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Development of the Mucus-Secreting Elements in Human Lung

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... The submucosal glands appeared first in the proximal airways and progressed towards the periphery to reach the main carina 7 days later [11]. Authors [12] described the appearance of goblet cells by 13 weeks and in the proximal intrasegmental generation between 12-24 weeks, but their appearance in the distal generation was only after 32 weeks. Cilia were seen in the main bronchi at 10 weeks and in the most peripheral airways by 13 weeks [4,12] and by term the ciliated cells reached the terminal bronchiole. ...
... Authors [12] described the appearance of goblet cells by 13 weeks and in the proximal intrasegmental generation between 12-24 weeks, but their appearance in the distal generation was only after 32 weeks. Cilia were seen in the main bronchi at 10 weeks and in the most peripheral airways by 13 weeks [4,12] and by term the ciliated cells reached the terminal bronchiole. At 12 th week of gestation the epithelium in the adult bronchial tree was pseudostratified ciliated columnar with well developed basement membrance [4]. ...
... The serous glands started decreasing in number after 25 weeks of gestation and were not visible by 30 weeks. This was similar to the observation by few authors [12,10,11], but the author 12 observed mucous glands also. Some authors [11] observed male superiority in gland number but other studies described no sex differences in the gland density during development. ...
... gland formation, employed only light microscopy or whole tissue mounts (Engel, 1947; Bucher & Reid, 1961; Thurlbeck et al. 1961; Avery, 1964; Reid, 1967; Tos, 1966, 1968 a, b; De Haller, 1969). Other reports, dealing with the later development of the gland, were based exclusively on light microscopy (Reid, 1959; Sorokin, 1960; Krause & Leeson, 1973; Hofliger & Stunzi, 1975). None of the foregoing reports mentioned the presence of lumina in the bud or in the cyli ...
... In man the submucosal glands begin to develop in fetal life. Most investigators have described an initial proliferation of basal cells to form a solid protrusion or bud (Bucher & Reid, 1961; Thurlbeck, Benjamin & Reid, 1961; Tos, 1966 Tos, , 1968a). According to Tos (1966 Tos ( , 1968a) the bud is transformed, by cellular proliferation, into a solid cylinder which extends into the submucosa and a lumen is formed by a rearrangement of cells which takes place after accumulation of mucin in the centre of the cylinder. ...
... The combination of multiple staining of serial sections for light microscopy with the high resolution of scanning electron microscopy has yielded a considerable amount of new information about the development of the submucosal gland. Previous studies, from which it was concluded that the gland bud is the first sign of gland formation, employed only light microscopy or whole tissue mounts (Engel, 1947; Bucher & Reid, 1961; Thurlbeck et al. 1961; Avery, 1964; Reid, 1967; Tos, 1966 Tos, , 1968 De Haller, 1969). Other reports, dealing with the later development of the gland, were based exclusively on light microscopy (Reid, 1959; Sorokin, 1960; Krause & Leeson, 1973; Hofliger & Stunzi, 1975). ...
Article
The development of submucosal glands in the respiratory tract was studied by light and scanning electron microscopy in the rat, fetal dog and fetal sheep. From the results obtained the present concepts about the formation of these glands in man were questioned and an alternative hypothesis proposed. With scanning electron microscopy the development of the submucosal gland was seen to begin with an aggregation of low electron-responsive cells. Within such an aggregate, a pit, several microns in diameter, was formed. This pit was usually surrounded by medium electron-responsive cells possessing primary cilia in the rat, and by low electron-responsive cells in the fetal dog. In the rat medium electron-responsive cells appeared in other areas of the aggregate, preceded by apical elevations on the low electron-responsive cells. Further development in the rat led to a disappearance of the low electron-responsive cells, differentiation of ciliated and brush cells, and enlargement of the gland orifice. With light microscopy it was observed that the initial gland buds in both the rat and fetal sheep contained lumina several microns in size. These have not been reported by previous investigators. The bud extended into the underlying tissue and developed many simple tubules. The lumina of these tubules were consistently larger than the channel close to the epithelial surface. The cells of these tubules were also the first to differentiate into mucous and serous cells. The development of glands in the rat, in contrast to the sheep, began after birth. In the sheep, unlike the rat, the lumina of the developing glands were often filled with acidic mucosubstances, even though the cells of these glands did not stain for such material. Hence it is suggested that this material is derived from the mucin-containing cells of the surface epithelium and is carried into the interior of the developing gland by the fluid present in the respiratory tract during intrauterine life.
... GandBrenek [2] in 1941 reported that mucus glands first appeared in the lungs in the 4th month offoetallife. U.Bucher and L.Reid [3] observed that in foetus of13 weeks that glands could be detected in the bronchial wall and Lumen was detected in them at 14 weeks giving rise to primitive pattern. The acini at 24weeks were of mucus type. ...
... The acini at 24weeks were of mucus type. Serious cells made their appearance by 26 weeks, and ducts could also be visible by then.In the present study, at 16 weeks glands could be seen as cluster of cells emerging from basal epithelium which concurred to the findings of BritesG and Brenek [2] .As against Bucher's [3] observations the appearance of tubular glands with lumen was found latter at 18 weeks but ducts of the glands were seen as early as21 weeks By 23 weeks mucous acinar pattern was noted and by 24 weeks serous acini could be seen. ...
... The number and distribution of goblet cells present in these bronchial preparations may not be constant. An early report [28] showed that there are more goblet cells in tissues derived from proximal airways in which cartilage is present as compared with tissues obtained from distal parts of the human lung in which little or no cartilage is present. Thus, a quantification of goblet cell number in these preparations may be required in order to resolve the variation in the mucin determinations reported. ...
... Because the role of these cells in lungs of other primates, which can be studied experimentally, has not been pursued in detail, this area represents a potentially fruitful avenue of investigation. What little work has been done on the differentiation and regulation of development of this cefl type in human lung strongly suggests that the ceIl of origin is similar to that in other species and that the pattern of differentiation closely follows that which has been described for other species (74,75). The differentiation pattern is proximal to distal in the conducting airways of the human lung (74), and the bronchiolar cells are only partially differentiated at birth (75). ...
... 33 The nearly unanimous positivity of PB and fetal epithelium for EMA has not been reported previously but may correspond to the evolution of secretory goblet cells in the fetal bronchus at 13 weeks gestation. 6 Neurosecretory granules develop in fetal bronchial epithelium in the tenth week of pregnancy and commonly contain calcitonin, bombesin, and gastrin-releasing pep-t i d e . 9 " 1 2 ' 3 Although we did not perform immunostains for these specific neuropeptides, the expression of CHG (ten often) and NSE (nine often) in fetal lungs provides generic evidence for their neuroendocrine potentiality. ...
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Pulmonary blastomas are believed to be mixed epithelial and mesenchymal tumors that recapitulate the developing lung at 10-16 weeks gestation. The authors compared nine blastomas with ten fetal lungs in the pseudoglandular stage of development with a panel of antibodies to various lung antigens to evaluate immunophenotypic homology. Both blastomas and embryonal lungs showed expression of cytokeratin, epithelial membrane antigen, and carcinoembryonic antigen in their epithelial elements, and both contained scattered chromogranin-positive neuroendocrine cells. Rare surfactant-producing and Clara cell antigen-elaborating cells were identified in both groups. The mesenchymal components of blastomas and fetal lung showed smooth muscle, myofibroblastic, and blastematous differentiation. The blastematous elements demonstrated vimentin and keratin coexpression in four cases, providing some support for the contention that pluripotential blastema may give rise to the epithelial and mesenchymal elements of the distal lobule.
... Humans and other primates share a mixture of cell phenotypes not found in non-primate species [7]. In rhesus monkeys [16,17] epithelial differentiation (especially the secretory cell types and glandular elements) occurs postnatally for both rhesus monkeys [16] and humans [18,19]. The secretory cell population differentiates in a proximal-to-distal pattern, with nearly mature cells lining proximal airways and immature cells in more distal portions. ...
Article
A number of different species of nonhuman primates, primarily macaque monkeys such as the rhesus monkey, have been used as experimental models of allergic airways disease because (i) all the epithelial and mesenchymal components of the walls of intrapulmonary and extrapulmonary conducting airways that are altered in human asthmatics are present in the lungs of adult macaque monkeys; (ii) a significant portion of lung development (which includes differentiation of these components) occurs postnatally in macaque monkeys as it does in humans; (iii) the principal immunologic, pathophysiologic, and histopathologic features of human asthma are found in the chronic experimental disease in macaque monkeys; and (iv) the response to inhaled allergen challenge also shares the same features in human asthmatics and macaque monkeys with chronic allergic airways disease. Among these shared features are positive skin test to allergen, allergen-specific circulating IgE, specific airway responsiveness to allergen as indicated by pulmonary function tests during allergen challenge, shedding of airway epithelial cells into the airway exudate, increased levels of eosinophils and IgE-positivecells in the airway exudate, increased levels of mucins in the airway exudate, nonspecific airway hyperresponsiveness to methacholine or histamine challenge which is elevated by allergen challenge, mucous cell hyperplasia in conducting airways, increased basement membrane zone thickness, subepithelial fibrosis, and migratory leukocyte (eosinophils, lymphocytes, and dendritic cells) accumulation in the airway wall and lumen. The majority of these features are enhanced or altered by exposure to oxidant air pollutants, especially when exposure occurs during postnatal development.
... Humans and other primates share a mixture of cell phenotypes within the conducting airways not found in nonprimate species [Plopper et al., 1992]. The overall pattern of conducting airway epithelial differentiation [Jeffery & Reid, 1977;Plopper et al., 1986] and its maturation during the postnatal period are also similar in rhesus monkeys and humans [Bucher & Reid, 1961;Plopper et al., 1986;Thurlbeck et al., 1961]. Collectively, the nonhuman primate exhibits features of lung architecture and immunity that make it highly appropriate for elucidating novel therapeutic approaches to treat chronic lung disease in humans [Plopper & Hyde, 2008]. ...
Article
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Research involving nonhuman primates (NHPs) has played a vital role in many of the medical and scientific advances of the past century. NHPs are used because of their similarity to humans in physiology, neuroanatomy, reproduction, development, cognition, and social complexity-yet it is these very similarities that make the use of NHPs in biomedical research a considered decision. As primate researchers, we feel an obligation and responsibility to present the facts concerning why primates are used in various areas of biomedical research. Recent decisions in the United States, including the phasing out of chimpanzees in research by the National Institutes of Health and the pending closure of the New England Primate Research Center, illustrate to us the critical importance of conveying why continued research with primates is needed. Here, we review key areas in biomedicine where primate models have been, and continue to be, essential for advancing fundamental knowledge in biomedical and biological research. Am. J. Primatol. © 2014 Wiley Periodicals, Inc.
... It may be possible to image that this hydrostatic pressure can be a driving force which generates a self-similar branching growth. At the end of pseudoglandular stage, this hydrostatic pressure may disappear because of the beginning of the amniotic circulation, however, at the same time, excretion of bronchial glands begins (BUCHER and REID, 1961b), which may make a hydrostatic pressure gradient between proximal and distal parts of the airway tree. This new pressure gradient may change the growth mode from self-similar branching into surface increasing as shown in viscous fingering experiments (VIZECK, 1990). ...
Article
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In order to characterize quantitatively the development of the fetal lung, we applied the method of fractal geometry to 3D images of human fetal airways reconstructed from serial histologic sections. Four human fetal right lungs were subjected, whose cranio-rump lengths were 103 mm, 132 mm, 145 mm, and 190 mm, respectively. The former and the latter two corresponded to the pseudogladular stages and the canalicular stages, respectively. Fractal analysis with 3D box-counting method was made for four cubes with side 0.432 mm. The means of fractal dimensions of the former two were 1.7, that of the third was 2.1, and the last was non-fractal. These results show that a self-similar branching growth remains in the pseudoglandular stage and a surface-increasing growth occurs in the canalicular stage. This transition of growth modes may correspond to the functional difference between the airway completed in the pseudoglandular stage and the air space developing in the canalicular stage.
... Airway epithelial GFP expression of immunoperoxidase-stained lung sections was evaluated via light microscopy (Leica DMRD) at a final magnification between 10× and 40×. A radial grid [12] was used to calculate the percentage of GFP-positive epithelium as previously described [9]. The internal diameter of the airway was calculated using a standardized microscopy legend and digital measuring tools within the IPLab Scientific Image Processing software and airways were divided into small (80-100μm), medium (200-400μm) and large (500-1000μm) airways. ...
Article
Purpose: Successful in utero or perinatal gene therapy for congenital lung diseases, such as cystic fibrosis and surfactant protein deficiency, requires identifying clinically relevant viral vectors that efficiently transduce airway epithelial cells. The purpose of the current preclinical large animal study was to evaluate lung epithelium transduction of adeno-associated viral (AAV) vector serotypes following intratracheal delivery. Methods: Six different AAV vector serotypes (AAV1, AAV5, AAV6, AAV8, AAV9, and AAVrh10) expressing the green fluorescent protein (GFP) as the transgene were injected into the right upper lobe of perinatal sheep via bronchoscopy. At 1 week, samples were harvested, analyzed by fluorescent stereomicroscopy and immunohistochemistry, and quantified using a radial grid and quantitative real-time polymerase chain reaction (qPCR). Results: Fluorescent stereomicroscopy demonstrated GFP expression in the right upper lobe following injection of all AAV serotypes assessed except AAV5. Immunohistochemistry analysis confirmed GFP expression in small- and medium-sized airways following intratracheal injection of AAV1, 6, 8, 9, and rh10. However, only AAV8 and AAVrh10 resulted in transgene expression in large airways. These results were confirmed by qPCR, yet, after 40 cycles, AAV1 did not show GFP gene amplification. Conclusion: Adeno-associated viral vector serotypes 6, 8, 9, and rh10 demonstrated efficient GFP transgene expression at early time points, and AAV8 demonstrated efficient transduction of all airway sizes with high pulmonary GFP expression tested using qPCR.
... Lungs are major respiratory organs in the human body (Peter Williams, 1931) and they appear to be the lost among the large organs of human body about which a complete unquestioned embryological story has been built [2] . They develop as a diverticulum of the foregut during 3-4 weeks of gestational age (Keith L. Moore & Persaud, 1992) [3] . Lungs have a dual origin like Kidney, according to this larynx, trachea bronchi, bronchioles and part of respiratory bronchioles lined with cuboidal epithelium arises from foregut diverticulum and remaining respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli arise from adjacent mesenchyme (Rose, 1953) [4] . ...
Article
Histogenesis of Lung was studied using 40 normal human fetuses ranging from 8 to 26 weeks of gestation, under Light Microscopy after sectioning the lung and staining with Haematoxylin and Eosin. The Bronchial buds undergo repeated division to form bronchial tubes that differentiate into different parts of intrapulmonary bronchial tree. In earlier weeks of Gestation Mesenchymal tissue are more. Developing Duct lined by Cubical Epithelium, Acini and Blood vessels are visible. Developing Bronchus lined with Pseudo stratified columnar ciliated epithelium surrounded by hyaline cartilage. In High Power Bronchus surrounded by hyaline variety of cartilage which extend into lobar and segmented bronchus. But cartilage actually appear in 4 th Week. Terminal bronchiole is developing with acini packed with cells are seen. In high power bronchus is thick walled and bronchiole is thin walled lined by epithelium. Multiple acini packed with cells are seen. Ducts were having tubular lumen. Well-developed hyaline variety of cartilage surrounded by pieces of bronchus. Bronchiole was visible. Acini are packed with cells. In later weeks of Gestation Bronchus with cartilage on High power. Bronchioles and acini are visible. Mucosal glands are developed on bronchial wall. Bronchioles were having simple columnar non-ciliated epithelium infolding. Mucosal glands were developed on wall of bronchiole. Bronchiole and Bronchi are in between well-developed septae and blood vessels were seen to be developing. Lymphatic element normally developed. Bronchioles were having low columnar to cuboidal epithelium. Serous acini was increased. Respiratory bronchiole and alveoli were increased. Each terminal bronchi were dividing into respiratory bronchiole which were seen to be dividing into alveoli.
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Although ciliary function is important in protecting the lung from recurrent chest infection, absent ciliary function is not incompatible with a relatively normal existence in the antibiotic era.
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Baseline rates for secretion of mucous glycoprotein were similar similar (680--830 microgram/g tissue/24 hour) for cultured tracheal epithelium from newborns of 26--32 weeks' gestation, full term newborns, and older children. Addition of methacholine to culture medium augmented secretory rates of glycoprotein from all tissue sources 3--5 fold. The overall composition of secreted mucous glycoproteins changed little with increasing age. A trend toward less sulfation and toward increased sialic acid and fucose content was noted in secreted glycoproteins from explants of older subjects. Histochemical observations of stored glycoprotein in tracheal tissue, which was subsequently used for organ culture experiments, confirmed that a modest, but consistent sulfate to sialic acid shift occurs during early life. In contrast, baseline secretory rates for lysozyme from tracheal epithelium of preterm infants were one-half as large as rates from epithelium of full term babies and were refractory to cholinergic stimulation. Stimulation of lysozyme secretion by a cholinergic agonist was achieved in all cases by 40 weeks' gestation. We conclude that basal glycoprotein secretion and the mechanism for glycoprotein response to cholinergic stimulation have developed by the earliest age of viability, but that lysozyme secretion is deficient and is unresponsive to cholinergic stimulation in tracheal tissue from preterm newborns.
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The extracellular matrix has been shown to influence the differentiation of epithelial cells. To identify cues from the extracellular matrix controlling the differentiation of tracheal gland serous cells, we examined the effects of culturing these cells on various extracellular matrix proteins. Bovine tracheal gland (BTG) serous cells attached to Type IV collagen (COL IV), laminin (LM), and fibronectin (FN) in a concentration-dependent manner. Morphologic analysis showed that cells formed confluent monolayers on COL IV or LM, whereas on FN, cells formed birefringent spheres. Metabolic labeling experiments showed that [35S]methionine-labeled protein bands at 68, 105, and 120 kD were prominent when cells were grown on COL IV or LM, but were lost or reduced when the cells were grown on FN. COL IV also enhanced the expression of proteins at 14, 16.5, 18, and 21.5 kD. Attachment to all substrates was inhibited by an antibody directed against beta 1 integrins. This antibody precipitated several integrin heterodimers from a BTG cell membrane extract, caused partial retraction of cells from all substrates, and strongly suppressed the expression of COL IV- and LM-dependent proteins. Control experiments indicated that the latter did not require conspicuous changes in cell shape. These results show that some biochemical properties of serous cells are regulated by integrin-mediated effects of extracellular matrix proteins in vitro and suggest that similar regulation may occur during normal development and remodeling of the glands in vivo.
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The distribution of immunoreactive surfactant-associated protein B (IR-SP-B) was studied immunohistochemically in 120 subjects from 10 weeks of gestation to 7 postnatal months with a polyclonal antibody against human SP-B. Electron microscopy (EM) was done in 72 subjects to document the presence of Type II cells containing lamellar bodies. Fetuses of less than 18 weeks' gestation showed no immunostaining. Beginning at 18 weeks, non-mucous cells of tracheal glands immunostained in a few instances. Fetuses of 19 through 23 weeks showed progressive immunostaining of cells lining terminal airways. Infants 26-40 weeks who died with or without pulmonary pathology showed immunostaining of Type II cells and bronchioloalveolar (BA) portal cells of the respiratory bronchioles. In infants with hyaline membrane disease (HMD) who died less than 12 days after birth, occasional tracheal gland cells, BA portal cells, and mature and relining Type II cells immunostained. In bronchopulmonary dysplasia (BPD), BA portal cells, relining Type II cells, macrophages, and luminal material immunostained. Occasional tracheal and bronchial gland cells and Clara cells immunostained. The appearance of IR-SP-B at mid-gestation correlated with differentiation of Type II cells. There was good correlation of immunostaining with the presence of lamellar bodies on EM. Accelerated maturation of the lung was often associated with premature rupture of membranes (PROM).
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Twenty two mid-trimester human fetal tracheae were processed for light microscopy and scanning, transmission and freeze-fracture replication electron microscopy. The tracheal pseudostratified columnar epithelium was found to be composed of four cell types: ciliated in various stages of development, non-ciliated, basal and degenerating cells. The ratio of ciliated to non-ciliated cells was approximately one-to-one. The non-ciliated cells were of two morphological sub-types. Of these, the vast majority contained characteristic secretory granules, approximately 0.5 microns diameter, found in abundance within the apical region of the cell cytoplasm. The second sub-type of the non-ciliated cell, the well differentiated goblet cell, was observed very infrequently. The relatively large number of non-ciliated cells in the fetal tracheal epithelium suggests a transition stage to the adult where the ratio of ciliated to non-ciliated cells is near 5-to-1. The nature of the first type of the non-ciliated cells, which have not been studied in depth previously, remains obscure. Their probable secretory function is discussed and comparisons are made with previously reported cell types showing similar features, in fetal or adult material from the distal airways of animal and human tissues. Approximately 15 to 20% of the epithelial cells show signs of degeneration. The probable causes of this degenerative process are discussed. Other cell types such as brush cells, endocrine and wandering lymphocytes were not observed. Well-differentiated muco-serous glands were observed within the tela submucosa.
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We explored the usefulness of the postnatal ferret as a model for early developmental events in the large airways, using light and scanning electron microscopy. In the first 28 postnatal days, ferret tracheal surface epithelium and glands undergo dramatic growth and development. Tracheal surface area increases 8-fold. At birth, ciliated cells are sparse (9.4 +/- 1.2% of total epithelial cells). A significant increase in ciliated cells is observed at weekly intervals and by day 28 the ciliated cell is the predominant cell type (54.2 +/- 2.8% of total epithelial cells). Secretory cells decrease from 66.4 +/- 1.0% at birth to 22.2 +/- 2.8% of total epithelial cells. Histochemical staining of the granules of the epithelial secretory cells changes from predominantly non-acidic (staining with PAS but not Alcian blue) to predominantly acidic (staining also with Alcian blue). During the same time interval, tracheal glands develop from intraepithelial cellular aggregates devoid of secretory granules at birth into complex, submucosal tubuloacinar structures composed predominantly of cells containing non-acidic secretory granules at 28 days. Therefore, infant ferrets offer an opportunity to examine the structural and functional components of the mucociliary clearance mechanism at developmental stages which occur prenatally in many laboratory animals and in humans.
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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.
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We characterized the chemical composition of mucins secreted by ferret tracheal explants and the activities of key mucin glycosyltransferases in ferret tracheal epithelium during a period of rapid postnatal maturation of the mucin-secreting structures. Ferret tracheal explants secrete three major groups of high molecular weight glycoconjugates: (1) those susceptible to bovine testicular hyaluronidase; (2) those resistant to hyaluronidase and exhibiting high density (p greater than or equal to 1.60 g/mL); and (3) those resistant to hyaluronidase and exhibiting low density (1.45 less than or equal to p less than 1.60 g/mL). The hyaluronidase-resistant, low-density glycoconjugates have typical mucin properties and constitute 36% of total glycoconjugates released in newborns but only 8% in adult ferrets. Mucin secretory rate per unit surface area of trachea progressively decreases with age. Mucin amino acid and total carbohydrate contents do not vary; however, the sialic acid content increases, and fucose content as well as blood group A activity of the mucins decreases with age. Four glycosyltransferases involved in mucin biosynthesis [Gal beta 3GalNAc:(GlcNAc-GalNAc)beta 6 N-acetylglucosaminyl-, GalNAc:beta 3 galactosyl-, Gal:alpha 2 fucosyl-, and GalNAc alpha 2----6 neuraminyltransferase] are present in tracheal epithelium of ferrets at all ages. Activities of all but the neuraminyltransferase decrease with age. The relatively greater neuraminyltransferase activity is consistent with increased incorporation of sialic acid into secreted mucins over the same age span. Conversely, diminution of fucosyltransferase relative to galactosyltransferase activity may contribute to the lower fucose content and lower blood group A activity of mucins secreted by mature ferret tracheas.(ABSTRACT TRUNCATED AT 250 WORDS)
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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.
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Segmental imaging studies of the respiratory epithelium from human embryos and fetuses of normal karyotype have demonstrated that ciliogenesis and ciliation of the respiratory epithelium starts at 7 weeks of gestation. Ciliated cell differentiation follows a pre-determined pattern of distribution. It starts exclusively in the upper segment of the membranous trachea and spreads distally. Ciliation of the carinal angle takes place at 8 weeks of gestation. Three patterns of basal body formation were identified. The various morphological features encountered are described and compared with those observed in cases of Immotile Cilia Syndrome and other pathological conditions. Ciliation of the respiratory epithelium in the cartilaginous trachea does not take place until after the 12th week of gestation. The morphological findings identified in our case material are in agreement with those observed in the developing respiratory epithelium of other higher mammals.
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Ultrastructural features of the developing, surface epithelium of ferrets from birth to 28 days of age were characterized. Progressive ciliogenesis in vivo was observed, beginning with cells covering the membranous portion of the trachea. Emerging cilia appeared in ultrathin sections and by scanning electron microscopy at sites correlating with accumulation of integral membrane particles seen in freeze-fracture preparations. Two patterns of ciliogenesis were observed: (1) the random emergence of cilia over the apical cell surface, and (2) initial emergence of cilia at the peripheral boundary of the luminal border of individual cells. Novel, ringlike structures were observed on the surfaces of nonciliated cells at all ages studied. Active ciliogenesis as well as the appearance of ring structures also were documented in the superficial epithelium from 1- to 5-day-old animals maintained in vitro for up to 4 days.
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Asthma is a worldwide health problem that affects 300 million people, as estimated by the World Health Organization. A key question in light of this statistic is: "what is the most appropriate laboratory animal model for human asthma?" The present authors used stereological methods to assess airways in adults and during post-natal development, and their response to inhaled allergens to compare rodents and nonhuman primates to responses in humans. An epithelial–mesenchymal trophic unit was defined in which all of the compartments interact with each other. Asthma manifests itself by altering not only the epithelial compartment but also other compartments (e.g. interstitial, vascular, immunological and nervous). All of these compartments show significant alteration in an airway generation-specific manner in rhesus monkeys but are limited to the proximal airways in mice. The rhesus monkey model shares many of the key features of human allergic asthma including the following: 1) allergen-specific immunoglobulin (Ig)E and skin-test positivity; 2) eosinophils and IgE+ cells in airways; 3) a T-helper type 2 cytokine profile in airways; 4) mucus cell hyperplasia; 5) subepithelial fibrosis; 6) basement membrane thickening; and 7) persistent baseline hyperreactivity to histamine or methacholine. In conclusion, the unique responses to inhaled allergens shown in rhesus monkeys make it the most appropriate animal model of human asthma.
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Published and original data on human lung morphogenesis during prenatal development are reviewed. Morphofunctional description of the lung at various phases of prenatal morphogenesis is given. Differentiation of various lung structures, surfactant system, development of pulmonary fluid, and the onset of breathing movements of the fetus are considered in chronological order. The critical periods when the fetal respiratory organs are most sensitive to unfavorable factors are considered. Morphofunctional tests for lung maturity applicable for predicting lung pathology of human fetus are described.
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Secretory cells in submucosal glands (SMGs) secrete antibacterial proteins and mucin glycoproteins into the apical lumen of the respiratory tract, and these are critical for innate immune mucosal integrity. Glandular hyperplasia is manifested in diseases with obstructive respiratory pathologies associated with mucous hypersecretion, and is predominant in the sinus mucosa of patients with chronic rhinosinusitis (CRS), cystic fibrosis (CF), and clinical symptoms of CRS. To gain insights into the molecular basis of SMG hyperplasia in CRS, gene expression microarray analyses were performed to identify the differences in global and specific gene expression in the sinus mucosa of control, CRS, and CRS/CF patients. A marked up-regulation of 11 glandular-associated genes in CRS and CRS/CF sinus mucosa was evident. The RNA and protein expressions of the four most highly up-regulated genes (DSG3, KRT14, PTHLH, and OTX2) were evaluated. An increased expression of DSG3, KRT14, and PTHLH was demonstrated at the mRNA and protein levels in both CRS and CRS/CF sinus mucosa, whereas the increased expression of OTX2 was evident only for CRS/CF sinus mucosa, implicating OTX2 as a CF-specific gene. Immunofluorescence analysis localized DSG3, PTHLH, and OTX2 to serous cells, and KRT14 to myoepithelial cells, in SMGs. Because glandular hyperplasia is a central histologic feature of CRS, the identification of overexpressed glandular genes in the sinus mucosa lays the groundwork for future studies of glandular hyperplasia, and may ultimately lead to the development of novel treatments for mucous hypersecretion in patients with CRS.
Article
The developing mammalian lung is challenged by the requisite need for a gas-exchange surface area extensive enough to meet the needs of an organism’s oxygen consumption and CO2removal. This is achieved first by the transformation of the primitive endoderm into the 105conducting and 107respiratory airways by iterative branching morphogenesis, followed by the extensive subdivision and successive maturation of the terminal airways into alveoli: the hundreds of millions of thin spherical cavities which facilitate gas exchange between the airways and the vascular system. Since the process of alveolar formation (alveolarization) occurs largely after birth, premature infants are at increased susceptibility to respiratory distress, often necessitating prolonged assisted ventilation. Despite major advances in the management of perinatal infant care, including improved mechanical ventilation modalities, prenatal steroid administration, and surfactant therapy, many such infants do not undergo normal alveolar development, resulting in the chronic lung disease, bronchopulmonary dysplasia (BPD). An appreciation of the complex cell and molecular interactions which govern normal lung morphogenesis is essential for understanding the aetiology of—and advancing treatments for—pulmonary diseases such as BPD.
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Two levels of epithelial progenitors are involved in lung morphogenesis: multipotent undifferentiated cells (lung primordial cells) and pluripotent regiospecific (bronchial, bronchiolar, and alveolar) stem cells. The trachea and bronchi are lined by pseudostratified columnar epithelium (ciliated, mucous and basal cells). The bronchioles are lined by simple columnar epithelium (ciliated and Clara cells). Pulmonary neuroendocrine cells (PNECs) are also present. The alveolar ducts and sacs and the alveolar zone of the respiratory bronchioles are lined by cuboid alveolar type II cells and squamous alveolar type I cells. These regions all originate from evagination of ventral foregut endoderm containing lung primordial cells, into the surrounding visceral mesoderm with budding and branching, with their specific determination established as early as the pseudoglandular period of lung development. Tracheobronchial glands arise from specialized outpockets of basally situated surface cells. Bronchial stem cells are identified as label-retaining cells after pulsing with 3H thymidine or BrdU and can be found after injury in tracheal gland ducts as well as systematically distributed along the surface of the trachea and bronchi. In vitro and in vivo studies suggest that basal cells and columnar cells retain plasticity to regenerate a complete mucociliary epithelium. Clara cells represent the principal progenitor pool of the bronchiolar epithelium and are an example of a transit-amplifying cell population. True stem cells may proliferate after injury and depletion of the Clara cell population and are located in association with PNECs and also at the junction between the bronchioli and alveolar ducts. The stem cell for the alveolar epithelium is the early embryonic type II cell, which can give rise to progeny that differentiate to type I or type II cells. The preferential distribution of type II cell clusters in the adult lung supports the existence of type II stem cell niches. According to the current theory, the regiospecific stem cells are the most relevant targets for transformation and thus the source of lung cancer. The mixed phenotype of many lung carcinomas and studies of bronchial carcinogenesis suggest origin from a common un- or retrodifferentiated stem cell. Prospective treatments for common lung diseases, transplantation, gene transfer, and tumor therapy would all be advanced by a greater understanding of lung stem cells.
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Fehlbildungen der Lunge sind gemessen an der großen Zahl erworbener pulmonaler Erkrankungen selten. In einem Obduktionsgut können bei etwa jedem 7. Kind (d.h. Totgeborene ab 28. SSW und Lebendgeborene bis zum vollendeten 14. Lebensjahr) mit Mißbildungen auch Fehlbildungen der Lunge gefunden werden. Zschoch u. Mahnke (1968) gaben - bezogen auf annähernd 12000 Kindersektionen - eine Frequenz von Mißbildungen der Atmungsorgane von 2,2% an.
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Die gemeinsame primäre Anlage von Larynx, Trachea und Lunge wird bei menschlichen Embryonen am 22. Tag post ovulationem von einer entodermalen Furche am ventralen Boden des distalen (kaudalen) Schlundes, der sog. Lungenrinne gebildet (Corner 1929; Heuser 1930; Streiter 1951). Noch in der 4. Embryonalwoche sproßt das Epithel röhrenförmig aus. Der Epithelschlauch wächst als primitive Trachea während der 5. Woche in kaudaler Richtung parallel zum primitiven Ösophagus. Gegen Ende des 1. Entwicklungsmonats ist bei Embryonen mit einer Scheitel-Steiß-Länge (SSL) von 4 mm das distale Ende der primitiven Trachea paarig knospenartig aufgetrieben (Heiss 1919). Diese epithelialen Ausbuchtungen sind die primären Bronchusknospen, im allgemeinen als Lungenknospen bezeichnet (Abb. 1). Sie weisen schon mit der Anlage eine Asymmetrie zugunsten der rechten Seite auf (His 1887; Girgis 1926; Atwell 1930; Streeter 1945; Smith 1957). Der größere rechte primäre Bronchus wachst dorso-kaudal, der linke zunächst fast quer. In der 5. Entwicklungswoche entspringen aus dem rechten Stammbronchus 2 Knospen und aus dem linken nur 1 Knospe (Heiss 1919; Streeter 1948), sodaß bei Embryonen mit einer SSL von 7 mm die Lappenbronchien angelegt sind (Abb. 2). In diesem Stadium wird von Lappenknospen oder Lappensäckchen gesprochen. Die Segmentbronchien werden in der 6. Woche (Wells u. Boyden 1954) und die Subsegmentbronchien in der 7.
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Knowledge of bronchial development is important to understanding many pathological processes of the adult organ. Development has been studied extensively in the human and the following brief summary highlights some of the key events.
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The olfactory mucosa of vertebrates contains secretory elements that produce a layer of mucus that covers the surface of the olfactory epithelium (Graziadei 1971; Yamamoto 1982). The secretions presumably play a role in olfactory function by (a) providing the ionic and macromolecular environment in which odorants interact with their receptor sites on the olfactory receptor neurons (Bannister 1974; TV Cetchell and ML Getchell 1977), (b) affecting access of odorants to the epithelial surface (Mozell 1971; Bostock 1974) and (c) facilitating odorant removal (Hornung and Mozell 1981; TV Getchell et al. 1985).
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Tracheobronchial airway development begins prenatally and continues for an extended period of postnatal life. In adults, the organization of tracheobronchial airway epithelium is highly complex and variable both within the airway tree of a single species and in the same airway generation in different species, including the composition of the cell populations, their secrectory products, and their metabolic capabilities. When the same differentiated cell phenotypes are present in many different airway generations, their relative abundance varies widely. Differentiation during pre- and postnatal development is a proximal and distal phenomenon, with each phenotype differentiating over a different period of time depending on the airway microenvironment in which it is differentiating. This developmental process balances between the active proliferation necessary for airway growth and the differentiated functions required for healthy airway function in neonates. All of these processes are highly susceptible to disruption by toxicants that target the respiratory system.
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Viral vector-mediated gene transfer to the postnatal respiratory epithelium has, in general, been of low efficiency due to physical and immunological barriers, non-apical location of cellular receptors critical for viral uptake and limited transduction of resident stem/progenitor cells. These obstacles may be overcome using a prenatal strategy. In this study, HIV-1-based lentiviral vectors (LVs) pseudotyped with the envelope glycoproteins of Jaagsiekte sheep retrovirus (JSRV-LV), baculovirus GP64 (GP64-LV), Ebola Zaire-LV or vesicular stomatitis virus (VSVg-LV) and the adeno-associated virus-2/6.2 (AAV2/6.2) were compared for in utero transfer of a green fluorescent protein (GFP) reporter gene to ovine lung epithelium between days 65 and 78 of gestation. GFP expression was examined on day 85 or 136 of gestation (term is ∼145 days). The percentage of the respiratory epithelial cells expressing GFP in fetal sheep that received the JSRV-LV (3.18 × 10(8)-6.85 × 10(9) viral particles per fetus) was 24.6±0.9% at 3 weeks postinjection (day 85) and 29.9±4.8% at 10 weeks postinjection (day 136). Expression was limited to the surface epithelium lining fetal airways <100 μm internal diameter. Fetal airways were amenable to VSVg-LV transduction, although the percentage of epithelial expression was low (6.6±0.6%) at 1 week postinjection. GP64-LV, Ebola Zaire-LV and AAV2/6.2 failed to transduce the fetal ovine lung under these conditions. These data demonstrate that prenatal lung gene transfer with LV engineered to target apical surface receptors can provide sustained and high levels of transgene expression and support the therapeutic potential of prenatal gene transfer for the treatment of congenital lung diseases.
Article
The tracheobronchial tree begins to form during the fourth week of development through a series of dichotomic divisions of an entoblastic evagination. The morphogenesis and maturation of the respiratory tract depend both on the nature of the extracellular matrix which facilitates cell migration and on epithelialmesenchymal interactions which induce the proliferation and differentiation of epithelial cells. The study of the plasticity and the phenotypic modifications of secretory cells during both development and inflammatory remodeling of the tracheobronchial mucosa suggests an important role for secretory cells during ciliogenesis and repair.
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gas exchange;oxygen;lung growth;alveolar epithelial cells;postnatal development
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The sections in this article are:
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Experimental animal models have contributed to our understanding of the aetiology, pathogenesis and potential for therapy of many human diseases. Several human airway conditions, such as chronic bronchitis, asthma, cystic fibrosis and bronchiectasis have mucus-hypersecretion as a common feature [1-15]. The major sources of airway mucus are (1) luminal mucosubstance present on surface epithelium whose cellular source is presently unclear [16-19], (2) the surface epithelial mucous cell, also called the “goblet cell”, and (3) the “mucous cells” of the submucosal glands [20-26]. The serous cells of the submucosal glands may also contribute to the glycoprotein component of mucus and in addition may secrete glycosaminoglycan, a small molecular weight antiprotease [27] and the secretory piece component of IgA. As we shall see, there is increasing evidence that other cell types including the ciliated cell may also contribute to the pool of airway mucus.
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The entire surface of the airways is lined with epithelia of various forms (Harkema et al., 1991). Almost all are ciliated, and their role in mucociliary clearance has long been appreciated; however, the development of high-quality primary cultures and cell lines (Gruenert et al., 1995) has revealed many new functions. It is now realized, for instance, that airway epithelia are capable of affecting rapid changes in the depth and composition of the thin film of liquid that lines the airways. In addition, production of a wide range of macromolecules allows the epithelium to signal to underlying cells and tissues (e.g., smooth muscle, fibroblasts and leukocytes). It has been increasingly appreciated that alterations in the function of airway epithelium are central to the pathology of cystic fibrosis, asthma, and chronic bronchitis.
Article
Anatomical and physiologic evidence for pulmonary problems most prevalent in the aged is reviewed. The lungs begin to age in utero. True aging must be distinguished from chronic environmental damage. The lung is essentially an “outdoor organ” vulnerable to the environment. Biochemically, aging is caused by both endogenous and exogenous free radical injury, inflicted by an over-balance of oxidants with respect to anti-oxidants. Glucose may also play a role in the aging process, by binding non-enzymatically with proteins in lung to form irreversible advanced glycosylation end-products. Physiological age-related lung changes result in: decreasing lung volumes and maximal rates of airflow; decreasing forced vital capacity (accelerated in smokers); hyperinflation (confirmed by the increased RV/TLC ratio); increased closing volume or capacity; decreased diffusing capacity; and hyporesponsive respiratory center and peripheral chemoreceptors. The clinical consequence of these age-related changes in the lung is disease in the elderly. Lung cancer and emphysema also occur as a result of chronic exposure to cigarette smoke and other environmental pollutants. Age-dependent pulmonary changes combine with non-pulmonary age-prevalent changes to cause additional diseases. Bacterial pneumonias, aspiration pneumonia, tuberculosis, and pulmonary thromboembolism are examples of these.
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The epidemiologic link between air pollutant exposure and asthma has been supported by experimental findings, but the mechanisms are not understood. In this study, we evaluated the impact of combined ozone and house dust mite (HDM) exposure on the immunophenotype of peripheral blood and airway lymphocytes from rhesus macaque monkeys during the postnatal period of development. Starting at 30 days of age, monkeys were exposed to 11 cycles of filtered air, ozone, HDM aerosol, or ozone + HDM aerosol. Each cycle consisted of ozone delivered at 0.5 ppm for 5 days (8 h/day), followed by 9 days of filtered air; animals received HDM aerosol during the last 3 days of each ozone exposure period. Between 2–3 months of age, animals co-exposed to ozone + HDM exhibited a decline in total circulating leukocyte numbers and increased total circulating lymphocyte frequency. At 3 months of age, blood CD4+/CD25+ lymphocytes were increased with ozone + HDM. At 6 months of age, CD4+/CD25+ and CD8+/CD25+ lymphocyte populations increased in both blood and lavage of ozone + HDM animals. Overall volume of CD25+ cells within airway mucosa increased with HDM exposure. Ozone did not have an additive effect on volume of mucosal CD25+ cells in HDM-exposed animals, but did alter the anatomical distribution of this cell type throughout the proximal and distal airways. We conclude that a window of postnatal development is sensitive to air pollutant and allergen exposure, resulting in immunomodulation of peripheral blood and airway lymphocyte frequency and trafficking.
Article
The submucosal glands are thought to be the primary source of the mucus overlying the primate trachea and conducting airways. This study characterizes the development of submucosal glands in the trachea of the rhesus monkey. Tracheas from 46 age-dated fetal, 8 postnatal and 3 adult rhesus were fixed in glutaraldehyde/paraformaldehyde and slices processed for electron microscopy. The earliest (70 days gestational age (DGA)) indication of gland development was the projection of a group of closely packed electron lucent cells with few organelles and small pockets of glycogen into the submucosa. This configuration was observed up to 110 DGA. In fetuses younger than 87 DGA it was present almost exclusively over cartilaginous areas. Between 80 and 140 DGA, a cylinder of electron lucent cells projected into the submucosal connective tissue perpendicular to the surface. In fetuses younger than 100 DGA, it was restricted to cartilaginous areas. By 90 DGA, some glycogen containing cells in proximal regions contained apical cored granules. By 106 DGA, cells in proximal areas contained apical electron lucent granules. More distal cells had abundant GER and electron dense granules. The most distal cells resembled the undifferentiated cells at younger ages. Ciliated cells were present in the most proximal portions of glands at 120 DGA. This glandular organization was found in older animals, including adults, with the following changes: abundance of proximal cells with electron lucent granules increased; abundance of distal cells with electron dense granules increased; and abundance of distal cells with abundant glycogen and few organelles decreased. We conclude that submucosal gland development in the rhesus monkey: is primarily a prenatal process; occurs first over cartilage; continues into the postnatal period; and involves secretory cell maturation in a proximal to distal sequence with mucous cells differentiating before serous cells.
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