Activation of immune complement by fly ash particles from coal combustion

Effects of beryllium metal particles on the viability and function of cultured rat alveolar macrophages

The physicochemical properties of particles influence their in vivo toxicity following deposition in the respiratory tract. To evaluate the relative contributions of mass and surface area to particle-induced toxicity, rat pulmonary alveolar macrophages (PAM) were exposed to four types of particles in vitro. We used three beryllium metal samples: relatively large (Be-II) and relatively small (Be-V) sized fractions of beryllium metal obtained from an aerosol cyclone, and a beryllium metal aerosol generated by laser vaporization of bulk beryllium metal in an argon atmosphere (Be-L). We also used glass beads (GB) as a negative control particle. End points examined included cell viability, determined by trypan blue dye exclusion, and changes in phagocytic ability, measured by counting the number of sheep red blood cells internalized by the PAM. Phagocytic ability was inhibited by exposure to beryllium particles at concentrations that did not cause appreciable cell death. Results describing effects based on the mass concentration of particles in culture medium were transformed by the amount of specific surface area of the particles to permit the expression of toxicity relative to the amount of particle surface per unit volume of culture medium. On a mass basis, the order of particle-related cytotoxicity was Be-L greater than Be-V greater than Be-II greater than GB, and for inhibition of phagocytosis, the order was Be-L approximately Be-V greater than Be-II greater than GB. When analyzed on a specific surface area basis, the cytotoxicity of the different materials became more similar in a fashion that was largely predicted by the amount of surface of the particles administered. However, because differences in specific surface area among the beryllium particle samples did not entirely predict cytotoxicity, we concluded that factors in addition to specific surface area influenced the expression of toxic effects in cultures of PAM exposed to beryllium metal.

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.

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)

Pulmonary macrophages are attracted to inhaled particles through complement activation

Pulmonary macrophages play a central role in clearing inhaled particles from the lung. Previously, we showed that inhaled asbestos fibers activate complement-dependent chemotactic factors on alveolar surfaces to facilitate macrophage recruitment to sites of fiber deposition. In the studies presented here, we have tested a variety of inorganic particles for complement activation in vitro and correlated these data with results on particle-induced macrophage accumulation in vivo. We found that significant chemotactic activity was activated in rat serum and concentrated lavaged proteins by chrysotile and crocidolite asbestos, iron-coated chrysotile asbestos, fiberglass, and wollastonite fibers, as well as by carbonyl iron and zymosan particles. Ash from the Mt. St. Helens volcano did not induce chemotactic activity in either the serum or lavaged proteins. Rats were exposed to brief aerosols of each of the particles listed above (except zymosan). All the particle types studied were deposited primarily at first alveolar duct bifurcations. In addition, all of the particles, except Mt. St. Helens ash, induced at 48 h postexposure significant accumulations of macrophages at these sites. Time-course studies of carbonyl iron particle exposure demonstrated that iron induced a rapid macrophage response, but both particles and phagocytic macrophages were cleared from alveolar surfaces within 8 days after exposure. The Mt. St. Helens ash induced no macrophage accumulation at any time postexposure. We conclude that particles with a wide variety of physical characteristics are capable of activating complement and consequently attracting macrophages, both in vitro and in vivo. We suggest that complement activation is a mechanism through which pulmonary macrophages can detect inhaled particles on alveolar surfaces.

Cytokinetic and morphological changes in the lungs and lung-associated lymph nodes of rats after inhalation of fly ash

Fischer-344 rats (male and female) were exposed to 36 mg/m3 of fluidized bed coal combustion fly ash or sham-exposed for 7 hr/day, 5 days/week for 4 weeks, and sacrificed after 2 or 4 weeks of exposure and at 2, 22, and 42 weeks after the end of exposure. Animals were injected with tritiated thymidine 2 hr before sacrifice and autoradiographs prepared from 1-micron sections of lung and lymph node tissue embedded in glycol methacrylate plastic. Differences in labeling indices of pulmonary epithelial cells, alveolar macrophages, airway epithelial cells, and cells of the lung-associated lymph nodes between the exposed and control animals were maximal after 2 and 4 weeks of exposure. Labeling indices for lung epithelial cells were about the same in control and exposed animals at 2, 22, and 42 weeks after the end of exposure. However, these values were elevated relative to earlier control levels. In contrast, morphological changes in the fly ash-exposed animals were most prominent after the end of the exposure. These changes included thickening of the alveolar walls, clusters of particle-filled macrophages in the alveolar region, and perivascular inflammation. Additionally, there were small granulomas in the alveolar region at 42 weeks after the end of exposure. Granulomas were also formed in the lung-associated lymph nodes and and bronchus-associated lymphoid tissue. We conclude that the inhalation of fly ash alone had little detrimental effect upon the rat lung. However, the increases in proliferation indicate the potential for fly ash combined with a carcinogen to enhance the carcinogen's effect.

Effects of lignite fly ash particulates and soluble components on the interferon system

Induction of interferon by influenza virus was depressed by approximately 50% when mammalian (LLC-MK2) cell monolayers were pretreated with lignite fly ash. The presence of fly ash, however, did not impair the ability of exogenous interferon to confer antiviral cellular resistance. Influenza virus multiplication in cell monolayers pretreated with fly ash attained a twofold higher level of growth than that noted in normal cell monolayers. This was related to suppression of viral interferon induction by fly ash. Whereas aqueous extracts of fly ash had no adverse effect on interferon induction, extractions of fly ash by either polar or nonpolar solvents, by horse serum with or without EDTA (a metal chelator), and fractionation of serum extracts yielded corresponding compounds, most likely organic and inorganic, that were antagonistic to viral interferon induction. Residual fly ash particulates after extraction by horse serum with EDTA were still capable of inhibiting viral induction of interferon. These findings indicate that several soluble components inherent to lignite fly ash and the particulate matrix per se may modify, independently or in concert, cellular defense behavior. Neither polar, nonpolar, nor horse serum extracts of lignite fly ash, however, showed mutagenic activity as determined by the Salmonella histidine reversion assay. Removal of cell-membrane-bound sialic acid (N-acetylneuraminic acid) by neuraminidase or pretreatment of lignite fly ash with sialic acid abolished the adverse activity of fly ash on viral interferon induction. This suggests that the interaction of cell-membrane-bound sialic acid residue with fly ash particulates may be involved in the altered state of cellular behavior described in response to viral induction of interferon.