Complex carbohydrates of rat tracheobronchial surface epithelium visualized ultrastructurally

Airway wall remodeling in young and adult rats with experimentally provoked bronchial asthma

BACKGROUND

Airway wall remodeling is a typical finding in patients suffering from bronchial asthma. While morphological changes have been thoroughly described in adults, less is known about such changes in children because of the limited accessibility of relevant material. To overcome this constraint, animal asthma models may be used instead of human specimens. This study examined rats with artificially stimulated chronic asthma-like symptoms.

METHODS

Brown Norway rats of two age categories (young and adult) were sensitized by ovalbumin (OA), and their intrapulmonary airways (IA) were studied using morphometric and histochemical methods.

RESULTS

OA administration induced a significant increase in lung resistance in young animals but not in adults. The total IA wall area was significantly increased in both young and adult OA rats. In young animals, thickening of the adventitia played a more crucial role in this increase than it did in adults, in which the mucosa and the submucosa participated to a higher degree. The IA walls of young OA rats had significantly higher levels of infiltrating eosinophils than those of adult OA animals. The multiplication of goblet cells was more pronounced in adult rats, which was associated with a tendency to produce a higher proportion of acidic glycoconjugates.

CONCLUSIONS

OA stimulation affected the IA of young rats differently than those of adult animals. Changes in the outer IA layer of young rats can be triggered by activated eosinophils; however, stimulated airway epithelium can be a source of factors that influence the inner IA layers in adult rats.

Cyclosporin A reduces airway mucus secretion and mucociliary clearance in rats

PURPOSE

To assay the effects of cyclosporin A on mucus secretion from goblet cells and on mucociliary transport in situ in rats.

METHODS

Twenty-one male Wistar rats were assigned to 3 groups: control (n = 5), saline (n = 8), and cyclosporin A (n = 8). After 30 days of drug therapy, the rats were killed, and the lungs were removed from the thoracic cavity. Mucus samples were collected, and the transport rate was evaluated in vitro using a bullfrog palate model. Mucociliary transport was timed in situ by direct view of particles trapped on the mucus moving across the respiratory tract. Finally, the amount of stored mucins in the goblet cells of the respiratory epithelium was measured.

RESULTS

Drug dosage measurements showed that cyclosporine blood concentration at the moment the rats were killed was 1246.57 +/- 563.88 ng/mL. The in vitro transport rate was significantly lower (P < .001) in the cyclosporin A-treated group. Also, the in-situ mucociliary transport rate was decreased in all cyclosporin A-treated animals when compared to the saline group (P = .02). Mucus quantity measurements showed a significant decrease on both acid (P = .01) and neutral (P = .02) mucus production from goblet cells in the animals submitted to cyclosporin A therapy. The correlation between the percentage of total mucus and in vitro transport rate was positive and significant (r = 0.706, P < .001), as was the correlation between the percentage of total mucus and the in situ mucociliary transport rate (r = 0.688, P = .001).

CONCLUSION

This study shows that cyclosporin A plays an important role in the impairment of the mucociliary clearance in rats by reducing both acid and neutral mucus production from goblet cells and causing a decrease in the mucociliary transport velocity.

Distribution of glycoconjugates during cochlea development in mice: light microscopic lectin study

During development, different epithelial cells in the mouse cochlea express different cell surface glycoconjugates, which may reflect membrane specialization. Some of the lectins tested in this study (SBA, succ-WGA, and PSA) labeled the sensory cells of the cochlea around birth. Other lectins (WGA, Con A, RCA-II, and PHA-E) labeled surfaces of the sensory cells, particularly the stereocilia, from early stages of development (gestation day (GD) 16) through 21 days after birth. These may be adhesion molecules needed to attach the newly forming tectorial membrane (TM) to the stereocilia. Lectin staining of the developing TM revealed that the substructures of the TM are biochemically distinct. Lectin staining also showed the temporal sequence of the expression of cytoplasmic glycoconjugates of the cochlear epithelium during development. Biochemical changes during development are probably the result of different cells being involved in the production of glycoconjugates, and may have functional significance, specifically with regard to the expression of adhesion and/or signaling molecules.

Glycocalyx of lung epithelial cells

Due to their diversity and external location on cell membranes, glycans, as glycocalyx components, are key elements in eukaryotic cell, tissue, and organ homeostasis. Although information on the lung glycocalyx is scarce, this article aims to review, discuss, and summarize what is known about bronchoalveolar glycocalyx composition, mainly the sialic acids. It was deemed relevant, however, to make a brief introductory overview of the cell glycocalyx and its particular development in epithelial cells. After that, follows a summary of the evolution of the knowledge regarding the bronchoalveolar glycocalyx composition throughout the years, particularly its morphological features. Since sialic acids are located terminally on the bronchoalveolar lining cells' glycocalyx and play crucial roles, we focused mainly on the existing lung histochemical and biochemical data of these sugar residues, as well as their evolution throughout lung development. The functions of the lung glycocalyx sialic acids are discussed and interpretations of their roles analyzed, including those related to the negative overall superficial shield provided by these molecules. The increasing presence of these sugar residues throughout postnatal lung development should be regarded as pivotal in the development and maintenance of a dynamic bronchoalveolar architecture, supporting the normal histophysiology of the respiratory system. The case for a profound knowledge of lung glycocalyx--given its potential to provide answers to serious clinical problems--is made with particular reference to cystic fibrosis. Finally, concluding remarks and perspectives for future research in this field are put forth.

Apical barriers to airway epithelial cell gene transfer with amphotropic retroviral vectors

Gene transfer to airway epithelia with amphotropic pseudotyped retroviral vectors is inefficient following apical vector application. To better understand this inefficiency, we localized the expression of Pit2, the amphotropic receptor, in polarized human airway epithelia. Pit2 was expressed on both the apical and basolateral surfaces of the cells, suggesting that factors other than receptor abundance may limit apical gene transfer efficiency. Binding studies performed with radiolabeled amphotropic MuLV suggested that the apically applied virus binds to Pit2. Hypothetical barriers to retroviral gene transfer include the apical glycocalyx and other secreted products of epithelia. In this study, we demonstrated that sialic acid, keratan sulfate and collagen type V are present on the apical surface of well-differentiated human airway epithelia. While enzyme treatment reduced the abundance of these components, the treatment also decreased the transepithelial resistance to approximately 35% of the controls, suggesting that the epithelial integrity was impaired. To attain an airway epithelial culture with a modified apical surface and intact epithelial integrity, we utilized 100 mM 2-deoxy-D-glucose, a glycosylation inhibitor, to prevent the glycocalyx from reforming following enzyme treatment. This approach allowed the resistance, but not the apical glycocalyx to recover. Despite this physical modification of the cell surface, the amphotropic retroviral vector failed to transduce airway epithelia following apical application. These results suggest that factors other than apical receptor abundance and the glycocalyx inhibit amphotropic retroviral gene transfer in human airway epithelia.

Eosinophilic granulated cells comprising a tumor in a Fischer rat

A systemic tumor developed in multiple organs, including spleen, bone marrow, lymph nodes, liver, ovaries, and thoracic and lumbar vertebrae, of a female F344Du/Crj rat. The tumor was composed of round to indented mononuclear cells containing abundant large eosinophilic granules in the cytoplasm. The peripheral blood smear revealed that the large granules in the cytoplasm of the tumor cells were stained basophilic with Giemsa, suggesting a basophil or mast cell origin. However, these granules did not show metachromasia with toluidine blue and were stained blue to dark blue with phosphotungstic acid hematoxylin. Cellular morphology and characteristics in the specific stains of tumor cells suggested the development of a tumor of globule leukocytes in a F344Du/Crj rat.

Microtiter plate adherence assay and receptor analogs for Mycoplasma hyopneumoniae

A microtiter plate adherence assay for Mycoplasma hyopneumoniae was established by use of purified swine tracheal cilia which contained receptors for the mycoplasmas. M. hyopneumoniae bound specifically to plates coated with solubilized cilia. The binding was dependent on both the concentration of cilia and the number of mycoplasmas. Dextran sulfate, heparin, chondroitin sulfate, laminin, mucin, and fucoidan significantly inhibited the binding of the mycoplasmas. The six inhibitors also disrupted the adherence of the mycoplasmas to intact ciliated cells. Preincubation with either mycoplasmas or cilia indicated that heparin, mucin, fucoidan, and chondroitin sulfate interacted with the adhesive molecules on the surface of the mycoplasmas, while laminin blocked the receptors in cilia. The basis for the inhibition induced by dextran sulfate was unknown. Treatment of cilia with neuraminidase appeared to promote adherence of the mycoplasmas, whereas treatment of cilia with sodium metaperiodate decreased binding. These results indicate that receptors for M. hyopneumoniae in the ciliated epithelium of the respiratory tract of pigs are glycoconjugate in nature.

Phenotypic marker expression during fetal and neonatal differentiation of rat tracheal epithelial cells

The expression of phenotypic markers was examined during fetal and neonatal differentiation of rat tracheal epithelial (RTE) cells. The rat counterpart of human keratin 18 was predominantly found in columnar cells in the adult trachea. It was detected in the primordial tracheal epithelium first seen on gestational day (GD) 12 (term = 21.5 days). Staining intensity gradually increased, and by GD 17 it was principally localized to the apical portion of the epithelium. The rat counterpart of human keratin 19 was barely detectable in the trachea on GD 13 but became abundant in almost all RTE cells on and after GD 19. Morphologically and immunocytochemically identifiable secretory and ciliated cells appeared on GD 18. Ciliated cell number slowly rose while secretory cells increased dramatically on GD 19 through postnatal day 1. The secretory granule antigens detected by monoclonal antibodies RTE 9 and 11 were rare in the adult trachea but were highly expressed in virtually all of the perinatal secretory cells. In contrast, the epitope detected by monoclonal antibody RTE 12, which was present in all adult tracheal surface secretory cells, did not appear until postnatal day 1 and slowly increased. These results demonstrate marked shifts in the biochemical composition of secretory cells during development and postnatal maturation. For the above-mentioned molecules, a similar expression pattern was observed during epithelial regeneration in tracheal grafts (Am. J. Respir. Cell Mol. Biol. 1992; 7:30-41). Pseudo-stratification of the epithelium and basal cells was first observed on GD 20. Keratin 14, which is confined to basal cells in the normal adult trachea, was not present in the nascent basal cells but appeared after postnatal day 1. In contrast to the present results, during epithelial regeneration in tracheal grafts keratin 14 appeared before markers of highly differentiated secretory or ciliated cells. Thus, the biochemical sequence of cellular differentiation during regeneration did not precisely recapitulate development.

The effect of human eosinophil granule major basic protein on airway responsiveness in the rat in vivo. A comparison with polycations

Major basic protein (MBP) is a highly cationic protein found in the granules of eosinophils. It has been postulated that MBP may participate in the pathogenesis of airway hyperresponsiveness exhibited by asthmatic patients. Accordingly, we used a rat model to investigate the effect of human MBP instillation on airway responsiveness and the possible role of cationic charge in the determination of this effect. Dose-response characteristics to inhaled methacholine (MDRC) were determined at baseline, and the animals were allowed to recover. Then animals in the experimental group received 100 micrograms of purified human MBP via direct instillation into the trachea. One hour after instillation, the MDRC were again assessed. Control animals received (in lieu of MBP) buffer from the void volume pool of the same chromatography column used to purify the MBP. One hour after instillation of MBP there was a significant increase in airway responsiveness to inhaled methacholine, whereas control animals exhibited no increase in airway responsiveness. Some animals from the MBP group were restudied 48 h after MBP instillation, by which time airway responsiveness had returned to baseline level. The effect of the polycations poly-L-arginine and poly-L-lysine on airway responsiveness was also examined. As with MBP, airway responsiveness to inhaled methacholine increased 1 h after the instillation of either polycation. In addition, acetylation of the charged groups on poly-L-lysine resulted in a loss of this effect. Histologic examination of the airways failed to reveal airway epithelial shedding 1 h after MBP or polycation instillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Histochemical study of glycoconjugates in the nasal mucosa of the rat and guinea pig

A histochemical study was carried out on the glycoconjugates of the nasal mucosa of rat and guinea pig using conventional techniques and peroxidase-labelled lectins. Both the respiratory mucosa and neuroepithelium were studied. Sulphate and sialic acid groups were found in the mucous layer of the neuroepithelia, Bowman's glands and goblet cells. In contrast, the nasal glands did not possess these groups, and only a few showed neutral mucins. Carbohydrate residues were more numerous in the acini of the Jacobson glands. Thus, the nasal glands in the rat and guinea pig are probably of a serous type because of the scarcity of carbohydrate residues.

Changes in the carbohydrate content of airway epithelium induced by human neutrophil elastase in the hamster

Hamster airway epithelial secretory cells were investigated by light and electron microscopic cytochemistry to study possible changes in their carbohydrate content induced by human neutrophil elastase (HNE), an agent known to cause replacement of Clara cells by mucous cells in hamster bronchi. Characterization of secretory cell carbohydrates by the AB/PAS, PA-TCH-SP, HID-TCH-SP, and LID-TCH-SP sequences indicated the existence of periodate-reactive acidic glycoconjugates, but the absence of sulfated or carboxylated glycoconjugates in both treated and control animals. Differences were seen in the quality and quantity of historeactive carbohydrates throughout various regions in the lower respiratory tract. This was especially evident in the HNE-treated animals. It is concluded that the HNE-induced expression of the mucous cell phenotype is associated with an increase in the amount of neutral and acidic nonsulfated and noncarboxylated polysaccharides stored in the secretory granules of these cells.

Monoclonal antibody (Mab) markers for subpopulations of rat tracheal epithelial (RTE) cells

We sought monoclonal antibodies (Mabs) that would recognize distinct subsets of rat tracheal epithelial (RTE) cells. Mice were immunized with pronase-dissociated RTE cells and hybridomas whose supernatants immunocytochemically stained subpopulations of tracheal cells were selected. We report the immunohistochemical staining properties of the antibodies and give the results of preliminary biochemical characterization of the antigens. Four different types of antibodies were produced. Antibody RTE 1 stained most RTE cells. Three antibodies (RTE 2, 7, and 13) recognized a subpopulation of nonciliated cells, both columnar and basal cells. Antibody RTE 3 intensely labeled the surface of ciliated cells. Three antibodies reacted with granule components of secretory cells; antibodies RTE 9 and 11 reacted with mucous-type secretory cells and antibody RTE 12 stained all tracheal surface secretory cells. As described in detail, some antibodies were RTE cell specific while others also reacted with cells and secretions in other organs; the antibodies did not cross react with guinea pig or rabbit tissues. Periodate sensitivity of the antigens suggested that some antibodies recognized carbohydrate moieties while others detected peptide epitopes. In some cases, Western blotting revealed the molecular weights of the antigens, but some antigens were denatured by sodium dodecyl sulfate (SDS) and heat treatment. These antibody probes provide a useful means to immunochemically study changes in cell type distribution and/or epitope expression during development, injury, and regeneration.

Expression of glycoconjugates in the human fetal cochlea

The distribution of glycoconjugates in the human fetal cochlea was analyzed using six biotinylated lectins: wheat germ agglutinin (WGA), abrus precatorius agglutinin (APA), ulex europaeus agglutinin I (UEA-I), ricinus communis agglutinin 120 (RCA120), helix pomatia agglutinin (HPA), concanavalin A (ConA). The tectorial membrane (TM) in the 11- and 15-week-old human fetuses was labelled with WGA, APA, RCA120 and ConA, but not with UEA-I and HPA. In the 19-week-old fetuses, the reaction of the TM decreased. In the 11-, 15- and 19-week-old fetuses, the surface of the greater and the lesser epithelial ridges were respectively labelled with WGA, APA and RCA120. Reissner's membrane was labelled with WGA, ConA, APA, RCA120 and HPA. WGA, RCA120 and APA strongly stained the stria vascularis, especially in the 15-week-old fetuses. HPA did not stain the 11-week-old fetal cochleas at all, while it stained the apical surface of the hair cells, Reissner's membrane, the cells within the stria vascularis and spiral osseous lamina in the 15-week-old fetuses. In the 19-week-old fetuses, the fluorescent reaction with HPA became decreased and the apical surface of the hair cells was not labelled with HPA at all. This result suggests that HPA reactive glycoconjugates may be related to the molecule responsible for stereociliary adhesion only during development.

Ultrastructural localization of sialylated glycoconjugates in cells of the salamander olfactory mucosa using lectin cytochemistry

An indirect gold-labeling method utilizing the lectin from Limax flavus was employed to characterize the subcellular distribution of sialic acid in glycoconjugates of the salamander olfactory mucosa. The highest density of lectin binding sites was in secretory vesicles of sustentacular cells. Significantly lower densities of lectin binding sites were found in secretory granules of acinar cells of both Bowman's and respiratory glands. Lectin binding in acinar cells of Bowman's glands was confined primarily to electron-lucent regions and membranes of secretory granules. In the olfactory mucus, the density of lectin binding sites was greater in the region of mucus closest to the nasal cavity than in that closest to the epithelial surface. At the epithelial surface, the density of lectin binding sites associated with olfactory cilia was 2.4-fold greater than that associated with microvilli of sustentacular cells or non-ciliary plasma membranes of olfactory receptor neurons, and 7.9-fold greater than non-microvillar sustentacular cell plasma membranes. Lectin binding sites were primarily associated with the glycocalyx of olfactory receptor cilia. The cilia on cells in the respiratory epithelium contained few lectin binding sites. Thus, sialylated glycoconjugates secreted by sustentacular cells are preferentially localized in the glycocalyx of the cilia of olfactory receptor neurons.

Release of mucus glycoconjugates by Pseudomonas aeruginosa rhamnolipid into feline trachea in vivo and human bronchus in vitro

Pseudomonas aeruginosa colonizes the lower respiratory tracts of patients with severe bronchiectasis, including cystic fibrosis, a condition associated with increased airway mucus output. We have shown that an extract containing chloroform-soluble extracellular products of P. aeruginosa releases glycoconjugates into the cat trachea in vivo. This activity was not related to pyocyanin, a major component of the extract, but was associated with the rhamnolipids. Purified monorhamnolipid (100 micrograms/ml) released radiolabeled and periodic acid-Schiff (PAS)-reactive glycoconjugates (delta 3H = +490 +/- 70%, delta 35S = +170 +/- 40%, delta PAS = +8.6 +/- 1.7 micrograms/min; n = 6, P less than 0.02 for each). Dirhamnolipid (200 micrograms/ml) was also effective (delta 3H = +640 +/- 70%, delta 35S = +130 +/- 20%, delta PAS = +9.3 +/- 1.5 micrograms/min; n = 6, P less than 0.02 for each). Monorhamnolipid (100 micrograms/ml) also released 35S-labeled and PAS-reactive glycoconjugates from human bronchial tissue in vitro (delta 35S = +189 +/- 47%, delta PAS = +26.3 +/- 8.5 micrograms/min; n = 7, P less than 0.001 versus control tissues in which no stimulus was given). The cat tracheal glycoconjugates released by the rhamnolipids differed from those released by pilocarpine 50 microM, in having a higher 3H:35S ratio (P less than 0.001). After gel chromatography on a Sepharose CL-4B column, the void volume fractions of the glycoconjugates also had different profiles in a cesium chloride density gradient. Those released by rhamnolipid banded at 1.62 g/ml, while those released by pilocarpine banded mainly at 1.50 g/ml, with some of the higher density material also present.(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.

Distribution and histochemical characterization of goblet cells in the nasal cavity of piglets

The present study was designed to compare the distribution of goblet cells and the histochemical composition of mucosubstances produced by these cells in the nasal cavity of piglets aged from 1 to 28 days. Serial transverse sections were stained to demonstrate neutral, acidic, and sulfated mucosubstances. Sections located at eight reference levels rostrocaudally in the nasal cavity and defined regions on these sections were used for goblet-cell counting. There was a nonhomogeneous distribution of goblet cells in the nasal cavity of piglets. A rostrocaudal increase in goblet-cell density was observed with the highest densities found in the ventral meatus and on the septum. There was no difference in this pattern of distribution according to age of the piglets. However, age-related differences were observed in the prevalence of goblet cells containing sialomucins, sulfomucins, or both. While sialomucins were prevalent at 1 and 14 days, sulfomucins predominated in the rostral half of the cavity at 28 days. Our results indicate a maturation of the products of secretion with aging in piglets. The affinity of infectious agents for sialylated glycoconjugates and the predominance of sialomucins in the nasal cavity of newborn piglets could account for their greater susceptibility to bacterial infection.

Lectin binding beneath the epithelium and in smooth muscle cells in the developing bronchial tree

Components of the subepithelial stratum in developing rat lung reacted transiently with Maclura pomifera agglutinin (MPA) and Aleuria aurantia agglutinin (OFA) conjugated to horseradish peroxidase. These lectins possess selective affinity for and serve to localize glycoconjugates (GCs) with terminal Gal/GalNAc and Fuc, respectively. Staining was strongest with both lectins in the proximal bronchial tree and decreased peripherally to growing buds where it was absent. MPA staining of subepithelial structures decreased from the pseudoglandular through the canalicular period and disappeared by the terminal sac stage. Disappearance of this subepithelial reactivity coincided with appearance of apical MPA-positive glycoconjugate in the canalicular period. OFA stained selectively a layer of flattened cells and a thin extracellular stratum under the epithelium of proximal bronchi in the canalicular period. This lectin affinity extended farther peripherally in the pseudoglandular interval and diminished thereafter. The layer of OFA-positive cells underlying the epithelium was identified immunohistochemically as immature smooth muscle. These muscle cells gained contractile protein while losing surface lectin reactivity during fetal development. The high iron diamine method localized sulfated GC in basement membrane of proximal respiratory passages in the fetal lung. The results attest to the involvement of specific GCs in mediating epithelial-mesenchymal cell interaction during critical stages of bronchial morphogenesis.

Histochemical characterization of glycoconjugates in the epithelium of the extrapulmonary airways of several vertebrates

The glycoconjugates of the extrapulmonary airways of 11 tetrapode vertebrates have been characterized by means of both conventional and lectin histochemistry. Abundant sialosulphomucins were detected in the secretory cells and periciliary layer of turtles, snakes, birds and mammals while only sialomucins were observed in amphibians. Neutral and traces of acidic mucins were detected in the secretory cells of lizards. The secretory cells of the amphibian airways were reactive to Con-A, DBA and WGA. No alpha-L-fucose residues reactive with UEA-I or LTA were detected in amphibians. The goblet cells of the turtles were stained by DBA, SBA and WGA. Secretory cells of snakes and lizards reacted with Con-A and WGA. The mucous goblet cells of the birds were reactive to Con-A, LTA and WGA. In the chicken, they also showed affinity for PNA and SBA. The ciliated cells of the avian species studied were stained by Con-A and WGA. Mammalian goblet cells were reactive to Con-A, UEA-I and WGA. In the rat, affinity for DBA and SBA was also observed. The present results reveal the existence of marked differences in the sugar residues of the glycoconjugates of the extrapulmonary airways of tetrapode vertebrates. Only sialic acid residues appear to be constant constituents of the glycoconjugates of the airways of all species studied.

Human neutrophil elastase causes glycoconjugate release from the epithelial cell surface of hamster trachea in organ culture

It is known that human neutrophil elastase (HNE) treatment of hamster tracheal explants causes the release of glycoconjugates, most of which appear to have the characteristics of mucus glycoproteins. This study was designed to determine the origin of HNE-induced glycoconjugate release from 1-day-old cultures of adult hamster trachea. After confirming that HNE treatment released glycoconjugates from cultures labeled with tritiated glucosamine, light microscopic autoradiograms and electron micrographs were prepared. Untreated cultures and cultures treated with inactivated HNE served as controls. HNE treatment caused a 40 to 50% decrease in the silver grain count on the external apical surfaces of secretory cells (p less than 0.05) and ciliated cells (p less than 0.01). Silver grain counts in secretory and ciliated cell cytoplasm, submucosa, and nontissue background were not significantly different from controls. The percentage of nongranulated secretory cells and the number of secretory granules in granulated secretory cells were similar in the HNE-treated and untreated controls. There was no evidence of constitutive release of radiolabeled glycoproteins, or of discharge of secretory granules from the secretory cells. We conclude that HNE releases mucins and other glycoconjugates from the external surfaces of both secretory and ciliated cells in tracheal organ culture.

Changes in epithelial secretory cells and potentiation of neurogenic inflammation in the trachea of rats with respiratory tract infections

In rats respiratory tract infections due to Sendai virus and coronavirus usually are transient, but they can have long-lasting consequences when accompanied by Mycoplasma pulmonis infections. Morphological alterations in the tracheal epithelium and a potentiation of the inflammatory response evoked by sensory nerve stimulation ("neurogenic inflammation") are evident nine weeks after the infections begin, but the extent to which these changes are present at earlier times is not known. In the present study we characterized these abnormalities in the epithelium and determined the extent to which they are present 3 and 6 weeks after the infections begin. We also determined the magnitude of the potentiation of neurogenic inflammation at these times, whether the potentiation can be reversed by glucocorticoids, and whether a proliferation of blood vessels contributes to the abnormally large amount of plasma extravasation associated with this potentiation. To this end, we studied Long-Evans rats that acquired these viral and mycoplasmal infections from other rats. We found that the tracheal epithelium of the infected rats had ten times as many Alcian blue-PAS positive mucous cells as did that of pathogen-free rats; but it contained none of the serous cells typical of pathogen-free rats, so the total number of secretory cells was not increased. In addition, the epithelium of the infected rats had three times the number of ciliated cells and had only a third of the number of globule leukocytes. In response to an injection of capsaicin (150 micrograms/kg i.v.), the tracheas of the infected rats developed an abnormally large amount of extravasation of two tracers, Evans blue dye and Monastral blue pigment, and had an abnormally large number of Monastral blue-labeled venules, particularly in regions of mucosa overlying the cartilaginous rings. This abnormally large amount of extravasation was blocked by dexamethasone (1 mg/day i.p. for 5 days). We conclude that M. pulmonis infections, exacerbated at the outset by viral infections, result within three weeks in the transformation of epithelial serous cells into mucous cells, the proliferation of ciliated cells, and the depletion of globule leukocytes. They also cause a proliferation of mediator-sensitive blood vessels in the airway mucosa, which is likely to contribute to the potentiation of neurogenic inflammation that accompanies these infections.

Tracheobronchial epithelium in the adult rhesus monkey: a quantitative histochemical and ultrastructural study

Previous studies of the intrapulmonary conducting airways of sheep and rabbit have demonstrated marked diversity in the epithelial populations lining them. Because studies of trachea and centriacinar regions of macaque monkeys suggested that primates may be even more diverse, the present study was designed to characterize the epithelial population throughout the airway tree of one primate species, the rhesus monkey. Trachea and intrapulmonary airways of the right cranial and middle lobes of glutaraldehyde/paraformaldehyde-infused lungs of five adult rhesus monkeys were microdissected following the axial pathway. Each branch was assigned a binary number indicating its specific location within the tree. The trachea and six generations of intrapulmonary airway from the right cranial lobe were evaluated for ultrastructure and quantitative histology as were those of the right middle lobe for quantitative carbohydrate histochemistry. Four cell types were identified throughout the tree: ciliated, mucous goblet, small mucous granule, and basal. The tallest epithelium lined the trachea; the shortest, the respiratory bronchiole. The most cells per unit length of basement membrane were in proximal intrapulmonary bronchi; the least, in the respiratory bronchiole. The nonciliated bronchiolar epithelial or Clara cell was restricted to respiratory bronchioles. Sulfomucins were present in the vast majority of surface goblet cells in the trachea and proximal bronchi. In proximal bronchi, neutral glycoconjugates predominated in glands and acidic glycoconjugates in surface epithelium. In terminal and respiratory bronchioles the ratio of acidic glycoconjugate to neutral glycoconjugate equaled that in proximal bronchi, although glands were not present. Sulfomucins were minimal in terminal airways. We conclude that the characteristics of the epithelial lining of the mammalian tracheobronchial airway tree are very species-specific. The lining of the rhesus monkey does not have the diversity in cell types in different airway generations observed in sheep and rabbit. Also, the populations lining these airways in the rhesus are very different from either the sheep or rabbit in number, proportions of different cell types, glycoconjugate content, and distribution of specific cell types.

Tracheal gland mucous cells stimulated in vitro with adrenergic and cholinergic drugs

To determine the responsiveness of tracheal mucous cells to adrenergic and cholinergic stimulation, we analyzed changes in their structure induced by neurotransmitter-like agonists. Ferret tracheal rings were exposed for 30 min in vitro to one of the following: phenylephrine, isoproterenol, or bethanechol (all at 10(-5) M), in the presence of absence of appropriate antagonists. Electron microscopy and morphometric analysis revealed that the volume density of mucous cells (Vvmc, i.e. the space occupied by mucous cells in the submucosa) significantly decreased, and the surface density of mucous cell apical membrane (Svam) increased in response to isoproterenol and bethanechol but not to phenylephrine. In metabolic labeling experiments, the morphological changes were accompanied by secretagogue-evoked release of 35S-labeled macromolecules. Taken together, these data suggest that tracheal mucous cells secrete 35S-labeled macromolecules in response to beta-adrenergic and muscarinic agonists by an exocytotic process that involves a reduction in cell size.

Cytochemical identification of secreted carbohydrates in the endolymphatic sac

Carbohydrate complexes were investigated in the murine endolymphatic sac by means of histochemical techniques in normal untreated animals as well as after ethacrynic acid treatment. The light epithelial cells were classified into three different types: normal, granular and vacuolar. The granular and vacuolar cells were believed to secrete glycoproteins and/or proteoglycans, the presence of which was closely correlated with the component of the precipitate in the lumen of the endolymphatic sac. This finding suggested that the light cells not only absorb endolymph but may also be involved with secretory activity. Such a dual modality in function may have several important implications, since it suggests that the endolymphatic sac has both absorptive and secretory functions.

The complexity of mucins

Mucins represent the main components of gel-like secretions, or mucus, secreted by mucosae or some exocrine glands. These high-molecular-weight glycoproteins are characterized by the large number of carbohydrate chains O-glycosidically linked to the peptide. The determination of mucin molecular weight and conformation has been controversial for several reasons: 1) the methods used to solubilize mucus and to purify mucins are different and 2) the molecules have a strong tendency to aggregate or to bind to other molecules (peptides or lipids). Recently, electron microscopy has shown the filamentous shape of most mucins and their polydisperse character which, in some secretions, might correspond to a polymorphism of the peptide part of these molecules. The recent development of high pressure liquid chromatography and high-resolution proton NMR spectroscopy has allowed major progress in the structural study of mucin carbohydrate chains. These chains may have from 1 to about 20 sugars and bear different antigenic determinants, such as A, B, H, I, i, X, Y or Cad antigens. In some mucins, such as human respiratory mucins, the carbohydrate chain diversity is remarkable, which raises many questions. Mucins are molecules located at the interface between mucosae and the external environment. The carbohydrate chain diversity might allow many interactions between mucins and microorganisms and play a major role in the colonization or the defense of mucosae.

Turnover of cell-surface macromolecules in cultured dog tracheal epithelial cells

We studied the metabolism of sulfated cell-surface macromolecules in dog tracheal epithelial cells in primary culture. To examine the time-course and rate of appearance of sulfated macromolecules at the cell surface, the cells were pulsed with 35SO4 for short periods (5-15 min), and the incubation medium was sampled for spontaneously released macromolecules (basal secretions) and for release induced by trypsin (trypsin-accessible secretions). Trypsin-accessible 35S-labeled macromolecules appeared on the cell surface within 5-10 min, increased linearly, and plateaued by 40 min; the median transit time for 35S-labeled macromolecules to reach the cell surface was 21 min. 35S-labeled macromolecules in basal secretions increased with a similar time-course, reaching a plateau by 40 min. Incorporation of [3H]serine into the protein moiety of trypsin-accessible macromolecules occurred more slowly; trypsin-accessible 3H-labeled macromolecules were barely detectable at 1 h and increased to a maximum after 2 h, suggesting the presence of a preformed pool of nonsulfated core protein. Pretreatment with cycloheximide, an inhibitor of protein synthesis, decreased trypsin-accessible 35S-labeled macromolecules log-linearly depending on the duration of pretreatment providing an estimate of the rate of depletion of the core protein pool (t1/2 = 32 min). During continuous exposure to 35SO4, 35S-labeled macromolecules accumulated on the cell surface (trypsin-accessible compartment) for 16 h, at which point the cell-surface pool was saturated (t1/2 = 7.5 h). After pulse-labeling the cells with 35SO4 for 15 min, the 35S-labeled macromolecules disappeared continuously from the cell surface (t1/2 = 4.6 h), and 79% of the radioactivity was recovered in the medium as nondialyzable macromolecules. Release of the 35S-labeled macromolecules from the cell surface was abolished at 4 degrees C, indicative of an energy-dependent process, but multiple proteinase inhibitors did not affect the release. We conclude that sulfate is metabolized rapidly into epithelial cell-surface macromolecules, which accumulate continuously into a relatively large cell-surface pool, before they are released by an undefined energy-dependent mechanism.

Tracheobronchial epithelium of the sheep: III. Carbohydrate histochemical and cytochemical characterization of secretory epithelial cells

We examined histochemically (light microscopy-LM) and cytochemically (electron microscopy-EM) the secretory epithelial cells in the tracheobronchial mucosa of sheep. Six morphologically distinct, granule-containing cells have been described, on the basis of their morphology and airway distribution: four mucous (M1-M4), serous (SC), and Clara (CC). Stereological and morphometric data indicated that M3, M4, SC, and CC were distinctly different from each other and from M1 and M2 cells. Mucous cells M1 and M2 differed in granule morphology. Samples of tracheas, sixth-generation bronchi, distal bronchi, and terminal bronchioles of 18 adult sheep were examined. At the LM level, methacrylate sections were reacted with an alcian blue (pH 2.5), periodic acid Schiff (PAS) sequence to differentiate neutral from acidic glycoconjugates (GC), and a high-iron diamine (HID), alcian blue sequence to differentiate sulfated from nonsulfated (sialylated) GC. At the EM level the periodic acid-thiocarbohydrazide localized hexose-rich, neutral GC. Dialyzed iron (DI) and high-iron diamine localized carboxylated and sulfated GC, respectively. Granules of all but Clara cells were PAS-positive. All mucous cells contained acidic groups, but only M1 and M4 cells had LM-detectable sulfated GC. At the ultrastructural level, minimal but discernible HID and LID reaction product was observed on granule profiles of M2, M3, and SC, indicating acidic and sulfated GC not detected at the LM level. Histochemically, the sheep tracheobronchial epithelium was more similar to that of humans than some other examined mammalian species.

Isolation and cytochemical characterization of globule leukocytes from rat tracheal epithelium

Globule leukocytes, dispersed throughout the respiratory epithelium as single cells, were isolated from rat trachea and were enriched by centrifugation on a discontinuous Percoll gradient. The isolation and enrichment procedure yields a cell fraction containing 75% globule leukocytes. The cell viability, as assessed by trypan blue exclusion, was at least 98%. Cells were maintained in short-term culture without apparent loss of viability and enzyme activity. The isolated globule leukocytes seem not to express significant levels of cytotoxicity against 51Cr-labeled YAC-1 target cells. In fixed cytocentrifuge smears, globule leukocytes appear as more or less rounded to oval cells with a low nucleo-cytoplasmic ratio and with a mostly eccentrically located nucleus. Characteristic intracytoplasmic granules are stained with toluidine blue, alcian blue, and May-Grünwald-Giemsa stains. The applied cytochemical methods demonstrate that tracheal globule leukocytes are stained for alpha naphthyl acetate esterase and naphthol-AS-D-chloroacetate esterase, but not for alpha naphthyl butyrate esterase, N-acetyl-DL-phenylalanine-B-naphthyl esterase, and endogenous peroxidase. Isolated rat peritoneal cells were used as positive control cells for the cytochemical reactions. The obtained cytochemical profile of tracheal globule leukocytes is compared to the known cytochemical profile of intestinal globule leukocytes and large granular lymphocytes. The cytochemical dissimilarities between tracheal and intestinal globule leukocytes may suggest that both kinds of globule leukocytes represent a different form of the same cell type or even different cell types. The cytochemical pattern of tracheal globule leukocytes is closely related to that of large granular lymphocytes, which have been postulated as a possible source for globule leukocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

An ultrastructural study of the response of hamster bronchial epithelium to human neutrophil elastase

The central intrapulmonary bronchi of hamsters were examined by transmission electron microscopy at varying times following intratracheal instillation of human neutrophil elastase (HNE) or its vehicle, saline. Two hours after HNE treatment, there was a marked irregularity of the surfaces of many nonciliated epithelial cells; a differential count of transepithelial cells (those with both a basal lamina and luminal border) demonstrated a significant decrease in the proportion of granule-containing (granulated) secretory cells and a corresponding increase in nongranulated secretory cells. By 3 days after HNE injection, the differential count had returned to control levels and cell surface alterations were less evident. By 8 days, the proportion of granulated secretory cells had significantly increased, while that of nongranulated secretory cells had decreased. Many Clara cells developed the characteristics of mucous cells so that mucous cells constituted 57% of the secretory cells compared to 14% for the saline controls. The mucous cells contained an increased number of mucous granules including bizarre forms never seen in controls. By day 16, the average mucous cell proportion had increased to 75%; the mucous cells were larger and contained many more secretory granules than at day 8. At no time was there evidence of overt cell injury or alteration of extracellular connective tissue due to HNE. Basal and pseudobasal cells, distinguished by the presence or absence of hemidesmosomes, did not change as a percentage of total nucleated epithelial cells. Saline had no effect on the differential cell count compared to untreated values. Our results indicate a strong likelihood that HNE causes early discharge of secretory granules and alters the phenotypic expression of Clara cells so that they produce abundant, often abnormal mucous granules. The mechanism of HNE-induced disturbance of epithelial homeostasis is unknown, but the early irregularity of nonciliated epithelial cell surfaces may signify an important event in the evolution of the resultant lesion.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.

Establishment and characterization of a cell line derived from bovine tracheal glands

Bovine tracheal submucosal gland cells have been isolated by enzymatic digestion and serially propagated in tissue culture for more than 12 mo. (40 passages). The cells exhibit an epithelioid appearance at confluence and contain alcian blue (pH 2.5)/periodic acid-Schiff-positive material within cytoplasmic granules. By electron microscopy numerous osmiophilic secretory granules are seen. Maximal growth is observed when the cells are grown on human placental collagen-coated culture vessels in medium supplemented with 20% fetal bovine serum. Scintillation spectrometry revealed that radiolabeled precursor (35SO4) was incorporated into high molecular weight molecules and released from cells. Isoproterenol (10(-6) to 10(-3) M) stimulated the release of 35SO4. The maximal response to isoproterenol was completely inhibited by the beta-adrenergic antagonist propranolol. It is concluded that the cultured cells retain features of tracheal gland cells and may serve as a useful model of synthesis and secretion of macromolecules by tracheal gland cells.

Biosynthesis and release of proteins by isolated pulmonary Clara cells

The major proteins synthesized and released by Clara cells were identified and compared with those synthesized and released by mixed lung cells. Highly purified Clara cells (85.9 +/- 2.4%) and mixed lung cells (Clara cells 4%, Type II cells 33%, granulocytes 18%, macrophages 2.7%, ciliated cells 1.2%) were isolated from rabbit lungs, incubated with Ham's F12 medium in collagen/fibronectin-coated plastic culture dishes in the presence of 35S-methionine for periods of 4 and 18 hrs. Radiolabelled proteins were isolated from the cells and from the culture medium, electrophoresed on polyacrylamide gels in the presence of SDS under reducing conditions, and then autoradiographed. After 4 and 18 hr of incubation of the Clara cells the major radiolabelled cell-associated proteins were those with molecular weights of 6, 48, and 180 Kd. The major radiolabelled proteins released by Clara cells into the medium after 4 hrs of incubation had molecular weights of 6, 48, and 180 Kd, accounting for 42, 16, and 10%, respectively, of the total extracellular protein-associated radioactivity. After 18 hr of incubation the 6 and 48 Kd proteins represented 30 and 18% of the total released radioactivity, and the relative amount of the 180 Kd protein had decreased to 3%. With the mixed lung cells, the major proteins released into the medium had molecular weights of 6 and 48 Kd. Under nonreducing conditions the 6 Kd protein released by Clara cells had an apparent molecular weight of 12 Kd. Labelling isolated Clara cells with a mixture of 14C-amino acids also identified this low molecular weight protein as the major secretory product of the Clara cell. The 6 Kd protein did not label when the cells were incubated with 14C-glucosamine indicating that it was not a glycoprotein. These data demonstrate the release of several proteins from isolated Clara cells but the major protein had a molecular weight of 6 Kd.

Lectin-binding affinities of the epithelium in the respiratory tract. A light microscopical study of ciliated epithelium in rat, guinea pig, and hamster

Complex carbohydrate components of surface coat and secretory granules were investigated in the laryngo-tracheo-bronchial epithelium of 3 laboratory animals (rat, guinea pig, and Syrian hamster). 2 groups of epithelial cells were distinguished in the light microscope: ciliated cells and non-ciliated cells. The latter mainly represent secretory cells and are subdivided into serous and mucous secretory cells. Apical glycocalix: In the rat, ciliated cells possess a significant number of Con A, RCA I, and WGA receptors, and a smaller number of UEA I binding sites. In hamsters and in guinea pigs additional binding sites for HPA could be demonstrated. The apical glycocalix of the non-ciliated cells in the rat evince marked staining with RCA I, WGA, and HPA, and less intensive binding of UEA I. In guinea pigs and in hamsters, the presence of additional Con A receptors was noted. Basolateral glycocalix: The basolateral surface coat of ciliated and non-ciliated cells shows identical lectin binding affinities. In the rat, the basolateral glycocalix binds RCA I; in the guinea pig, in addition, positive staining with UEA I and HPA is observed; in the hamster, the basolateral surface coat is outlined by RCA I and HPA receptors. Secretory products: Secretory granules of mucous cells in the rat react with Con A, UEA I and HPA lectins. In guinea pigs, these substances also bind RCA I and WGA lectins. Mucous granules in the secretory cells of the hamster are positive for Con A, RCA I, and HPA lectins. Granules of non-ciliated serous cells of rats bind Con A, UEA I, and HPA lectins. In the guinea pig, this reaction is weaker for UEA I lectin but comparable for Con A and HPA binding. A positive reaction with RCA I lectin only is found in the serous secretory granules of the hamster.

Globule leukocytes in the respiratory epithelium of human upper airways: an ultrastructural study

The ultrastructure of globule leukocytes is described in the nasal and tracheal respiratory epithelium of three boys suffering from chronic airway infections. The globule leukocytes lie free in the intercellular spaces and appear to be migratory cells. They are characterized by intracytoplasmic membrane-bound globules, variable in number, size, shape, and internal structure. The globules may apparently release their content between the neighboring epithelial cells. Human globule leukocytes are also characterized by the presence of intracytoplasmic rod-shaped bodies, the significance of which is not known. They usually display an extended juxta-nuclear Golgi apparatus, presumably involved in the formation of the globules. Comparison of the fine structure of the globules in the globule leukocytes with that of the granules found in the subepithelial mast cells does not support a mast cell origin for human globule leukocytes. On morphological grounds, natural killer cells are postulated as a possible source for globule leukocytes. The function of globule leukocytes is briefly discussed. We presume that the globule leukocytes belong to the group of migrating and secreting cells involved in the defense of the organism against foreign material.

Ultrastructural and immunohistochemical studies on non-ciliated cells of the tracheal epithelium of normal, phenobarbital-treated and 3-methylcholanthrene-treated mice

Non-ciliated SER-rich cells of the tracheal epithelium of normal, phenobarbital-treated and 3-methylcholanthrene-treated mice were studied ultrastructurally and immunohistochemically. The apical portion of these cells protrudes into the tracheal lumen, especially in the mice treated with the two compounds, and the apical cytoplasm is filled with numerous tubular elements of SER. Besides, the non-ciliated cells of 3-methylcholanthrene-treated mice show a strong positive reaction to the antiserum against microsomal cytochrome P-450 of liver. These findings support the concept that the non-ciliated tracheal cell may be involved in the metabolism of endogeneous and exogeneous chemical compounds.

Carbohydrate cytochemistry of rhesus monkey tracheal epithelium

Three types of nonciliated secretory epithelial cells contribute material to the mucous lining of pulmonary airways: mucous cells, serous cells, and Clara cells. Extensive interspecies variation exists, especially between humans and laboratory mammals, with regard to occurrence, distribution, and granule content of these secretory cells. This study was designed to characterize one aspect of these differences in one species of nonhuman primate, the rhesus monkey. The complex carbohydrates of secretory granules present in the tracheal epithelium were characterized cytochemically. The tracheas of seven monkeys were fixed by airway infusion, processed, and embedded for both light and transmission electron microscopy. Histochemical stains including Alcian blue-periodic acid Schiff, dialyzed iron, and high iron diamine-Alcian blue were applied to serial methacrylate sections. The mucous cells were the predominant secretory cell type of the trachea and contained periodate-reactive sulfated glycoconjugates. The mucous secretory granules, as resolved with the electron microscope, consisted of a mesh or matrix surrounding a biphasic core. The matrix was stained by all cytochemical reactions used, which included periodic acid-thiocarbohydrazide-silver proteinate, dialyzed iron, low iron diamine, and high iron diamine. The biphasic core also reacted with the four stains, but most intensely with high iron diamine. We conclude from this study that 1) the mucous secretory granule contains carbohydrate throughout all phases of the granule, 2) the mucous granule contains periodate-reactive sulfated glycoconjugates, with sulfate esters concentrated in the core of the granule, and 3) the mucous granules of rhesus trachea morphologically and cytochemically resemble those described in human airways.

Morphologic and cytochemical characteristics of amine-containing globule leukocytes in rat tracheal epithelium

Amine-containing cells in the tracheal epithelium are typically of the small-granule type (diameter approximately 100 nm). However, in the rat, another amine-containing cell type has been identified that possesses the amine-handling features of the APUD-series of cells (amine precursor uptake and decarboxylation) but not the ultrastructural characteristics. It has been postulated that these cells may be related to cutaneous melanocytes. In this study, fluorescent cells were present in the laryngeal and tracheal epithelial lining of adult Sprague-Dawley rats following freeze-drying and exposure to formaldehyde vapor (FIF or formaldehyde-induced fluorescence). Microspectrofluorimetry revealed an emission maximum at 493 nm. The excitation maximum could not be calculated but appeared to be around or below 350 nm (to record spectra below requires the use of quartz optics). Yellow fluorescence also emanated from serotonin-containing mast cells (excitation and emission maxima: 401/515 nm). Tracheal segments processed according to the aqueous formaldehyde ( AFIF ) technique, for the demonstration of 5- hydroxytryptophan (5-HTP) or serotonin (5-HT), failed to identify fluorescent cells in the epithelial lining even though connective-tissue mast cells were evident. Subsequent treatment of AFIF -fixed sections with formaldehyde and HCl vapors ( AFIF -HCl) resulted in the formation of a fluorogenic compound within numerous cells in the tracheal lining (455/537 nm). This spectral shift and increase in intensity of fluorescence following acidification are characteristic for standards and/or cells that contain tryptamine, tryptophan, or peptides with NH2-terminal tryptophan and are markedly different from microspectrofluorimetric data reported for the phenylethylamines or serotonin. It is therefore postulated that these cells contain a closely related beta-(3-indolyl) ethylamine-like compound, serotonin excluded. The morphology of the fluorescent cells was similar when prepared according to the FIF or AFIF -HCl techniques. Conjunctive staining, the examination of a single section first by fluorescence microscopy and subsequently by other histochemical and cytochemical methods, demonstrated that the fluorescent granules were also methylene blue, alcian blue, periodic-acid Schiff, and ferric- fericyanide positive. Subsequent correlative electron microscopic examination of Epon-embedded AFIF -HCl-treated tracheal sections demonstrated that these amine-containing cells were globule leukocytes.

Growth and differentiation of hamster tracheal epithelial cells in culture

The purpose of these studies was to define culture conditions that support growth and differentiation of normal epithelial cells obtained from hamster tracheas. Epithelial cells from tracheas of adult hamsters were collected using enzymatic procedures and cultured under various conditions. The medium used consisted of a 1:1 mixture of medium 199 and Dulbecco's modified Eagle's medium with 2% fetal bovine serum, which was conditioned by mouse 3T3 cells before use. Insulin, transferrin, hydrocortisone, epidermal growth factor, and an extract from bovine hypothalamus were used as supplements. When seeded on uncoated or collagen-coated tissue culture dishes, the hamster cells grew only poorly. When the cells were seeded on collagen gels, however, rapid and prolonged growth ensued. The cultures had a population doubling time of 20 hr and a colony-forming efficiency of 7-10%, and they could be grown for up to three passages. Growth was dependent on the presence of transferrin, insulin, epidermal growth factor, and 3T3 conditioning factors in the medium. The latter could be omitted if the concentration of serum was increased. Less important for growth was the presence of hydrocortisone and bovine hypothalamus extract. In contrast to results with tracheal epithelial cells from adult rabbits, rats, and mice, differentiation into ciliated cells regularly occurred in cultures of cells derived from hamster tracheas. The appearance of ciliated cells in the cultures was dependent on the presence of collagen gel as a substratum and of 3T3 conditioning factors in the medium. In addition, there were numerous cells that contained electron-dense cytoplasmic granules. The granules were not stained by dialyzed iron, which stains acidic glycoproteins, but were stained positively by periodic acid-Schiff reagents and the periodic acid-thiocarbohydrazide-silver proteinate method, suggesting the presence of secretory granules containing neutral glycoproteins. A similar staining pattern was observed for the secretory granules of intact hamster tracheas. The culture system described supports growth and cellular differentiation of normal tracheal epithelial cells of hamsters. We believe therefore that it will be a useful model for studying the regulation of tracheal cell function on the cellular and biochemical level.

Comparison of nonciliated tracheal epithelial cells in six mammalian species: ultrastructure and population densities

Three types of nonciliated epithelial cells in mammalian conducting respiratory airways are thought to be secretory: mucous (goblet) cells, serous epithelial cells, and Clara cells. Mucous and serous cells are considered to be the secretory cells of the trachea. Clara cells are considered to be the secretory cells of the most distal conducting airways or bronchioles. To ascertain if mucous and serous epithelial cells are common to the tracheal epithelium of mammalian species, we characterized the ultrastructure and population densities of tracheal epithelial cells in six species: hamster (H), rat (Rt), rabbit (Rb), cat (C), Bonnet monkey (M. radiata) (B), and sheep (S). Following fixation by airway infusion with glutaraldehyde/paraformaldehyde, tracheal tissue was processed for light and electron microscopy (EM) by a selective embedding technique. Tracheal epithelium over cartilage was quantitated by light microscopy and characterized by transmission EM. Mucous cells were defined by abundant large nonhomogeneous granules, numerous Golgi complexes, basally located nuclei and granular endoplasmic reticulum (GER). The percentage of mucous cells in the tracheal epithelium was: H (0%), Rt (0.5%), Rb (1.3%), C (20.2%), B (8%), S (5.1%). Serous cells had homogeneous, electron-dense granules and extensive GER. Serous cells were present only in rats (39.2%). Clara cells had homogeneous electron-dense granules, abundant agranular endoplasmic reticulum (AER) and basal GER. Clara cells were found in hamsters (41.4%) and rabbits (17.6%). In sheep trachea, 35.9% of the epithelial cells had small electron-lucent granules, abundant AER and numerous Golgi complexes. In Bonnet monkey trachea, 16% of the epithelial cells had small electron-lucent granules, numerous polyribosomes, perinuclear Golgi apparatus and moderate GER. In cat trachea, 5.4% of the epithelial cells lacked granules, and had moderate numbers of mitochondria, moderate amounts of polyribosomes, a central nucleus, and long luminal microvilli. The percentage of the tracheal epithelial population occupied by basal, ciliated and nonciliated cells was: H (5.6%, 47.5%, 46.7%), Rt (13.4%, 40.6%, 45.9%), Rb (28.2%, 43.0%, 28.3%), C (37.3%, 36.1%, 26.7%), B (31%, 41%, 28%), S (28.5%, 30.6%, 41%). We conclude: 1) mucous and serous cells are not common to the tracheal epithelial lining of all mammalian species; 2) there is significant interspecies heterogeneity in the abundance, distribution and ultrastructure of tracheal secretory cells; 3) potential differences in the roles of nonciliated cells in tracheal function exists within tracheal epithelial populations and between species.

Distribution of nonciliated bronchiolar epithelial (Clara) cells in intra- and extrapulmonary airways of the rabbit

Three types of nonciliated secretory epithelial cells are thought to contribute to the mucous lining of intrapulmonary airways: mucous cells, serous cells, and Clara cells. The Clara cell is distinguished from the other two by low cuboidal shape, presence of membrane-bound electron-dense ovoid secretory granuLes, abundant apical agranular endoplasmic reticulum (AER), and its location as the lining cell of distal conducting airways (bronchioles). The present study was designed to define the distribution of the Clara cell within the trachea and intrapulmonary airway tree. We correlated airway size, generation of branching, and airway wall components with Clara cell morphology and abundance. Lungs of 6 male rabbits (8-15 weeks old) free of respiratory disease were fixed by airway infusion of glutaraldehyde/paraformaldehyde at 30 cm pressure. The trachea, primary bronchi, and airways of the right cranial lobe of each lung were exposed by microdissection. The branching pattern was recorded and numbered. One half of the dissected lung was processed for scanning electron microscopy and the other half embedded as large epoxy blocks for simultaneous transmission electron and light microscopy. The percentages of ciliated, mucous, nonciliated, and basal epithelial cells were quantitated by light microscopy. Basal cells and peribronchial cartilage were absent distal to the fourth intrapulmonary generation in both the axial airway and its first major branch. Mucous (goblet) cells were present (less than 2%) only in trachea and primary and lobar bronchi. Nonciliated cells were more abundant distally, constituting 21%-45% of the epithelium in cartilaginous airways and 35%-65% in noncartilaginous ones. In the first six airway generations including trachea, nonciliated cells were without large apical protrusions but were covered by long microvilli. Cells of more distal airways had prominent apical protrusions and lacked microvilli. Nonciliated cells in all airways had abundant apical AER, granular endoplasmic reticulum (GER), and electron-dense ovoid granules. Cells in proximal airways were columnar rather than low cuboidal and had more GER. Only nonciliated cell shape, luminal surface, and granule abundance varied with airway size and generation. We concluded that the nonciliated secretory cell lining all intrapulmonary airways in the rabbit lung is one cell type, the Clara cell.

The influence of embedding media and fixation on the post-embedment ultrastructural demonstration of complex carbohydrates. I. Morphology and periodic acid-thiocarbohydrazide-silver proteinate staining of vicinal diols

The influence of fixation and embedding medium on the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining reactivity in the mouse intestine was studied. It was found that the combination of osmium tetroxide and epoxy resins was the least sensitive for the demonstration of complex carbohydrate with the PA-TCH-SP method. Post-osmication reduced, but did not abolish, PA-TCH-SP reactivity (except for the Golgi complex) when non-epoxy resins were used. The staining pattern of a particular organelle differed depending on the embedding medium used. Golgi cisternae exhibited the most intense PA-TCH-SP reactivity in non-osmicated tissues embedded in non-epoxy resins. Post-osmication of tissues was required to reveal the fine structure of the glycocalyx as well as to preserve the fine structure of tissues embedded in styrene-methacrylate and styrene-Rigolac 2004. The choice of fixation procedures and embedding media in a given study should be governed primarily by the sites of interest.

Tracheobronchial epithelium of the sheep: I. Quantitative light-microscopic study of epithelial cell abundance, and distribution

Glutaraldehyde-infused tracheas and airways of five castrated sheep were microdissected following the axial airway of the left cranial and caudal lobes. Airway branches were assigned binary numbers indicating their specific location in the tracheobronchial tree. Samples of known airway generation were resin embedded and examined by light-microscopy. Based on differences in cell morphology, staining properties, and distribution, eight major cell groups were recognized and quantified: four mucous cell categories (M1, M2, M3, and M4), ciliated, basal, Clara, and serous cells. The last cell category was restricted to submucosal glands. Tracheal epithelium had the most cells per unit length, primarily due to large numbers of basal cells. Basal cells are found in the epithelium of airways without cartilage or glands. The total mucous cell population (M1, M2, and M3) in proximal airways was relatively constant. M4 mucous cells were present in glands of proximal airways and in the epithelial lining of the airways without glands. The most distal airways were lined by Clara and ciliated cells. A small number of the most proximal noncartilaginous airways had mucous (M1, M2, M3, and M4), basal, and Clara cells sharing the epithelial lining. We conclude that in the sheep lung: (1) epithelial cell distribution does not correlate with airway wall components; (2) more than one type of secretory epithelial cell can share the lining of the same airway; and (3) Clara cell distribution is based on airway generation and proximity to alveoli.

Ultrastructural and histochemical observations of respiratory epithelium and gland

Secretory products of epithelial cells of the human respiratory tract have been studied biochemically and by a variety of histochemical methods for differentiating and characterizing complex carbohydrates at the light and electron microscopic level. By light microscopy a majority of mucous secretory cells of the surface epithelium secret glycoprotein with terminal sialic acid, penultimate galactose residues, and variable sulfate esters. Ultrastructurally the mucous cells of the surface epithelium vary within and between regions of the respiratory tree and comprise a heterogeneous population of cells differing in the fine structure and cytochemistry of their secretory granules. Serous tubules and demilunes in glands of the lamina propria produce a secretion that contains less carbohydrate than that in the nearby mucous cells, resembles the latter in content of sulfate esters, and differs in having little or no sialic acid and no terminal or penultimate galactose. Mucous tubules produce a carbohydrate-rich secretion containing glycoconjugate with terminal sialic acids, penultimate galactose residues, and a variable degree of sulfation like the glycoconjugate of surface mucous cells. Heterogeneity of cells can be demonstrated in the serous and mucous tubules by ultrastructural, morphologic, and cytochemical methods.

The influence of embedding media and fixation on the post-embedment ultrastructural demonstration of complex carbohydrates. II. Dialyzed iron staining

The influence of fixation and the embedding medium on post-embedment dialyzed iron (DI) staining of acidic complex carbohydrates in mouse colon was studied at the ultrastructural level. DI staining of ultrathin sections from non-osmicated tissues embedded in epoxy resins was very weak, whereas DI staining of non-osmicated tissues embedded in non-epoxy resins such as polystyrene, polyester resins, methacrylates and newly developed embedding mixtures was strong. Brief exposure to OsO4 (5 min) abolished the DI staining in stored secretions of goblet and mucous cells, in apical cytoplasmic vesicles and at the microvillous surface of columnar absorptive cells and in the Golgi cisternae of all colonic cell types in epoxy embedded tissues, but only reduced slightly or had no effect on the DI reactivity observed in these sites in tissues embedded in non-epoxy resins. Prolonged exposure to OsO4 (60 min) prior to embedment in non-epoxy resins further reduced DI staining in all reactive sites and abolished the staining in Golgi cisternae of all colonic epithelial cells. Embedment of non-osmicated tissues in a styrene-Vestopal W mixture and of tissues briefly exposed to OsO4 after primary glutaraldehyde fixation in styrene-methacrylate is recommended for optimal post-embedment DI staining of the acidic groups of complex carbohydrates.