Electronic cigarettes disrupt lung lipid homeostasis and innate immunity independent of nicotine

Electronic nicotine delivery systems (ENDS) or e-cigarettes have emerged as a popular recreational tool among adolescents and adults. Although the use of ENDS is often promoted as a safer alternative to conventional cigarettes, few comprehensive studies have assessed the long-term effects of vaporized nicotine and its associated solvents, propylene glycol (PG) and vegetable glycerin (VG). Here, we show that compared with smoke exposure, mice receiving ENDS vapor for 4 months failed to develop pulmonary inflammation or emphysema. However, ENDS exposure, independent of nicotine, altered lung lipid homeostasis in alveolar macrophages and epithelial cells. Comprehensive lipidomic and structural analyses of the lungs revealed aberrant phospholipids in alveolar macrophages and increased surfactant-associated phospholipids in the airway. In addition to ENDS-induced lipid deposition, chronic ENDS vapor exposure downregulated innate immunity against viral pathogens in resident macrophages. Moreover, independent of nicotine, ENDS-exposed mice infected with influenza demonstrated enhanced lung inflammation and tissue damage. Together, our findings reveal that chronic e-cigarette vapor aberrantly alters the physiology of lung epithelial cells and resident immune cells and promotes poor response to infectious challenge. Notably, alterations in lipid homeostasis and immune impairment are independent of nicotine, thereby warranting more extensive investigations of the vehicle solvents used in e-cigarettes.

A Novel Animal Model of Emphysema Induced by Anti-Elastin Autoimmunity

Loss of immune tolerance to self-antigens can promote chronic inflammation and disrupt the normal function of multiple organs, including the lungs. Degradation of elastin, a highly insoluble protein and a significant component of the lung structural matrix, generates proinflammatory molecules. Elastin fragments (EFs) have been detected in the serum of smokers with emphysema, and elastin-specific T cells have also been detected in the peripheral blood of smokers with emphysema. However, an animal model that could recapitulate T cell-specific autoimmune responses by initiating and sustaining inflammation in the lungs is lacking. In this study, we report an animal model of autoimmune emphysema mediated by the loss of tolerance to elastin. Mice immunized with a combination of human EFs plus rat EFs but not mouse EFs showed increased infiltration of innate and adaptive immune cells to the lungs and developed emphysema. We cloned and expanded mouse elastin-specific CD4⁺ T cells from the lung and spleen of immunized mice. Finally, we identified TCR sequences from the autoreactive T cell clones, suggesting possible pathogenic TCRs that can cause loss of immune tolerance against elastin. This new autoimmune model of emphysema provides a useful tool to examine the immunological factors that promote loss of immune tolerance to self.

Selective cleavage of fibrinogen by diverse proteinases initiates innate allergic and antifungal immunity through CD11b

Proteinases are essential drivers of allergic airway disease and innate antifungal immunity in part through their ability cleave the clotting factor fibrinogen (FBG) into fibrinogen cleavage products (FCPs) that signal through Toll-like receptor 4 (TLR4). However, the mechanism by which FCPs engage TLR4 remains unknown. Here, we show that the proteinases from Aspergillus melleus (PAM) and other allergenic organisms rapidly hydrolyze FBG to yield relatively few FCPs that drive distinct antifungal mechanisms through TLR4. Functional FCPs, termed cryptokines, were characterized by rapid loss of the FBG α chain with substantial preservation of the β and γ chains, including a γ chain sequence (Fibγ390-396) that binds the integrin Mac-1 (CD11b/CD18). PAM-derived cryptokines could be generated from multiple FBG domains, and the ability of cryptokines to induce fungistasis in vitro and innate allergic airway disease in vivo strongly depended on both Mac-1 and the Mac-1-binding domain of FBG (Fibγ390-396). Our findings illustrate the essential concept of proteinase-activated immune responses and for the first time link Mac-1, cryptokines, and TLR4 to innate antifungal immunity and allergic airway disease.

Microglia and amyloid precursor protein coordinate control of transient Candida cerebritis with memory deficits

Bloodborne infections with Candida albicans are an increasingly recognized complication of modern medicine. Here, we present a mouse model of low-grade candidemia to determine the effect of disseminated infection on cerebral function and relevant immune determinants. We show that intravenous injection of 25,000 C. albicans cells causes a highly localized cerebritis marked by the accumulation of activated microglial and astroglial cells around yeast aggregates, forming fungal-induced glial granulomas. Amyloid precursor protein accumulates within the periphery of these granulomas, while cleaved amyloid beta (Aβ) peptides accumulate around the yeast cells. CNS-localized C. albicans further activate the transcription factor NF-κB and induce production of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor (TNF), and Aβ peptides enhance both phagocytic and antifungal activity from BV-2 cells. Mice infected with C. albicans display mild memory impairment that resolves with fungal clearance. Our results warrant additional studies to understand the effect of chronic cerebritis on cognitive and immune function.

The potential links between infections and neurodegenerative disorders are unclear. Here, Wu et al. present a mouse model of low-grade candidemia characterized by highly localized cerebritis, accumulation of amyloid precursor protein and beta peptides, and mild memory impairment that resolves with fungal clearance.

MicroRNA-22 controls interferon alpha production and erythroid maturation in response to infectious stress in mice

MicroRNA-22 (miR-22) is a highly conserved microRNA that can regulate cell proliferation, oncogenesis, and cell maturation, especially during stress. In hematopoietic stem cells (HSCs), miR-22 has been reported to be involved in the regulation of key self-renewal factors, including Tet2. Recent work demonstrates that miR-22 also participates in regulation of the interferon (IFN) response, and expression profiling studies suggest that it is variably expressed at different stages in erythroid differentiation. We thus hypothesized that miR-22 regulates maturation of erythroid progenitors during stress hematopoiesis through its interaction with IFN. We compared the blood and bone marrow of wild-type (WT) and miR-22-deficient mice at baseline and upon infectious challenge with systemic lymphochoriomeningitis (LCMV) virus. miR-22-deficient mice maintained platelet counts better than WT mice during infection, but they showed significantly reduced red blood cells and hemoglobin. Analysis of bone marrow progenitors demonstrated better overall survival and improved HSC homeostasis in infected miR-22-null mice compared with WT, which was attributable to a blunted IFN response to LCMV challenge in the miR-22-null mice. We found that miR-22 was expressed exclusively in stage II erythroid precursors and downregulated upon infection in WT mice. Our results indicate that miR-22 promotes the IFN response to viral infection and that it functions at baseline as a brake to slow erythroid differentiation and maintain adequate erythroid potential. Impaired regulation of erythrogenesis in the absence of miR-22 can lead to anemia during infection.

Fibrinogen cleavage products and Toll-like receptor 4 promote the generation of programmed cell death 1 ligand 2-positive dendritic cells in allergic asthma

BACKGROUND

Inhaled protease allergens preferentially trigger T_H2-mediated inflammation in allergic asthma. The role of dendritic cells (DCs) on induction of T_H2 cell responses in allergic asthma has been well documented; however, the mechanism by which protease allergens induce T_H2-favorable DCs in the airway remains unclear.

OBJECTIVE

We sought to determine a subset of DCs responsible for T_H2 cell responses in allergic asthma and the mechanism by which protease allergens induce the DC subset in the airway.

METHODS

Mice were challenged intranasally with protease allergens or fibrinogen cleavage products (FCPs) to induce allergic airway inflammation. DCs isolated from mediastinal lymph nodes were analyzed for surface phenotype and T-cell stimulatory function. Anti-Thy1.2 and Mas-TRECK mice were used to deplete innate lymphoid cells and mast cells, respectively. Adoptive cell transfer, bone marrow DC culture, anti-IL-13, and Toll-like receptor (TLR) 4-deficient mice were used for further mechanistic studies.

RESULTS

Protease allergens induced a remarkable accumulation of T_H2-favorable programmed cell death 1 ligand 2 (PD-L2)⁺ DCs in mediastinal lymph nodes, which was significantly abolished in mice depleted of mast cells and, to a lesser extent, innate lymphoid cells. Mechanistically, FCPs generated by protease allergens triggered IL-13 production from wild-type mast cells but not from TLR4-deficient mast cells, which resulted in an increase in the number of PD-L2⁺ DCs. Intranasal administration of FCPs induced an increase in numbers of PD-L2⁺ DCs in the airway, which was significantly abolished in TLR4- and mast cell-deficient mice. Injection of IL-13 restored the PD-L2⁺ DC population in mice lacking mast cells.

CONCLUSION

Our findings unveil the "protease-FCP-TLR4-mast cell-IL-13" axis as a molecular mechanism for generation of T_H2-favorable PD-L2⁺ DCs in allergic asthma and suggest that targeting the PD-L2⁺ DC pathway might be effective in suppressing allergic T-cell responses in the airway.