Molecular staging of epithelial maturation using secretory cell-specific genes as markers

Bronchiolar Clara cells undergo phenotypic changes during development and in disease. These changes are poorly described due to a paucity of molecular markers. We used chemical and transgenic approaches to ablate Clara cells, allowing identification of their unique gene expression profile. Flavin monooxygenase 3 (Fmo3), paraoxonase 1 (Pon1), aldehyde oxidase 3 (Aox3), and claudin 10 (Cldn10) were identified as novel Clara cell markers. New and existing Clara cell marker genes were categorized into three classes based on their unique developmental expression pattern. Cldn10 was uniformly expressed in the epithelium at Embryonic Day (E)14.5 and became restricted to secretory cells at E18.5. This transition was defined by induction of CCSP. Maturation of secretory cells was associated with progressive increases in the expression of Fmo3, Pon1, Aox3, and Cyp2f2 between late embryonic and postnatal periods. Messenger RNA abundance of all categories of genes was dramatically decreased after naphthalene-induced airway injury, and displayed a sequence of temporal induction during repair that suggested sequential secretory cell maturation. We have defined a broader repertoire of Clara cell-specific genes that allows staging of epithelial maturation during development and repair.

Conditional stabilization of beta-catenin expands the pool of lung stem cells

Maintenance of classic stem cell hierarchies is dependent upon stem cell self-renewal mediated in part by Wnt/beta-catenin regulation of the cell cycle. This function is critical in rapidly renewing tissues due to the obligate role played by the tissue stem cell. However, the stem cell hierarchy responsible for maintenance of the conducting airway epithelium is distinct from classic stem cell hierarchies. The epithelium of conducting airways is maintained by transit-amplifying cells in the steady state; rare bronchiolar stem cells are activated to participate in epithelial repair only following depletion of transit-amplifying cells. Here, we investigate how signaling through beta-catenin affects establishment and maintenance of the stem cell hierarchy within the slowly renewing epithelium of the lung. Conditional potentiation of beta-catenin signaling in the embryonic lung results in amplification of airway stem cells through attenuated differentiation rather than augmented proliferation. Our data demonstrate that the differentiation-modulating activities of stabilized beta-catenin account for expansion of tissue stem cells.

CCSP regulates cross talk between secretory cells and both ciliated cells and macrophages of the conducting airway

Pulmonary host defense employs a combination of biochemical and biophysical activities to recognize, inactivate, and mediate clearance of environmental agents as well as modulate the overall response to such challenge. Dysregulation of the inflammatory arm of this response is associated with chronic lung diseases (CLD) including cystic fibrosis and chronic obstructive lung disease. Although mechanisms mediating immunoregulation are incompletely characterized, decrements in levels of the nonciliated secretory cell product Clara cell secretory protein (CCSP) in numerous CLD and identification of proinflammatory state in mice homozygous for a null allele of the CCSP gene (CCSP−/−) suggest a central role for the nonciliated secretory cell in this process. In an effort to determine the molecular basis for immunoregulatory defects associated with CCSP deficiency, we utilized difference gel electrophoresis in combination with matrix-assisted laser desorption ionization time-of-flight to compare the proteomes of wild-type and CCSP−/− mice. We demonstrate a shift in the isoelectric point of the immunomodulatory protein annexin A1 (ANXA1) to more acidic isoforms in CCSP−/− mice. Similar ANXA1 mRNA and protein abundance in wild-type and CCSP−/− tissue and identical localization of ANXA1 protein to alveolar macrophages and the ciliary bed of ciliated cells demonstrated that CCSP deficiency was associated exclusively with altered posttranslational modification of ANXA1. These results suggest that both long- and short-range paracrine signaling between nonciliated secretory cells and cells of the immune system and epithelium impact modification of cell type-specific proteins and implicate nonciliated secretory cells in a regulatory axis that might integrate critical aspects of host defense.

Molecular and functional properties of lung SP cells

Previous analysis of lung injury and repair has provided evidence for region-specific stem cells that maintain proximal and distal epithelial compartments. However, redundant expression of lineage markers by cells at several levels of the stem cell hierarchy has complicated phenotypic and functional characterization of clonogenic airway cells. Based on the demonstration that rapid efflux of the DNA dye Hoechst 33342 can be used to prospectively purify long-term repopulating hematopoietic stem cells, we hypothesized that lung cells with similar biochemical properties would be enriched for clonogenic progenitors. We demonstrate that Hoechst-dim side population (SP) cells isolated from proximal and distal compartments of the mouse lung were relatively small and agranular, exhibited low red and green autofluorescence, and that the SP fraction was highly enriched in clonogenic cells. Quantitative RT-PCR indicated that vimentin mRNA was enriched and that epithelial markers were depleted in these preparations of SP cells. Bleomycin exposure was associated with decreased clonogenicity among alveolar SP and suggested that SP cell function was compromised under profibrotic conditions. We conclude that the SP phenotype is common to clonogenic cells at multiple airway locations and suggest that Hoechst efflux is a property of cells expressing a wound-repair phenotype.

Elevation of susceptibility to ozone-induced acute tracheobronchial injury in transgenic mice deficient in Clara cell secretory protein

Increases in Clara cell abundance or cellular expression of Clara cell secretory protein (CCSP) may cause increased tolerance of the lung to acute oxidant injury by repeated exposure to ozone (O3). This study defines how disruption of the gene for CCSP synthesis affects the susceptibility of tracheobronchial epithelium to acute oxidant injury. Mice homozygous for a null allele of the CCSP gene (CCSP-/-) and wild type (CCSP+/+) littermates were exposed to ozone (0.2 ppm, 8 h; 1 ppm, 8 h) or filtered air. Injury was evaluated by light and scanning electron microscopy, and the abundance of necrotic, ciliated, and nonciliated cells was estimated by morphometry. Proximal and midlevel intrapulmonary airways and terminal bronchioles were evaluated. There was no difference in airway epithelial composition between CCSP+/+ and CCSP-/- mice exposed to filtered air, and exposure to 0.2 ppm ozone caused little injury to the epithelium of both CCSP+/+ and CCSP-/- mice. After exposure to 1.0 ppm ozone, CCSP-/- mice suffered from a greater degree of epithelial injury throughout the airways compared to CCSP+/+ mice. CCSP-/- mice had both ciliated and nonciliated cell injury. Furthermore, lack of CCSP was associated with a shift in airway injury to include proximal airway generations. Therefore, we conclude that CCSP modulates the susceptibility of the epithelium to oxidant-induced injury. Whether this is due to the presence of CCSP on the acellular lining layer surface and/or its intracellular distribution in the secretory cell population needs to be defined.

Clara cell secretory protein and phospholipase A2activity modulate acute ventilator-induced lung injury in mice

Lung vascular permeability is acutely increased by high-pressure and high-volume ventilation. To determine the roles of mechanically activated cytosolic PLA2(cPLA2) and Clara cell secretory protein (CCSP), a modulator of cPLA2activity, we compared lung injury with and without a PLA2inhibitor in wild-type mice and CCSP-null mice (CCSP−/−) ventilated with high and low peak inflation pressures (PIP) for 2- or 4-h periods. After ventilation with high PIP, we observed significant increases in the bronchoalveolar lavage albumin concentrations, lung wet-to-dry weight ratios, and lung myeloperoxidase in both genotypes compared with unventilated controls and low-PIP ventilated mice. All injury variables except myeloperoxidase were significantly greater in the CCSP−/−mice relative to wild-type mice. Inhibition of cPLA2in wild-type and CCSP−/−mice ventilated at high PIP for 4 h significantly reduced bronchoalveolar lavage albumin and total protein and lung wet-to-dry weight ratios compared with vehicle-treated mice of the same genotype. Membrane phospho-cPLA2and cPLA2activities were significantly elevated in lung homogenates of high-PIP ventilated mice of both genotypes but were significantly higher in the CCSP−/−mice relative to the wild-type mice. Inhibition of cPLA2significantly attenuated both the phospho-cPLA2increase and increased cPLA2activity due to high-PIP ventilation. We propose that mechanical activation of the cPLA2pathway contributes to acute high PIP-induced lung injury and that CCSP may reduce this injury through inhibition of the cPLA2pathway and reduction of proinflammatory products produced by this pathway.

Freeze drying--principles and practice for successful scale-up to manufacturing

Freeze Drying involves transfer of heat and mass to and from the product under preparation, respectively, thus it is necessary to scale these transport phenomena appropriately from pilot plant to manufacturing-scale units to maintain product quality attributes. In this manuscript we describe the principal approach and tools utilized to successfully transfer the lyophilization process of a labile pharmaceutical product from pilot plant to manufacturing. Based on pilot plant data, the lyophilization cycle was tested during limited scale-up trials in manufacturing to identify parameter set-point values and test process parameter ranges. The limited data from manufacturing were then used in a single-vial mathematical model to determine manufacturing lyophilizer heat transfer coefficients, and subsequently evaluate the cycle robustness at scale-up operating conditions. The lyophilization cycle was then successfully demonstrated at target parameter set-point values.

Mucin is produced by clara cells in the proximal airways of antigen-challenged mice

Airway mucus hypersecretion is a prominent feature of many obstructive lung diseases. We thus determined the ontogeny and exocytic phenotype of mouse airway mucous cells. In naive mice, ciliated (approximately 40%) and nonciliated (approximately 60%) epithelial cells line the airways, and > 95% of the nonciliated cells are Clara cells that contain Clara cell secretory protein (CCSP). Mucous cells comprise < 5% of the nonciliated cells. After sensitization and a single aerosol antigen challenge, alcian blue-periodic acid Schiff's positive mucous cell numbers increase dramatically, appearing 6 h after challenge (21% of nonciliated/nonbasal cells), peaking from Days 1-7 (99%), and persisting at Day 28 (65%). Throughout the induction and resolution of mucous metaplasia, ciliated and Clara cell numbers identified immunohistochemically change only slightly. Intracellular mucin content peaks at Day 7, and mucin expression is limited specifically to a Clara cell subset in airway generations 2-4 that continue to express CCSP. Functionally, Clara cells are secretory cells that express the regulated exocytic marker Rab3D and, in antigen-challenged mice, rapidly secrete mucin in response to inhaled ATP in a dose-dependent manner. Thus, Clara cells show great plasticity in structure and secretory products, yet have molecular and functional continuity in their identity as specialized apical secretory cells.

Airway injury in lung disease pathophysiology: selective depletion of airway stem and progenitor cell pools potentiates lung inflammation and alveolar dysfunction

Identification of early events that contribute to the establishment of chronic lung disease has been complicated by the variable involvement of the airway and alveolar compartments in the complex physiology of end-stage disease. In particular, the impact of airway injury on alveolar integrity and function has not been addressed and would be facilitated by development of animal models of lung disease that specifically target a single cell type within the airway epithelium. We have previously demonstrated that ganciclovir treatment of CCtk transgenic mice, which express the herpes simplex thymidine kinase gene under regulation of the mouse Clara cell secretory protein (CCSP) promoter, results in elimination of the airway progenitor and stem cell pools and a consequent failure of airway regeneration that is associated with rapid morbidity and mortality. In this study, we used the CCtk model to test the hypothesis that selective airway injury initiates profound lung dysfunction through mechanisms that compromise alveolar integrity. Results demonstrate that elimination of the CCSP-expressing cell population results in secondary alveolar inflammation, edema, and depletion of the alveolar type II cell population. On the basis of these data we conclude that selective airway injury can serve as the inciting injury in diseases characterized by severely compromised alveolar function.

In vivo differentiation potential of tracheal basal cells: evidence for multipotent and unipotent subpopulations

The composition of the conducting airway epithelium varies significantly along the proximal to distal axis, with that of the tracheal epithelium exhibiting the greatest complexity. A number of progenitor cells have been proposed to contribute to the maintenance of this cellular diversity both in the steady state and in response to injury. However, individual roles for each progenitor cell type are poorly defined in vivo. The present study was undertaken to investigate the hypothesis that basal cells represent a multipotent progenitor cell type for renewal of the injured tracheal epithelium. To understand their contribution to epithelial repair, mice were exposed to naphthalene to induce airway injury and depletion of the secretory cell progenitor pool. Injury resulted in a rapid induction of cytokeratin 14 (K14) expression among the majority of GSI-B4-reactive cells and associated hyperplasia of basal cells. Restoration of depleted secretory cells occurred after 6 days of recovery and was associated with regression of the basal cell hyperplasia, suggesting a progenitor-progeny relationship. Multipotent differentiation of basal cells was confirmed using a bitransgenic ligand-regulated Cre-loxP reporter approach in which expression of a ubiquitously expressed LacZ reporter was activated within K14-expressing progenitor cells during airway repair. With the use of this approach, it was determined that K14-expressing cells include subsets capable of either multipotent or unipotent differentiation in vivo. We conclude that basal cells have the capacity for restoration of a fully differentiated epithelium.

Molecular phenotype of airway side population cells

Lung epithelial-specific stem cells have been localized to discrete microenvironments throughout the adult conducting airway. Properties of these cells include pollutant resistance, multipotent differentiation, and infrequent proliferation. Goals of the present study were to use Hoechst 33342 efflux, a property of stem cells in other tissues, to purify and further characterize airway stem cells. Hoechst 33342 effluxing lung cells were identified as a verapamil-sensitive side population by flow cytometry. Lung side population cells were further subdivided on the basis of hematopoietic (CD45 positive) or nonhematopoietic (CD45 negative) origin. Nonhematopoietic side population cells were enriched for stem cell antigen-1 reactivity and expressed molecular markers specific to both airway and mesenchymal lineages. Analysis of the molecular phenotype of airway-derived side population cells indicates that they are similar to neuroepithelial body-associated variant Clara cells. Taken together, these data suggest that the nonhematopoietic side population isolated from lung is enriched for previously identified airway stem cells.

Basal cells are a multipotent progenitor capable of renewing the bronchial epithelium

Commitment of the pulmonary epithelium to bronchial and bronchiolar airway lineages occurs during the transition from pseudoglandular to cannalicular phases of lung development, suggesting that regional differences exist with respect to the identity of stem and progenitor cells that contribute to epithelial maintenance in adulthood. We previously defined a critical role for Clara cell secretory protein-expressing (CE) cells in renewal of bronchiolar airway epithelium following injury. Even though CE cells are also the principal progenitor for maintenance of the bronchial airway epithelium, CE cell injury is resolved through a mechanism involving recruitment of a second progenitor cell population that we now identify as a GSI-B(4) reactive, cytokeratin-14-expressing basal cell. These cells exhibit multipotent differentiation capacity as assessed by analysis of cellular phenotype within clones of LacZ-tagged cells. Clones were derived from K14-expressing cells tagged in a cell-type-specific fashion by ligand-regulable Cre recombinase-mediated genomic rearrangement of the ROSA26 recombination substrate allele. We conclude that basal cells represent an alternative multipotent progenitor cell population of bronchial airways and that progenitor cell selection is dictated by the type of airway injury.

Time and pressure dependence of transvascular Clara cell protein, albumin, and IgG transport during ventilator-induced lung injury in mice

We compared the transport of three proteins with different hydrodynamic radii with ultrastructural changes in lungs of intact mice ventilated at peak inflation pressures (PIP) of 15, 35, 45, and 55 cmH2O for 2 h and PIP of 55 cmH2O for 0.5 and 1 h. After 2 h of ventilation, significant increases were observed in plasma Clara cell secretory protein (1.9 nm radius) at 35 cmH2O PIP and in bronchoalveolar lavage fluid albumin (3.6 nm radius) at 45 cmH2O PIP and IgG (5.6 nm radius) at 55 cmH2O PIP. Increased concentrations of all three proteins and lung wet-to-dry weight ratios were significantly correlated with PIP and ventilation time. Clara cell secretory protein and albumin increased significantly after 0.5 h of 55 cmH2O PIP, but IgG increased only after 2 h. Separation of endothelium or epithelium to form blebs was apparent only in small vessels (15-30 μm diameter) at 45 cmH2O PIP and after 0.5 h at 55 cmH2O PIP but became extensive after 2 h of ventilation at 55 cmH2O PIP. Junctional gaps between cells were rarely observed. Ultrastructural lung injury and protein clearances across the air-blood barrier were related to ventilation time and PIP levels. Protein clearances increased in relation to molecular size, consistent with increasing dimensions and frequency of transmembrane aqueous pathways.

Secretoglobins SCGB3A1 and SCGB3A2 define secretory cell subsets in mouse and human airways

Clara cell secretory protein (CCSP) is expressed abundantly within the conducting airway epithelium and is thought to have immunoregulatory functions. Differences in the localization of CCSP between mouse and human airways led us to hypothesize that functional homologues of CCSP may compensate for the lack of CCSP expression in proximal airway locations. We previously identified an expressed sequence tag (W82219) whose expression is induced within Clara cells of CCSP knockout mice. Expressed sequence tag W82219 is distantly related to CCSP and represents a member of a new subfamily of secretoglobins (MmSCGB3A2). Another member of the mouse SCGB3 family (MmSCGB3A1) as well as human orthologues (HsSCGB3A1 and HsSCGB3A2) that possess structural homology to CCSP were identified, suggesting they may share common functional properties. SCGB3A1 messenger RNA localizes to a subset of SCGB3A2-expressing cells within bronchi of both mouse and neonatal human lungs. CCSP, SCGB3A1, and SCGB3A2 were decreased in airways of neonates with bronchopulmonary dysplasia and in mice after airway injury. We conclude that secretory cells of the conducting airway epithelium express distinct members of the secretoglobin family in a partially overlapping fashion. Altered expression of secretoglobins in airway disease may contribute to immunoregulatory perturbations commonly seen in chronic airway disease.

Clara cell secretory protein deficiency alters clara cell secretory apparatus and the protein composition of airway lining fluid

Clara cells represent the predominant secretory cell within distal conducting airways of mammals and exhibit functional alterations with chronic lung disease. We previously demonstrated that Clara cell secretory protein (CCSP) deficiency results in enhanced susceptibility to environmental agents. The present study was undertaken to define changes in Clara cell secretory function associated with CCSP deficiency in knockout mice. Comparative morphometry of Clara cell ultrastructure revealed dramatic alterations in secretory apparatus between wild-type (WT) and CCSP knockout (CCSP-/-) mice. Secretory granules, which occupy greater than 2% of Clara cell cytoplasmic volume in WT mice, were completely absent among Clara cells of CCSP-/- mice. Moreover, Clara cells of CCSP-/- mice exhibited a > 95% reduction in rough endoplasmic reticulum and alterations to Golgi apparatus, relative to WT controls. Ultrastructural perturbations to Clara cells were associated with altered protein composition of airway lining fluid as revealed by two-dimensional gel analysis of bronchoalveolar lavage proteins, but were not associated with altered abundance or secretion of CC26, another Clara cell secretory protein. We conclude that CCSP is required for the appearance of Clara cell secretory granules and that functional changes to Clara cells that result from CCSP deficiency lead to alterations in the composition of epithelial lining fluid.

Altered lung gene expression in CCSP-null mice suggests immunoregulatory roles for Clara cells

Clara cell secretory protein (CCSP) is one of the most abundant proteins present in airway lining fluid of mammals. In an effort to elucidate the function of CCSP, we established CCSP-null [CCSP(-/-)] mice and demonstrated altered sensitivity to various environmental agents including oxidant pollutants and microorganisms. Although CCSP deficiency itself may be central to the observed changes in environmental susceptibility, altered lung gene expression associated with CCSP deficiency may contribute to the observed phenotype. To determine whether CCSP deficiency results in altered lung gene expression, high-density cDNA microarrays were used to profile gene expression in the total lung RNA of wild-type and CCSP(-/-) mice. Genes that were differentially expressed between wild-type and CCSP(-/-) mice included a previously non-annotated expressed sequence tag (EST W82219) and immunoglobulin A (IgA), both of which were elevated with CCSP deficiency. mRNA expression of EST W82219 and IgA was localized in the lungs of wild-type and CCSP(-/-) mice to airway Clara cells and peribronchial lymphoid tissues, respectively. We conclude that CCSP deficiency is associated with 1) altered gene expression in Clara cells of the conducting airway epithelium and 2) alterations to peribronchial B lymphocytes. These findings identify new roles for Clara cells and their secretions in airway homeostasis.

Clara cell secretory protein-expressing cells of the airway neuroepithelial body microenvironment include a label-retaining subset and are critical for epithelial renewal after progenitor cell depletion

Stem cells with potential to contribute to the re-establishment of the normal bronchiolar epithelium have not been definitively demonstrated. We previously established that neuroepithelial bodies (NEBs) sequester regenerative cells that contribute to bronchiolar regeneration after selective chemical depletion of Clara cells, a major progenitor cell population. Two candidate stem cells were identified on the basis of proliferative potential after chemical ablation: a pollutant-resistant subpopulation of Clara cells that retain their expression of Clara cell secretory protein (CCSP) (variant CCSP-expressing [CE] cells or vCE cells) and calcitonin gene-related peptide (CGRP)-expressing pulmonary neuroendocrine cells (PNECs). In the present study, two populations of label-retaining cells were identified within the NEB: CGRP-expressing cells and a subpopulation of CE cells. To investigate contributions made by CE and CGRP-expressing cells to epithelial renewal, CE cells were ablated through acute administration of ganciclovir to transgenic mice expressing herpes simplex virus thymidine kinase under the regulatory control of the mouse CCSP promoter. CGRP-immunoreactive PNECs proliferated after depletion of CE cells, yet were unable to repopulate CE cell-depleted airways. These results support the notion that vCE cells represent either an airway stem cell or are critical for stem cell maintenance, and suggest that PNECs are not sufficient for epithelial renewal.

Phenotypic consequences of lung-specific inducible expression of FGF-3

Members of the fibroblast growth factor (FGF) family play a critical role in embryonic lung development and adult lung physiology. The in vivo investigation of the role FGFs play in the adult lung has been hampered because the constitutive pulmonary expression of these factors often has deleterious effects and frequently results in neonatal lethality. To circumvent these shortcomings, we expressed FGF-3 in the lungs under the control of the progesterone antagonist-responsive binary transgenic system. Four binary transgenic lines were obtained that showed ligand-dependent induction of FGF-3 with induced levels of FGF-3 expression dependent on the levels of expression of the GLp65 regulator as well as the dose of the progesterone antagonist, RU486, administered. FGF-3 expression in the adult mouse lung resulted in two phenotypes depending on the levels of induction of FGF-3. Low levels of FGF-3 expression resulted in massive free alveolar macrophage infiltration. High levels of FGF-3 expression resulted in diffuse alveolar type II cell hyperplasia. Both phenotypes were reversible after the withdrawal of RU486. This system will be a valuable means of investigating the diverse roles of FGFs in the adult lung.

Pulmonary phenotype of CCSP/UG deficient mice: a consequence of CCSP deficiency or altered Clara cell function?

Clara cell secretory protein (CCSP) is the most abundant secreted protein within airways of the lung. Moreover, CCSP levels are modulated in human lung disease, supporting a potentially important role for CCSP and/or Clara cells in lung homeostasis. However, in vivo roles for CCSP remain elusive. A popular hypothesis is that CCSP is a regulator of the inflammatory response. The purpose of this review is to provide an overview of the phenotype of CCSP null mice and relate this phenotype to proposed functions for the protein. Phenotypic analysis of mice homozygous for the CCSP-1 null allele of the CCSP gene (CCSP-/-1) revealed susceptibility to inhaled oxidant gases. Sensitivity of CCSP-/-1 mice to inhaled ozone is unrelated to alterations in antioxidant defenses, but is associated with increased cellular injury. Additional studies investigating inflammatory control in CCSP deficient mice found no differences between wild-type and CCSP-/-1 mice in their inflammatory response to low-dose inhaled endotoxin exposure, arguing against a role for CCSP in regulation of pulmonary inflammation. The findings among CCSP-/-1 mice of ultrastructural alterations to Clara cell secretory apparatus, with associated changes in airway lining fluid protein composition, demonstrate that the CCSP-/-1 genotype results in more complex changes to airways than CCSP deficiency per se. It can be concluded that CCSP does not regulate endotoxin-induced pulmonary inflammation. Moreover, CCSP-/-1 mice represent a valuable tool for probing functional roles for Clara cells in regulation of airway lining fluid composition and lung pollutant susceptibility.

Conditional clara cell ablation reveals a self-renewing progenitor function of pulmonary neuroendocrine cells

The neuroepithelial body (NEB) is a highly dynamic structure that responds to chronic airway injury through hyperplasia of associated pulmonary neuroendocrine (PNE) cells. Although NEB dysplasia is correlated with preneoplastic conditions and PNE cells are thought to serve as a precursor for development of small cell lung carcinoma, mechanisms regulating expansion of the PNE cell population are not well understood. Based on studies performed in animal models, it has been suggested that NEB-associated progenitor cells that are phenotypically distinct from PNE cells contribute to PNE cell hyperplasia. We have previously used a Clara cell-specific toxicant, naphthalene, to induce airway injury in mice and have demonstrated that naphthalene-resistant Clara cells, characterized by their expression of Clara cell secretory protein (CCSP), and PNE cells contribute to airway repair and associated hyperplasia of NEBs. This study was conducted to define the contribution of NEB-associated CCSP-expressing progenitor cells to PNE cell hyperplasia after Clara cell ablation. Transgenic (CCtk) mice were generated in which herpes simplex virus thymidine kinase was expressed within all CCSP-expressing cells of the conducting airway epithelium through the use of transcriptional regulatory elements from the mouse CCSP promoter. Chronic administration of ganciclovir (GCV) to CCtk transgenic mice resulted in selective ablation of CCSP-expressing cells within conducting airways. Proliferation and hyperplasia of PNE cells occurred in the absence of detectable proliferation among any other residual airway epithelial cell populations. These results demonstrate that PNE cells function as a self-renewing progenitor population and that NEB-associated Clara cells are not necessary for PNE cell hyperplasia.

Cloning of the chick BMP1/Tolloid cDNA and expression in skeletal tissues

The astacin-related metalloproteases Bone Morphogenetic Protein-1 (BMP1) and Tolloid possess multiple functions in the maturation of extracellular matrices containing fibrillar collagens. We are interested in developing an in-vitro model system to study the role of BMP1 and Tolloid in chondrocytes and osteoblasts. Cloning of the cDNAs for chick BMP1 and Tolloid reveals that the two gene products are more than 80% identical to their human and mouse homologs and are similarly derived from the same genetic locus. Anti-BMP1/Tolloid antibodies have been developed, and detect two proteins of 80 and 116kDa. Chick BMP1 and Tolloid message and proteins are found in a variety of embryonic and juvenile tissues, including chondrocytes and osteoblasts. Tolloid message and protein are generally less abundant than BMP1 message; this discrepancy is greatest in growth plate chondrocytes. Tolloid protein is more tightly bound than BMP1 to the extracellular matrix produced by cultured osteoblasts. The Chordin gene is also expressed in chondrocytes and osteoblasts, suggesting that BMP1 and Tolloid influence BMP signaling as well as matrix maturation during skeletogenesis.

Neuroepithelial bodies of pulmonary airways serve as a reservoir of progenitor cells capable of epithelial regeneration

Remodeling of the conducting airway epithelium is a common finding in the chronically injured lung and has been associated with increased risk for developing lung cancer. Pulmonary neuroendocrine cells and clusters of these cells termed neuroepithelial bodies (NEBs) play a central role in each of these processes. We previously developed an adult mouse model of airway injury and repair in which epithelial regeneration after naphthalene-induced Clara cell ablation occurred preferentially at airway branch points and gave rise to nascent Clara cells. Continued repair was accompanied by NEB hyperplasia. We now provide the following evidence that the NEB microenvironment serves as a source of airway progenitor cells that contribute to focal regeneration of the airway epithelium: 1) nascent Clara cells and NEBs localize to the same spatial domain; 2) within NEB, both Clara cell secretory protein- and calcitonin gene-related peptide-immunopositive cells are proliferative; 3) the NEB microenvironment of both the steady-state and repairing lung includes cells that are dually immunopositive for Clara cell secretory protein and calcitonin gene-related peptide, which were previously identified only within the embryonic lung; and 4) NEBs harbor variant Clara cells deficient in cytochrome P450 2F2-immunoreactive protein. These data suggest that the NEB microenvironment is a reservoir of pollutant-resistant progenitor cells responsive to depletion of an abundant airway progenitor such as the Clara cell.

Normal function and lack of fibronectin accumulation in kidneys of Clara cell secretory protein/uteroglobin deficient mice

Clara cell secretory protein (CCSP), also known as uteroglobin (Ug), is a 16-kDa homodimeric protein of unknown function. Within rodent species, CCSP is expressed predominantly by nonciliated Clara cells that line conducting airways of the lung. To investigate in vivo functions for CCSP, we established mice homozygous for a null allele of the CCSP gene (CCSP-/-). We previously showed no overt phenotypic consequences associated with CCSP deficiency when CCSP-/- mice are maintained in the absence of environmental stress. However, CCSP-/- mice show an oxidant-sensitive phenotype that cannot be attributed to alterations in the inflammatory response when challenged by inhaled oxidant gases. The current study was undertaken to determine whether CCSP deficiency results in pathological changes to the kidney. This study was prompted by the recent description of severe systemic disease and kidney fibrosis/dysfunction in an independent line of CCSP-deficient mice, termed Ug-/- (Zhang et al, Science 276:1408-1412, 1997). CCSP-/- mice show normal growth and reproductive performance when maintained in two independent genetic backgrounds, inbred 129 and congenic C57BL/6. Strain 129 CCSP-/- mice have normal kidney function, as assessed by urinary glucose, lactate dehydrogenase, and glomerular filtration rate; they show no kidney fibrosis or abnormalities in fibronectin accumulation and no histological abnormalities in proximal convoluted tubules or glomeruli at either light or electron microscopic levels. CCSP deficiency is associated with mild proteinurea involving a modest increase in mouse major urinary protein-1. We conclude that CCSP (Ug) deficiency, per se, is not the cause of severe renal pathology and systemic disease reported for Ug-/- mice.

Inflammatory and antioxidant gene expression in C57BL/6J mice after lethal and sublethal ozone exposures

Ozone (O3) is a highly reactive and toxic oxidant pollutant. The objective of this study is to compare cytokine, chemokine, and metallothionein (Mt) changes elicited by lethal and sublethal exposure to ozone in a genetically sensitive strain of mice. Eight-week-old C57BL/6J mice were exposed to 0.3 ppm ozone for 0, 24, or 96 hours; 1.0 ppm ozone for 0, 1, 2, or 4 hours; or 2.5 ppm ozone for 0, 2, 4, or 24 hours. After 24 hours of exposure to 0.3 ppm ozone, increases in mRNA abundance were detected for messages encoding eotaxin, macrophage inflammatory protein (MIP)-1 alpha, and MIP-2. These increases persisted through 96 hours of exposure. At this time point messages encoding lymphotactin (Ltn) and metallothionein were also increased. After 4 hours of 1.0 ppm ozone exposure, increases in mRNA abundance were detected for messages encoding eotaxin, MIP-1 alpha, MIP-2, and interleukin (IL)-6. Mt mRNA abundance was increased after 1 hour of exposure and persisted through 4 hours, although the magnitude of the alterations increased. After 2 hours of 2.5 ppm ozone exposure, increases were detected for messages encoding eotaxin, MIP-1 alpha, MIP-2, IL-6, and Mt. These increases persisted through 4 hours of exposure. Lung weights of mice exposed to 2.5 ppm ozone for 24 hours were approximately 2 times greater than air-exposed mice. At this dose lethality occurred by 36 hours. Increased mRNAs for eotaxin, MIP-1 alpha, MIP-2, and Mt were to a higher magnitude than were detected after 2 and 4 hours of exposure. Messages encoding IL-12, IL-10, interferon (IFN)-gamma, IL-1 alpha, IL-1 beta, and IL-1Ra were unaltered at all time points and doses examined. Our results demonstrate dose- and time-dependent changes in chemokine, cytokine, and Mt mRNA abundance and that early acute changes may be predictive of subacute and chronic responses to ozone.

Clara cell secretory protein-deficient mice differ from wild-type mice in inflammatory chemokine expression to oxygen and ozone, but not to endotoxin

The in vivo function of Clara cell secretory protein (CCSP) is unknown. Biologic and biochemical properties associated with CCSP have led to speculation that it participates in pulmonary inflammatory control. Our earlier studies have demonstrated that CCSP-deficient mice are more sensitive to either hyperoxia or ozone toxicity and show altered oxidant-induced pulmonary proinflammatory responses. In this study we test the hypothesis that altered chemokine responses seen in CCSP-/- mice following oxidant stress are a direct consequence of altered immunoregulation associated with CCSP deficiency. To test this hypothesis we utilized three distinct models of inducing pulmonary toxicity: hyperoxia and ozone (O3), which cause epithelial cell injury, and endotoxin, which causes pulmonary inflammation independent of direct epithelial cell injury. Wild-type (WT) or CCSP-/- strain 129 mice were exposed to O3 at 1.0 ppm for 24 hours, oxygen (O2) > 99% for 68 hours or inhalation of 0.0575 microgram endotoxin per mouse for 10 minutes and examined 6 hours postexposure. Mice displayed increased sensitivity to O3, as demonstrated by increased abundance of mRNAs encoding Eotaxin, macrophage inflammatory protein (MIP)-1 alpha, and MIP-2, after 4 hours of exposure, whereas WT mice were unaltered from controls. Increased sensitivity to hyperoxia was also observed, as demonstrated by increased abundance of mRNAs encoding Eotaxin, MIP-1 alpha, MIP-1 beta, MIP-2, and interferon-gamma inducible (IP)-10 after 68 hours of exposure, whereas WT mice were unaltered from controls. In contrast, WT and CCSP-/- mice responded identically 6 hours postinhalation of 0.0575 microgram lipopolysaccharide (LPS) per mouse. PMN response was 63% and 64% in WT and CCSP-/- mice, respectively. Messenger RNAs encoding Eotaxin, MIP-1 alpha, MIP-1 beta, MIP-2, IP-10, and MCP-1 were increased identically. We conclude that CCSP does not participate in regulation of the endotoxin-elicited pulmonary inflammatory response. Identical inflammatory and chemokine responses of CCSP-/- and WT mice in response to a nonepithelial toxic agent (endotoxin) suggest that altered inflammatory control observed between WT and CCSP-/- mice following O2 and O3 exposure is not the result of altered immunoregulation.

Clara cell secretory protein deficiency increases oxidant stress response in conducting airways

Little is known about the molecular basis for differential pulmonary oxidant sensitivity observed between genetically disparate members of the same species. We have generated mice that are deficient in Clara cell secretory protein (CCSP -/-) and that exhibit an oxidant-sensitive phenotype. We characterized the kinetics and distribution of altered stress-response [interleukin-6 (IL-6) and metallothionein (MT)] and epithelial cell-specific [cytochrome P-450 2F2 (CYP2F2)] gene expression to further understand the cellular and molecular basis for altered oxidant sensitivity in 129 strain CCSP -/- mice. Increases in IL-6 and MT mRNA abundance were detected by 2 h of exposure to 1 part/million ozone and preceded reductions in Clara cell CYP2F2 mRNA expression. Despite being qualitatively similar, increases in IL-6 and MT mRNA expression were enhanced in CCSP -/- mice with respect to coexposed 129 strain wild-type mice. Increased MT mRNA expression, indicative of the stress response, localized to the airway epithelium, surrounding mesenchyme, and endothelium of blood vessels. These results demonstrate a protective role for Clara cells and their secretions and indicate potential genetic mechanisms that may influence susceptibility to oxidant stress.

Bone morphogenetic protein-7 in growth-plate chondrocytes: regulation by retinoic acid is dependent on the stage of chondrocyte maturation

Although the bone morphogenetic proteins stimulate chondrogenesis, little is known regarding their expression and regulation in growth-plate chondrocytes. The expression of bone morphogenetic protein-7 was examined in chick growth-plate chondrocyte cultures. Low basal levels of bone morphogenetic protein-7 mRNA and protein expression were stimulated by increasing doses of all-trans retinoic acid, a metabolite of vitamin A. The addition of 10 microM retinoic acid resulted in approximately a 6-fold increase in bone morphogenetic protein-7 mRNA levels. In contrast, other growth regulators, including basic fibroblast growth factor, transforming growth factor-beta, vitamin D, bone morphogenetic protein-6, bone morphogenetic protein-7, and parathyroid hormone-related peptide, did not alter bone morphogenetic protein-7 transcript levels. The increase in bone morphogenetic protein-7 transcripts, although present at 6 hours, was maximal following a 12-hour exposure to retinoic acid. Retinoic acid induction of bone morphogenetic protein-7 transcript levels was dependent on protein synthesis because the induction could be blocked by cyclohexamide. In maturationally distinct subpopulations of chondrocytes separated by countercurrent centrifugal elutriation, retinoic acid markedly induced bone morphogenetic protein-7 mRNA levels in the least differentiated chondrocytes but had no effect in the most terminally differentiated hypertrophic chondrocytes. Immunohistochemical localization of bone morphogenetic protein-7 demonstrates its expression throughout the developing and adolescent growth plate consistent with the constitutive pattern of expression seen in isolated chondrocytes. The addition of exogenous bone morphogenetic protein-7 to chondrocyte cultures stimulated maturation in undifferentiated chondrocyte populations. The data support a role for bone morphogenetic protein-7 as an autocrine regulator of chondrocyte maturation in the growth plate. Regulation of bone morphogenetic protein-7 by retinoic acid may be important in normal growth and development as well as in pathologic conditions of an excess or deficiency of vitamin A.

Increased levels of tumor necrosis factor-alpha and interleukin-6 protein and messenger RNA in human peripheral blood monocytes due to titanium particles

Cytokines produced by macrophages in the periprosthetic membranes surrounding joint replacements have been implicated as causal agents in osteolysis and prosthetic loosening. The present study characterizes the response of human peripheral blood monocytes to titanium particles. Monocytes were obtained from volunteers and blood that had been donated to the American Red Cross and were cultured in the presence of titanium particles (one to three micrometers in diameter). There were consistent dose-dependent increases in the production of TNF-alpha (tumor necrosis factor-alpha) and IL-6 (interleukin-6) protein, with the greatest stimulation generally observed with a concentration of 6 x 10(5) to 6 x 10(6) particles of titanium per milliliter. The level of TNF-alpha was the greatest (fifty to 1000 times greater than the control level) after eight hours of exposure to titanium particles; the level of IL-6 was two to five times greater than the control level after sixteen hours of exposure. These increases were similar to those observed after stimulation with lipopolysaccharide and depended on de novo synthesis rather than on release from intracellular stores. The production of TNF-alpha was inhibited in a dose-dependent manner by the translational inhibitor cycloheximide and the transcriptional inhibitor actinomycin D, indicating the requirement for both mRNA (messenger RNA) and protein synthesis for the induction of cytokine synthesis by titanium particles. Although the increase in the levels of cytokine mRNA in response to titanium was rapid (thirty to ninety minutes), the increase in the level of TNF-alpha mRNA preceded that of IL-6 mRNA. The level of TNF-alpha mRNA was the greatest at ninety minutes and the level of IL-6 mRNA was the greatest at three hours. After stimulation with titanium particles, the level of TNF-alpha mRNA was increased as much as fivefold and the level of IL-6 mRNA, as much as twelvefold.

Identification and characterization of a unique chondrocyte gene involved in transition to hypertrophy

The character of differentiating chondrocytes in growing long bones has been defined by altered expression of a limited number of genes. To expand this set we have applied differential display to identify genes expressed in either mineralizing or nonmineralizing chondrocytes. One such gene, Band 17, has the following characteristics: (1) Band 17 expression is predominantly found in cartilage destined for mineralization. Band 17 mRNA is undetectable in articular cartilage and undetectable or weak in all other tissues tested. (2) Band 17 expression is spatially restricted to the lower proliferative/upper hypertrophic zone of chondrocytes in the growth plate of long bones and embryonic vertebrae. (3) Induction of a hypertrophic phenotype in progenitor sternal chondrocytes by treatment with ascorbate increases expression of Band 17. (4) Induction of hypertrophy in growth plate chondrocytes in short-term monolayer cultures correlates with a rapid but transient rise in Band 17 message. Our interpretation of these findings is that Band 17 expression is associated with the transition to hypertrophy, not maintenance of the hypertrophic phenotype. Molecular analysis of the 3' end of Band 17 cDNAs and genomic structure has shown that Band 17 is a single copy gene transcribed into four messages. Alternative splicing of these messages is predicted to result in two proteins that differ at the C-terminal by 131 amino acids. The longer protein contains a C-terminal consensus sequence that potentially targets this protein to the lumen of the endoplasmic reticulum. There is a Band 17 homologue in humans, suggesting conservation of Band 17 function in mammals. In summary, the pattern of expression and the predicted primary structure identify Band 17 as unique among all previously known chondrocyte genes.

Characterization of a SpAN promoter sufficient to mediate correct spatial regulation along the animal-vegetal axis of the sea urchin embryo

In order to investigate how the maternally specified animal-vegetal axis of the sea urchin embryo is established, we have examined the molecular basis of regulation of several genes transcribed differentially in nonvegetal and vegetal domains of the very early blastula. Here we present an initial characterization of the regulatory region of one of these, SpAN, which encodes a protease in the astacin family related to Drosophila tolloid and vertebrate BMP-1 (Reynolds et al., Development 114, 769-786). Tests of SpAN promoter function in vivo show that high-level activity and correct not-vegetal expression are mediated by sequences within 300 bp upstream of the basal promoter. In vitro studies have identified six protein binding sites serviced by at least five different proteins. Comparison of the structure of the SpAN promoter to that of SpHE, whose expression pattern is identical, shows that both promoters contain multiple positively acting upstream elements close to the basal promoter. We show that two elements are critical for high-level transcription of SpAN, since exact replacement of either results in 10- to 20-fold reduction in promoter strength. These shared elements are, however, not essential for spatially correct SpHE gene transcription. We conclude that the coordinate strong activities of the SpAN and SpHE promoters in the nonvegetal domain of the embryo rely primarily on different transcription factor activities.

Regulation of osteoclastic activity in infection

Figure 4 is a diagrammatic representation of five pathways involved in the activation of osteoclastic and osteoblastic cell activity during an infectious process. Pathways 1 and 2 are involved in the recruitment and activation of osteoclasts. These pathways are controlled by systemic hormones and cytokines of the infection/immune axis. As described above, many of the cytokines are synergistic and can evoke very strong stimuli for bone resorption; however, under normal conditions for any given number of bone-resorbing sites, there is always an equivalent compensatory stimulus to enhance bone formation. Pathways 3 to 5 govern the formation stimuli. Thus, for bone to be permanently lost there must be a disruption in the cellular communication that exists between pathways 1 and 2 and pathways 3 to 5. Such a disruption occurs in periodontal disease and osteomyelitis. At present, the molecular mechanisms that create the disruption in cell communication are not known. They may be complex and involve as yet unidentified cell biological principles, or they may be relatively simple reactions involving known factors and enzymes.

Centrifugal elutriation of large fragile cells: isolation of RNA from fixed embryonic blastomeres

In order to analyze the RNA populations present in different cells of very early embryos, we have developed a protocol to purify these large blastomeres using counterflow centrifugal elutriation (CCE). This procedure employs ethanol fixation to stabilize the cells against shear forces encountered during CCE. Using this method, we fractionated the three different blastomere types of the 16-cell sea urchin embryo, the micromeres, mesomeres, and macromeres, achieving 96, 94, and 96% mean purities, respectively. We show here that intact RNA is recovered with equal efficiency from each blastomere preparation. Using this method, we have identified several RNAs that are distributed non-uniformly among these cells.

Early mRNAs, spatially restricted along the animal-vegetal axis of sea urchin embryos, include one encoding a protein related to tolloid and BMP-1

The cloning and characterization of cDNAs representing four genes or small gene families that are coordinately expressed in a spatially restricted pattern during the very early blastula (VEB) stage of sea urchin development are presented. The VEB genes encode multiple transcripts that are expressed transiently in embryos of Strongylocentrotus purpuratus between 16-cell stage and hatching, with peak abundance 12 to 15 hours post-fertilization (approximately 150–250 cells). The VEB transcripts share the same spatial pattern in the early blastula embryo: they are asymmetrically distributed along the animal-vegetal axis but their distribution around this axis is uniform. Thus, the VEB transcripts are the earliest messages to reveal asymmetry along the primary axis in the sea urchin embryo. The temporal and spatial patterns of VEB transcript accumulation are not consistent with involvement of these gene products in cell division or in tissue-specific functions. Furthermore, VEB messages cannot be detected in either ovary or adult tissues, suggesting that these genes function exclusively during embryogenesis. We suggest that the VEB genes function in constructing the early blastula. Two VEB genes encode metalloendoproteases: one (SpHE) is hatching enzyme and the other (SpAN) is similar to bone morphogenetic protein-1 (BMP-1; Wozney et al., Science 242: 1528–1534, 1988) and the Tolloid gene product (tld) (Shimell et al., Cell 67: 459–482, 1991). Several lines of evidence suggest that the VEB genes are regulated directly by factors or regulatory activities localized along the maternally specificed animal-vegetal axis.

Renal vein thrombosis. Initial manifestation of Goodpasture's syndrome

We report a patient who presented with renal vein thrombosis and nephrosis that progressed to alveolar hemorrhage and renal failure. Renal biopsy immunofluorescence and serum antiglomerular basement membrane antibody titer studies confirmed the diagnosis of Goodpasture's syndrome. To our knowledge, this is the first report of renal vein thrombosis as the initial presentation of Goodpasture's syndrome.

Role of epidermal cell thymocyte-activating factor in the proliferation and differentiation of murine B cells

The role of antigen nonspecific cytokines in T- and B-lymphocyte responses is now well established. Interleukin-1 (IL-1) has been shown to augment B-cell maturation and proliferation. While the major source of IL-1 is from monocytes or macrophages, other cell types have been shown to produce IL-1-like cytokines. Epidermal cells produce a cytokine termed "epidermal cell-derived thymocyte-activating factor" (ETAF) which is similar if not identical with monocyte-derived IL-1. In this report we show that ETAF induces polyclonal stimulation of murine B cells. We show that ETAF augments B cell proliferation and differentiation in the absence of any added antigens or mitogens. This activity can be partially inhibited by anti-IL-1 antibodies. ETAF appears to activate B cells directly, although its activity is increased in the presence of T cells. Thus, ETAF may be involved in local polyclonal antibody responses occurring in the skin.

Differential expression of a surface antigen recognized by a monoclonal antibody, J11d, on unprimed and primed B cells

Functional studies of both polyclonal and antigen-specific responses have suggested that murine B cells differ in the expression of an antigen recognized by a rat anti-mouse monoclonal antibody, called J11d. Using both positive and negative selection, we now demonstrate that the J11d marker is differentially displayed on B lymphocytes responding to LPS vs anti-mu, as well as on unprimed vs specific antigen-primed B cells. Thus, cytotoxic elimination of cells expressing high levels of J11d (J11d-hi) reduced LPS-driven B cell proliferation by 60 to 80% but had no effect on anti-mu stimulated B cell growth. Interestingly, equal numbers of positively selected J11d-hi B cells responded similarly to LPS and anti-mu plus B cell growth factors, a result that suggests that the response to anti-mu of the J11d-lo B cells is normally masked by the majority J11-d-hi cells. In further studies, the primary PFC response of normal murine spleen cells to fluorescein (FL)-coupled TI antigens or to LPS in vitro was reduced dramatically by cytotoxic J11d antibody treatment. In contrast, the anti-FL PFC response of spleen cells from mice primed 1 wk previously with FL-Ficoll was not affected by J11d antibody treatment, whereas the response of these FL-primed B cells to TNP (to which the mice were not primed) was greatly reduced by J11d + complement treatment. Our data indicate that antigen-experienced (activated) B cells are primarily found in the J11d-lo B cell subset and that unprimed (resting) B cells are found in the J11d-hi population, although both populations of murine B cells can respond to anti-mu. These studies also provide further evidence for B cell heterogeneity.

Differential expression of a surface antigen recognized by a monoclonal antibody, J11d, on unprimed and primed B cells

Functional studies of both polyclonal and antigen-specific responses have suggested that murine B cells differ in the expression of an antigen recognized by a rat anti-mouse monoclonal antibody, called J11d. Using both positive and negative selection, we now demonstrate that the J11d marker is differentially displayed on B lymphocytes responding to LPS vs anti-mu, as well as on unprimed vs specific antigen-primed B cells. Thus, cytotoxic elimination of cells expressing high levels of J11d (J11d-hi) reduced LPS-driven B cell proliferation by 60 to 80% but had no effect on anti-mu stimulated B cell growth. Interestingly, equal numbers of positively selected J11d-hi B cells responded similarly to LPS and anti-mu plus B cell growth factors, a result that suggests that the response to anti-mu of the J11d-lo B cells is normally masked by the majority J11-d-hi cells. In further studies, the primary PFC response of normal murine spleen cells to fluorescein (FL)-coupled TI antigens or to LPS in vitro was reduced dramatically by cytotoxic J11d antibody treatment. In contrast, the anti-FL PFC response of spleen cells from mice primed 1 wk previously with FL-Ficoll was not affected by J11d antibody treatment, whereas the response of these FL-primed B cells to TNP (to which the mice were not primed) was greatly reduced by J11d + complement treatment. Our data indicate that antigen-experienced (activated) B cells are primarily found in the J11d-lo B cell subset and that unprimed (resting) B cells are found in the J11d-hi population, although both populations of murine B cells can respond to anti-mu. These studies also provide further evidence for B cell heterogeneity.

Job analysis in the clinical laboratory

Questionnaires were sent to 111 hospitals located within a 100-mile radius of Morgantown, West Virginia. In the 55 responding hospitals, 1,532 laboratory workers were employed; of this total, 399 were MT(ASCP), 55 were MLT(ASCP), 262 were CLA(ASCP), and 816 were not certified by the Board of Registry of the American Society of Clinical Pathologists (ASCP). Participating hospital laboratory directors were asked to distribute task inventories to medical technologists and to individuals not certified as MT(ASCP). One hundred sixty-five task inventories were completed and returned for analysis. Using the chi square test, comparison was made between the tasks performed by ASCP-certified medical technologists and ASCP-certified laboratory assistants. Both performed essentially the same tasks in the clinical laboratories included in this study. In the final analysis, teaching and supervision were performed more frequently by MTs than by CLAs.