Lee, Nancy A.

Key Points Eosinophils recruited to the airways in response to A fumigatus sensitization and challenge degranulate in response to virus infection. Activated eosinophils are antiviral and promote survival from an otherwise lethal respiratory virus infection.

Abstract Leukotrienes (i.e., products of the 5-lipoxygenase pathway) are thought to be contributors to lung pathologies. Moreover, eosinophils have been linked with pulmonary leukotriene activities both as potential sources of these mediators and as responding effector cells. The objective of the present study was to define the role(s) of leukotrienes in the lung pathologies accompanying eosinophil-associated chronic respiratory inflammation. A transgenic mouse model of chronic T helper (Th) 2–driven inflammation expressing IL-5 from T cells and human eotaxin-2 locally in the lung (I5/hE2) was used to define potential in vivo relationships among eosinophils, leukotrienes, and chronic Th2-polarized pulmonary inflammation. Airway levels of cys-leukotrienes and leukotriene B4 (LTB4) are both significantly elevated in I5/hE2 mice. The eosinophil-mediated airway hyperresponsiveness (AHR) characteristic of these mice was abolished in the absence of leukotrienes (i.e., 5-lipoxygenase–deficient I5/hE2). More importantly, the loss of leukotrienes led to an unexpectedly significant decrease in collagen deposition (i.e., pulmonary fibrosis) that accompanied elevated levels of IL-4/-13 and TGF-β in the lungs of I5/hE2 mice. Further studies using mice deficient for the LTB4 receptor (BLT-1−/− /I5/hE2) and I5/hE2 animals administered a cys-leukotriene receptor antagonist (montelukast) demonstrated that the AHR and the enhanced pulmonary fibrosis characteristic of the I5/hE2 model were uniquely cys-leukotriene–mediated events. These data demonstrate that, similar to allergen challenge models of wild-type mice, cys-leukotrienes underlie AHR in this transgenic model of severe pulmonary Th2 inflammation. These data also suggest that an underappreciated link exists among eosinophils, cys-leukotriene–mediated events, and fibrotic remodeling associated with elevated levels of IL-4/-13 and TGF-β.

Key PointsThe loss of the two most abundant eosinophil granule proteins disrupts the production of blood eosinophils from marrow progenitors. Knockout animals deficient for both MBP-1 and EPX represent a novel strain of mice with a specific and congenital loss of eosinophils.

ABSTRACT Eosinophils are generally linked to innate host defense against helminths, as well as the pathologies associated with allergic diseases, such as asthma. Nonetheless, the activities of eosinophils remain poorly understood, which in turn, has prevented detailed definitions of their role(s) in health and disease. Homologous recombination in embryonic stem cells was used to insert a mammalianized Cre recombinase in the ORF encoding Epx. This knock-in strategy overcame previous inefficiencies associated with eosinophil-specific transgenic approaches and led to the development of a knock-in strain of mice (eoCRE), capable of mediating recombination of “floxed” reporter cassettes in >95% of peripheral blood eosinophils. We also showed that this Cre expression was limited exclusively to eosinophil-lineage committed cells with no evidence of Cre-mediated toxicity. The efficiency and specificity of Cre expression in eoCRE mice were demonstrated further in a cross with a knock-in mouse containing a “(flox-stop-flox)” DTA cassette at the ROSA26 locus, generating yet another novel, eosinophil-less strain of mice. The development of eoCRE mice represents a milestone in studies of eosinophil biology, permitting eosinophil-specific gene targeting and overexpression in the mouse as part of next-generation studies attempting to define eosinophil effector functions.

Abstract The eosinophil-associated ribonuclease (Ear) family in the mouse consists of thirteen genes, eleven of which encode RNases that have physical/functional properties similar to the human Ears, eosinophil-derived neurotoxin and eosinophil cationic protein. The expression of Ear genes in the mouse is confined to sites of known eosinophilopoiesis, with the exception of the lung. Two Ear genes, Ear1 and Ear2, are predominantly expressed in the lungs of naive mice. Total Ear gene expression and RNase activity in bronchoalveolar lavage fluid increases significantly upon the induction of pulmonary inflammation using an ovalbumin (OVA) model of allergic sensitization and challenge. Interestingly, pulmonary Ear11 transcripts, which are absent in naive mice, accumulate as a consequence of OVA-mediated TH2 inflammation in the lung. The induction of Ear11 expression is dependent on the presence of T cells, in particular, CD4+ T lymphocytes. This effect is likely the result of the elaboration of TH2 cytokine levels, because pulmonary instillation of interleukin-4 or interleukin-13 induces the accumulation of Ear11 transcripts in naive animals. This study demonstrates that despite an allergen-mediated pulmonary eosinophilia and earlier studies showing that Ears are constituents of eosinophil secondary granules, alveolar macrophages are a significant source of these RNases in lungs of OVA-treated mice.

Objective Eosinophilic oesophagitis (EoE) is a chronic inflammatory condition of the oesophagus with limited treatment options. No previous transgenic model has specifically targeted the oesophageal mucosa to induce oesophageal eosinophilia. Design We developed a mouse model that closely resembles EoE by utilising oxazolone haptenation in mice with transgenic overexpression of an eosinophil poietic and survival factor (interleukin (IL)-5) in resident squamous oesophageal epithelia. Results Overexpression of IL-5 in the healthy oesophagus was achieved in transgenic mice ( L2-IL5 ) using the squamous epithelial promoter Epstein–Barr virus ED-L2. Oxazolone-challenged L2-IL5 mice developed dose-dependent pan-oesophageal eosinophilia, including eosinophil microabscess formation and degranulation as well as basal cell hyperplasia. Moreover, oesophagi expressed increased IL-13 and the eosinophil agonist chemokine eotaxin-1. Treatment of these mice with corticosteroids significantly reduced eosinophilia and epithelial inflammation. Conclusions L2-IL5 mice provide a novel experimental model that can potentially be used in preclinical testing of EoE-related therapeutics and mechanistic studies identifying pathogenetic features associated with mucosal eosinophilia.

AbstractSurprisingly, the role(s) of eosinophils in health and disease is often summarized by clinicians and basic research scientists as a pervasive consensus opinion first learned in medical/graduate school. Eosinophils are rare white blood cells whose activities are primarily destructive and are only relevant in parasitic infections and asthma. However, is this consensus correct? This review argues that the wealth of available studies investigating the role(s) of eosinophils in both health and disease demonstrates that the activities of these granulocytes are far more expansive and complex than previously appreciated. In turn, this greater understanding has led to the realization that eosinophils have significant contributory roles in a wide range of diseases. Furthermore, published studies even implicate eosinophil-mediated activities in otherwise healthy persons. We suggest that the collective reports in the literature showing a role for eosinophils in an ever-increasing number of novel settings highlight the true complexity and importance of this granulocyte. Indeed, discussions of eosinophils are no longer simple and more often than not now begin with the question/statement “Did you know …?”

Abstract Eosinophils play important roles in regulation of cellular responses under conditions of homeostasis or infection. Intestinal infection with the parasitic nematode, Trichinella spiralis, induces a pronounced eosinophilia that coincides with establishment of larval stages in skeletal muscle. We have shown previously that in mouse strains in which the eosinophil lineage is ablated, large numbers of T. spiralis larvae are killed by NO, implicating the eosinophil as an immune regulator. In this report, we show that parasite death in eosinophil-ablated mice correlates with reduced recruitment of IL-4+ T cells and enhanced recruitment of inducible NO synthase (iNOS)-producing neutrophils to infected muscle, as well as increased iNOS in local F4/80+CD11b+Ly6C+ macrophages. Actively growing T. spiralis larvae were susceptible to killing by NO in vitro, whereas mature larvae were highly resistant. Growth of larvae was impaired in eosinophil-ablated mice, potentially extending the period of susceptibility to the effects of NO and enhancing parasite clearance. Transfer of eosinophils into eosinophil-ablated ΔdblGATA mice restored larval growth and survival. Regulation of immunity was not dependent upon eosinophil peroxidase or major basic protein 1 and did not correlate with activity of the IDO pathway. Our results suggest that eosinophils support parasite growth and survival by promoting accumulation of Th2 cells and preventing induction of iNOS in macrophages and neutrophils. These findings begin to define the cellular interactions that occur at an extraintestinal site of nematode infection in which the eosinophil functions as a pivotal regulator of immunity.

Abstract Reports have recently suggested that eosinophils have the potential to modulate allergen-dependent pulmonary immune responses. The studies presented expand these reports demonstrating in the mouse that eosinophils are required for the allergen-dependent Th2 pulmonary immune responses mediated by dendritic cells (DCs) and T lymphocytes. Specifically, the recruitment of peripheral eosinophils to the pulmonary lymphatic compartment(s) was required for the accumulation of myeloid DCs in draining lymph nodes and, in turn, Ag-specific T effector cell production. These effects on DCs and Ag-specific T cells did not require MHC class II expression on eosinophils, suggesting that these granulocytes have an accessory role as opposed to direct T cell stimulation. The data also showed that eosinophils uniquely suppress the DC-mediated production of Th17 and, to smaller degree, Th1 responses. The cumulative effect of these eosinophil-dependent immune mechanisms is to promote the Th2 polarization characteristic of the pulmonary microenvironment after allergen challenge.