Developing a mouse model of human coronavirus NL63 infection: comparison with rhinovirus-A1B and effects of prior rhinovirus infection.

Human coronavirus (HCoV)-NL63 causes respiratory tract infections in humans and employs angiotensin-converting enzyme 2 (ACE2) as a receptor. We sought to establish a mouse model of HCoV-NL63 and determine if prior RV-A1B infection affected HCoV-NL63 replication. HCoV-NL63 was propagated in LLC-MK2 cells expressing human ACE2. RV-A1B was grown in HeLa-H1 cells. C57BL6/J or transgenic mice expressing human ACE2 were infected intranasally with sham LLC-MK2 cell supernatant or 1 x 105 TCID50 units HCoV-NL63. Wild-type mice were infected with 1 x 106 PFU RV-A1B. Lungs were assessed for vRNA, bronchoalveolar lavage (BAL) cells, histology, HCoV-NL63 non-structural protein 3 (nsp3), and host gene expression by next generation sequencing and qPCR. To evaluate sequential infections, mice were infected with RV-A1B followed by HCoV-NL63 infection four days later. We report that hACE2 mice infected with HCoV-NL63 showed evidence of replicative infection with increased levels of vRNA, BAL neutrophils and lymphocytes, peribronchial and perivascular infiltrates, and expression of nsp3. Viral replication peaked three days after infection and inflammation persisted six days after infection. HCoV-NL63-infected hACE2 mice showed increased mRNA expression of IFNs, IFN-stimulated proteins and pro-inflammatory cytokines. Infection with RV-A1B four days before HCoV-NL63 significantly decreased both HCoV-NL63 vRNA levels and airway inflammation. Mice infected with RV-A1B prior to HCoV-NL63 showed increased expression of antiviral proteins compared to sham-treated mice. In conclusion, we established a mouse model of HCoV-NL63 replicative infection characterized by relatively persistent viral replication and inflammation. Prior infection with RV-A1B reduced HCoV-NL63 replication and airway inflammation, indicative of viral interference.

Early-life heterologous rhinovirus infections induce an exaggerated asthma-like phenotype.

BACKGROUND: Early-life wheezing-associated respiratory tract infection by rhinovirus (RV) is a risk factor for asthma development. Infants are infected with many different RV strains per year. OBJECTIVE: We previously showed that RV infection of 6-day-old BALB/c mice induces a mucous metaplasia phenotype that is dependent on type 2 innate lymphoid cells (ILC2s). We hypothesized that early-life RV infection alters the response to subsequent heterologous infection, inducing an exaggerated asthma-like phenotype. METHODS: Wild-type BALB/c mice and Rorafl/flIl7rcre mice lacking ILC2s were treated as follows: (1) sham on day 6 of life plus sham on day 13 of life, (2) RV-A1B on day 6 plus sham on day 13, (3) sham on day 6 plus RV-A2 on day 13, and (4) RV-A1B on day 6 plus RV-A2 on day 13. RESULTS: Mice infected with RV-A1B at day 6 and sham at day 13 showed an increased number of bronchoalveolar lavage eosinophils and increased expression of IL-13 mRNA but not expression of IFN-γ mRNA (which is indicative of a type 2 immune response), whereas mice infected with sham on day 6 and RV-A2 on day 13 of life demonstrated increased IFN-γ expression (which is a mature antiviral response). In contrast, mice infected with RV-A1B on day 6 before RV-A2 infection on day 13 showed increased expression of IL-13, IL-5, Gob5, Muc5b, and Muc5ac mRNA; increased numbers of eosinophils and IL-13-producing ILC2s; and exaggerated mucus metaplasia and airway hyperresponsiveness. Compared with Rorafl/fl mice, Rorafl/flIl7rcre mice showed complete suppression of bronchoalveolar lavage eosinophils and mucous metaplasia. CONCLUSION: Early-life RV infection alters the response to subsequent heterologous infection, inducing an intensified asthma-like phenotype that is dependent on ILC2s.

IL-1ß prevents ILC2 expansion, type 2 cytokine secretion, and mucus metaplasia in response to early-life rhinovirus infection in mice.

BACKGROUND: Early-life wheezing-associated respiratory infection with human rhinovirus (RV) is associated with asthma development. RV infection of 6-day-old immature mice causes mucous metaplasia and airway hyperresponsiveness which is associated with the expansion of IL-13-producing type 2 innate lymphoid cells (ILC2s) and dependent on IL-25 and IL-33. We examined regulation of this asthma-like phenotype by IL-1ß. METHODS: Six-day-old wild-type or NRLP3-/- mice were inoculated with sham or RV-A1B. Selected mice were treated with IL-1 receptor antagonist (IL-1RA), anti-IL-1ß, or recombinant IL-1ß. RESULTS: Rhinovirus infection induced Il25, Il33, Il4, Il5, Il13, muc5ac, and gob5 mRNA expression, ILC2 expansion, mucus metaplasia, and airway hyperresponsiveness. RV also induced lung mRNA and protein expression of pro-IL-1ß and NLRP3 as well as cleavage of caspase-1 and pro-IL-1ß, indicating inflammasome priming and activation. Lung macrophages were a major source of IL-1ß. Inhibition of IL-1ß signaling with IL-1RA, anti-IL-1ß, or NLRP3 KO increased RV-induced type 2 cytokine immune responses, ILC2 number, and mucus metaplasia, while decreasing IL-17 mRNA expression. Treatment with IL-1ß had the opposite effect, decreasing IL-25, IL-33, and mucous metaplasia while increasing IL-17 expression. IL-1ß and IL-17 each suppressed Il25, Il33, and muc5ac mRNA expression in cultured airway epithelial cells. Finally, RV-infected 6-day-old mice showed reduced IL-1ß mRNA and protein expression compared to mature mice. CONCLUSION: Macrophage IL-1ß limits type 2 inflammation and mucous metaplasia following RV infection by suppressing epithelial cell innate cytokine expression. Reduced IL-1ß production in immature animals provides a mechanism permitting asthma development after early-life viral infection.

Myristoylated rhinovirus VP4 protein activates TLR2-dependent proinflammatory gene expression.

Asthma exacerbations are often caused by rhinovirus (RV). We and others have shown that Toll-like receptor 2 (TLR2), a membrane surface receptor that recognizes bacterial lipopeptides and lipoteichoic acid, is required and sufficient for RV-induced proinflammatory responses in vitro and in vivo. We hypothesized that viral protein-4 (VP4), an internal capsid protein that is myristoylated upon viral replication and externalized upon viral binding, is a ligand for TLR2. Recombinant VP4 and myristoylated VP4 (MyrVP4) were purified by Ni-affinity chromatography. MyrVP4 was also purified from RV-A1B-infected HeLa cells by urea solubilization and anti-VP4 affinity chromatography. Finally, synthetic MyrVP4 was produced by chemical peptide synthesis. MyrVP4-TLR2 interactions were assessed by confocal fluorescence microscopy, fluorescence resonance energy transfer (FRET), and monitoring VP4-induced cytokine mRNA expression in the presence of anti-TLR2 and anti-VP4. MyrVP4 and TLR2 colocalized in TLR2-expressing HEK-293 cells, mouse bone marrow-derived macrophages, human bronchoalveolar macrophages, and human airway epithelial cells. Colocalization was absent in TLR2-null HEK-293 cells and blocked by anti-TLR2 and anti-VP4. Cy3-labeled MyrVP4 and Cy5-labeled anti-TLR2 showed an average fractional FRET efficiency of 0.24 ± 0.05, and Cy5-labeled anti-TLR2 increased and unlabeled MyrVP4 decreased FRET efficiency. MyrVP4-induced chemokine mRNA expression was higher than that elicited by VP4 alone and was attenuated by anti-TLR2 and anti-VP4. Cytokine expression was similarly increased by MyrVP4 purified from RV-infected HeLa cells and synthetic MyrVP4. We conclude that, during RV infection, MyrVP4 and TLR2 interact to generate a proinflammatory response.

The Innate Cytokines IL-25, IL-33, and TSLP Cooperate in the Induction of Type 2 Innate Lymphoid Cell Expansion and Mucous Metaplasia in Rhinovirus-Infected Immature Mice.

Early-life respiratory viral infection is a risk factor for asthma development. Rhinovirus (RV) infection of 6-d-old mice, but not mature mice, causes mucous metaplasia and airway hyperresponsiveness that are associated with the expansion of lung type 2 innate lymphoid cells (ILC2s) and are dependent on IL-13 and the innate cytokine IL-25. However, contributions of the other innate cytokines, IL-33 and thymic stromal lymphopoietin (TSLP), to the observed asthma-like phenotype have not been examined. We reasoned that IL-33 and TSLP expression are also induced by RV infection in immature mice and are required for maximum ILC2 expansion and mucous metaplasia. We inoculated 6-d-old BALB/c (wild-type) and TSLP receptor-knockout mice with sham HeLa cell lysate or RV. Selected mice were treated with neutralizing Abs to IL-33 or recombinant IL-33, IL-25, or TSLP. ILC2s were isolated from RV-infected immature mice and treated with innate cytokines ex vivo. RV infection of 6-d-old mice increased IL-33 and TSLP protein abundance. TSLP expression was localized to the airway epithelium, whereas IL-33 was expressed in epithelial and subepithelial cells. RV-induced mucous metaplasia, ILC2 expansion, airway hyperresponsiveness, and epithelial cell IL-25 expression were attenuated by anti-IL-33 treatment and in TSLP receptor-knockout mice. Administration of intranasal IL-33 and TSLP was sufficient for mucous metaplasia. Finally, TSLP was required for maximal ILC2 gene expression in response to IL-25 and IL-33. The generation of mucous metaplasia in immature RV-infected mice involves a complex interplay among the innate cytokines IL-25, IL-33, and TSLP.

Hyperoxic Exposure of Immature Mice Increases the Inflammatory Response to Subsequent Rhinovirus Infection: Association with Danger Signals.

Infants with a history of prematurity and bronchopulmonary dysplasia have a high risk of asthma and viral-induced exacerbations later in life. We hypothesized that hyperoxic exposure, a predisposing factor to bronchopulmonary dysplasia, modulates the innate immune response, producing an exaggerated proinflammatory reaction to viral infection. Two- to 3-d-old C57BL/6J mice were exposed to air or 75% oxygen for 14 d. Mice were infected intranasally with rhinovirus (RV) immediately after O2 exposure. Lung mRNA and protein expression, histology, dendritic cells (DCs), and airway responsiveness were assessed 1-12 d postinfection. Tracheal aspirates from premature human infants were collected for mRNA detection. Hyperoxia increased lung IL-12 expression, which persisted up to 12 d postexposure. Hyperoxia-exposed RV-infected mice showed further increases in IL-12 and increased expression of IFN-γ, TNF-α, CCL2, CCL3, and CCL4, as well as increased airway inflammation and responsiveness. In RV-infected, air-exposed mice, the response was not significant. Induced IL-12 expression in hyperoxia-exposed, RV-infected mice was associated with increased IL-12-producing CD103(+) lung DCs. Hyperoxia also increased expression of Clec9a, a CD103(+) DC-specific damaged cell-recognition molecule. Hyperoxia increased levels of ATP metabolites and expression of adenosine receptor A1, further evidence of cell damage and related signaling. In human preterm infants, tracheal aspirate Clec9a expression positively correlated with the level of prematurity. Hyperoxic exposure increases the activation of CD103(+), Clec9a(+) DCs, leading to increased inflammation and airway hyperresponsiveness upon RV infection. In premature infants, danger signal-induced DC activation may promote proinflammatory airway responses, thereby increasing respiratory morbidity.

IFN-γ Blocks Development of an Asthma Phenotype in Rhinovirus-Infected Baby Mice by Inhibiting Type 2 Innate Lymphoid Cells.

Early-life wheezing-associated infections with rhinovirus (RV) have been associated with asthma development in children. We have shown that RV infection of 6-day-old mice induces mucous metaplasia and airways hyperresponsiveness, which is dependent on IL-13, IL-25, and type 2 innate lymphoid cells (ILC2s). Infection of immature mice fails to induce lung IFN-γ expression, in contrast to mature 8-week-old mice with a robust IFN-γ response, consistent with the notion that deficient IFN-γ production in immature mice permits RV-induced type 2 immune responses. We therefore examined the effects of intranasal IFN-γ administration on RV-induced ILC2 expansion and IL-13 expression in 6-day-old BALB/c and IL-13 reporter mice. Airway responses were assessed by histology, immunofluorescence microscopy, quantitative polymerase chain reaction, ELISA, and flow cytometry. Lung ILC2s were also treated with IFN-γ ex vivo. We found that, compared with untreated RV-infected immature mice, IFN-γ treatment attenuated RV-induced IL-13 and Muc5ac mRNA expression and mucous metaplasia. IFN-γ also reduced ILC2 expansion and the percentage of IL-13-secreting ILC2s. IFN-γ had no effect on the mRNA or protein expression of IL-25, IL-33, or thymic stromal lymphoprotein. Finally, IFN-γ treatment of sorted ILC2s reduced IL-5, IL-13, IL-17RB, ST2, and GATA-3 mRNA expression. We conclude that, in immature mice, IFN-γ inhibits ILC2 expansion and IL-13 expression in vivo and ex vivo, thereby attenuating RV-induced mucous metaplasia. These findings demonstrate the antagonistic function of IFN-γ on ILC2 expansion and gene expression, the absence of which may contribute to the development of an asthma-like phenotype after early-life RV infection.

RORα-dependent type 2 innate lymphoid cells are required and sufficient for mucous metaplasia in immature mice.

Early-life wheezing-associated respiratory tract infection by rhinovirus (RV) is considered a risk factor for asthma development. We have shown that RV infection of 6-day-old BALB/c mice, but not mature mice, induces an asthmalike phenotype that is associated with an increase in the population of type 2 innate lymphoid cells (ILC2s) and dependent on IL-13 and IL-25. We hypothesize that ILC2s are required and sufficient for development of the asthmalike phenotype in immature mice. Mice were infected with RV1B on day 6 of life and treated with vehicle or a chemical inhibitor of retinoic acid receptor-related orphan receptor-α (RORα), SR3335 (15 mg·kg-1·day-1 ip for 7 days). We also infected Rorasg/sg mice without functional ILC2s. ILC2s were identified as negative for lineage markers and positive for cluster of differentiation 25 (CD25)/IL-2Rα and CD127/IL-7Rα. Effects of SR3335 on proliferation and function of cultured ILC2s were determined. Finally, sorted ILC2s were transferred into naïve mice, and lungs were harvested 14 days later for assessment of gene expression and histology. SR3335 decreased the number of RV-induced lung lineage-negative, CD25+, CD127+ ILC2s in immature mice. SR3335 also attenuated lung mRNA expression of IL-13, Muc5ac, and Gob5 as well as mucous metaplasia. We also found reduced expansion of ILC2s in RV-infected Rorasg/sg mice. SR3335 also blocked IL-25 and IL-33-induced ILC2 proliferation and IL-13 production ex vivo. Finally, adoptive transfer of ILC2s led to development of asthmalike phenotype in immature and adult mice. RORα-dependent ILC2s are required and sufficient for type 2 cytokine expression and mucous metaplasia in immature mice.

Toll-like receptor 2-expressing macrophages are required and sufficient for rhinovirus-induced airway inflammation.

BACKGROUND: We have shown that rhinovirus, a cause of asthma exacerbation, colocalizes with CD68+ and CD11b+ airway macrophages after experimental infection in human subjects. We have also shown that rhinovirus-induced cytokine expression is abolished in Toll-like receptor (TLR2)-/- bone marrow-derived macrophages. OBJECTIVE: We hypothesize that TLR2+ macrophages are required and sufficient for rhinovirus-induced airway inflammation in vivo. METHODS: Naive and ovalbumin (OVA)-sensitized and challenged C57BL/6 wild-type and TLR2-/- mice were infected with RV1B, followed by IgG or anti-TLR2, to determine the requirement and sufficiency of TLR2 for rhinovirus-induced airway responses. Bone marrow chimera experiments using OVA-treated C57BL/6 and TLR2-/- mice were also performed. Finally, naive TLR2-/- mice underwent intranasal transfer of bone marrow-derived wild-type macrophages. RESULTS: RV1B infection of naive wild-type mice induced an influx of airway neutrophils and CD11b+ exudative macrophages, which was reduced in TLR2-/- mice. After allergen exposure, rhinovirus-induced neutrophilic and eosinophilic airway inflammation and hyperresponsiveness were reduced in TLR2-/- and anti-TLR2-treated mice. Transfer of TLR2-/- bone marrow into wild-type, OVA-treated C57BL/6 mice blocked rhinovirus-induced airway responses, whereas transfer of wild-type marrow to TLR2-/- mice restored them. Finally, transfer of wild-type macrophages to naive TLR2-/- mice was sufficient for neutrophilic inflammation after rhinovirus infection, whereas macrophages treated with IL-4 (to induce M2 polarization) were sufficient for eosinophilic inflammation, mucous metaplasia, and airways hyperresponsiveness. CONCLUSIONS: TLR2 is required for early inflammatory responses induced by rhinovirus, and TLR2+ macrophages are sufficient to confer airway inflammation to TLR2-/- mice, with the pattern of inflammation depending on the macrophage activation state.

Rhinovirus infection induces interleukin-13 production from CD11b-positive, M2-polarized exudative macrophages.

Rhinovirus (RV) causes asthma exacerbations. Previously, we showed that adherent bronchoalveolar cells from allergen-treated mice produce IL-13 when stimulated with RV ex vivo, implicating cells of the monocyte/macrophage lineage in viral-induced airway inflammation. In this study, we hypothesized that RV infection of allergen-treated mice results in IL-13 production by CD11b+ exudative macrophages in vivo. We sensitized and challenged BALB/c mice with ovalbumin (OVA), after which mice were inoculated with RV or sham HeLa cell lysate. After 1 day, lungs were harvested, and cell suspensions were analyzed by flow cytometry. We repeated this process in IL-13 reporter mice, CD11b-DTR mice in which diphtheria toxin selectively depletes CD11b+ cells, and chemokine receptor 2 (CCR2) null mice. We found that lungs of mice infected with RV alone showed increases in CD45+, CD68+, F4/80+, Ly6C+, and CD11b(high) cells, indicating an influx of inflammatory monocytes and exudative macrophages. The combination of OVA and RV had synergistic effects on the exudative macrophage number. However, CD11b+ cells from OVA-treated, RV-infected mice showed M2 polarization, including expression of CD206 and CD301 and production of IL-13. Similar results were obtained in IL-13 reporter mice. Diphtheria toxin depleted CD11b+, IL-13-producing cells in OVA-treated, RV-infected, CD11b-DTR mice, decreasing airway inflammation and responsiveness. CD11b+, Ly6C+ cells were reduced in CCR2 knockout mice. We conclude that, in contrast to naive mice, RV infection of mice with allergic airways disease induces an influx of IL-13-producing CD11b+ exudative macrophages bearing M2 macrophage markers. This finding further implicates alternatively activated macrophages in RV-induced asthma exacerbations.

Periostin is required for maximal airways inflammation and hyperresponsiveness in mice.

BACKGROUND: Periostin, a secreted extracellular matrix protein, has been localized to deposits of subepithelial fibrosis in asthmatic patients, and periostin levels have been linked to increases in IL-13. OBJECTIVE: We hypothesized that periostin is required for airway inflammatory responses to a physiologic aeroallergen, house dust mite (HDM). METHODS: We studied F4-F6 B6;129-Postn(tm1Jmol)/J wild-type (Postn(+/+)) and null (Postn(-/-)) mice, as well as C57BL/6 mice treated with either IgM or OC-20 periostin neutralizing antibody. Mice were exposed to 5 doses of HDM intranasally over a 16-day period. RESULTS: HDM increased airways responsiveness in Postn(+/+) but not Postn(-/-) mice. In addition, HDM-treated C57BL/6 mice injected with OC-20 had lower airways responsiveness than HDM-treated mice injected with IgM. Compared with Postn(+/+) mice, Postn(-/-) mice showed decreases in HDM-induced inflammation and mucous metaplasia, as well as reduced IL-4, IL-25, CD68, Gob5, and periostin mRNA expression. OC-20 antibody produced similar results. HDM exposure increased periostin expression in the airway epithelium, subepithelium, smooth muscle and inflammatory cells. OC-20 blocked the HDM-induced IgE response, and T cells incubated with dendritic cells (DCs) from Postn(-/-) mice or treated with OC-20 showed deficient DNA synthesis and IL-13 responses compared with T cells incubated with wild-type DCs. Finally, adoptive transfer of bone marrow-derived DCs from Postn(+/+) mice was sufficient to promote allergic responses in F6 Postn(-/-) littermates. CONCLUSIONS: In mice, periostin is required for maximal airways hyperresponsiveness and inflammation after HDM sensitization and challenge. Periostin is required for maximal HDM-induced T-cell responses.

Neonatal rhinovirus induces mucous metaplasia and airways hyperresponsiveness through IL-25 and type 2 innate lymphoid cells.

BACKGROUND: Early-life human rhinovirus infection has been linked to asthma development in high-risk infants and children. Nevertheless, the role of rhinovirus infection in the initiation of asthma remains unclear. OBJECTIVE: We hypothesized that, in contrast to infection of mature BALB/c mice, neonatal infection with rhinovirus promotes an IL-25-driven type 2 response, which causes persistent mucous metaplasia and airways hyperresponsiveness. METHODS: Six-day-old and 8-week-old BALB/c mice were inoculated with sham HeLa cell lysate or rhinovirus. Airway responses from 1 to 28 days after infection were assessed by using quantitative PCR, ELISA, histology, immunofluorescence microscopy, flow cytometry, and methacholine responsiveness. Selected mice were treated with a neutralizing antibody to IL-25. RESULTS: Compared with mature mice, rhinovirus infection in neonatal mice increased lung IL-13 and IL-25 production, whereas IFN-γ, IL-12p40, and TNF-α expression was suppressed. In addition, the population of IL-13-secreting type 2 innate lymphoid cells (ILC2s) was expanded with rhinovirus infection in neonatal but not mature mice. ILC2s were the major cell type secreting IL-13 in neonates. Finally, anti-IL-25 neutralizing antibody attenuated ILC2 expansion, mucous hypersecretion, and airways responsiveness. CONCLUSIONS: These findings suggest that early-life viral infection could contribute to asthma development by provoking age-dependent, IL-25-driven type 2 immune responses.

Rhinovirus-induced macrophage cytokine expression does not require endocytosis or replication.

Rhinovirus (RV) is responsible for the majority of virus-induced asthma exacerbations. We showed previously that RV infection of ovalbumin-sensitized and -challenged BALB/c mice induces production of type 2 cytokines from M2-polarized macrophages. In the present study, we sought to determine the mechanism of RV-induced cytokine expression. We infected bone marrow-derived macrophages (BMMs) from BALB/c mice with RV serotype 1B, a minor group virus that infects mouse cells. Selected cultures were pretreated with IL-4, a type 2 cytokine increased in allergic asthma. RV infection of untreated cells increased messenger RNA and protein expression of the M1 cytokines TNF-α, CXCL1, and IL-6 but failed to induce expression of the M2 cytokines CCL22 and CCL24. Cells pretreated with IL-4 showed decreased expression of M1 cytokines but increased expression of Ym-1, Arg-1 (M2 markers), CCL22, and CCL24. Infection with ultraviolet (UV)-irradiated, replication-deficient RV elicited similar cytokine responses, suggesting that the outcome is replication independent. Consistent with this, viral RNA copy number did not increase in RV-treated BMMs or bronchoalveolar macrophages. RV-induced cytokine expression was not affected when cells were pretreated with cytochalasin D, suggesting that viral endocytosis is not required for the response. Finally, RV-induced cytokine expression and viral attachment were abolished in BMMs from myeloid differentiation factor 88 and Toll-like receptor (TLR)2 KO mice, suggesting a specific requirement of TLR2. We conclude that RV elicits a proinflammatory cytokine response in BMMs through a cell-surface-mediated, TLR2-dependent mechanism that does not require viral endocytosis or replication.

Suppression of inflammatory cell trafficking and alveolar simplification by the heme oxygenase-1 product carbon monoxide.

Bronchopulmonary dysplasia (BPD), a lung disease of prematurely born infants, is characterized in part by arrested development of pulmonary alveolae. We hypothesized that heme oxygenase (HO-1) and its byproduct carbon monoxide (CO), which are thought to be cytoprotective against redox stress, mitigate lung injury and alveolar simplification in hyperoxia-exposed neonatal mice, a model of BPD. Three-day-old C57BL/6J mice were exposed to air or hyperoxia (FiO2, 75%) in the presence or absence of inhaled CO (250 ppm for 1 h twice daily) for 21 days. Hyperoxic exposure increased mean linear intercept, a measure of alveolar simplification, whereas CO treatment attenuated hypoalveolarization, yielding a normal-appearing lung. Conversely, HO-1-null mice showed exaggerated hyperoxia-induced hypoalveolarization. CO also inhibited hyperoxia-induced pulmonary accumulation of F4/80+, CD11c+, and CD11b+ monocytes and Gr-1+ neutrophils. Furthermore, CO attenuated lung mRNA and protein expression of proinflammatory cytokines, including the monocyte chemoattractant CCL2 in vivo, and decreased hyperoxia-induced type I alveolar epithelial cell CCL2 production in vitro. Hyperoxia-exposed CCL2-null mice, like CO-treated mice, showed attenuated alveolar simplification and lung infiltration of CD11b+ monocytes, consistent with the notion that CO blocks lung epithelial cell cytokine production. We conclude that, in hyperoxia-exposed neonatal mice, inhalation of CO suppresses inflammation and alveolar simplification.

Reduced platelet-derived growth factor receptor expression is a primary feature of human bronchopulmonary dysplasia.

Animal studies have shown that platelet-derived growth factor (PDGF) signaling is required for normal alveolarization. Changes in PDGF receptor (PDGFR) expression in infants with bronchopulmonary dysplasia (BPD), a disease of hypoalveolarization, have not been examined. We hypothesized that PDGFR expression is reduced in neonatal lung mesenchymal stromal cells (MSCs) from infants who develop BPD. MSCs from tracheal aspirates of premature infants requiring mechanical ventilation in the first week of life were studied. MSC migration was assessed in a Boyden chamber. Human lung tissue was obtained from the University of Rochester Neonatal Lung Biorepository. Neonatal mice were exposed to air or 75% oxygen for 14 days. PDGFR expression was quantified by qPCR, immunoblotting, and stereology. MSCs were isolated from 25 neonates (mean gestational age 27.7 wk); 13 developed BPD and 12 did not. MSCs from infants who develop BPD showed lower PDGFR-α and PDGFR-ß mRNA and protein expression and decreased migration to PDGF isoforms. Lungs from infants dying with BPD show thickened alveolar walls and paucity of PDGFR-α-positive cells in the dysmorphic alveolar septa. Similarly, lungs from hyperoxia-exposed neonatal mice showed lower expression of PDGFR-α and PDGFR-ß, with significant reductions in the volume of PDGFR-α-positive alveolar tips. In conclusion, MSCs from infants who develop BPD hold stable alterations in PDGFR gene expression that favor hypoalveolarization. These data demonstrate that defective PDGFR signaling is a primary feature of human BPD.

Macrophage activation state determines the response to rhinovirus infection in a mouse model of allergic asthma.

BACKGROUND: The mechanisms by which viruses cause asthma exacerbations are not precisely known. Previously, we showed that, in ovalbumin (OVA)-sensitized and -challenged mice with allergic airway inflammation, rhinovirus (RV) infection increases type 2 cytokine production from alternatively-activated (M2) airway macrophages, enhancing eosinophilic inflammation and airways hyperresponsiveness. In this paper, we tested the hypothesis that IL-4 signaling determines the state of macrophage activation and pattern of RV-induced exacerbation in mice with allergic airways disease. METHODS: Eight week-old wild type or IL-4 receptor knockout (IL-4R KO) mice were sensitized and challenged with OVA and inoculated with RV1B or sham HeLa cell lysate. RESULTS: In contrast to OVA-treated wild-type mice with both neutrophilic and eosinophilic airway inflammation, OVA-treated IL-4R KO mice showed increased neutrophilic inflammation with few eosinophils in the airways. Like wild-type mice, IL-4R KO mice showed OVA-induced airway hyperreactivity which was further exacerbated by RV. There was a shift in lung cytokines from a type 2-predominant response to a type 1 response, including production of IL-12p40 and TNF-α. IL-17A was also increased. RV infection of OVA-treated IL-4R KO mice further increased neutrophilic inflammation. Bronchoalveolar macrophages showed an M1 polarization pattern and ex vivo RV infection increased macrophage production of TNF-α, IFN-γ and IL-12p40. Finally, lung cells from OVA-treated IL-4R KO mice showed reduced CD206+ CD301+ M2 macrophages, decreased IL-13 and increased TNF-α and IL-17A production by F4/80+, CD11b+ macrophages. CONCLUSIONS: OVA-treated IL-4R KO mice show neutrophilic airway inflammation constituting a model of allergic, type 1 cytokine-driven neutrophilic asthma. In the absence of IL-4/IL-13 signaling, RV infection of OVA-treated mice increased type 1 cytokine and IL-17A production from conventionally-activated macrophages, augmenting neutrophilic rather than eosinophilic inflammation. In mice with allergic airways inflammation, IL-4R signaling determines macrophage activation state and the response to subsequent RV infection.

Neonatal rhinovirus infection induces mucous metaplasia and airways hyperresponsiveness.

Recent studies link early rhinovirus (RV) infections to later asthma development. We hypothesized that neonatal RV infection leads to an IL-13-driven asthma-like phenotype in mice. BALB/c mice were inoculated with RV1B or sham on day 7 of life. Viral RNA persisted in the neonatal lung up to 7 d postinfection. Within this time frame, IFN-α, -ß, and -γ peaked 1 d postinfection, whereas IFN-λ levels persisted. Next, we examined mice on day 35 of life, 28 d after initial infection. Compared with sham-treated controls, virus-inoculated mice demonstrated airways hyperresponsiveness. Lungs from RV-infected mice showed increases in several immune cell populations, as well as the percentages of CD4-positive T cells expressing IFN-γ and of NKp46/CD335(+), TCR-ß(+) cells expressing IL-13. Periodic acid-Schiff and immunohistochemical staining revealed mucous cell metaplasia and muc5AC expression in RV1B- but not sham-inoculated lungs. Mucous metaplasia was accompanied by induction of gob-5, MUC5AC, MUC5B, and IL-13 mRNA. By comparison, adult mice infected with RV1B showed no change in IL-13 expression, mucus production, or airways responsiveness 28 d postinfection. Intraperitoneal administration of anti-IL-13 neutralizing Ab attenuated RV-induced mucous metaplasia and methacholine responses, and IL-4R null mice failed to show RV-induced mucous metaplasia. Finally, neonatal RV increased the inflammatory response to subsequent allergic sensitization and challenge. We conclude that neonatal RV1B infection leads to persistent airways inflammation, mucous metaplasia, and hyperresponsiveness, which are mediated, at least in part, by IL-13.

Tuft cells are required for a rhinovirus-induced asthma phenotype in immature mice.

Infection of immature mice with rhinovirus (RV) induces an asthma-like phenotype consisting of type 2 inflammation, mucous metaplasia, eosinophilic inflammation, and airway hyperresponsiveness that is dependent on IL-25 and type 2 innate lymphoid cells (ILC2s). Doublecortin-like kinase 1-positive (DCLK1+) tuft cells are a major source of IL-25. We sought to determine the requirement of tuft cells for the RV-induced asthma phenotype in wild-type mice and mice deficient in Pou2f3, a transcription factor required for tuft cell development. C57BL/6J mice infected with RV-A1B on day 6 of life and RV-A2 on day 13 of life showed increased DCLK1+ tuft cells in the large airways. Compared with wild-type mice, RV-infected Pou2f3-/- mice showed reductions in IL-25 mRNA and protein expression, ILC2 expansion, type 2 cytokine expression, mucous metaplasia, lung eosinophils, and airway methacholine responsiveness. We conclude that airway tuft cells are required for the asthma phenotype observed in immature mice undergoing repeated RV infections. Furthermore, RV-induced tuft cell development provides a mechanism by which early-life viral infections could potentiate type 2 inflammatory responses to future infections.

Macrophage/epithelial cell CCL2 contributes to rhinovirus-induced hyperresponsiveness and inflammation in a mouse model of allergic airways disease.

Human rhinovirus (HRV) infections lead to exacerbations of lower airways disease in asthmatic patients but not in healthy individuals. However, underlying mechanisms remain to be completely elucidated. We hypothesized that the Th2-driven allergic environment enhances HRV-induced CC chemokine production, leading to asthma exacerbations. Ovalbumin (OVA)-sensitized and -challenged mice inoculated with HRV showed significant increases in the expression of lung CC chemokine ligand (CCL)-2/monocyte chemotactic protein (MCP)-1, CCL4/macrophage inflammatory protein (MIP)-1ß, CCL7/MCP-3, CCL19/MIP-3ß, and CCL20/MIP3α compared with mice treated with OVA alone. Inhibition of CCL2 with neutralizing antibody significantly attenuated HRV-induced airways inflammation and hyperresponsiveness in OVA-treated mice. Immunohistochemical stains showed colocalization of CCL2 with HRV in epithelial cells and CD68-positive macrophages, and flow cytometry showed increased CCL2(+), CD11b(+) cells in the lungs of OVA-treated, HRV-infected mice. Compared with lung macrophages from naïve mice, macrophages from OVA-exposed mice expressed significantly more CCL2 in response to HRV infection ex vivo. Pretreatment of mouse lung macrophages and BEAS-2B human bronchial epithelial cells with interleukin (IL)-4 and IL-13 increased HRV-induced CCL2 expression, and mouse lung macrophages from IL-4 receptor knockout mice showed reduced CCL2 expression in response to HRV, suggesting that exposure to these Th2 cytokines plays a role in the altered HRV response. Finally, bronchoalveolar macrophages from children with asthma elaborated more CCL2 upon ex vivo exposure to HRV than cells from nonasthmatic patients. We conclude that CCL2 production by epithelial cells and macrophages contributes to HRV-induced airway hyperresponsiveness and inflammation in a mouse model of allergic airways disease and may play a role in HRV-induced asthma exacerbations.

MDA5 and TLR3 initiate pro-inflammatory signaling pathways leading to rhinovirus-induced airways inflammation and hyperresponsiveness.

Rhinovirus (RV), a single-stranded RNA picornavirus, is the most frequent cause of asthma exacerbations. We previously demonstrated in human bronchial epithelial cells that melanoma differentiation-associated gene (MDA)-5 and the adaptor protein for Toll-like receptor (TLR)-3 are each required for maximal RV1B-induced interferon (IFN) responses. However, in vivo, the overall airway response to viral infection likely represents a coordinated response integrating both antiviral and pro-inflammatory pathways. We examined the airway responses of MDA5- and TLR3-deficient mice to infection with RV1B, a minor group virus which replicates in mouse lungs. MDA5 null mice showed a delayed type I IFN and attenuated type III IFN response to RV1B infection, leading to a transient increase in viral titer. TLR3 null mice showed normal IFN responses and unchanged viral titers. Further, RV-infected MDA5 and TLR3 null mice showed reduced lung inflammatory responses and reduced airways responsiveness. Finally, RV-infected MDA5 null mice with allergic airways disease showed lower viral titers despite deficient IFN responses, and allergic MDA5 and TLR3 null mice each showed decreased RV-induced airway inflammatory and contractile responses. These results suggest that, in the context of RV infection, binding of viral dsRNA to MDA5 and TLR3 initiates pro-inflammatory signaling pathways leading to airways inflammation and hyperresponsiveness.