An early innate response underlies severe influenza-induced exacerbations of asthma in a novel steroid-insensitive and anti-IL-5-responsive mouse model.

BACKGROUND: Acute worsening of asthma symptoms (exacerbation) is predominantly triggered by respiratory viruses, with influenza causing the most severe exacerbations. The lack of an adequate animal model hampers mechanistic insight and the development of new therapeutics. AIM: We developed and characterized a robust, consistent, and reproducible mouse model of severe exacerbation of chronic allergic asthma. METHODS: Chronic allergic airway inflammation was induced following a house dust mite (HDM) sensitization protocol. HDM-sensitized mice and controls were infected with influenza virus A/X31 H3N2 and either or not treated with inhaled fluticasone propionate (FP), systemic corticosteroids (Pred), or anti-IL-5. Mice were killed at different time points after infection: Cellular accumulation and cytokines levels in the airways, PenH as a measure of airway hyper-responsiveness (AHR), and lung histology and viral replication were assessed. RESULTS: Infection with low-dose A/X31 H3N2 led to prolonged deterioration of lung function, aggravated mucus production, peri-vascular, peri-bronchial, and allergic inflammation that was unresponsive to inhaled corticosteroids, but responsive to systemic corticosteroids. The exacerbation was preceded at 14 h after virus exposure by a marked innate, but no Th2 and Th1 response subsequently followed by enhanced numbers of eosinophils, neutrophils, dendritic, and T cells into the lung lumen, parenchyma, and draining lymph nodes in HDM-sensitized mice. Anti-IL-5 treatment attenuated eosinophils and prevented the X31-induced exacerbation. CONCLUSIONS: Together, these findings indicate that an early innate response that involves eosinophils underlies the exacerbation. This model recapitulates all major features of severe asthma exacerbations and can serve to discern driving mechanisms and promote the development of novel therapeutics.

Experimental food allergy to peanut enhances the immune response to house dust mite in the airways of mice.

BACKGROUND: Food allergy has been associated with an increased risk for the development of allergic asthma. Asthma is a risk factor for the development of an anaphylactic response to food allergens. An immunological interplay between sensitization to different allergens in different compartments of the body might be involved. OBJECTIVE: To evaluate the immunological interplay between intragastrical peanut (PE) sensitization and respiratory sensitization to house dust mite (HDM) allergens. METHODS: BALB/c mice were intragastrically sensitized to peanut or sham-sensitized and challenged systemically to PE. Between sensitization and challenge, mice were intranasally exposed to HDM extract or PBS, as a control. The response to HDM (eosinophil recruitment, cytokine response, HDM-specific immunoglobulins and airway hyper-reactivity) and to PE (cytokine response, mast cells in gut, mMCP-1 in serum and body temperature) was assessed. RESULTS: A preceding PE sensitization increased HDM-induced production of IL-4, IL-5, IL-13 and IFNγ in lung-draining lymph nodes and total IgE levels in HDM-sensitized mice. However, recruitment of inflammatory cells to the airways or airway hyper-reactivity was not aggravated in PE/HDM double-sensitized mice. Alternatively, HDM-induced airway inflammation did not significantly affect the immune response or the anaphylactic response to a systemic challenge with peanut. CONCLUSION AND CLINICAL RELEVANCE: Our data show that a preceding peanut sensitization boosted IgE- and HDM-specific Th2 response in the airways in mice. It contributes to the understanding of the underlying immunological mechanism of polysensitization which often occurs in allergic individuals over time.

Birch pollen immunotherapy inhibits anaphylaxis to the cross-reactive apple allergen Mal d 1 in mice.

BACKGROUND: Cross-reactive apple allergy is a common co-morbidity of birch pollen allergy, caused by the presence of a Bet v 1 homologue allergen in apple, Mal d 1. Treatment of tree pollen hay fever by immunotherapy is well established, but its effect on the accompanying apple allergy is debated. OBJECTIVE: To establish a mouse model of birch pollen induced cross-reactivity to Mal d 1 and investigate the effect of birch pollen immunotherapy on the cross-reactivity to Mal d 1. METHODS: Respiratory allergy was induced in Balb/c mice by intraperitoneal exposure to alum-adsorbed birch pollen extract (BPE) in combination with short or prolonged intranasal exposure to BPE. To evaluate the response to Mal d 1, mice were exposed intraperitoneally to Mal d 1. Immunoglobulin responses and cytokine production by splenocytes were measured by ELISA. Allergic symptoms were evaluated by measuring airway hyper-reactivity and hypothermia as a surrogate marker for anaphylaxis. Immunotherapy was performed subcutaneously with alum-adsorbed BPE. RESULTS: Mice exposed to BPE develop cross-reactive IgE to Mal d 1. Early after exposure to BPE, this response is still weak and does not yet translate into anaphylaxis. Interestingly, later re-challenge with BPE increased cross-reactivity to a level where Mal d 1 exposure induced anaphylaxis. Cross-sensitization can also be induced by systemic Mal d 1 exposure. Birch pollen immunotherapy significantly reduced the anaphylactic response of mice to Mal d 1. CONCLUSION & CLINICAL RELEVANCE: A mouse model mimicking birch pollen induced cross-reactivity to Mal d 1 was successfully established. In this model, birch pollen immunotherapy significantly ameliorated the anaphylaxis induced by Mal d 1. Our experimental data suggest that boosting of Mal d 1 recognizing immunoglobulins by BP SCIT is important for the amelioration of apple allergy in human.

Deficiency of FHL2 attenuates airway inflammation in mice and genetic variation associates with human bronchial hyper-responsiveness.

BACKGROUND: Asthma is an inflammatory disease that involves airway hyper-responsiveness and mucus hypersecretion. The LIM-only protein FHL2 is a crucial modulator of multiple signal transduction pathways and functions as a scaffold in specific protein-protein interactions. OBJECTIVE: We sought to investigate the role of FHL2 in airway inflammation. METHODS: Allergic airway inflammation was induced in WT and FHL2-knock out (FHL2-KO) mice with ovalbumin (OVA). Lung tissue, bronchoalveolar lavage fluid (BALF) and draining lymph node cells were analysed for inflammation. FHL2 loss and gain of function studies were performed in lung epithelial cells. RESULTS: FHL2-deficient mice challenged with OVA show significantly reduced airway inflammation as evidenced by reduced infiltration of inflammatory cells including eosinophils, dendritic cells, B cells and T cells. Furthermore, mucus production was decreased in FHL2-KO mice. In BALF, the levels of IL-5, IL-13, eotaxin-1 and eotaxin-2 were significantly lower in FHL2-KO mice. In addition, draining lymph node cells from FHL2-KO mice show reduced levels of IL-5 and IL-13. Consistent with this, OVA-specific serum IgG and IgE levels were reduced in FHL2-KO mice. We also found that phosphorylation of ERK1/2 is markedly attenuated in FHL2-KO lung. Knock-down of FHL2 in human lung epithelial cells resulted in a striking decrease in ERK1/2 phosphorylation and mRNA levels of inflammatory cytokines and MUC5AC, whereas FHL2 overexpression exhibited opposite effects. Finally, the SNP rs4851765 shows an association with the severity of bronchial hyper-responsiveness. CONCLUSION: These results highlight functional involvement of FHL2 in airway inflammation and identify FHL2 as a novel gene associated with asthma severity in human.

Allergic sensitization is associated with inadequate antioxidant responses in mice and men.

BACKGROUND: Allergies arise from aberrant Th2 responses to allergens. The processes involved in the genesis of allergic sensitization remain elusive. Some allergens such as derived from house dust mites have proteolytic activity which can induce oxidative stress in vivo. A reduced capacity of the host to control oxidative stress might prime for allergic sensitization. METHODS: Two different strains of mice were compared for their antioxidant and immune response to HDM. Protease activity of the HDM extract was reduced to investigate its role in oxidative stress induction in the airways and whether this induction could determine allergic sensitization and inflammation. The role of oxidative stress in allergic sensitization was also investigated in humans. An occupational cohort of animal workers was followed for the development of sensitization to rodent urinary proteins. Levels of oxidative stress in serum and antioxidant responses by PBMCs were determined. RESULTS: Susceptibility to allergic sensitization to mite allergens in mice was highly dependent on host genetic background and was associated with oxidative stress in the lungs before allergen exposure and poor antioxidant response after allergen exposure. Reduction in mite protease activity limited its capacity to induce oxidative stress and allergic inflammation in mice. We showed that also in human subjects, oxidative stress before allergen exposure and poor antioxidant responses were associated with predisposition to occupational allergy. CONCLUSION: Our study indicates that oxidative stress condition before allergen exposure due to an inadequate antioxidant response may prime for allergic Th2 responses.

IL-33 promotes the induction of immunoglobulin production after inhalation of house dust mite extract in mice.

BACKGROUND: The initial immune response to house dust mite (HDM) is orchestrated by an interplay between epithelial cells (ECs) and dendritic cells (DCs). Innate cytokines released by HDM-exposed ECs activate airway DCs and effector inflammatory cells, which together induce a HDM-specific Th2 cell response. Here, we investigate the respective roles of DCs and IL-33 in sensitization to HDM. METHOD: Balb/c mice were exposed via the airways to different HDM extracts, differing in at least endotoxin levels [Lotox (LT) and HiTox (HT)]. Alternatively, HDM-pulsed DCs in the presence or absence of additional LT-HDM, or administration of LT-HDM plus recombinant IL-33, were intratracheally (i.t.) administered to induce allergic airway inflammation. Eosinophil recruitment, cytokine production, serum immunoglobulins, and airway histology were analyzed. RESULTS: Direct exposure of airways with HT-HDM induced an eosinophilic airway inflammation, Th2 cytokine production, and an increase in total IgE and HDM IgG1, while LT-HDM was not able to do so. In contrast, i.t. instillation of LT-HDM-pulsed DCs induced a similar airway inflammation, mucus production, and cytokine production, but IgE or HDM IgG1 was not induced. Administration of HDM-pulsed DCs together with LT-HDM, to supply B cells with unprocessed antigen, was not sufficient to induce antibody production. Simultaneous administration of recombinant IL-33 with LT-HDM induced an antibody response, besides a cellular immune response. CONCLUSION: These results demonstrate that HDM-pulsed DCs were able to drive a Th2 response but that IL-33 was needed to induce a humoral immune response to a single inhalational challenge to HDM.

House dust mite allergic airway inflammation facilitates neosensitization to inhaled allergen in mice.

BACKGROUND: The mechanism by which many monosensitized allergic individuals progress to polysensitization over time remains to be elucidated. Mouse models have contributed greatly to the understanding of sensitization to inhaled allergens in healthy airways but hardly any studies have addressed sensitization during established allergy. We hypothesized that an allergic inflammatory milieu might facilitate sensitization to inhaled allergens by the presence of mature dendritic cells (DCs) and IL-4. METHODS: Mice with house dust mite (HDM)-induced allergic airway inflammation received a single intratracheal dose of ovalbumin (OVA), 2 days after the last HDM exposure. Ten days later, sensitization was assessed by rechallenge with OVA. We evaluated the following factors for their importance in neosensitization: (1) maturation and recruitment of DCs to the airways, (2) dependency on DCs using CD11cDTR conditional knockout mice, (3) presence of ongoing airway inflammation by comparing sensitization at day 2 and day 14 after the last HDM exposure and (4) dependency on IL-4 by treatment with blocking antibodies. RESULTS: House dust mite -induced inflammation facilitated neosensitization to OVA. HDM-induced inflammation increased the number of airway DCs with a mature phenotype but a DC reduction of 93% did not inhibit sensitization. Neosensitization to OVA was dependent on ongoing inflammation and in particular on IL-4. CONCLUSIONS: These findings show that HDM-induced allergic airway inflammation facilitates neosensitization to a second inhaled allergen in an IL-4-dependent manner and provide insight into the underlying mechanism of the frequently observed progression to polysensitization in HDM-monosensitized individuals.