Jesse P. Joad

Allergic asthma induced in rhesus monkeys by house dust mite (Dermatophagoides farinae)

To establish whether allergic asthma could be induced experimentally in a nonhuman primate using a common human allergen, three female rhesus monkeys (Macaca mulatta) were sensitized with house dust mite (Dermatophagoides farinae) allergen (HDMA) by subcutaneous injection, followed by four intranasal sensitizations, and exposure to allergen aerosol 3 hours per day, 3 days per week for up to 13 weeks. Before aerosol challenge, all three monkeys skin-tested positive for HDMA. During aerosol challenge with HDMA, sensitized monkeys exhibited cough and rapid shallow breathing and increased airway resistance, which was reversed by albuterol aerosol treatment. Compared to nonsensitized monkeys, there was a fourfold reduction in the dose of histamine aerosol necessary to produce a 150% increase in airway resistance in sensitized monkeys. After aerosol challenge, serum levels of histamine were elevated in sensitized monkeys. Sensitized monkeys exhibited increased levels of HDMA-specific IgE in serum, numbers of eosinophils and exfoliated cells within lavage, and elevated CD25 expression on circulating CD4(+) lymphocytes. Intrapulmonary bronchi of sensitized monkeys had focal mucus cell hyperplasia, interstitial infiltrates of eosinophils, and thickening of the basement membrane zone. We conclude that a model of allergic asthma can be induced in rhesus monkeys using a protocol consisting of subcutaneous injection, intranasal instillation, and aerosol challenge with HDMA.

Repeated episodes of ozone inhalation amplifies the effects of allergen sensitization and inhalation on airway immune and structural development in Rhesus monkeys

Twenty-four infant rhesus monkeys (30 days old) were exposed to 11 episodes of filtered air (FA), house dust mite allergen aerosol (HDMA), ozone (O3), or HDMA + O3 (5 days each followed by 9 days of FA). Ozone was delivered for 8 h/day at 0.5 ppm. Twelve of the monkeys were sensitized to house dust mite allergen (Dermatophagoides farinae) at ages 14 and 28 days by subcutaneous inoculation (SQ) of HDMA in alum and intraperitoneal injection of heat-killed Bordetella pertussis cells. Sensitized monkeys were exposed to HDMA aerosol for 2 h/day on days 3-5 of either FA (n = 6) or O3 (n = 6) exposure. Nonsensitized monkeys were exposed to either FA (n = 6) or O3 (n = 6). During the exposure regimen, parameters of allergy (i.e., serum IgE, histamine, and eosinophilia), airways resistance, reactivity, and structural remodeling were evaluated. Eleven repeated 5-day cycles of inhaling 0.5 ppm ozone over a 6-month period had only mild effects on the airways of nonsensitized infant rhesus monkeys. Similarly, the repeated inhalation of HDMA by HDMA-sensitized infant monkeys resulted in only mild airway effects, with the exception of a marked increase in proximal airway and terminal bronchiole content of eosinophils. In contrast, the combined cyclic inhalation of ozone and HDMA by HDMA sensitized infants monkeys resulted in a marked increase in serum IgE, serum histamine, and airways eosinophilia. Furthermore, combined cyclic inhalation of ozone and HDMA resulted in even greater alterations in airway structure and content that were associated with a significant elevation in baseline airways resistance and reactivity. These results suggest that ozone can amplify the allergic and structural remodeling effects of HDMA sensitization and inhalation.

Early Childhood Lower Respiratory Illness and Air Pollution

Background Few studies of air pollutants address morbidity in preschool children. In this study we evaluated bronchitis in children from two Czech districts: Teplice, with high ambient air pollution, and Prachatice, characterized by lower exposures. Objectives Our goal was to examine rates of lower respiratory illnesses in preschool children in relation to ambient particles and hydrocarbons. Methods Air monitoring for particulate matter < 2.5 μm in diameter (PM2.5) and polycyclic aromatic hydrocarbons (PAHs) was conducted daily, every third day, or every sixth day. Children born May 1994 through December 1998 were followed to 3 or 4.5 years of age to ascertain illness diagnoses. Mothers completed questionnaires at birth and at follow-up regarding demographic, lifestyle, reproductive, and home environmental factors. Longitudinal multivariate repeated-measures analysis was used to quantify rate ratios for bronchitis and for total lower respiratory illnesses in 1,133 children. Results After adjustment for season, temperature, and other covariates, bronchitis rates increased with rising pollutant concentrations. Below 2 years of age, increments in 30-day averages of 100 ng/m3 PAHs and of 25 μg/m3 PM2.5 resulted in rate ratios (RRs) for bronchitis of 1.29 [95 % confidence interval (CI), 1.07–1.54] and 1.30 (95% CI, 1.08–1.58), respectively; from 2 to 4.5 years of age, these RRs were 1.56 (95% CI, 1.22–2.00) and 1.23 (95% CI, 0.94–1.62), respectively. Conclusion Ambient PAHs and fine particles were associated with early-life susceptibility to bronchitis. Associations were stronger for longer pollutant-averaging periods and, among children > 2 years of age, for PAHs compared with fine particles. Preschool-age children may be particularly vulnerable to air pollution–induced illnesses.

Five-fold increase in pediatric parapneumonic empyema since introduction of pneumococcal conjugate vaccine.

A retrospective review of medical records for all pediatric parapneumonic empyema (PPE) patients admitted to our hospital from 1996 to 2006 revealed that PPE increased 5-fold in the post-heptavalent pneumococcal conjugate vaccine (PCV7) period (2001–2005) relative to the pre-PCV7 period (1996–2000), from 13 cases to 65. Most of this increase was associated with culture-negative empyema, which accounted for 61% of all post-2000 cases; 19% was culture-positive pneumococcal empyema. Our analysis indicates that non-PCV7 serotypes became more prevalent at our institution after introduction of the vaccine.

Neurones in commissural nucleus tractus solitarii required for full expression of the pulmonary C fibre reflex in rat.

1. The pulmonary C fibre reflex, triggered by activating pulmonary C fibre endings in the lung, consists of rapid shallow breathing (which may be preceded by apnoea), bradycardia, and hypotension. The purpose of this work was to identify proximal synapses in this reflex. From pilot data, we hypothesized that neurones in a discrete region of the commissural nucleus in the nucleus tractus solitarii (NTS) are required for full expression of the pulmonary C fibre reflex. Studies were carried out in urethane‐anaesthetized, unilaterally vagotomized, spontaneously breathing rats, in which diaphragm electromyogram, arterial pressure, and blood gases were measured. Phenyldiguanide (PDG) was injected in the right atrium to elicit the pulmonary C fibre reflex. Unilateral NTS injections were made through multibarrelled pipettes containing DL‐homocysteic acid (DLH) to mimic the reflex, cobalt chloride to reversibly impair the reflex, and/or dye to mark the injection sites. 2. PDG (5‐16 micrograms kg‐1) injected in the right atrium of twenty‐six rats produced the classic pulmonary C fibre reflex: a vagally mediated, rapid onset of rapid shallow breathing, bradycardia and hypotension. 3. Injection of DLH (3‐12 nl of 20 mM for a total of 60‐240 pmol) in the dorsomedial aspect of the commissural nucleus of the NTS in thirty rats mimicked the pulmonary C fibre reflex, producing rapid shallow breathing, hypotension, and a slight bradycardia. 4. Interruption of neuronal transmission by injecting cobalt chloride (15‐30 nl of 100 mM) in the site where DLH produced rapid shallow breathing, reversibly impaired the rapid shallow breathing and bradycardia produced by right atrial injections of PDG in fifteen rats. The commissural region where DLH produced rapid shallow breathing and cobalt impaired the pulmonary C fibre reflex extended from 720‐1100 microns caudal to the obex, 30‐200 microns lateral to mid‐line, and 200‐600 microns ventral to the dorsal surface of the brain stem within the NTS. 5. Taken together, the results suggest that neurones within a discrete region in the dorsomedial commissural nucleus in caudal NTS are required for full expression of the pulmonary C fibre reflex.

Substance P contributes to rapidly adapting receptor responses to pulmonary venous congestion in rabbits.

1. This study tested the hypothesis that substance P stimulates rapidly adapting receptors (RARs), contributes to the increase in RAR activity produced by mild pulmonary congestion, and evokes an augmented response from RARs when combined with near‐threshold levels of pulmonary congestion. 2. RAR activity, peak tracheal pressure, arterial blood pressure and left atrial pressure were measured in paralysed, anaesthetized and ventilated rabbits. Substance P was given i.v. in one‐half log incremental doses to a maximum of 3 micrograms kg‐1. Mild pulmonary congestion was produced by inflating a balloon in the left atrium to increase left atrial pressure by 5 mmHg. Near‐threshold levels of pulmonary congestion were produced by increasing left atrial pressure by 2 mmHg. 3. Substance P produced dose‐dependent increases in RAR activity. The highest dose given increased the activity from 1.3 +/‐ 0.5 to 11.0 +/‐ 3.1 impulses bin‐1. Increases in left atrial pressure of 5 mmHg increased RAR activity from 3.8 +/‐ 1.4 to 14.7 +/‐ 3.9 impulses bin‐1. Blockade of NK1 receptors with CP 96345 significantly attenuated RAR responses to substance P and to mild pulmonary congestion. 4. Doses of substance P, which alone had no effect, stimulated the RARs when delivered during near‐threshold levels of pulmonary congestion. 5. The findings suggest that substance P augments the stimulatory effect of mild pulmonary congestion on RAR activity, most probably by enhancing hydraulically induced microvascular leak.

Substance P presynaptically depresses the transmission of sensory input to bronchopulmonary neurons in the guinea pig nucleus tractus solitarii

Substance P modulates the reflex regulation of respiratory function by its actions both peripherally and in the CNS, particularly in the nucleus tractus solitarii (NTS), the first central site for synaptic contact of the lung and airway afferent fibres. There is considerable evidence that the actions of substance P in the NTS augment respiratory reflex output, but the precise effects on synaptic transmission have not yet been determined. Therefore, we determined the effects of substance P on synaptic transmission at the first central synapses by using whole‐cell voltage clamping in an NTS slice preparation. Studies were performed on second‐order neurons in the slice anatomically identified as receiving monosynaptic input from sensory nerves in the lungs and airways. This was done by the fluorescent labelling of terminal boutons after 1,1′‐dioctadecyl‐3,3,3′,3′‐tetra‐methylindocarbo‐cyanine perchlorate (DiI) was applied via tracheal instillation. Substance P (1.0, 0.3 and 0.1 μM) significantly decreased the amplitude of excitatory postsynaptic currents (eEPSCs) evoked by stimulation of the tractus solitarius, in a concentration‐dependent manner. The decrease was accompanied by an increase in the paired‐pulse ratio of two consecutive eEPSCs, and a decrease in the frequency, but not the amplitude, of spontaneous EPSCs and miniature EPSCs, findings consistent with a presynaptic site of action. The effects were consistently and significantly attenuated by a neurokinin‐1 (NK1) receptor antagonist (SR140333, 3 μM). The data suggest a new site of action for substance P in the NTS (NK1 receptors on the central terminals of sensory fibres) and a new mechanism (depression of synaptic transmission) for regulating respiratory reflex function.

Asthma/Allergic Airways Disease : Does Postnatal Exposure to Environmental Toxicants Promote Airway Pathobiology?

The recent, dramatic increase in the incidence of childhood asthma suggests a role for environmental contaminants in the promotion of interactions between allergens and the respiratory system of young children. To establish whether exposure to an environmental stressor, ozone (O3), and an allergen, house dust mite (HDMA), during early childhood promotes remodeling of the epithelial-mesenchymal trophic unit (EMTU) of the tracheobronchial airway wall by altering postnatal development, infant rhesus monkeys were exposed to cyclic episodes of filtered air (FA), HDMA, O3, or HDMA plus O3. The following alterations in the EMTU were found after exposure to HDMA, O3, or HDMA plus O3: (1) reduced airway number; (2) hyperplasia of bronchial epithelium; (3) increased mucous cells; (4) shifts in distal airway smooth muscle bundle orientation and abundance to favor hyperreactivity; (5) interrupted postnatal basement membrane zone differentiation; (6) modified epithelial nerve fiber distribution; and (7) reorganization of the airway vascular and immune system. Conclusions: cyclic challenge of infants to toxic stress during postnatal lung development modifies the EMTU. This exacerbates the allergen response to favor development of intermittent airway obstruction associated with wheeze. And, exposure of infants during early postnatal lung development initiates compromises in airway growth and development that persist or worsen as growth continues, even with cessation of exposure.

Plasticity of brainstem mechanisms of cough.

The cough reflex is a brainstem reflex, consisting of specific sensory afferent nerves which trigger the reflex, by transmitting the sensory input over vagal or laryngeal nerves to a brainstem circuitry which processes and ultimately transforms the sensory input into a complex motor output to generate cough. The first synaptic target for the primary cough-related sensory input is the second-order neurons in the nucleus tractus solitarius (NTS). This position in the reflex pathway and intricate local circuits within the nucleus make it a strategic site where the sensory information can be modified. Plasticity at this synapse will change the nature of the output--exaggerating it, suppressing it or transforming it into some other complex pattern. This review integrates evidence implicating the NTS in exaggerated cough with proof of the concept that NTS neurons undergo plasticity to contribute to an exaggeration of cough.

Chronic passive cigarette smoke exposure augments bronchopulmonary C‐fibre inputs to nucleus tractus solitarii neurones and reflex output in young guinea‐pigs

Children chronically exposed to environmental tobacco smoke (passive cigarette smoke) have more wheeze, cough, bronchoconstriction, airway hyper‐reactivity and mucous secretion, which may result, in part, from stimulation of the vagal bronchopulmonary C‐fibre reflex. Environmental tobacco smoke increases the sensitivity of bronchopulmonary C‐fibre endings, but the physiological relevance of this sensitization is unknown. If this exposure augments the reflex responses via a central mechanism, then the responses of higher‐order neurones in the reflex pathway and some components of the reflex output should also be augmented. Guinea‐pigs were chronically exposed to sidestream tobacco smoke (surrogate for environmental tobacco smoke) or filtered air for 5 days week−1 from age 1 to 6 weeks (age equivalent of human childhood) and were then anaesthetized, paralysed, ventilated and prepared with pneumothoraces. Baseline and left atrial capsaicin (0.5 and 2.0 μg kg−1)‐ evoked changes in the impulse activity of vagal C‐fibre‐activated neurones in nucleus tractus solitarii (NTS), phrenic nerve activity, tracheal pressure, arterial blood pressure and heart rate were compared in the two groups. Sidestream smoke exposure significantly augmented the peak (P= 0.02) and duration (P= 0.01) of the NTS neuronal responses and the prolongation of expiratory time (P= 0.003) at the higher capsaicin dose. Thus, the sensitization of the bronchopulmonary C‐fibre endings by chronic exposure to sidestream tobacco smoke is transmitted to the NTS and is associated with a prolonged reflexively evoked expiratory apnoea. The findings may help to explain some related respiratory symptoms in children and be a factor in sudden infant death syndrome.