at birth versus age 5 demonstrated that LPS-induced interferon responses but not responses triggered by viral nucleic acid sensing pathways may be subject to strong developmental regulation. These data suggest that the risk of sLRI in early life is in part already determined at birth, and additionally that the developmental status of LPS-induced interferon responses may be a key determinant of susceptibility. Our findings provide a rationale for the identification of at-risk infants for early intervention aimed at sLRI prevention and identifies targets which may be relevant for drug development., Competing Interests: JFR and AB are co-inventors on a provisional patent filed subsequent to this work. JFR and AB are co-founders, equity holders, and directors of a startup company Respiradigm Pty Ltd related to this provisional patent. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Read, Serralha, Mok, Holt, Cruickshank, Karpievitch, Broadhurst, Sly, Strickland, Reinke, Holt and Bosco.)

A significant proportion of chronic obstructive pulmonary disease exacerbations are strongly associated with rhinovirus infection (HRV). In this study, we combined long-term cigarette smoke exposure with HRV infection in a mouse model. Our aim was to better understand the effects of HRV infection on such exacerbations, using a realistic method for generating a COPD-like phenotype. After 12-weeks of cigarette smoke exposure, adult female BALB/c mice were infected with HRV-1A and three days later we assessed a range of outcomes including lung volume and function, collected lung tissue for measurement of viral titre, bronchoalveolar lavage for assessment of pulmonary inflammation and levels of key mediators, and fixed lungs for stereological structural analyses. Cigarette smoke exposure alone significantly increased total cells and macrophages, and reduced MIP-2 in bronchoalveolar lavage. HRV-1A infection alone increased neutrophilic inflammation, IP-10 and total protein in lavage and also increased specific airway resistance measured at functional residual capacity. Cigarette smoke and HRV-1A together impacted various lung structural parameters including increasing stereological lung volume. Our results show that long-term cigarette smoke exposure and HRV-1A infection both individually impact respiratory outcomes and combine to alter aspects of lung structure in a mouse model, thus providing insight into the development of future mechanistic studies and appropriate interventions in human disease., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Environmental exposures during pregnancy that alter both the maternal gut microbiome and the infant's risk of allergic disease and asthma include a traditional farm environment and consumption of unpasteurized cow's milk, antibiotic use, dietary fiber, and psychosocial stress. Multiple mechanisms acting in concert may underpin these associations and prime the infant to acquire immune competence and homeostasis following exposure to the extrauterine environment. Cellular and metabolic products of the maternal gut microbiome can promote the expression of microbial pattern recognition receptors, as well as thymic and bone marrow hematopoiesis relevant to regulatory immunity. At birth, transmission of maternally derived bacteria likely leverages this in utero programming to accelerate postnatal transition from a T H 2- to T H 1- and T H 17-dominant immune phenotype and maturation of regulatory immune mechanisms, which in turn reduce the child's risk of allergic disease and asthma. Although our understanding of these phenomena is rapidly evolving, the field is relatively nascent, and we are yet to translate existing knowledge into interventions that substantially reduce disease risk in humans. Here, we review evidence that the maternal gut microbiome impacts the offspring's risk of allergic disease and asthma, discuss challenges and future directions for the field, and propose the hypothesis that maternal carriage of Prevotella copri during pregnancy decreases the offspring's risk of allergic disease via production of succinate, which in turn promotes bone marrow myelopoiesis of dendritic cell precursors in the fetus., (Copyright © 2021 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Brown adipose tissue (BAT) may be an important metabolic regulator of whole-body glucose. While important roles have been ascribed to macrophages in regulating metabolic functions in BAT, little is known of the roles of other immune cells subsets, particularly dendritic cells (DCs). Eating a high-fat diet may compromise the development of hematopoietic stem and progenitor cells (HSPCs)-which give rise to DCs-in bone marrow, with less known of its effects in BAT. We have previously demonstrated that ongoing exposure to low-dose ultraviolet radiation (UVR) significantly reduced the 'whitening' effect of eating a high-fat diet upon interscapular (i) BAT of mice. Here, we examined whether this observation may be linked to changes in the phenotype of HSPCs and myeloid-derived immune cells in iBAT and bone marrow of mice using 12-colour flow cytometry. Many HSPC subsets declined in both iBAT and bone marrow with increasing metabolic dysfunction. Conversely, with rising adiposity and metabolic dysfunction, conventional DCs (cDCs) increased in both of these tissues. When compared with a low-fat diet, consumption of a high-fat diet significantly reduced proportions of myeloid, common myeloid and megakaryocyte-erythrocyte progenitors in iBAT, and short-term hematopoietic stem cells in bone marrow. In mice fed the high-fat diet, exposure to low-dose UVR significantly reduced proportions of cDCs in iBAT, independently of nitric oxide release from irradiated skin [blocked using the scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO)], but did not significantly modify HSPC subsets in either tissue. Further studies are needed to determine whether changes in these cell populations contribute towards metabolic dysfunction ., (© 2021 Australian and New Zealand Society for Immunology, Inc.)

High risk for virus-induced asthma exacerbations in children is associated with an IRF7lo immunophenotype, but the underlying mechanisms are unclear. Here, we applied a Systems Biology approach to an animal model comprising rat strains manifesting high (BN) versus low susceptibility (PVG) to experimental asthma, induced by virus/allergen coexposure, to elucidate the mechanism(s)-of-action of the high-risk asthma immunophenotype. We also investigated potential risk mitigation via pretreatment with the immune training agent OM-85. Virus/allergen coexposure in low-risk PVG rats resulted in rapid and transient airways inflammation alongside IRF7 gene network formation. In contrast, responses in high-risk BN rats were characterized by severe airways eosinophilia and exaggerated proinflammatory responses that failed to resolve, and complete absence of IRF7 gene networks. OM-85 had more profound effects in high-risk BN rats, inducing immune-related gene expression changes in lung at baseline and reducing exaggerated airway inflammatory responses to virus/allergen coexposure. In low-risk PVG rats, OM-85 boosted IRF7 gene networks in the lung but did not alter baseline gene expression or cellular influx. Distinct IRF7-associated asthma risk immunophenotypes have dichotomous responses to virus/allergen coexposure and respond differentially to OM-85 pretreatment. Extrapolating to humans, our findings suggest that the beneficial effects OM-85 pretreatment may preferentially target those in high-risk subgroups., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 de Jong, Lauzon-Joset, Leffler, Serralha, Larcombe, Christophersen, Holt, Strickland and Bosco.)

The gut microbiota is influenced by environmental factors such as food. Maternal diet during pregnancy modifies the gut microbiota composition and function, leading to the production of specific compounds that are transferred to the fetus and enhance the ontogeny and maturation of the immune system. Prebiotics are fermented by gut bacteria, leading to the release of short-chain fatty acids that can specifically interact with the immune system, inducing a switch toward tolerogenic populations and therefore conferring health benefits. In this study, pregnant BALB/cJRj mice were fed either a control diet or a diet enriched in prebiotics (Galacto-oligosaccharides/Inulin). We hypothesized that galacto-oligosaccharides/inulin supplementation during gestation could modify the maternal microbiota, favoring healthy immune imprinting in the fetus. Galacto-oligosaccharides/inulin supplementation during gestation increases the abundance of Bacteroidetes and decreases that of Firmicutes in the gut microbiota, leading to increased production of fecal acetate, which was found for the first time in amniotic fluid. Prebiotic supplementation increased the abundance of regulatory B and T cells in gestational tissues and in the fetus. Interestingly, these regulatory cells remained later in life. In conclusion, prebiotic supplementation during pregnancy leads to the transmission of specific microbial and immune factors from mother to child, allowing the establishment of tolerogenic immune imprinting in the fetus that may be beneficial for infant health outcomes., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Brosseau, Selle, Duval, Misme-Aucouturier, Chesneau, Brouard, Cherbuy, Cariou, Bouchaud, Mincham, Strickland, Barbarot and Bodinier.)

Objectives: Incomplete maturation of immune regulatory functions at birth is antecedent to the heightened risk for severe respiratory infections during infancy. Our forerunner animal model studies demonstrated that maternal treatment with the microbial-derived immune training agent OM-85 during pregnancy promotes accelerated postnatal maturation of mechanisms that regulate inflammatory processes in the offspring airways. Here, we aimed to provide proof of concept for a novel solution to reduce the burden and potential long-term sequelae of severe early-life respiratory viral infection through maternal oral treatment during pregnancy with OM-85, already in widespread human clinical use., Methods: In this study, we performed flow cytometry and targeted gene expression (RT-qPCR) analysis on lungs from neonatal offspring whose mothers received oral OM-85 treatment during pregnancy. We next determined whether neonatal offspring from OM-85 treated mothers demonstrate enhanced protection against lethal lower respiratory infection with mouse-adapted rhinovirus (vMC 0 ), and associated lung immune changes., Results: Offspring from mothers treated with OM-85 during pregnancy display accelerated postnatal seeding of lung myeloid populations demonstrating upregulation of function-associated markers. Offspring from OM-85 mothers additionally exhibit enhanced expression of TLR4/7 and the IL-1β/NLRP3 inflammasome complex within the lung. These treatment effects were associated with enhanced capacity to clear an otherwise lethal respiratory viral infection during the neonatal period, with concomitant regulation of viral-induced IFN response intensity., Conclusion: These results demonstrate that maternal OM-85 treatment protects offspring against lethal neonatal respiratory viral infection by accelerating development of innate immune mechanisms crucial for maintenance of local immune homeostasis in the face of pathogen challenge., Competing Interests: All authors declare that no competing interests exist., (© 2021 The Authors. Clinical & Translational Immunology published by John Wiley & Sons Australia, Ltd on behalf of Australian and New Zealand Society for Immunology, Inc.)

We recently reported that offspring of mice treated during pregnancy with the microbial-derived immunomodulator OM-85 manifest striking resistance to allergic airways inflammation, and localized the potential treatment target to fetal conventional dendritic cell (cDC) progenitors. Here, we profile maternal OM-85 treatment-associated transcriptomic signatures in fetal bone marrow, and identify a series of immunometabolic pathways which provide essential metabolites for accelerated myelopoiesis. Additionally, the cDC progenitor compartment displayed treatment-associated activation of the XBP1-ERN1 signalling axis which has been shown to be crucial for tissue survival of cDC, particularly within the lungs. Our forerunner studies indicate uniquely rapid turnover of airway mucosal cDCs at baseline, with further large-scale upregulation of population dynamics during aeroallergen and/or pathogen challenge. We suggest that enhanced capacity for XBP1-ERN1-dependent cDC survival within the airway mucosal tissue microenvironment may be a crucial element of OM-85-mediated transplacental innate immune training which results in postnatal resistance to airway inflammatory disease., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Mincham, Jones, Bodinier, Scott, Lauzon-Joset, Stumbles, Bosco, Holt and Strickland.)

The prenatal and perinatal environments can have profound effects on the development of chronic inflammatory diseases. However, mechanistic insight into how the early-life microenvironment can impact upon development of the lung and immune system and consequent initiation and progression of respiratory diseases is still emerging. Recent studies investigating the developmental origins of lung diseases have started to delineate the effects of early-life changes in the lung, environmental exposures and immune maturation on the development of childhood and adult lung diseases. While the influencing factors have been described and studied in mostly animal models, it remains challenging to pinpoint exactly which factors and at which time point are detrimental in lung development leading to respiratory disease later in life. To advance our understanding of early origins of chronic lung disease and to allow for proper dissemination and application of this knowledge, we propose four major focus areas: 1) policy and education; 2) clinical assessment; 3) basic and translational research; and 4) infrastructure and tools, and discuss future directions for advancement. This review is a follow-up of the discussions at the European Respiratory Society Research Seminar "Early origins of lung disease: towards an interdisciplinary approach" (Lisbon, Portugal, November 2019)., Competing Interests: Conflict of interest: N.D.J. Ubags has nothing to disclose. Conflict of interest: M.A. Alejandre Alcazar reports grants from Deutsche Forschungsgemeinschaft, Marga and Walter Boll Stiftung and Stiftung Oskar-Helene-Heim, during the conduct of the study. Conflict of interest: S.G. Kallapur has nothing to disclose. Conflict of interest: S. Knapp reports grants from Austrian Science Fund, during the conduct of the study. Conflict of interest: S. Lanone has nothing to disclose. Conflict of interest: C.M. Lloyd has nothing to disclose. Conflict of interest: R.E. Morty has nothing to disclose. Conflict of interest: C. Pattaroni has nothing to disclose. Conflict of interest: N.L. Reynaert reports grants from Lung Foundation Netherlands, during the conduct of the study. Conflict of interest: R.J. Rottier has nothing to disclose. Conflict of interest: H.H. Smits has nothing to disclose. Conflict of interest: W.A.A. de Steenhuijsen Piters has nothing to disclose. Conflict of interest: D.H. Strickland has nothing to disclose. Conflict of interest: J.J.P. Collins reports grants from Lung Foundation Netherlands, during the conduct of the study., (Copyright ©ERS 2020.)

Background: Low vitamin D levels have been associated with allergic diseases. Vitamin D has potent immunomodulatory properties, but the mechanisms remain unclear. We have investigated the effect of oral vitamin D supplementation on circulating immune cell phenotypes in infants., Method: A double-blinded randomised controlled trial was conducted to investigate the effect of oral vitamin D supplementation (400 IU/d) on eczema and immune development. A subset of 78 infants was included in this analysis. Phenotypic analysis of immune cell subsets was performed using flow cytometry., Results: Vitamin D supplementation resulted in median 25(OH)D levels of 80.5 vs 59.5 nmol/L in the placebo group at 3 months of age (P = .002) and 87.5 vs 77 nmol/L at 6 months of age (P = .08). We observed significant changes in immune cell composition from birth (cord blood) to 6 months of age. Vitamin D supplementation did not impact these changes, nor did immune cell composition correlate with plasma 25(OH)D levels. Through exploratory analysis, we identified possible associations with eczema development and increased abundance of naïve CD4 - T cells at birth, as well as associations with basophils, iNKT and central memory CD4 + T cells, and altered expression patterns of IgE receptor (FcεR1) on monocytes and dendritic cells with eczema at 6 months., Conclusions: Vitamin D supplementation in infants who were vitamin D sufficient at birth did not affect developmental changes in immune cells during the first 6 months of life. However, immune cell profiles at birth and at 6 months of age were associated with early life eczema., (© 2020 EAACI and John Wiley and Sons A/S. Published by John Wiley and Sons Ltd.)

Nasopharyngeal colonization with nontypeable Haemophilus influenzae (NTHi) is a prerequisite for developing NTHi-associated infections, including otitis media. Therapies that block NTHi colonization may prevent disease development. We previously demonstrated that Haemophilus haemolyticus , a closely related human commensal, can inhibit NTHi colonization and infection of human respiratory epithelium in vitro We have now assessed whether Muribacter muris (a rodent commensal from the same family) can prevent NTHi colonization and disease in vivo using a murine NTHi otitis media model. Otitis media was modeled in BALB/c mice using coinfection with 1 × 10 4.5 PFU of influenza A virus MEM H3N2, followed by intranasal challenge with 5 × 10 7 CFU of NTHi R2866 Spec r Mice were pretreated or not with an intranasal inoculation of 5 × 10 7 CFU M. muris 24 h before coinfection. NTHi and M. muris viable counts and inflammatory mediators (gamma interferon [IFN-γ], interleukin-1β [IL-1β], IL-6, keratinocyte chemoattractant [KC], and IL-10) were measured in nasal washes and middle ear tissue homogenate. M. muris pretreatment decreased the median colonization density of NTHi from 6 × 10 5 CFU/ml to 9 × 10 3 CFU/ml ( P  = 0.0004). Only 1/12 M. muris -pretreated mice developed otitis media on day 5 compared to 8/15 mice with no pretreatment (8% versus 53%, P  = 0.0192). Inflammation, clinical score, and weight loss were also lower in M. muris -pretreated mice. We have demonstrated that a single dose of a closely related commensal can delay onset of NTHi otitis media in vivo Human challenge studies investigating prevention of NTHi colonization are warranted to reduce the global burden of otitis media and other NTHi diseases., (Copyright © 2020 Granland et al.)

Background: The prevalence and severity of asthma, particularly the most common (atopic) form of the disease, increase amongst females but not males after puberty, and asthma activity also changes throughout the menstrual cycle and during pregnancy. The contribution of female sex hormones to asthma pathogenesis is incompletely understood., Objective: To obtain insight into the role of oestrogen (E2) in experimental atopic asthma, and guide future research on sex-related variations in atopic asthma susceptibility/intensity in humans., Methods: We utilized an experimental model comprising rat strains expressing dichotomous Th2-high vs Th2-low immunophenotypes exemplified by eosinophilia, mirroring differences between human atopics/non-atopics. We compared the efficiency of Th2-associated immunoinflammatory mechanisms, which differed markedly between the two strains, and between sexes in the Th2-high strain, and determined the effects of E2 administration on these differences., Results: Unique to the Th2-high strain, eosinophil: neutrophil ratios in the airways at baseline and following sensitization/aeroallergen challenge were logfold higher in females relative to males, and this was reflected by higher baseline blood eosinophil numbers in females. Pretreatment of Th2-high males with E2 abrogated this sex difference by selectively boosting Th2-associated genes in the airways and eosinophilia, but was without corresponding effect in the Th2-low strain. In contrast, parallel E2 effects on myeloid and lymphoid cell populations were relatively modest., Conclusions and Clinical Relevance: E2 acts to amplify the eosinophilic component of pre-existing Th2-high immunophenotype, possibly acting at the level of the common eosinophil/neutrophil precursor in bone marrow to preferentially drive eosinophil differentiation. Constitutive granulocyte profiles in which the balance between eosinophils and neutrophils is skewed towards eosinophils have been identified in independent cohort studies as markers of asthma risk, and these findings suggest that more detailed studies on the role of E2 in this context, and in relation to asthma pathogenesis in post-pubertal females in particular, appear warranted., (© 2019 John Wiley & Sons Ltd.)

Dendritic cells (DCs) play a central role in regulating innate and adaptive immune responses. It is well accepted that their regulatory functions change over the life course. In order to study DCs function during early life it is important to characterize the function of neonatal DCs. However, the availability of neonatal DCs is limited due to ethical reasons or relative small samples of cord blood making it difficult to perform large-scale experiments. Our aim was to establish a robust protocol for the generation of neonatal DCs from cord blood derived CD34+ hematopoietic stem cells. For the expansion of DC precursor cells we used a cytokine cocktail containing Flt-3 L, SCF, TPO, IL-3 and IL-6. The presence of IL-3 and IL-6 in the first 2 weeks of expansion culture was essential for the proliferation of DC precursor cells expressing CD14. After 4 weeks in culture, CD14+ precursor cells were selected and functional DCs were generated in the presence of GM-CSF and IL-4. Neonatal DCs were then stimulated with Poly(I:C) and LPS to mimic viral or bacterial infections, respectively. Poly(I:C) induced a higher expression of the maturation markers CD80, CD86 and CD40 compared to LPS. In line with literature data using cord blood DCs, our Poly(I:C) matured neonatal DCs cells showed a higher release of IL-12p70 compared to LPS matured neonatal DCs. Additionally, we demonstrated a higher release of IFN-γ, TNF-α, IL-1β and IL-6, but lower release of IL-10 in Poly(I:C) matured compared to LPS matured neonatal DCs derived from cord blood CD34+ hematopoietic stem cells. In summary, we established a robust protocol for the generation of large numbers of functional neonatal DCs. In line with previous studies, we showed that neonatal DCs generated form CD34+ cord blood progenitors have a higher inflammatory potential when exposed to viral than bacterial related stimuli., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Antigen-specific IgE binds the Fcε receptor I (FcεRI) expressed on several types of immune cells, including dendritic cells (DCs). Activation of FcεRI on DCs in atopics has been shown to modulate immune responses that potentially contribute to asthma development. However, the extent to which DC subsets differ in FcεRI expression between atopic children with or without asthma is currently not clear. This study aimed to analyse the expression of FcεRI on peripheral blood mononuclear cells (PBMCs) from atopic children with and without asthma, and non-atopic/non-asthmatic age-matched healthy controls., Methods: We performed multiparameter flow cytometry on PBMC from 391 children across three community cohorts and one clinical cohort based in Western Australia., Results: We confirmed expression of FcεRI on basophils, monocytes, plasmacytoid and conventional DCs, with higher proportions of all cell populations expressing FcεRI in atopic compared to non-atopic children. Further, we observed that levels of FcεRI expression were elevated across plasmacytoid and conventional DC as well as basophils in atopic asthmatic compared to atopic non-asthmatic children also after adjusting for serum IgE levels., Conclusion: Our data suggest that the expression pattern of FcεRI on DC and basophils differentiates asthmatic from non-asthmatic atopic children. Given the significant immune modulatory effects observed as a consequence of FcεRI expression, this altered expression pattern is likely to contribute to asthma pathology in children., (© 2019 EAACI and John Wiley and Sons A/S. Published by John Wiley and Sons Ltd.)

Rationale: A subset of infants are hypersusceptible to severe/acute viral bronchiolitis (AVB), for reasons incompletely understood. Objectives: To characterize the cellular/molecular mechanisms underlying infant AVB in circulating cells/local airway tissues. Methods: Peripheral blood mononuclear cells and nasal scrapings were obtained from infants (<18 mo) and children (≥18 mo to 5 yr) during AVB and after convalescence. Immune response patterns were profiled by multiplex analysis of plasma cytokines, flow cytometry, and transcriptomics (RNA-Seq). Molecular profiling of group-level data used a combination of upstream regulator and coexpression network analysis, followed by individual subject-level data analysis using personalized N -of-1-pathways methodology. Measurements and Main Results: Group-level analyses demonstrated that infant peripheral blood mononuclear cell responses were dominated by monocyte-associated hyperupregulated type 1 IFN signaling/proinflammatory pathways (drivers: TNF [tumor necrosis factor], IL-6, TREM1 [triggering receptor expressed on myeloid cells 1], and IL-1B), versus a combination of inflammation (PTGER2 [prostaglandin E receptor 2] and IL-6) plus growth/repair/remodeling pathways (ERBB2 [erbb-b2 receptor tyrosine kinase 2], TGFB1 [transforming growth factor-β1], AREG [amphiregulin], and HGF [hepatocyte growth factor]) coupled with T-helper cell type 2 and natural killer cell signaling in children. Age-related differences were not attributable to differential steroid usage or variations in underlying viral pathogens. Nasal mucosal responses were comparable qualitatively in infants/children, dominated by IFN types 1-3, but the magnitude of upregulation was higher in infants (range, 6- to 48-fold) than children (5- to 17-fold). N -of-1-pathways analysis confirmed differential upregulation of innate immunity in infants and natural killer cell networks in children, and additionally demonstrated covert AVB response subphenotypes that were independent of chronologic age. Conclusions: Dysregulated expression of IFN-dependent pathways after respiratory viral infections is a defining immunophenotypic feature of AVB-susceptible infants and a subset of children. Susceptible subjects seem to represent a discrete subgroup who cluster based on (slow) kinetics of postnatal maturation of innate immune competence.

Background: Influenza virus infection during pregnancy is associated with enhanced disease severity. However, the underlying mechanisms are still not fully understood. We hypothesized that normal alveolar macrophage (AM) functions, which are central to maintaining lung immune homeostasis, are altered during pregnancy and that this dysregulation contributes to the increased inflammatory response to influenza virus infection., Methods: Time-mated BALB/c mice were infected with a low dose of H1N1 influenza A virus at gestation day 9.5. Inflammatory cells in bronchoalveolar lavage (BAL) fluid were assessed by flow cytometry., Results: Our findings confirm previous reports of increased severity of influenza virus infection in pregnant mice. The heightened inflammatory response detected in BAL fluid from infected pregnant mice was characterized by neutrophil-rich inflammation with concomitantly reduced numbers of AM, which were slower to return to baseline counts, compared with nonpregnant infected mice. The increased infection severity and inflammatory responses to influenza during pregnancy were associated with a pregnancy-induced shift in AM phenotype at homeostatic baseline, from the M1 (ie, classical activation) state toward the M2 (ie, alternative activation) state, as evidence by increased expression of CD301 and reduced levels of CCR7., Conclusion: These results show that pregnancy is associated with an alternatively activated phenotype of AM before infection, which may contribute to heightened disease severity., (© The Author(s) 2018. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Murine models of allergic airway disease are frequently used as a tool to elucidate the cellular and molecular mechanisms of tissue-specific asthmatic disease pathogenesis. Paramount to the success of these models is the induction of experimental antigen sensitization, as indicated by the presence of antigen-specific serum immunoglobulin E. The quantification of antigen-specific serum IgE is routinely performed via enzyme-linked immunosorbent assay. However, the reproducibility of these in vitro assays can vary dramatically in our experience. Furthermore, quantifying IgE via in vitro methodologies does not enable the functional relevance of circulating IgE levels to be considered. As a biologically appropriate alternative method, we describe herein a highly reproducible in vivo passive cutaneous anaphylaxis assay using Sprague Dawley rats for the quantification of ovalbumin-specific IgE in serum samples from ovalbumin-sensitized murine models. Briefly, this in vivo assay involves subcutaneous injections of serum samples on the back of a Sprague Dawley rat, followed 24 h later by intravenous injection of ovalbumin and a blue detection dye. The subsequent result of antigen-IgE mediated inflammation and leakage of blue dye into the initial injection site indicates the presence of ovalbumin-specific IgE within the corresponding serum sample., Competing Interests: Competing interestsThe authors declare no financial or non-financial competing interests related to this work., (Copyright © 2019 The Authors; exclusive licensee Bio-protocol LLC.)

The early life period represents a time of immunological plasticity whereby the functionally immature immune system is highly susceptible to environmental stimulation. Perennial aeroallergen and respiratory viral infection induced sporadic episodes of lung inflammation during this temporal window represent major risk factors for initiation of allergic asthmatic disease. Murine models are widely used as an investigative tool to examine the pathophysiology of allergic asthma; however, models in current usage typically do not encapsulate the early life period which represents the time of maximal risk for disease inception in humans. To address this issue, this protocol adapted an experimental animal model of disease for sensitization to ovalbumin during the immediate post-weaning period beginning at 21 days of age. By initially sensitizing mice during this early life post-weaning period, researchers can more closely align experimental allergic airway disease models with the human age group most at risk for asthma development., Competing Interests: Competing interestsThe authors declare no financial or non-financial competing interests related to this work., (Copyright © 2019 The Authors; exclusive licensee Bio-protocol LLC.)

Chronic allergic inflammatory diseases are a major cause of morbidity, with allergic asthma alone affecting over 300 million people worldwide. Epidemiological studies demonstrate that environmental stimuli are associated with either the promotion or prevention of disease. Major reductions in asthma prevalence are documented in European and US farming communities. Protection is associated with exposure of mothers during pregnancy to microbial breakdown products present in farm dusts and unprocessed foods and enhancement of innate immune competence in the children. We sought to develop a scientific rationale for progressing these findings toward clinical application for primary disease prevention. Treatment of pregnant mice with a defined, clinically approved immune modulator was shown to markedly reduce susceptibility of their offspring to development of the hallmark clinical features of allergic airway inflammatory disease. Mechanistically, offspring displayed enhanced dendritic cell-dependent airway mucosal immune surveillance function, which resulted in more efficient generation of mucosal-homing regulatory T cells in response to local inflammatory challenge. We provide evidence that the principal target for maternal treatment effects was the fetal dendritic cell progenitor compartment, equipping the offspring for accelerated functional maturation of the airway mucosal dendritic cell network following birth. These data provide proof of concept supporting the rationale for developing transplacental immune reprogramming approaches for primary disease prevention.

Allergic (Th2 high immunophenotype) asthmatics have a heightened susceptibility to common respiratory viral infections such as human rhinovirus. Evidence suggests that the innate interferon response is deficient in asthmatic/atopic individuals, while other studies show no differences in antiviral response pathways. Unsensitized and OVA-sensitized/challenged Th2 high (BN rats) and Th2 low immunophenotype (PVG rats) animals were inoculated intranasally with attenuated mengovirus (vMC 0 ). Sensitized animals were exposed/unexposed during the acute viral response phase. Cellular and transcriptomic profiling was performed on bronchoalveolar lavage cells. In unsensitized PVG rats, vMC 0 elicits a prototypical antiviral response (neutrophilic airways inflammation, upregulation of Th1/type I interferon-related pathways). In contrast, response to infection in the Th2 high BN rats was associated with a radically altered intrinsic host response to respiratory viral infection, characterized by macrophage influx/Th2-associated pathways. In sensitized animals, response to virus infection alone was not altered compared to unsensitized animals. However, allergen exposure of sensitized animals during viral infection unleashes a notably exaggerated airways inflammatory response profile orders of magnitude higher in BN versus PVG rats despite similar viral loads. The co-exposure responses in the Th2 high BN incorporated type I interferon/Th1, alternative macrophage activation/Th2 and Th17 signatures. Similar factors may underlie the hyper-susceptibility to infection-associated airways inflammation characteristic of the human Th2 high immunophenotype.

IgE sensitisation has increased significantly over the last decades and is a crucial factor in the development of allergic diseases. IgE antibodies are produced by B cells through the process of antigen presentation by dendritic cells, subsequent differentiation of CD4⁺ Th2 cells, and class switching in B cells. However, many of the factors regulating these processes remain unclear. These processes affect males and females differently, resulting in a significantly higher prevalence of IgE sensitisation in males compared to females from an early age. Before the onset of puberty, this increased prevalence of IgE sensitisation is also associated with a higher prevalence of clinical symptoms in males; however, after puberty, females experience a surge in the incidence of allergic symptoms. This is particularly apparent in allergic asthma, but also in other allergic diseases such as food and contact allergies. This has been partly attributed to the pro- versus anti-allergic effects of female versus male sex hormones; however, it remains unclear how the expression of sex hormones translates IgE sensitisation into clinical symptoms. In this review, we describe the recent epidemiological findings on IgE sensitisation in male and females and discuss recent mechanistic studies casting further light on how the expression of sex hormones may influence the innate and adaptive immune system at mucosal surfaces and how sex hormones may be involved in translating IgE sensitisation into clinical manifestations.

Respiratory IgE-sensitization to innocuous antigens increases the risk for developing diseases such as allergic asthma. Dendritic cells (DC) residing in the airways orchestrate the immune response following antigen exposure and their ability to sample and present antigens to naïve T cells in airway draining lymph nodes contributes to allergen-specific IgE-sensitization. In order to characterize inhaled antigen capture and presentation by DC subtypes in vivo, we used an adjuvant-free respiratory sensitization model using two genetically distinct rat strains, one of which is naturally resistant and the other naturally susceptible to allergic sensitization. Upon multiple exposures to ovalbumin (OVA), the susceptible strain developed OVA-specific IgE and airway inflammation, whereas the resistant strain did not. Using fluorescently tagged OVA and flow cytometry, we demonstrated significant differences in antigen uptake efficiency and presentation associated with either IgE-sensitization or resistance to allergen exposures in respective strains. We further identified CD4 + conventional DC (cDC) as the subset involved in airway antigen sampling in both strains, however, CD4 + cDC in the susceptible strain were less efficient in OVA sampling and displayed increased MHC-II expression compared with the resistant strain. This was associated with generation of an exaggerated Th2 response and a deficiency of airway regulatory T cells in the susceptible strain. These data suggest that subsets of cDC are able to induce either sensitization or resistance to inhaled antigens as determined by genetic background, which may provide an underlying basis for genetically determined susceptibility to respiratory allergic sensitization and IgE production in susceptible individuals., (© 2017 Australasian Society for Immunology Inc.)

Infection-associated inflammatory stress during pregnancy is the most common cause of fetal growth restriction and/or miscarriage. Treatment strategies for protection of at-risk mothers are limited to a narrow range of vaccines, which do not cover the bulk of the common pathogens most frequently encountered. Using mouse models, we demonstrate that oral treatment during pregnancy with a microbial-derived immunomodulator (OM85), currently used clinically for attenuation of infection-associated airway inflammatory symptoms in infants-adults, markedly reduces risk for fetal loss/growth restriction resulting from maternal challenge with bacterial lipopolysaccharide or influenza. Focusing on LPS exposure, we demonstrate that the key molecular indices of maternal inflammatory stress, notably high levels of RANTES, MIP-1α, CCL2, KC, and G-CSF (granulocyte colony-stimulating factor) in gestational tissues/serum, are abrogated by OM85 pretreatment. Systems-level analyses conducted in parallel using RNASeq revealed that OM85 pretreatment selectively tunes LPS-induced activation in maternal gestational tissues for attenuated expression of TNF, IL1, and IFNG-driven proinflammatory networks, without constraining Type1-IFN-associated networks central to first-line antimicrobial defense. This study suggests that broad-spectrum protection-of-pregnancy against infection-associated inflammatory stress, without compromising capacity for efficient pathogen eradication, represents an achievable therapeutic goal.

The pulmonary parenchymal and mucosal microenvironments are constantly exposed to the external environment and thus require continuous surveillance to maintain steady-state immunological homeostasis. This is achieved by a mobile network of pulmonary dendritic cells (DC) and macrophages (mø) that constantly sample and process microenvironmental antigens into signals that can initiate or dampen inflammation, either locally or after onward migration to draining lymph nodes. The constant steady-state turnover of pulmonary DC and mø requires replenishment from bone marrow precursors; however, the nature of the pulmonary precursor cell (PC) remains unclear, although recent studies suggest that subsets of pulmonary DC may derive from circulating monocytic precursors. In the current study, we describe a population of cells in steady-state mouse lung tissue that has the surface phenotypic and ultrastructural characteristics of a common DC progenitor. Irradiation and reconstitution studies confirmed the bone marrow origins of this PC and showed that it had rapid depletion and reconstitution kinetics that were similar to those of DC, with a 50% repopulation by donor-derived cells by Days 7-9 after reconstitution. This was significantly faster than the rates observed for mø, which showed 50% repopulation by donor-derived cells beyond Days 16-21 after reconstitution. Purified PC gained antigen-presenting function and a cell surface phenotype similar to that of pulmonary DC after maturation in vitro, with light and electron microscopy confirming a myeloid DC morphology. To the best of our knowledge, this is the first study to describe a PC for DC in lung tissue; the findings have implications for the restoration of pulmonary immunological homeostasis after bone marrow transplant.

The integrin CD103 is the α E chain of integrin α E β 7 that is important in the maintenance of intraepithelial lymphocytes and recruitment of T cells and dendritic cells (DC) to mucosal surfaces. The role of CD103 in intestinal immune homeostasis has been well described, however, its role in allergic airway inflammation is less well understood. In this study, we used an ovalbumin (OVA)-induced, CD103-knockout (KO) BALB/c mouse model of experimental allergic airways disease (EAAD) to investigate the role of CD103 in disease expression, CD4 + T-cell activation and DC activation and function in airways and lymph nodes. We found reduced airways hyper-responsiveness and eosinophil recruitment to airways after aerosol challenge of CD103 KO compared to wild-type (WT) mice, although CD103 KO mice showed enhanced serum OVA-specific IgE levels. Following aerosol challenge, total numbers of effector and regulatory CD4 + T-cell subsets were significantly increased in the airways of WT but not CD103 KO mice, as well as a lack of DC recruitment into the airways in the absence of CD103. While total airway DC numbers, and their in vivo allergen capture activity, were essentially normal in steady-state CD103 KO mice, migration of allergen-laden airway DC to draining lymph nodes was disrupted in the absence of CD103 at 24 h after aerosol challenge. These data support a role for CD103 in the pathogenesis of EAAD in BALB/c mice through local control of CD4 + T cell and DC subset recruitment to, and migration from, the airway mucosa during induction of allergic inflammation., (© 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

Immunological homeostasis in the respiratory tract is thought to require balanced interactions between networks of dendritic cell (DC) subsets in lung microenvironments in order to regulate tolerance or immunity to inhaled antigens and pathogens. Influenza A virus (IAV) poses a serious threat of long-term disruption to this balance through its potent pro-inflammatory activities. In this study, we have used a BALB/c mouse model of A/PR8/34 H1N1 Influenza Type A Virus infection to examine the effects of IAV on respiratory tissue DC subsets during the recovery phase following clearance of the virus. In adult mice, we found differences in the kinetics and activation states of DC residing in the airway mucosa (AMDC) compared to those in the parenchymal lung (PLDC) compartments. A significant depletion in the percentage of AMDC was observed at day 4 post-infection that was associated with a change in steady-state CD11b+ and CD11b- AMDC subset frequencies and significantly elevated CD40 and CD80 expression and that returned to baseline by day 14 post-infection. In contrast, percentages and total numbers of PLDC were significantly elevated at day 14 and remained so until day 21 post-infection. Accompanying this was a change in CD11b+and CD11b- PLDC subset frequencies and significant increase in CD40 and CD80 expression at these time points. Furthermore, mice infected with IAV at 4 weeks of age showed a significant increase in total numbers of PLDC, and increased CD40 expression on both AMDC and PLDC, when analysed as adults 35 days later. These data suggest that the rate of recovery of DC populations following IAV infection differs in the mucosal and parenchymal compartments of the lung and that DC populations can remain disrupted and activated for a prolonged period following viral clearance, into adulthood if infection occurred early in life.

Hematopoiesis occurs in a complex bone marrow microenvironment in which bone marrow stromal cells provide critical support to the process through direct cell contact and indirectly through the secretion of cytokines and growth factors. We report that connective tissue growth factor (Ctgf, also known as Ccn2) is highly expressed in murine bone marrow stromal cells. In contrast, connective tissue growth factor is barely detectable in unfractionated adult bone marrow cells. While connective tissue growth factor has been implicated in hematopoietic malignancies, and is known to play critical roles in skeletogenesis and regulation of bone marrow stromal cells, its role in hematopoiesis has not been described. Here we demonstrate that the absence of connective tissue growth factor in mice results in impaired hematopoiesis. Using a chimeric fetal liver transplantation model, we show that absence of connective tissue growth factor has an impact on B-cell development, in particular from pro-B to more mature stages, which is linked to a requirement for connective tissue growth factor in bone marrow stromal cells. Using in vitro culture systems, we demonstrate that connective tissue growth factor potentiates B-cell proliferation and promotes pro-B to pre-B differentiation in the presence of interleukin-7. This study provides a better understanding of the functions of connective tissue growth factor within the bone marrow, showing the dual regulatory role of the growth factor in skeletogenesis and in stage-specific B lymphopoiesis., (Copyright© Ferrata Storti Foundation.)

The relative importance of respiratory viral infections vs inhalant allergy in asthma pathogenesis is the subject of ongoing debate. Emerging data from long-term prospective birth cohorts are bringing increasing clarity to this issue, in particular through the demonstration that while both of these factors can contribute independently to asthma initiation and progression, their effects are strongest when they act in synergy to drive cycles of episodic airways inflammation. An important question is whether susceptibility to infection and allergic sensitization in children with asthma arises from common or shared defect(s). We argue here that susceptibility to recurrent respiratory viral infections, failure to generate protective immunologic tolerance to aeroallergens, and ultimately the synergistic interactions between inflammatory pathways triggered by concomitant responses to these agents all result primarily from functional deficiencies within the cells responsible for local surveillance for antigens impinging on airway surfaces: the respiratory mucosal dendritic cell (DC) network. The effects of these defects in DCs from children wtih asthma are accentuated by parallel attenuation of innate immune functions in adjacent airway epithelial cells that reduce their resistance to the upper respiratory viral infections, which are the harbingers of subsequent inflammatory events at asthma lesion site(s) in the lower airways. An important common factor underpinning the innate immune functions of these unrelated cell types is use of an overlapping series of pattern recognition receptors (exemplified by the Toll-like receptor family), and variations in the highly polymorphic genes encoding these receptors and related molecules in downstream signaling pathways appear likely contributors to these shared defects. Findings implicating recurrent respiratory infections in adult-onset asthma, much of which is nonatopic, suggest a similar role for deficient immune surveillance in this phenotype of the disease.

The respiratory tract is an attractive target organ for novel diagnostic and therapeutic applications with nano-sized carriers, but their immune effects and interactions with key resident antigen-presenting cells (APCs) such as dendritic cells (DCs) and alveolar macrophages (AMs) in different anatomical compartments remain poorly understood. Polystyrene particles ranging from 20 nm to 1,000 nm were instilled intranasally in BALB/c mice, and their interactions with APC populations in airways, lung parenchyma, and lung-draining lymph nodes (LDLNs) were examined after 2 and 24 hours by flow cytometry and confocal microscopy. In the main conducting airways and lung parenchyma, DC subpopulations preferentially captured 20-nm particles, compared with 1,000-nm particles that were transported to the LDLNs by migratory CD11blow DCs and that were observed in close proximity to CD3⁺ T cells. Generally, the uptake of particles increased the expression of CD40 and CD86 in all DC populations, independent of particle size, whereas 20-nm particles induced enhanced antigen presentation to CD4⁺ T cells in LDLNs in vivo. Despite measurable uptake by DCs, the majority of particles were taken up by AMs, irrespective of size. Confocal microscopy and FACS analysis showed few particles in the main conducting airways, but a homogeneous distribution of all particle sizes was evident in the lung parenchyma, mostly confined to AMs. Particulate size as a key parameter determining uptake and trafficking therefore determines the fate of inhaled particulates, and this may have important consequences in the development of novel carriers for pulmonary diagnostic or therapeutic applications.

Alterations to dendritic cell (DC) progenitors in the bone marrow (BM) may contribute to long-lasting systemic immunosuppression (>28 d) following exposure of the skin of mice to erythemal UV radiation (UVR). DCs differentiated in vitro from the BM of mice 3 d after UVR (8 kJ/m(2)) have a reduced capacity to initiate immunity (both skin and airways) when adoptively transferred into naive mice. Studies in IL-10(-/-) mice suggested that UV-induced IL-10 was not significantly involved. To investigate the immune capabilities of peripheral tissue DCs generated in vivo from the BM of UV-irradiated mice, chimeric mice were established. Sixteen weeks after reconstitution, contact hypersensitivity responses were significantly reduced in mice reconstituted with BM from UV-irradiated mice (UV-chimeric). When the dorsal skin of UV-chimeric mice was challenged with innate inflammatory agents, the hypertrophy induced in the draining lymph nodes was minimal and significantly less than that measured in control-chimeric mice challenged with the same inflammatory agent. When DCs were differentiated from the BM of UV-chimeric mice using FLT3 ligand or GM-CSF + IL-4, the cells maintained a reduced priming ability. The diminished responses in UV-chimeric mice were not due to different numerical or proportional reconstitution of BM or the hematopoietic cells in blood, lymph nodes, and skin. Erythemal UVR may imprint a long-lasting epigenetic effect on DC progenitors in the BM and alter the function of their terminally differentiated progeny.

Background: One explanation for the high burden of allergic and autoimmune diseases in industrialized countries is inappropriate immune development under modern environmental conditions. There is increasing evidence that the process of immune deviation already begins in utero, but the underlying immunologic mechanisms are not clear., Objective: We sought to identify differences in the function of neonatal antigen-presenting cells (APCs) in children born in settings that are more traditional versus those of modern societies., Methods: Cord blood mononuclear cells were collected from newborns from Papua New Guinea (PNG; traditional) and Australia (modern) and compared for differences in APCs and T-cell phenotype and function., Results: Australian cord naive T cells (CD4(+)CD25(-)CD127(+) cells) showed an enhanced and more rapid proliferative response in an autologous, APC-dependent culture system, a result of differences in neonatal APCs rather than T-cell function. This included an increased capacity to process antigen and to upregulate activation markers after stimulation. In contrast, resting PNG APCs exhibited higher baseline levels of activation and inhibitory markers and were less responsive or nonresponsive to stimulation in vitro., Conclusions: This study supports the hypothesis that prenatal environments can influence the developing immune system in utero. Children born under modern environmental conditions exhibit increased APC reactivity at birth compared with children born under traditional environmental conditions. The functionally more quiescent nature of PNG neonatal APCs might protect against the development of harmful inflammatory responses in early life., (Copyright © 2012 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Inflammatory mediators from peripheral tissues may control dendritic cell (DC) development in the bone marrow. In this study, DCs (CD11c(+) cells) differentiated from the bone marrow of mice with inflammation of the airways, or the peritoneal cavity had poor priming ability resulting in reduced, long-lived responses to that antigen in vivo. This indicates enhancement of regulatory mechanisms of immune responses through a peripheral tissue-bone marrow axis. If CD11c(+) cells, expanded from the bone marrow of mice with tissue inflammation were antigen pre-loaded and injected into mice already sensitized to that antigen, then subsequent contact hypersensitivity responses were significantly reduced. The effects of inflammation were imprinted in vivo and were independent of in vitro culture conditions for DC differentiation. The effect of tissue inflammation on the bone marrow DC precursors was not detected in mice treated subcutaneously with slow-release indomethacin pellets, suggesting a role for prostanoids, including prostaglandin E(2), in differentiation of regulatory CD11c(+) cells from bone marrow. Our study represents an important homeostatic process with potential for therapeutic use in the future., (Copyright © 2012 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

A hallmark of atopic asthma is development of chronic airways hyper-responsiveness (AHR) that persists in the face of ongoing exposure to perennial aeroallergens. We investigated underlying mechanisms in sensitized rats focusing on a strain expressing the high-allergen-responder phenotype characteristic of human atopic asthmatics, and find that their high susceptibility to aeroallergen-induced persistent AHR is associated with deficiencies in the immunoregulatory and mucosal trafficking properties of inducible T-regulatory cells (iTregs). Counterintuitively, AHR susceptibility was inversely related to aeroallergen exposure level, high exposures conferring protection. We demonstrate that underlying this AHR-susceptible phenotype is reduced capacity of airway mucosal dendritic cells (AMDCs) for allergen sampling in vivo; this defect is microenvironmentally acquired, as allergen uptake by these cells in vitro is normal. Moreover, intranasal transfer of in vitro aeroallergen-loaded AMDC from naïve animals into AHR-susceptible animals during prolonged aerosol challenge markedly boosts subsequent accumulation of iTregs in the airway mucosa and rapidly resolves their chronic AHR, suggesting that compromised antigen surveillance by AMDC resulting in defective functional programming of iTreg may be causally related to AHR susceptibility.