Estimation of cell numbers and volumes of bronchiolar epithelium during rabbit lung maturation

Histopathologic Lesion Scoring and Histomorphometric Methods for Measuring Vaccine Reactions in the Trachea of Broiler Chickens

Severity of the tracheal histologic inflammatory response induced in broilers by ocular inoculation of two infectious bronchitis (IBV) and three Newcastle disease virus (NDV) commercial vaccines were evaluated. The vaccine was delivered by eye drop with a coarse spray to day-old chicks. The vaccines were given individually or in various combinations and were evaluated relative to nonvaccinated controls. Evaluations were performed on postvaccination (PV) days 7 and 14. Histologic endpoints included semiquantitative severity scoring of inflammatory components and quantitative morphometric determinations of inflammatory cell concentration, mucosal thickness, and percentage of ciliated mucosal surface. Strong positive correlations were observed between routine severity scoring and morphometric inflammatory parameters, whereas a negative correlation was present between inflammation severity and the percentage of mucosal ciliation. Variable, sometimes extensive, and often statistically significant differences in inflammatory responses were observed between the various vaccines. One IBV Massachusetts strain vaccine (IBV-A) produced the greatest overall inflammatory response when given alone or in combination with the NDV vaccines. Enhancement of tracheitis was seen on PV day 14 by covaccination of IBV-A with the NDV vaccines, but not by covaccination of another IBV Massachusetts strain vaccine (IBV-B) with NDV. Reduction in cilia percentage was observed for all vaccine groups relative to controls on PV day 7. However, although reactive cilia regeneration occurred on PV day 14 for most vaccine groups, a cilia regenerative response was not apparent for individual or NDV combination vaccination for IBV-A. The study also demonstrates that substantial microscopic trachea pathology may be present in vaccinated birds not exhibiting apparent clinical respiratory signs.

Differential Alterations of the Mitochondrial Morphology and Respiratory Chain Complexes during Postnatal Development of the Mouse Lung

Mitochondrial biogenesis and adequate energy production in various organs of mammals are necessary for postnatal adaptation to extrauterine life in an environment with high oxygen content. Even though transgenic mice are frequently used as experimental models, to date, no combined detailed molecular and morphological analysis on the mitochondrial compartment in different lung cell types has been performed during postnatal mouse lung development. In our study, we revealed a significant upregulation of most mitochondrial respiratory complexes at protein and mRNA levels in the lungs of P15 and adult animals in comparison to newborns. The majority of adult animal samples showed the strongest increase, except for succinate dehydrogenase protein (SDHD). Likewise, an increase in mRNA expression for mtDNA transcription machinery genes (Polrmt, Tfam, Tfb1m, and Tfb2m), mitochondrially encoded RNA (mt-Rnr1 and mt-Rnr2), and the nuclear-encoded mitochondrial DNA polymerase (POLG) was observed. The biochemical and molecular results were corroborated by a parallel increase of mitochondrial number, size, cristae number, and complexity, exhibiting heterogeneous patterns in distinct bronchiolar and alveolar epithelial cells. Taken together, our results suggest a specific adaptation and differential maturation of the mitochondrial compartment according to the metabolic needs of individual cell types during postnatal development of the mouse lung.

Cellular differentiation and proliferation in the ovine lung during gestation and early postnatal development

This study investigates epithelial cell differentiation and proliferation in specific anatomical regions of the ovine lung during prenatal and postnatal development. Immunohistochemistry was used to identify ciliated epithelial cells, Clara cells, neuroepithelial bodies and type II pneumocytes in the lungs of preterm (67, 127 and 140 days of gestation), full-term (147 days) and postnatal (9, 16 and 91 days old) lambs. Differentiation of ciliated epithelial cells was seen at 67 days of gestation and at term for Clara cells. Neuroepithelial bodies were first detected at 127 days of gestation. From 16 to 91 days of age there was a significant (P <0.05) increase in beta-tubulin (present in ciliated epithelial cells) and Clara cell protein (present in Clara cells) in multiple regions of the lung. Detection of Ki67, a marker of proliferation, in preterm lambs showed a reduction in proliferation index in multiple anatomical regions of the lung between 70 days of gestation and term. Cell proliferation increased following parturition, and then decreased between 16 and 91 days of age, with the largest reduction occurring in the alveolar compartment. Knowledge of which cells are present at specific times of lung development provides valuable information on the anatomy of the ovine lung, improving its use as a model for ovine and human neonatal disease. In addition, the antibodies used here will be valuable for future studies requiring the identification and quantification of respiratory epithelial cell phenotypes in the sheep lung.

Roles for β-catenin and doxycycline in the regulation of respiratory epithelial cell frequency and function

The expression of β-catenin-dependent genes can be increased through the Cre recombinase (Cre)-mediated elimination of the exon 3-encoded sequence. This mutant β-catenin is termed DE3, and promotes the expression of β-catenin-dependent genes. Our previous study used the DE3 model to demonstrate that persistent β-catenin activity inhibited bronchiolar Clara-to-ciliated cell differentiation. The present study was designed to evaluate the roles of β-catenin in regulating the tracheal progenitor cell hierarchy. However, initial experiments demonstrated that the tetracycline-responsive element-Cre transgene (TRE-Cre) was active in the absence of a reverse tetracycline transactivator driver or inducer, doxycycline (Dox). This spurious TRE-Cre transgene activity was not detected using the ROSA26-floxed STOP-LacZ reporter. To determine if the phenotype was a consequence of genotype or treatment with Dox, tracheal and lung specimens were evaluated using quantitative histomorphometric techniques. Analyses of uninduced mice demonstrated a significant effect of genotype on tracheal epithelial cell mass, involving basal, Clara-like cell types. The bronchial and bronchiolar Clara cell mass was also decreased. Paradoxically, an effect on ciliated cell mass was not detected. Activation of the β-catenin reporter transgene TOPGal demonstrated that β-catenin-dependent gene expression led to the genotype-dependent tracheal and bronchiolar phenotype. Comparative analyses of wild-type or keratin 14-rtTA(+/0)/TRE-cre(+/0)/DE3(+/+) mice receiving standard or Dox chow demonstrated an effect of treatment with Dox on basal, Clara-like, and Clara cell masses. We discuss these results in terms of cautionary notes and with regard to alterations of progenitor cell hierarchies in response to low-level injury.

Tracheal Basal cells: a facultative progenitor cell pool

Analysis of lineage relationships in the naphthalene-injured tracheal epithelium demonstrated that two multipotential keratin 14-expressing cells (K14ECs) function as progenitors for Clara and ciliated cells. These K14EC were distinguished by their self-renewal capacity and were hypothesized to reside at the stem and transit amplifying tiers of a tissue-specific stem cell hierarchy. In this study, we used gene expression and histomorphometric analysis of the steady-state and naphthalene-injured trachea to evaluate the predictions of this model. We found that the steady-state tracheal epithelium is maintained by two progenitor cell pools, secretory and basal cells, and the latter progenitor pool is further divided into two subsets, keratin 14-negative and -positive. After naphthalene-mediated depletion of the secretory and ciliated cell types, the two basal cell pools coordinate to restore the epithelium. Both basal cell types up-regulate keratin 14 and generate a broadly distributed, abundant, and highly mitotic cell pool. Furthermore, basal cell proliferation is associated with generation of differentiated Clara and ciliated cells. The uniform distribution of basal cell progenitors and of their differentiated progeny leads us to propose that the hierarchical organization of tracheal reparative cells be revised to include a facultative basal cell progenitor pool.

Morphometry of the respiratory tract: avoiding the sampling, size, orientation, and reference traps

The extrapolation to humans of studies of infectious or toxic agents injurious to the respiratory system using animal models assumes comparability in the structure and function of animal models and humans. Measurement of conducting airways and parenchyma yields quantitative data for parameters like volume, surface area, length, cell number and cell size. Over the past few decades, there has been an evolution of rigorous uniform sampling designs of stereology that ensure unbiased estimates of number, length, surface area, and volume. This approach has been termed 'design-based' stereology because of the reliance on sampling design rather than geometric model-based stereology that makes assumptions. The aim of this paper is to define new design-based stereological approaches for the direct estimation of anatomical structures and epithelial, interstitial and endothelial cells of specific regions of the lung independent of the sampling, size, orientation and reference traps. An example is provided using wildtype and transgenic mice expressing transforming growth factor-alpha to show the importance of the reference trap in stereologic estimates of postnatal lung growth.

Acute injury to differentiating Clara cells in neonatal rabbits results in age-related failure of bronchiolar epithelial repair

Nonciliated bronchiolar (Clara) cells are progenitor cells during lung development. During differentiation, they have a heightened injury susceptibility to environmental toxicants bioactivated by cytochrome P450 monooxygenase. When neonatal rabbits are treated with the P450-mediated cytotoxicant 4-ipomeanol (IPO), abnormal bronchiolar epithelium results. This study establishes the impact of IPO cytotoxicity on 3 stages of rabbit Clara cell differentiation, early (2.5 and 5 days postnatal [DPN]), intermediate (7 and 9 DPN), and late (15 and 21 DPN), and relates the cytotoxicity to the extent of bronchiolar repair. Neonates received a single dose of IPO (5 mg/kg) and were assessed by qualitative pathology 48 hours later for injury or at 4 weeks for repair. IPO injured the 3 stages of Clara cell differentiation to the same degree; epithelium was swollen, exfoliated, and squamated. Epithelial repair differed among the 3 stages. Bronchioles of animals treated during early and intermediate stages had simple squamous and irregularly shaped cuboidal cells. Animals treated during late stages were similar to controls. Thus, differentiating Clara cells are susceptible to injury by the P450-mediated cytotoxicant IPO, but the extent of repair varies based on when the initial injury occurs.

Neonatal Clara cell toxicity by 4-ipomeanol alters bronchiolar organization in adult rabbits

Nonciliated bronchiolar (Clara) cells metabolize environmental toxicants, are progenitor cells during development, and differentiate postnatally. Because differentiating Clara cells of neonatal rabbits are injured at lower doses by the cytochrome P-450-activated cytotoxicant 4-ipomeanol than are those of adults, the impact of early injury on the bronchiolar epithelial organization of adults was defined by treating neonates (3-21 days) and examining them at 4-6 wk. Bronchiolar epithelium of 6-wk-old animals treated on day 7 was most altered from that of control animals. Almost 100% of the bronchioles were lined by zones of squamous epithelial cells. Compared with control animals, the distal bronchiolar epithelium of 4-ipomeanol-treated animals had more squamous cells (70-90 vs. 0%) with a reduced overall epithelial thickness (25% of control value), fewer ciliated cells (0 vs. 10-20%), a reduced expression of Clara cell markers of differentiation (cytochrome P-4502B, NADPH reductase, and 10-kDa protein), and undifferentiated nonciliated cuboidal cell ultrastructure. We conclude that early injury to differentiating rabbit Clara cells by a cytochrome P-450-mediated toxicant inhibits bronchiolar epithelial differentiation and greatly affects repair.

Naphthalene cytotoxicity of differentiating Clara cells in neonatal mice

Selective Clara cell injury produced by many bioactivated lung toxicants is thought to result from high levels of activating enzymes found in differentiated Clara cells. A recent study found an elevated susceptibility to the Clara cell toxicant 4-ipomeanol in neonatal rabbits when Clara cell P450 activity is low. To determine whether differentiating Clara cells in another species (mouse) are more susceptible to injury by a different bioactivated Clara cell toxicant (naphthalene), adult, 14-day postnatal (DPN) and 7DPN male mice were given a single intraperitoneal dose (25, 50, or 100 mg/kg) of naphthalene and killed 24 hr later. Epithelial damage, as assessed by quantitative histopathology, included cellular swelling, vacuolization, and exfoliation. In 7DPN mice, bronchiolar epithelium was severely injured at the lowest dose of naphthalene tested, 25 mg/kg. Bronchiolar epithelium in 14DPN mice was moderately injured at 25 mg/kg; injury severity was greatest at 50 and 100 mg/kg. Minimal bronchiolar epithelial injury occurred in adult mice at 50 mg/kg and moderate injury at 100 mg/kg. In proximal bronchi, epithelium of 7DPN mice showed signs of injury only at 100 mg/kg. Bronchial epithelium of adult mice was not injured at any dose. Isolated distal airways from 7DPN and 14DPN mice were more sensitive to naphthalene exposure than isolated distal airways from adult mice. Despite the low levels of P450 activity, differentiating Clara cells in neonatal mice are more susceptible to injury by the bioactivated cytotoxicant naphthalene than are differentiated Clara cells in adult mice.

The role of the nonciliated bronchiolar epithelial (Clara) cell as the progenitor cell during bronchiolar epithelial differentiation in the perinatal rabbit lung

Although it is well established that the nonciliated bronchiolar epithelial (Clara) cell serves as the progenitor for itself and ciliated cells in the adult lung following bronchiolar epithelial injury, the nature of this relationship during development has not been well characterized. To define the pattern of proliferation and differentiation of bronchiolar ciliated and nonciliated cells, lungs of fetuses and offspring from time-mated New Zealand White rabbits, ranging in age from 24 days of gestation to 25 wk postnatal (PN), were fixed by airway infusion and embedded for simultaneous light and transmission electron microscopy. Three categories of cells could be distinguished in terminal bronchioles: nonciliated cells with abundant glycogen and variable numbers of organelles; nonciliated cells with little glycogen, large numbers of polyribosomes, and variable numbers of basal bodies; and ciliated cells with cilia of varying height. Together, both types of nonciliated cells were 100% of the epithelium at 24 and 27 days gestation age (DGA). At 30 days DGA, they were 85% of the population; at all postnatal ages, they ranged from 75 to 81% of the total population. Nonciliated cells with polyribosomes and basal bodies were 10 to 20% of the total nonciliated cell population between 24 DGA and 1 wk PN and not found thereafter. Ciliated cells were not observed in animals younger than 30 DGA. Labeling indices of bronchiolar epithelium in fetuses of pregnant rabbits injected with tritiated thymidine, as determined by autoradiography, were 57 cells per thousand at 28 DGA (1 h postinjection [PI]), 76 at 29 DGA (24 h PI), and 114 at 30 DGA (48 h PI).(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric assessment of pulmonary toxicity in the rodent lung

An overview of the epithelial and interstitial composition of rat respiratory airways shows complexity and variability. Airway epithelium varies in 1) different airway levels; 2) the types and ultrastructure of cells present; and 3) the abundance, type, and composition of stored secretory product. Unbiased sampling of airways is done using airway microdissection with a specific binary numbering system for airway generation. Vertical sections of selected airways are used to sample epithelium and interstitium. We determine the ratios of the volume of epithelial or interstitial cells to the total epithelial or interstitial volume (Vv). The surface of the epithelial basal lamina to the total epithelial or interstitial volume (Sv) is determined using point and intersection counting with a cycloid grid. Using the selector method on serial plastic sections, we determine the number of epithelial or interstitial cells per volume (Nv) of total epithelium or interstitium. We calculate the number of epithelial or interstitial cells per surface of epithelial basal lamina (Ns) by dividing Nv by Sv where the volumes are the same compartment. We calculate average cell volumes (v) for specific epithelial and interstitial cells by dividing the absolute nuclear volume by the ratio of the nucleus to cell volume (Vv). By multiplying the average cell volume (v) by the ratio of organellar volume to cell volume (Vv), we calculate the average organellar volume per cell. These unbiased stereological approaches are critical in a quantitative evaluation of toxicological injury of rat tracheobronchial airways.

Cytodifferentiation of two epithelial populations of the respiratory bronchiole during fetal lung development in the rhesus monkey

This study describes the cytodifferentiation of the two populations of epithelial cells found in the respiratory bronchiole of the adult rhesus monkey. One population, pseudostratified and containing ciliated, nonciliated secretory, and basal cells, is found overlying the pulmonary artery (PA). The other population, not associated with the PA, contains nonciliated cuboidal cells between alveolar outpockets. In this study we used terminal conducting airways from the lungs of fetal (90 to 155 days gestational age [DGA]), postnatal, and adult rhesus monkeys. Ciliated cells were partially differentiated at 90 DGA (54% gestation) and completely differentiated by 134 DGA (80% gestation). Nonciliated secretory cells were partially differentiated at 95 DGA (57% gestation) but did not lose all glycogen until the postnatal period. Basal cells appeared by 134 DGA (80% gestation) and matured in the postnatal period. Small mucous granule cells appeared at 125 DGA (74% gestation) and did not change throughout fetal development. Neuroendocrine cells were present throughout the entire period studied. Nonciliated cuboidal bronchiolar cells of the nonciliated population of the respiratory bronchiole appeared at 105 DGA (62% gestation) and matured in the postnatal period. We conclude that 1) although most of the differentiation of the lower airway occurs before birth, most of the cell types are not completely differentiated at birth; 2) the sequence of differentiation for the cells of the ciliated pseudostratified epithelial population is ciliated, nonciliated secretory, and basal; 3) the sequence of differentiation for the nonciliated secretory cell is similar to that of the secretory cells in more proximal airways; and 4) basal, neuroendocrine, and small mucous granule cells are not a part of the differentiation sequence of the other cell types.

Postnatal growth of pulmonary acini and alveoli in normal and oxygen-exposed rats studied by serial section reconstructions

Three-dimensional reconstructions from serial sections were used to examine postnatal lung development of rats reared in air (control) or oxygen. From birth to age 21 days, control lung volume increased ninefold, and the average volume of each ventilatory unit (all airspaces distal to a single respiratory bronchiole) increased seven times. There were approximately 5,000 ventilatory units at birth and on day 21, indicating that the lung grew by enlargement and subdivision of ventilatory units and not by their multiplication. Growth in hyperoxia (greater than 97%) for 7 days had no effect on the number of ventilatory units but, compared to controls, total lung volume and ventilatory unit volume were reduced 32% and 16%, respectively. At birth there were 0.6 x 10(6) alveoli, and at age 7 days in controls alveolar number increased 16-fold while the average volume of a single alveolus fell to one-sixth that at birth. Exposure to hyperoxia for 7 days stopped alveolarization; the surface area to volume ratio (Sa/V) of the ventilatory unit was lower, alveolar number was the same as at birth, and the alveoli present were large. At age 21 days, after 14 days of recovery in air, lung volume and ventilatory unit volume were greater than in controls but the Sa/V of the ventilatory unit was still depressed 20%. Alveoli from oxygen-exposed lungs were larger than in controls, and a greater size distribution coefficient showed them to be more variable. A shape coefficient for alveoli did not change as a function of the animal's age or oxygen treatment; it demonstrated proportional growth of alveolar height and diameter.

Antileucoprotease in the developing fetal lung

The distribution of antileucoprotease in the lungs of 25 fetuses of 9-40 weeks' gestation was studied with monoclonal antibodies and an indirect immunoperoxidase technique. Antileucoprotease was detected from 16 weeks in submucosal glands and collecting ducts in the trachea and main and lobar bronchi: it was also found in the surface epithelium of the trachea at 20 weeks, in main and lobar bronchi at 20 weeks, and in smaller bronchi at 20-25 weeks. Non-ciliated cells containing antileucoprotease were observed in the bronchiolar epithelium at 36 and 40 weeks. The results of this study indicate that antileucoprotease is available from birth. It may therefore form part of the first line of defence of the lung.

Morphogenesis of the respiratory bronchiole in rhesus monkey lungs

The epithelium of the respiratory bronchiole in the adult rhesus monkey consists of two populations: a pseudostratified epithelium with basal, mucous goblet, and ciliated cells located near the pulmonary artery (PA); and a simple cuboidal epithelium composed only of nonciliated bronchiolar epithelial (or Clara) cells in areas away from the PA. This study describes the pattern of differentiation of these two epithelial populations, and their relationship to the PA and to the time of appearance of alveoli in the respiratory bronchiole of the rhesus monkey during the period of 90-125 days gestational age (DGA). These events were related to changes in the adjacent parenchyma. Dissected airways of infusion-fixed, critical-point-dried lungs were evaluated by scanning microscopy followed by light microscopy of the same airways. At 54% of gestation (90 DGA), the distal airway was lined by a mixture of ciliated and nonciliated cells. By 67% of gestation (110 DGA), the ciliated cells were confined to the epithelium over the PA. The underlying connective tissue initially was cellular containing few fibers but was fibrous by 76% of gestation (125 DGA). Alveolarization began near the most distal cartilage at 57% of gestation (95 DGA), the same period at which secondary septation occurred in the distal acinus. Thus, alveolarization occurred simultaneously in two centers: 1) the proximal centriacinar region in the vicinity of the most distal cartilage and 2) the distal lung parenchyma. The duration of centriacinar alveolarization was short, approximately 5 days.

Effects of inhalation of 0.25 ppm ozone on the terminal bronchioles of juvenile and adult rats

Cells of the terminal bronchioles are particularly susceptible to the effects of inhalation of low levels of ozone (O3). One-day-old (juvenile) or 6-week-old (adult) rats were exposed to 0.25 ppm O3 for 12 h/day or to continuous room air for 6 weeks. Morphometric analysis of perpendicular cross sections of terminal bronchioles demonstrated that exposure to O3 produced alterations in the surface characteristics of ciliated and nonciliated (Clara) cells in both groups of rats. There were significant losses (20-30%) of the surface area contributed by cilia and the luminal surface of Clara cells was decreased by 16-25%. O3 exposure also produced significant decreases in the number of brush cells per square millimeter of terminal bronchiolar basement membrane. The results of this study indicate that the normal structure of terminal bronchiolar epithelial cells is significantly altered by inhalation of 0.25 ppm O3. No statistically significant interactions between the effects of O3 and animal age at the beginning of the exposure were found.

The ultrastructure of epithelial cells of the distal lung

This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli. In all, five cells types were considered: Clara cells, types I, II, and III pneumocytes, and alveolar macrophages. In addition, a very brief mention of the structure and influence of the basement membrane in alveolar development and repair was included, as well as a brief review of the role of epithelial cells in response to selected deleterious influences. No attempt was made to extend this review to cover the structure and functions of the epithelial lining of the conducting portions of the respiratory system, or the exciting and expanding complexities and interrelationships of the septal stroma. Since the volume of literature encircling this subject has virtually exploded during the last 15 years, it becomes almost impossible to review all reports. However, attempts were made to be selective in citations. Insofar as future developments are concerned, much remains to be understood concerning (1) the responses of all cell types to cytotoxic influences, including their respective abilities to repair induced damage, (2) cell-cell and cell-extracellular matrix relationships in response to injury, (3) the uniqueness of the basement membrane in the lung in controlling permeability and gaseous exchange, (4) the role(s) of alveolar macrophages in response to injury and their relationships to the septal macrophage population, (5) the aberrations in the respective cell types that can give rise to neoplastic growth, and (6) the role of the immune system in responding to the general defense of the lung. Indeed much has been learned in the past 2 decades, and it is expected that a review of this sort 1 or 2 decades hence will elucidate many of the functions and structural modifications of the lung.

Ozone-induced adaptive and reactive cellular changes in respiratory bronchioles of bonnet monkeys

To characterize the response of respiratory bronchioles (RBs) to chronic high ambient levels of ozone, bonnet monkeys were exposed for 90 days to 0, 0.4, or 0.64 ppm ozone (UV photometric standard; 3 monkeys/exposure). Morphologic changes in respiratory bronchiolar epithelium and interstitium were evaluated quantitatively at both the light and transmission electron microscopic levels. Significant changes in respiratory bronchioles following exposure included: a thicker wall and a narrower lumen, a thicker epithelial compartment and a much thicker interstitial compartment, shifts in epithelial cell populations with many more nonciliated bronchiolar epithelial cells and fewer squamous type I epithelial cells, larger nonciliated bronchiolar epithelial cells with a larger complement of cellular organelles associated with protein synthesis, greater amounts of both interstitial fibers and amorphous ground substance, greater numbers of interstitial smooth muscle cells per epithelial basal lamina surface area, and greater volumes of interstitial smooth muscle, macrophages, mast cells, and neutrophils per epithelial basal lamina surface area. These observations imply that chronic ozone exposure causes a concentration-dependent reactive peribronchiolar inflammatory response and an adaptive response consisting of hypertrophy and hyperplasia of the nonciliated bronchiolar cell.

Application of morphometric methods to study diffuse and focal injury in the lung caused by toxic agents

Morphometric techniques are now being widely applied to a variety of toxicologic problems in order to obtain reproducible and quantitative data about changes in lung structure caused by environmental pollutants. Many environmental pollutants cause lung injury which is concentrated in specific regions of the lung, such as, in small airways and in the proximal portions of alveolar ducts. Morphometric techniques to obtain unbiased estimates of tissue changes occurring in these specific regions are reviewed and contrasted to well-established techniques for morphometric analysis of the distal alveolar regions of the lung. Specific applications of morphometric studies in different toxicologic problems are illustrated and include quantification of the changes in lung tissue and in lung cellular population pattern in response to exposure of small animals to hyperoxic atmospheres and to ozone. Pulmonary oxygen toxicity is an example of a diffuse lesion throughout the distal portion of the acinus whereas ozone exposure is an example of an environmental pollutant causing a greater degree of lung injury in the proximal alveolar region and in the small airways.

The neonatal porcine lung: ultrastructural morphology and postnatal development of the terminal airways and alveolar region

Morphology and postnatal development of the porcine lung are described in animals ranging in age from newborn through 60 days. Standardized fixation was accomplished by intratracheal instillation of glutaraldehyde under constant pressure. Light microscopic, scanning, and transmission electron microscopic investigations revealed that the porcine lung follows the common architecture of mammalian lungs, but has certain peculiarities as well: intravascular macrophages, ultrastructurally similar to Kupffer cells, are attached to endothelial cells in pulmonary capillaries and are involved in erythrophagocytosis during the first postnatal weeks. Type II pneumocytes of newborn pigs exhibit signs of cell activation, mainly complex nuclear bodies in the cell nuclei. At the same time high levels of 17-hydroxycorticosteroids are observed in the newborn blood plasma. Terminal airways of the porcine lung are nonalveolarized and are, therefore, of purely conductive function. At birth the porcine lung exhibits a high degree of maturity, and thick-walled primary saccules, as described in newborn rodents, are not seen. Septa appear straight and smooth, owing to rare ramification. Septal buds are discernible, and two capillary networks visible on both sides of septal cross sections are seen. Further subdivision of the airspaces occurs in the first two postnatal weeks. Precociousness and fast postnatal growth of the porcine species are assumed to be the reason of this advanced degree of lung maturity at birth and the following rapid pulmonary development.

The tracheobronchial epithelium of the bonnet monkey (Macaca radiata): a quantitative ultrastructural study

Since there are major differences between the airway epithelium of man and that of common laboratory species, the tracheobronchial epithelium of the bonnet macaque was characterized to evaluate its usefulness as a model for study of human conducting airways. This study compared the light microscopic, scanning electron microscopic, and ultrastructural appearance of epithelium from the posterior membranous and anterior cartilaginous trachea and mainstem bronchus. Population densities, epithelial volumetric densities, and frequency distributions of cross-sectional areas of nuclei were determined for cell types present on electron micrographs. Four epithelial cell types were distinguished by ultrastructural criteria. Basal cells were 31% of the population and were similar to those described in other species. Ciliated cells were also similar to those of other species and composed 41% of the population; their nuclei were larger than those of other cell types. Mucous goblet cells had large numbers of secretory granules with electron-dense cores and a lucent periphery. They were only 8% of the population by nuclear count but composed 20% of the epithelial volume. The fourth cell type had multiple small vesicles containing small amounts of granular material and was termed a "small mucous granule cell." Small mucous granule cells (16% of the population) were present in greater numbers than mucous goblet cells but were a smaller proportion of the epithelial volume (8%). While population densities of cell types determined from transmission electron micrographs did not vary between sample sites, scanning electron microscopy demonstrated longitudinal streaks of secretory cells in the posterior trachea suggesting that regional differences in epithelial organization exist. We conclude that the macaque extrapulmonary airway epithelium differs from published descriptions of laboratory rodents in both cell types present and relative abundance of those cell types. Although detailed quantitative studies of human extrapulmonary airways are not available, the primate airways resemble those of man in both the types of cells present and the complexity of pseudostratification.