Activation of human eosinophils in vitro by respiratory syncytial virus

Host Responses to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) infections are a constant public health problem, especially in infants and older adults. Virtually all children will have been infected with RSV by the age of two, and reinfections are common throughout life. Since antigenic variation, which is frequently observed among other respiratory viruses such as SARS-CoV-2 or influenza viruses, can only be observed for RSV to a limited extent, reinfections may result from short-term or incomplete immunity. After decades of research, two RSV vaccines were approved to prevent lower respiratory tract infections in older adults. Recently, the FDA approved a vaccine for active vaccination of pregnant women to prevent severe RSV disease in infants during their first RSV season. This review focuses on the host response to RSV infections mediated by epithelial cells as the first physical barrier, followed by responses of the innate and adaptive immune systems. We address possible RSV-mediated immunomodulatory and pathogenic mechanisms during infections and discuss the current vaccine candidates and alternative treatment options.

Eosinophils in transbronchial biopsies: a predictor of chronic lung allograft dysfunction and reduced survival after lung transplantation - a retrospective single-center cohort study

Long-term outcomes after lung transplantation remain inferior to those of other solid organ groups. The significance of eosinophils detected on transbronchial biopsies (TBBx) after lung transplantation and their relationship to long-term outcomes remain unknown. A retrospective single-center cohort study was performed of patients transplanted between January 01, 2001, and July 31, 2018, who had at least 1 TBBx with evaluable parenchymal tissue. Multivariable Cox proportional hazard models were used to assess the associations between eosinophil detection and: all-cause mortality and Chronic Lung Allograft Dysfunction (CLAD). 8887 TBBx reports from 1440 patients were reviewed for the mention of eosinophils in the pathology report. 112 (7.8%) patients were identified with eosinophils on at least one TBBx. The median (95% CI) survival time for all patients was 8.28 (7.32-9.31) years. Multivariable analysis, adjusted for clinical variables known to affect post-transplant outcomes, showed that the detection of eosinophils was independently associated with an increased risk of death (HR 1.51, 95% CI 1.24-1.85, p < 0.01) and CLAD (HR 1.35, 95% CI 1.07-1.70, P = 0.01). Eosinophils detected in TBBx are associated with an increased risk of CLAD and death. There may be benefit in specifically reporting the presence of eosinophils in TBBx reports and incorporating their presence in clinical decision-making.

Corticosteroid Withdrawal-Induced Loss of Control in Mild to Moderate Asthma Is Independent of Classic Granulocyte Activation

BACKGROUND

Loss of asthma control and asthma exacerbations are associated with increased sputum eosinophil counts. However, whether eosinophils, or the also present neutrophils, actively contribute to the accompanying inflammation has not been extensively investigated.

METHODS

Twenty-three patients with mild to moderate asthma were included in a standardized prospective inhaled corticosteroid (ICS) withdrawal study; 22 of the patients experienced loss of asthma control. The study assessed various immune, inflammatory, and oxidative stress parameters, as well as markers of eosinophil and neutrophil activity, in exhaled breath condensate, plasma, and sputum collected at three phases (baseline, during loss of control, and following recovery).

RESULTS

Loss of asthma control was characterized by increased sputum eosinophils, whereas no differences were detected between the three phases for most inflammatory and oxidative stress responses. There were also no differences detected for markers of activated eosinophils (eosinophil cationic protein and bromotyrosine) and neutrophils (myeloperoxidase and chlorotyrosine). However, free eosinophilic granules and citrullinated histone H₃, suggestive of eosinophil cytolysis and potentially eosinophil extracellular trap formation, were enhanced. Baseline blood eosinophils and changes in asymmetric dimethylarginine (an inhibitor of nitric oxide synthase) in plasma were found to correlate with the decrease in FEV₁ percent predicted upon ICS withdrawal (both, r_s = 0.46; P = .03).

CONCLUSIONS

The clinical effect in mild to moderate asthma upon interruption of ICS therapy is not related to the classic inflammatory activation of eosinophils and neutrophils. It may, however, reflect another pathway underlying the onset of loss of disease control and asthma exacerbations.

TRIAL REGISTRY

The Netherlands Trial Register; No.: NTR3316; URL: trialregister.nl/trial/3172.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

Induction of Porcine Dermatitis and Nephropathy Syndrome in Piglets by Infection with Porcine Circovirus Type 3

Porcine circovirus type 3 (PCV3) is an emerging porcine circovirus that has been associated with porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, cardiac pathologies, and multisystemic inflammation in piglets and sows. Many aspects of PCV3 infection biology and pathogenesis, however, remain unknown. Here, we used a PCV3 virus stock from the rescue of an infectious PCV3 DNA clone to intranasally inoculate 4- and 8-week-old specific-pathogen-free piglets for evaluation of PCV3 pathogenesis. For 4-week-old piglets, typical clinical signs resembling those of PDNS-like disease were observed when piglets were inoculated with PCV3 alone or PCV3 combined with immunostimulation by keyhole limpet hemocyanin, with a mortality of 40% (2/5) for both types of inoculated piglets during a 28-day observation period postinoculation. Both types of inoculated piglets showed similar progressive increases in viral loads in the sera and had seroconverted to PCV3 capsid antibody after inoculation. Pathological lesions and PCV3-specific antigen were detected in various tissues and organs, including the lung, heart, kidney, lymph nodes, spleen, liver, and small intestine, in both types of inoculated piglets. The levels of proinflammatory cytokines and chemokines, including interleukin 1 beta (IL-1β), IL-6, IL-23α, gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and chemokine ligand 5 (CCL5), were significantly upregulated in both groups of inoculated piglets. Eight-week-old piglets also exhibited a similar PDNS-like disease but without death after PCV3 inoculation, as evidenced by pathological lesions and PCV3 antigen in various tissues and organs. These results show for the first time successful reproduction of PDNS-like disease by PCV3 infection and further provide significant information regarding the pathogenesis of PCV3 in piglets.IMPORTANCE Porcine circovirus type 3 (PCV3), an emerging porcine circovirus, is considered the cause of porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs and other systemic diseases in piglets and sows. To evaluate the pathogenesis of PCV3 infection in vivo, we used a PCV3 virus stock from the rescue of an infectious PCV3 DNA clone to intranasally inoculate 4- and 8-week-old specific-pathogen-free piglets and demonstrated successful reproduction of PDNS-like disease in animals that were inoculated with PCV3 alone or PCV3 combined with immunostimulation by keyhole limpet hemocyanin. Both 4- and 8-week-old PCV3-inoculated piglets showed similar increases in viral loads in the sera and had seroconverted to PCV3 capsid antibody. Pathological lesions and PCV3-specific antigen were detected in various tissues and organs, while numerous proinflammatory cytokines and chemokines in the sera were significantly upregulated after PCV3 inoculation. These results will provide significant information regarding the pathogenesis of PCV3 in piglets.

Eosinophils from Physiology to Disease: A Comprehensive Review

Despite being the second least represented granulocyte subpopulation in the circulating blood, eosinophils are receiving a growing interest from the scientific community, due to their complex pathophysiological role in a broad range of local and systemic inflammatory diseases as well as in cancer and thrombosis. Eosinophils are crucial for the control of parasitic infections, but increasing evidence suggests that they are also involved in vital defensive tasks against bacterial and viral pathogens including HIV. On the other side of the coin, eosinophil potential to provide a strong defensive response against invading microbes through the release of a large array of compounds can prove toxic to the host tissues and dysregulate haemostasis. Increasing knowledge of eosinophil biological behaviour is leading to major changes in established paradigms for the classification and diagnosis of several allergic and autoimmune diseases and has paved the way to a "golden age" of eosinophil-targeted agents. In this review, we provide a comprehensive update on the pathophysiological role of eosinophils in host defence, inflammation, and cancer and discuss potential clinical implications in light of recent therapeutic advances.

Eosinophils Promote Antiviral Immunity in Mice Infected with Influenza A Virus

Eosinophils are multifunctional cells of the innate immune system linked to allergic inflammation. Asthmatics were more likely to be hospitalized but less likely to suffer severe morbidity and mortality during the 2009 influenza pandemic. These epidemiologic findings were recapitulated in a mouse model of fungal asthma wherein infection during heightened allergic inflammation was protective against influenza A virus (IAV) infection and disease. Our goal was to delineate a mechanism(s) by which allergic asthma may alleviate influenza disease outcome, focused on the hypothesis that pulmonary eosinophilia linked with allergic respiratory disease is able to promote antiviral host defenses against the influenza virus. The transfer of eosinophils from the lungs of allergen-sensitized and challenged mice into influenza virus-infected mice resulted in reduced morbidity and viral burden, improved lung compliance, and increased CD8+ T cell numbers in the airways. In vitro assays with primary or bone marrow-derived eosinophils were used to determine eosinophil responses to the virus using the laboratory strain (A/PR/08/1934) or the pandemic strain (A/CA/04/2009) of IAV. Eosinophils were susceptible to IAV infection and responded by activation, piecemeal degranulation, and upregulation of Ag presentation markers. Virus- or viral peptide-exposed eosinophils induced CD8+ T cell proliferation, activation, and effector functions. Our data suggest that eosinophils promote host cellular immunity to reduce influenza virus replication in lungs, thereby providing a novel mechanism by which hosts with allergic asthma may be protected from influenza morbidity.

Respiratory syncytial virus infection: mechanisms of redox control and novel therapeutic opportunities

Respiratory syncytial virus (RSV) is one of the most important causes of upper and lower respiratory tract infections in infants and young children, for which no effective treatment is currently available. Although the mechanisms of RSV-induced airway disease remain incompletely defined, the lung inflammatory response is thought to play a central pathogenetic role. In the past few years, we and others have provided increasing evidence of a role of reactive oxygen species (ROS) as important regulators of RSV-induced cellular signaling leading to the expression of key proinflammatory mediators, such as cytokines and chemokines. In addition, RSV-induced oxidative stress, which results from an imbalance between ROS production and airway antioxidant defenses, due to a widespread inhibition of antioxidant enzyme expression, is likely to play a fundamental role in the pathogenesis of RSV-associated lung inflammatory disease, as demonstrated by a significant increase in markers of oxidative injury, which correlate with the severity of clinical illness, in children with RSV infection. Modulation of ROS production and oxidative stress therefore represents a potential novel pharmacological approach to ameliorate RSV-induced lung inflammation and its long-term consequences.

Role of eosinophils and their clinical significance in allergic inflammation

Eosinophils are believed to play roles in the pathophysiology of allergic inflammation, such as bronchial asthma. However, recent studies on anti-interleukin-5 monoclonal antibody treatment of asthmatic patients raised the possibility that eosinophils may play only a limited role. More recent studies established that eosinophils are essentially involved in the development of airway remodeling. Moreover, it is theoretically conceivable that eosinophils are a cellular source of lipid mediators, such as cysteinyl leukotrienes or platelet-activating factor in asthma. Even in the absence of interleukin-5, it is likely that the 'T-helper Type 2 network', including a cascade of vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, CC chemokines, granulocyte-macrophage colony-stimulating factor, for example, can maintain sufficient eosinophilic infiltration and effector functions, such as superoxide anion generation and degranulation. Long-term studies, wherein tissue eosinophils are eliminated effectively will be required to establish the exact roles of these cells in asthma. Finally, the authors will demonstrate that eosinophils have the potential for not only playing detrimental roles but also beneficial ones.

Respiratory viruses and eosinophils: exploring the connections

In this review, we consider the role played by eosinophilic leukocytes in the pathogenesis and pathophysiology of respiratory virus infection. The vast majority of the available information on this topic focuses on respiratory syncytial virus (RSV; Family Paramyxoviridae, genus Pneumovirus), an important pediatric pathogen that infects infants worldwide. There is no vaccine currently available for RSV. A formalin-inactivated RSV vaccine used in a trial in the 1960s elicited immunopathology in response to natural RSV infection; this has been modeled experimentally, primarily in inbred mice and cotton rats. Eosinophils are recruited to the lung tissue in response to formalin-inactivated RSV vaccine antigens in humans and in experimental models, but they may or may not be involved in promoting the severe clinical sequelae observed. Pulmonary eosinophilia elicited in response to primary RSV infection has also been explored; this response is particularly evident in the youngest human infants and in neonatal mouse models. Although pulmonary eosinophilia is nearly always perceived in a negative light, the specific role played by virus-elicited eosinophils - negative, positive or neutral bystander - remain unclear. Lastly, we consider the data that focus on the role of eosinophils in promoting virus clearance and antiviral host defense, and conclude with a recent study that explores the role of eosinophils themselves as targets of virus infection.

Targeting eosinophils in asthma

Recruitment of eosinophils has long been recognized as a hallmark of the inflammatory response in asthma. However, the functions of this population of cells in host defense remain poorly understood. Eosinophils play an important part in the inflammatory response and have key regulatory roles in the afferent arm of the immune response. More recently, eosinophils have been demonstrated to participate in host defense against respiratory viruses. The specific contributions of eosinophils to the pathophysiology of asthma remain controversial. However, the balance of evidence indicates that they have a significant role in the disease, suggesting that they may be appropriate targets for therapy. Towards this end, a novel intervention of considerable potential interest is the use of an antibody directed against the beta common chain of the receptor for interleukin-3, interleukin-5 and granulocyte-macrophage colony-stimulating factor. However, eliminating eosinophils may not be a risk-free therapeutic strategy, as there is potentially an increased likelihood of respiratory viral infections. This may predispose to the development of acute exacerbations of asthma, an outcome that would have significant clinical implications.

Asthma

Asthma has been recognized as a disease since the earliest times. In the Corpus Hippocraticum, Hippocrates used the term “ασθμα” to indicate any form of breathing difficulty manifesting itself by panting. Aretaeus of Cappadocia, a well-known Greek physician (second century A.D.), is credited with providing the first detailed description of an asthma attack [13], and to Celsus it was a disease with wheezing and noisy, violent breathing. In the history of Rome, we find many members of the Julio-Claudian family affected with probable atopic respiratory disorders: Caesar Augustus suffered from bronchoconstriction, seasonal rhinitis as well as a highly pruritic skin disease. Claudius suffered from rhinoconjunctivitis and Britannicus was allergic to horse dander [529]. Maimonides (1136–1204) warned that to neglect treatment of asthma could prove fatal, whereas until the 19th century, European scholars defined it as “nervous asthma,” a term that was given to mean a defect of conductivity of the ninth pair of cranial nerves.

Persistent airway obstruction after virus infection is not associated with airway inflammation

BACKGROUND

This study examined the contribution of airway inflammation to the delayed lung function recovery that occurs in some people following virus-induced asthma exacerbations.

METHODS

Subjects (n = 40) were recruited at hospital admission for acute asthma exacerbation. Respiratory virus infection was diagnosed by viral nucleic acid detection and/or cell culture, using induced sputum, nasal, or throat swabs. Data collected included lung function, answers to common cold and asthma control questionnaires, and induced sputum cellular profiles. Subjects were reexamined 4 to 6 weeks postexacerbation and were compared with stable asthmatic subjects (n = 26) who had been recruited from ambulatory care clinics.

RESULTS

Persistent airway obstruction, defined as lung function improvement at follow-up (ie, change in FEV1 percent predicted [Delta%FEV1]) of <15%, was observed in 10 subjects (25%). Airway recovery (Delta%FEV1, > or = 15%) was observed in the remaining subjects (30 subjects; 75%). During the acute episode, the airway-recovery group had increased total cell count (p = 0.019), increased number of neutrophils (p = 0.005), and increased percentage of neutrophils (p = 0.0043) compared to the group of stable subjects with asthma. Postexacerbation, the airway-recovery group had reduced numbers of neutrophils and an increased percentage of eosinophils. In contrast, during exacerbation, subjects with persistent airway obstruction showed no differences in inflammatory cell counts compared to stable subjects with asthma, nor did cell counts change postexacerbation. Symptoms improved in both groups postexacerbation. However, in the persistent-airway-obstruction group, asthma remained uncontrolled.

CONCLUSION

Persistent airway obstruction and uncontrolled asthma are observed in some people after viral asthma exacerbations. These abnormalities are not associated with inflammatory cell influx into the airway lining fluid during the exacerbation and may reflect the involvement of noncellular elements. Further work should explore other mechanisms leading to incomplete airway recovery.

Elevations of local leukotriene C4 levels during viral upper respiratory tract infections

BACKGROUND

One potential mechanism by which respiratory viruses trigger illness and complications is via the local elaboration of inflammatory mediators.

OBJECTIVE

To determine whether there is an increase in local leukotriene C4 (LTC4) levels during experimental infection with influenza A virus (FLU), rhinovirus (RV), or respiratory syncytial virus (RSV).

METHODS

Healthy adults were intranasally inoculated with a safety-tested strain of FLU (n = 29), RV (n = 16), or RSV (n = 21). Nasal lavage samples were collected, symptoms were recorded, and expelled nasal secretions were weighed before and then daily after challenge. Lavage samples were submitted for viral culture and assayed for LTC4 levels by radioimmunoassay. Serum antibody titers to the challenge viruses were assayed at baseline and 21 days after challenge.

RESULTS

All subjects were infected as evidenced by viral shedding and/or seroconversion. Following infection, significant increases (P < 0.05 by analysis of variance) in LTC4 levels were measured for each virus. Furthermore, there was a temporal association between the local LTC4 levels and the development of illness.

CONCLUSIONS

The results of this study, which used an adult experimental model, demonstrate elevations in locally produced LTC4 during respiratory infection with FLU, RV, and RSV. Future studies using antileukotriene agents may help elucidate the precise role of leukotrienes in mediating disease expression.

The complex relationship between respiratory syncytial virus and allergy in lung disease

Epidemiologic studies suggest a strong link between severe respiratory syncytial virus (RSV)-induced bronchiolitis in infancy and allergic disease; however, the mechanisms determining this relationship are currently unknown. In this review article, we summarize data from human clinical studies that explore the association between RSV infection and allergy, some that suggest that RSV bronchiolitis requiring hospitalization leads to an increased incidence of the allergic phenotype and others that suggest that pre-existing allergy is a risk factor for severe RSV bronchiolitis. We also review the published murine models that combine RSV infection and allergic sensitization that attempt to explain the complex relationship between these two factors in regard to lung immunopathology and physiologic dysfunction.

Infectious triggers of pediatric asthma

Respiratory infections can cause wheezing illnesses in children of all ages and also can influence the causation and disease activity of asthma. For years it has been recognized that respiratory syncytial virus infections often produce the first episode of wheezing in children who go on to develop chronic asthma. More recently, it has been proposed that repeated infections with other common childhood viral pathogens might help the immune system develop in such a way as to prevent the onset of allergic diseases and possibly asthma. In addition to the effects of viral infections, infections with certain intracellular pathogens, such as chlamydia and mycoplasma, may cause acute and chronic wheezing in some individuals, whereas common cold and acute sinus infections can trigger acute symptoms of asthma. In this article, the epidemiologic, mechanistic, and treatment implications of the association between respiratory infections and asthma are discussed.

CD8+ T lymphocytes in viral hyperreactivity and M2 muscarinic receptor dysfunction

In the airways, inhibitory M2 muscarinic receptors (M2Rs) on parasympathetic nerves limit acetylcholine release. Viral infection causes M2R dysfunction, which increases acetylcholine release and leads to airway hyperreactivity. In these studies we tested the role of CD8+ T cells in parainfluenza virus-induced hyperreactivity and M2R dysfunction in normal guinea pigs and in guinea pigs previously sensitized to ovalbumin. Depleting CD8+ T cells prevented virus-induced M2R dysfunction and hyperreactivity in sensitized animals, but not in nonsensitized animals. Sensitization increased the number of eosinophils in close relation to the airway nerves where, when activated, they release major basic protein, which binds to and blocks the M2Rs. Regardless of sensitization, viral infection decreased the number of visible tissue eosinophils, likely reflecting eosinophil degranulation via cytolysis. Depleting CD8+ T cells prevented this virus-induced eosinophil degranulation. In addition, an antiviral effect of sensitization, which we previously showed to be eosinophil mediated, was again seen. This was prevented by depletion of CD8+ Tcells. Thus, CD8+ T cells play a role in airway hyperreactivity and M2R dysfunction of sensitized virus-infected guinea pigs by mediating eosinophil degranulation near airway nerves. In contrast, CD8+ T cells are not necessary for virus-induced hyperreactivity and M2R dysfunction in nonsensitized guinea pigs.

RANTES may be predictive of later recurrent wheezing after respiratory syncytial virus bronchiolitis in infants

BACKGROUND

In vitro studies have shown that RANTES is strongly induced by respiratory syncytial virus (RSV) infection in cultures of upper airway epithelial cells. RANTES is known as a chemoattractant and activator for eosinophils.

OBJECTIVES

We performed this study to investigate whether RANTES is increased in the airway during naturally acquired RSV bronchiolitis. RANTES levels were then evaluated in relation to the severity of illness and later development of recurrent wheezing.

METHODS

We measured RANTES in nasal secretions of 30 patients with acute RSV bronchiolitis. Eosinophil cationic protein (ECP) was determined to evaluate the activation of eosinophils. The severity of illness was determined by the initial PaO2 values and the duration of wheezing. At a 1-year followup, all infants were re-evaluated if they had experienced subsequent wheezing, and we investigated if RANTES levels could predict the later development of recurrent wheezing.

RESULTS

Both RANTES and ECP in RSV bronchiolitis were significantly higher than in controls. There was a significant correlation between the levels of RANTES and ECP. RANTES was not significantly higher in patients with severe symptoms than in patients with mild symptoms. RANTES in infants who had experienced subsequent wheezing was significantly higher than in infants who had not.

CONCLUSIONS

Our results showed that RANTES is increased in nasal secretion during acute RSV bronchiolitis and suggest that high levels of RANTES may be predictive of later development of recurrent wheezing.

Oxidant tone regulates RANTES gene expression in airway epithelial cells infected with respiratory syncytial virus. Role in viral-induced interferon regulatory factor activation

Respiratory syncytial virus (RSV) produces intense pulmonary inflammation, in part, through its ability to induce chemokine synthesis in infected airway epithelial cells. RANTES (regulated upon activation, normal T-cells expressed and secreted) is a CC chemokine which recruits and activates monocytes, lymphocytes, and eosinophils, all cell types present in the lung inflammatory infiltrate induced by RSV infection. In this study we investigated the role of reactive oxygen species in the induction of RANTES gene expression in human type II alveolar epithelial cells (A549), following RSV infection. Our results indicate that RSV infection of airway epithelial cells rapidly induces reactive oxygen species production, prior to RANTES expression, as measured by oxidation of 2',7'-dichlorofluorescein. Pretreatment of airway epithelial cells with the antioxidant butylated hydroxyanisol (BHA), as well a panel of chemically unrelated antioxidants, blocks RSV-induced RANTES gene expression and protein secretion. This effect is mediated through the ability of BHA to inhibit RSV-induced interferon regulatory factor binding to the RANTES promoter interferon-stimulated responsive element, that is absolutely required for inducible RANTES promoter activation. BHA inhibits de novo interferon regulator factor (IRF)-1 and -7 gene expression and protein synthesis, and IRF-3 nuclear translocation. Together, these data indicates that a redox-sensitive pathway is involved in RSV-induced IRF activation, an event necessary for RANTES gene expression.

Bronchoalveolar lavage cellular composition in acute asthma and acute bronchiolitis

OBJECTIVE

To compare cellular inflammation in the airways between acute bronchiolitis and asthma.

STUDY DESIGN

Using a bronchoalveolar lavage with flexible bronchoscopy procedure, we investigated the cellular constituents of BAL fluid in children with acute exacerbation of asthma (n = 18) and infants with acute bronchiolitis caused by respiratory syncytial virus (n = 20). These results were compared with those of healthy control subjects (n = 14).

RESULTS

Total lavage fluid recovered was similar in all groups. The total cell numbers were highest in the bronchiolitis group. The BAL cellular profile in the asthma group was characterized by a higher median (interquartile range) ratio of eosinophils (2.4% [1.6%-9.5%]; P <.01) than in the bronchiolitis group (0% [0%-0%]) or the control group (0% [0%-0%]). Neutrophil ratio was higher in the bronchiolitis group (40.0% [26.5%-50.0%]; P <.01), with no difference found between the asthma group (3.3% [2.0%-7.9%]) and the control group (2.0% [0.8%-5.5%]).

CONCLUSIONS

Asthma and acute bronchiolitis are characterized by an elevated cellular percentage of eosinophils and neutrophils, respectively, in bronchoalveolar lavage fluid.

The chemokine macrophage-inflammatory protein-1 alpha and its receptor CCR1 control pulmonary inflammation and antiviral host defense in paramyxovirus infection

In this work, we explore the responses of specific gene-deleted mice to infection with the paramyxovirus pneumonia virus of mice (PVM). We have shown previously that infection of wild type mice with PVM results in pulmonary neutrophilia and eosinophilia accompanied by local production of macrophage-inflammatory protein-1 alpha (MIP-1 alpha). Here we examine the role of MIP-1 alpha in the pathogenesis of this disease using mice deficient in MIP-1 alpha or its receptor, CCR1. The inflammatory response to PVM in MIP-1 alpha-deficient mice was minimal, with approximately 10-60 neutrophils/ml and no eosinophils detected in bronchoalveolar lavage fluid. Higher levels of infectious virus were recovered from lung tissue excised from MIP-1 alpha-deficient than from fully competent mice, suggesting that the inflammatory response limits the rate of virus replication in vivo. PVM infection of CCR1-deficient mice was also associated with attenuated inflammation, with enhanced recovery of infectious virus, and with accelerated mortality. These results suggest that the MIP-1 alpha/CCR1-mediated acute inflammatory response protects mice by delaying the lethal sequelae of infection.

Evaluation of the measurement of leukotriene B4 concentrations in exhaled condensate as a noninvasive method for assessing mediators of inflammation in the lungs of calves

OBJECTIVE

To determine whether measurement of an inflammatory mediator in exhaled condensate could provide a noninvasive method for evaluating lungs of calves.

ANIMALS

84 calves < or = 2 months old.

PROCEDURE

Concentration of leukotriene B4 (LTB4) was evaluated in the exhaled condensate of healthy calves and calves with experimentally induced respiratory tract infections. For collection of samples of exhaled condensate, the total amount of exhaled air was directed into a cooled double-jacketed tube. Each tube was sealed and stored at -80 C. The LTB4 concentration was measured, using an ELISA.

RESULTS

In exhaled condensates of clinically healthy calves, normally distributed and highly reproducible LTB4 concentrations (mean +/- SD, 116.1 +/- 55.4 pg/ml) were measured. After experimentally induced infection with Pasteurella multocida serovar D, LTB4 in exhaled condensate increased significantly (mean, 179% increase), compared with basal concentrations before infection; this increase in LTB4 was significantly correlated with deterioration in lung function. In 2 of 4 calves experimentally infected with bovine respiratory syncytial virus, the LTB4 concentration in exhaled condensate increased (300 to 400% increase), compared with baseline values, which was associated with development of bronchial hyperresponsiveness after infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Collection of exhaled condensate is tolerated well by calves and is an acceptable method for obtaining fluid from exhaled air originating from the lungs. This method provides alternatives for diagnosing and evaluating treatment of naturally acquired and experimentally induced diseases of the lungs and airways in calves.

Eosinophils, ribonucleases and host defense: solving the puzzle

The eosinophil ribonucleases eosinophil-derived neurotoxin (EDN/RNase 2) and eosinophil cationic protein (ECP/RNase 3) are among the major secretory effector proteins of human eosinophilic leukocytes, cells whose role in host defense remains controversial and poorly understood. We have recently described the unusual manner in which this ribonuclease lineage has evolved, with extraordinary diversification observed in primate as well as in rodent EDNs and ECPs. The results of our evolutionary studies suggest that the EDN/ ECP ribonucleases are in the process of being tailored for a specific, ribonuclease-related goal. With this in mind, we have begun to look carefully at some of the intriguing associations that link eosinophils and their ribonucleases to disease caused by the single-stranded RNA viral pathogen, respiratory syncytial virus (RSV). Recent work in our laboratory has demonstrated that eosinophils can mediate a direct, ribonuclease-dependent reduction in infectivity of RSV in vitro, and that EDN can function alone as an independent antiviral agent. The results of this work have led us to consider the possibility that the EDN/ECP ribonucleases represent a heretofore unrecognized element of innate and specific antiviral host defense.

The role of respiratory viruses in acute and chronic asthma

Respiratory infections can have dual effects related to asthma. First, there is increasing evidence that severe infections with RSV and PIV in infancy can alter lung development and physiology to increase the risks of subsequent wheezing and asthma. Second, infections with common cold viruses and influenza commonly precipitate wheezing symptoms in children and adults who already have established asthma, and RV appears to be the most important virus in producing exacerbations of the disease. The principal mechanisms by which this occurs appears to be viral replication in epithelial cells, triggering a cascade of inflammation involving granulocytes, macrophages, T cells, and secreted cytokines and mediators. The inflammatory process, although essential to clear the infection, augments pre-existing airway inflammation in asthma, leading to increased airway obstruction and lower respiratory tract symptoms. Greater understanding of virus-induced changes in inflammation and corresponding changes in airway physiology may lead to new therapeutic approaches to the treatment and prevention of virus-induced airway dysfunction.

The role of viruses in development or exacerbation of atopic asthma

Respiratory viral infections in early childhood have been linked to the development of persistent wheezing and asthma. Epidemiologic data indicate that, for the majority of children, virus-induced wheezing is a self-limited condition, with no long-term consequences. For a substantial minority, however, virus-induced wheezing is associated with persistent asthma and the potential for enhanced allergic sensitization. For the most part, this subset of patients is genetically predisposed; they are atopic children in whom respiratory viral infections trigger the early development of asthma by mechanisms that have not been fully elucidated. Both inflammatory and noninflammatory mechanisms may be involved. It does not appear that viral infection per se in early life is responsible for the induction of atopic asthma. Data from animal models provide support for the concept that enhanced allergic sensitization caused by increased uptake of allergen during infection may play a critical role, as well as T-cell-mediated immune responses to viral infection, which may favor eosinophilic inflammatory responses and the development of altered airway function to inhaled methacholine. Recent advances in our understanding of the interactions between respiratory viruses and the development of reactive airway disease offer new possibilities for preventive treatment in children at risk for developing persistent wheezing and asthma exacerbation as a result of viral infection.

Mechanisms of eosinophil-associated inflammation

Increasing evidence supports a critical role for the eosinophil in disease. Here, the mechanisms underlying eosinophil-associated inflammation are reviewed including eosinophil constituents, eosinophil maturation and release from the bone marrow, and eosinophil tissue recruitment and activation. Eosinophil effector functions in bronchial asthma are summarized with particular attention to pulmonary M2 muscarinic receptors and bronchial hyperreactivity. Recent findings supporting roles for IL-5, the eosinophil, and its ribonucleases in viral immunity are presented. Overall, this information supports an expanded view of eosinophil participation in health and disease.

Ovalbumin sensitization changes the inflammatory response to subsequent parainfluenza infection. Eosinophils mediate airway hyperresponsiveness, m(2) muscarinic receptor dysfunction, and antiviral effects

Asthma exacerbations, many of which are virus induced, are associated with airway eosinophilia. This may reflect altered inflammatory response to viruses in atopic individuals. Inhibitory M(2) muscarinic receptors (M(2)Rs) on the airway parasympathetic nerves limit acetylcholine release. Both viral infection and inhalational antigen challenge cause M(2)R dysfunction, leading to airway hyperresponsiveness. In antigen-challenged, but not virus-infected guinea pigs, M(2)R dysfunction is due to blockade of the receptors by the endogenous antagonist eosinophil major basic protein (MBP). We hypothesized that sensitization to a nonviral antigen before viral infection alters the inflammatory response to viral infection, so that M(2)R dysfunction and hyperreactivity are eosinophil mediated. Guinea pigs were sensitized to ovalbumin intraperitoneally, and 3 wk later were infected with parainfluenza. In sensitized, but not in nonsensitized animals, virus-induced hyperresponsiveness and M(2)R dysfunction were blocked by depletion of eosinophils with antibody to interleukin (IL)-5 or treatment with antibody to MBP. An additional and unexpected finding was that sensitization to ovalbumin caused a marked (80%) reduction in the viral content of the lungs. This was reversed by the antibody to IL-5, implicating a role for eosinophils in viral immunity.

PEDIATRIC ALLERGY

The current paradigm of allergy pathogenesis is that allergy develops in individuals with a genetic predisposition only after they are exposed to allergens (Fig. 1). This hypothesis implies that factors in the environment can determine the initiation of allergic sensitization and can potentially influence the clinical manifestations and severity of disease. Because the prevalence of atopic diseases such as allergic rhinitis, asthma, atopic dermatitis, and food allergy have increased worldwide in the past several decades, and there is no mechanism for changes in population genetics over this short period of time, changes in the human environment are most likely responsible for these trends. From this line of reasoning, it follows that if the factors responsible for the increasing prevalence can be identified, then there would be an opportunity to develop strategies to reverse these trends. It also would be helpful to identify infants who are at risk for developing allergy, so that preventive strategies could be used most effectively.

In this article, studies to determine the contributions of genetics and the environment to the development of allergic diseases in childhood are explored. In addition, progress in identifying risk factors for allergy and preventive therapies for those children at risk are also addressed.

Respiratory syncytial virus infection: immune response, immunopathogenesis, and treatment

Respiratory syncytial virus (RSV) is the single most important cause of lower respiratory tract infection during infancy and early childhood. Once RSV infection is established, the host immune response includes the production of virus-neutralizing antibodies and T-cell-specific immunity. The humoral immune response normally results in the development of anti-RSV neutralizing-antibody titers, but these are often suboptimal during an infant's initial infection. Even when the production of RSV neutralizing antibody following RSV infection is robust, humoral immunity wanes over time. Reinfection during subsequent seasons is common. The cellular immune response to RSV infection is also important for the clearance of virus. This immune response, vital for host defense against RSV, is also implicated in the immunopathogenesis of severe lower respiratory tract RSV bronchiolitis. Many details of the immunology and immunopathologic mechanisms of RSV disease known at present have been learned from rodent models of RSV disease and are discussed in some detail. In addition, the roles of immunoglobulin E, histamine, and eosinophils in the immunopathogenesis of RSV disease are considered. Although the treatment of RSV bronchiolitis is primarily supportive, the role of ribavirin is briefly discussed. Novel approaches to the development of new antiviral drugs with promising anti-RSV activity in vitro are also described.

Cell-specific expression of RANTES, MCP-1, and MIP-1alpha by lower airway epithelial cells and eosinophils infected with respiratory syncytial virus

Respiratory syncytial virus (RSV) is the major cause of acute bronchiolitis in infancy, a syndrome characterized by wheezing, respiratory distress, and the pathologic findings of peribronchial mononuclear cell infiltration and release of inflammatory mediators by basophil and eosinophil leukocytes. Composition and activation of this cellular response are thought to rely on the discrete target cell selectivity of C-C chemokines. We demonstrate that infection in vitro of human epithelial cells of the lower respiratory tract by RSV induced dose- and time-dependent increases in mRNA and protein secretion for RANTES (regulated upon activation, normal T-cell expressed and presumably secreted), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1alpha (MIP-1alpha). Production of MCP-1 and MIP-1alpha was selectively localized only in epithelial cells of the small airways and lung. Exposure of epithelial cells to gamma interferon (IFN-gamma), in combination with RSV infection, induced a significant increase in RANTES production that was synergistic with respect to that obtained by RSV infection or IFN-gamma treatment alone. Epithelial cell-derived chemokines exhibited a strong chemotactic activity for normal human blood eosinophils. Furthermore, eosinophils were susceptible to RSV and released RANTES and MIP-1alpha as a result of infection. Therefore, the inflammatory process in RSV-induced bronchiolitis appears to be triggered by the infection of epithelial cells and further amplified via mechanisms driven by IFN-gamma and by the secretion of eosinophil chemokines.

Respiratory Syncytial Virus-Infected Pulmonary Epithelial Cells Induce Eosinophil Degranulation by a CD18-Mediated Mechanism

Respiratory syncytial virus (RSV)-induced bronchiolitis in infants is characterized by wheezing, respiratory distress, and the histologic findings of necrosis and sloughing of airway epithelium. High concentrations of eosinophil cationic protein (ECP), a cytotoxic protein contained in the granules of eosinophils, have been found in the airways of RSV-infected infants. The mechanisms of eosinophil degranulation in vivo remain largely unknown. Since RSV-infected respiratory epithelial cells are a rich source of cytokines with eosinophil-activating properties, our studies were designed to mimic in vitro the interaction between RSV, pulmonary epithelial cells (A549), and eosinophils in the airway mucosa. We report in this work that, in the absence of epithelial cells, neither RSV, in the form of purified virions, nor UV-irradiated culture supernatant of RSV-infected epithelial cells (RSV-CM) induced eosinophil degranulation. On the other hand, eosinophils released significant amount of ECP when cultured with RSV-infected A549 cells. Uninfected A549 cells, which failed to induce eosinophil degranulation, were equally effective in triggering ECP release if they were cultured with eosinophils in the presence of RSV-CM. Although RSV-CM induced the up-regulation of the β2 integrin CD11b on eosinophils and the expression of ICAM-1 on A549 cells, release of ECP was inhibited significantly by anti-CD18 mAb, but not by anti-ICAM-1 mAb. These results suggest a novel mechanism by which respiratory viruses may trigger the detrimental release of eosinophil granule proteins in the airway mucosa.

Airway hyperresponsiveness: first eosinophils and then neuropeptides

Airway hyperreactivity to bronchoconstrictor mediators is a main characteristic in the majority of asthmatic patients and correlates well with the severity of the disease. The airways of asthmatic patients are characterized by an inflammatory state resulting in activation of lung tissue cells and attraction and infiltration of leukocytes from the blood. The accumulation of eosinophilic leukocytes is a prominent feature of inflammatory reactions that occurs in allergic asthma. The increase in number of eosinophils is important since it correlates in time with an increase in bronchial hyperresponsiveness. Viral respiratory infections can also induce eosinophilia and airway hyperresponsiveness in humans and animals and can worsen asthmatic reactions. This report reviews current opinions on the relationship between inflammation-induced eosinophil accumulation/activation and the development of airway hyperresponsiveness and the possible role for sensory neuropeptides in this process. Firstly, CC chemokines play an important role in allergic airway inflammation and respiratory viral infections leading to eosinophil recruitment. Secondly, it can be concluded that IL5 is involved in the development in airway hyperresponsiveness. IL5 has profound effects on eosinophils as promoter of growth, differentiation and proliferation, chemoattractant, activator and primer. However, it is conceivable that in animal models for allergic asthma besides IL5 other regulatory mediators may be involved in eosinophil migration and activation in the lung, which in turn will lead to airway hyperresponsiveness. Recent data support the possible role of eotaxin and its eosinophil-specific receptor CCR-3 in eosinophil chemotaxis and activation in allergic asthma. Moreover, it is suggested that the development of airway eosinophilia in vivo involves a two-step mechanism, elicited by eotaxin and IL5. The precise mechanism by which eosinophils induce bronchial hyperresponsiveness is at present unknown. Sensory neuropeptides could be important mediators in this process, since it has been demonstrated that airway nerves are surrounded by and infiltrated with eosinophils after antigen challenge. Sensory neuropeptides could be the final, more downstream, common pathway after eosinophil infiltration and activation in inducing airway hyperresponsiveness due to allergen inhalation or respiratory viral infections. In conclusion, in the process of the development of airway hyperresponsiveness observed during viral infections or in allergic asthma, the IL5/eotaxin-induced infiltration and activation of eosinophils in the airways is evident. Following this step, eosinophil-derived inflammatory mediators will induce the release of sensory neuropeptides (possibly NK2-receptor activating tachykinins) which in turn will lead to airway hyperresponsiveness.

Epstein-Barr Virus Modulates 5-Lipoxygenase Product Synthesis in Human Peripheral Blood Mononuclear Cells

The effect of short-term coincubations of Epstein-Barr virus (EBV) with mononuclear cells on the synthesis of leukotrienes (LT) by monocytes was investigated. Although treatment of mononuclear cells with EBV alone had no significant effect on LT synthesis by monocytes, the preincubation of mononuclear cells with EBV before the further stimulation of the cells with either the ionophore A23187, the chemoattractant formyl-Met-Leu-Phe, or the phagocytic particles zymosan strikingly enhanced the formation of both LTB4 and LTC4 above the levels of synthesis observed with the stimuli alone. Such priming effect of EBV on LT synthesis was maximal after 15 minutes of preincubation of mononuclear cells with EBV and slowly declined at longer preincubation times; the priming effect of EBV was observed both in Hank's Balanced Salt Solution and plasma. The effect of EBV was abolished by prior treatment of viral particles by heat or by antibody raised against the glycoprotein gp350 of the viral envelope, but not by UV irradiation of the viral particles. Exposure of mononuclear cells to EBV was shown to strongly enhance the activation of the 5-lipoxygenase and the release of arachidonic acid induced upon cell stimulation with a second agonist. The release of arachidonic acid by the EBV-treated mononuclear cells was inhibitable by arachidonyl trifluoromethyl ketone, an inhibitor of the 80-kD cytosolic phospholipase A2 . Furthermore, EBV was shown to rapidly increase (maximum effect within 15 minutes) the levels of phosphorylated form of the cytosolic phospholipase A2 (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis), a process related to the activation of this enzyme. These data show that the interaction of EBV with monocytes upregulates the formation of important lipid mediators of inflammation.

Generation of atypical pulmonary inflammatory responses in BALB/c mice after immunization with the native attachment (G) glycoprotein of respiratory syncytial virus

The feasibility of using the highly purified native attachment (G) protein in a subunit vaccine against respiratory syncytial virus (RSV) was examined in a murine model with or without the fusion (F) protein of RSV and the adjuvant QS-21. The studies established that QS-21 was more potent than AIOH as an adjuvant for both F and G glycoproteins. Augmented antigen-dependent killer cell activity and complement-assisted serum neutralizing and anti-F and G protein immunoglobulin G2a antibody titers were observed. Immunization with G/QS-21 generated immune responses that were characterized by low levels of antigen-dependent killer cell activity, elevated levels of interleukin-5 (IL-5) and percentages of eosinophils in the bronchoalveolar lavage fluids after challenge, and splenic immunocytes that secreted IL-5 but not gamma interferon (IFN-gamma) after in vitro stimulation with purified whole virus antigens. The pulmonary eosinophilia was similar to that induced by a facsimile of a formalin-inactivated vaccine used in previous clinical trials and was prevented by prior in vivo treatment with anti-IL-5 but not with control immunoglobulin G or anti-IFN-gamma neutralizing monoclonal antibodies. Thus the data implied that vaccination with G/QS-21 generated helper T-cell immune responses that were type 2 in nature. Alternatively, the data suggested that the helper T-cell immune responses elicited by F/QS-21 were more type 1 in character. Neither eosinophilia nor elevated levels of IL-5 were observed in the lungs of mice after challenge. Noteworthy levels of antigen-dependent killer cell activity was observed, and splenic immunocytes secreted copious quantities of IFN-gamma. Immunization with a combination vaccine composed of highly purified native F and G proteins plus QS-21 (F+G/QS-21) resulted in augmented complement-assisted serum neutralizing antibody titers compared with vaccination with either F/QS-21 or G/QS-21 alone. However, following vaccination with F+G/QS-21, the bronchoalveolar lavage fluids contained significant increases in IL-5 and percentages of eosinophils after challenge, the spleen cells appeared to secrete less IFN-gamma after in vitro stimulation, and there was no evidence of increased numbers of antigen-dependent killer cell precursors. Taken together, the data imply that native G protein influences the nature of the immune responses elicited by F/QS-21. The results therefore suggest that G, not F, protein has more potential to bias the host for atypical pulmonary inflammatory responses.

An ultrastructural study of the interaction of human eosinophils with respiratory syncytial virus

It was shown previously that eosinophils are activated in vivo and in vitro by respiratory syncytial virus (RSV) (Garofalo et al., J Pediatr 1992: 120: 28-32; Kimpen et al., Pediatr Res 1992: 32: 160-4). For study of the interaction of eosinophils and RSV on the ultrastructural level, normodense eosinophils were purified from peripheral blood of healthy human volunteers. After incubation with RSV in the presence or absence of autologous serum, the eosinophils were examined with immunofluorescence microscopy employing an RSV-specific monoclonal antibody, and with transmission electron microscopy. After 2-h incubation in the presence of live RSV, 25.6 +/- 12.9% of the eosinophils demonstrated positive fluorescence. This increased to 62.8 +/- 8.9% when fresh autologous serum was added during incubation (P = 0.015). The effect was abolished when the serum was heat-treated, indicating Fc-receptor-independent enhancement of viral uptake by the cells. In transmission electron microscopy, virions were seen in phagocytic vacuoles at the periphery of the cells. Eosinophil activation characterized by piece-meal degranulation was evident. In conclusion, activation of eosinophils during RSV bronchiolitis probably occurs in part by direct interaction of the cells with the virus.

Viral respiratory infections

Viral infections constitute more than 60% of acute lower respiratory illnesses. Respiratory syncytial virus (RSV) and parainfluenza viruses are the most frequent etiologic agents. After transmission by large droplet aerosol or direct contact, the viruses gain entry into host cells through specific viral surface proteins; subsequently, pathogenetic mechanisms cause tissue injury and result in clinical disease. In the intensive care unit the mainstay of treatment is primarily supportive. Nonspecific treatment may include nebulized beta-agonists, aminophylline, and steroids. Ribavarin is the only specific antiviral agent approved for respiratory syncytial virus infection but its efficacy remains controversial. New therapies and vaccines offer hope for improved outcome from viral respiratory infections such as RSV.

Analysis of cells obtained by bronchial lavage of infants with respiratory syncytial virus infection

To study the cellular infiltrate that occurs within the airways of infants with respiratory syncytial virus bronchiolitis, samples of airways secretions were obtained by bronchial lavage from the lower respiratory tract of infants ventilated for this condition and from the upper airway of non-intubated infants with this disorder using nasopharyngeal aspirates. Cytospin samples were prepared so that differential cell counts could be performed on the cells obtained and alkaline phosphatase-antialkaline phosphatase immunocytochemical analysis of lymphocyte subsets was carried out using a panel of monoclonal antibodies, which included anti-CD3, anti-CD4, anti-CD8, anti-CD19, and anti-TcR gamma delta. Results from the lower and upper airways were similar. Large numbers of inflammatory cells were obtained, of which neutrophils accounted for a median of 93% in the upper airway and 76% in the lower airway. The numbers of CD8 positive cells detected were small and consistently less than CD4 positive cells, median CD4:CD8 ratios being 22.5:1 and 15:1 for the lower and upper airways. CD19 positive cells were rarely observed and no gamma delta positive lymphocytes were detected. These results indicate that neutrophils probably play a major part in causing symptoms in these infants. They do not support the concept that excessive lymphocyte mediated cytotoxic activity is principally responsible for the pathology in respiratory syncytial virus bronchiolitis.

Mice immunized with a chlamydial extract have no increase in early protective immunity despite increased inflammation following genital infection by the mouse pneumonitis agent of Chlamydia trachomatis

We have determined that immunization with a detergent extract of the mouse pneumonitis agent of Chlamydia trachomatis fails to induce a protective inflammatory immune response following genital infection by C. trachomatis. We demonstrated that mice immunized with the detergent extract have increased cutaneous delayed-type hypersensitivity and increased splenic T-cell proliferation in response to the chlamydial extract. After genital infection by C. trachomatis, extract-sensitized mice had significantly increased genital inflammation (P = 0.044) compared with controls. The inflammation was characterized by significantly increased eosinophils in the genitalia (P < 0.0005) and increased genital edema (P < 0.0005). However, the increased genital inflammation of extract-sensitized mice provided no increase in protection against infection (P = 0.92).

Airway inflammation, bronchial reactivity and asthma

Asthma is a common disease of children the basis of which is a state of chronic immunological inflammation which causes bronchial hyperreactivity and renders the patient liable to develop widespread airways obstruction in response to a variety of stimuli. In many instances it is likely that the immunological inflammation results from ongoing antigenic stimuli with the release of chemical mediators responsible for short term bronchospasm and cytokines responsible for the ongoing inflammatory process. Other insults can apparently result in very similar immunological events in asthmatics, particularly viral infections and a similar process can be initiated in children without asthma, including those with chronic bacterial infections of the lungs. There are differences in the bronchial hyperreactivity of asthma and other diseases which suggest that in the asthmatic the mast cell is either different structurally or functionally and this renders the patient susceptible to exercise induced asthma in addition to the bronchial hyperreactivity to chemical mediators common to a number of diseases with hyperreactivity. There is good evidence of direct genetic control of atopy and the large majority of children with asthma are atopic but there is no direct genetic link between atopy and asthma and twin studies strongly suggest the existence of a 'permissive' asthma gene which will allow the disease to develop if there is an appropriate external trigger. The only drugs which have been shown to significantly reduce bronchial reactivity are the corticosteroids with a lesser effect noted for sodium cromoglycate and nedocromil. Inhaled corticosteroids can reverse the immunologic inflammatory process and reduce bronchial reactivity, sometimes to normal levels, but on stopping treatment the patient reverts back to the asthmatic state. At the present time it appears that controlled longterm inhaled corticosteroid therapy is the most rational treatment for significant perennial childhood asthma.