Infections and asthma: new insights into old ideas.

A relationship between infections and allergic airway disease has long been recognized, and many reviews have been written on this topic. However, both clinical and basic science studies published in the last 3 years provide new insights into the relationship between infection and allergic conditions. In this review, we focus on these very recent studies, which address the role of infection in the development, maintenance, and exacerbation of asthma. Bacterial, viral, fungal, and parasitic infections have each been examined and provide a framework for these novel concepts.

PD-1 up-regulation on CD4+ T cells promotes pulmonary fibrosis through STAT3-mediated IL-17A and TGF-ß1 production.

Pulmonary fibrosis is a progressive inflammatory disease with high mortality and limited therapeutic options. Previous genetic and immunologic investigations suggest common intersections between idiopathic pulmonary fibrosis (IPF), sarcoidosis, and murine models of pulmonary fibrosis. To identify immune responses that precede collagen deposition, we conducted molecular, immunohistochemical, and flow cytometric analysis of human and murine specimens. Immunohistochemistry revealed programmed cell death-1 (PD-1) up-regulation on IPF lymphocytes. PD-1+CD4+ T cells with reduced proliferative capacity and increased transforming growth factor-ß (TGF-ß)/interleukin-17A (IL-17A) expression were detected in IPF, sarcoidosis, and bleomycin CD4+ T cells. PD-1+ T helper 17 cells are the predominant CD4+ T cell subset expressing TGF-ß. Coculture of PD-1+CD4+ T cells with human lung fibroblasts induced collagen-1 production. Strikingly, ex vivo PD-1 pathway blockade resulted in reductions in TGF-ß and IL-17A expression from CD4+ T cells, with concomitant declines in collagen-1 production from fibroblasts. Molecular analysis demonstrated PD-1 regulation of the transcription factor STAT3 (signal transducer and activator of transcription 3). Chemical blockade of STAT3, using the inhibitor STATTIC, inhibited collagen-1 production. Both bleomycin administration to PD-1 null mice or use of antibody against programmed cell death ligand 1 (PD-L1) demonstrated significantly reduced fibrosis compared to controls. This work identifies a critical, previously unrecognized role for PD-1+CD4+ T cells in pulmonary fibrosis, supporting the use of readily available therapeutics that directly address interstitial lung disease pathophysiology.

Conditional regulation of cyclooxygenase-2 in tracheobronchial epithelial cells modulates pulmonary immunity.

Cyclooxygenase-2 (COX-2) gene expression in the lung is induced in pathological conditions such as asthma and pneumonia; however, the exact impact of COX-2 gene expression in the airway in regulating inflammatory and immunological response in the lung is not understood. To define a physiological role of inducible COX-2 in airway epithelial cells, we developed a novel line of transgenic mice, referred to as CycloOxygenase-2 TransActivated (COTA) mice, that overexpress a COX-2 transgene in the distribution of the CC-10 promoter in response to doxycycline. In response to doxycycline treatment, COX-2 expression was increased in airway epithelium of COTA mice and whole lung tissue contained a three- to sevenfold increase in prostaglandin E(2) (PGE(2)), prostaglandin D(2) (PGD(2)) thromboxane B(2) (TXB(2)) and 6-Keto prostaglandin F(2alpha) (PGF(2alpha)) compared to wild-type and untreated COTA mice. Interestingly, primary mouse tracheal epithelial cells from COTA mice produced only PGE(2) by doxycycline-induced COX-2 activation, providing an indication of cellular specificity in terms of mediator production. In the ovalbumin model, in which doxycycline was given at the sensitization stage, there was an increase in interleukin (IL)-4 level in lung tissue from COTA mice compared to untreated COTA and wild-type mice. In addition, COTA mice that were treated with doxycycline had impaired clearance of Pseudomonas aeruginosa pneumonia compared to wild-type mice. COX-2 gene expression in airway epithelial cells has an important role in determining immunological response to infectious and allergic agents.

Abnormal B-cell function in HTLV-I-tax transgenic mice.

Transgenic mice that carry the HTLV-I Tax gene develop an exocrinopathy with some similarities to Sjoegren's syndrome. Our experiments reveal that these mice have lymphadenopathy and splenomegaly composed primarily of B lymphocytes, as well as abnormal levels of secreted immunoglobulins. To gain insight into whether the lymphadenopathy manifested by these transgenic mice was the result of induction of cytokines by Tax, we utilized cell lines from these mice to study in vitro B-cell responses. Conditioned media (CM) derived from the cell lines caused B-cells to proliferate when a second signal, surface Ig cross-linking, was provided. The CM also caused a marked enhancement of IgM secretion by spleen cells or by purified B-cells treated with supplemental cytokines. The B-cell proliferative response and enhanced IgM secretion have not been attributed to a known cytokine. These results suggest that the CM from the cell lines contain a factor(s) involved in novel pathways of B-cell growth and differentiation that may participate in the pathologic development of autoimmune disease.

Stimulation of the high-affinity IgE receptor results in the tyrosine phosphorylation of a 60 kD protein which is associated with the protein-tyrosine kinase, Csk.

The protein tyrosine kinase Csk downregulates the activity of the Src family of kinases and has a negative effect on signal transduction through several Src kinase-associated receptors. Because the Src-family kinase Lyn plays a pivotal role in FcepsilonRI-mediated cellular activation, we examined whether Csk is involved in FcepsilonRI signaling events. Using anti-Csk antibodies and recombinant fusion proteins we detected a single tyrosine-phosphorylated protein of 60 kD (herein referred to as 'p60') that associates with the SH2 domain of Csk after stimulation of the FcepsilonRI. p60 phosphorylation reached a maximum within one minute and remained constant while the receptors were aggregated; disaggregation of the receptors resulted in rapid dephosphorylation of p60. The phosphorylation of p60 was only detected after activation by IgE and antigen and not by stimulation with PMA and/or ionomycin. Phosphorylated p60 was associated entirely with the membrane fraction of the cells. A considerable fraction of Csk was associated with the membrane in both unstimulated and stimulated cells, this fraction did not change upon activation. p60 coprecipitated with Csk from both unstimulated and FcepsilonRI stimulated cells and was phosphorylated by the immunocomplex. Total kinase activity of Csk immunoprecipitates increased upon FcepsilonRI stimulation. p60 did not react with antibodies to a number of known signaling molecules, including the recently cloned, GAP-associated protein, p62dok. Our data demonstrate that Csk associates with a membrane-anchored protein complex that is directly involved in FcepsilonRI signal transduction.

IgA, IgG and IgM quantification in bronchoalveolar lavage fluids from allergic rhinitics, allergic asthmatics, and normal subjects by monoclonal antibody-based immunoenzymetric assays.

Recent reports have suggested that human secretory IgA (sIgA) may have a role in the mediation of atopic disease. We have studied the levels of sIgA, IgA, IgG and IgM in bronchoalveolar lavage (BAL) fluids collected from lungs of healthy non-allergic adults (n = 14), allergic subjects with rhinitis (n = 15), and allergic asthmatics (n = 13), using a panel of monoclonal antibody-based immunoenzymetric assays (IEMAs). In contrast to commercially available immunodiffusion and nephelometric assays, these IEMAs employ highly specific monoclonal antibodies and demonstrate required precision (intra-assay CVs < 17%), parallelism (inter-dilutional CVs < 20%) at minimal detectable immunoglobulin levels in the ng/ml range, and excellent specificity with < 0.1% crossreactivity for heterologous immunoglobulin isotypes. Using these assays, we have observed a significant correlation between sIgA levels and total IgA levels in BAL fluids from all the study patients (r = 0.94; p < 0.01). The percentage of sIgA to total IgA was 84.0 +/- 2.2%. sIgA in BAL fluids from allergic rhinitics (18.0 +/- 2.5 micrograms/ml) and allergic asthmatics (15.5 +/- 2.5 micrograms/ml) were higher than those from nonallergic subjects (10.2 +/- 1.9 micrograms/ml). The only statistically significant difference in sIgA levels was observed in BAL fluids from the rhinitics and nonallergic groups (p = 0.03). Similar differences among the groups were found for levels of total IgA in BAL fluid. There were no significant differences in the levels of IgM and IgG in BAL fluids among the three groups of subjects. We conclude from these results that IgA is the predominant immunoglobulin on the airway surface and that it appears to be produced locally.

Inadequate outpatient medical therapy for patients with asthma admitted to two urban hospitals.

PURPOSE: To determine the patterns of chronic outpatient management in urban patients with moderate and severe asthma, and to assess medical practice adherence to the Guidelines for the Diagnosis and Management of Asthma from the National Asthma Education Program (NAEP). PATIENTS AND METHODS: This is a cross-sectional survey of adult patients with asthma admitted to the general medical services at the Johns Hopkins Medical Institutes (Johns Hopkins Hospital and Johns Hopkins Bayview Medical Center) Baltimore, Maryland. Subjects were 101 adults admitted with an asthma exacerbation from February 1992 through January 1993. Using a validated questionnaire, these subjects were surveyed within 48 hours of admission concerning their chronic outpatient medical management and the measures patients or their physicians took to alleviate symptoms during the asthma exacerbation leading to hospitalization. RESULTS: The average asthma admission rate in the past year for this group of patients was 2.5, indicative of moderate to severe disease. Less than half of these patients had been prescribed inhaled anti-inflammatory therapy. Of the patients who had previously been shown the metered dose inhaler technique by a health care professional, 11% could perform all components of this technique correctly. Only 28% of patients had been given an action plan by their physician in the event of an acute exacerbation. Sixty percent of patients who contacted their physician during the exacerbation that preceded admission had no changes made in their treatment regimen. In those whose exacerbation lasted at least 24 hours, the average beta-agonist metered dose inhaler use during the 24 hour prior to admission was 44.8 +/- 7.8 puffs (mean +/- standard error of the mean). Older age, (current smoking, and race (black) were the most significant correlates of inhaled beta-agonist use during this period. CONCLUSIONS: This is the first documentation of multiple problems in conforming with the standards of care delineated by the NAEP as they relate to the outpatient management of inner-city patients with moderate to severe asthma in the United States. In this population of patients with asthma, management was characterized by underutilization of anti-inflammatory therapy, inability to use inhalation devices properly, inadequate communication between patient and physician of an action plan to be utilized in the event of an acute exacerbation and inadequate physician intervention during the acute stages of the exacerbation. There was also overutilization of inhaled beta-agonists during exacerbations. It is imperative that these aspects of management, for which the NAEP has set standards of care, are addressed as part of the effort to reduce asthma morbidity in the urban United States.

Dietary antioxidants and adult asthma.

The triggers and causes of asthma have long been topics of investigation by epidemiologists. The current concept of asthma and atopy is that the onset of the disease and its clinical course are determined by gene environment interactions; that is, those individuals who develop asthma are both genetically susceptible and receive appropriate environmental stimuli. One potential environmental factor that may relate to disease etiology is diet. This article will review the published evidence for the effects of dietary antioxidants on asthma incidence and disease control.

Mediastinal fibrosis is associated with human leukocyte antigen-A2.

OBJECTIVE: To determine the association between mediastinal fibrosis and human leukocyte antigen (HLA) genes. DESIGN: Case-control study. SETTING: Vanderbilt University Medical Center. SUBJECTS: Nineteen consecutive patients with mediastinal fibrosis who presented to the pulmonary clinic at Vanderbilt University Medical Center from 1987 to 1996. The control subjects were 21,086 whites who were cadaveric kidney donors from October 1987 through December 1993. MEASUREMENTS: HLA testing was performed on blood samples from all 19 cases. Information on HLA typing for the control subjects was obtained from the United Network for Organ Sharing. Frequency of HLA class I and II antigens found in the cases was compared with the frequency in the control subjects. RESULTS: The relative risk of mediastinal fibrosis among subjects with the HLA-A2 antigen was 3.32 times that of those who lacked this antigen (95% confidence interval, 1.19 to 9. 2). CONCLUSION: HLA-A2 was strongly associated with mediastinal fibrosis, suggesting that an abnormal immune response is important in the pathogenesis of this disease. Key words: Histoplasma capsulatum; human leukocyte antigen-A2; mediastinal fibrosis

Rapid reversibility of the allergen-induced pulmonary late-phase reaction by an intravenous beta2-agonist.

This study was performed to determine the degree to which beta2-adrenergic receptor agonists can reverse the allergen-induced late reduction in lung function. On two occasions, seven asthmatic subjects were administered terbutaline or its vehicle by intravenous infusion 7 h after inhaled allergen, at which point the forced expiratory volume in 1 s was 57% of baseline. On another occasion, terbutaline was infused at baseline to determine maximal attainable bronchodilation. After allergen challenge, terbutaline rapidly improved lung function. At the end of terbutaline infusion, the forced expiratory volume in 1 s reached 100 +/- 1.3% of baseline and 84.2 +/- 4.3% of maximal attainable value, but the bronchodilating effect of the beta-agonist did not plateau. The values for forced vital capacity were 102 +/- 1.3% of baseline and 95.1 +/- 3% of maximal attainable value. The kinetics of the terbutaline effect, when it was infused at baseline, were similar to those in the late phase. Because the late-phase reduction in lung function is rapidly reversible by beta2-adrenergic agonists, we conclude that it is caused mainly by bronchial smooth muscle spasm.

Viral infections in asthma.

This article summarizes recent findings regarding the impact of viruses on reactive airway disease. Technical breakthroughs are improving our ability to diagnosis viral infections. However, the real breakthrough will come when pharmacologic interventions can specifically prevent the symptoms of virally induced asthma.

Epithelial nuclear factor-κB signaling promotes lung carcinogenesis via recruitment of regulatory T lymphocytes.

The mechanisms by which chronic inflammatory lung diseases, particularly chronic obstructive pulmonary disease, confer enhanced risk for lung cancer are not well-defined. To investigate whether nuclear factor (NF)-κB, a key mediator of immune and inflammatory responses, provides an interface between persistent lung inflammation and carcinogenesis, we utilized tetracycline-inducible transgenic mice expressing constitutively active IκB kinase ß in airway epithelium (IKTA (IKKß trans-activated) mice). Intraperitoneal injection of ethyl carbamate (urethane), or 3-methylcholanthrene (MCA) and butylated hydroxytoluene (BHT) was used to induce lung tumorigenesis. Doxycycline-treated IKTA mice developed chronic airway inflammation and markedly increased numbers of lung tumors in response to urethane, even when transgene expression (and therefore epithelial NF-κB activation) was begun after exposure to carcinogen. Studies using a separate tumor initiator/promoter model (MCA+BHT) indicated that NF-κB functions as an independent tumor promoter. Enhanced tumor formation in IKTA mice was preceded by increased proliferation and reduced apoptosis of alveolar epithelium, resulting in increased formation of premalignant lesions. Investigation of inflammatory cells in lungs of IKTA mice revealed a substantial increase in macrophages and lymphocytes, including functional CD4+/CD25+/FoxP3+ regulatory T lymphocytes (Tregs). Importantly, Treg depletion using repetitive injections of anti-CD25 antibodies limited excessive tumor formation in IKTA mice. At 6 weeks following urethane injection, antibody-mediated Treg depletion in IKTA mice reduced the number of premalignant lesions in the lungs in association with an increase in CD8 lymphocytes. Thus, persistent NF-κB signaling in airway epithelium facilitates carcinogenesis by sculpting the immune/inflammatory environment in the lungs.

Viruses, dendritic cells and the lung.

The interaction between viruses and dendritic cells (DCs) is varied and complex. DCs are key elements in the development of a host response to pathogens such as viruses, but viruses have developed survival tactics to either evade or diminish the immune system that functions to kill and eliminate these micro-organisms. In the present review we summarize current concepts regarding the function of DCs in the immune system, our understanding of how viruses alter DC function to attenuate both the virus-specific and global immune response, and how we may be able to exploit DC function to prevent or treat viral infections.

In vivo diagnostic procedures: skin testing, nasal provocation, and bronchial provocation.

In vivo challenge procedures can be very useful in the analysis of allergic symptoms. Skin testing has a high degree of sensitivity and specificity for determining antigens that cause allergic disease. However, positive skin tests do not necessarily indicate that a specific allergen causes symptoms specific for a certain organ. Nasal and whole lung provocation testing can help define relevant allergens that cause rhinitis or asthma symptoms. These tests are safe when performed properly under close medical supervision and have predictive values that make them useful diagnostic tools.

Effect of phenobarbital on hepatic eicosanoid concentrations in rats.

Phenobarbital is an efficacious tumor-promoting agent in the liver. Studies using inhibitors of eicosanoid synthesis have suggested that eicosanoids are important in the promotion of hepatocarcinogenesis by phenobarbital. We therefore hypothesized that hepatic eicosanoid concentrations are altered following phenobarbital administration. Male Sprague-Dawley rats were fed one of four levels of phenobarbital (0, 0.02, 0.05, and 0.1%). Eight rats from each of the four groups were killed after 10, 24, and 44 days for determination of liver weight and for preparation of microsomes. No significant difference was found among rat weights; however, liver weights were significantly higher in rats fed phenobarbital. Assay of benzyloxyresorufin-O-dealkylase activity showed that cytochromes P-450 2B1 and 2B2 were induced in response to phenobarbital administration. Prostaglandin E2 concentrations were found to be significantly decreased by phenobarbital treatment after 10 and 24 days, but not after 44 days. Prostaglandin F2 alpha levels were decreased only by the lowest dietary phenobarbital concentration. Hepatic concentrations of leukotriene C4 were decreased significantly at 10 days and at 44 days (only for the group administered the highest percentage concentration of phenobarbital), but not at 24 days. These results show that the investigated eicosanoids are generally slightly decreased by phenobarbital administration. Elevated eicosanoid levels therefore do not appear to be necessary for the promoting activity of phenobarbital.

Epidemiology of asthma: the year in review.

Asthma is a worldwide problem, with more than 17 million persons in the United States estimated to have asthma, and there is evidence that the prevalence is increasing. This article reviews the latest epidemiologic evidence for an increase in asthma prevalence and morbidity, and the evidence that environment plays a significant role in this disease. This review focuses on five specific areas: prevalence, incidence, natural history, environmental factors, and morbidity and mortality.

Respiratory viruses and asthma.

Viral infections have become increasingly recognized as a significant cause of asthma exacerbations, mainly because of improved viral detection techniques. Unfortunately, the ability to specifically treat viral infections and to limit the asthma morbidity associated with these agents has not kept pace with diagnostic technology. This article focuses on current concepts of the epidemiology of viruses in asthma exacerbations, investigations studying the physiologic and immunologic consequences of viral infection, and potential therapies to minimize virally-induced airway hyperresponsiveness. To impact this significant health problem, researchers must definitively ascertain the mechanisms by which viruses induce airway reactivity and must develop rational, safe approaches to prevent the consequences of viral infection in the patient with asthma.

Immune-mediated disease pathogenesis in respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is an important cause of severe respiratory disease in persons at both extremes of age. Wheezing is a cardinal sign of infection and the illness is associated with an increased incidence of childhood asthma. Data from both humans and animal models have linked severe disease in infants and the syndrome of vaccine-enhanced illness with an aberrant composition of CD4+ T cells, suggestive of an exaggerated Th2 response. Studies in murine models have shown that prior vaccination, coexisting allergic inflammation, or direct modulation of the cytokine milieu can profoundly influence the immune response to RSV and thereby affect the expression of disease. In addition, there are intrinsic antigenic properties of the RSV G glycoprotein that promote Th2 responses and eosinophilia. This paper proposes an integrated working model of how host and virus factors interact to determine the characteristics of RSV-induced illness. This model suggests strategies for the development of new vaccine and immunotherapeutic interventions, and creates a framework for asking additional questions about the immunopathogenesis of RSV.

Vaccination with pertussis toxin alters the antibody response to simultaneous respiratory syncytial virus challenge.

Many bacterial toxins, including pertussis toxin (PT), exert potent adjuvant effects on antibody synthesis to coadministered antigens. In these studies, we examined whether locally or peripherally administered PT similarly altered the antibody isotype selection to replicating virus after intranasal (inl) challenge. Mice primed intramuscularly with PT and inl with respiratory syncytial virus (RSV) produced RSV-specific antibodies of the IgG2a isotype at a level similar to that of unprimed controls, with some increase in IgG1 production. Mice primed inl with both PT and RSV showed elevated RSV-specific IgG1, increased serum IgE levels, and increased interleukin (IL)-4 in lung supernatants. Splenocytes from these animals produced increased IL-4 when stimulated in vitro with RSV or PT antigens after infection. These results suggest that PT can influence the local production of IL-4 to alter the humoral and cellular immune responses to viral infection as well as to coadministered antigens.

Allergen-induced changes in airway responsiveness are not related to indices of airway edema.

BACKGROUND: The mechanisms behind airway hyperresponsiveness in asthma are unknown. Airway wall edema has been proposed as one possible culprit of this phenomenon. OBJECTIVE: To test the hypothesis that airway edema may be the cause of allergen-induced increases in airway responsiveness in asthma, this trial aimed at determining the relationship between allergen-induced changes in airway responsiveness to inhaled methacholine and indirect indices of edema, namely peripheral airway resistance and the levels of the plasma protein fibrinogen in bronchoalveolar lavage (BAL) fluids. METHODS: Twenty-six atopic individuals with mild asthma were subjected to bronchoscopy at baseline and 28 hours after allergen inhalation. Before each bronchoscopy, methacholine bronchoprovocation was performed. During bronchoscopy, peripheral airway resistance measurements were obtained by wedged bronchoscopy. BAL fluids were analyzed for fibrinogen, as well as for eosinophilic cationic protein. Cytology was performed, and cytokine gene expression was assessed with competitive reverse transcriptase PCR from cell pellets. RESULTS: A significant increase in airway responsiveness to methacholine was recorded after allergen, but this did not correlate with changes in peripheral airway resistance (which was not affected) or with BAL fibrinogen (which decreased after allergen). Other BAL outcomes confirmed that airway inflammation was produced and was characterized by a T(H)2 cytokine pattern. CONCLUSIONS: Airway responsiveness in asthma increases after exposure to allergen in the absence of increased indirect indices of edema. The role of edema in this phenomenon should therefore be tested more vigorously.