Lung Pathologies in a Chronic Inflammation Mouse Model Are Independent of Eosinophil Degranulation

RATIONALE

The release of eosinophil granule proteins in the lungs of patients with asthma has been dogmatically linked with lung remodeling and airway hyperresponsiveness. However, the demonstrated inability of established mouse models to display the eosinophil degranulation occurring in human subjects has prevented a definitive in vivo test of this hypothesis.

OBJECTIVES

To demonstrate in vivo causative links between induced pulmonary histopathologies/lung dysfunction and eosinophil degranulation.

METHODS

A transgenic mouse model of chronic T-helper cell type 2-driven inflammation overexpressing IL-5 from T cells and human eotaxin 2 in the lung (I5/hE2) was used to test the hypothesis that chronic histopathologies and the development of airway hyperresponsiveness occur as a consequence of extensive eosinophil degranulation in the lung parenchyma.

MEASUREMENT AND MAIN RESULTS

Studies targeting specific inflammatory pathways in I5/hE2 mice surprisingly showed that eosinophil-dependent immunoregulative events and not the release of individual secondary granule proteins are the central contributors to T-helper cell type 2-induced pulmonary remodeling and lung dysfunction. Specifically, our studies highlighted a significant role for eosinophil-dependent IL-13 expression. In contrast, extensive degranulation leading to the release of major basic protein-1 or eosinophil peroxidase was not causatively linked to many of the induced pulmonary histopathologies. However, these studies did define a previously unappreciated link between the release of eosinophil peroxidase (but not major basic protein-1) and observed levels of induced airway mucin.

CONCLUSIONS

These data suggest that improvements observed in patients with asthma responding to therapeutic strategies ablating eosinophils may occur as a consequence of targeting immunoregulatory mechanisms and not by simply eliminating the destructive activities of these purportedly end-stage effector cells.

Frontline Science: Eosinophil-deficient MBP-1 and EPX double-knockout mice link pulmonary remodeling and airway dysfunction with type 2 inflammation

Eosinophils and the release of cationic granule proteins have long been implicated in the development of the type 2-induced pathologies linked with respiratory inflammation. Paradoxically, the ablation of the two genes encoding the most abundant of these granule proteins, major basic protein-1 (MBP-1) and eosinophil peroxidase (EPX), results in a near collapse of eosinophilopoiesis. The specificity of this lineage ablation and the magnitude of the induced eosinopenia provide a unique opportunity to clarify the importance of eosinophils in acute and chronic inflammatory settings, as well as to identify potential mechanism(s) of action linked with pulmonary eosinophils in those settings. Specifically, we examined these issues by assessing the induced immune responses and pathologies occurring in MBP-1^-/-/EPX^-/- mice after 1) ovalbumin sensitization/provocation in an acute allergen-challenge protocol, and 2) crossing MBP-1^-/-/EPX^-/- mice with a double-transgenic model of chronic type 2 inflammation (i.e., I5/hE2). Acute allergen challenge and constitutive cytokine/chemokine expression each induced the accumulation of pulmonary eosinophils in wild-type controls that was abolished in the absence of MBP-1 and EPX (i.e., MBP-1^-/-/EPX^-/- mice). The expression of MBP-1 and EPX was also required for induced lung expression of IL-4/IL-13 in each setting and, in turn, the induced pulmonary remodeling events and lung dysfunction. In summary, MBP-1^-/-/EPX^-/- mice provide yet another definitive example of the immunoregulatory role of pulmonary eosinophils. These results highlight the utility of this unique strain of eosinophil-deficient mice as part of in vivo model studies investigating the roles of eosinophils in health and disease settings.

Cys-leukotrienes promote fibrosis in a mouse model of eosinophil-mediated respiratory inflammation

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.

Local hypersensitivity reaction in transgenic mice with squamous epithelial IL-5 overexpression provides a novel model of eosinophilic oesophagitis

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.

Androgen receptor-positive triple negative breast cancer: a unique breast cancer subtype

BACKGROUND

The significance of androgen receptor (AR) expression in triple-negative breast cancer (TNBC) is unclear, and published studies so far have been inconclusive.

METHODS

A tissue microarray was constructed using tissue obtained from 119 patients with primary TNBC and stained for AR expression. Other tissue types obtained included recurrent TNBC, normal breast tissue, adjacent ductal carcinoma-in situ (DCIS), lymph node (LN) and distant metastases. Positive AR expression was defined as ≥10% nuclear staining.

RESULTS

Epithelial tissue was present and evaluable in 94 TNBC patients with a total of 177 tissue cores. AR expression in TNBC was 22 of 94 (23%). AR expression was higher in normal breast tissue (88%) and adjacent DCIS (73% overall). All LN metastases from AR-positive TNBC patients were also AR positive; in addition, no AR-negative TNBC patient had AR-positive LNs. AR expression was associated with older patient age (63 vs. 57 years, respectively, p = 0.051) and LN metastases (p = 0.033). Locoregional recurrence and overall/disease-specific survival were similar between AR-positive and AR-negative patients, although AR-positive patients had more advanced disease. On multivariate analysis, the presence of LN metastases was associated with poorer recurrence-free survival in AR-positive patients (hazard ratio, 4.34) (p = 0.031).

CONCLUSIONS

The AR is expressed in normal breast tissue, and expression decreases with advancement to DCIS and invasive cancer. AR-positive TNBC was more common in older patients and had a higher propensity for LN metastases. AR-positive TNBC may represent a breast cancer subtype with unique features that may be amenable to treatment with alternative targeted therapies.

Predicting response to bacillus Calmette-Guérin (BCG) in patients with carcinoma in situ of the bladder

PURPOSE

Currently, there is no reliable tool to predict response to intravesical bacillus Calmette-Guérin (BCG). Based on the fact that BCG is a Th1-polarizing immunotherapy, we attempt to correlate the pretreatment immunologic tumor microenvironment (Th1 or Th2) with response to therapy.

MATERIALS AND METHODS

Bladder cancer patients with initial diagnosis of carcinoma in situ (Tis) were stratified based on their response to BCG treatment. A total of 38 patients met inclusion criteria (20 patients who responded and 18 patients who did not respond). Immunohistochemical (IHC) methods known to assess the type of immunologic microenvironment (Th1 vs. Th2) were performed on tumor tissue obtained at initial biopsy/resection: the level of tumor eosinophil infiltration and degranulation (Th2 response); the number of tumor-infiltrating GATA-3(+) (Th2-polarized) lymphocytes; and the number of tumor-infiltrating T-bet(+) (Th1-polarized) lymphocytes. Results obtained from these metrics were correlated with response to treatment with BCG immunotherapy.

RESULTS

The IHC metrics of the tumor immune microenvironment prior to BCG treatment were each statistically significant predictors of responders (R) vs. nonresponders (NR). Eosinophil infiltration and degranulation was higher for R vs. NR: 1.02 ± 0.17 vs. 0.5 ± 0.12 (P = 0.01) and 1.1 ± 0.15 vs. 0.56 ± 0.15 (P = 0.04), respectively. Ratio of GATA-3(+) (Th2-polarized) lymphocytes to T-bet(+) (Th1-polarized) lymphocytes was higher for R vs. NR: 4.85 ± 0.94 vs. 0.98 ± 0.19 (P<0.001). The 3 markers were combined to create a Th2 signature biomarker, which was a statistically significant (P<0.0001) predictor of R vs. NR. All IHC markers demonstrated that a preexisting Th1 immunologic environment within the tumor was predictive of BCG failure.

CONCLUSION

The Th1 vs. Th2 polarization of bladder tumor immune microenvironment prior to treatment with BCG represents a prognostic metric of response to therapy. If a patient has a preexisting Th1 immunologic response within the tumor, there is no value in using a therapy intended to create a Th1 immunologic response. An algorithm integrating 3 IHC methods provided a sensitive and specific technique that may become a useful tool for pathologists and urologists to predict response to BCG in patients with carcinoma in situ of the bladder.

Bladder cancer: Predicting response to BCG

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Background: Our preliminary immunohistochemical studies of bladder cancer patients have shown that the inflammatory/immune responses associated with bladder cancer appear to be Th2-polarized as judged by the preponderance of tumor infiltrating GATA-3+ (Th2) vs. T-bet+ (Th1) T cells, as well as by evidence of tumor-associated eosinophil infiltration and activation. The standard-of-care treatment for Tis bladder cancer is intravesical administration of BCG, a Th1-polarizing immunomodulator. The aim of the present study was to assess the Th2/Th1 ratio correlation with response to BCG therapy in patients with Tis bladder cancer. Methods: Two groups of patients were studied. Group A included 20 patients that responded to BCG, and Group B included 20 patients that did not respond to therapy. Response to BCG was determined as presence/absence of disease at 6 months post-BCG therapy. The initial diagnostic biopsies of these patients were subjected to immunohistochemical analysis using commercially available antibodies specific for Th2 (GATA-3+) and Th1 (T-bet+) lymphocytes, and our unique monoclonal antibody specific for eosinophil peroxidase (EPX-mAb). Ten random high powered (400X) fields at the maximum focus of mononuclear infiltration were examined and the number of GATA 3+ and T-bet+ tumor infiltrating T cells were counted to define the G/T ratio for each patient sample. Eosinophils and their degranulation activity were counted in the same fields. Results: Patients with response to BCG therapy had a G/T ratio of ≥ 3 and patients with non-response to BCG therapy had a G/T ratio of ≤ 1.5. Correlation of these scores with subsequent patient outcomes following BCG immune therapy demonstrated that patient responsiveness (i.e., tumor elimination at 6 months) trended with the higher G/T ratio patients. In addition, initial biopsies of BCG responsive patients display a higher number of eosinophils and degranulation relative to BCG non-responsive patients. Conclusions: Evaluations of initial biopsies revealed a strong correlation between Th1 and Th2 immune response with BCG therapy outcomes. The development of specific and novel tools to identify/measure Th2 immune responses in Tis bladder cancer provides a unique opportunity to predict outcomes at the time of diagnosis.

Human versus mouse eosinophils: "that which we call an eosinophil, by any other name would stain as red"

The respective life histories of human subjects and mice are well defined and describe a unique story of evolutionary conservation extending from sequence identity within the genome to the underpinnings of biochemical, cellular, and physiologic pathways. As a consequence, the hematopoietic lineages of both species are invariantly maintained, each with identifiable eosinophils. This canonical presence nonetheless does not preclude disparities between human and mouse eosinophils, their effector functions, or both. Indeed, many books and reviews dogmatically highlight differences, providing a rationale to discount the use of mouse models of human eosinophilic diseases. We suggest that this perspective is parochial and ignores the wealth of available studies and the consensus of the literature that overwhelming similarities (and not differences) exist between human and mouse eosinophils. The goal of this review is to summarize this literature and in some cases provide experimental details comparing and contrasting eosinophils and eosinophil effector functions in human subjects versus mice. In particular, our review will provide a summation and an easy-to-use reference guide to important studies demonstrating that although differences exist, more often than not, their consequences are unknown and do not necessarily reflect inherent disparities in eosinophil function but instead species-specific variations. The conclusion from this overview is that despite nominal differences, the vast similarities between human and mouse eosinophils provide important insights as to their roles in health and disease and, in turn, demonstrate the unique utility of mouse-based studies with an expectation of valid extrapolation to the understanding and treatment of patients.

A sensitive high throughput ELISA for human eosinophil peroxidase: a specific assay to quantify eosinophil degranulation from patient-derived sources

Quantitative high throughput assays of eosinophil-mediated activities in fluid samples from patients in a clinical setting have been limited to ELISA assessments for the presence of the prominent granule ribonucleases, ECP and EDN. However, the demonstration that these ribonucleases are expressed by leukocytes other than eosinophils, as well as cells of non-hematopoietic origin, limits the usefulness of these assays. Two novel monoclonal antibodies recognizing eosinophil peroxidase (EPX) were used to develop an eosinophil-specific and sensitive sandwich ELISA. The sensitivity of this EPX-based ELISA was shown to be similar to that of the commercially available ELISA kits for ECP and EDN. More importantly, evidence is also presented confirming that among these granule protein detection options, EPX-based ELISA is the only eosinophil-specific assay. The utility of this high throughput assay to detect released EPX was shown in ex vivo degranulation studies with isolated human eosinophils. In addition, EPX-based ELISA was used to detect and quantify eosinophil degranulation in several in vivo patient settings, including bronchoalveolar lavage fluid obtained following segmental allergen challenge of subjects with allergic asthma, induced sputum derived from respiratory subjects following hypotonic saline inhalation, and nasal lavage of chronic rhinosinusitis patients. This unique EPX-based ELISA thus provides an eosinophil-specific assay that is sensitive, reproducible, and quantitative. In addition, this assay is adaptable to high throughput formats (e.g., automated assays utilizing microtiter plates) using the diverse patient fluid samples typically available in research and clinical settings.

Eosinophilic esophagitis: epithelial mesenchymal transition contributes to esophageal remodeling and reverses with treatment

BACKGROUND

Mechanisms underlying esophageal remodeling with subepithelial fibrosis in subjects with eosinophilic esophagitis (EoE) have not been delineated.

OBJECTIVES

We sought to explore a role for epithelial mesenchymal transition (EMT) in subjects with EoE and determine whether EMT resolves with treatment.

METHODS

Esophageal biopsy specimens from 60 children were immunostained for epithelial (cytokeratin) and mesenchymal (vimentin) EMT biomarkers, and EMT was quantified. Subjects studied had EoE (n = 17), indeterminate EoE (n = 15), gastroesophageal reflux disease (n = 7), or normal esophagus (n = 21). EMT was analyzed for relationships to diagnosis, eosinophil counts, and indices of subepithelial fibrosis, eosinophil peroxidase, and TGF-β immunostaining. EMT was assessed in pretreatment and posttreatment biopsy specimens from 18 subjects with EoE treated with an elemental diet, 6-food elimination diet, or topical corticosteroids (n = 6 per group).

RESULTS

TGF-β1 treatment of esophageal epithelial cells in vitro for 24 hours induced upregulation of mesenchymal genes characteristic of EMT, including N-cadherin (3.3-fold), vimentin (2.1-fold), and fibronectin (7.5-fold). EMT in esophageal biopsy specimens was associated with EoE (or indeterminate EoE) but not gastroesophageal reflux disease or normal esophagus and was correlated to eosinophil counts (r = 0.691), eosinophil peroxidase (r = 0.738), and TGF-β (r = 0.520) immunostaining and fibrosis (r = 0.644) indices. EMT resolved with EoE treatments that induced clinicopathologic remission with reduced eosinophil counts. EMT decreased significantly after treatment by 74.1% overall in the 18 treated subjects with EoE; pretreatment versus posttreatment EMT scores were 3.17 ± 0.82 versus 0.82 ± 0.39 (P < .001), with similar decreases within treatment groups. Pretreatment/posttreatment EMT was strongly correlated with eosinophil counts for combined (r = 0.804, P < .001) and individual treatment groups.

CONCLUSIONS

EMT likely contributes to subepithelial fibrosis in subjects with EoE and resolves with treatments that decrease esophageal inflammation, and its resolution correlates with decreased numbers of esophageal eosinophils.

Immunodetection of occult eosinophils in lung tissue biopsies may help predict survival in acute lung injury

BACKGROUND

Acute lung injury (ALI) is a serious respiratory disorder for which therapy is primarily supportive once infection is excluded. Surgical lung biopsy may rule out other diagnoses, but has not been generally useful for therapy decisions or prognosis in this setting. Importantly, tissue and peripheral blood eosinophilia, the hallmarks of steroid-responsive acute eosinophilic pneumonia, are not commonly linked with ALI. We hypothesized that occult eosinophilic pneumonia may explain better outcomes for some patients with ALI.

METHODS

Immunohistochemistry using a novel monoclonal antibody recognizing eosinophil peroxidase (EPX-mAb) was used to assess intrapulmonary eosinophil accumulation/degranulation. Lung biopsies from ALI patients (n = 20) were identified following review of a pathology database; 45% of which (i.e., 9/20) displayed classical diffuse alveolar damage (ALI-DAD). Controls were obtained from uninvolved tissue in patients undergoing lobectomy for lung cancer (n = 10). Serial biopsy sections were stained with hematoxylin and eosin (H&E) and subjected to EPX-mAb immunohistochemistry.

RESULTS

EPX-mAb immunohistochemistry provided a >40-fold increased sensitivity to detect eosinophils in the lung relative to H&E stained sections. This increased sensitivity led to the identification of higher numbers of eosinophils in ALI patients compared with controls; differences using H&E staining alone were not significant. Clinical assessments showed that lung infiltrating eosinophil numbers were higher in ALI patients that survived hospitalization compared with non-survivors. A similar conclusion was reached quantifying eosinophil degranulation in each biopsy.

CONCLUSION

The enhanced sensitivity of EPX-mAb immunohistochemistry uniquely identified eosinophil accumulation/degranulation in patients with ALI relative to controls. More importantly, this method was a prognostic indicator of patient survival. These observations suggest that EPX-mAb immunohistochemistry may represent a diagnostic biomarker identifying a subset of ALI patients with improved clinical outcomes.

Allergic pulmonary inflammation promotes the recruitment of circulating tumor cells to the lung

Allergen-induced respiratory inflammation facilitates and/or elicits the extravasation of proinflammatory leukocytes by well-understood mechanisms that mediate the movement of multiple cell types. The nonspecific character of these pathways led us to hypothesize that circulating cancer cells use similar mechanisms, promoting secondary tumor formation at distal sites. To test this hypothesis, the frequency of metastasis to the lung as a function of allergic pulmonary inflammation was assessed following the i.v. injection of B16-F10 melanoma cells in mice. These studies showed that allergen-induced pulmonary inflammation resulted in a >3-fold increase in lung metastases. This increase was dependent on CD4(+) T-cell activities; however, it occurred independent of the induced eosinophilia associated with allergen provocation. Interventional strategies showed that existing therapeutic modalities for asthma, such as inhaled corticosteroids, were sufficient to block the enhanced pulmonary recruitment of cancer cells from circulation. Additional mechanistic studies further suggested that the ability of circulating cancer cells to extravasate to surrounding lung tissues was linked to the activation of the vascular endothelium via one or more Galpha(i)-coupled receptors. Interestingly, a survey of a clinical breast cancer surgical database showed that the incidence of asthma was higher among patients with lung metastases. Thus, our data show that allergic respiratory inflammation may represent a risk factor for the development of lung metastases and suggest that amelioration of the pulmonary inflammation associated with asthma will have a direct and immediate benefit to the 7% to 8% of breast cancer patients with this lung disease.

Allergic pulmonary inflammation in mice is dependent on eosinophil-induced recruitment of effector T cells

The current paradigm surrounding allergen-mediated T helper type 2 (Th2) immune responses in the lung suggests an almost hegemonic role for T cells. Our studies propose an alternative hypothesis implicating eosinophils in the regulation of pulmonary T cell responses. In particular, ovalbumin (OVA)-sensitized/challenged mice devoid of eosinophils (the transgenic line PHIL) have reduced airway levels of Th2 cytokines relative to the OVA-treated wild type that correlated with a reduced ability to recruit effector T cells to the lung. Adoptive transfer of Th2-polarized OVA-specific transgenic T cells (OT-II) alone into OVA-challenged PHIL recipient mice failed to restore Th2 cytokines, airway histopathologies, and, most importantly, the recruitment of pulmonary effector T cells. In contrast, the combined transfer of OT-II cells and eosinophils into PHIL mice resulted in the accumulation of effector T cells and a concomitant increase in both airway Th2 immune responses and histopathologies. Moreover, we show that eosinophils elicit the expression of the Th2 chemokines thymus- and activation-regulated chemokine/CCL17 and macrophage-derived chemokine/CCL22 in the lung after allergen challenge, and blockade of these chemokines inhibited the recruitment of effector T cells. In summary, the data suggest that pulmonary eosinophils are required for the localized recruitment of effector T cells.

Coexpression of IL-5 and eotaxin-2 in mice creates an eosinophil-dependent model of respiratory inflammation with characteristics of severe asthma

Mouse models of allergen provocation and/or transgenic gene expression have provided significant insights regarding the cellular, molecular, and immune responses linked to the pathologies occurring as a result of allergic respiratory inflammation. Nonetheless, the inability to replicate the eosinophil activities occurring in patients with asthma has limited their usefulness to understand the larger role(s) of eosinophils in disease pathologies. These limitations have led us to develop an allergen-naive double transgenic mouse model that expresses IL-5 systemically from mature T cells and eotaxin-2 locally from lung epithelial cells. We show that these mice develop several pulmonary pathologies representative of severe asthma, including structural remodeling events such as epithelial desquamation and mucus hypersecretion leading to airway obstruction, subepithelial fibrosis, airway smooth muscle hyperplasia, and pathophysiological changes exemplified by exacerbated methacholine-induced airway hyperresponsiveness. More importantly, and similar to human patients, the pulmonary pathologies observed are accompanied by extensive eosinophil degranulation. Genetic ablation of all eosinophils from this double transgenic model abolished the induced pulmonary pathologies, demonstrating that these pathologies are a consequence of one or more eosinophil effector functions.

T(H)2-mediated pulmonary inflammation leads to the differential expression of ribonuclease genes by alveolar macrophages

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 T(H)2 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 T(H)2 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.