Pulmonary macrophages are attracted to inhaled particles through complement activation

In Vitro Models for Studying Respiratory Host-Pathogen Interactions

Respiratory diseases and lower respiratory tract infections are among the leading cause of death worldwide and, especially given the recent severe acute respiratory syndrome coronavirus-2 pandemic, are of high and prevalent socio-economic importance. In vitro models, which accurately represent the lung microenvironment, are of increasing significance given the ethical concerns around animal work and the lack of translation to human disease, as well as the lengthy time to market and the attrition rates associated with clinical trials. This review gives an overview of the biological and immunological components involved in regulating the respiratory epithelium system in health, disease, and infection. The evolution from 2D to 3D cell biology and to more advanced technological integrated models for studying respiratory host-pathogen interactions are reviewed and provide a reference point for understanding the in vitro modeling requirements. Finally, the current limitations and future perspectives for advancing this field are presented.

Transcriptomic and epigenomic effects of insoluble particles on J774 macrophages

Here we report epigenomic and transcriptomic changes in a prototypical J774 macrophage after engulfing talc or titanium dioxide particles in presence of estrogen. Macrophages are the first immune cells to engage and clear particles of various nature. A novel paradigm is emerging, that exposure to so-called 'inert' particulates that are considered innocuous is not really free of consequences. We hypothesized that especially the insoluble, non-digestible particles that do not release a known hazardous chemical can be underappreciated agents acting to affect the regulation inside macrophages upon phagocytosis. We performed gene chip microarray profiling and found that talc alone, and especially with oestrogen, has induced a substantially more prominent gene expression change than titanium dioxide; the affected genes were involved in pathways of cell proliferation, immune response and regulation, and, unexpectedly, enzymes and proteins of epigenetic regulation. We therefore tested the DNA methylation profiles of these cells via epigenome-wide bisulphite sequencing and found vast epigenetic changes in hundreds of loci, remarkably after a very short exposure to particles; ELISA assay for methylcytosine levels determined the particles induced an overall decrease in DNA methylation. We found a few loci where both the transcriptional changes and epigenetic changes occurred in the pathways involving immune and inflammatory signalling. Some transcriptomic and epigenomic changes were shared between talc and titanium dioxide, however, it is especially interesting that each of the two particles of similar size and insoluble nature has also induced a specific pattern of gene expression and DNA methylation changes which we report here.

A novel human 3D lung microtissue model for nanoparticle-induced cell-matrix alterations

BACKGROUND

Multi-walled carbon nanotubes (MWCNT) have been shown to elicit the release of inflammatory and pro-fibrotic mediators, as well as histopathological changes in lungs of exposed animals. Current standards for testing MWCNTs and other nanoparticles (NPs) rely on low-throughput in vivo studies to assess acute and chronic toxicity and potential hazard to humans. Several alternative testing approaches utilizing two-dimensional (2D) in vitro assays to screen engineered NPs have reported conflicting results between in vitro and in vivo assays. Compared to conventional 2D in vitro or in vivo animal model systems, three-dimensional (3D) in vitro platforms have been shown to more closely recapitulate human physiology, providing a relevant, more efficient strategy for evaluating acute toxicity and chronic outcomes in a tiered nanomaterial toxicity testing paradigm.

RESULTS

As inhalation is an important route of nanomaterial exposure, human lung fibroblasts and epithelial cells were co-cultured with macrophages to form scaffold-free 3D lung microtissues. Microtissues were exposed to multi-walled carbon nanotubes, M120 carbon black nanoparticles or crocidolite asbestos fibers for 4 or 7 days, then collected for characterization of microtissue viability, tissue morphology, and expression of genes and selected proteins associated with inflammation and extracellular matrix remodeling. Our data demonstrate the utility of 3D microtissues in predicting chronic pulmonary endpoints following exposure to MWCNTs or asbestos fibers. These test nanomaterials were incorporated into 3D human lung microtissues as visualized using light microscopy. Differential expression of genes involved in acute inflammation and extracellular matrix remodeling was detected using PCR arrays and confirmed using qRT-PCR analysis and Luminex assays of selected genes and proteins.

CONCLUSION

3D lung microtissues provide an alternative testing platform for assessing nanomaterial-induced cell-matrix alterations and delineation of toxicity pathways, moving towards a more predictive and physiologically relevant approach for in vitro NP toxicity testing.

Association of high-level humidifier disinfectant exposure with lung injury in preschool children

BACKGROUND

Children aged ≤6years reportedly account for 52% of victims of humidifier disinfectant-associated lung injuries.

OBJECTIVES

To evaluate the association of humidifier disinfectants with lung injury risk among children aged ≤6years.

METHODS

Patients with humidifier disinfectant-associated lung injuries (n=214) who were clinically evaluated to have a definite (n=108), probable (n=49), or possible (n=57) association with humidifier disinfectants as well as control patients (n=123) with lung injury deemed unlikely to be associated with humidifier disinfectant use were evaluated to determine factors associated with increased risk of humidifier disinfectant-associated lung injury using unconditional multiple logistic regression analysis.

RESULTS

For estimated airborne humidifier disinfectant concentrations, risk of humidifier disinfectant-associated lung injury increased ≥two-fold in a dose-dependent manner in the highest quartile (Q4, 135-1443μg/m³) compared with that in the lowest quartile (Q1, ≤33μg/m³). Registered patients using more than two humidifier disinfectant brands were at an increased risk of humidifier disinfectant-associated lung injury (adjusted OR, 2.2; 95% confidence interval, 1.3-3.8) compared with those using only one brand. With respect to the duration of humidifier disinfectant use, risk of humidifier disinfectant-associated lung injury increased ≥two-fold in the lowest quartile (≤5months) compared with that in the highest quartile (≥14months; adjusted OR 0.3; 95% confidence interval, 0.2-0.6).

CONCLUSIONS

Younger children are more vulnerable to HDLI when exposed to HD chemicals within short period in early life.

Mechanisms of Asbestos Carcinogenicity

We present a brief review of different potential mechanisms at the molecular and cellular levels that may be involved in asbestos-induced carcinogenicity. The usefulness of considering such mechanisms in developing appropriate biologically based models to estimate carcinogenic risk at environmental levels of asbestos fibers is discussed.

Functional consequences for primary human alveolar macrophages following treatment with long, but not short, multiwalled carbon nanotubes

PURPOSE

Multiwalled carbon nanotubes (MWCNTs) are a potential human health hazard, primarily via inhalation. In the lung, alveolar macrophages (AMs) provide the first line of immune cellular defense against inhaled materials. We hypothesized that, 1 and 5 days after treating AMs with short (0.6 μm in length; MWCNT-0.6 μm) and long (20 μm in length; MWCNT-20 μm) MWCNTs for 24 hours, AMs would exhibit increased markers of adverse bioreactivity (cytokine release and reactive oxygen species generation) while also having a modified functional ability (phagocytosis and migration).

METHODS

Primary human AMs were treated with short and long MWCNTs for 24 hours, 1 and 5 days after which toxicity end points, including cell death, reactive oxygen species generation, and inflammatory mediator release, were measured. AM functional end points involving phagocytic ability and migratory capacity were also measured.

RESULTS

AM viability was significantly decreased at 1 and 5 days after treatment with MWCNT-20 μm, while superoxide levels and inflammatory mediator release were significantly increased. At the same time, there was reduced phagocytosis and migratory capacity alongside increased expression of MARCO; this coincided with frustrated phagocytosis observed by scanning electron microscopy. In contrast, the adverse bioreactivity of the shorter MWCNT-0.6 μm with AMs (and any resulting reduction in AM functional ability) was substantially less marked or absent altogether.

CONCLUSION

This study shows that after 24-hour treatment with long, but not short, MWCNTs, AM function is severely affected up to 5 days after the initial exposure. This has potentially significant pathophysiological consequences for individuals who may be intentionally (via therapeutic applications) or unintentionally exposed to these nanomaterials.

Variability and consistency in lung inflammatory responses to particles with a geogenic origin

BACKGROUND AND OBJECTIVE

Particulate matter <10 μm (PM10 ) is well recognized as being an important driver of respiratory health; however, the impact of PM10 of geogenic origin on inflammatory responses in the lung is poorly understood. This study aimed to assess the lung inflammatory response to community sampled geogenic PM10 .

METHODS

This was achieved by collecting earth material from two regional communities in Western Australia (Kalgoorlie-Boulder and Newman), extracting the PM10 fraction and exposing mice by intranasal instillation to these particles. The physicochemical characteristics of the particles were assessed and lung inflammatory responses were compared to control particles. The primary outcomes were cellular influx and cytokine production in the lungs of the exposed mice.

RESULTS

The physical and chemical characteristics of the PM10 from Kalgoorlie and Newman differed with the latter having a higher concentration of Fe and a larger median diameter. Control particles (2.5 μm polystyrene) caused a significant influx of inflammatory cells (neutrophils) with little production of proinflammatory cytokines. In contrast, the geogenic particles induced the production of MIP-2, IL-6 and a significant influx of neutrophils. Qualitatively, the response following exposure to particles from Kalgoorlie and Newman were consistent; however, the magnitude of the response was substantially higher in the mice exposed to particles from Newman.

CONCLUSIONS

The unique physicochemical characteristics of geogenic particles induced a proinflammatory response in the lung. These data suggest that particle composition should be considered when setting community standards for PM exposure, particularly in areas exposed to high geogenic particulate loads.

Transmigration and phagocytosis of macrophages in an airway infection model using four-dimensional techniques

During infection, recruited phagocytes transmigrate across the epithelium to remove the pathogens deposited on the airway surface. However, it is difficult to directly observe cellular behaviors (e.g., transmigration) in single-cell layer cultures or in live animals. Combining a three-dimensional (3D) cell coculture model mimicking airway infection with time-lapse confocal imaging as a four-dimensional technique allowed us to image the behaviors of macrophages in 3D over time. The airway infection model was moved to a glass-bottomed dish for live-cell imaging by confocal laser scanning microscopy. Using time-lapse confocal imaging, we recorded macrophages transmigrating across the polyethylene terephthalate (PET) membrane of the inserts through the 5-μm pores in the PET membrane. Macrophages on the apical side of the insert exhibited essentially three types of movements, one of which was transmigrating across the epithelial cell monolayer and arriving at the surface of monolayer. We found that adding Staphylococcus aureus to the model increased the transmigration index but not the transmigration time of the macrophages. Only in the presence of S. aureus were the macrophages able to transmigrate across the epithelial cell monolayer. Apical-to-basal transmigration of macrophages was visualized dynamically. We also imaged the macrophages phagocytizing S. aureus deposited on the surface of the monolayer in the airway infection model. This work provides a useful tool to study the cellular behaviors of immune cells spatially and temporally during infection.

Critical role of MARCO in crystalline silica-induced pulmonary inflammation

Chronic exposure to crystalline silica can lead to the development of silicosis, an irreversible, inflammatory and fibrotic pulmonary disease. Although, previous studies established the macrophage receptor with collagenous structure (MARCO) as an important receptor for binding and uptake of crystalline silica particles in vitro, the role of MARCO in regulating the inflammatory response following silica exposure in vivo remains unknown. Therefore, we determined the role of MARCO in crystalline silica-induced pulmonary pathology using C57Bl/6 wild-type (WT) and MARCO(-/-) mice. Increased numbers of MARCO(+) pulmonary macrophages were observed following crystalline silica, but not phosphate-buffered saline and titanium dioxide (TiO(2)), instillation in WT mice, highlighting a specific role of MARCO in silica-induced pathology. We hypothesized that MARCO(-/-) mice will exhibit diminished clearance of silica leading to enhanced pulmonary inflammation and exacerbation of silicosis. Alveolar macrophages isolated from crystalline silica-exposed mice showed diminished particle uptake in vivo as compared with WT mice, indicating abnormalities in clearance mechanisms. Furthermore, MARCO(-/-) mice exposed to crystalline silica showed enhanced acute inflammation and lung injury marked by increases in early response cytokines and inflammatory cells compared with WT mice. Similarly, histological examination of MARCO(-/-) lungs at 3 months post-crystalline silica exposure showed increased chronic inflammation compared with WT; however, only a small difference was observed with respect to development of fibrosis as measured by hydroxyproline content. Altogether, these results demonstrate that MARCO is important for clearance of crystalline silica in vivo and that the absence of MARCO results in exacerbations in innate pulmonary immune responses.

Ultrafine particle-lung interactions: does size matter?

Epidemiological studies continue to indicate associations between exposure to increased concentrations of ambient fine and ultrafine particles and adverse health effects in susceptible individuals. The ultrafine particle fraction in the ambient atmosphere seems to play a specific role. Yet, the dosimetry (including deposition patterns in the respiratory tract and, particularly, the biokinetic fate of ultrafine particles) is not fully understood. In contrast to fine particles, inhaled ultrafine particles seem to follow different routes in the organism. Cardiovascular effects observed in epidemiological studies triggered the discussion on enhanced translocation of ultrafine particles from the respiratory epithelium towards circulation and subsequent target organs, such as heart, liver, and brain, eventually causing adverse effects on cardiac function and blood coagulation, as well as on functions of the central nervous system. Current knowledge on systemic translocation of ultrafine particles in humans and animal models is reviewed. Additionally, an estimate of accumulating particle numbers in secondary target organs during chronic exposure is extrapolated from long-term translocation data obtained from rats. Toxicological studies aim to provide the biological plausibility of health effects of ultrafine particles and to identify cascades of mechanisms that are causal for the gradual transition from the physiological status towards pathophysiologcal alterations and eventually chronic disease. Considering the interaction between insoluble ultrafine particles and biological systems (such as body fluids, proteins, and cells), there still are gaps in the current knowledge on how ultrafine particles may cause adverse reactions. This paper reviews the current concept of interactions between insoluble ultrafine particles and biological systems.

In vivo particle uptake by airway macrophages in healthy volunteers

We combined two techniques, radiolabeled aerosol inhalation delivery and induced sputum, to examine in vivo the time course of particle uptake by airway macrophages in 10 healthy volunteers. On three separate visits, induced sputum was obtained 40, 100, and 160 min after inhalation of radiolabeled sulfur colloid (SC) aerosol (Tc99 m-SC, 0.2 microm colloid size delivered in 6-microm droplets). On a fourth visit (control) with no SC inhalation, induced sputum was obtained and SC particles were incubated (37 degrees C) in vitro with sputum cells for 40, 100, and 160 min (matching the times associated with in vivo sampling). Total and differential cell counts were recorded for each sputum sample. Compared with 40 min (6 +/- 3%), uptake in vivo was significantly elevated at 100 (31 +/- 5%) and 160 min (27 +/- 4%); both were strongly associated with the number of airway macrophages (R = 0.8 and 0.7, respectively); and the number and proportion of macrophages at 40 min were significantly (P < 0.05) elevated compared with control (1,248 +/- 256 versus 555 +/- 114 cells/mg; 76 +/- 6% versus 60 +/- 5%). Uptake in vitro increased in a linear fashion over time and was maximal at 160 min (40 min, 12 +/- 2%; 100 min, 16 +/- 4%; 160 min, 24 +/- 6%). These data suggest that airway surface macrophages in healthy subjects rapidly engulf insoluble particles. Further, macrophage recruitment and phagocytosis-modifying agents are factors in vivo that likely affect particle uptake and its time course.

Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles

Although humans have been exposed to airborne nanosized particles (NSPs; < 100 nm) throughout their evolutionary stages, such exposure has increased dramatically over the last century due to anthropogenic sources. The rapidly developing field of nanotechnology is likely to become yet another source through inhalation, ingestion, skin uptake, and injection of engineered nanomaterials. Information about safety and potential hazards is urgently needed. Results of older biokinetic studies with NSPs and newer epidemiologic and toxicologic studies with airborne ultrafine particles can be viewed as the basis for the expanding field of nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices. Collectively, some emerging concepts of nanotoxicology can be identified from the results of these studies. When inhaled, specific sizes of NSPs are efficiently deposited by diffusional mechanisms in all regions of the respiratory tract. The small size facilitates uptake into cells and transcytosis across epithelial and endothelial cells into the blood and lymph circulation to reach potentially sensitive target sites such as bone marrow, lymph nodes, spleen, and heart. Access to the central nervous system and ganglia via translocation along axons and dendrites of neurons has also been observed. NSPs penetrating the skin distribute via uptake into lymphatic channels. Endocytosis and biokinetics are largely dependent on NSP surface chemistry (coating) and in vivo surface modifications. The greater surface area per mass compared with larger-sized particles of the same chemistry renders NSPs more active biologically. This activity includes a potential for inflammatory and pro-oxidant, but also antioxidant, activity, which can explain early findings showing mixed results in terms of toxicity of NSPs to environmentally relevant species. Evidence of mitochondrial distribution and oxidative stress response after NSP endocytosis points to a need for basic research on their interactions with subcellular structures. Additional considerations for assessing safety of engineered NSPs include careful selections of appropriate and relevant doses/concentrations, the likelihood of increased effects in a compromised organism, and also the benefits of possible desirable effects. An interdisciplinary team approach (e.g., toxicology, materials science, medicine, molecular biology, and bioinformatics, to name a few) is mandatory for nanotoxicology research to arrive at an appropriate risk assessment.

Estudo de imunoglobulinas, complementos e auto-anticorpos em 58 trabalhadores expostos à sílica

INTRODUÇÃO: A silicose é a doença pulmonar ocupacional de maior prevalência em nosso meio. O agente patogênico da silicose é a poeira de sílica-livre ou dióxido de silício (SiO2) na forma cristalina. O processo inflamatório envolvendo o sistema imunológico na silicose ainda não está bem esclarecido. OBJETIVO: Estudar o perfil de IgG, IgM, IgA, C3, C4 e alguns auto-anticorpos no soro de trabalhadores expostos à sílica, com ou sem silicose, através de avaliação laboratorial imunológica, abrangendo tanto a imunidade inespecífica quanto a específica. MÉTODO: Foi examinada uma amostra de 58 pacientes ambulatoriais, do sexo masculino, constituída por trabalhadores expostos à sílica. Foram realizadas avaliações imunológica, radiológica e funcional pulmonar. Foram dosadas as imunoglobulinas IgG, IgA e IgM, os componentes C3 e C4 do sistema complemento e determinados auto-anticorpos. RESULTADOS: Vinte trabalhadores apresentaram radiograma normal e 38 apresentaram-no alterado, compatível com silicose. As médias dos valores de IgG no grupo com silicose foi maior que no grupo com radiograma normal (p < 0,05). Para a IgA e IgM, assim como para o C3 e C4, não houve diferença estatisticamente significativa nas médias (p > 0.05). O percentual de positividade dos auto-anticorpos foi maior no grupo silicótico em relação ao grupo com radiograma normal. CONCLUSÃO: O aumento de IgG nos doentes com silicose constitui um achado importante pois pode indicar a continuidade da reação granulomatosa, mesmo com o trabalhador afastado da exposição. Entretanto, ainda são necessários estudos que possibilitem a compreensão do processo imunogênico na silicose.

Morphological aspects of particle uptake by lung phagocytes

Macrophages residing on the inner epithelial surfaces of airways and alveoli are the only lung phagocytes exposed directly to the environment. Their phagocytic and microbicidal activities are essential for maintaining this organ in a clean and sterile state. The morphology of these phagocytes can be investigated in situ only after implementing special techniques, which involve intravascular triple-perfusion of aqueous fixatives or instillation of nonpolar ones. Such studies have revealed the engulfment of particles by these cells to be rapid, the process being essentially complete within a day. Particles are entrapped within phagosomes and the host cells eventually transported out of the lungs by mucociliary action, macrophages with higher loads being more rapidly eliminated than those with lower ones. Very small particles or those persisting on the epithelial surfaces may be taken up by the eponymous cells. Translocation of particles into the underlying connective tissue and their subsequent phagocytosis by interstitial macrophages prolongs their retention time in the lungs. The still poorly studied pleural macrophages might be involved in cell-mediated immune responses within the pleural space. Intravascular pulmonary macrophages figure largely in the phagocytosis of circulating particles. The role played by dendritic cells in particle uptake by the lungs is not well understood. Airway and alveolar macrophages are the primary phagocytes of the lung. In nonoverload situations and for particles >1 microm, a small proportion of those recruited suffices to remove material from the epithelial surface before other phagocytes, with an apparently greater immunological potential, gain access to it.

Is the trachea a marker of the type of environmental pollution?

OBJECTIVES/HYPOTHESIS

The differentiated character of changes in the mucous relief of the trachea as induced by air containing pollutants from the wastes of nickel-, mercury-, and cement-producing plants and by Candida albicans occurring in the waste disposal site of a large town are identified. The trachea was chosen because it is the entrance gate for the penetration of polluted air into the lungs. Changes on the trachea influence the character and extent of changes in lungs.

STUDY DESIGN

Histological study with Viennese grey strain laboratory rabbits and rats caught directly on an investigated site.

METHODS

We present new results of the functional morphology of the respiratory system as the results of scanning and transmission electron microscopy studies that can reveal character and range of damage of mucosal relief of trachea relevant to the functional dynamics of mucociliary clearance. Under physiological conditions this mechanism allows that only respirable dust particles enter the deep respiratory tract.

RESULTS

In case of a damaged tracheal relief because of exposure to various aerosols, the functional morphology is changed, which aids in understanding the mechanisms damaging to mucociliary clearance induced by living in heavily polluted areas.

CONCLUSION

Understanding of these morphological changes on base of detailed electron microscopic findings sheds new light on elaborating novel diagnostic methods for clinical practice.

Interaction of alveolar macrophages with inhaled mineral particulates

Pulmonary disorders triggered by inhalation of occupational and environmental mineral particulates can be endpoints of a chronic inflammatory process in which alveolar macrophages (AMs), as a first line of defense, play a crucial role. The biological processes involved in particulate-induced activation of AMs include indirect or direct interactions of particulates with the cell membrane, subsequent stimulation of signal transduction pathways, and activation of gene transcription. Depending on the nature of particulate involved, particulate-induced activation of AMs has been shown to result in the release of potent mediators, such as reactive oxygen and nitrogen species, cytokines, eicosanoids, and growth factors. The prolonged and enhanced production of such effector molecules may result in a complex cascade of events that can contribute to the development of pulmonary disorders. This paper will give a short review of the present knowledge of AM interaction with inhaled mineral particulates and of the possible implications these interactions may have in the development of pulmonary disorders.

Detection of poly(ADP-ribose) synthetase activity in alveolar macrophages of rats exposed to nitrogen dioxide and ozone

The toxic effects of nitrogen dioxide (NO2) and ozone (O3) are mediated through the formation of free radicals, which can cause DNA strand breaks. The present study demonstrates that exposure to NO2 and O3 causes a stimulation of poly(ADP-ribose) (polyADPR) synthetase in alveolar macrophages of rats. Three-month-old male Sprague-Dawley rats, specific pathogen free, were exposed to either 1.2 ppm NO2 or 0.3 ppm O3 alone or a combination of these 2 oxidants continuously for 3 days. The control group was exposed to filtered room air. To evaluate whether exposure to these two oxidants (NO2 and O3) caused DNA damage to lung cells, the activity of polyADPR synthetase was measured. Cellular DNA repair is dependent upon the formation of poly(ADP-ribose) polymerase, which is catalyzed by polyADPR synthetase. PolyADPR synthetase is known to be activated in response of DNA damage. The results showed that the enzyme activity was stimulated after exposure to O3 or exposure to NO2 + O3. Ozone exposure caused a 25% increase in the enzyme activity as compared to the control. Combined exposure to NO2 + O3 showed a 53% increase in the enzyme activity. These results were statistically significant as compared to the control and NO(2) exposure groups. Other parameters such as total cell count, cell viability, and differential cell count were also determined. The stimulation of polyADPR synthetase activity after O3 exposure or NO2 + O3 exposure reflects a response to lung cellular DNA repair, which may be used as an indicator for assessing DNA damage caused by oxidant injury.

Inhalation of poorly soluble particles. II. Influence Of particle surface area on inflammation and clearance

In this article the volumetric overload hypothesis, which predicts the impairment of clearance of particles deposited in the lung in terms of particle volume, is reevaluated. The degree to which simple expressions of retained lung burden explain pulmonary responses to overload was investigated using data from a series of chronic inhalation experiments on rats with two poorly soluble dusts, titanium dioxide and barium sulfate. The results indicated that the difference between the dusts in the level of inflammation and translocation to the lymph nodes could be explained most simply when the lung burden was expressed as total particle surface area. The shape of the statistical relationship for both lung responses indicated the presence of a threshold at approximately 200-300 cm(2) of lung burden. On the basis of this and other similar results, a hypothesis regarding a generic mechanism for the impairment of clearance and associated lung responses is proposed for such "low-toxicity" dusts.

Mathematical modeling of the retention and clearance of low-toxicity particles in the lung

A mathematical model has been formulated to describe the mechanisms that determine the retention or clearance of insoluble inhaled particles in the rat lung. The hypotheses underlying the model are described-for example, the phagocytosis of free particles by macrophages, the transport of particles in macrophages from the alveolar region, the effect of the life cycle of macrophages leading to the eventual release of phagocytosed particles, the effect of lung burden on the macrophage activity, the transport of particles into the interstitium, the role of interstitial macrophages, the formation of granulomata, and transport of interstitialized particles to the thoracic lymph nodes. With these hypotheses, the fate of particles is described mechanistically via the cellular response of the lung. The mathematical model expresses these particle transitions as differential equations quantifying the transport of particles from one compartment to another, where the compartments represent the alveolar surface, the alveolar macrophages, overloaded alveolar macrophages, the interstitium, interstitial macrophages, and the thoracic lymph nodes. A companion article describes the application of the model to a data set from rats exposed to a low-toxicity dust at several concentrations and for a range of exposure times.

DNA strand breaks caused by exposure to ozone and nitrogen dioxide

The present study demonstrates that exposure to ozone (O3) and nitrogen dioxide (NO2) can cause DNA single-strand breaks in alveolar macrophages. Three-month-old male Sprague-Dawley rats, specific pathogen free, were exposed to either 1.2 ppm NO2 or 0.3 ppm O3 alone or a combination of these two oxidants continuously for 3 days. The control group was exposed to filtered room air. The oxidant effects were substantiated by determining total and differential cell counts, lactate dehydrogenase activity, and total soluble protein in bronchoalveolar lavage. DNA damage was measured as single-strand breaks by alkaline elution assay. The results showed that, relative to control, NO2 exposure did not cause any significant change in the parameters studied. Exposure to O3 and combined exposure to NO2 and O3 caused significant changes in all parameters studied except cell viability. The rates of elution (Kc) of single-strand DNA from polycarbonate filter for O3 exposure and combined exposure were 73 and 79% faster than that of the control, respectively. The amounts of DNA single-strand breaks caused by O3 and combined exposure were significantly greater than the amounts detected for the NO2-exposed and control groups.

Cellular and biochemical response of the human lung after intrapulmonary instillation of ferric oxide particles

Bronchoalveolar lavage (BAL) was used to sample lung cells and biochemical components in the lung air spaces at various times from 1 to 91 d after intrapulmonary instillation of 2.6 microm-diameter iron oxide particles in human subjects. The instillation of particles induced transient acute inflammation during the first day post instillation (PI), characterized by increased numbers of neutrophils and alveolar macrophages as well as increased amounts of protein, lactate dehydrogenase, and interleukin-8 in BAL fluids. This response was subclinical and was resolved within 4 d PI. A similar dose-dependent response was seen in rats 1 d after intratracheal instillation of the same particles. The particles contained small amounts of soluble iron (240 ng/mg) and possessed the capacity to catalyze oxidant generation in vitro. Our findings indicate that the acute inflammation after particle exposure may, at least partially, be the result of oxidant generation catalyzed by the presence of residual amounts of ferric ion, ferric hydroxides, or oxyhydroxides associated with the particles. These findings may have relevance to the acute health effects associated with increased levels of ambient particulate air pollutants.

Retention and intracellular distribution of instilled iron oxide particles in human alveolar macrophages

Bronchoalveolar lavage (BAL) was used to sample retention of particles within the alveolar macrophage (AM) compartment at various times from 1 to 91 d following intrapulmonary instillation of 2. 6-microm-diameter iron oxide (Fe2O3) particles in human subjects. Particles were cleared from the lavagable AM compartment in a biphasic pattern, with a rapid-phase clearance half-time of 0.5 d and long-term clearance half-time of 110 d, comparable to retention kinetics determined by more traditional methods. The intracellular distribution of particles within lavaged AMs was similar in bronchial and alveolar BAL fractions. AMs with high intracellular particle burdens disappeared from the lavagable phagocytic AM population disproportionately more rapidly (shorter clearance half-time) than did AMs with lower particle burdens, consistent with the occurrence of a particle redistribution phenomenon as previously described in similar studies in rats. The rates of AM disappearance from the various particle burden categories was generally slightly slower in bronchial fractions than in alveolar fractions. The instillation of particles induced a transient acute inflammatory response at 24 h postinstillation (PI), characterized by increased numbers of neutrophils and alveolar macrophages in BAL fluids. This response was subclinical and was resolved within 4 d PI.

Relation between pulmonary clearance and particle burden: a Michaelis-Menten-like kinetic model

OBJECTIVES

To test the validity of a Michaelis-Menten-like kinetic model of pulmonary clearance of insoluble dusts.

METHODS

Data were investigated from studies of pulmonary clearance in F344 rats exposed to antimony trioxide (Sb2O3), photocopy test toner, polyvinyl chloride powder (PVC), and diesel exhaust particles. The Michaelis-Menten-like model was used to develop a relation in which the pulmonary clearance half time was a linear function of lung burden. After combining all data, linear regression techniques were applied to investigate the underlying relations. With the estimated intercepts and slopes, the Michaelis-Menten-like kinetic parameters kmax (maximal clearance rate) and m1/2 (a characteristic lung burden at which kmax is reduced by 50%) were derived for the four dusts.

RESULTS

The experimental data fit the linear regression very well (R2 = 0.989), suggesting that pulmonary clearance for the four dusts followed Michaelis-Menten-like kinetics. Values of the intercept terms were not significantly different among the four dusts (P = 0.294), indicating that the intrinsic clearance rates of F344 rats were the same among the four experiments. The intrinsic clearance half time was estimated to be 77.8 days, leading to an estimated kmax of 0.0089 day-1. However, the slopes of the linear relations were significantly different among the four dusts (P < 0.001). Values of m1/2 were ranked in the order of: Sb2O3 (0.69 mg) < photocopy test toner (0.97 mg) < diesel exhaust (2.49 mg) congruent to PVC (2.90 mg).

CONCLUSION

This study suggests that the Michaelis-Menten-like kinetic model reasonably describes the kinetic behavior of pulmonary clearance in F344 rats. The parameters m1/2 can be used to differentiate the potency of a particular dust for impairing pulmonary clearance.

Assessment of in vivo attachment/phagocytosis by alveolar macrophages

Alveolar macrophages (AMs) are recognized as an important first line of cellular host defense within the lung. Although mechanisms underlying AM response to microorganisms or particulates are well characterized in vitro, experimental approaches to the study of AMs in vivo are limited. To circumvent these limitations, a new assay was developed using fluorescently labelled liposomes or Pneumocystis carinii (PC) organisms which were administered intratracheally into mechanically ventilated rats. After 30 min, the lungs were lavaged and the percentage of administered liposomes or PC bound to AMs was determined by quantifying fluorescence. Factors known to enhance attachment/phagocytosis by AMs in vitro were assayed to determine their effect in vivo. For example, vitronectin (VN)-coated liposomes increased attachment from 25.2 +/- 2.4% to 47.2 +/- 3.0% (p < 0.001), while addition of VN increased the binding of PC to AMs from 16.5 +/- 1.7% to 24.5 +/- 2.2% (p < 0.05). Confocal laser microscopy of cells obtained by lavage provided morphologic evidence of attachment/phagocytosis by AMs. This model will permit the quantitative assessment of the interaction of fluorescently labelled liposomes or microorganisms with AMs in the lower respiratory tract of living animals.

Current perspectives on particulate induced pulmonary tumours

1. Chronic exposure to insoluble particulates can lead to the development of pulmonary tumours. These have been classified as broncho-alveolar or squamous/epidermoid according to their histopathological characteristics and have been reported in inhalation studies in rats of materials ranging from diesel exhaust and silica to titanium dioxide. 2. The sequence of changes within the rat lung leading to tumours has been characterised. It is apparent that one prerequisite is that the lung load of the particulate matter must exceed the normal clearance capacity, either by overloading the normal alveolar macrophage mediated mechanism or by induction of toxicity with materials such as silica. This results in inflammatory responses, including, or resulting in, epithelial hypertrophy and/or hyperplasia and squamous metaplasia. The persistence of these tissue responses over chronic time periods can lead to tumorigenesis. 3. Research into the mechanisms involved in the initiation and progression of both the inflammatory response and subsequent tumorigenic response to lung particulate loading is in progress. Impairment of macrophage function and mobility by inert particles constitutes one route by which this can arise, as does toxicity to this cell type by biologically reactive particles. At the molecular level, the role of inflammatory mediators, especially the cytokines, has received much attention. 4. Particulate induced lung tumours are perceived to be a phenomenon specific to the rat and their relevance to man is questionable.

Role of alveolar macrophage chemotaxis and phagocytosis in pulmonary clearance responses to inhaled particles: comparisons among rodent species

Alveolar macrophages (AM) play an important role in clearing inhaled particles from the lung. The mechanisms through which macrophages identify particles that have been deposited in the alveolar regions is not well understood, although macrophage motility and phagocytic functions appear to be prerequisites for efficient clearance of inhaled materials. In previous studies, we assessed the mechanisms of macrophage-mediated clearance of inhaled particles using a rat model. In this regard, it appears that one mechanism by which rat alveolar macrophages are recruited to sites of particle or fiber deposition is through complement activation and consequent generation of chemotactic factors by the inhaled particulates. Whether this mechanism is operative in other rodent species remains an unanswered question. The current studies were undertaken to compare pulmonary clearance responses in several rodent species exposed to carbonyl iron (CI) particles. In vitro and in vivo pulmonary clearance responses were evaluated using one strain each of mouse, hamster, rat, and guinea pig. In vitro studies showed that hamster AM had the greatest phagocytic activity and that rat AM migrated best to complement-dependent chemotactic factors. Subsequently, groups of animals from each species were exposed to CI particles for 1 or 6 hr at aerosol concentrations of 100 mg/m3. Particle depositions patterns in the distal lung were nearly identical for all species, although enhanced numbers of CI particles were deposited on alveolar duct bifurcations of either rats or mice compared to hamsters, and particle deposition in guinea pigs was substantially lower. Time course studies showed that enhanced numbers of rat AM migrated to deposition sites and phagocytized particles, and this correlated with increased numbers and percentages of phagocytic macrophages recovered by lavage (P < 0.01). In vivo phagocytic rates were the lowest in the mouse, and this correlated with reduced phagocytic rates in vitro. It is concluded from these studies that the rat may be the most efficient rodent species in clearing inhaled iron particles. In addition, it is conceivable that hamster AM are recruited to sites of particle deposition by a noncomplement-mediated mechanism.

Chrysotile asbestos upregulates gene expression and production of alpha-receptors for platelet-derived growth factor (PDGF-AA) on rat lung fibroblasts

PDGF isoforms have been postulated to serve as mediators of fibroblast proliferation and chemotaxis during lung fibrogenesis induced by asbestos inhalation. We have studied the interaction of chrysotile asbestos fibers with rat lung fibroblasts (RLF) in vitro and the consequent changes in PDGF receptor mRNA expression, PDGF binding, and mitogenic activity of PDGF isoforms. Northern blot analysis revealed that mRNA for the PDGF-receptor alpha subtype (PDGF-R alpha) on RLF was upregulated after a 24-h exposure to asbestos in culture (0.5-15 micrograms fibers/cm2). [125I]PDGF-BB receptor assays showed that normal RLF possess mainly PDGF-R beta and a paucity of PDGF-R alpha. In agreement with the Northern data, saturation binding of [125I]PDGF-BB to RLF exposed to asbestos demonstrated an approximately 40% increase in binding sites accompanied by a twofold decrease in receptor affinity. Treating asbestos-exposed RLF with PDGF-AA, which binds only PDGF-R alpha, blocked the PDGF binding sites that were upregulated by fiber exposure. PDGF-AA had increased mitogenic potency for fiber-exposed RLF, but PDGF-BB was a less potent mitogen for these RLF. Nonfibrogenic carbonyl iron spheres induced similar changes in PDGF growth responses. These data show that inorganic particulates alter the PDGF-R alpha population on RLF without significant change in PDGF-R beta.

Inorganic particles induce secretion of a macrophage homologue of platelet-derived growth factor in a density-and time-dependent manner in vitro

The inhalation of inorganic dust can lead to the development of interstitial pulmonary fibrosis, characterized by the accumulation of fibroblasts and connective tissue matrix in the lung interstitium. The fibrosis causes alterations in the architecture of the lung parenchyma, resulting in abnormal gas exchange and hypoxemia. In a rat model of asbestos exposure, inhaled fibers are deposited on alveolar duct bifurcations, followed by an accumulation of alveolar macrophages at the sites of dust deposition. The alveolar macrophage is thought to be a major mediator of the pulmonary inflammatory response to inhaled dust. Platelet-derived growth factor (PDGF) is a cytokine that has potent chemotactic and mitogenic effects on mesenchymal cells, such as fibroblasts and smooth muscle cells. We studied the secretion of an alveolar macrophage-derived homologue of PDGF in response to carbonyl iron spheres or chrysotile asbestos fibers in vitro. We demonstrate here that rat alveolar macrophages attached to a plastic substrate produce 69 +/- 79 picograms (pg) of PDGF per 10 million macrophages. This is similar to amounts recovered from human platelets. In contrast, macrophages exposed to iron spheres secrete 429 +/- 177 pg of PDGF/10(6) macrophages after 24 h in culture. Exposure to asbestos fibers increased the PDGF production to 628 +/- 213 pg/10(6) cells. PDGF secretion was influenced by the particles in a density- and time-dependent manner. We hypothesize that PDGF and other cytokines secreted by macrophages mediate the development of dust-induced lung disease.

Physiological and pathophysiological pulmonary responses to inhaled nuisance-like or fibrogenic dusts

A short-term bioassay has been developed to assess pulmonary toxicity and predict pathological effects in animals exposed to aerosolized particulates. To test the reliability and predictive value of our bioassay, we have exposed rats to 2 materials with different biological activities. Rats were exposed for 1 or 3 days to selected concentrations of crystalline silica (a known fibrogenic dust), or to carbonyl iron (CI) particles (a material with activity reputedly similar to nuisance dusts). Pulmonary cells and tissues were evaluated at several time points after exposure. In a companion manuscript we reported that brief exposures of silica produced a sustained pulmonary inflammatory response, characterized by increases in biochemical indicators, whereas no significant effects were measured in CI-exposed animals. In the current study, our results showed that although deposition patterns for the 2 dusts were similar (i.e., at alveolar duct bifurcations), brief doses of silica produced a sustained granulocytic inflammatory response at the sites of particle deposition, while CI particles were phagocytized and cleared from the lung by normal pulmonary macrophage mechanisms which included transport via the airway mucociliary escalator. Light, scanning, and transmission electron microscopy of silica-exposed lung tissue revealed a chronically active pulmonary inflammatory response characterized by hyperplasia of type II alveolar epithelial cells and the infiltration of pulmonary macrophages and neutrophils into interstitial tissues and alveoli. The lesions were progressive leading to a granulomatous pneumonitis within 2 months postexposure. In contrast to the alterations in pulmonary tissues produced by silica, no CI-related lesions were detected at any time postexposure. The results justify the utility of this bioassay as a reliable approach to evaluating the pulmonary toxicity of inhaled particulates.

Immunologic aspects of pneumoconiosis

This review summarizes recent research bearing on the role played by cells of the immune system in the development of pneumoconiosis. Findings related to the cellular and humoral immune responses to silica and asbestos are highlighted. Experimental results from humans and animal models are integrated into our current understandings of cellular and cytokine-mediated pathways leading to the generation of immune responses that may contribute to fibrogenesis and fibrosis. Potential mechanisms leading to the generation of an immune response by particulates are discussed, together with the indirect effects of particulates on fibroblasts by way of the cytokine network in the lung. Finally, suggestions are given for future research to help further elucidate the relationships between the cellular components of the immune system of the lung and the fibroblast that lead to fibrosis.

Development of a short-term inhalation bioassay to assess pulmonary toxicity of inhaled particles: comparisons of pulmonary responses to carbonyl iron and silica

This paper describes a short-term inhalation bioassay for evaluating the lung toxicity of inhaled particulate materials. To validate the method, rats were exposed for 6 hr or 3 days to various concentrations of either aerosolized alpha-quartz silica or carbonyl iron particles. Cells and fluids from groups of sham- and dust-exposed animals were recovered by bronchoalveolar lavage (BAL). Alkaline phosphatase, lactate dehydrogenase (LDH), and protein values were measured in BAL fluids at several time points postexposure. Cells were identified, counted, and evaluated for viability. Pulmonary macrophages (PM) were cultured and studied for morphology, chemotaxis, and phagocytosis by scanning electron microscopy. The lungs of additional exposed animals were processed for histopathology and transmission electron microscopy. Brief exposures to silica elicited a sustained granulocytic inflammatory response (primarily neutrophils) with concomitant increases in alkaline phosphatase, LDH, and protein in the lavage fluids (p less than 0.05). In addition, PM functional capacity was depressed (p less than 0.05) and histopathologic lesions were observed within 1 month after exposure. In contrast, 6-hr or 3-day exposures to CI produced no cellular, cytotoxic, or alveolar/capillary membrane permeability changes at any time postexposure. PM function was either enhanced or unchanged from controls. These data demonstrate that short-term, high-dose inhalation exposures of silica produce effects similar to those previously observed using intratracheal instillation or chronic inhalation models, and lend support to this method as a reliable short-term bioassay for evaluating the pulmonary toxicity and mechanisms associated with exposures to new and untested materials.

Persistent biological reactivity of quartz in the lung: raised protease burden compared with a non-pathogenic mineral dust and microbial particles

This study assessed the potential harmfulness of particles in the lung by measuring their ability to elicit and maintain an inflammatory response and to damage lung tissue. It compared the inflammogenicity of two nondurable, biological particulates (Corynebacterium parvum and zymosan) with a pathogenic mineral dust (quartz) and a nonpathogenic dust (titanium dioxide) by dosing rats via the intratracheal route and measuring the consequent alveolitis. The magnitude and duration of the inflammatory response were assessed by measuring the total number of leucocytes and the percentage of neutrophils obtained by bronchoalveolar lavage. Two key functional parameters of the lavaged leucocytes--ability to degrade fibronectin and production of plasminogen activator--were also measured. A marked inflammatory response had occurred by one day after instillation, characterised by increases in total leucocyte numbers and percentage of neutrophils in the bronchoalveolar lavages, with all four test materials. In all but the quartz exposed animals, the inflammation subsided rapidly thereafter, approaching control levels by 15 days after injection; in the quartz exposed animals the alveolitis persisted for up to 30 days. All of the inflammogens generated chemotaxins in rat serum in vitro and so, by analogy, might also be expected to generate chemotactic activity in alveolar lining fluid which could contribute to the generation of an inflammatory response. The cellular inflammatory response was accompanied by a concomitant increase in the proteolytic activity of the bronchoalveolar lavage leucocytes but production of plasminogen activator remained unchanged. In vitro exposure to the inflammogens had no effect on the proteolytic activity against fibronectin or on the plasminogen activator activity of bronchoalveolar leucocytes.

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

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

Particle distribution in lung and lymph node tissues of rats and dogs and the migration of particle-containing alveolar cells in vitro

Whole rat lungs and individual dog lung lobes were instilled either with low numbers (10(7)) or high numbers (10(9)) of fluorescent polystyrene microspheres (PLM), or with saline alone. Particle distributions in dog and rat lung lobes and tracheobronchial lymph nodes (TBLN) were studied up to several weeks after particle instillations using methacrylate-embedded tissues and epifluorescence light microscopy. Free alveolar cells were obtained from rats and dogs by lung lavage 1 or 7 d after particle instillations. Lavaged cells were tested for directed migration toward the chemoattractant N-formylmethionyl-leucyl-phenylalanine (FMLP). Random migration in the absence of the FMLP was used as a control. The dog lung interstitium contained many more particles than did the rat lung interstitium, and particle numbers in interstitial and TBLN cells of dogs were higher than in those of rats. FMLP enhanced the number of migrating cells about twofold. Increasing particle numbers in lavaged phagocytes (greater than 10 particles/phagocyte in dogs; greater than 20 particles/phagocyte in rats) decreased their ability to migrate. The higher fractions of particles in the dog lung interstitium are thought to be an important reason for prolonged retention and increased TBLN transport of deposited particles in dogs as compared with rats. Our results suggest that cell mobility is lost after ingestion of high numbers of particles, and that this occurs earlier with dog than with rat lung cells.

Species comparisons of proximal alveolar deposition patterns of inhaled particulates

Previous studies have shown that inhaled particles and fibers that are small enough to pass through the conducting airways deposit preferentially at alveolar duct bifurcations in the distal lungs of exposed rats. Because it is well documented that anatomic and physiologic differences exist among common experimental animals that may influence deposition patterns, we compared inhaled particle deposition patterns in alveolar regions of four rodent species. Proximal alveolar regions of hamsters and guinea pigs contain rudimentary respiratory bronchioles, whereas in rats and mice, terminal bronchioles lead directly into alveolar ducts. Groups of animals from one strain each of rats, mice, hamsters, and guinea pigs were exposed to aerosols of carbonyl iron (CI) particles for 1 h at design concentrations of 100 mg/m3. Immediately after exposure, the lungs of sham- and CI-exposed animals were perfusion fixed through the vasculature. Subsequently, lung tissues from exposed animals was analyzed for iron concentration; data indicated that total lung deposition of iron particles was highest in mice and hamsters. In addition, scanning electron microscopy of dissected lung tissue revealed that particle deposition patterns in the proximal regions of the distal lung were similar for all species, although greater numbers of CI particles per bifurcation were deposited in rats and mice compared to hamsters (p less than 0.05) and greater numbers were deposited in hamsters compared to guinea pigs (p less than 0.05). The data suggest that the presence of undeveloped respiratory bronchioles in the lungs of hamsters and guinea pigs has little influence on distal lung particle deposition patterns. It remains to be determined whether inhaled particles are deposited at similar sites in the lungs of species with well-developed respiratory bronchioles such as cats, nonhuman primates, and humans.

Quantitative relationships between single-cell and cell-population model parameters for chemosensory migration responses of alveolar macrophages to C5a

Phenomenological parameters from a mathematical model of cell motility are used to quantitatively characterize chemosensory migration responses of rat alveolar macrophages migrating to C5a in the linear under-agarose assay, simultaneously at the levels of both single cells and cell populations. This model provides theoretical relationships between single-cell and cell-population motility parameters. Our experiments offer a critical test of these theoretical linking relationships, by comparison of results obtained at the cell population level to results obtained at the single-cell level. Random motility of a cell population is characterized by the random motility coefficient, mu (analogous to a particle diffusion coefficient), whereas single-cell random motility is described by cell speed, s, and persistence time, P (related to the period of time that a cell moves in one direction before changing direction). Population chemotaxis is quantified by the chemotactic sensitivity, chi 0, which provides a measure of the minimum attractant gradient necessary to elicit a specified chemotactic response. Single-cell chemotaxis is characterized by the chemotactic index, CI, which ranges from 0 for purely random motility to 1 for perfectly directed motility. Measurements of cell number versus migration distance were analyzed in conjunction with the phenomenological model to determine the population parameters while paths of individual cells in the same experiment were analyzed in order to determine the single-cell parameters. The parameter mu shows a biphasic dependence on C5a concentration with a maximum of 1.9 x 10(-8) cm2/sec at 10(-11) M C5a and relative minima of 0.86 x 10(-8) cm2/sec at 10(-7) M C5a and 1.1 x 10(-8) cm2/sec in the absence of Ca; s and P remain fairly constant with C5a concentration, with s ranging from 2.1 to 2.5 microns/min and P varying from 22 to 32 min. chi 0 is equal to 1.0 x 10(-6) cm/receptor for all C5a concentrations tested, corresponding to 60% correct orientation for a difference of 500 bound C5a receptors across a 20 microns cell length. The maximum CI measured was 0.2. Values for the population parameters mu and chi 0 were calculated from single-cell parameter values using the aforementioned theoretical linking relationships. The values of mu and chi 0 calculated from single-cell parameters agreed with values of mu and chi 0 determined independently from population migrations, over the full range of C5a concentrations, confirming the validity of the linking equations. Experimental confirmation of such relationships between single-cell and cell-population parameters has not previously been reported.

Histologic changes in the respiratory tract induced by inhalation of xenobiotics: physiologic adaptation or toxicity?

Toxicologists and pathologists are often faced with the dilemma of categorizing changes observed in the respiratory tract of laboratory animals as either "adaptive" or "toxic." However, it is often difficult to interpret the nature of a given change as either "adaptive" or "toxic." Certain lesions or changes in the respiratory tract are to be expected from the concentration of materials given or the experimental design of a study. Careful analysis suggests that some of these changes may be more properly described as adaptive rather than toxic within the context of a given study or situation. Tissue changes discussed in this paper include squamous metaplasia of laryngeal epithelium, goblet cell change in respiratory epithelium, macrophage accumulation within alveoli, and bronchiolization of alveolar epithelium. Examples provided show that some of these changes observed in inhalation studies are similar in severity but slightly increased in frequency over sham control animals. The introduction of exogenous material into the respiratory tract of laboratory animals in an experimental setting should be expected to result in certain changes. The challenge scientists must accept is to interpret these changes so that toxic events may be separated from adaptive changes. In order to meet this challenge, studies incorporating several species and novel technologies may have to be utilized.

Alveolar macrophage-particle relationships during lung clearance

Retention kinetics for insoluble particles that deposit in the lung oftentimes resemble a multicomponent process during alveolar clearance, with each component appearing to follow simple first-order kinetics. Inasmuch as alveolar macrophages (AM) are thought to play an important role in particle removal from the lung, a study was undertaken to examine particle-AM relationships during the clearance of particles to obtain information on potential AM mechanisms that could provide the underlying bases for the lung retention kinetics of the particles. Adult, Fischer 344 rats were intratracheally instilled with 1.6 x 10(7) (approximately 86 micrograms) polystyrene microspheres (approximately 2 microns diam). On Days 7, 14, 57, 85, and 176 thereafter, subgroups were killed, their lungs were lavaged, recovered cells (greater than 95% AM) were counted, the frequency distribution of the particles among the AM was determined (e.g., zero, 1 to 2, 3 to 4 particles/AM), and the total numbers of particles lavaged were estimated. The lavaged lungs were solubilized, and unlavaged particles were also counted. The sums of the lavaged and unlavaged particles were used to estimate retained lung burdens at each postinstillation time. The lung retention data followed a pattern consistent with the sum of two negative exponential components, i.e., an earlier, more rapid component and a slower, longer term component. The rates at which the AM disappeared from a given particle category also were biphasic for AM that contained up to 14 microspheres. The rates of both the earlier and longer term components of such disappearance were found to increase with increasing AM burdens. Over an AM burden range of 1 to 10 microspheres, the proportion of AM that disappeared via rapid components also increased as the particle burden defining an AM category increased. At higher particle burdens, the proportion of AM that disappeared by an early component appeared to markedly diminish; an early component for AM disappearance was no longer resolvable for AM that contained greater than 15 microspheres. The net effect of these phenomena was that retained lung burdens over time became progressively contained in AM with lesser burdens of particles. The results from this study suggest that the rate(s) of translocation of particle-containing AM from the lung during lung clearance may be related to their individual particulate burdens. These findings, however, are also consistent with a gradual redistribution of particles among the lung's AM population over time concurrent with AM removal from the lung. Regardless, the biphasic nature of the lung retention data qualitatively was generally evident for particle-containing AM as well.

Interspecies comparisons of lung responses to inhaled particles and gases

Two important challenges for inhalation toxicologists involve the elucidation of mechanisms of lung toxicity caused by inhalation of chemicals or particulate materials, as well as the extrapolation of animal data to humans. Because risk estimates of toxicity generally are dependent upon experimental data for which a variety of species are utilized, a fundamental knowledge of species similarities and differences in lung anatomy, physiology, biochemistry, cell biology, and corresponding disease processes is essential. In the present review, the known mechanisms of particle deposition and clearance among various species have been highlighted and related to structure/function relationships and pathogenetic responses to some selected inhaled toxicants. In the aggregate, there is remarkable homogeneity in form and function among the species. Morphologic aspects of the respiratory tract and lung defense mechanisms are qualitatively similar among species. On the other hand, quantitative differences between humans and experimental animals are known to exist with respect to deposition and mucociliary clearance of inhaled particulates, and these factors are likely to influence the dose that is delivered to specific target sites in the lung. It is interesting to consider that pathologic cellular events following asbestos, ozone, and nitrogen dioxide exposure are likely to occur at similar sites in humans, nonhuman primates, and rodents. In this respect, it has been demonstrated that the early lesions of asbestos-induced lung disease in both rats and humans are initiated at similar anatomical sites, i.e., the junctions of terminal airways and alveolar regions. PMs and complement-mediated mechanisms have been implicated in the development of asbestosis in rats; however, it remains to be determined whether complement activation plays an important role in human asbestosis, although pulmonary and interstitial macrophages clearly are associated with the fibrogenic process associated with this restrictive lung disease. The toxic pulmonary effects following ozone exposure have been well studied in rodents and nonhuman primates. It has been established that distal airway and alveolar epithelial cells are principal targets of oxidant pollutants, and this is well supported by dosimetry considerations, morphologic observations, and morphometric analyses. Chronic ozone exposure in rats and monkeys causes epithelial injury at the level of the terminal bronchiole and proximal alveolar regions of the lung.(ABSTRACT TRUNCATED AT 400 WORDS)