Mapping of adrenergic receptors in the trachea by autoradiography

Galactomannan and Zymosan Block the Epinephrine-Induced Particle Transport in Tracheal Epithelium

BACKGROUND

Ciliary beating by respiratory epithelial cells continuously purges pathogens from the lower airways. Here we investigated the effect of the fungal cell wall polysaccharides Galactomannan (GM) and Zymosan (Zym) on the adrenergic activated particle transport velocity (PTV) of tracheal epithelium.

METHODS

Experiments were performed using tracheae isolated from male C57BL/6J mice. Transport velocity of the cilia bearing epithelial cells was measured by analysing recorded image sequences. Generation of reactive oxygen species (ROS) were determined using Amplex Red reagents. PCR experiments were performed on isolated tracheal epithelium to identify adrenergic receptor mRNA.

RESULTS

The adrenergic receptors α1D, α2A, β1 and β2 have been identified in isolated tracheal epithelium. We found epinephrine responsible for an increase in PTV, which could only be reduced by selective β-receptor-inhibition. In addition, either GM or Zym prevented the epinephrine induced PTV increase. Furthermore, we observed a strong ROS generation evoked by GM or Zym. However, epinephrine induced increase in PTV recovered in the presence of GM and Zym after application of ROS scavengers.

CONCLUSION

Both GM or Zym trigger reversible ROS generation in tracheal tissue leading to inhibition of the β-adrenergic increase in PTV.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Tiotropium bromide suppresses smoke inhalation and burn injury-induced ERK 1/2 and SMAD 2/3 signaling in sheep bronchial submucosal glands

The effects of tiotropium bromide on ERK 1/2, SMAD 2/3 and NFκB signaling in bronchial submucosal gland (SMG) cells of sheep after smoke inhalation and burn injury (S + B) were studied. We hypothesized that tiotropium would modify intracellular signaling processes within SMG cells after injury. Bronchial tissues were obtained from uninjured (sham, n = 6), S + B injured sheep 48 h after injury (n = 6), and injured sheep nebulized with tiotropium (n = 6). The percentage (mean ± SD) of cells showing nuclear localization of phosphorylated ERK 1/2, pSMAD 2/3, and NFκB (p65) was determined by immunohistochemistry. Nuclear pERK 1/2 staining was increased in injured animals as compared to sham, (66 ± 20 versus 14 ± 9), p = 0.0022, as was nuclear pSMAD, 84 ± 10 versus 20 ± 10, p = 0.0022. There was a significant decrease in pERK 1/2 labeling in the tiotropium group compared to the injured group (31 ± 20 versus 66 ± 20, p = 0.013), and also a decrease in pSMAD labeling, 62 ± 17 versus 84 ± 10, p = 0.04. A significant increase for NFκB (p65) was noted in injured animals as compared to sham (73 ± 16 versus 7 ± 6, p = 0.0022). Tiotropium-treated animals showed decreased p65 labeling as compared to injured (35 ± 17 versus 74 ± 16, p = 0.02). The decrease in nuclear expression of pERK, pSMAD and NFκB molecules in SMG cells with tiotropium treatment is suggestive that their activation after injury is mediated in part through muscarinic receptors.

Regulation of secretion from serous and mucous cells in the trachea

The physical properties of mucus and the efficiency of tracheal mucociliary clearance depend on maintenance of a balanced interaction among several epithelial cell types. Some of these cell types are specialized to perform ion and water transport, others to perform synthesis and secretion of macromolecules. Our studies have been aimed specifically at identifying the neural mechanisms regulating macromolecule secretion from two of these cell types, i.e. serous and mucous gland cells. Because these cells occur as part of a complex epithelium, it is difficult to monitor the properties and functions of each cell type individually. We have therefore relied principally on morphological methods, which can potentially focus on a single cell type within a heterogeneous tissue. Such studies, however, depend on the availability of visible markers (enzyme-labelled antibodies, radioligands, etc.), and many important aspects of gland cell function cannot be assessed morphologically. Two alternative approaches are therefore being developed: the isolation and segregation of gland cells according to type, and the production of monoclonal antibodies that recognize secretory products of individual cell types. These methods allow serous and mucous cells to be studied by biochemical as well as morphological methods.

Effects of beta-agonists on airway epithelial cells

beta-Adrenergic receptor (betaAR) agonists exert a variety of effects on airway epithelial cells. Among their best known actions is their ability to increase ciliary beat frequency, mediated by cyclic adenosine monophosphate (cAMP) production, stimulation of protein kinase A (PKA), and phosphorylation of an outer dynein arm light chain. Submucosal glands express betaARs, and beta-agonists may stimulate secretion of mucus from airways, although human data are controversial. beta-Agonists may also affect ion transport across epithelial cells by opening apical ion channels such as the cystic fibrosis transmembrane regulator. This effect, likely to occur in submucosal glands, can influence water fluxes across the airway epithelium and may have profound influences on mucus hydration. betaAR activation can increase intracellular calcium in some ciliated cells, thereby stimulating ciliary beating and possibly influencing transepithelial ion transport. betaAR-mediated activation of cAMP-dependent protein kinase accelerates epithelial cell migration, thereby enhancing epithelial wound repair. beta-Agonists reduce the ultrastructural damage seen with infection and potentiate secretion of certain cytokines from epithelial cells while inhibiting secretion of others. Finally, beta-agonists may have effects on airway epithelial cells that are mediated through betaARs but do not require cAMP production. The signaling mechanisms of some beta-agonist effects are not well understood but are important to our understanding of airway epithelial cell growth, differentiation, and function.

Mucociliary transport and cough in humans

The mucus lining of the respiratory tract originates from products of secretory cells interspersed among mucosal cells or within submucosal glands and protects the underlying mucosa from dehydration. Current understanding is that the lining is a two-fluid model in which the upper layer is a viscoelastic gel (mucus, cross-linked glycoproteins) that overlies a sol layer (serous). Thus mucus propelled by ciliary beating, flows above the sol layer and contains sloughed cells and xenobiotic materials that come into contact with it. Sensory stimuli enhance mucus secretion and cause bronchoconstriction; responses that are usually coupled to cough and two-phase gas-liquid clearance of mucus. Airway clearance can be measured by scintigraphy using insoluble radio-labeled markers deposited by aerosol delivery onto the mucus layer. In a healthy airway, lung inflation/deflation reflexes and perhaps shearing forces at the airway surface during high rates of airflow, stimulate mucociliary clearance. During the early stages of smoke-related airway pathology and mucus hypersecretion, mucus layer transport is delayed, and abnormal clearance predominates in the smaller peripheral airways. If high velocity of expiratory airflow is preserved then even with chronic exposure to respiratory irritants and cigarette smoke, mucus clearance remains effective due to cough and two-phase, gas-liquid interactions. However, in patients with advanced airway obstruction and incapable of generating forceful expiratory flows, cough and shearing are ineffective and mucociliary clearance is disparate with markedly slowed mucus layer transport within central airways. Mucolytic therapy for patients with advanced airway obstruction improves ventilation and reduces the frequency of exacerbation.

Differential regulation of Cl- transport proteins by PKC in Calu-3 cells

Cl- transport proteins expressed in a Calu-3 airway epithelial cell line were differentiated by function and regulation by protein kinase C (PKC) isotypes. mRNA expression of Cl- transporters was semiquantitated by RT-PCR after transfection with a sense or antisense oligonucleotide to the PKC isotypes that modulate the activity of the cystic fibrosis transmembrane conductance regulator [CFTR (PKC-epsilon)] or of the Na/K/2Cl (NKCC1) cotransporter (PKC-delta). Expression of NKCC1 and CFTR mRNAs and proteins was independent of antisense oligonucleotide treatment. Transport function was measured in cell monolayers grown on a plastic surface or on filter inserts. With both culture methods, the antisense oligonucleotide to PKC-epsilon decreased the amount of PKC-epsilon and reduced cAMP-dependent activation of CFTR but not alpha(1)-adrenergic activation of NKCC1. The antisense oligonucleotide to PKC-delta did not affect CFTR function but did block alpha(1)-adrenergic activation of NKCC1 and reduce PKC-delta mass. These results provide the first evidence for mRNA and protein expression of NKCC1 in Calu-3 cells and establish the differential regulation of CFTR and NKCC1 function by specific PKC isotypes at a site distal to mRNA expression and translation in airway epithelial cells.

Intranasal salmeterol inhibits allergen-induced vascular permeability but not mast cell activation or cellular infiltration

BACKGROUND

Salmeterol is a long-acting beta2-adrenergic agonist that is widely used in the treatment of asthma. It has been suggested that non-bronchodilator actions of salmeterol may contribute to its efficacy.

OBJECTIVE

To further evaluate the potential non-bronchodilator actions of salmeterol in vivo, using a model of nasal challenge with allergen.

METHODS

Twelve asymptomatic subjects with seasonal allergic rhinitis participated in a randomized, double-blind, placebo-controlled crossover trial of the effects of a single dose of 100 microg of salmeterol on the response to allergen challenge. Sneezing and symptom scores, and levels of histamine and albumin in nasal lavages, were measured throughout the protocol. Concentrations of tryptase, prostaglandin D2 and lysozyme were measured during the acute allergic response, while levels of IL-3, IL-5 and IL-8 were measured at later time points. Numbers of eosinophils and of total white blood cells were also recorded.

RESULTS

Salmeterol did not affect sneezing or symptom scores at any point. During the immediate response to allergen challenge, mast cell activation, reflected by concentrations of histamine, tryptase and prostaglandin D2, and serous glandular secretion, assessed by measurements of lysozyme, were unaffected by salmeterol treatment but vascular permeability, reflected by concentrations of albumin in nasal lavages, was significantly reduced. At later time points, salmeterol had no effect on levels of histamine or albumin and did not affect cellular infiltration. Concentrations of IL-3, IL-5 and IL-8 were not increased by allergen challenge in these subjects, so the effects of salmeterol could not be evaluated.

CONCLUSIONS

Treatment with a single dose of salmeterol had no effect on activation of mast cells or cellular infiltration but inhibited vascular permeability. The ability of salmeterol to inhibit antigen-induced vascular permeability may contribute to its therapeutic efficacy in asthma.

Culture and characterization of human tracheal gland cells

In order to study the composition and regulation of human tracheal gland (HTG) cell secretion, we cultured HTG cells isolated by enzymatic digestion from tracheal mucosa obtained 30 to 60 min after death. On microscopic observation, isolated cells were mainly composed of secretory glandular cells. Maximal HTG cell growth was observed when cells were cultured on type I collagen in the presence of 2% Ultroser G. Under these conditions, 3 to 6 HTG cell passages, corresponding to 20 to 30 population doublings, could be achieved. Lysozyme and bronchial inhibitor (Brl), two secretory protein markers specific to the serous HTG cells, were released in the culture medium, maximal secretion being observed 7 days after the cells had reached confluency. At that time, Brl could be detected, with an immunoperoxidase technique, in about 90% of the cells in culture, suggesting that most cells in culture were serous cells. Using transmission electron microscopy, after in situ fixation, HTG cells exhibited an epithelioid appearance at confluency. Using the biotin-streptavidin gold technique, we identified Brl in cytoplasmic vesicles and in small, immature electron-dense secretory granules. In high cell density cultures, we observed dome formation, suggesting active ion transport mechanisms in HTG cell culture. At confluency, a dose-dependent increase of Brl secretion was induced by phenylephrine, isoproterenol, and carbochol. These results suggest that HTG cell culture provides a useful tool to study the biochemistry and regulation of human tracheobronchial gland cell secretion.

Receptors on airway gland cells

Airway submucosal glands are by volume the most important source of macromolecules in airway secretions. These secretions, containing gel-forming mucins, antibacterial proteins, and antiproteases, comprise the major defensive barrier protecting the host against airborne pathogens. The identification of the mechanisms regulating secretion from the submucosal glands is key to understanding the genesis of this barrier and how it is altered by disease processes. Using a variety of methods, we and others have identified on the gland cells of several species receptors specific for ACh, norepinephrine, substance P, VIP, PGE1, PGE2, PGA1, PGD2, histamine and bradykinin. These receptors all participate in modulating the secretory activity of the airway submucosal glands. Studies of homogeneous cultures of bovine airway serous cells have yielded detailed information regarding the beta-adrenergic receptor on these cells. Using radioligand binding techniques, we found evidence for the presence of a single high affinity beta receptor of beta-2 subtype. Occupancy of this receptor by isoproterenol causes an elevation in the concentration of intracellular cAMP, which in turn stimulates the phosphorylation of a subset of cytoplasmic and membrane proteins. Based on the kinetics and pharmacology of these effects, it is likely that cAMP functions as a second messenger in the serous cell secretory pathway, probably acting through protein kinases. Current efforts are directed at identification of those phosphoproteins whose phosphorylation and dephosphorylation times are consistent with their possible roles in secretion.

Adrenoceptors in airway smooth muscle

This review examines the roles and functional significance of alpha and beta-adrenoceptor subtypes in airway smooth muscle, with emphasis on human airway function and the influence of asthma. Specifically, we have examined the distribution of beta-adrenoceptors in lung and the influence of age, the epithelium, respiratory viruses and inflammation associated with asthma on airway smooth muscle beta-adrenoceptor function. Sites of action, beta 2-selectivity, efficacy and tolerance are also examined in relation to the use of beta 2-agonists in man. In addition, alpha-adrenoceptor function in airway smooth muscle has been reviewed, with some emphasis on comparing observations made in airway smooth muscle with those in animal models.

Autoradiographic localization of changes in pulmonary beta-adrenoceptors in an animal model of atopy

Vaccination of guinea pigs with Haemophilus influenzae leads to an impairment of beta-adrenoceptor function in lung. We have used an autoradiographic technique to study the distribution of changes in lung beta-adrenoceptor density. H. influenzae induced a decrease in beta-adrenoceptors in peripheral lung membranes of 22 +/- 5% (mean +/- S.E.M., n = 7), while the affinity of binding was unaffected. Tracheal beta-adrenoceptor binding was not influenced by H. influenzae. Autoradiography revealed a 27% reduction in beta-adrenergic binding sites on alveolar septa. Bronchial epithelial beta-adrenoceptors were decreased for 36%, and vascular smooth muscle and endothelial beta-adrenoceptors were also reduced. beta-Adrenoceptors on airway smooth muscle were unaffected. H. influenzae affected both the beta 1- and beta 2-subtypes of receptors. It is concluded that in this animal model of atopy beta-adrenoceptors may be decreased on several different cell types within the lungs, which may influence overall airway and vascular reactivity.

Characterization of beta-adrenergic receptors in cultured bovine tracheal gland cells

We characterized the beta-adrenergic receptors that mediate secretory responses to isoproterenol in cultured bovine tracheal submucosal gland cells. Previous studies have shown that these cells have morphological and biochemical features characteristic of serous cells. Isoproterenol, epinephrine, and norepinephrine each stimulated the secretion of 35SO4-labeled macromolecules from these cultured serous cells with a rank order of potency (isoproterenol greater than epinephrine greater than norepinephrine) consistent with the presence of beta 2-adrenergic receptors. These functional studies were supported by radioligand-binding studies using [I125]-iodocyanopindolol (125I-CYP) to identify beta-adrenergic receptors. 125I-CYP binding to membrane particulates prepared from cultured serous cells was saturable and of high affinity (equilibrium dissociation constant 20 +/- 3 pM; mean +/- SE, n = 6) and was antagonized stereoselectively by propranolol. Adrenergic agonists competed for 125I-CYP-binding sites with a rank order of potency characteristic of the beta 2-adrenergic receptor subtype. A specific beta 2-adrenergic receptor antagonist, ICI 118.551, competed for a single class of 125I-CYP-binding sites with high affinity (inhibition constant 1.8 +/- 0.3 nM, n = 3). We concluded that the secretory response of cultured tracheal gland cells to isoproterenol is a response mediated by beta-adrenergic receptors of the beta 2 subtype.

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.

Effect of phorbol ester and calcium ionophore on chloride secretion in canine tracheal epithelium

The control of Cl- secretion was examined by two of the terminal events in the phosphoinositide regulatory pathway: activation of protein kinase C and an increase in cell Ca2+. The phorbol ester phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C, stimulated Cl- secretion in both native and cultured monolayers of tracheal epithelium. Approximately 1.5 nM of mucosal PMA was required for half-maximal stimulation. Stimulation was not dependent on prostaglandin production nor was it accompanied by an increase in cellular levels of cAMP. Although the maximal rate of PMA-induced Cl- secretion was less than that induced by cAMP, there was a synergistic effect between PMA and forskolin, an agent that activates adenylate cyclase. The response to PMA was at least partly transient and PMA may also attenuate Cl- secretion under some circumstances. Thus the response to PMA, and presumably protein kinase C activation, may be complex. An increase in cell Ca2+ produced by addition of the Ca2+ ionophore A23187 also stimulated Cl- secretion. However, the effect was at least partly indirect. A23187 enhanced prostaglandin E2 production and the prostaglandin synthesis inhibitor, indomethacin, blocked A23187-induced secretion in native epithelia and attenuated the effect of A23187 in cultured monolayers. These results indicate the presence of a non-cAMP-dependent regulatory pathway capable of controlling Cl- secretion in tracheal epithelium. Activation of protein kinase C may stimulate secretion directly or modulate the response to cAMP. An increase in cell Ca2+ may stimulate secretion at least partly by stimulating endogenous prostaglandin production.

Adrenergic regulation of ion transport by primary cultures of canine tracheal epithelium: cellular electrophysiology

We examined the effect of adrenergic agents on the cellular electrical properties of primary cultures of canine tracheal epithelium. Both isoproterenol and epinephrine stimulated Cl secretion, as evidenced by an increase in transepithelial voltage and a fall in transepithelial resistance. Moreover, both agents appear to increase the conductance of apical and basolateral membranes. However, the pattern of response was different. Isoproterenol initially depolarized apical voltage psi a and decreased the fractional resistance of the apical membrane fR. These changes are consistent with an initial increase in apical Cl conductance. In contrast, epinephrine acutely hyperpolarized psi a and increased fR, changes consistent with an initial increase in basolateral K conductance. Following the acute effect of epinephrine, psi a depolarized and fR decreased to values not significantly different from those observed with isoproterenol. The acute increase in basolateral K conductance produced by epinephrine appeared to result from stimulation of alpha adrenergic receptors because it was reproduced by addition of the alpha agonist phenylephrine, and blocked by the alpha antagonist phentolamine. The ability of prazosin but not yohimbine to block the acute epinephrine-induced increase in K permeability indicates the presence of alpha 1 adrenergic receptors. The acute alpha adrenergic-induced increase in basolateral K conductance may be mediated by an increase in cell Ca because the response was mimicked by addition of the Ca ionophore A23187. In contrast, the response to isoproterenol was similar to that observed with addition of 8-bromo-cAMP and theophylline. These results indicate that both beta and alpha adrenergic agents mediate the ion transport processes in canine tracheal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic localisation of ascorbic acid-dependent binding sites for [125I]iodocyanopindolol in guinea-pig trachea

Light microscopic autoradiography showed that the supposedly beta-adrenoceptor-selective radioligand [125I]iodocyanopindolol (I-CYP) bound to sites in both the guinea-pig tracheal epithelium and smooth muscle that were sensitive to propranolol and isoprenaline. Low levels of binding were associated with sub-epithelial mucosal cells. Ascorbic acid caused a concentration-related increase in total I-CYP binding which was predominantly associated with the sub-epithelial mucosa, was not inhibited by propranolol, and was thus not associated with beta-adrenoceptors.

Influence of the epithelium on responsiveness of guinea-pig isolated trachea to contractile and relaxant agonists

The potency (pD2) and maximal contractile effect (Emax) of histamine, acetylcholine, carbachol and K+ were assessed from cumulative concentration-effect curves in guinea-pig isolated tracheal ring preparations with and without an intact epithelium. Estimates of Emax were not significantly different in epithelium-denuded preparations compared with those measured in intact preparations; pD2 values for acetylcholine, carbachol and K+ were not significantly altered. In contrast, the potency of histamine was significantly increased by about 4 fold in preparations devoid of epithelial cells. Estimates of potency and Emax were also determined for the smooth muscle relaxants isoprenaline, forskolin and theophylline (which increase intracellular cyclic AMP) and for nitroglycerin (which increases cyclic GMP) in both intact and epithelium-stripped tracheal rings. The pD2 values for these relaxants were not significantly altered by the removal of the epithelium. However, with the exception of nitroglycerin, Emax values for these relaxants were significantly lower in stripped than in intact tracheal rings that had been maximally precontracted with carbachol. The autoradiographic localisation of binding sites for the non-selective beta-adrenoceptor ligand [125I]-iodocyanopindolol (I-CYP) showed that the epithelium of the guinea-pig trachea had a 75 +/- 16% greater density of beta-adrenoceptors than the smooth muscle. Removing the epithelium did not significantly alter either the density of smooth muscle binding sites or the affinity of I-CYP binding. It was concluded that the reduced functional response of guinea-pig trachea to isoprenaline was probably not due to smooth muscle beta-adrenoceptor dysfunction. Results indicate that the epithelium plays an important role in the modulation of responsiveness of guinea-pig trachea to histamine and relaxants that mediate their effects by selectively increasing intracellular cyclic AMP levels.

Monoclonal antibodies as probes for unique antigens in secretory cells of mixed exocrine organs

In the past, it has been difficult to identify the secretory product and control mechanisms associated with individual cell types making up mixed exocrine organs. This report establishes the feasibility of using immunological methods to characterize both the biochemical constituents and regulatory mechanisms associated with secretory cells in the trachea. Monoclonal antibodies directed against components of tracheal mucus were produced by immunizing mice with dialyzed, desiccated secretions harvested from tracheal organ culture. An immunofluorescence assay revealed that of the total 337 hybridomas screened, 100 produced antibodies recognizing goblet cell granules; 64, gland cell granules; and 3, antigen confined to the ciliated apical surface of the epithelium. The tracheal goblet cell antibody described in this report was strongly cross-reactive with intestinal goblet cells, as well as with a subpopulation of submandibular gland cells, but not with cells of Brunner's glands or the ciliated cell apical membrane. The serous cell antibody was not cross-reactive with goblet, Brunner's gland, or submandibular cells, or the ciliated cell apical membrane. The antibody directed against the apical membrane of ciliated cells did not cross-react with gland or goblet cells or the apical membrane of epithelial cells in the duodenum. Monoclonal antibodies, therefore, represent probes by which products unique to specific cells or parts of cells in the trachea can be distinguished. The antibodies, when used in enzyme immunoassays, can be used to quantitatively monitor secretion by individual cell types under a variety of physiological and pathological conditions. They also provide the means for purification and characterization of cell-specific products by immunoaffinity chromatography.