Citations

Abstract Eosinophilia is a feature of the host immune response that distinguishes parasitic worms from other pathogens, yet a discrete function for eosinophils in worm infection has been elusive. The aim of this study was to clarify the mechanism(s) underlying the striking and unexpected observation that eosinophils protect intracellular, muscle-stage Trichinella spiralis larvae against NO-mediated killing. Our findings indicate that eosinophils are specifically recruited to sites of infection at the earliest stage of muscle infection, consistent with a local response to injury. Early recruitment is essential for larval survival. By producing IL-10 at the initiation of infection, eosinophils expand IL-10+ myeloid dendritic cells and CD4+ IL-10+ T lymphocytes that inhibit inducible NO synthase (iNOS) expression and protect intracellular larvae. The results document a novel immunoregulatory function of eosinophils in helminth infection, in which eosinophil-derived IL-10 drives immune responses that eventually limit local NO production. In this way, the parasite co-opts an immune response in a way that enhances its own survival.

Abstract IL-17 is known to play important roles in immune and inflammatory disease, such as in asthma, but its functions in allergic airway inflammation are still controversial, and the molecular mechanisms mediating these functions remain unclear. Increased production of eosinophils in bone marrow and their emergence in the airway have been linked to the onset and progression of allergic asthma. In this study, we investigated the effects of exogenous IL-17 on allergic airway inflammation and explored the underlying molecular mechanisms through eosinophil generation. Exogenous IL-17 significantly attenuated the features of allergic inflammation induced by ovalbumin in mice. It inhibited eosinophil differentiation both in vivo and in vitro, accompanied by down-regulated expression of CC chemokine receptor 3, GATA binding protein 1 (GATA-1), and GATA binding protein 2 (GATA-2), as well as reduced formation of common myeloid progenitors and eosinophil progenitors, but without influencing eosinophil apoptosis. IL-17 also significantly decreased the number of eosinophils in IL-5–transgenic mice, although it notably increased the levels of IL-3, IL-5, and granulocyte/macrophage colony–stimulating factor. In addition, IL-17 had little effect on secretion of the inflammatory cytokines by eosinophils. Neutralization of endogenous IL-17 significantly augmented eosinophil recruitment in the airways. Together, these findings suggest that exogenous IL-17 protects against allergic airway inflammation, most likely through inhibition of the eosinophil differentiation in bone marrow.

Abstract Allergen provocation of allergic asthma patients is often characterized by an initial period of bronchoconstriction, or early phase reaction (EPR), that leads to maximal airway narrowing within 15–30 min, followed by a recovery period returning airway function to baseline within 1–2 h. In this study, we used a defined OVA provocation model and mice deficient for specific leukocyte populations to investigate the cellular/molecular origins of the EPR. OVA-sensitized/challenged wild-type (C57BL/6J) mice displayed an EPR following OVA provocation. However, this response was absent in gene knockout animals deficient of either B or T cells. Moreover, transfer of OVA-specific IgG, but not IgE, before the OVA provocation, was capable of inducing the EPR in both strains of lymphocyte-deficient mice. Interestingly, an EPR was also observed in sensitized/challenged mast cell-deficient mice following an OVA provocation. These data show that the EPR in the mouse is an immunologically based pathophysiological response that requires allergen-specific IgG but occurs independent of mast cell activities. Thus, in the mouse the initial period of bronchoconstriction following allergen exposure may involve neither mast cells nor IgE-mediated events.

Abstract Paradigms of eosinophil effector function in the lungs of asthma patients invariably depend on activities mediated by cationic proteins released from secondary granules during a process collectively referred to as degranulation. In this study, we generated knockout mice deficient for eosinophil peroxidase (EPO) to assess the role(s) of this abundant secondary granule protein in an OVA-challenge model. The loss of EPO had no effect on the development of OVA-induced pathologies in the mouse. The absence of phenotypic consequences in these knockout animals extended beyond pulmonary histopathologies and airway changes, as EPO-deficient animals also displayed OVA-induced airway hyperresponsiveness after provocation with methacholine. In addition, EPO-mediated oxidative damage of proteins (e.g., bromination of tyrosine residues) recovered in bronchoalveolar lavage from OVA-treated wild-type mice was <10% of the levels observed in bronchoalveolar lavage recovered from asthma patients. These data demonstrate that EPO activities are inconsequential to the development of allergic pulmonary pathologies in the mouse and suggest that degranulation of eosinophils recruited to the lung in this model does not occur at levels comparable to those observed in humans with asthma.

Abstract The relationship between eosinophils and the development of Ag-induced pulmonary pathologies, including airway hyper-responsiveness, was investigated using mice deficient for the secondary granule component, major basic protein-1 (mMBP-1). The loss of mMBP-1 had no effect on OVA-induced airway histopathologies or inflammatory cell recruitment. Lung function measurements of knockout mice demonstrated a generalized hyporeactivity to methacholine-induced airflow changes (relative to wild type); however, this baseline phenotype was observable only with methacholine; no relative airflow changes were observed in response to another nonspecific stimulus (serotonin). Moreover, OVA sensitization/aerosol challenge of wild-type and mMBP-1−/− mice resulted in identical dose-response changes to either methacholine or serotonin. Thus, the airway hyper-responsiveness in murine models of asthma occurs in the absence of mMBP-1.

Abstract Asthma and mouse models of allergic respiratory inflammation are invariably associated with a pulmonary eosinophilia; however, this association has remained correlative. In this report, a causative relationship between eosinophils and allergen-provoked pathologies was established using eosinophil adoptive transfer. Eosinophils were transferred directly into the lungs of either naive or OVA-treated IL-5−/− mice. This strategy resulted in a pulmonary eosinophilia equivalent to that observed in OVA-treated wild-type animals. A concomitant consequence of this eosinophil transfer was an increase in Th2 bronchoalveolar lavage cytokine levels and the restoration of intracellular epithelial mucus in OVA-treated IL-5−/− mice equivalent to OVA-treated wild-type levels. Moreover, the transfer also resulted in the development of airway hyperresponsiveness. These pulmonary changes did not occur when eosinophils were transferred into naive IL-5−/− mice, eliminating nonspecific consequences of the eosinophil transfer as a possible explanation. Significantly, administration of OVA-treated IL-5−/− mice with GK1.5 (anti-CD4) Abs abolished the increases in mucus accumulation and airway hyperresponsiveness following adoptive transfer of eosinophils. Thus, CD4+ T cell-mediated inflammatory signals as well as signals derived from eosinophils are each necessary, yet alone insufficient, for the development of allergic pulmonary pathology. These data support an expanded view of T cell and eosinophil activities and suggest that eosinophil effector functions impinge directly on lung function.

Abstract Protective immunity to Strongyloides stercoralis infective larvae in mice has been shown to be dependent on IL-5 based on mAb depletion studies. The goal of this study was to determine the functional role of IL-5 during the innate and adaptive immune response to larval S. stercoralis in mice. In these studies, three strains of mice were used: wild-type C57BL/6J (WT), IL-5 knockout (KO), and IL-5 transgenic (TG). Innate responses to the larvae indicated that there was enhanced survival in the KO animals and decreased survival in the TG animals compared with WT. Furthermore, killing of larvae in TG mice was associated with eosinophil infiltration and degranulation. In studying the adaptive immune response, it was observed that immunization of KO mice did not lead to the development of protective immunity. Experiments were then performed to determine whether KO mice reconstituted with Abs or cells could then develop protective immunity. KO mice displayed protective immunity via a granulocyte-dependent mechanism following injection of purified IgM from immune wild-type animals. Immunity in KO mice could also be reconstituted by the injection of eosinophils at the time of immunization. These eosinophils did not participate in actively killing the challenge infection, but rather were responsible for the induction of a protective Ab response. We conclude that IL-5 is required in the protective immune response for the production of eosinophils, and that eosinophils were involved in larval killing during innate immunity and in the induction of protective Abs in the adaptive immune response.

Abstract The complexity and magnitude of interactions leading to the selective infiltration of eosinophils in response to inhaled allergens are formidable obstacles to a larger understanding of the pulmonary pathology associated with allergic asthma. This study uses knockout mice to demonstrate a novel function for the heterotrimeric G protein, Gq, in the regulation of pulmonary eosinophil recruitment. In the absence of Gq signaling, eosinophils failed to accumulate in the lungs following allergen challenge. These studies demonstrate that the inhibition of eosinophil accumulation in the airways is attributed to the failure of hemopoietically derived cells to elaborate GM-CSF in the airways. The data suggest that activation of a Gq-coupled receptor(s) on resident leukocytes in the lung elicits expression of GM-CSF, which, in turn, is required for allergen-induced pulmonary eosinophilia, identifying a novel pathway of eosinophil-associated effector functions leading to pulmonary pathology in diseases such as asthma.

Abstract The precise role that individual inflammatory cells and mediators play in the development of gastrointestinal (GI) dysfunction and extraintestinal clinical manifestations of ulcerative colitis (UC) is unknown. In this study, we have used a mouse model of UC to establish a central role for eotaxin and, in turn, eosinophils in the development of the immunopathogenesis of this disease. In this model the administration of dextran sodium sulfate (DSS) induces a prominent colonic eosinophilic inflammation and GI dysfunction (diarrhea with blood and shortening of the colon) that resembles UC in patients. GI dysfunction was associated with evidence of eosinophilic cytolytic degranulation and the release of eosinophil peroxidase (EPO) into the colon lumen. By using IL-5 or eotaxin-deficient mice, we show an important role for eotaxin in eosinophil recruitment into the colon during experimental UC. Furthermore, using EPO-deficient mice and an EPO inhibitor resorcinol we demonstrate that eosinophil-derived peroxidase is critical in the development of GI dysfunction in experimental UC. These findings provide direct evidence of a central role for eosinophils and EPO in GI dysfunction and potentially the immunopathogenesis of UC.

Abstract Adenosine signaling has been implicated in chronic lung diseases such as asthma and chronic obstructive pulmonary disease; however, the specific roles of the various adenosine receptors in processes central to these disorders are not well understood. In this study, we have investigated the role(s) of the A3 adenosine receptor in adenosine-dependent pulmonary inflammation observed in adenosine deaminase (ADA)-deficient mice. The A3 receptor (A3R) was found to be expressed in eosinophils and mucus-producing cells in the airways of ADA-deficient mice. Treatment of ADA-deficient mice with MRS 1523, a selective A3R antagonist, prevented airway eosinophilia and mucus production. Similar findings were seen in the lungs of ADA/A3 double knockout mice. Although eosinophils were decreased in the airways of ADA-deficient mice following antagonism or removal of the A3R, elevations in circulating and lung interstitial eosinophils persisted, suggesting signaling through the A3R is needed for the migration of eosinophils into the airways. These findings identify an important role for the A3R in regulating lung eosinophilia and mucus production in an environment of elevated adenosine.