Craig M. Schramm

Shifts in Lung Lymphocyte Profiles Correlate with the Sequential Development of Acute Allergic and Chronic Tolerant Stages in a Murine Asthma Model

T lymphocytes have a central regulatory role in the pathogenesis of asthma. We delineated the participation of lymphocytes in the acute allergic and chronic tolerant stages of a murine model of asthma by characterizing the various subsets of lymphocytes in bronchoalveolar lavage and lung tissue associated with these responses. Acute (10-day) aerosol challenge of immunized C57BL/6J mice with ovalbumin resulted in airway eosinophilia, histological evidence of peribronchial and perivascular airway inflammation, clusters of B cells and TCRgammadelta cells in lung tissue, increased serum IgE levels, and airway hyperresponsiveness to methacholine. In mice subjected to chronic (6-week) aerosol challenge with ovalbumin, airway inflammation and serum IgE levels were significantly attenuated and airway hyperresponsiveness was absent. The marked increases in lung B and T cell populations seen in the acute stage were also significantly reduced in the chronic stage of this model. Thus, acute ovalbumin challenge resulted in airway sensitization characteristic of asthma, whereas chronic ovalbumin challenge elicited a suppressed or tolerant state. The transition from antigenic sensitization to tolerance was accompanied by shifts in lymphocyte profiles in the lung and bronchoalveolar lavage fluid.

Childhood obesity increases duration of therapy during severe asthma exacerbations

Objectives: Childhood obesity contributes to a wide array of medical conditions, including asthma. There is also increasing evidence in adult patients admitted to the intensive care unit (ICU) that obesity contributes to increased morbidity and to a prolonged length of stay. We hypothesized that obesity is associated with the need for increased duration of therapy in children admitted to the ICU with status asthmaticus. Design: Retrospective cohort study. Setting: A tertiary pediatric ICU in a university-affiliated childrens hospital. Patients: We retrospectively examined data from all children older than 2 yrs admitted to the ICU with status asthmaticus between April 1997 and June 2004. Children were classified as normal weight (<95% weight-for-age percentile) or obese (>95% weight-for-age). Interventions: None. Measurements and Main Results: Of the 209 children admitted to the ICU with asthma, 45 (22%) were obese. Compared with children of normal weight, the obese children were older (9.7 ± 4.4 vs. 8.0 ± 4.3 yrs, p = .02), more likely to be female (60% vs. 37%, p < .01), and more likely to have been admitted to the ICU previously (40% vs. 20%, p = .01). The obese children also had a statistically significant difference in race (more likely to be Hispanic) and in baseline asthma classification (more likely to have persistent asthma). Despite similar severity of illness at ICU admission, obese children had a significantly longer ICU length of stay (116 ± 125 hrs vs. 69 ± 57 hrs, p = .02) and hospital length of stay (9.8 ± 7.0 vs. 6.5 ± 3.4 days, p < .01). Obese children also received longer courses of supplemental oxygen, continuous albuterol, and intravenous steroids. Conclusions: Childhood obesity significantly affects the health of children with asthma. Obese children with status asthmaticus recovered more slowly from an acute exacerbation, even after adjustment for baseline asthma severity and admission severity of illness.

Regulatory Role of B Cells in a Murine Model of Allergic Airway Disease

Mice sensitized to OVA and subjected to acute OVA aerosol exposures develop allergic airway disease (AAD). However, chronic continuous Ag exposure results in resolution of AAD and the development of local inhalational tolerance (LIT). Because we have previously observed the persistence of B cells in the bronchoalveolar lavage (BAL) and hilar lymph nodes (HLN) at the resolution stage of this model, we investigated the role of B cells in the modulation of AAD. Although B cell-deficient mice developed LIT, adoptive transfer of HLN B cells from LIT mice to OVA-sensitized recipients resulted in attenuated AAD following subsequent OVA aerosol exposure, as determined by reduced BAL leukocytosis and eosinophilia, decreased tissue inflammation, and absent methacholine hyper-responsiveness. In similar adoptive transfer studies, HLN B cells from AAD mice were without effect. The protection transferred by LIT HLN B cells was Ag specific and was associated with accumulation of Foxp3+ T regulatory cells regionally in BAL and HLN, but not systemically in the spleen. Fluorescent labeling of LIT HLN B cells before adoptive transfer demonstrated that these cells had the capacity to migrate to local inflammatory sites. In vitro assessment demonstrated that the LIT HLN B cells exerted this regulatory effect via TGF-β induced conversion of CD4+CD25− T effector cells into functionally suppressive CD4+CD25+Foxp3+ T regulatory cells. These findings illustrated a novel regulatory role for regional B cells in AAD and suggested a possible contributory role of B cells, along with other cell types, in the establishment of LIT.

Chronic inhaled ovalbumin exposure induces antigen-dependent but not antigen-specific inhalational tolerance in a murine model of allergic airway disease.

Sensitized mice acutely challenged with inhaled ovalbumin (OVA) develop allergic airway inflammation, characterized by OVA-specific IgE production, airway eosinophilia, increased pulmonary B and T lymphocytes, and airway hyperreactivity. In this study, a chronic exposure model was developed and two distinct patterns of response were observed. Discontinuous inhalational exposure to OVA (6 weeks) produced airway inflammation and hyperreactivity that were similar to acute (10 days) responses. Continuous inhalational exposure to OVA (6 or 11 weeks) resulted in attenuation of airway eosinophilia and hyperresponsiveness without reduction of OVA-specific IgE and IgG(1) levels. The inhibition of airway inflammation was dependent on continuous exposure to antigen, because continuously exposed mice with attenuated inflammatory responses redeveloped allergic airway disease if the OVA aerosols were interrupted and then restarted (11-week-discontinuous). Inhalational tolerance induced by continuous OVA exposure demonstrated bystander suppression of cockroach allergen-mediated airway eosinophilia. These findings may be attributed to changes in production of the anti-inflammatory cytokine interleukin-10 during continuous OVA aerosol exposure. The symptomatic and asymptomatic allergic responses in human asthmatics could be explained by similar variable or discontinuous exposures to aeroantigens.

Regulatory B cells from hilar lymph nodes of tolerant mice in a murine model of allergic airway disease are CD5+, express TGF-β, and co-localize with CD4+Foxp3+ T cells.

In a biphasic, ovalbumin (OVA)-induced murine asthma model where allergic airway disease is followed by resolution and the development of local inhalational tolerance (LIT), transforming growth factor (TGF)-β-expressing CD5+ B cells were selectively expanded locally in hilar lymph nodes (HLN) of LIT mice. LIT HLN CD5+ B cells, but not LIT HLN CD5– B cells, induced expression of Foxp3 in CD4+CD25– T cells in vitro. These CD5+ regulatory B cells (Breg) and CD4+Foxp3+ T cells demonstrated similar increases in expression of chemokine receptors (CXCR4 and CXCR5) and co-localized in HLN B cell zones of LIT mice. The adoptive transfer of LIT HLN CD5+ B cells, but not LIT HLN CD5– B cells, increased the number of CD4+Foxp3+ T cells in the lung and inhibited airway eosinophilia in this OVA model. Thus, Breg in HLNs of LIT mice reside in a CD5+ TGF-β-producing subpopulation and co-localize with CD4+Foxp3+ T cells.

Noninvasive positive pressure ventilation for the treatment of status asthmaticus in children

BACKGROUND Noninvasive positive pressure ventilation (NPPV) has been used safely and effectively to improve gas exchange and to treat respiratory failure in a variety of disease states. Although this technique has some benefits in the treatment of status asthmaticus in adults, the use of NPPV in pediatric patients with asthma has not been described. OBJECTIVE To describe the use of NPPV in the treatment of pediatric status asthmaticus. METHODS Retrospective review of children admitted to the intensive care unit with asthma who received NPPV as part of their treatment between October 2002 and April 2004. Before and after initiation of NPPV, data were collected regarding degree of respiratory dysfunction. RESULTS Of seventy-nine children admitted to the intensive care unit during the study period for treatment of status asthmaticus, 5 children (mean +/- SD age, 9.6 +/- 4.2 years) were treated with NPPV. Four of the 5 children were morbidly obese, with a mean +/- SD body mass index of 32 +/- 5. There was a statistically significant improvement in respiratory rate (43 +/- 20 vs 31 +/- 12/min, P = .03) and Modified Pulmonary Index Score (13.4 +/- 1.8 vs 11.4 +/- 1.5, P = .03) after initiation of NPPV. The mean +/- SD duration of therapy was 33.2 +/- 23.9 hours, and children tolerated this therapy well, requiring little or no anxiolytics. CONCLUSIONS NPPV was well tolerated in this series of children with status asthmaticus and can improve subjective and objective measures of respiratory dysfunction. NPPV may be a useful adjunct in the treatment of status asthmaticus in children.

β2-Adrenergic Receptor Polymorphisms Affect Response to Treatment in Children With Severe Asthma Exacerbations

BACKGROUND beta(2)-adrenergic receptor (AR) agonists are the mainstay of treatment for severe asthma exacerbations, one of the most common causes of critical illness in children. Genotypic differences in the beta(2)-AR gene, particularly at amino acid positions 16 and 27, have been shown to affect the response to beta(2)-AR agonist therapy. Our hypothesis is that genotypic differences contribute to patient response to beta(2)-AR agonist treatment during severe asthma exacerbations in children. METHODS Children admitted to the hospital ICU for a severe asthma exacerbation between 2002 and 2005 were located, and genetic samples were obtained from saliva. Children hospitalized during this period were treated with a protocol that titrated beta(2)-AR therapy (first nebulized, then IV) according to a validated clinical asthma score. RESULTS Thirty-seven children hospitalized during the study period were enrolled into the study. At amino acid position 16 in the beta(2)-AR gene, 13 children were homozygous for the glycine (Gly) allele (Gly/Gly), 8 were homozygous for the arginine (Arg) allele (Arg/Arg), and 16 were heterozygous (Arg/Gly). Despite similar clinical asthma scores on hospital admission, the children with the Gly/Gly genotype had significantly shorter hospital ICU length of stay and duration of continuously nebulized albuterol therapy and were significantly less likely to require IV beta(2)-AR therapy than those with Arg/Arg or Arg/Gly genotypes. No association existed among polymorphisms at amino acid position 27 and response to beta(2)-AR therapy. CONCLUSIONS In this cohort of children with severe asthma exacerbations, children whose genotypes were homozygous for Gly at amino acid position 16 of the beta(2)-AR gene had a more rapid response to beta(2)-AR agonist treatment. The beta(2)-AR genotype appears to influence the response to therapy in this population.

Current concepts of respiratory complications of neuromuscular disease in children.

Chronic neuromuscular diseases affect the respiratory muscles in varying patterns and degrees. As a result, patients with these disorders develop restrictive pulmonary disease, ineffective cough, atelectasis and pneumonia, and chronic respiratory insufficiency leading to respiratory failure. Therapeutic strategies are evolving to augment cough and airway clearance, improve lung volumes, and support the patient with progressive ventilatory failure. These techniques have improved longevity and quality of life for many patients with neuromuscular disease.

Endotracheal intubation and pediatric status asthmaticus: Site of original care affects treatment*

Objectives: Status asthmaticus is a common cause of admission to a pediatric intensive care unit (PICU). Children unresponsive to medical therapies may require endotracheal intubation; however, this treatment carries significant risk, and thresholds for intubation vary. Our hypothesis was that children who sought care at community hospitals received less aggressive treatment and more frequent intubation than children who sought care at a childrens hospital. Design: Retrospective cohort study. Setting: A university-affiliated childrens hospital PICU. Patients: We retrospectively examined data from all children older than 2 yrs admitted to the PICU with status asthmaticus between April 1997 and July 2005. Interventions: None. Measurements and Main Results: Of the 251 children admitted to the PICU with status asthmaticus, 130 initially presented to the emergency department of a childrens hospital and 116 presented to the emergency department of a community hospital. Despite similar illness severity, children presenting to a community hospital were significantly more likely to be intubated than those presenting to a childrens hospital (17% vs. 5%; p = .004). In addition, those children intubated at community hospitals were intubated sooner after presentation (2.4 ± 5.2 vs. 7.5 ± 5.8 hrs; p = .009), had shorter durations of intubation (71 ± 73 vs. 151 ± 81 hrs; p = .02), and had shorter PICU length of stays (129 ± 82 vs. 230 ± 84 hrs; p = .01). Conclusions: Children with status asthmaticus are more likely to be intubated, and intubated sooner, at a community hospital. The shorter duration of intubation suggests that some children may not have been intubated had they presented to a childrens hospital or received more aggressive therapy at their community hospital.

Murine Cytomegalovirus Infection Alters Th1/Th2 Cytokine Expression, Decreases Airway Eosinophilia, and Enhances Mucus Production in Allergic Airway Disease

Concomitant infection of murine CMV (MCMV), an opportunistic respiratory pathogen, altered Th1/Th2 cytokine expression, decreased bronchoalveolar lavage (BAL) fluid eosinophilia, and increased mucus production in a murine model of OVA-induced allergic airway disease. Although no change in the total number of leukocytes infiltrating the lung was observed between challenged and MCMV/challenged mice, the cellular profile differed dramatically. After 10 days of OVA-aerosol challenge, eosinophils comprised 64% of the total leukocyte population in BAL fluid from challenged mice compared with 11% in MCMV/challenged mice. Lymphocytes increased from 11% in challenged mice to 30% in MCMV/challenged mice, and this increase corresponded with an increase in the ratio of CD8+ to CD4+TCRαβ lymphocytes. The decline in BAL fluid eosinophilia was associated with a change in local Th1/Th2 cytokine profiles. Enhanced levels of IL-4, IL-5, IL-10, and IL-13 were detected in lung tissue from challenged mice by RNase protection assays. In contrast, MCMV/challenged mice transiently expressed elevated levels of IFN-γ and IL-10 mRNAs, as well as decreased levels of IL-4, IL-5, and IL-13 mRNAs. Elevated levels of IFN-γ and reduced levels of IL-5 were also demonstrated in BAL fluid from MCMV/challenged mice. Histological evaluation of lung sections revealed extensive mucus plugging and epithelial cell hypertrophy/hyperplasia only in MCMV/challenged mice. Interestingly, the development of airway hyperresponsiveness was observed in challenged mice, not MCMV/challenged mice. Thus, MCMV infection can modulate allergic airway inflammation, and these findings suggest that enhanced mucus production may occur independently of BAL fluid eosinophilia.