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Biomedical subjects

Charles G Plopper

Publications and source records attributed to Charles G Plopper.

At least 37 records · Page 2Linked to original sources
PubMed2004

Epithelial cell distribution and abundance in rhesus monkey airways during postnatal lung growth and development.

Lung development is both a pre- and postnatal process. Although many lung diseases have their origins in early childhood, few quantitative data are available on the normal growth and differentiation of both the conducting airways and the airway epithelium during the postnatal period. We examined rhesus monkey lungs from five postnatal ages: 4-6 days and 1, 2, 3, and 6 mo. Airways increase significantly in both length and circumference as monkeys increase significantly in body weight from 5 days to 6 mo. In this study we asked: as basement membrane surface area increases, does the epithelial cell organization change? To answer this question, we quantified total epithelial cell mass using high-resolution light micrographs and morphometric techniques on sections from defined airway regions: trachea, proximal intrapulmonary bronchus (generations 1 or 2), and distal intrapulmonary bronchus (generations 6-8). Epithelial thickness decreased in the smaller, more distal, airways compared with trachea but did not change with age in the trachea and proximal bronchus. The volume fraction of all cell types measured did not change significantly. Ciliated cells in the distal bronchus and goblet cells in the trachea both decreased in abundance with increasing age. Overall, the epithelial cell populations changed little in terms of mass or relative abundance to each other during this period of active postnatal lung growth. Regarding the proximal conducting airway epithelium, we conclude that 1) the steady-state abundance is tightly regulated to keep the proportion of cell types constant, and 2) establishment of these cell types occurs before 4-6 days postnatal age. We conclude that growth of the proximal airways occurs primarily in length and lags behind that of the lung parenchyma.

Animals↗
PubMed2004

Proximal airway mucous cells of ovalbumin-sensitized and -challenged Brown Norway rats accumulate the neuropeptide calcitonin gene-related peptide.

Mucous cell hypersecretion and increased neuropeptide production play a role in the exacerbation of symptoms associated with asthma. The source of these neuropeptides have been confined to the contributions of small afferent nerves or possibly neuroendocrine cells. We tested the hypothesis that repeated exposure to allergen would alter the sources and abundance of neuropeptides in airways. Right middle lobes from rats (8 wk old) exposed to 2.5% ovalbumin (OVA) for five episodes (30 min each) or filtered air were inflation fixed with paraformaldehyde. The lobes were dissected to expose the airway tree, permeabilized with DMSO, and incubated in antibody to rat calcitonin gene-related peptide (CGRP), followed with a fluorochrome-labeled second antibody. CGRP-positive structures were imaged via confocal microscopy. Airways were later embedded in plastic and sectioned for cell identification. In animals challenged with OVA, CGRP-positive cells, not neuroendocrine or neuronal in origin (confirmed by a lack of protein gene product 9.5 signal), were recorded along the axial path. In section, this fluorescent signal was localized to granules within epithelial cells. Alcian blue/periodic acid-Schiff staining of these same sections positively identify these cells as mucous cells. Mucous cells of animals not challenged with OVA were not positive for CGRP. We conclude that episodic allergen exposure results in the accumulation of CGRP within mucous cells, creating a new source for the release of this neuropeptide within the airway.

Allergens↗
PubMed2004

Postnatal remodeling of the neural components of the epithelial-mesenchymal trophic unit in the proximal airways of infant rhesus monkeys exposed to ozone and allergen.

Nerves and neuroendocrine cells located within the airway epithelium are ideally situated to sample a changing airway environment, to transmit that information to the central nervous system, and to promote trophic interactions between epithelial and mesenchymal cellular and acellular components. We tested the hypothesis that the environmental stresses of ozone (O(3)) and house dust mite allergen (HDMA) in atopic infant rhesus monkeys alter the distribution of airway nerves. Midlevel bronchi and bronchioles from 6-month-old infant monkeys that inhaled filtered air (FA), house dust mite allergen HDMA, O(3), or HDMA + O(3) for 11 episodes (5 days each, 0.5 ppm O(3), 8 h/day followed by 9 days recovery) were examined using immunohistochemistry for the presence of Protein gene product 9.5 (PGP 9.5), a nonspecific neural indicator, and calcitonin gene-related peptide (CGRP). Along the axial path between the sixth and the seventh intrapulmonary airway generations, there were small significant (P < 0.05) decrements in the density of epithelial nerves in monkeys exposed to HDMA or O(3), while in monkeys exposed to HDMA + O(3) there was a greater significant (P < 0.05) reduction in epithelial innervation. In animals exposed to O(3) or HDMA + O(3) there was a significant increase in the number of PGP 9.5 positive/CGRP negative cells that were anchored to the basal lamina and emitted projections in primarily the lateral plain and often intertwined with projections and cell bodies of other similar cells. We conclude that repeated cycles of acute injury and repair associated with the episodic pattern of ozone and allergen exposure alter the normal development of neural innervation of the epithelial compartment and the appearance of a new population of undefined PGP 9.5 positive cells within the epithelium.

Allergens↗
PubMed2004

Comparison of pulmonary/nasal CYP2F expression levels in rodents and rhesus macaque.

Naphthalene is a ubiquitous environmental contaminant that results in dose-dependent and tissue-, species-, and cell-selective necrosis of murine Clara cells upon exposure. Naphthalene is metabolized by CYP2F to a 1,2-epoxide, the first and obligate step in events leading to cytotoxicity. The studies reported here examine the relationship between levels of transcript (mRNA) and CYP2F protein in the respiratory tract of rodents with tissue susceptibility to injury. In both mice and rats, the lung contains more CYP2F transcript than liver; levels in kidney were undetectable. Mice expressed 4- and 8-fold greater CYP2F transcript in lung and liver tissue, respectively, than rats. Quantitative immunoblot blot analysis of CYP2F in airway subcompartments revealed mice to have 30- (minor daughters/terminal bronchioles), 20- (major daughter), 40- (trachea), and 6- (parenchyma) fold higher levels of CYP2F protein than rats. Within the lungs of both rodent species, the highest CYP2F expression was found in the distal airways. The kidney contained undetectable amounts of CYP2F; multiple immunoreactive bands in liver precluded quantification. The olfactory epithelium contains the greatest amount of cytochrome P450 protein of all tissues studied in the rat, consistent with the observed pattern of in vivo injury. Overall, these studies in rodents demonstrate a strong association between CYP2F expression levels and susceptibility to naphthalene-induced cytotoxicity. Of all primate tissues studied, only the nasal ethmoturbinates contain quantifiable amounts of CYP2F, roughly 10- and 20-fold less than the corresponding tissues in rats and mice, respectively. These results suggest that rhesus macaques may be refractory to naphthalene-induced pulmonary injury.

Animals↗
PubMed2004

Chemokine networks and in vivo T-lymphocyte trafficking in nonhuman primates.

T-lymphocyte migratory circuits in human and nonhuman primates remain largely unexplored due to the difficulty of defining cell trafficking in vivo. However, this knowledge may reveal critical aspects of immunity and T-lymphocyte homeostasis in both health and disease. Furthermore, in vivo T-lymphocyte trafficking studies may facilitate defining mechanism(s) of immune dysfunction in the nonhuman primate model for acquired immunodeficiency syndrome (AIDS). Here, we developed a model for in vivo T-lymphocyte trafficking in nonhuman primates, and delineated homing characteristics of unstimulated peripheral blood mononuclear cells (PBMCs) to lymphoid and nonlymphoid compartments in healthy rhesus macaques. T-lymphocyte homing of autologous, carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled PBMCs was defined within 48 h of intravenous transfer. The highest relative frequency of CFSE+ T lymphocytes was observed in peripheral blood and spleen. Expression of chemokine receptor CCR7 and its ligands correlated with recirculation of T lymphocytes through the periphery and homing to paracortical regions of lymph node, where cells remained largely excluded from B-cell follicles. T-lymphocyte trafficking was also detected to the liver and bone marrow, and at low levels to the thymus and small intestine. The liver contained the highest proportion of CD45RA- T lymphocytes, consistent with homing of activated/memory T lymphocytes to this nonlymphoid site. Our data suggest that lymphoid and nonlymphoid organs are under continuous immunosurveillance in healthy macaques, and that this model may serve to investigate aberrant patterns in disease.

Animals↗
PubMed2003

Foxj1 is required for apical localization of ezrin in airway epithelial cells.

Establishment and maintenance of epithelial cell polarity depend on cytoskeletal organization and protein trafficking to polarized cortical membranes. ERM (ezrin, radixin, moesin) family members link polarized proteins with cytoskeletal actin. Although ERMs are often considered to be functionally similar, we found that, in airway epithelial cells, apical localization of ERMs depend on cell differentiation and is independently regulated. Moesin was present in the apical membrane of all undifferentiated epithelial cells. However, in differentiated cells, ezrin and moesin were selectively localized to apical membranes of ciliated airway cells and were absent from secretory cells. To identify regulatory proteins required for selective ERM trafficking, we evaluated airway epithelial cells lacking Foxj1, an F-box factor that directs programs required for cilia formation at the apical membrane. Interestingly, Foxj1 expression was also required for localization of apical ezrin, but not moesin. Additionally, membrane-cytoskeletal and threonine-phosphorylated ezrin were decreased in Foxj1-null cells, consistent with absent apical ezrin. Although apical moesin expression was present in null cells, it could not compensate for ezrin because ERM-associated EBP50 and the beta2 adrenergic receptor failed to localize apically in the absence of Foxj1. These findings indicate that Foxj1 regulates ERM proteins differentially to selectively direct the apical localization of ezrin for the organization of multi-protein complexes in apical membranes of airway epithelial cells.

Adenoviridae↗
PubMed2003

Assessing gene expression in lung subcompartments utilizing in situ RNA preservation.

The mechanisms of toxicant-mediated lung injury and repair are influenced by the considerable spatial heterogeneity that exists within the conducting airways of the lungs. As a result of this heterogeneity, significant differences and similarities in gene expression are observed throughout lung subcompartments. RNA-based technologies such as real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and cDNA microarray analysis of gene expression provide valuable clues to understanding the mechanisms of toxicant-induced injury. Isolating RNA from lung subcompartments has previously involved considerable time and labor-intensive processes that limit the number of animals that could be processed in a day. The aim of this study was to determine if intact, high-quality RNA could be preserved in situ over a period of time to delay the need to immediately perform site-specific lung subcompartment microdissections and RNA isolations. Two hours after 1-nitronaphthalene treatment, rat lungs were inflated with and stored in RNA preservation solution and stored at 4 degrees C for 7 days. RNA was isolated from the lung subcompartments isolated by microdissection. After 7 days of storage, the RNA was intact, of high quality, and could be used for real-time RT-PCR to examine heterogeneous gene expression in the lung subcompartments. In summary, this simplified technique of in situ RNA preservation and site-specific lung subcompartment microdissection allows the isolation of intact, high-quality RNA that may be used with molecular RNA-based technologies that will significantly accelerate our understanding of pulmonary injury and repair mechanisms.

Animals↗
PubMed2003

Isolation of rodent airway epithelial cell proteins facilitates in vivo proteomics studies of lung toxicity.

Recent developments in genomics, proteomics, and metabolomics hold substantial promise for understanding cellular responses to toxicants. Gene expression profiling is now considered standard procedure, but numerous publications reporting a lack of correlation between mRNA and protein expression emphasize the importance of conducting parallel proteomics studies. The cellular complexity of the lung presents great challenges for in vivo proteomics, and improved isolation methods for proteins from specific lung cell phenotypes are required. To address this issue, we have developed a novel method for isolation of rodent airway epithelial cell proteins that facilitates in vivo proteomics studies of two target-cell pheno-types of the lung, Clara cells and ciliated cells. The airway epithelial cell proteins are reproducibly solubilized, leaving the underlying basement membrane and smooth muscle intact as shown by histopathological analyses. The method yields epithelial cell-specific proteins in fivefold higher concentrations and reduces the yield of nonepithelial cell proteins 13-fold compared with homogenates from microdissected airways. In addition, 36% more protein spots were detectable by two-dimensional gel electrophoresis.

Actins↗
PubMed2003

Pulmonary heat shock protein expression after exposure to a metabolically activated Clara cell toxicant: relationship to protein adduct formation.

Heat shock proteins/stress proteins (Hsps) participate in regulation of protein synthesis and degradation and serve as general cytoprotectants, yet their role in lethal Clara cell injury is not clear. To define the pattern of Hsp expression in acute lethal Clara cell injury, mice were treated with the Clara cell-specific toxicant naphthalene (NA), and patterns of expression compared to electrophilic protein adduction and previously established organellar degradation and glutathione (GSH) depletion. In sites of lethal injury (distal bronchiole), prior to organellar degradation (1 h post-NA), protein adduction is detectable and ubiquitin, Hsp 25, Hsp 72, and heme-oxygenase 1 (HO-1) are increased. Maximal Hsp expression, protein adduction, and GSH depletion occur simultaneous (by 2-3 h) with early organelle disruption. Hsp expression is higher later (6-24 h), only in exfoliating cells. In airway sites (proximal bronchiole) with nonlethal Clara cell injury elevation of Hsp 25, 72, and HO-1 expression follows significant GSH depletion (greater than 50% 2 h post-NA). This data build upon our previous studies and we conclude that (1) in lethal (terminal bronchiole) and nonlethal (proximal bronchiole) Clara cell injury, Hsp induction is associated with the loss of GSH and increased protein adduction, and (2) in these same sites, organelle disruption is not a prerequisite for Hsp induction.

Animals↗
PubMed2003

Proliferation during early phases of bronchiolar repair in neonatal rabbits following lung injury by 4-ipomeanol.

Nonciliated bronchiolar (Clara cells) are progenitor cells during development. During differentiation, they are more susceptible to injury by environmental toxicants metabolized by the cytochrome P450 monooxygenase system, and injury results in altered bronchiolar repair and development. Squamous cells and abnormal cuboidal epithelium persist into early adulthood. The hypothesis tested in this study was that the failure of bronchiolar epithelium to repair normally in neonates following injury is due to an inhibition of proliferation. A model of differential repair in rabbit kits was used. Proliferation was followed for 1 week post injury in rabbit kits treated with a single dose of the P450-mediated cytotoxicant 4-ipomeanol (IPO) at 7 days old (repair abnormal) and compared to rabbits treated with a single dose of IPO at 21 days old (repair normal). Proliferation was measured by the nuclear incorporation of 5-chloro-2'-deoxyuridine (CldU) within epithelium at the target site (terminal bronchiole). The repair pattern between the two age groups was histologically defined. There was no difference in the CldU labeling index during the week of repair between the two age groups, even though the bronchiolar epithelium did not return to normal in the animals treated at 7 days old. In summary, proliferation (through S-phase) is not inhibited during repair in neonatal rabbits treated with IPO at 7 days old compared to animals treated at 21 days old, and we conclude that other factors may be responsible for the altered repair in the young neonates injured by a P450-mediated cytotoxicant.

Animals↗
PubMed2003

Gene expression analysis in response to lung toxicants: I. Sequencing and microarray development.

A key challenge in measuring gene expression changes in the lung in response to site-selective toxicants is differentiating between target and nontarget areas. The toxicity for the cytotoxicant 1-nitronaphthalene is highly localized in the airway epithelium. Target cells comprise but a fraction of the total lung cell mass; measurements from whole lung homogenates are not likely to reflect what occurs at the target site. Additionally, the use of generic microarrays to measure expression in airway epithelium may not provide a good representation of transcripts present at the site of toxic action. cDNA libraries from airway and alveolar subcompartments of rat lung were sequenced for the development of a custom microarray representative of these lung regions. We identified 7,460 nonredundant rat lung sequences. Nearly 30% of the sequences on this array are not present on the Affymetrix Rat GeneChip 230. A 20,000-element microarray was developed that delineates differences in gene expression between subcompartments. This is the first in a series of articles employing this microarray for detecting gene expression changes during acute injury produced by 1-nitronaphthalene and subsequent repair.

Animals↗
PubMed2003

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.

Administration, Inhalation↗
PubMed2003

Detection of viral infection in the respiratory tract of virus antibody free mice: advantages of high-resolution imaging for respiratory toxicology.

Using a highly sensitive membrane permeability assay, a viral infection was discovered in the lungs of virus antibody free (VAF) Swiss-Webster mice purchased for respiratory toxicology studies. The assay is based on the uptake of a charged fluorescent compound by cells lacking an intact plasma membrane. Lungs from 74% of the untreated animals from a single vendor tested positive for injury in this assay. High-resolution histopathologic analysis of 1-microm epoxy resin sections from affected animals identified increased peribronchiolar lymphocytic infiltration and markers of epithelial cell injury. Viral particles were directly observed to be budding from the membranes of infiltrating lymphocytic cells by transmission electron microscopy. Standard histological analysis of paraffin-embedded tissues from lungs of the same mice failed to detect obvious pathology. Serological analyses failed to detect the presence of a virus in the affected mice. Therefore, we conclude that (1) a pathogenic condition was present in the respiratory systems of mice judged pathogen free by standard methodologies, (2) the observed condition produced a pattern of injury comparable to those caused by pulmonary toxicants, (3) high-resolution histopathology and advanced imaging techniques can increase the potential for detection of pathological conditions, and (4) apparently healthy animals can have unrecognized infections with the potential for confounding respiratory toxicology studies.

Animals↗
PubMed2003

Atypical development of the tracheal basement membrane zone of infant rhesus monkeys exposed to ozone and allergen.

Development of the basement membrane zone (BMZ) occurs postnatally in the rhesus monkey. The purpose of this study was to determine whether house dust mite allergen (HDMA) plus ozone altered this process. Rhesus monkeys were exposed to a regimen of HDMA and/or ozone or filtered air for 6 mo. To detect structural changes in the BMZ, we measured immunoreactivity of collagen I. To detect functional changes in the BMZ, we measured perlecan and fibroblast growth factor-2 (FGF-2). We also measured components of the FGF-2 ternary signaling complex [fibroblast growth factor receptor-1 (FGFR-1) and syndecan-4]. The width of the BMZ was irregular in the ozone groups, suggesting atypical development of the BMZ. Perlecan was also absent from the BMZ. In the absence of perlecan, FGF-2 was not bound to the BMZ. However, FGF-2 immunoreactivity was present in basal cells, the lateral intercellular space (LIS), and attenuated fibroblasts. FGFR-1 immunoreactivity was downregulated, and syndecan-4 immunoreactivity was upregulated in the basal cells. This suggests that FGF-2 in basal cells and LIS may be bound to the syndecan-4. We conclude that ozone and HDMA plus ozone effected incorporation of perlecan into the BMZ, resulting in atypical development of the BMZ. These changes are associated with specific alterations in the regulation of FGF-2, FGFR-1, and syndecan-4 in the airway epithelial-mesenchymal trophic unit, which may be associated with the developmental problems of lungs associated with exposure to ozone.

Allergens↗
PubMed2003

Repeated inhalation exposures to the bioactivated cytotoxicant naphthalene (NA) produce airway-specific Clara cell tolerance in mice.

Repeated exposures to bioactivated cytotoxicants such as naphthalene (NA) render the target population, Clara cells, resistant to further injury through a glutathione-dependent mechanism. The current studies were designed to test the hypothesis that the mechanism for tolerance is localized in Clara cells. We used three approaches to test this hypothesis. First, using airway explants from tolerant mice maintained in culture, we sought to determine if the mechanism of Clara cell tolerance was airway-specific. Second, using inhalation as the route of exposure, we sought to determine if Clara cells at all airways levels become tolerant to repeated inhalation exposures of NA. Third, by measuring gamma-glutamylcysteine synthetase (gamma-GCS) activity and expression we determined if tolerance to inhaled NA resulted from shifts in phase-II metabolism. Our results indicate that Clara cells in explants from tolerant mice remained tolerant to NA injury in culture. When mice were exposed to repeated inhalation exposures of NA (15 ppm), we found that Clara cells at all airway levels became tolerant. Expression and activity analysis revealed that gamma-GCS, the rate-limiting enzyme in glutathione synthesis, is induced in tolerant Clara cells. Buthionine sulfoximine, a gamma-GCS inhibitor, was able to eliminate the resistance of these tolerant cells. We conclude: (1) the mechanism of NA tolerance in Clara cells is airway specific, (2) the specific mechanism allows Clara cells to become tolerant to NA vapor at levels relevant to human exposure, and (3) the mechanism of tolerance to inhaled NA is highly dependent on induction of the catalytic enzyme, gamma-GCS.

Administration, Inhalation↗
PubMed2003

Mild hypoxia impairs alveolarization in the endothelial nitric oxide synthase-deficient mouse.

In addition to its vasodilator properties, nitric oxide (NO) promotes angiogenesis in the systemic circulation and tumors. However, the role of NO in promoting normal lung vascular growth and its impact on alveolarization during development or in response to perinatal stress is unknown. We hypothesized that NO modulates lung vascular and alveolar growth and that decreased NO production impairs distal lung growth in response to mild hypoxia. Litters of 1-day-old mouse pups from parents that were heterozygous for endothelial nitric oxide synthase (eNOS) deficiency were placed in a hypobaric chamber at a simulated altitude of 12,300 ft (Fi(O(2)) = 0.16). After 10 days, the mice were killed, and lungs were fixed for morphometric and molecular analysis. Compared with wild-type controls, mean linear intercept (MLI), which is inversely proportional to alveolar surface area, was increased in the eNOS-deficient (eNOS -/-) mice [51 +/- 2 micro m (eNOS -/-) vs. 41 +/- 1 micro m (wild type); P < 0.01]. MLI was also increased in the eNOS heterozygote (+/-) mice (44 +/- 1 micro m; P < 0.03 vs. wild type). Vascular volume density was decreased in the eNOS -/- mice compared with wild-type controls (P < 0.03). Lung vascular endothelial growth factor (VEGF) protein and VEGF receptor-1 (VEGFR-1) protein content were not different between the study groups. In contrast, lung VEGFR-2 protein content was decreased from control values by 63 and 34% in the eNOS -/- and eNOS +/- mice, respectively (P < 0.03). We conclude that exposure to mild hypoxia during a critical period of lung development impairs alveolarization and reduces vessel density in the eNOS-deficient mouse. We speculate that NO preserves normal distal lung growth during hypoxic stress, perhaps through preservation of VEGFR-2 signaling.

Animals↗
PubMed2003

Repeated episodes of ozone inhalation attenuates airway injury/repair and release of substance P, but not adaptation.

To determine the impact of repeated episodes of ozone exposure on physiologic adaptation, epithelial injury/repair, and tracheal substance P levels, adult rats were subjected to episodes of ozone (5 days, 1 ppm, 8 h/day) followed by 9 days of filtered air for four cycles. Rats were sampled on days 1 and 5 of each episode and 9 days after day 5 of episodes 1, 2, and 4. One hour before being euthanized each rat was injected with 5-bromo-2'-deoxyuridine to label proliferating cells. Each 5-day episode showed a characteristic pattern of rapid shallow breathing (days 1 and 2), epithelial injury, and interstitial and intraluminal inflammation. In contrast, the neutrophil component of inflammation, tracheal substance P release, and cell proliferation became attenuated with each consecutive episode of exposure. Concurrent with this cyclic and attenuated response there was progressive hypercellularity and hyperplasia in all airways studied and a progressive remodeling present in the terminal bronchioles. Our findings are consistent with the notion that the cumulative distal airway lesion is at least in part the result of a depressed cell proliferative response to injury in these airways. This depressed cell proliferative response may be in part the result of diminished neutrophil inflammation and/or release of mitogenic neuropeptides in response to ozone-induced injury.

Adaptation, Physiological↗