Innate IFNs and plasmacytoid dendritic cells constrain Th2 cytokine responses to rhinovirus: a regulatory mechanism with relevance to asthma

Polymorphism of the rs1800896 IL10 promoter gene protects children from post-bronchiolitis asthma

Viral bronchiolitis is a major cause of hospitalization in infancy, with increased asthma risk in later childhood. However, the principal mechanisms behind post-bronchiolitic asthma have remained unclear. Previously, different cytokine polymorphisms have been associated with asthma occurrence, but no previous follow-up study has investigated cytokine polymorphisms in relation to post-bronchiolitic asthma. We hypothesized that former bronchiolitis patients with cytokine gene variants associating with Th2 cell up-regulation are at asthma risk at preschool age. Our emphasis was in IL10 rs1800896, since IL-10 has an important role in immune tolerance, and lower production of IL-10 has been associated with Th2-type immunology, and accordingly, with increased asthma risk. IL10 rs1800896, IFNG rs2430561, and IL18 rs1872387 polymorphims and their associations with asthma and allergy were studied in 135 preschool-aged children hospitalized for bronchiolitis at age 0-6 months. Parents were interviewed to record asthma and allergy from infancy to present. At age 6.4 years (mean), asthma was present in 17(12.6%), atopic eczema in 47(34.8%) and allergic rhinitis in 36(26.7%) children. IL10 rs1800896 SNP associated significantly with asthma; only 1/32 (3.1%) of those with G/G genotype had asthma (P = 0.04). In logistic regression adjusted for gender, age and atopy, the carriage of allele A (rs1800896) was a significant risk factor for preschool asthma. IFNG rs2430561 or IL18 rs1872387 SNP's had no associations with asthma or allergy. In conclusion, IL10 rs1800896 SNP was significantly associated with preschool asthma after severe lower respiratory tract infection in early infancy.

Clinical view on the importance of dendritic cells in asthma

Allergic asthma is characterized by airway hyperresponsiveness and inflammation and may lead to airway remodeling in uncontrolled cases. Genetic predisposition to an atopic phenotype plays a major component in the pathophysiology of asthma. However, with tremendous role of epigenetic factors and environmental stimuli in precipitating an immune response, the underlying pathophysiological mechanisms are complicated. Dendritic cells are principal antigen-presenting cells and initiators of the immune response in allergic asthma. Their phenotype, guided by multiple factors may dictate the immune reaction to an allergic or tolerogenic response. Involvement of the local cytokine milieu, microbiome and interplay between immune cells add dimension to the fate of immune response. In addition to allergen exposure, these factors modulate DC phenotype and function. In this article, integration of many factors and pathways associated with the recruitment and activation of DCs in the pathophysiology of allergic asthma is presented in a clinical and translational manner.

Type I and III interferon production in response to RNA viruses

The biology of RNA viruses is closely linked to the type I and type III interferon (IFN) response of the host. These viruses display a range of molecular patterns that may be detected by host cells resulting in the induction of IFNs. Consequently, there are many examples of mechanisms employed by RNA viruses to block or delay IFN induction and reduce the expression of IFN-stimulated genes (ISGs), a necessary step in the virus lifecycle because of the capacity of IFNs to block virus replication. Efficient transmission of viruses depends, in part, on maintaining a balance between virus replication and host survival; specialized host cells, such as plasmacytoid dendritic cells, can sense viral molecular patterns and produce IFNs to help maintain this balance. There are now many examples of RNA viruses inducing type I and type III IFNs, and although these IFNs act through different receptors, in many systems studied, they induce a similar spectrum of genes. However, there may be a difference in the temporal expression pattern, with more prolonged expression of ISGs in response to type III IFN compared with type I IFN. There are also examples of synergy between type I and type III IFNs to induce antiviral responses. Clearly, it is important to understand the different roles of these IFNs in the antiviral response in vivo. One of the most striking differences between these 2 IFN systems is the distribution of the receptors: type I IFN receptors are expressed on most cells, yet type III receptor expression is restricted primarily to epithelial cells but has also been demonstrated on other cells, including dendritic cells. There is increasing evidence that type III IFNs are a key control mechanism against RNA viruses that infect respiratory and enteric epithelia.

The expression of dendritic cell subsets in severe chronic rhinosinusitis with nasal polyps is altered

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized as a Th2-driven disease. Activated dendritic cells (DCs) are the main T-cell activators; their role in the chronic inflammatory process of nasal polyposis is still unclear.

METHODS

The regulation of DC subsets was analyzed in nasal polyp tissue from CRSwNP patients and compared to inferior turbinate tissue from healthy subjects. Tissue localization and expression of both plasmacytoid and myeloid DCs were assayed by means of immunohistochemistry and flow cytometry. Plasmacytoid DCs were also assayed by PCR, and tissue homogenates were assayed for various inflammatory markers.

RESULTS

The number of plasmacytoid (pDCs) and myeloid (mDCs) dendritic cells was significantly increased in nasal polyp tissue when compared to non-inflamed nasal mucosa. The number of pDCs, but not mDCs, was down-regulated in more severe cases (nasal polyps with asthma) and varied with the cytokine milieu. The amount of pDCs was significantly decreased in IL5+IFNγ - nasal polyp tissue compared to tissues with high IFNγ levels (IL5+IFNγ+). Furthermore, levels of indoleamine 2,3-dioxygenase were increased in nasal polyp compared to inferior turbinate tissue and correlated negatively with the number of pDCs.

CONCLUSIONS

There is an altered balance of pDC and mDC numbers in nasal polyp tissue. pDCs seem to be more susceptible to an inflammatory cytokine milieu and may play a crucial role in disease severity.

Comparison of rhinovirus antibody titers in children with asthma exacerbations and species-specific rhinovirus infection

BACKGROUND

Asthma exacerbations are associated with human rhinovirus (HRV) infections, and more severe exacerbations are associated with HRV-C. We have previously shown that the HRV-C-specific antibody response is low in healthy adult sera and that most of the antibody to HRV-C is cross-reactive with HRV-A.

OBJECTIVES

To compare the antibody response to each HRV species in asthmatic and nonasthmatic children in whom the type of HRV infection was known.

METHODS

Total and specific IgG₁ binding to HRV viral capsid protein antigens of HRV-A, -B, and -C were tested in the plasma from nonasthmatic children (n = 47) and children presenting to the emergency department with asthma exacerbations (n = 96). HRV, found in most of the children at the time of their exacerbation (72%), was analyzed using molecular typing.

RESULTS

Asthmatic children had higher antibody responses to HRV. The titers specific to HRV-A, and to a lesser extent HRV-B, were higher than in nonasthmatic controls. The species-specific responses to HRV-C were markedly lower than titers to HRV-A and HRV-B in both asthmatic and nonasthmatic children (P < .001). The titers both at presentation and after convalescence were not associated with the HRV genotype detected during the exacerbation.

CONCLUSIONS

The higher total anti-HRV antibody titers of asthmatic children and their higher anti-HRV-A and -B titers show their development of a heightened antiviral immune response. The low species-specific HRV-C titers found in all groups, even when the virus was found, point to a different and possibly less efficacious immune response to this species.

Th9/IL-9 profile in human echinococcosis: their involvement in immune response during infection by Echinococcus granulosus

Th9 cells have been reported to contribute to immune responses; however, the role of Th9 cells in Echinococcus granulosus infection is unknown. This study is to determine whether Th9 cells and IL-9 are involved in human Echinococcus granulosus infection. Compared with healthy controls (HC group), the mRNA levels of PU.1, IL-9, and GATA-3 were significantly increased in patients before therapy (CE group), as revealed by qRT-PCR. Flow cytometry analysis showed that the percentages of Th9 and Th2 cells in CE group were significantly higher. The levels of IL-9, IL-4, IL-10, and TGF-β in CE group were also significantly increased, as detected by CBA assay. The percentages of Th9 and Th2 cells in CE group were positively correlated. After treatments of surgery in combination with albendazole, the PU.1 and GATA-3 mRNA levels were significantly decreased in patients after therapy (PCE group) compared with CE group. The numbers of Th9 and Th2 cells and levels of IL-9, IL-4, IL-10, and TGF-β were also significantly decreased in PCE group. In conclusion, the ratios of Th9 cells and IL-9 levels were significantly decreased after treatment, suggesting that Th9/IL-9 may be involved in immune response induced by Echinococcus granulosus infection.

Anti-viral agents: potential utility in exacerbations of asthma

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Respiratory virus infections are the single greatest precipitants of asthma exacerbations.

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Current treatment options for AE are limited and have developed little in recent years.

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Development of effective anti-viral treatments remains a key target for therapeutic intervention.

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Approaches include therapies that either target the virus or boost host response to the virus.

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New clinical studies are needed to further our understanding of the mechanisms of virus induced asthma exacerbation.

Asthma is the most common chronic respiratory disease and its prevalence is on the increase. Respiratory viral infections in early life have been suggested to increase the risk of development of asthma in later life and virus infection remains the single greatest precipitant of asthma exacerbations. The development of effective anti-viral treatments remains a key target for therapeutic intervention. Here we discuss the role of respiratory viral infection in asthma exacerbation and highlight current and potential anti-viral agents and their mechanisms of action.

Rhinovirus and dsRNA induce RIG-I-like receptors and expression of interferon β and λ1 in human bronchial smooth muscle cells

Rhinovirus (RV) infections cause exacerbations and development of severe asthma highlighting the importance of antiviral interferon (IFN) defence by airway cells. Little is known about bronchial smooth muscle cell (BSMC) production of IFNs and whether BSMCs have dsRNA-sensing receptors besides TLR3. dsRNA is a rhinoviral replication intermediate and necrotic cell effect mimic that mediates innate immune responses in bronchial epithelial cells. We have explored dsRNA-evoked IFN-β and IFN-λ1 production in human BSMCs and potential involvement of TLR3 and RIG-I-like receptors (RLRs). Primary BSMCs were stimulated with 0.1-10 µg/ml dsRNA, 0.1-1 µg/ml dsRNA in complex with the transfection agent LyoVec (dsRNA/LyoVec; selectively activating cytosolic RLRs) or infected with 0.05-0.5 MOI RV1B. Both dsRNA stimuli evoked early (3 h), concentration-dependent IFN-β and IFN-λ1 mRNA expression, which with dsRNA/LyoVec was much greater, and with dsRNA was much less, after 24 h. The effects were inhibited by dexamethasone. Further, dsRNA and dsRNA/LyoVec concentration-dependently upregulated RIG-I and MDA5 mRNA and protein. dsRNA and particularly dsRNA/LyoVec caused IFN-β and IFN-λ1 protein production (24 h). dsRNA- but not dsRNA/LyoVec-induced IFN expression was partly inhibited by chloroquine that suppresses endosomal TLR3 activation. RV1B dose-dependently increased BSMC expression of RIG-I, MDA5, IFN-β, and IFN-λ1 mRNA. We suggest that BSMCs express functional RLRs and that both RLRs and TLR3 are involved in viral stimulus-induced BSMC expression of IFN-β and IFN-λ1.

Vascular endothelial growth factor as a key inducer of angiogenesis in the asthmatic airways

Asthma is a chronic inflammatory disease of the airways characterized by structural airway changes, which are known as airway remodeling, including smooth muscle hypertrophy, goblet cell hyperplasia, subepithelial fibrosis, and angiogenesis. Vascular remodeling in asthmatic lungs results from increased angiogenesis, which is mainly mediated by vascular endothelial growth factor (VEGF). VEGF is a key regulator of blood vessel growth in the airways of asthma patients by promoting proliferation and differentiation of endothelial cells and inducing vascular leakage and permeability. In addition, VEGF induces allergic inflammation, enhances allergic sensitization, and has a role in Th2 type inflammatory responses. Specific inhibitors of VEGF and blockers of its receptors might be useful to control chronic airway inflammation and vascular remodeling, and might be a new therapeutic approach for chronic inflammatory airway disease like asthma.

Toll-like receptor 7 gene deficiency and early-life Pneumovirus infection interact to predispose toward the development of asthma-like pathology in mice

BACKGROUND

Respiratory tract viruses are a major environmental risk factor for both the inception and exacerbations of asthma. Genetic defects in Toll-like receptor (TLR) 7-mediated signaling, impaired type I interferon responses, or both have been reported in asthmatic patients, although their contribution to the onset and exacerbation of asthma remains poorly understood.

OBJECTIVE

We sought to determine whether Pneumovirus infection in the absence of TLR7 predisposes to bronchiolitis and the inception of asthma.

METHODS

Wild-type and TLR7-deficient (TLR7(-/-)) mice were inoculated with the rodent-specific pathogen pneumonia virus of mice at 1 (primary), 7 (secondary), and 13 (tertiary) weeks of age, and pathologic features of bronchiolitis or asthma were assessed. In some experiments infected mice were exposed to low-dose cockroach antigen.

RESULTS

TLR7 deficiency increased viral load in the airway epithelium, which became sloughed and necrotic, and promoted an IFN-α/β(low), IL-12p70(low), IL-1β(high), IL-25(high), and IL-33(high) cytokine microenvironment that was associated with the recruitment of type 2 innate lymphoid cells/nuocytes and increased TH2-type cytokine production. Viral challenge of TLR7(-/-) mice induced all of the cardinal pathophysiologic features of asthma, including tissue eosinophilia, mast cell hyperplasia, IgE production, airway smooth muscle alterations, and airways hyperreactivity in a memory CD4(+) T cell-dependent manner. Importantly, infections with pneumonia virus of mice promoted allergic sensitization to inhaled cockroach antigen in the absence but not the presence of TLR7.

CONCLUSION

TLR7 gene defects and Pneumovirus infection interact to establish an aberrant adaptive response that might underlie virus-induced asthma exacerbations in later life.

Innate interferons inhibit allergen and microbial specific T(H)2 responses

Several studies provided evidence of innate interferons (IFNs) regulating T(H)2 cytokine production using purified CD4(+) memory cells and T(H)2 polarisation via interleukin-4 (IL-4). Vitally, none of these previous studies examined IFN attenuation of T(H)2 responses to allergen or antigen. This study therefore sought to investigate the abrogation of specific allergen- and antigen-stimulated T(H)2 response in peripheral blood mononuclear cells (PBMC) derived from 12 sensitised individuals by IFN-β and IFN-λ. PBMC were cultured in the presence of house dust mite (HDM) allergen, rhinovirus (RV), influenza vaccine and tetanus toxoid (TT)±either IFN-β or IFN-λ for 3 and 5 days. IFN-γ, IL-5 and IL-13 protein levels were measured by ELISA. Quantitative PCR (qPCR) was used to investigate induction of genes involved in control of T(H)2 cytokines. No alteration in T(H)1 IFN-γ allergen/antigen response was observed with addition of IFN-β or IFN-λ. Consistent abrogation of T(H)2 response to HDM and influenza was observed with IFN-β at both time points; attenuation was observed by day 5 with RV and TT. IFN-λ had no consistent effect on T(H)2 production except in the presence of RV (multiplicity of infection=5); a decrease in IL-5 alone was observed in the presence of trivalent inactivated influenza vaccine. GATA binding protein 3 (GATA3) and suppressors of cytokine signalling3 mRNA were differentially regulated in HDM and influenza-stimulated cultures±IFN-β. We concluded that IFN-β produced a strong and consistent abrogation of T(H)2 cytokine production in the presence of a range of allergen and antigen stimulants.

Dendritic cells, viruses, and the development of atopic disease

Dendritic cells are important residents of the lung environment. They have been associated with asthma and other inflammatory diseases of the airways. In addition to their antigen-presenting functions, dendritic cells have the ability to modulate the lung environment to promote atopic disease. While it has long been known that respiratory viral infections associate with the development and exacerbation of atopic diseases, the exact mechanisms have been unclear. Recent studies have begun to show the critical importance of the dendritic cell in this process. This paper focuses on these data demonstrating how different populations of dendritic cells are capable of bridging the adaptive and innate immune systems, ultimately leading to the translation of viral illness into atopic disease.

Activation of the small G-protein Rac by human rhinovirus attenuates the TLR3/IFN-α axis while promoting CCL2 release in human monocyte-lineage cells

Although rhinoviral infections, a major cause of asthma exacerbations, occur predominantly in upper airway bronchial epithelial cells, monocytic-lineage cells are implicated in establishing the inflammatory microenvironment observed during the disease. Human rhinovirus (HRV) is unique in that nearly genetically identical viruses bind either the ICAM-1 or low-density lipoprotein receptor (LDL-R). Within minutes of binding, HRV is capable of eliciting a signaling response in both epithelial cells and monocyte-derived macrophages. It is unclear whether this signaling response is important to the subsequent release of inflammatory mediators, particularly in cells not capable of supporting viral replication. We show here that the small molecular mass G-protein Rac is activated following exposure of macrophages to HRV serotypes known to be ICAM-1- and LDL-R-tropic. We demonstrate that inhibiting Rac resulted in the upregulation of TLR3 in macrophages exposed to major- and minor-group HRV, and resulted in increased release of IFN-α. Furthermore, inhibiting Rac in HRV-exposed macrophages attenuated activation of the stress kinase p38 and release of the pro-inflammatory cytokine CCL2, but inhibiting Rac did not affect release of the pro-inflammatory cytokine CCL5. These findings suggest that Rac is an important regulator in establishing the inflammatory microenvironment that is initiated in the human airway upon exposure to rhinovirus.