Pathogenesis of pleurisy, pleural fibrosis, and mesothelial proliferation

Inflammation of the Pleural Cavity: A Review on Pathogenesis, Diagnosis and Implications in Tumor Pathophysiology

Pleural effusions are a common respiratory condition with many etiologies. Nonmalignant etiologies explain most pleural effusions and despite being nonmalignant, they can be associated with poor survival; thus, it is important to understand their pathophysiology. Furthermore, diagnosing a benign pleural pathology always harbors the uncertainty of a false-negative diagnosis for physicians and pathologists, especially for the group of non-specific pleuritis. This review aims to present the role of the inflammation in the development of benign pleural effusions, with a special interest in their pathophysiology and their association with malignancy.

Pulmonary embolism with abdominal pain as the chief complaint: A case report and literature review

RATIONALE

Pulmonary embolism (PE) is one of the serious cardiopulmonary diseases that can endanger life. Early diagnosis and timely treatment are key factors to reduce its high mortality rate. Abdominal pain is not currently included in the symptoms of PE in textbooks and guidelines.

PATIENT CONCERNS

A 49-year-old man was hospitalized for an exacerbation of right upper quadrant abdominal pain and sudden left upper quadrant pain that lasted for 2 hours.

DIAGNOSES

The patient was initially misdiagnosed as cholecystitis and pneumonia, and later was diagnosed as PE by computed tomography pulmonary angiography (CTPA).

INTERVENTIONS

The patient received low molecular weight heparin for anticoagulant therapy.

OUTCOMES

His abdominal pain disappeared after one week. The patient was later discharged.

LESSONS

Sometimes abdominal pain may be the only manifestation of PE. However, most clinicians do not think of the possibility of PE in patients with abdominal pain. This might have contributed greatly to the rate of misdiagnosis of PE in the past. We hope to improve the alertness of the diagnosis of PE in clinical practice. In patients with abdominal pain, the possibility of PE should be considered to avoid mis- or under-diagnosis.

Pulmonary Embolism Presenting as Abdominal Pain: An Atypical Presentation of a Common Diagnosis

Pulmonary embolism (PE) is a frequent diagnosis made in the emergency department and can present in many different ways. Abdominal pain is an unusual presenting symptom for PE. It is essential to maintain a high degree of suspicion in these patients, as a delay in diagnosis can be devastating for the patient and confers a high risk of mortality if left untreated. Here, we report the case of a 53-year-old male who presented to the emergency department with worsening right upper quadrant abdominal pain with fevers. Initial imaging was benign, although lab work showed worsening leukocytosis and bilirubin. Abdominal pathology seemed most likely, but the team kept PE on the differential. Further imaging revealed acute pulmonary embolus in the segmental branch of the right lower lobe extending distally into subsegmental branches. The patient was started on anticoagulation and improved drastically. This case highlights the necessity of keeping a broad differential and maintaining a systematic approach when dealing with nonspecific complaints. Furthermore, a discussion on the pathophysiology on why PE can present atypically as abdominal pain, as well as fevers, is reviewed. Using this information can hopefully lead to a subtle diagnosis of PE in the future and lead to a life-saving diagnosis.

Direct lipiodol injection used for a radio-opaque lung marker: stability and histopathologic effects

The objective of this study was to evaluate the effects on the histopathologic findings of directly injected lipiodol into lung and to identify the existence of remaining lipiodol in the lung according to the follow-up time. Forty rats were randomly assigned to 1 of 4 groups: group I (n = 10) served as the control group and received 0.2 mL of normal saline; groups II (n = 10), III (n = 10), and IV (n = 10) served as experimental groups and received 0.1-0.2 mL of lipiodol under fluoroscopy. At 3 hours (groups I and II), 24 hours (group III), and 1 week (group IV) after injection, the radiographic presence of lipiodol and histopathologic findings of each group were evaluated. Minimal acute lung injuries developed and the radio-opaque lipiodol nodule remained in group II. In group III, acute lung injuries were the most serious. However, acute injuries disappeared and foamy macrophages accumulated within the alveolar space in group IV. In this group, remaining lipiodol was also identified on radiograph. Directly injected lipiodol caused acute lung injury, which disappeared at 1 week along with the resolving process. On radiographs, directly injected lipiodol remained after 1 week. Lipiodol could be used as a safe and stable biomaterial for marking pulmonary nodules.

Plasmin enhances cell surface tissue factor activity in mesothelial and endothelial cells

BACKGROUND

Mesothelial cells that line the thoracic cavity play an important role in maintaining the local balance between procoagulant and fibrinolytic activity, a role akin to the endothelial cells in blood vessels. The mechanism(s) responsible for increased tissue factor (TF) expression in mesothelial cells in response to injury are at present unclear.

OBJECTIVE

To investigate whether plasmin or thrombin, two major proteases that may be generated on the pleural surface upon injury, induce TF expression in human pleural mesothelial cells (HMC) and elucidate the underlying mechanism(s).

METHODS

Confluent monolayers of HMC and human umbilical vein endothelial cells (HUVEC) were exposed to plasmin or thrombin for varying time periods and TF expression was analyzed by measuring its activity in a factor Xa generation assay, TF antigen levels by immunoblot analysis and TF mRNA by Northern blot analysis.

RESULTS

Both plasmin and thrombin treatments increased cell surface TF activity in HMC by 3- to 4-fold. In contrast to thrombin, plasmin-induced TF activity is not dependent on the de novo synthesis of TF. In HUVEC, plasmin had a minimal effect on unperturbed HUVEC whereas it markedly increased TF activity of activated HUVEC. Plasmin treatment neither affected anionic phospholipid levels at the cell surface nor released protein disulfide isomerase, an oxidoreductase protein that was newly described to play a role in TF activation. Plasmin cleaved cell-associated TFPI.

CONCLUSION

Thrombin up-regulates TF activity in HMC through the transcriptional activation of TF whereas plasmin increases TF activity by inactivating the cell-associated TFPI by a limited proteolysis.

Electron microscopic alterations of the rat's pleura after experimental haemothorax

The initial signs of pleural reactivity and the subsequent mechanisms of pleural healing still remain unsolved. The visceral and parietal (costal and diaphragmatic) pleura were investigated following an experimental haemothorax (EH) by transmission electron microscopy. Young-adult Wistar rats were divided in five groups and survived 6 hours, 1, 3, 8 and 15 days respectively after EH. Six hours after EH the mesothelial cells had a more prominent lysosomal system and electron-dense material in the vesicles, as in the dilatated intercellular spaces. On the 1st day of the EH the mesothelial cytoplasm formed a thin interrupted band. The extravasal cells built multiple layers over the basal lamina, leading to a thicker submesothelial layer, occupying the superficial position toward the pleural cavity. The activated mesothelial cells covered both pleural sheets on the 3rd day after EH. Eight days after EH different membrane bodies, large apical evaginations, elastic-like formations, an extensive vesicular and cytofilamentous systems characterized the mesothelium. The wider elastic membrane showed thickenings, protrusions, bifurcations and double course. Fifteen days after EH larger zones in both pleural sheets displayed thinner basal lamina, remnants of elastic membrane and a thicker submesothelial layer. In conclusion, different newly formed structures (reversible and stable) retain the tendency of enlargement of the pleural surface in all investigated periods. Simultaneous intercellular and transcellular transport, as an increase of the lysosomal system characterize the passing of the electron-dense material through the mesothelium. The early period (until 3rd day after EH) is characterized by more prominent mesothelial changes, involving activated cells. The initiation of the late period (on the 8th day after EH) begins with the appearance of lamellar bodies and newly formed elastic membrane. The following late changes (on the 15th day after EH) concern predominantly the components of the connective tissue layer, such as collagen accumulations and blood capillaries. The present data suggest that the alterations over the entire pleura are irregular and asynchronous, showing significant morphological differences in both pleura sheets, some of them are diffuse in character, the final ones appear to be stable and ensure incomplete pleural restoration.

Pulmonary deposition modeling with airborne fiber exposure data: a study of workers manufacturing refractory ceramic fibers

Increasing production of refractory ceramic fiber (RCF), a synthetic vitreous material with industrial applications (e.g., kiln insulation), has created interest in potential respiratory effects of exposure to airborne fibers during manufacturing. An ongoing study of RCF manufacturing workers in the United States has indicated an association between cumulative fiber exposure and pleural plaques. Fiber sizing data, obtained from electron microscopy analyses of 118 air samples collected in three independent studies over a 20-year period (1976-1995), were used with a computer deposition model to estimate pulmonary dose of fibers of specified dimensions for 652 former and current RCF production workers. Separate dose correction factors reflecting differences in fiber dimensions in six uniform job title groups were used with data on airborne fiber concentration and employment duration to calculate cumulative dose estimates for each worker. From review of the literature, critical dimensions (diameter <0.4 microm, length <10 microm) were defined for fibers that may translocate to the parietal pleura. Each of three continuous exposure/dose metrics analyzed in separate logistic regression models was significantly related to plaques, even after adjusting for possible past asbestos exposure: cumulative fiber exposure, chi(2) = 15.2 (p < 0.01); cumulative pulmonary dose (all fibers), chi(2) = 14.6 (p < 0.01); cumulative pulmonary dose (critical dimension fibers), chi(2) = 12.4 (p < 0.01). Odds ratios (ORs) were calculated for levels of each metric. Increasing ORs were statistically significant for the two highest dose levels of critical dimension fibers (level three, OR = 11, 95%CI = [1.4, 98]; level four, OR = 25, 95%CI = [3.2, 190]). Similar associations existed for all metrics after adjustment for possible asbestos exposure. It was concluded that development of pleural plaques follows exposure- and dose-response patterns, and that airborne fibers in RCF manufacturing facilities include those with critical dimensions associated with pleural plaque formation. Analysis of additional air samples may improve estimates of the dose-response relationship.

The suction mechanism as a factor in intrathoracic oedema, connective tissue or pleural effusion

In pathological conditions, the negative intrapleural pressures (Ppl) may increase unequally. At some sites they may remain increased. We maintain that at these sites the increased pressures may lead to the production of oedema in the adjacent pleural walls and in adjacent pre-existing connective tissue, which may remain as oedema or may become connective tissue. Occasionally the increased negative Ppl may contribute to the production of pleural effusion. We term all these processes the suction mechanism (SM). This mechanism affords an interpretation of a series of images observed in chest X-rays. According to this view, lung shrinkage, narrowing of the pulmonary vessels and impairment of the lung function are not caused by the diffuse pleural fibrosis, but result from damage to the lung parenchyma. We also interpret the apical cap, the blunting of the costophrenic sulci, the broadening of the mediastinum and the retrosternal stripe in terms of the SM.

Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry

BACKGROUND

To determine dimensions of airborne fibers in the U.S. refractory ceramic fiber (RCF) manufacturing industry, fibers collected through personal air sampling for employees at RCF manufacturing and processing operations have been measured.

METHODS

Data were derived from transmission electron microscopy analyses of 118 air samples collected over a 20-year period.

RESULTS

Characteristics of sized fibers include: diameter measurements of <60; 0.19 to 1.0 micron, m of which 75% are less than 0.6 micron and length ranging from < 0.6 to > 20 micron, with 68% of fibers between 2.4 and 20 micron.

CONCLUSIONS

Exposures in RCF manufacturing include airborne fibers with dimensions (diameter < 0.1-0.4 micron, length < 10 micron) historically associated with biological effects in pleural tissues. Air sampling data and a review of studies relating fiber size to pleural effects in animals and humans support the belief that information on fiber dimensions is essential for studies with synthetic vitreous fibers.

Quantitation in inflammatory pleural disease to distinguish tuberculous and paramalignant from chronic non-specific pleuritis

AIM

To determine by morphometry if pleural biopsies with the histopathological diagnosis of "non-specific pleuritis", malignant, and tuberculous disease could be distinguished morphologically from those with truly non-specific disease.

METHODS

Each pleural biopsy was reviewed taking into account three compartments of reference: the visceral/parietal mesothelial compartment, the submesothelial screen compartment, and the submesothelial adipose tissue compartment. Normal connective tissue, granulation tissue, fibrocellular proliferation, fibrin, polymorphonuclear cells, mononuclear cells, and mesothelial cells were measured using conventional point counting procedures in terms of the fractional area occupied by each parameter within each compartment of reference. Ranking was carried out on 164 patients, based on their diagnosis: chronic non-specific disease (n = 57), tuberculosis (n = 27), malignant disease (n = 58), and conditions associated with transudative effusions (n = 22).

RESULTS

Stepwise discriminant analysis of the resulting data showed that biopsies from patients with tuberculosis, malignant disease, and chronic non-specific disease could be distinguished between themselves and normal cases. Statistical differences among the four groups were observed for eight morphometric parameters related to components of inflammation and extension throughout the three pleural anatomical compartments. A robust discriminant function permitted an adequate classification of the three groups of disease in 88.41% of the cases. Pleural biopsies with fibrin incorporated within granulation tissue on the submesothelial screen compartment showed 100% specificity for patients with tuberculosis, while mononuclear cells in a band-like infiltrate on the submesothelial adipose tissue compartment showed 93.1% specificity for patients with malignant disease. The truly non-specific pleuritis was characterised by deposits of fibrin in the subpleural compartment and discrete signs of chronic inflammation and reparatory fibrosis on the submesothelial screen.

CONCLUSIONS

Morphometric analysis of pleural biopsies may be a useful supplementary histological procedure to support the diagnosis of pleural tuberculosis and malignant disease.

Tissue factor expression in mesothelial cells: induction both in vivo and in vitro

Exudative pleural effusions are characterized by a high protein content and frequently progress to loculation and fibrosis. To test the hypothesis that tissue factor (TF) plays an integral role in this process, we investigated the expression of TF by human mesothelial cells (HMC) both in vivo and in vitro, and measured the effect of serum on HMC expression of TF in vitro. In vivo TF expression was not detected in HMC of normal pleura, but was detected in HMC of pleura overlying inflamed lung. In vitro, quiescent HMC demonstrated negligible levels of TF expression; however, upon serum stimulation there was a marked induction in both TF protein level and activity, peaking at 8-9 h. In contrast, treating quiescent HMC with plasma resulted in a further small, but significant, decrease in TF expression. This serum-induced rise in TF was also reflected in TF mRNA levels and did not require de novo protein synthesis. These results suggest that induction of HMC TF expression may be important in triggering both the intrapleural activation of prothrombin and the deposition of fibrin characteristic of inflammatory effusions.

The serous membranes in the cat. Electron microscopic observations

Visceral and parietal pleura, peritoneum and pericardium of 26 adult cats were studied by means of transmission electron microscopy. The main components of the three serous membranes follow a general plan: mesothelium, basal lamina (BL) and submesothelial connective tissue layer. They show significant diversities in both sheets of the three serous membranes in the different organs and regions. The elastic membrane under the BL is an obligatory component of the visceral pleura. Two basic cell types - high and flat, as well as intermediate and degenerative cell forms are described in the mesothelial layer. The high cells are especially characteristic of the visceral sheets, while the flat cells predominate in the parietal sheets. The involvement of the mesothelium in the homeostasis in the cavities is discussed. A detailed characteristic of the BL of both sheets and its variation in individual organs is presented. Varieties of cells, collagen and elastic fibers, blood and lymph capillaries of the connective tissue layers of the visceral and parietal sheets are described with special reference to their relation to different underlying tissues. An attempt to find a structure-functional correlation of these observations is made. The transport capability of the pleura and peritoneum is investigated by the intrapleural and intraperitoneal application of horseradish peroxidase (HRP).

Extensive idiopathic benign bilateral asynchronous pleural fibrosis

We describe a young man who had been healthy until he developed extensive benign left pleural fibrosis. He subsequently developed disabling right pleural thickening a year later. No clear cause was discovered.

Cytogenetic response to asbestos fibers in cultured human primary mesothelial cells from 10 different donors

The ability of amosite asbestos fibers to induce chromosomal aberrations in human primary mesothelial cells obtained from pleural effusions of 10 noncancerous patients was investigated. The glutathione S-transferase M1 (GSTM1) genotypes of the patients were determined, since the GSTM1 null genotype has been associated with increased susceptibility to lung cancer and chemically induced cytogenetic damage. Four of the patients represented the GSTM1 null genotype, and six the GSTM1 positive genotype. Successful chromosome aberration analyses were obtained from six cases, three of them with the GSTM1 null genotype. The level of aberrant cells in unexposed cultures ranged from 2.0% to 7.5%. Statistically significant increases (2.3-3.0-fold compared to controls) in the number of aberrant cells were observed in two cases only: in one case treated with 1 microgram/cm2 of amosite, and in another treated with 2 micrograms/cm2 of amosite. Cell cultures from four individuals showed minor or no increases in the numbers of aberrant cells in the doses tested (1 and 2 micrograms/cm2). Chromosome breaks were the major type of aberration. The amosite exposed cells with significantly increased aberrations were from patients with GSTM1 positive genotypes. Two cases that showed no cytogenetic response to asbestos fibers were of the GSTM1 null genotype. Thus, our results suggest that the lack of the GSTM1 gene does not render human mesothelial cells more susceptible to chromosomal damage induced by asbestos. GSTM1 null cells appeared, however, to be more sensitive to the growth inhibitory effects of asbestos than did GSTM1 positive cells. Variation in the cytogenetic response of human primary mesothelial cells to asbestos fibers was observed to exist, but the fibers do not appear to be potent inducers of structural chromosomal aberrations in these cells. It remains to be established whether individual sensitivity to asbestos fibers, due to specific genetic traits, exists.

Diffuse thickening superimposed on circumscribed pleural thickening related to asbestos exposure

Circumscribed and diffuse pleural thickening (PT), the most common radiographic manifestations of asbestos-related disease, have different pathogeneses, differential diagnostic criteria, and effects on pulmonary function. The important distinction between the two disorders is demonstrated by six patients in whom typical circumscribed PT was followed by diffuse PT in the same hemithorax. The diffuse PT came on 18-47 (mean 32.3) years after first exposure to asbestos. In four patients, clinically evident pleural effusions preceded the diffuse PT; the latter left all with moderate to severe restrictive ventilatory impairment. Patients with stable pleural plaques are at risk for diffuse PT and consequent greater ventilatory impairment, even though they are many years from first exposure to asbestos.

Production of interleukin 1 by rat pleural leucocytes in culture after intratracheal instillation of crocidolite asbestos

This study was undertaken to investigate the production of interleukin 1 (IL-1) by pleural leucocytes in culture and to evaluate the influence of intratracheal instillation of crocidolite asbestos on this production. Normal pleural leucocytes spontaneously released IL-1 in culture and stimulation with lipopolysaccharide (LPS) dramatically increased production. Intratracheal instillation with crocidolite asbestos induced recruitment of pleural leucocytes in the longer term and changed IL-1 production by the leucocytes. Reduced production of IL-1 was found by one day after instillation of asbestos and this was correlated with the dose of asbestos. With increasing time after instillation, however, release of IL-1 by pleural leucocytes gradually recovered to normal until, one month after asbestos injection, the leucocytes produced augmented IL-1 in culture compared with control pleural leucocytes. Our data show that pleural leucocytes possess the potential to produce IL-1 in vitro and this capability is altered by intratracheal instillation of crocidolite asbestos. This may be relevant to development of pleural diseases associated with inhalation of asbestos.

Intratracheal injection of crocidolite asbestos depresses the secretion of tumor necrosis factor by pleural leukocytes in vitro

Tumor necrosis factor (TNF) is a cytokine released predominantly by monocytes/macrophages that has been shown to modulate a variety of different immune and metabolic functions. To understand the regulatory mechanisms of TNF in governing responses in the pleural cavity following deposition of fibrous dust in the airspace of the lung, we studied the capability of leukocytes, lavaged from the pleural cavity, to release TNF in culture. TNF production by lavaged pleural leukocytes was measured using the L-929 TNF-sensitive cell line, after intratracheal instillation of crocidolite asbestos. A high level of TNF activity was found in the supernatants of normal, unstimulated pleural leukocytes; the addition of 100 ng/ml lipopolysaccharide to the culture increased the activity up to threefold. Following intratracheal instillation of 5 mg crocidolite asbestos, the pleural leukocytes secreted less TNF than the control. With increasing mass of intratracheally instilled asbestos, there was a dose-dependent reduction in TNF release. Changes in the population of the pleural leukocytes or their number could not be related to variation in TNF activity. These results suggest that exposure of rat lungs to crocidolite asbestos by intratracheal instillation affects the response of pleural leukocytes without causing changes in the population. Such changes in the bronchoalveolar space may be related to the pleural pathology found in asbestos-exposed individuals.

Spontaneous hypoglycaemia and pleural fibroma: role of insulin like growth factors

Spontaneous hypoglycaemia was the presenting feature of a man with a large subpleural fibroma. Preoperative and postoperative studies support the view that the tumour induced hypoglycaemia was due to the secretion of peptide hormones by the tumour.

Fibre distribution in the lungs and pleura of subjects with asbestos related diffuse pleural fibrosis

The lungs from 13 cases of diffuse pleural fibrosis associated with a history of exposure to asbestos were examined. Samples were taken from the visceral pleura and central and subpleural zones of the lungs for histopathological and mineralogical studies. The fibre type, size, and number were estimated for each of these regions by transmission electron microscopy and energy dispersive x ray analysis. Amphibole fibre counts were raised when compared with a non-occupationally exposed group and matched those seen in cases of pleural plaques, mild asbestosis, and mesothelioma. A wide case to case variation of distribution was seen. No significant difference was apparent between central and subpleural zones, whereas low asbestos counts were found in the pleura; these were mainly short chrysotile fibres. Within the lungs more (45%) of the longer (greater than 4 microns) and thinner (less than 0.25 micron) amphibole fibres were retained in keeping with other studies implicating such fibre profiles in the pathogenesis of asbestos related disease.

Atypical mesothelial hyperplasia associated with bronchogenic carcinoma

Atypical mesothelial hyperplasia encountered in pleural fluid or in a pleural biopsy specimen raises the suspicion that one may be dealing with a diffuse malignant mesothelioma of the pleura. We studied eight cases with cytologic or histologic changes of mesothelial atypia thought to be suspicious for diffuse malignant mesothelioma. In each case, the hyperplasia was associated with a bronchogenic carcinoma in the lung subjacent to the mesothelial hyperplasia. Bronchogenic carcinoma should be added to the list of causes of atypical mesothelial hyperplasia. This combination of reactive and malignant processes should be appreciated, since pleural carcinomatosis and diffuse malignant mesothelioma must be separated for clinical and epidemiologic reasons.

Inflammation of the visceral pleura, a nonspecific asbestos-related pleural reaction: chest radiograph and computed tomograph correlation

Nonspecific pleuritis, i.e., inflammation of the visceral pleura, is recognized by the presence of pleural strands on the routine posteroanterior chest radiograph. The computed tomograph counterparts of these strands are seen as interlobular septal intrusions and lenticular or wedge-shaped subpleural opacities. The pleural reaction is nonspecific and may be found with asbestos exposure, traumatic hemorrhagic effusions, pulmonary embolism, viral pleurisy, malignant pleural effusions, and lupus or rheumatoid effusions. The asbestos-related pleural changes may be found alone or in association with parietal pleural plaque formation or with asbestotic lung fibrosis.

Radiological features of asbestos-related visceral pleural changes

The radiological manifestations of asbestos-related visceral pleural changes are described. Generally, visceral pleural reactions follow the mesothelial cells response to various injurious substances, including asbestos, and even saline. The changes are nonspecific. They may occur subsequent to pleural reactions associated with many conditions, which include tuberculosis, viral pleurisy, malignancy and lymphoma, lupus, or rheumatoid-induced effusions, cardiac failure, and pulmonary embolism, among other etiologies. The failure to absorb the fibrinous exudate on the visceral pleural surface can lead to the development of diffuse fibrosis of the serosal surface, interlobar pleural thickening, localized pleural filaments (strands), subpleural wedge, and lenticular-shaped masses, and could be the forerunner of lobular atelectasis (pseudotumor) formation. Some of the features are recognized on posteroanterior chest radiographs and the counterparts corroborated with the use of routine and high-resolution computed tomography studies.

Secretion of plasminogen activator inhibitor by normal rat pleural leukocytes in culture

The normal balance between coagulation and fibrinolysis in the pleural cavity is poorly understood despite the critical role of the pleura in the movement of the lungs. To determine the fibrinolytic activity and the interaction between plasminogen activators and their inhibitors in the normal pleural space, we tested normal rat pleural leukocytes, principally macrophages and mast cells, and their supernatants, for activity in an [125I]fibrin degradation assay. It was found that pleural leukocytes did not release plasminogen activator, but the leukocytes and their supernatants inhibited the plasminogen-dependent fibrinolysis caused by both alveolar leukocytes and mesothelial cells. Further experiments demonstrated that pleural leukocytes produce a protein inhibitor primarily against urokinase-induced fibrinolysis in culture and that macrophages are the main source of the inhibitor. The lysate of mast cell-enriched population exhibited high plasminogen activator activity while no such activity could be determined in macrophage-enriched lysate. These data show that normal rat pleural leukocytes contain plasminogen activator inside the cells and synthesize a urokinase-type plasminogen activator inhibitor in culture that may be important in the fibrinolysis/coagulation balance in the pleural space.

Reactive lesions of the pleura. Immunohistochemical characterization

The visceral pleura of 8 lung tissue specimens with non-tumorous pleural lesions and of 10 specimens with secondary pleural infiltration of different primary tumours were tested by avidin-biotin-method with the following antibodies: anti-keratin KL1, anti-vimentin V9, anti-CEA (BMA 130c), HEA 125, Leu M1, HMFG 2 and anti-collagen type IV. In all cases anti-keratin positive subserosal cells could be proved. Activated mesothelial cells expressed vimentin additionally to keratin. The antibodies Leu M1, HEA 125 and BMA 130c (against CEA) showed no reaction in subserosal and mesothelial cells. With the antibody HMFG 2, however, a weak reaction could be observed. A distinction between reactive and neoplastic pleural lesions is not possible by using these antibodies. The antibodies LeuM1, HEA 125 and BMA 130c can be helpful for differential diagnosis in single cases with pleural carcinosis. The antibody against collagen type IV demonstrates newly developed basal membrane structures in areas with proliferating subserosal cells. Considering our results the entity of mesothelium and submesothelium is discussed with regard to the histogenetical aspect of mesothelioma.

Discrete pleural masses without effusion in a young man: an unusual presentation of tuberculosis

Extensive tuberculous infection of the pleura presented radiographically as multiple discrete nodules, without associated effusion or lesions of lung parenchyma.

Fibrinolysis by rat mesothelial cells in vitro: the effect of mineral dusts at non-toxic doses

Rat mesothelial cell cultures were shown to have considerable plasminogen dependent and independent fibrinolytic activity in vitro using an 125I fibrin degradation assay. At non-toxic doses of the mineral dusts titanium dioxide, quartz and crocidolite asbestos, as assessed by 51Cr release, the fibrinolytic activity of mesothelial cells was inhibited. Quartz had the greatest inhibitory effect and crocidolite asbestos had the least. These results suggests that inhibition of mesothelial cell fibrinolysis does not, on its own, explain pleural fibrosis due to toxic mineral dusts.

A study of the two-way transport of horseradish peroxidase across the visceral pleura

The authors report on a study of the transpleural transport of horseradish peroxidase after intrapleural and intracardiac application. Following intrapleural introduction, a retention of the marker on the apical membrane of mesothelial cells was observed, with subsequent transcellular transfer after incorporation into microvesicles. Following intracardiac injection, the marker moved out of the pulmonary capillaries across the endothelial vesicles and progressed to the pleural cavity across the intercellular spaces and mesothelial vesicles. With either route of injection, reaction product was noted in the basal lamina of the mesothelium, elastic membrane, alveolar macrophages and pneumocytes type II.

Cryptogenic bilateral fibrosing pleuritis

We describe four patients with bilateral pleural effusions progressing to diffuse pleural thickening for which we have been unable to find any evidence of an infective, embolic or occupational aetiology. In order to avoid confusion with diffuse pleural thickening attributable to asbestos-related disease, the term cryptogenic bilateral fibrosing pleuritis is suggested. The patients differed from those with pleural shadowing due to asbestos in that none of them gave a history of asbestos exposure, all were ill, presented with chest pain which was not always pleuritic in character, and had dyspnoea, cough or malaise. They had pleural effusions of variable size, pleural shadowing radiographically and raised sedimentation rates. Computed tomography revealed bilateral extensive pleural thickening in all cases. All four were HLA B44 positive. Histology showed that in all cases the pleura was thickened by fibrous tissue. Both layers were affected and the pleural space was often obliterated. Otherwise the pleural surface was covered by organizing fibrin. Focal collections of lymphocytes were often present when the fibrous tissue abutted on the subpleural fat. No asbestos bodies were seen in any of the cases and in one patient electron microscopic fibre counts showed no excess of asbestos. Pleural decortication was successful in three patients. In one of these, contralateral disease was successfully controlled with corticosteroids, but the fourth patient has not improved on corticosteroids.

Between- and within-reader variability in the assessment of pleural abnormality using the ILO 1980 international classification of pneumoconioses

Although there are published data concerning reader variability in the assessment of parenchymal pneumoconiotic changes using the ILO Classification of Radiographs, nothing has been published on reader variability with regard to pleural abnormalities. Therefore, in the context of an epidemiologic study, we assessed between- and within-reader variability in the reading of chest radiographs for pleural abnormality using the ILO 1980 International Classification of Radiographs of Pneumoconioses. Chest radiographs of 182 insulation workers interspersed with 24 subjects without documented exposure to asbestos were assembled and read blindly by two readers, reading separately on two occasions, 1 week apart. The results of this study suggest that confident separation of pleural plaques and diffuse pleural thickening may be difficult to achieve using the present guidelines of the ILO 1980 classification. In the evaluation of the width of chest wall pleural abnormality, within-reader agreement improves as the width increases, while between-reader agreement was much less satisfactory. Excellent agreement is obtained in the evaluation of other sites, especially costophrenic angle obliteration and the presence of pleural calcification.

Acute injury and regeneration of the mesothelium in response to asbestos fibers

The mesothelium is a target of the toxic and carcinogenic effects of asbestos fibers. Fibers greater than 8 mu in length and less than 0.25 mu in diameter have been found to be highly tumorigenic in rodents, while shorter asbestos fibers or spherical mineral particles have not been shown to produce mesotheliomas. For investigation of early mesothelial reactions associated with the development of mesotheliomas, C57BL/6 mice were given intraperitoneal injections of 200 micrograms of short or long crocidolite asbestos fibers, toxic silica particles, or nontoxic titanium dioxide particles. At intervals between 3 hours and 21 days after a single injection, the mesothelial surface of the diaphragm was examined by stereomicroscopy, scanning electron microscopy, and autoradiography. Within 6 hours after injection of asbestos fibers, mesothelial cells in the lacunar regions of the diaphragm retracted opening stomata 10.7 +/- 2.3 mu in diameter leading to the submesothelial lymphatic plexus. Short asbestos fibers (90.6% less than or equal to 2 mu in length), silica, or titanium dioxide particles (less than or equal to 5 mu in diameter) were cleared through these stomata without provoking an inflammatory reaction or mesothelial injury. In contrast, long asbestos fibers (60.3% greater than or equal to 2 mu in length) were trapped at the lymphatic stomata in the lacunar regions on the peritoneal surface of the diaphragm. At these sites, an intense inflammatory reaction developed with accumulation of activated macrophages and a 5.5-fold increase in albumin recovered in the peritoneal lavage fluid after 3 days. As early as 12 hours after injection of long asbestos fibers, the adjacent mesothelial cells were unable to exclude trypan blue and lost their surface microvilli, developed blebs, and detached. Recovery of lactate dehydrogenase activity in the peritoneal lavage fluid was increased 5.8-fold after 3 days and returned to normal levels after 14 days. Regenerating mesothelial cells appeared at the periphery of asbestos fiber clusters 3 days after injection. Maximal incorporation of 3H-thymidine by mesothelial cells occurred after 7 days, followed by partial restoration of the mesothelial lining after 14-21 days. As late as 6 months after a single injection of crocidolite asbestos fibers, clusters of fibers remained in the lacunar regions, partially covered by mesothelium but surrounded by macrophages and regenerating mesothelial cells. The anatomic distribution and size of lymphatic stomata on the peritoneal surface of the diaphragm account for the selective accumulation of long asbestos fibers in these regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Asbestos induced diffuse pleural fibrosis: pathology and mineralogy

Lungs from seven cases of diffuse pleural fibrosis with known asbestos exposure were studied to determine the gross and microscopic pathological features and relate these to the analysed mineral fibre content of the lung. All seven individuals had had substantial exposure, ranging from two to 25 years, and chronic chest problems and at necropsy all cases met the criteria for compensatable disease. Macroscopically, all had extensive visceral pleural fibrosis and extensive areas of adhesions, and four also had discrete parietal pleural plaques. The histological features were similar in all the cases--most strikingly the basket weave pattern of the thickened pleura and a dense subpleural parenchymal interstitial fibrosis with fine honeycombing, extending up to 1 cm into the underlying lung. The similar histological appearances raise the possibility that diffuse pleural fibrosis and pleural plaques have a similar pathogenesis. Amphibole asbestos (crocidolite and amosite) counts were high in six of the seven cases and chrysotile counts in four; four cases had high mullite counts, but the importance of this is not known. It is concluded that diffuse pleural fibrosis is a specific asbestos associated entity, of uncertain pathogenesis, with mineral fibre counts falling between those found with plaques and those in minimal asbestosis.