Intrinsic AHR in IL-5 transgenic mice is dependent on CD4(+) cells and CD49d-mediated signaling

Revisiting the NIH Taskforce on the Research needs of Eosinophil-Associated Diseases (RE-TREAD)

Eosinophil-associated diseases (EADs) are rare, heterogeneous disorders characterized by the presence of eosinophils in tissues and/or peripheral blood resulting in immunopathology. The heterogeneity of tissue involvement, lack of sufficient animal models, technical challenges in working with eosinophils, and lack of standardized histopathologic approaches have hampered progress in basic research. Additionally, clinical trials and drug development for rare EADs are limited by the lack of primary and surrogate endpoints, biomarkers, and validated patient-reported outcomes. Researchers with expertise in eosinophil biology and eosinophil-related diseases reviewed the state of current eosinophil research, resources, progress, and unmet needs in the field since the 2012 meeting of the NIH Taskforce on the Research of Eosinophil-Associated Diseases (TREAD). RE-TREAD focused on gaps in basic science, translational, and clinical research on eosinophils and eosinophil-related pathogenesis. Improved recapitulation of human eosinophil biology and pathogenesis in murine models was felt to be of importance. Characterization of eosinophil phenotypes, the role of eosinophil subsets in tissues, identification of biomarkers of eosinophil activation and tissue load, and a better understanding of the role of eosinophils in human disease were prioritized. Finally, an unmet need for tools for use in clinical trials was emphasized. Histopathologic scoring, patient- and clinician-reported outcomes, and appropriate coding were deemed of paramount importance for research collaborations, drug development, and approval by regulatory agencies. Further exploration of the eosinophil genome, epigenome, and proteome was also encouraged. Although progress has been made since 2012, unmet needs in eosinophil research remain a priority.

Prostaglandins and Their Receptors in Eosinophil Function and As Therapeutic Targets

Of the known prostanoid receptors, human eosinophils express the prostaglandin D₂ (PGD₂) receptors DP1 [also D-type prostanoid (DP)] and DP2 (also chemoattractant receptor homologous molecule, expressed on Th2 cells), the prostaglandin E₂ receptors EP2 and EP4, and the prostacyclin (PGI₂) receptor IP. Prostanoids can bind to either one or multiple receptors, characteristically have a short half-life in vivo, and are quickly degraded into metabolites with altered affinity and specificity for a given receptor subtype. Prostanoid receptors signal mainly through G proteins and naturally activate signal transduction pathways according to the G protein subtype that they preferentially interact with. This can lead to the activation of sometimes opposing signaling pathways. In addition, prostanoid signaling is often cell-type specific and also the combination of expressed receptors can influence the outcome of the prostanoid impulse. Accordingly, it is assumed that eosinophils and their (patho-)physiological functions are governed by a sensitive prostanoid signaling network. In this review, we specifically focus on the functions of PGD₂, PGE₂, and PGI₂ and their receptors on eosinophils. We discuss their significance in allergic and non-allergic diseases and summarize potential targets for drug intervention.

A novel synthetic lipopeptide is allergy-protective by the induction of LPS-tolerance

BACKGROUND

Exposure to the environment of traditional farms can protect children from some allergic disease. Due to this exposure, TLR2 expression in these children is increased. TLR2 ligands derived from gram-positive bacteria are found in the dust of these farms.

OBJECTIVES

We proved whether a synthetic lipopeptide binding to the TLR1/2 heterodimer is able to protect from allergic disease in two different murine models of allergy. We also investigated the immunological mechanisms underlying the protective properties of the lipopeptide.

METHODS

We synthesized a lipopeptide derived from a germination lipoprotein of Bacillus cereus (LPGerD). We evaluated the immunomodulatory activity of LPGerD in a murine model of systemic sensitization (OVA/Alum) and in a model in which mice were sensitized with OVA pulsed bone-marrow-derived dendritic cells (BMDCs) via the airways. Furthermore, the induction of LPS tolerance was studied.

RESULTS

Treatment of mice with LPGerD in a mouse model of asthma led to protection against sensitization and airway inflammation. Similarly, bone-marrow-derived dendritic cells (BMDCs) pre-treated with LPGerD were not able to prime mice for allergic immune response. We observed that pre-treatment with LPGerD led to the induction of a LPS-tolerant state in BMDCs. These cells secreted markedly lower amounts of pro-inflammatory cytokines upon LPS stimulation. Furthermore, we observed an up-regulation of IRAK-M mRNA in BMDCs pre-treated with LPGerD.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results suggest that induction of a LPS-tolerant state in antigen-presenting cells (APCs) may contribute to the protective effect of a farming environment. TLR2 agonists similar to those appearing in cowshed dust extracts, such as our synthetic LPGerD, lead to the ignorance of the LPS stimulus, which is important for the activation of APCs to mount a Th2 immune response. This substance might be a promising candidate for allergy-preventive treatments as LPGerD had only low pro-inflammatory characteristics.

Nonhematopoietic NADPH oxidase regulation of lung eosinophilia and airway hyperresponsiveness in experimentally induced asthma

Pulmonary eosinophilia is one of the most consistent hallmarks of asthma. Infiltration of eosinophils into the lung in experimental asthma is dependent on the adhesion molecule vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Ligation of VCAM-1 activates endothelial cell NADPH oxidase, which is required for VCAM-1-dependent leukocyte migration in vitro. To examine whether endothelial-derived NADPH oxidase modulates eosinophil recruitment in vivo, mice deficient in NADPH oxidase (CYBB mice) were irradiated and received wild-type hematopoietic cells to generate chimeric CYBB mice. In response to ovalbumin (OVA) challenge, the chimeric CYBB mice had increased numbers of eosinophils bound to the endothelium as well as reduced eosinophilia in the lung tissue and bronchoalveolar lavage. This occurred independent of changes in VCAM-1 expression, cytokine/chemokine levels (IL-5, IL-10, IL-13, IFNgamma, or eotaxin), or numbers of T cells, neutrophils, or mononuclear cells in the lavage fluids or lung tissue of OVA-challenged mice. Importantly, the OVA-challenged chimeric CYBB mice had reduced airway hyperresponsiveness (AHR). The AHR in OVA-challenged chimeric CYBB mice was restored by bypassing the endothelium with intratracheal administration of eosinophils. These data suggest that VCAM-1 induction of NADPH oxidase in the endothelium is necessary for the eosinophil recruitment during allergic inflammation. Moreover, these studies provide a basis for targeting VCAM-1-dependent signaling pathways in asthma therapies.

A small molecule, orally active, alpha4beta1/alpha4beta7 dual antagonist reduces leukocyte infiltration and airway hyper-responsiveness in an experimental model of allergic asthma in Brown Norway rats

alpha(4)beta(1) and alpha(4)beta(7) integrins are preferentially expressed on eosinophils and mononuclear leukocytes and play critical roles in their recruitment to inflammatory sites. We investigated the effects of TR14035, a small molecule, alpha(4)beta(1)/alpha(4)beta(7) dual antagonist, in a rat model of allergic asthma. Actively sensitized rats were challenged with aerosol antigen or saline on day 21, and the responses evaluated 24 and 48-h later. TR14035 (3 mg kg(-1), p.o.) was given 1-h before and 4-h after antigen or saline challenge. Airway hyper-responsiveness to intravenous 5-hydroxytryptamine was suppressed in TR14035-treated rats. Eosinophil, mononuclear cell and neutrophil counts, and eosinophil peroxidase and protein content in the bronchoalveolar lavage fluid (BALF) were decreased in TR14035-treated rats. Histological study showed a marked reduction of lung inflammatory lesions by TR14035. At 24-h postchallenge, antigen-induced lung interleukin (IL)-5 mRNA upregulation was suppressed in TR14035-treated rats. By contrast, IL-4 levels in BALF were not significantly affected by TR14035 treatment. IL-4 selectively upregulates vascular cell adhesion molecule-1 (VCAM-1), which is the main endothelial ligand of alpha(4) integrins. Intravital microscopy within the rat mesenteric microcirculation showed that 24-h exposure to 1 microg per rat of IL-4 induced a significant increase in leukocyte rolling flux, adhesion and emigration. These responses were decreased by 48, 100 and 99%, respectively in animals treated with TR14035. In conclusion, TR14035, by acting on alpha(4)beta(1) and alpha(4)beta(7) integrins, is an orally active inhibitor of airway leukocyte recruitment and hyper-responsiveness in animal models with potential interest for the treatment of asthma.

4-1 BB stimulation inhibits allergen-specific immunoglobulin E production and airway hyper-reactivity but partially suppresses bronchial eosinophilic inflammation in a mouse asthma model

BACKGROUND

4-1 BB, a member of the tumour necrosis factor receptor superfamily, functions as a co-stimulatory molecule. Recently, stimulation of the 4-1 BB pathway was shown to suppress antigen-specific CD4(+) T cell and subsequent T cell-dependent humoral immune responses.

OBJECTIVE

We examined the effect of agonistic anti-4-1 BB monoclonal antibody (mAb) treatment on allergic asthma, in which allergen-specific type 2 helper T cells (Th2) have been shown to play an important role.

METHODS

BALB/c mice were systemically sensitized with intraperitoneal injections of ovalbumin (OVA) and alum on days 0 and 14, and then challenged with inhaled OVA on days 28, 29 and 30. In test groups, the agonistic anti-4-1 BB mAb was administered at the time of initial systemic sensitization with OVA. On day 31, mice were challenged with inhaled methacholine, and enhanced pause was measured as an index of airway hyper-responsiveness (AHR). Levels of OVA-specific IgE in serum, and levels of various cytokines in bronchoalveolar lavage (BAL) fluids were measured. The severity of airway inflammation was determined by differential cell counts in BAL fluids and histopathologic lung analysis. To evaluate local immunity, we cultured lymphocytes from draining perihilar lymph nodes and evaluated the proliferative response to OVA and the levels of IL-5 in the culture supernatant. In addition, the functional mechanism of 4-1 BB stimulation was evaluated in splenocytes obtained at day 7 after systemic OVA sensitization.

RESULTS

We found that treatment with the anti-4-1 BB mAb significantly decreased AHR and the production of allergen-specific IgE. Bronchial inflammation, however, had only partially improved and the levels of IL-4 and IL-5 in BAL fluids showed only a small degree of reduction compared with the control Ig-treated mice. Thoracic lymphocytes from anti-4-1 BB-treated mice showed significant suppression of OVA-induced proliferation and IL-5 production. In anti-4-1 BB-treated mice, splenocytes exhibited poor proliferation and marked apoptosis 7 days after systemic OVA challenge.

CONCLUSION

These results suggest that stimulation of the 4-1 BB pathway effectively suppresses some features of allergic asthma, including allergen-specific IgE production and AHR, through deletion of allergen-specific Th2 cells. However, we found that bronchial allergic inflammation was not strictly mediated by suppression of the Th2 immune response in this murine model of asthma. Despite these somewhat contradictory effects, intervention in the 4-1 BB pathway might provide a potential novel immunotherapeutic approach for treatment of allergic asthma.

CD4(+) T cell-dependent airway mucus production occurs in response to IL-5 expression in lung

The potential role of airway interleukin-5 (IL-5) expression in eliciting mucus production was demonstrated in a pulmonary IL-5 transgenic mouse model (NJ.1726) in which naive transgenic mice display comparable levels of airway mucus relative to allergen-sensitized and -challenged wild-type mice. The intrinsic mucus accumulation of NJ.1726 was abolished in compound transgenic-gene knockout mice deficient of either CD4(+) cells [NJ.1726/CD4(-/-)] or alphabeta T cell receptor-positive (TCR(+)) cells [NJ.1726/alphabeta TCR(-/-)]. In addition, mucus production in naive NJ.1726 was inhibited by >90% after administration of the soluble anti-IL-4 receptor alpha-subunit antagonist. The loss of mucus production in NJ.1726/CD4(-/-), NJ.1726/alphabeta TCR(-/-), and anti-IL-4 receptor alpha-subunit antagonist-treated mice occurred notwithstanding the significant pulmonary eosinophilia and expansion of airway B cells induced by ectopic IL-5 expression. Furthermore, the loss of mucus accumulation occurred in these mice despite elevated levels of airway and peripheral IL-5, indicating that IL-5 does not directly induce goblet cell metaplasia and mucus production. Thus pulmonary expression of IL-5 alone is capable of inducing CD4(+) T cell-dependent goblet cell metaplasia, apparently mediated by IL-4 receptor alpha-subunit-ligand interactions, and represents a previously unrecognized novel pathway for augmenting allergen-induced mucus production.

Ectopic expression of IL-5 identifies an additional CD4(+) T cell mechanism of airway eosinophil recruitment

CD4(+) T cells have a critical role in the development of allergic pulmonary inflammation, including the recruitment of eosinophils to the airway lumen and interstitium. The expression of interleukin (IL)-5 by CD4(+) cells has, in particular, often been lionized as the central link between allergic inflammation and the concomitant expansion or recruitment of eosinophils. The mechanism(s) by which CD4(+) T cells mediates eosinophil recruitment was assessed with gene knockout mice deficient for T cells or T cell subtypes and a unique IL-5 transgenic mouse (line NJ.1726) that constitutively overexpresses this cytokine in the lung epithelium. Pulmonary IL-5 expression is significantly attenuated in T cell- and CD4(+) but not CD8(+) cell-deficient animals, suggesting an obvious explanation for the lack of eosinophils in the lungs of T cell-deficient and CD4(-/-) mice. However, although the constitutive expression of IL-5 in the lung epithelium of NJ.1726 mice elicited an eosinophilia in the airway lumen of both naive and ovalbumin-treated mice, in the absence of CD4(+) cells, allergen-mediated eosinophil recruitment to the bronchoalveolar lavage fluid was abolished. Moreover, intranasal instillation of the potent eosinophil-specific chemokine eotaxin-2 was incapable of eliciting eosinophil recruitment in naive and ovalbumin-treated NJ.1726 CD4(-/-) mice, suggesting that eosinophil trafficking during allergic inflammatory responses is a consequence of a CD4(+) cell-mediated event(s) in addition to IL-5 expression and the establishment of a pulmonary chemokine gradient.