Granulocyte–macrophage colony‐stimulating factor (GM‐CSF) is a cytokine that stimulates the proliferation and differentiation of granulocyte and macrophage precursors. The mouse gene‐encoding GM‐CSF, ...Csf2, is regulated at both transcriptional and post‐transcriptional levels. An adenine–uridine‐rich element (ARE) within the 3′‐untranslated region of Csf2 mRNA was shown in cell transfection studies to confer instability on this transcript. To explore the physiological importance of this element in an intact animal, we generated mice with a knock‐in deletion of the 75‐nucleotide ARE. Mice heterozygous for this ARE deletion developed severe respiratory distress and death within about 12 weeks of age. There was dense infiltration of lung alveolar spaces by crystal‐containing macrophages. Increased stability of Csf2 mRNA was confirmed in bone marrow‐derived macrophages, and elevated GM‐CSF levels were observed in serum and lung. These mice did not exhibit notable abnormalities in blood or bone marrow, and transplantation of bone marrow from mutant mice into lethally irradiated WT mice did not confer the pulmonary phenotype. Mice with a conditional deletion of the ARE restricted to lung type II alveolar cells exhibited an essentially identical lethal lung phenotype at the same ages as the mice with the whole‐body deletion. In contrast, mice with the same conditional ARE deletion in myeloid cells, including macrophages, exhibited lesser degrees of macrophage infiltration into alveolar spaces much later in life, at approximately 9 months of age. Post‐transcriptional Csf2 mRNA stability regulation in pulmonary alveolar epithelial cells appears to be essential for normal physiological GM‐CSF secretion and pulmonary macrophage homeostasis.
A novel knock‐in mouse expresses modified GM‐CSF (Csf2) mRNA, in which an AU‐rich mRNA decay regulatory element was deleted in the 3′‐untranslated region. This work shows that post‐transcriptional GM‐CSF mRNA turnover regulation in pulmonary alveolar type II epithelial cells (AT2 cells) is an essential mechanism for maintaining alveolar macrophages (AM) and surfactant homeostasis in normal physiological conditions.
Abstract
Air pollution levels across the globe continue to rise despite government regulations. The increase in global air pollution levels drives detrimental human health effects, including 7 ...million premature deaths every year. Many of these deaths are attributable to increased incidence of respiratory infections. Considering the COVID-19 pandemic, an unprecedented public health crisis that has claimed the lives of over 6.5 million people globally, respiratory infections as a driver of human mortality is a pressing concern. Therefore, it is more important than ever to understand the relationship between air pollution and respiratory infections so that public health measures can be implemented to ameliorate further morbidity and mortality. This article aims to review the current epidemiologic and basic science research on interactions between air pollution exposure and respiratory infections. The first section will present epidemiologic studies organized by pathogen, followed by a review of basic science research investigating the mechanisms of infection, and then conclude with a discussion of areas that require future investigation.
The past 20 years has seen tremendous advances in human immunodeficiency virus (HIV)--related care and survival. Though HIV infections and acquired immunodeficiency syndrome--related deaths continue ...to be a key public health threat, particularly worldwide, the advent of combination antiretroviral therapies (cART) has significantly increased the number of people living with HIV (PLHIV). As the number of and life expectancy for PLHIV increase, it is becoming clear that PLHIV are at an increased risk of chronic diseases like chronic obstructive pulmonary disease (COPD), even when controlling for confounding comorbidities. Interestingly, this effect in PLHIV is still present even when controlling for tobacco use, though PLHIV are more frequently smokers. Increased COPD incidence has raised the question of direct HIV effects on COPD pathogenesis. Though potential mechanisms have been suggested, specific mechanisms linking HIV and COPD remain unclear. In particular, little information exists on early events in PLHIV that occur prior to the development of COPD. Here, Tighe and Patel highlight the study by Corleis et al that sought to address this gap by exploring the effect of HIV and/or smoking on lung T-cell composition.
Lung disease causes significant morbidity and mortality, and is exacerbated by environmental injury, for example through lipopolysaccharide (LPS) or ozone (O
). Toll-like receptors (TLRs) orchestrate ...immune responses to injury by recognizing pathogen- or danger-associated molecular patterns. TLR4, the prototypic receptor for LPS, also mediates inflammation after O
, triggered by endogenous hyaluronan. Regulation of TLR4 signaling is incompletely understood. TLR5, the flagellin receptor, is expressed in alveolar macrophages, and regulates immune responses to environmental injury. Using in vivo animal models of TLR4-mediated inflammations (LPS, O
, hyaluronan), we show that TLR5 impacts the in vivo response to LPS, hyaluronan and O
. We demonstrate that immune cells of human carriers of a dominant negative TLR5 allele have decreased inflammatory response to O
exposure ex vivo and LPS exposure in vitro. Using primary murine macrophages, we find that TLR5 physically associates with TLR4 and biases TLR4 signaling towards the MyD88 pathway. Our results suggest an updated paradigm for TLR4/TLR5 signaling.
Occupational exposure to inhaled crystalline silica dust (cSiO2) is linked to systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis, and anti-neutrophil cytoplasmic autoantibody ...vasculitis. Each disease has a characteristic autoantibody profile used in diagnosis and implicated in pathogenesis. A role for cSiO2 in modulating humoral autoimmunity
is supported by findings in mice, where respirable cSiO2 induces ectopic lymphoid structures as well as inflammation in exposed lungs across genetically diverse backgrounds. In lupus-prone mice cSiO2 exposure also leads to early onset autoantibody production and accelerated disease. Elevated autoantibody levels in bronchoalveolar lavage fluid (BALF) and lung transcriptome analysis suggest that the lung is a hub of cSiO2-evoked autoimmune activity. However, mechanisms by which cSiO2 and lung microenvironments interact to promote autoantibody production remain unclear. We previously demonstrated elevated anti-DNA Ig in BALF but not in lung cell cultures from cSiO2-exposed C57BL/6 mice, suggesting that BALF autoantibodies did not arise locally in this non-autoimmune strain. Autoantibodies were also elevated in BALF of cSiO2-exposed lupus-prone BXSB mice. In this report we test the hypothesis that dysregulated autoreactive B cells recruited to cSiO2-exposed lungs in the context of autoimmune predisposition contribute to local autoantibody production. We found that anti-DNA and anti-myeloperoxidase (MPO) Ig were significantly elevated in cultures of TLR ligand-stimulated lung cells from cSiO2-exposed BXSB mice. To further explore the impact of strain genetic susceptibility versus B cell intrinsic dysfunction on cSiO2-recruited B cell fate, we used an anti-basement membrane autoantibody transgenic (autoAb Tg) mouse line termed M7. In M7 mice, autoAb Tg B cells are aberrantly regulated and escape from tolerance on the C57BL/6 background. Exposure to cSiO2 elicited prominent pulmonary B cell and T cell aggregates and autoAb Tg Ig were readily detected in lung cell culture supernatants. Taken together, diverse disease-relevant autoreactive B cells, including cells specific for DNA, MPO, and basement membrane, are recruited to lung ectopic lymphoid aggregates in response to cSiO2 instillation. B cells that escape tolerance can contribute to local autoantibody production. Our demonstration of significantly enhanced autoantibody induction by TLR ligands further suggests that a coordinated environmental co-exposure can magnify autoimmune vulnerability.
There is increasing evidence that early life microbial exposure aids in immune system maturation, more recently known as the “old friends” hypothesis. To test this hypothesis, 4-week-old mice were ...exposed to soils of increasing microbial diversity for four weeks followed by an intranasal challenge with either live or heat inactivated influenza A virus and monitored for 7 additional days. Perturbations of the gut and lung microbiomes were explored through 16S rRNA amplicon sequencing. RNA-sequencing was used to examine the host response in the lung tissue through differential gene expression. We determined that compared to the gut microbiome, the lung microbiome is more susceptible to changes in beta diversity following soil exposure with Lachnospiraceae ASVs accounting for most of the differences between groups. While several immune system genes were found to be significantly differentially expressed in lung tissue due to soil exposures, there were no differences in viral load or weight loss. This study shows that exposure to diverse microbial communities through soil exposure alters the gut and lung microbiomes resulting in differential expression of specific immune system related genes within the lung following an influenza challenge.
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•Soil exposure affected gut and lung microbiome composition and changes were driven by the family Lachnospiraceae•Cytokine and chemokine genes were generally upregulated in the soil exposed mice•The lung shapes microbiome diversity; soil exposure alters lung gene expression with no effect on viral load or weight loss.
The innate immune components that modulate allergic contact hypersensitivity (CHS) responses are poorly defined. Using human skin from contact dermatitis patients and a mouse model of CHS, we find ...that hapten allergens disrupt the Arginase1 (Arg1) and inducible NO synthase (iNOS) dynamic in monocytes/macrophages (mono/MΦ), which renders those cells ineffectual in suppressing skin inflammation. Mice lacking Arg1 in MΦ develop increased CHS characterized by elevated ear thickening, mono/MΦ-dominated dermal inflammation, and increased iNOS and IL-6 expression compared with control mice. Treatment of Arg1
; LysMCre
mice with a selective NOS inhibitor or knockout of
, encoding iNOS, significantly ameliorates CHS. Our findings suggest a critical role for Arg1 in mono/MΦ in suppressing CHS through dampening
expression. These results support that increasing Arg1 may be a potential therapeutic avenue in treating allergic contact dermatitis.
Azobenzene disperse dyes are the fastest-growing category of commercial dyestuffs and have been found in indoor house dust and in children's polyester apparel. Azobenzene disperse dyes are implicated ...as potentially allergenic; however, little experimental data is available on allergenicity of these dyes. Here, we examine the binding of azobenzene disperse dyes to nucleophilic peptide residues as a proxy for their potential reactivity as electrophilic allergenic sensitizers. The Direct Peptide Reactivity Assay (DPRA) was utilized via both a spectrophotometric method and a high-performance liquid chromatography (HPLC) method. We tested dyes purified from commercial dyestuffs as well as several known transformation products. All dyes were found to react with nucleophilic peptides in a dose-dependent manner with pseudo-first order kinetics (rate constants as high as 0.04 h
). Rates of binding reactivity were also found to correlate to electrophilic properties of dyes as measured by Hammett constants and electrophilicity indices. Reactivities of polyester shirt extracts were also tested for DPRA activity and the shirt extracts with high measured abundances of azobenzene disperse dyes were observed to induce greater peptide reactivity. Results suggest that azobenzene disperse dyes may function as immune sensitizers, and that clothing containing these dyes may pose risks for skin sensitization.
Ozone (O
), a criterion air pollutant produced as a product of internal combustion, generates increased inflammation, lung permeability, and airway hyperreactivity when exposed to rodents in ...laboratory settings. Airway hyperreactivity is defined as an exaggerated acute obstructive response of the airways to one or more nonspecific stimuli. Lung permeability is a measure of barrier functions that separate internal and external environments to limit access of pathogens and other noxious material. By modeling in vivo O
exposure in rodents, this allows investigators to explore pulmonary and nonpulmonary O
effects as a means of understanding its impact on human health and lung function. Furthermore, direct effects of O
on epithelial permeability can be defined using in vitro exposures to airway epithelial cells. This chapter will focus on methods of generating O
and then exposing rodents and cultured epithelial cells in laboratory settings.
Microbial dysbiosis is a potential mediator of air pollution-induced adverse outcomes. However, a systemic comparison of the lung and gut microbiome alterations and lung-gut axis following air ...pollution exposure is scant. In this study, we exposed male C57BL/6J mice to inhaled air, CB (10 mg/m
), O
(2 ppm) or CB + O
mixture for 3 h/day for either one day or four consecutive days and were euthanized 24 h post last exposure. The lung and gut microbiome were quantified by 16 s sequencing.
Multiple CB + O
exposures induced an increase in the lung inflammatory cells (neutrophils, eosinophils and B lymphocytes), reduced absolute bacterial load in the lungs and increased load in the gut. CB + O
exposure was more potent as it decreased lung microbiome alpha diversity just after a single exposure. CB + O
co-exposure uniquely increased Clostridiaceae and Prevotellaceae in the lungs. Serum short chain fatty acids (SCFA) (acetate and propionate) were increased significantly only after CB + O
co-exposure. A significant increase in SCFA producing bacterial families (Ruminococcaceae, Lachnospiraceae, and Eubacterium) were also observed in the gut after multiple exposures. Co-exposure induced significant alterations in the gut derived metabolite receptors/mediator (Gcg, Glp-1r, Cck) mRNA expression. Oxidative stress related mRNA expression in lungs, and oxidant levels in the BALF, serum and gut significantly increased after CB + O
exposures.
Our study confirms distinct gut and lung microbiome alterations after CB + O
inhalation co-exposure and indicate a potential homeostatic shift in the gut microbiome to counter deleterious impacts of environmental exposures on metabolic system.
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