Functional morphology of the distal lung

Evaluation of Innate Immune Mediators Related to Respiratory Viruses in the Lung of Stable COPD Patients

Background: Little is known about the innate immune response to viral infections in stable Chronic Obstructive Pulmonary Disease (COPD). Objectives: To evaluate the innate immune mediators related to respiratory viruses in the bronchial biopsies and lung parenchyma of stable COPD patients. Methods: We evaluated the immunohistochemical (IHC) expression of Toll-like receptors 3-7-8-9 (TLR-3-7-8-9), TIR domain-containing adaptor inducing IFNβ (TRIF), Interferon regulatory factor 3 (IRF3), Phospho interferon regulatory factor 3 (pIRF3), Interferon regulatory factor 7 (IRF7), Phospho interferon regulatory factor 7 (pIRF7), retinoic acid-inducible gene I (RIG1), melanoma differentiation-associated protein 5 (MDA5), Probable ATP-dependent RNA helicase DHX58 (LGP2), Mitochondrial antiviral-signaling protein (MAVS), Stimulator of interferon genes (STING), DNA-dependent activator of IFN regulatory factors (DAI), forkhead box protein A3(FOXA3), Interferon alfa (IFNα), and Interferon beta (IFNβ) in the bronchial mucosa of patients with mild/moderate (n = 16), severe/very severe (n = 1618) stable COPD, control smokers (CS) (n = 1612), and control non-smokers (CNS) (n = 1612). We performed similar IHC analyses in peripheral lung from COPD (n = 1612) and CS (n = 1612). IFNα and IFNβ were assessed in bronchoalveolar lavage (BAL) supernatant from CNS (n = 168), CS (n = 169) and mild/moderate COPD (n = 1612). Viral load, including adenovirus-B, -C, Bocavirus, Respiratory syncytial Virus (RSV), Human Rhinovirus (HRV), Coronavirus, Influenza virus A (FLU-A), Influenza virus B (FLU-B), and Parainfluenzae-1 were measured in bronchial rings and lung parenchyma of COPD patients and the related control group (CS). Results: Among the viral-related innate immune mediators, RIG1, LGP2, MAVS, STING, and DAI resulted well expressed in the bronchial and lung tissues of COPD patients, although not in a significantly different mode from control groups. Compared to CS, COPD patients showed no significant differences of viral load in bronchial rings and lung parenchyma. Conclusions: Some virus-related molecules are well-expressed in the lung tissue and bronchi of stable COPD patients independently of the disease severity, suggesting a “primed” tissue environment capable of sensing the potential viral infections occurring in these patients.

Status of fluid and electrolyte absorption in cystic fibrosis

Salt and fluid absorption is a shared function of many of the body's epithelia, but its use is highly adapted to the varied physiological roles of epithelia-lined organs. These functions vary from control of hydration of outward-facing epithelial surfaces to conservation and regulation of total body volume. In the most general context, salt and fluid absorption is driven by active Na(+) absorption. Cl(-) is absorbed passively through various available paths in response to the electrical driving force that results from active Na(+) absorption. Absorption of salt creates a concentration gradient that causes water to be absorbed passively, provided the epithelium is water permeable. Key differences notwithstanding, the transport elements used for salt and fluid absorption are broadly similar in diverse epithelia, but the regulation of these elements enables salt absorption to be tailored to very different physiological needs. Here we focus on salt absorption by exocrine glands and airway epithelia. In cystic fibrosis, salt and fluid absorption by gland duct epithelia is effectively prevented by the loss of cystic fibrosis transmembrane conductance regulator (CFTR). In airway epithelia, salt and fluid absorption persists, in the absence of CFTR-mediated Cl(-) secretion. The contrast of these tissue-specific changes in CF tissues is illustrative of how salt and fluid absorption is differentially regulated to accomplish tissue-specific physiological objectives.

Oat cells in the pathology of ovine pneumonia-pleurisy

Light microscope observations on oat cells in the ovine pneumonia-pleurisy complex are presented. This study is based on the experimental production of the disease by viruses and Pasteurella haemolytica. Oat cells appeared only in necrotic lesions associated with large numbers of P. haemolytica in the pneumonic lung. It is suggested that oat cells originate from blood monocytes, which transform into the oat shape when developing in the necrotic, hypoxic environment created by P. haemolytica. They were not, however, observed to be phagocytic. Oat cells are characteristic of pneumonic pasteurellosis but are not pathognomonic because they can also be found in extrapulmonary locations and in other pathological conditions of the lungs.

Gamma-aminobutyric acid nurtures allergic asthma

Asthma often occurs as a result of immune-based inflammatory responses, which consequently cause pathological changes in airway structural cells. However, the underlying mechanisms of airway pathology in asthma are still not fully understood. Our recent studies revealed a critical role of gamma-aminobutyric acid (GABA) signalling pathway in the airway epithelium of allergic asthma through its ability to stimulate mucus production. This review briefly describes the GABAergic signalling system and its role in the regulation of mucus protein production in bronchial airway epithelial cells.

Ultrastructure of goblet-cell metaplasia from Clara cell in the allergic asthmatic airway inflammation in a mouse model of asthma in vivo

Mucus overproduction from goblet cells, a characteristic feature of the allergic asthmatic inflammation induced by ovalbumin (OVA) in mice, was examined morphologically. In OVA-untreated (normal) mice, there were no goblet cells in intrapulmonary bronchus and bronchiole. However, goblet cells with or without hyperplasia in the mucosa of inflamed bronchus-bronchiole were recognized in the allergic asthmatic mice. The non-ciliated epithelium containing electron lucent granules (mucus) showed many similarities to Clara cells, which have characteristic secretory granules and many mitochondria, except for the less-developed smooth endoplasmic reticulum seen in normal mice. Ciliated Clara cells with or without mucus were rarely recognized. In addition, mucus was found in neither ciliated nor basal epithelium. The present study suggests that goblet-cell metaplasia in the bronchus and bronchiole of inflamed mucosa may be derived, at least in part, from Clara cells.

Stop inhaling smoke: prevent coronary heart disease

Acute myocardial infarction (AMI) was rare a century ago and was diagnosed in few living patients prior to 1925. By 1950, it was the most common heart problem seen by clinicians. Thought at first to have been overlooked, there were many explanations offered for its neglect. Smoking, hypertension, and elevated cholesterol are associated with AMI, but of these only smoking should be considered a cause. Hypertension and hypercholesterolemia may be co-effects, perhaps of inflammation stimulated in the lung and blood vessels by smoking and air pollution, thus affecting vessels and arteries subjected to systemic blood pressure. Air pollution--the 20th century's other "big smoke"--deserves consideration as a 2nd cause. Auto exhaust blankets the world's cities. It consists of smoke and other effluents of petroleum vaporization and combustion that emanate from the crankcases and exhaust pipes of trucks and automobiles. The major living spaces (conurbations) of the world now imitate and exceed Los Angeles in their levels of air pollution. Auto exhaust gases fit the timeline, and their increasing amounts parallel the worldwide rise in coronary heart disease. Increasing doses of these chemicals imitate cigarette smoke and stimulate inflammation in the lungs. They appear to be absorbed into the blood, where they cause inflammation in blood vessels, increased blood pressure, and clogged coronary arteries. Avoidance is the obvious solution. Quit inhaling cigarette smoke and motor vehicle exhaust. The benefits have been shown and can be proved by intervention. The quest for clean air is hygienic-like avoiding water contaminated with feces was 150 yr ago. Clear air must be made a moral right. Its attainment requires a major revolution in priorities for energy use and lifestyle. Two types of smoke must be avoided. The world's most lethal disease.

Bronchiolar nonciliated secretory (Clara) cells: source of guanylin in the mammalian lung

The peptide guanylin, which has recently been isolated from the intestine, is involved in the regulation of fluid secretion in the intestinal epithelium by activation of guanylate cyclase C, the putative guanylin receptor. Since the latter protein is also expressed in airway epithelia, we investigated the lung of three mammalian species for the presence and cellular localization of guanylin by immunoblot (Western blot) analyses and light and electron microscopical immunocytochemistry. In Western blots of bovine, guinea pig, and rat lung extracts, three different guanylin antisera directed against the midportion and against the C terminus of the precursor molecule identified a peptide band corresponding to the apparent molecular mass of guanylin. Localization studies in the lung revealed that guanylin is exclusively confined to nonciliated secretory (Clara) cells in the lining of distal conducting airways. The presence of guanylin in the lung and particularly its specific localization to Clara cells indicate that these cells may play a pivotal role in the local (paracrine) regulation of electrolyte/water transport in airway epithelia.

Migratory behaviors of alveolar macrophages during the alveolar clearance of light to heavy burdens of particles

We investigated the unstimulated and stimulated migratory activities of lavaged alveolar macrophages (AMs) in vitro over the course of alveolar clearance of three different mass lung burdens of microspheres. Our intent was to uncover potentially important relationships between the migratory behaviors of the AM and the retention kinetics of particles. Groups of adult, male Fischer-344 rats were intratracheally instilled with approximately 86 micrograms (low burden, LB), approximately 1 mg (medium burden, MB), or approximately 3.7 mg (high burden, HB) of polystyrene microspheres (2.13 microns diameter), or with carrier vehicle (phosphate buffered saline, PBS) alone. The lung retention kinetics of the particles were determined over an approximately 170 day period. On days 14, approximately 57, and approximately 85, lavaged AMs were assessed for their abilities to migrate through 5-microns pore membranes in response to inactivated rat serum (unstimulated condition) and yeast-activated rat serum (stimulated condition). The retention characteristics of the three burdens could be satisfactorily described by two-component, negative exponential equations. The kinetics of retention of the LB and MB were similar, although some evidence indicated the MB slightly retarded the lung clearance process. Deposition of the HB resulted in more marked prolongations of both the early, more rapid, and the slower, longer term components of alveolar clearance. The unstimulated migration indices of AMs from the particle-instilled lungs were generally not significantly different from those of AMs from PBS-instilled lungs except for a significant increase in the migration indices of LB AMs at the last assay time. The stimulated migration indices of MB and HB AMs were significantly decreased on assay days 14 and approximately 57. On day approximately 85, however, the migration indices of LB, MB, and HB AMs were all increased above the PBS AMs. Comparisons of the frequency distributions of particles in the unstimulated and stimulated AM that migrated to those in corresponding parent AM populations consistently indicated a preferential migration of particle-free AMs and of AMs with lesser loads of microspheres. The overall results of this study suggest that the unstimulated and stimulated migratory activities of particle-laden AMs are depressed in vitro. Our results also suggest that the migratory activities of generally particle-free AMs may be enhanced over a prolonged period of time following the deposition of particles in the lung.

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.

Ion transport by rabbit nonciliated bronchiolar epithelial cells (Clara cells) in culture

The functions of epithelia that line small airways in mammalian lungs are unknown. To gain insight into the role of small-airway epithelia in lung liquid balance, Clara cells were isolated from excised rabbit lungs by enzymatic digestion, enriched by centrifugal elutriation and density centrifugation, and further purified by differential adherence to collagen matrices. The resulting cell population was composed of 85% Clara cells, 3% ciliated cells, and less than 1% macrophages. The remainder of the cells were not definitively identified. The transepithelial potential difference peaked on day 3 in culture. Preparations studied in Ussing flux chambers exhibited a potential difference of 8 mV (apical bath negative), a resistance of 500 ohm X cm2, and an equivalent short-circuit current (ISCeq) of 16 microA/cm2. Inhibition of the Na+/K+-ATPase by ouabain abolished ISCeq. Exposure of the apical surface to amiloride or replacement of Na+ in the apical bathing solution with an impermeant cation (N-methyl-D-glucamine) decreased ISCeq by 66% and 93%, respectively. Neither amiloride in the basolateral bathing solution, nor bumetanide, nor isoproterenol significantly altered basal ISCeq. These findings indicate that Clara cells in culture form polarized monolayers, Clara cells transport Na+ from the apical to the basolateral bathing solution, and the small airways of the rabbit may function in liquid absorption.

Presence of abundant filaments in apical caps of the nonciliated bronchiolar epithelial (Clara) cells

The nonionic detergent Triton X-100 has often been used for the extraction of cytoplasmic materials. We used the detergent in a vascular perfusion medium when preparing rat lung in order to observe the cytoskeleton of the nonciliated bronchiolar epithelial (Clara) cells. To eliminate some cytoplasmic materials selectively and to maintain good fine cell structure simultaneously, the lungs were perfused sequentially with the detergent (0.2% Triton X-100) alone for 2 min, with a mixture of low-concentration (0.1%) glutaraldehyde and detergent (0.2% Triton X-100) for 15 min, and finally with 2.5% glutaraldehyde for 5-10 min. After fixation, the nonciliated bronchiolar epithelial (Clara) cells were observed by scanning and transmission electron microscopy. At the apical region of the cells, there were central cytoplasmic protuberances (apical caps) filled with microfilaments. These filaments were bound at one end to the cytoplasmic side of the cell membrane and ran into the interior of the cytoplasm at the other end. As a control, the Clara cells were observed by transmission electron microscopy after perfusion with 2.5% glutaraldehyde solution. The luminal surfaces of the cells were covered with short, thick microvilli. The apical caps also had microvillus-like protrusions. These results suggest that the apical cap is not an apocrine droplet but rather is a stable structure involved in the function of the Clara cells.

Alveolar macrophage mediated pulmonary clearance suppressed by drug-induced phospholipidosis

Drug-induced phospholipidosis in rats treated with chlorphentermine (CP) for 4-7 days suppressed totally alveolar pulmonary clearance in the first days after a TiO2 aerosol exposure. Reversing phospholipidosis by treatment interruption led to a recovery of particle clearance. Morphological observations indicated that "foam cells" contained less TiO2 particles than alveolar macrophages (AM) of control rats. Clearance of ZnO particles which seems not to be mediated by AM was not affected by CP treatment. A grand average retention curve based on data from control groups of past experiments suggests that alveolar clearance of TiO2 particles has a phase 1 (T 1/2 = 7 days) lasting about 2 weeks and a phase 2 (T 1/2 = 69 days). The results with drug-induced phospholipidosis suggest that phase 1 is practically totally AM-mediated. Drug-induced phospholipidosis is a promising method for the study of AM involvement in defensive functions.

Ultrastructure of the nonciliated bronchiolar epithelial (Clara) cell of mammalian lung: I. A comparison of rabbit, guinea pig, rat, hamster, and mouse

The morphologic characteristics have been used to define the nonciliated bronchiolar epithelial: (1) abundance of agranular endoplasmic reticulum (AER) and (2) numerous membrane-bound ovoid granules. To quantitatively and qualitatively assess the ultrastructural homogeneity of this lung cell type among laboratory mammals used in lung research, we examined tissue from adult male rabbits, guinea pigs, rats, hamsters and mice. Following fixation by airway infusion at constant pressure (30 cm H2O), lungs were processed by a selective embedding technique and bronchioles of known anatomic location were examined by electron microscopy. Nonciliated bronchiolar epithelium of all five species contained avoid granules and abundant AER. Granules were most abundant in the rat (11.1 +/- 8.8 per cell) and least in the hamster (4.4 +/- 5.2 per cell). Granules were largest in hamster (0.72 +/- 0.25 micrometer) versus 0.44 micrometer or less in the other species. Granules were of uniform electron density except in the guinea pig. AER spherical mitochondria with few cristae were present only in mice, rabbit, and guinea pig. We concluded that there was considerable interspecies variation in abundance, size, and morphology of the granules, in abundance and distribution of AER; and in mitochondrial morphology.

Ultrastructure of the nonciliated bronchiolar epithelial (Clara) cell of mammalian lung: II. A comparison of horse, steer, sheep, dog, and cat

Two morphologic characteristics have been used to define the nonciliated bronchiolar epithelial cell: abundant agranular endoplasmic reticulum (AER) and membrane-bound avoid granules. To assess the ultrastructural homogeneity of this cell type in the lungs of large domestic mammals used as experimental models in pulmonary research, we evaluated lungs of horse, steer, sheep, dog, and cat. Bronchioles of known anatomic location were examined by electron microscopy following fixation by airway infusion at standard pressure and processing by selective embedding techniques. Nonciliated bronchiolar epithelium of the horse and sheep had numerous avoid granules (averaging above 15 per cell) and abundant AER. Granules were scarce (averaging less than 2 per cell) in steer and dog and absent in cat. AER was minimal in these species compared to horse and sheep. Glycogen was the dominant cytoplasmic feature in steer, dog, and cat, variable in sheep and rare in horse. Large mitochondria with few cristae and densely staining matrix were present only in cat. We concluded that nonciliated bronchiolar cells of horse and sheep were similar in essential features to this cell type in laboratory mammals, having granules and AER in abundance, while those of steer, dog, and cat were not.

Ultrastructure of the nonciliated bronchiolar epithelial (Clara) cell of mammalian lung. III. A study of man with comparison of 15 mammalian species

Two morphologic characteristics have been used to define the nonciliated bronchiolar epithelial cell: (1) abundance of agranular endoplasmic reticulum (AER) and (2) numerous membrane-bound ovoid granules. In this study, we examined lobectomy specimens from three nonsmoking humans: one male (9.5 yr) and two females (62 and 43 yr) for comparison with lung specimens from mammalian species used as experimental models in lung research. Following fixation by airway infusion at constant pressure (20 cm), lung tissue was processed by a selective embedding technique and bronchioles of known anatomic location were studied by electron microscopy. Nonciliated bronchiolar epithelial cells of man contained numerous membrane-bound granules (averaging 6 per cell) in the apical cytoplasm and abundant granular endoplasmic reticulum (GER), AER was not observed. Granules averaged 0.3 micrometer in diameter and contained a fine granular matrix and parallel tubular arrays. After comparing these features in man with those of fifteen other species, we concluded that there is a great deal of interspecies variability in the cellular morphology of the nonciliated epithelial cell of distal conducting airways in mammalian lung. Three categories of this cell were observed: (1) with abundant granules and AER, characteristic of rabbit, guinea pig, rat, hamster, mouse, horse, sheep, and pig; (2) with abundant granules of GER, but no AER, characteristic of man and other primates; and (3) with few granules, little AER, and abundant glycogen, characteristic of steer, dog, cat, and ferret.

The distribution and structure of cells in the tracheal epithelium of the mouse

The tracheal epithelium of the mouse is a single layer of columnar cells resting on a basement membrane. Many of the cell types resemble those of other species. However, goblet cells are rare and ciliated cells occur only in scattered patches. Submucosal glands are absent from all but the highest reaches of the airway. The major proportion of the epithelial cells are non-ciliated. These usually project into the lumen of the trachea. Large amounts of smooth endoplasmic reticulum and many secretory vesicles occur within the cytoplasm. Secretory activity of these cells may be either apocrine or merocrine and these cells may transform into other cell types. It is suggested that these non-ciliated cells are Clara cells and that the mouse tracheal epithelium may make a useful model for the study of this type of cell.

Sclerosing hemangioma of the lung: an ultrastructural study

A well-circumscribed nodular mass was excised from the lingula of the left lung of a 40-year-old-female. The lesion was discovered on routine chest x-ray examination and corresponded to a typical "sclerosing hemangioma" described by Liebow and Hubbell. Electron microscopic study revealed unequivocal epithelial cells in both the irregular spaces and the solid areas of the tumor; some of these cells were identical to granular pneumonocytes. The true vascular component was sparsely distributed. We concluded that "sclerosing hemangioma" was a misnomer because we were dealing with an essentially epithelial lesion.

Injury and repair of the lung: response to intravenous Freund's adjuvant

Tissue from the lungs of rabbits was examined at intervals up to 24 weeks after the animals had received a single intravenous injection of Freund's complete adjuvant. Though this is not a conventional method for damaging the peripheral lung, it had the advantage of producing multiple lesions in which most tissue components were altered for a prolonged period. White blood cells were present within the tissue and air spaces of these damaged areas. They persisted for 6 weeks in large numbers and gradually decreased over the next 12 weeks. There was replacement of type A by type B alveolar lining cells. Basement membranes were displaced and lost. Elastic and collagen fibres were distorted and destroyed. Blood vessels were occluded. Epithelioid cell and foreign body granulomas developed. Interalveolar septa disappeared, and air spaces were compressed. Despite all these changes the lungs regained near normal structure by 24 weeks after the initial injury. These results do not support the importance that has been placed on damage to various structural components of the lung as an explanation for chronic pulmonary disease. They do give some insight into the capacity of peripheral lung tissue for regenerationa following a single injury that induces a prolonged inflammatory response.

Peripheral pulmonary carcinoid tumors

The light microscopic and ultrastructural features of five asymptomatic peripheral carcinoids presented as distinct pulmonary solitary nodules are described. By conventional microscopy the tumors displayed a variety of histologic patterns, the most unusual one showing tumor cells embedded in a richly vascular hyalinized stroma and forming papillary structures or cystic spaces lined by low cuboidal cells which ultrastructurally bore a strong resemblance to intermediate or transitional forms between types I and II pneumocytes. A striking feature of these tumors was their rich vasculature associated with a marked perivascular sclerosis composed of basement membrane-like material and collagen fibrils most likely produced by the increased numbers of pericytes surrounding these sclerotic vessels. The clinical implications, biologic behavior, and association of these tumors with other pulmonary neoplasms are also discussed.

Enzyme histochemical observations of diffuse pulmonary fibrosis of rats experimentally induced by ionizing irradiation

The right lungs of Sprague-Dauley rats were irradiated with single doses of 1000 r, 2000 r or 3000 r to induce radiation pneumonitis and diffuse fibrosis, and the alkaline and acid phosphatase (A1-Pase, Ac-Pase) activities of the lungs were observed histochemically. Only the lungs irradiated with 3000 r steadily exhibited sequential changes leading to radiation pneumonitis and subsequent diffuse fibrosis, whereas the lungs irradiated with 2000 r developed only some degree of radiation pneumonitis. Alveolar capillary endothelia in the lesion of pulmonary fibrosis exhibited an intense activity of A1-Pase, while the endothelia in all the other experimental conditions did not show this activity. Alveolar macrophages increased their sizes and the activity of Ac-Pase after the irradiation. In the later stages, large foamy macrophages with thin diffuse deposits of the reaction products became predominant. These macrophages never exhibited A1-Pase activity. Type II alveolar epithelial cells showed an intense A1-Pase activity on their microvilli, and their Ac-Pase activity was negligible in non-irradiated lungs. Bizarre cells, appearing at the stage of radiation pneumonitis, showed an intense A1-Pase activity on their cell membranes and a weak and diffuse Ac-Pase activity in their cytoplasms. Septal cells achieved the A1-Pase activity 3 or 4 weeks after the irradiation when mast cells were not yet seen in the alveolar septa.