Tumorigenicity of cellulose fibers injected into the rat peritoneal cavity.

Cellulose fibers, along with many other organic fibers, are durable. Therefore, if inhaled, they have the potential to persist within the lung, and may then cause disease. Here we report the effects of injecting high-purity cellulose fibers into the abdominal cavity of rats. A respirable fraction of cellulose fiber was collected from an aerosol of a thermo-mechanically-processed wood pulp. A sample of respirable crocidolite asbestos, known to produce mesotheliomas in rats, was used as a positive control. Total doses of 10(6), 10(7), 10(8), or 10(9) WHO fibers were injected intraperitoneally as 3 weekly aliquots. A negative control was provided by phosphate-buffered saline used to suspend the fibers for injection. There were 50 rats per treatment group except for the 10(8) and 10(9) fibers crocidolite groups which were reduced to 26 rats because of the expectation of high tumor incidence in these groups. The two higher doses of crocidolite asbestos caused greatly reduced survival compared to the saline controls. With cellulose there was a much less marked effect on survival. In the highest dose cellulose group, multiple large nodules (granulomas) and widespread adhesions (bands of new tissue connecting organs to each other and to the abdominal wall) were present in all animals. Granulomas were not observed in the 10(9) fibers crocidolite group. More than 80% of animals in the 10(8) and 10(9) crocidolite asbestos groups had mesotheliomas, a type of tumor sometimes observed in people exposed to asbestos. In contrast, there were only 2 animals in the cellulose groups with mesothelioma tumors, 1 in the 10(7) and 1 in the 10(8) groups. However, 9 (18%) of the 10(9) cellulose group had malignant tumors that, in contrast to the usual pattern of mesothelioma development following treatment with mineral fibers in rats, showed no obvious involvement of mesothelial tissues, were not associated with blood-stained ascites fluid, and were thus classified as sarcomas. This study has demonstrated that a high dose of cellulose fibers is capable of producing tumors when injected into the abdominal cavity of rats.

Inhalation of poorly soluble particles. I. Differences in inflammatory response and clearance during exposure.

Results from animal studies have indicated some uncertainties over the validity of a single general occupational control limit for all types of "particulates (insoluble) not otherwise classified" (PNOC) (ACGIH, 2000). Therefore, to examine the extent to which a given control limit may be valid for nontoxic dusts with different physical characteristics, this study compared the pulmonary effects in rats of inhalation exposure to two poorly soluble dusts of similar density and with relatively low toxicity: titanium dioxide and barium sulfate. The objectives were to compare the dusts in (a) their buildup and clearance in the lungs during inhalation; (b) their transfer to lymph nodes; (c) the changes, with time, in the lavageable cell population; and (d) the pathological change from histology. The exposure aerosol concentrations were selected to achieve similar mass and volume lung burdens for both dusts and to attain "overload" over the common exposure periods of about 4 mo and 7 mo. Despite obtaining similar lung burdens for both dusts, there was significantly more translocation of TiO(2) to the hilar lymph nodes than with BaSO(4). It was also found that clearance of TiO(2) was retarded whereas clearance of BaSO(4) was not. Trends in these data were clarified by the use of a simple model of particle clearance. Retardation of particle clearance and translocation to the lymph nodes are markers of the condition known as "overload" in which the alveolar macrophage-based clearance of particles from the deep lung is impaired. In addition, bronchoalveolar lavage showed that TiO(2) caused significantly more recruitment of inflammatory neutrophils to lungs than BaSO(4). These differences between the dusts were not due to differences in toxicity, solubility, or lung deposition. The explanation that the different responses are due to the different particle size distributions of the two dust types is examined in a companion paper (Tran et al., this issue).

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.

In vitro toxicology of respirable Montserrat volcanic ash.

OBJECTIVES: In July 1995 the Soufriere Hills volcano on the island of Montserrat began to erupt. Preliminary reports showed that the ash contained a substantial respirable component and a large percentage of the toxic silica polymorph, cristobalite. In this study the cytotoxicity of three respirable Montserrat volcanic ash (MVA) samples was investigated: M1 from a single explosive event, M2 accumulated ash predominantly derived from pyroclastic flows, and M3 from a single pyroclastic flow. These were compared with the relatively inert dust TiO(2) and the known toxic quartz dust, DQ12. METHODS: Surface area of the particles was measured with the Brunauer, Emmet, and Teller (BET) adsorption method and cristobalite content of MVA was determined by x ray diffraction (XRD). After exposure to particles, the metabolic competence of the epithelial cell line A549 was assessed to determine cytotoxic effects. The ability of the particles to induce sheep blood erythrocyte haemolysis was used to assess surface reactivity. RESULTS: Treatment with either MVA, quartz, or titanium dioxide decreased A549 epithelial cell metabolic competence as measured by ability to reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). On addition of mannitol, the cytotoxic effect was significantly less with M1, quartz, and TiO(2). All MVA samples induced a dose dependent increase in haemolysis, which, although less than the haemolysis induced by quartz, was significantly greater than that induced by TiO(2). Addition of mannitol and superoxide dismutase (SOD) significantly reduced the haemolytic activity only of M1, but not M2 or M3, the samples derived from predominantly pyroclastic flow events. CONCLUSIONS: Neither the cristobalite content nor the surface area of the MVA samples correlated with observed in vitro reactivity. A role for reactive oxygen species could only be shown in the cytotoxicity of M1, which was the only sample derived from a purely explosive event. These results suggest that in general the bioreactivity of MVA samples in vitro is low compared with pure quartz, but that the bioreactivity and mechanisms of biological interaction may vary according to the ash source.

Pathogenicity of a special-purpose glass microfiber (E glass) relative to another glass microfiber and amosite asbestos.

This article describes the activity of an E-glass microfiber (104E) during chronic inhalation and intraperitoneal injection studies in rats. Results are compared with another microfiber of similar dissolution rate (k(dis)), code 100/475, and the more durable amosite asbestos, both of which we had previously used in similar experiments (Davis et al., 1996). Rats were exposed to aerosol concentrations of 1000 fibers (longer than 5 microm)/ml, as measured by optical microscopy, for 7 h/day, 5 days/wk. Subgroups of rats were followed for mean lung burden, early and late signs of fibrosis, and tumor incidence. At the end of 12 mo of exposure, the mean number of 104E fibers of all lengths in the lungs was approximately double that for amosite but two-thirds of that for 100/475. For fibers longer than 15 microm, the mean 104E burden was similar to that for the amosite and more than twice that of the 100/475. After a 12-mo recovery period, the retained lung burdens (of fibers of all lengths) were approximately 30% of those at 12 mo for both microfibers, and somewhat higher (approximately 44%) for amosite. Amosite and 100/475 fibers longer than 15 microm were more persistent in the lungs than 104E fibers. The chemical composition of 104E fibers did not appear to have been significantly altered by up to 24 mo of residence in lung tissue, whereas the composition of 100/475 was substantially altered over the same time period. From the inhalation study, out of the pathology subgroup of 43 animals exposed to 104E microfibers, 10 had lung tumors (7 carcinoma, 3 adenoma) and 2 had mesotheliomas, whereas in 42 rats exposed to amosite asbestos, there were 16 lung tumors (7 carcinoma, 9 adenoma) and 2 mesotheliomas. The 104E- and amosite-treated animals had similar levels of fibrosis. In contrast, 38 animals treated with 100/475 had little fibrosis, 4 lung tumors (adenomas), and no mesotheliomas. The greater pathogenicity of the 104E fibers, compared to 100/475 fibers, might be partly explained by the greater numbers of long fibers retained in the lung after 12 mo of inhalation. However, we speculate that modification of surface properties by extensive selective leaching of some glass components reduces the toxic potential of 100/475. In a parallel intraperitoneal injection study, 104E caused considerably more mesotheliomas (21 rats out of 24) than 100/475 (8 rats out of 24). In addition, 104E appeared to be more active than amosite asbestos, since mesotheliomas appeared much more quickly in the 104E-treated animals. In conclusion, we have shown that two microfiber types, 100/475 and 104E, of similar dissolution rates, had markedly different pathogenicity in rats. We believe that this contrast is only partly due to differences in numbers of long fibers and that differences in surface properties of the fibers, possibly due to proportionately greater leaching of 100/475 fibers, play an important role.

Pulmonary and intraperitoneal inflammation induced by cellulose fibres.

The inflammatory effects of respirable cellulose fibres were studied in two short-term animal models: intraperitoneal injection in mice, and inhalation in rats. The mouse peritoneal cavity is particularly sensitive to fibrous compared to non-fibrous particles. Both cellulose fibres and the positive control fibre, crocidolite asbestos, were administered in doses ranging from 10(4) to 10(8) fibres and caused marked, dose-dependent recruitment of inflammatory cells to the mouse peritoneal cavity, which was highest 1 day following injection. Crocidolite was much more active than cellulose, despite the mass dose of cellulose being 66 times greater for an equivalent number of fibres. Crocidolite at the higher doses caused inflammation to persist through 7 days. For the inhalation study, rats were exposed daily, 5 days per week, to aerosols of cellulose dust for ca. 3 weeks at a concentration of 1000 fibres ml(-1). Inhalation exposure induced an early inflammatory response in rat lungs, as determined by bronchoalveolar lavage, which peaked at 1 day following the start of inhalation and thereafter declined, despite a further 13 days of exposure over a period of 18 calendar days. In vitro production of the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-alpha) by lavaged alveolar macrophages was markedly depressed by the end of the exposure period in cellulose-exposed animals, compared to sham-exposed controls, and this effect was still present in rats that had been allowed to recover for 28 days beyond the end of exposure. We conclude that the cellulose material studied is less inflammogenic than crocidolite and that the extent of the inflammatory response within the lung appears to reduce with continued exposure over a 14-day period.

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.

Exploration of the mechanisms of retention and clearance of low-toxicity particles in the rat lung using a mathematical model.

A mathematical model of the mechanisms of clearance or retention of inhaled particles in rat lungs is used to explore the extent to which a hypothesized sequence of events (including phagocytosis, macrophage-mediated clearance, transfer into the interstitium, transfer to lymph nodes, and overloading of the defense mechanisms) can account for data from a series of inhalation experiments with a low-toxicity, insoluble dust-titanium dioxide, TiO(2). These data include mean lung burdens and mean lymph-node burdens in groups of rats exposed to concentrations of 1, 10, 30, 50, and 90 mg m(-3), with exposure periods for as long as 2 yr (at 10 mg m(-3)), up to 7 mo at 50 mg m(-3), and 3.5 mo at 1 and 30 mg m(-3). The estimation of the parameters in the model is based mainly on information from other experimental studies or prior modeling. Values within the biologically plausible range were evaluated for the main parameters by inspection of predictions in comparison with data from the lowest concentration experiments. The suitability of the selected values was then confirmed by comparison of model predictions with data from the higher concentration experiments (at 30, 50, and 90 mg m(-3)). During inhalation, clearance rates are affected by translocation of dust and by overloading. The characterization of overload appears to describe these experiments well. Comparison with the effect of lung burden reported for other types of particles supports the hypothesis that overload is more dependent on the volume rather than the mass of the particles.

Biopersistence and durability of nine mineral fibre types in rat lungs over 12 months.

The study objectives were to assess the ability of intratracheal injection methods to discriminate between nine fibre types in respect of pulmonary biopersistence, and to provide approximate estimates of relative biopersistence and durability for a study of general relationships with biological and toxicological responses. The test fibres included six samples of size-selected fibre types specially prepared for research purposes, two commercially available fibres, and amosite. A 1 mg dose of each fibre type was administered to rats by intratracheal injection. The relative biopersistence of fibres in different size categories was assessed from the changes in mean lung burden, as determined by electron microscopy, at 3 days and 1, 6 and 12 months after injection. The ability of the test materials to resist dissolution was measured in a parallel series of simple in vitro acellular experiments at two pHs and in a continuous flow dissolution test. The observed differences in the persistence of fibres of differing length recovered from rat lungs were consistent with the current hypothesis that short fibres are cleared by cellular processes and long fibres by dissolution and disintegration. Differences in persistence of long (> 20 microns) fibres were correlated with measured rates of dissolution in vitro. Differences in persistence among those fibre types also studied by others workers were consistent with their findings after inhalation and intratracheal injection. Overall, the differences in the biopersistences of the test fibres following intratracheal injection were sufficient to enable an examination of the relationship of biopersistence with other biological and toxicological responses. Biopersistence was influenced by both fibre dimensions and solubility.

Influence of fibre length, dissolution and biopersistence on the production of mesothelioma in the rat peritoneal cavity.

A range of respirable man-made mineral fibres were tested for evidence of carcinogenicity by injection into the peritoneal cavity of male SPF Wistar rats; and differences in carcinogenicity were related to the dimensions and biopersistence of the injected fibres. The fibres tested included an amosite asbestos, a silicon carbide whisker, a special purpose glass microfibre, and a range of other man-made vitreous fibres (MMVFs) and refractory ceramic fibres (RCFs) from the TIMA fibre repository. The injected dose of each was designed as the estimated mass required to contain 10(9) fibres > 5 microns in length, as determined by optical microscopy. The numbers of long fibres (> 15 microns) contained in these doses ranged across fibres from 0.1 x 10(9) to 0.8 x 10(9) fibres; the number of long fibres thinner than 0.95 micron ranged from 0.015 x 10(9) to 0.4 x 10(9). The treatment groups contained between 18 and 24 animals. Animals were killed when they showed signs of debilitation. At autopsy, the diagnosis of mesothelioma was usually obvious macroscopically. Otherwise, histological examination of peritoneal organs was used to search for early tumour development. Judged by median survival time, four of the fibre types, in the doses administered, presented higher mesothelioma activity than amosite asbestos. The other fibres tested were less carcinogenic than the amosite. Only a ceramic material derived by extreme heating to simulate the effect of furnace or oven conditions, produced no mesotheliomas. Attempts were made, using regression models, to relate these differences to fibre dimensions and to measures of durability from separate experiments. The results pointed principally to a link with the injected numbers of fibres > 20 microns in length and with biopersistence in the rat lung of fibres longer than 5 microns. Improved quantification of the relative importance of fibre dimensions and biopersistence indices requires experimentation with a range of doses.

Influence of characteristics of inhaled fibres on development of tumours in the rat lung.

The objective was to examine and quantify the influence of fibre dimensions, persistence in the lung, and dissolution and cell toxicity in vitro, on the risks of developing lung tumours in rats. Data were brought together from the studies carried out at the IOM under the Colt Fibre Research Programme, and from studies carried out in Switzerland and the USA under the programme of the Thermal Insulation Manufacturers Association. In both studies, groups of rats were exposed by inhalation to a range of airborne fibres. At the end of their lives they were examined for the presence of benign and malignant lung tumours and mesothelioma. The studies differed in a number of details, but were combined on the basis of approximate equivalence of cumulative exposure to airborne fibres. Logistic regression models were used to relate differences in carcinogenicity to fibre characteristics; dimensions, persistence in the lung after intratracheal injection, dissolution rates from bench-top flow-through experiments, measures of inflammation, and other cell responses to fibres in vitro. Despite the small number of data points, the results suggested a primary influence of the airborne concentrations of the numbers of fibres thinner than 1 micron diameter and longer than 20 microns, and of the measured dissolution rate of the fibres. While these results are based on only a small number of fibre types, the statistical model fits the data reasonably well, and enables some cautious insights into the quantitative influences of dimensions and biopersistence. Results were broadly consistent with those from intraperitoneal injection studies of the same fibres, in that the responses were dependent on both the durability of the fibres and the numbers of long thin fibres. In vitro and in vivo cell responses did not predict significantly the risk of cancer following inhalation.

Total and respirable airborne dust endotoxin concentrations in three equine management systems.

The concentrations of total and respirable airborne endotoxin in the breathing zone of a pony in 3 different management systems, on 8 occasions, are reported. Airborne endotoxin concentrations in all 3 systems were lower than those reported for many other agricultural environments. However, total airborne endotoxin concentrations in many of the conventional stables exceeded those which can induce pulmonary inflammation and bronchial hyper-responsiveness in normal human subjects, and exceeded those which can induce bronchoconstriction in humans with pre-existing pulmonary inflammation. Therefore, airborne endotoxin may contribute to the development of airway inflammation and dysfunction in conventionally stabled horses. Potentially detrimental effects of airborne endotoxins on the welfare and exercise performance of stabled horses can be reduced by maintaining horses in 'low dust' stables or at pasture, since these environments had significantly lower airborne dust and endotoxin concentrations.

Short-term inhalation and in vitro tests as predictors of fiber pathogenicity.

A wide range of fiber types was tested in two in vitro assays: toxicity to A549 epithelial cells, as detachment from substrate, and the production of the proinflammatory cytokine tumor necrosis factor (TNF) by rat alveolar macrophages. Three of the fibers were also studied in vivo, using short-term inhalation followed by a) bronchoalveolar lavage to assess the inflammatory response and b) measurement of cell proliferation in terminal bronchioles and alveolar ducts, using incorporation of bromodeoxyuridine (BrdU). The amount of TNF produced by macrophages in vitro depended on the fiber type, with the man-made vitreous fibers, and refractory ceramic fibers being least stimulatory and silicon carbide (SiC) whiskers providing the greatest stimulation. In the epithelial detachment assay there were dose-dependent differences in the toxicity of the various fibers, with long amosite being the most toxic. However, there was no clear relationship to known chronic pathogenicity. Fibers studied by short-term inhalation produced some inflammation, but there was no clear discrimination between the responses to code 100/475 glass fibers and the more pathogenic amosite and SiC. However, measurements of BrdU uptake into lung cells showed that amosite and SiC produced a greater reaction than code 100/475, which itself caused no more proliferation than that seen in untreated lungs. These results mirror the pathogenicity ranking of the fibers in long-term experiments. In conclusion, the only test to show potential as a predictive measure of pathogenicity was that of cell proliferation in lungs after brief inhalation exposure (BrdU assay). We believe that this assay should be validated with a wider range of fibers, doses, and time points.

Assessment of human risks from exposure to low toxicity occupational dusts.

Recent animal studies have demonstrated three separate and distinct mechanisms by which low toxicity dusts can cause important chronic pulmonary effects; through overloading of clearance mechanisms, through increased toxicity associated with ultrafine particle size or by increasing the toxicity of known carcinogens in mixed exposures. The problem to be addressed is how the pathogenicity to man of various airborne dusts should be evaluated, when epidemiological evidence is often insufficient, and the reliability of extrapolation of quantitative risks from animals to man is not established. In this paper we examine the feasibility of evaluating the likely human risks of low toxicity dusts by: (1) semi-quantitative comparisons of the ability of various dusts, in animal studies, to cause overload of clearance and resulting inflammation and fibrosis; (2) postulating that these relativities apply quantitatively to human risks; and (3) estimating approximate human risks by comparisons with reference dusts for which adequate animal and human data are available. Such a decision-making framework appears feasible, provided: (1) comparable and quantitative methods are used consistently in animal studies for the measurement of impairment of clearance leading to overload and resulting inflammation and fibrosis; (2) the quantitative relationships between impairment of clearance leading to overload, and resulting inflammation and fibrosis, can be defined adequately in animals for various dusts; (3) the particle size distributions, including those in the ultrafine range, for dusts to which animals and/or humans are exposed, are taken into account (or are comparable); (4) at least two reference dusts with well-documented activities spanning the range of toxicity can be identified; and (5) the reliability of the predictions of human pathogenicity of a sample of other dusts is tested, in toxicological studies and by observation in humans. Some possible candidate reference and test dusts are identified.

Use of the short-term inflammatory response in the mouse peritoneal cavity to assess the biological activity of leached vitreous fibers.

We used a special-purpose glass microfiber sample, Johns-Manville Code 100/475, to study the effects of various acid and alkali treatments on biological activity as assessed by inflammation in the mouse peritoneal cavity, the leaching of Si, and the phase contrast optical microscopy (PCOM) fiber number. We used mild and medium treatments with oxalic acid and Tris buffer and harsh treatment with concentrated HCl and NaOH. Mild oxalic acid and Tris treatment for 2 weeks had no effect on any of the end-points, but prolonging the mild oxalic acid treatment time to 2 months reduced the biological activity and the fiber number. Medium oxalic acid treatment reduced the biological activity and the fiber number and caused a loss of Si. Medium Tris alkali treatment reduced the PCOM-countable fibers and the biological activity but did not cause a substantial loss of Si. Harsh treatment with strong HCl did not affect the fiber number or cause leaching but the biological activity was reduced; strong NaOH reduced the fiber number and biological activity, and caused marked leaching of Si. The medium oxalic acid conditions (pH 1.4) were more acid than those found in lung cells but produced the same effects (reduction in fiber number and biological activity) as the more physiological mild treatment (pH 4.0), when prolonged. This study suggests that medium oxalic acid treatment can be used as a short-term assay to compare loss of Si, reduction in fiber number, and change in biological activity of vitreous fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune responses to colophony, an agent causing occupational asthma.

BACKGROUND: Inhalation of fumes from heated colophony (pine resin) is a recognised cause of occupational asthma, although the mechanisms by which colophony produces symptoms are unclear and specific immune responses to colophony have not been reported in sensitised workers. A study was carried out to determine whether colophony is antigenic. METHODS: The immune responses to colophony were studied in C57BL/6 mice and Dunkin Hartley guinea pigs after intraperitoneal injection of colophony conjugated to bovine serum albumin (BSA) or human IgG by a mixed anhydride procedure. Colophony and dinitrofluorobenzene were also compared in an assay of dermal sensitisation. RESULTS: Mice immunised with the colophony conjugates produced antibodies which recognised conjugates of both BSA and human IgG irrespective of which had been used as the immunogen. Solutions of unconjugated colophony inhibited the binding of antibodies to the BSA-colophony and BSA-abietic acid conjugates, confirming that the antibodies recognised one or more components in the colophony. Portuguese colophony also abrogated the antigen binding of serum from guinea pigs immunised with the BSA-colophony conjugate. Spleen cells from immunised mice proliferated in the presence of the conjugates. Although there was some cross reactivity in these responses, it was not as marked as in the antibody assays. Unconjugated colophony failed to induce an immune response when injected intraperitoneally with adjuvant. Skin sensitisation could not be induced in mice by topical application, or by subcutaneous or intradermal injection of unconjugated colophony. CONCLUSIONS: Colophony components have the potential to act as haptens and an immune component could be involved in the pathogenesis of occupational asthma in workers exposed to colophony. Colophony is not readily immunogenic unless conjugated ex vivo to proteins.

Immunomodulation in mineral dust-exposed lungs: stimulatory effect and interleukin-1 release by neutrophils from quartz-elicited alveolitis.

Quartz deposition in the rat lung causes an intense and persistent neutrophil alveolitis leading to parenchymal fibrosis. Bronchoalveolar leucocytes (BAL) from quartz-exposed rat lungs were studied for their effects on splenic lymphocyte proliferation; titanium dioxide (TiO2) was used as a control, non-fibrogenic dust. Seven days after the intratracheal instillation of 1 mg of quartz or TiO2 suspended in phosphate-buffered saline (PBS), BAL were recovered by lavage; the effect of PBS alone was also studied. TiO2-elicited BAL (macrophages greater than 98%) inhibited splenocytes responding to suboptimal phytohaemagglutinin (PHA) more than PBS-elicited BAL (macrophages greater than 98%); the effect was dependent on the BAL:splenic lymphocyte ratio. Quartz-elicited whole BAL (macrophages 49%, neutrophils 51%), and an alveolar macrophage-enriched population with purity of 87% separated from it, were less inhibitory to splenocyte mitogenesis than PBS-elicited BAL. A neutrophil-enriched population, with a purity of 80%, markedly enhanced splenocyte response to PHA. In addition, whole quartz BAL and the macrophage-enriched population obtained from it enhanced the mitogenesis of T cell-enriched lymphocytes at a much lower BAL:lymphocyte ratio. The neutrophil-enriched quartz BAL enhanced mitogenesis substantially more than the whole or macrophage-enriched population from quartz-exposed lung. Supernatants from normal macrophages, PBS BAL, TiO2 BAL, quartz BAL and both alveolar macrophage and neutrophil-enriched quartz populations were assessed for interleukin-1 (IL-1) activity. Quartz-BAL, quartz macrophages and quartz neutrophils all produced significantly higher IL-1 levels than PBS BAL; the supernatants from quartz neutrophils, however, showed the highest IL-1 activity. These findings suggest that quartz-elicited bronchoalveolar leukocytes, especially neutrophils, enhance lymphocyte proliferation and that increased IL-1 secretion by these cells is likely to be the effector molecule involved. These findings have important implications for immune response in mineral dust-stimulated lung and for inflammatory lung disease in general.

Inflammation in the lungs of rats after deposition of dust collected from the air of wool mills: the role of epithelial injury and complement activation.

In a previous study assessing respiratory symptoms in individuals employed in wool textile mills in the north of England relations between symptoms of chronic bronchitis, breathlessness and wheeze, and rhinitis and current exposure to airborne mass concentration of dust were shown. As preliminary steps in defining the potential hazard associated with dust from the air of wool mills the ability of inspirable dust, collected from the air of wool textile mills, to cause inflammation when injected into the lungs of rats was determined. Dusts were collected from the beginning of wool processing (opening) in one factory and from the middle (combing) and late (backwinding) stages of the process in two other factories. Ability of the dusts to cause inflammation was assessed by instillation into the lungs of rats followed by bronchoalveolar lavage. All the dusts caused some inflammation which peaked on day 1 and did not persist beyond one week. A distinctive aggregation response of mononuclear cells in the lavage, however, had a different time course, peaking at day 7. An attempt was made to determine how the wool mill dusts caused inflammation and experiments showed that the dusts themselves had no inherent chemotactic activity but that they did have a pronounced ability to generate chemotaxins in serum and so could activate complement in lung fluid. In addition, dust collected from ledges in the mills had the ability to injure epithelial cells in vitro which could also contribute to inflammation. A role for endotoxin in the inflammatory activity of the dusts was not discounted and a leachate of the dust had the ability to cause inflammation when injected into the lungs of rats. Wool mill dust is likely to be a complex mixture of materials and these experiments represent a preliminary approach to understanding the biological activity of the whole unfractionated dust and further studies are in progress to define more accurately the toxic material(s) in the dust.