Targeted delivery of amikacin into granuloma

RATIONALE

Nontuberculous mycobacterial (NTM) infection is a growing problem in the United States and remains underrecognized in the developing world. The management of NTM infections is further complicated by several factors, including the need to use high systemic doses of toxic agents, the length of therapy, and the development of drug resistance.

OBJECTIVES

We have evaluated the use of monocyte-derived dendritic cells (DCs) as a delivery vehicle for a luminescent derivative of amikacin prepared by conjugation to fluorescein isothiocyanate (FITC) (amikacin-FITC) into granulomas formed in the tissues of mice infected with Mycobacterium avium.

METHODS

Amikacin-FITC was prepared and quantitative fluorescence was used to track the intracellular uptake of this modified antibiotic. The antibiotic activity of amikacin-FITC was also determined to be comparable to unmodified amikacin against M. avium. Amikacin-FITC-loaded DCs were first primed with M. avium, and then the cells were injected into the tail vein of infected mice. After 24 hours, the mice were sacrificed and the tissues were analyzed under fluorescence microscope.

MEASUREMENTS AND MAIN RESULTS

We found that we were able to deliver amikacin into granulomas in a mouse model of disseminated mycobacterial infection. No increase in levels of monocyte chemoattractant protein-1 and its CCR2 as markers of inflammation were found when DCs were treated with amikacin-FITC.

CONCLUSIONS

DC-based drug delivery may be an adjunct and useful method of delivering high local concentrations of antibiotics into mycobacterial granulomas.

Pleural mesothelial cell transformation into myofibroblasts and haptotactic migration in response to TGF-beta1 in vitro

Idiopathic pulmonary fibrosis (IPF) is a disease of unknown etiology characterized by the development of subpleural foci of myofibroblasts that contribute to the exuberant fibrosis noted in the pulmonary parenchyma. Pleural mesothelial cells (PMC) are metabolically dynamic cells that cover the lung and chest wall as a monolayer and are in intimate proximity to the underlying lung parenchyma. The precise role of PMC in the pathogenesis of pulmonary parenchymal fibrosis remains to be identified. Transforming growth factor (TGF)-beta1, a cytokine known for its capacity to induce proliferative and transformative changes in lung cells, is found in significantly higher quantities in the lungs of patients with IPF. High levels of TGF-beta1 in the subpleural milieu may play a key role in the transition of normal PMC to myofibroblasts. Here we demonstrate that PMC activated by TGF-beta1 undergo epithelial-mesenchymal transition (EMT) and respond with haptotactic migration to a gradient of TGF-beta1 and that the transition of PMC to myofibroblasts is dependent on smad-2 signaling. The EMT of PMC was marked by upregulation of alpha-smooth muscle actin (alpha-SMA), fibroblast specific protein-1 (FSP-1), and collagen type I expression. Cytokeratin-8 and E-cadherin expression decreased whereas vimentin remained unchanged over time in transforming PMC. Knockdown of smad-2 gene by silencing small interfering RNA significantly suppressed the transition of PMC to myofibroblasts and significantly inhibited the PMC haptotaxis. We conclude that PMC undergo EMT when exposed to TGF-beta1, involving smad-2 signaling, and PMC may be a possible source of myofibroblasts in IPF.

Erythromycin improves gastric emptying half-time in adult cystic fibrosis patients with gastroparesis

BACKGROUND

Gastrointestinal manifestations are frequently encountered in cystic fibrosis patients. Gastroparesis evidenced by a variety of diagnostic methods has been described in patients with cystic fibrosis, predominantly in children and in individuals with advanced lung disease. The presence of gastroparesis in adult patients with different degrees of lung involvement and its response to the acute and chronic administration of macrolides have not been reported.

METHODS

Using the University of Florida Cystic Fibrosis database we identified symptomatic patients who had gastroparesis confirmed by a prolonged half-time during gastric emptying scintigraphy.

RESULTS

Of 86 cystic fibrosis patients, periodically followed in our institution, we found five who had classical symptoms and prolonged gastric emptying half-time. Age 25.2+/-8 years, 80% females, BMI 22+/-9 kg/m(2), HbA1c 5.8+/-0.6 g/dl, FEV1 53.2+/-15% of predicted. Gastric emptying half-time was 191.4+/-91.4 min (range 100-300 min) and decreased to 12.2+/-6 min (range 5-20 min) after IV administration of erythromycin (p=0.043). Patients were followed up for 3+/-2.1 years. All patients but one, who was taking opiods, had good clinical response to PO macrolides.

CONCLUSIONS

Gastroparesis occurs in patients with cystic fibrosis, even in patients with relatively preserved lung function and in those without cystic-fibrosis related diabetes. Macrolides may be an effective therapy in cystic fibrosis patients with gastroparesis when administered acutely or chronically.

Thioredoxin as a biomarker for graft rejection in lung transplant recipients

Primary graft dysfunction and rejection are common complications in lung transplant recipients. Increased expression of thioredoxin-1 (Trx), a 12-kDa redox-regulatory protein, has been reported in multiple lung pathophysiological conditions involving oxidative and inflammatory mediated injury including graft rejection in canine and rat models of lung transplantation. Our objective was to determine whether increased Trx expression is associated with progression of rejection pathophysiology in human lung transplant recipients. Bronchoalveolar lavage (BAL) fluid and transbronchial biopsy samples were collected as a routine part of post-transplant clinical care from 18 lung transplant patients from our adult lung transplant programme. Lung transplant recipient profile included age/sex, ethnic background, days on ventilator, total ischaemic time, and cytomegalovirus (CMV) status. Based on histopathological grading criteria, patients were divided into two groups, rejecting (A1/A2 or B1) and non-rejecting (A0/B0). Rejecting and non-rejecting group total BAL cell counts and differential cell counts for neutrophils, macrophages, lymphocytes and eosinophils as well as total BAL cell Trx levels were analysed. Total BAL cell counts were significantly (p <0.05) elevated in graft rejecting versus non-rejecting patients. Differential BAL macrophage counts were comparable in rejection and non-rejection groups, whereas there were significant increases in neutrophils and lymphocytes but not eosinophils in patients with rejection versus non-rejection pathology (p <0.05). Total ischaemic time and days on ventilator in rejection and non-rejection groups were comparable. However, Trx levels were significantly elevated in BAL cells from graft-rejecting patients compared with non-rejecting patients (p <0.05). These data suggest that surveillance monitoring of BAL Trx levels after lung transplantation can serve as a biomarker to assess severity of graft rejection.

Innate immune responses in murine pleural mesothelial cells: Toll-like receptor-2 dependent induction of beta-defensin-2 by staphylococcal peptidoglycan

The innate immune response is mediated in part by pattern recognition receptors including Toll-like receptors (TLRs). The pleural mesothelial cells (PMCs) that line the pleural surface are in direct contact with pleural fluid and accordingly carry the risk of exposure to infiltrating microorganisms or their components in an event of a complicated parapneumonic effusion. Here we show that murine primary PMCs constitutively express TLR-1 through TLR-9 and, upon activation with peptidoglycan (PGN), mouse PMC produce antimicrobial peptide beta-defensin-2 (mBD-2). Treatment of PMCs with staphylococcal PGN, a gram-positive bacterial cell wall component and a TLR-2 agonist, resulted in a significant increase in TLR-2 and mBD-2 expression. Silencing of TLR-2 expression by small interfering RNA led to the downregulation of PGN-induced mBD-2 expression, thereby establishing causal relationship between the activation of TLR-2 receptor and mBD-2 production. PMCs exposed to PGN showed increased p38 MAPK activity. In addition, PGN-induced mBD-2 expression was attenuated by SB203580, a p38 MAPK inhibitor, underlining the importance of p38 MAPK in mBD-2 induction. Inhibition of erk1/erk2 or phosphatidylinositol 3-kinase did not block PGN-induced mBD-2 expression in PMC. PGN-activated PMC-derived mBD-2 significantly killed Staphylococcus aureus, and mBD-2-neutralizing antibodies blunted this antimicrobial activity. Taken together, these data indicate that PMCs may contribute to host innate immune defense upon exposure to gram-positive bacteria or their products within the pleural space by upregulating TLR-2 and mBD-2 expression.

Pathophysiology of the pleura

The pleural mesothelial cell is an essential cell in maintaining the normal homeostasis of the pleural space and it is also a central component of the pathophysiologic processes affecting the pleural space. In this review, we will review the defense mechanisms of the pleural mesothelium and changes in pleural physiology as a result of inflammatory, infectious, and malignant conditions with a focus on cytokine and chemokine networks. We will also review the processes involved in the pathogenesis of pleural fibrosis.

Receptor EphA2 activation with ephrinA1 suppresses growth of malignant mesothelioma (MM)

The objective of this study was to understand the possible mechanisms of activation of receptor EphA2 by its ligand ephrinA1 in malignant mesothelioma cell (MMC) growth. Activation of receptor EphA2 by its ligand ephrinA1 triggered the phosphorylation of EphA2. Ligand activation of EphA2 also induced phosphorylation of ERK1/2 and significantly decreased MMC proliferation. Ligand activated and ephrinA1 vector (pcDNA/EFNA1) transfected MMC demonstrated decreased clonal growth in 3-D matrigels when compared to resting MMC. These studies suggest that EphA2 activation by its ligand ephrinA1 transmits intracellular signals from cell membrane to nucleus via ERK1/2 signaling cascade and inhibits MM growth.

Bacterial induction of early response genes and activation of proapoptotic factors in pleural mesothelial cells

In bacterial empyema the pleural mesothelium is constantly exposed to microorganisms. Staphylococcus aureus (S. aureus) is one of the most frequent pathogens associated with empyema. In an earlier study we demonstrated that S. aureus induced barrier dysfunction in pleural mesothelial cell monolayers. In the present study we report that S. aureus activates the early response genes c-fos and c-jun and activator protein-1 (AP-1), and induces proapoptosis genes Bad and Bak in primary mouse pleural mesothelial cells (PMCs). Our data indicate that in PMCs S. aureus induces apoptosis in a time- and multiplicity of infection (MOI)-dependent manner. Staphylococcus aureus induced Bcl (2), Bcl-X (L), c-fos, c-jun, and AP-1 expression in PMCs during the initial phase of infection. In S. aureus-infected PMCs, Bad and Bak gene expression was increased and correlated with DNA fragmentation and cytochrome-c release. Bcl (2) and Bcl-X (L) gene expression was significantly lower in S. aureus-infected PMCs than in uninfected PMCs 12 h postinfection. We conclude that at the initial stage of infection S. aureus modulates expression of early response genes c-fos and c-jun, and in the late phase of infection S. aureus induces expression of proapoptotic genes Bak and Bad in PMCs. Silencing AP-1 significantly inhibited S. aureus-induced Bak and Bad expression in PMCs. The upregulation of early response genes during the early phase of infection may contribute to the activation of proapoptotic genes Bak and Bad and release of cytochrome-c, caspase-3 thereby resulting in apoptosis in PMCs.

Induction of cell cycle arrest and apoptosis by BCG infection in cultured human bronchial airway epithelial cells

Bronchial airway epithelial cells (BAEpC) are among the first cells to encounter M. tuberculosis following airborne infection. However, the response of BAEpC to M. tuberculosis infection has been little studied. This study investigates the response of a human BAEpC cell line (BEAS-2B) to infection with Mycobacterium bovis Bacille Calmette Guerin (BCG). Cultured human BEAS-2B cells were experimentally infected with BCG. Uninfected BEAS-2B cultures were included as controls. Following infection, BEAS-2B cells were evaluated by various methods at various time points up to 3 days. Cell proliferation was evaluated by cellular bioreduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Distribution of cells along the cell cycle was evaluated by FACS analysis of cellular DNA. Apoptotic cells were identified by cell death ELISA and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling method. Eighty-four apoptosis-relevant genes were screened by PCR gene microarray. Translation of Fas, Fas ligand (Fas-L), and Fas-associated death domain (FADD) were evaluated quantitatively by real-time PCR. Expression of Fas and FADD proteins was evaluated by immunofluorescence and Western blot. Activity of caspase-3 and caspase-8 was evaluated by colorimetric assay of their enzymatic activity. BCG infection of BEAS-2B cells inhibits proliferation, induces cell cycle arrest at the G(0)/G(1) phase, causes apoptosis, modulates transcription of multiple apoptosis-relevant genes, promotes translation of Fas, Fas-L, and FADD, upregulates expression of Fas and FADD proteins, and increases activity of caspase-3 and caspase-8. Infection with BCG does not cause any significant change in the secretion of TGF-beta. The roles of Fas and FADD as mediators of BCG-induced apoptosis in BEAS-2B cells were tested by partial blockade of Fas and FADD expression with silencing RNA. Partial blockade of Fas or FADD expression results in a decreased apoptotic response to BCG infection. In conclusion, BCG induces cell cycle arrest and apoptosis in BEAS-2B cells. BCG induced apoptosis of BEAS-2B cells via the Fas death receptor pathway.

Cyclic stretch induces PlGF expression in bronchial airway epithelial cells via nitric oxide release

Mechanical strain of lung tissue is an important stimulus for the production of growth factors that are critical for lung growth and development. However, excessive mechanical strain, as may occur during mechanical ventilation, may produce an increase in growth factors that may contribute to lung injury. We hypothesized that mechanical strain of primary bronchial airway epithelial cells (BAEpCs) induced the production of placental growth factor (PlGF), a member of the VEGF family. BAEpCs were cultured on a deformable silicoelastic membrane and exposed to different magnitudes of stretch. Stretch induced PlGF and nitric oxide (NO) production that increased with increasing magnitude of stretch. Stretch also induced PlGF and inducible NO synthase ( iNOS) gene expression. The stretch-induced PlGF production and NO synthesis were attenuated by PD98059, a specific mitogen-activated protein kinase kinase-1 and -2 inhibitor. Inhibition of NO generation by l-NAME or l-NMMA or scavenging NO by carboxy-PTIO prevented stretch-mediated erk1/2 activation. In addition, in unstretched BAEpCs, exogenous NO enhanced erk1/erk2 activation. Our data suggest that mechanical stretch of BAEpCs induces iNOS expression and induces PlGF release in an erk1/2 activation-dependent manner.

Talc mediates angiostasis in malignant pleural effusions via endostatin induction

Talc remains the most effective sclerosing agent for pleurodesis. However, its mechanism of action in resolving pleural malignant disease remains unclear. The present study evaluated the angiogenic balance in the pleural space in patients with malignant pleural effusions (MPE) following talc insufflation. Patient pleural fluid samples were collected both before and after talc insufflation. The ability of pleural mesothelial cells (PMC) and malignant mesothelioma cells (MMC) to produce endostatin in vitro was compared. The biological effects of pleural fluids and conditioned media from talc-activated PMC on endothelial cells were evaluated by performing proliferation, invasion, tube formation and apoptosis assays. Pleural fluids from patients with MPE who received thoracoscopic talc insufflation contained significantly higher levels of endostatin (median 16.75 ng.mL(-1)) compared with pre-talc instillation (1.06 ng.mL(-1)). Talc-activated PMC released significantly greater amounts of endostatin (mean+/-SEM 1052.39+/-38.66 pg.mL(-1)) when compared with a MMC line (134.73+/-8.72 pg.mL(-1)). In conclusion, talc alters the angiogenic balance in the pleural space from a biologically active and angiogenic environment to an angiostatic milieu. Functional improvement following talc poudrage in patients with malignant pleural effusions may, in part, reflect these alterations in the pleural space.

Silencing the receptor EphA2 suppresses the growth and haptotaxis of malignant mesothelioma cells

BACKGROUND

The over-expression of the ephrin-A1 ligand receptor EphA2 is associated with the growth and metastatic potential of tumors. Although EphA2 is expressed in a variety of tumors, its expression and function in malignant mesothelioma (MM) remain unknown. The authors hypothesized that expression of the receptor EphA2 in MM cells (MMCs) plays a key role in the growth and haptotactic migration of MM. They also hypothesized that silencing EphA2 expression by using small-interfering RNA (siRNA) inhibits the proliferation and haptotaxis of MMCs and induces apoptosis in MMCs.

METHODS

The expression of EphA2 in MMCs and in normal pleural mesothelial cells (PMCs) was studied by using real-time quantitative polymerase chain reaction analysis and Western blot analysis. The growth of MMCs was determined with the WST-1 cell-proliferation assay. The haptotactic migration of MMCs and PMCs was determined with a Boyden chamber assay. Expression of caspases was determined with calorimetric assays.

RESULTS

The results demonstrated that silencing the receptor EphA2 by siRNA significantly reduced the proliferation and haptotactic migration of MMCs compared with controls. Over-expression of EphA2 with plasmid pcDNA/EphA2 enhanced the proliferation and haptotaxis of MMCs significantly. Knocking down EphA2 expression initiated caspase-9-mediated apoptosis in MMCs.

CONCLUSIONS

The current results suggested that constitutive expression of EphA2 may contribute to the aggressive behavior and cellular survival of MMCs. EphA2 may be an effective therapeutic target in patients with mesothelioma. Silencing the receptor EphA2 gene is a novel approach for the containment of growth and migration of tumor in patients with malignant mesothelioma.

Pleural fibrosis

Pleural fibrosis can result from a variety of inflammatory processes. The response of the pleural mesothelial cell to injury and the ability to maintain its integrity are crucial in determining whether normal healing or pleural fibrosis occurs. The pleural mesothelial cell, various cytokines, and disordered fibrin turnover are involved in the pathogenesis of pleural fibrosis. The roles of these mediators in producing pleural fibrosis are examined. This article reviews the most common clinical conditions associated with the development of pleural fibrosis. Fibrothorax and trapped lung are two unique and uncommon consequences of pleural fibrosis. The management of pleural fibrosis, including fibrothorax and trapped lung, is discussed.

RSV causes HIF-1alpha stabilization via NO release in primary bronchial epithelial cells

RSV infection is characterized by airway edema. Stabilization of hypoxia inducible factor-1alpha (HIF-1alpha) is important in both inflammation and edema formation. In this study we evaluated whether RSV induced release of nitric oxide (NO) by bronchial airway epithelial cells leading to the stabilization of HIF-1alpha and subsequent transcription of VEGF(165). Primary human bronchial epithelial cells (HBEpC) were used; cell supernatants were analyzed. Western blot analysis was used for the detection of HIF-1alpha. Bronchial airway epithelial monolayer permeability was assessed using electric cell-substrate impedance sensing (ECIS) in real time. There was increased stabilization of HIF-1alpha in RSV infected cells. Addition of an NO inhibitor blocked RSV mediated HIF-1alpha expression. Antagonism of NO also inhibited VEGF production and HBEpC monolayer permeability. Our results demonstrate that in HBEpC, RSV induced NO causes stabilization of HIF-1alpha in vitro.

Th2 cytokines IL-4 and IL-13 downregulate paxillin expression in bronchial airway epithelial cells

Asthma is characterized by infiltration and shedding of the bronchial epithelium. The Th2 cytokines IL-4 and IL-13 are involved in the cellular recruitment and infiltration seen in asthma. The effects of IL-4 and IL-13 on cell-matrix interactions and epithelial shedding are unknown. We hypothesize that bronchial airway epithelial cells (BAEC) express paxillin, a structural focal adhesion protein, and downregulation of paxillin by Th2 cytokines lead to BAEC hyperpermeability. We showed by confocal microscopy the presence of paxillin in BAEC. We demonstrated by Western blot analysis that IL-4 and IL-13 stimulation results in downregulation of paxillin production. IL-4 and IL-13 stimulation decreased epithelial cell-matrix attachment as measured by electrical cell-substrate impedance sensing system (ECIS). Our results suggest that Th2 cytokines IL-4 and IL-13 downregulate paxillin production by BAEC, thereby disrupting the cell-matrix interactions. This may help explain the epithelial shedding and epithelial membrane hyperpermeability that occurs in asthma.

Respiratory system responsiveness in rabbits in vivo is reduced by prolonged continuous positive airway pressure

Active, nonanesthetized, tracheotomized rabbits were subjected to continuous positive airway pressure (CPAP) for 4 days to determine the effects of chronic mechanical strain on lung and airway function. Rabbits were maintained for 4 days at a CPAP of 6 cmH(2)O (high CPAP), at a CPAP of 0 cmH(2)O (low CPAP), or without tracheostomy (no CPAP). After treatment with CPAP, changes in respiratory resistance in response to increasing concentrations of inhaled ACh were measured during mechanical ventilation to evaluate respiratory system responsiveness in vivo. Intraparenchymal bronchial segments were isolated from the lungs of all animals to evaluate airway smooth muscle responsiveness and bronchial compliance in vitro. Rabbits maintained for 4 days at high CPAP demonstrated significantly lower responsiveness to ACh compared with rabbits that were maintained at low CPAP or with no CPAP. Airways isolated from the lungs of animals subjected to the chronic application of high CPAP were also less responsive to ACh in vitro than the airways isolated from animals subjected to low CPAP or no CPAP. The persistence of the decreased responsiveness in the excised airway tissues suggests that the decreased respiratory system responsiveness observed in vivo results primarily from direct effects on the airways. The results demonstrate that the application of prolonged mechanical strain in vivo can reduce airway reactivity.

The mysterious pulmonary brush cell: a cell in search of a function

Brush cells, also termed tuft, caveolated, multivesicular, and fibrillovesicular cells, are part of the epithelial layer in the gastrointestinal and respiratory tracts. The cells are characterized by the presence of a tuft of blunt, squat microvilli (approximately 120-140/cell) on the cell surface. The microvilli contain filaments that stretch into the underlying cytoplasm. They have a distinctive pear shape with a wide base and a narrow microvillous apex. The function of the pulmonary brush cell is obscure. For this reason, a working group convened on August 23, 2004, in Bethesda, Maryland, to review the physiologic role of the brush (microvillous) cell in normal airways and alveoli and in respiratory diseases involving the alveolar region (e.g., emphysema and fibrosis) and airway disease characterized by either excessive or insufficient amounts of airway fluid (e.g., cystic fibrosis, chronic bronchitis, and exercise-induced asthma). The group formulated several suggestions for future investigation. For example, it would be useful to have a panel of specific markers for the brush cell and in this way separate these cells for culture and more direct examination of their function (e.g., microarray analysis and proteomics). Using quantitative analysis, it was suggested to examine the number and location of the cells in disease models. Understanding the function of these cells in alveoli and airways may provide clues to the pathogenesis of several disease states (e.g., cystic fibrosis and fibrosis) as well as a key for new therapeutic modalities.

Talc Pleurodesis

STUDY OBJECTIVES

Patients with recurrent pleural effusions secondary to malignancy are subjected to pleurodesis if clinically indicated. Pleurodesis involves the introduction of a sclerosing agent into the pleural space. Talc is one of the most commonly used sclerosing agents in treating patients with recurrent, symptomatic malignant pleural effusions. However, the mechanisms whereby talc mediates pleural fibrosis remain unclear. We hypothesized that the intrapleural instillation of talc induces the pleural mesothelial production of basic fibroblast growth factor (bFGF), which is responsible for pleural fibrosis.

METHODS

Samples of pleural fluid collected from 23 patients with malignant pleural effusions and 6 patients with congestive heart failure (control group) were included in this study. A tumor grading scale (1 to 9) was used to demonstrate the extent of the tumor. In vitro pleural mesothelial cells (PMCs) were activated with talc, and the conditioned medium was collected to evaluate bFGF levels by enzyme-linked immunosorbent assay. The bFGF-induced proliferation of fibroblasts was studied by [(3)H]thymidine incorporation. The messenger RNA expression of bFGF in talc-activated PMCs was determined by Northern analysis.

RESULTS

In this study, we demonstrated that patients who have undergone successful pleurodesis following intrapleural talc insufflation have significantly higher levels of bFGF in their pleural fluid compared to those who do not respond to pleurodesis. In addition, we found a significant negative correlation between bFGF levels and tumor size. Talc-activated PMCs produce significantly higher levels of bFGF compared to control, which correlates with bFGF messenger RNA expression in PMCs stimulated with talc. The neutralization of pleural fluids and conditioned medium from talc-stimulated PMCs with bFGF antibodies significantly inhibits the bFGF-induced proliferation of pleural fibroblasts.

CONCLUSIONS

An important outcome of this study was the finding that patients with extensive tumor involvement of the pleural mesothelium have a significantly lower pleural fluid bFGF response to talc compared to those who have limited involvement. Patients with limited pleural disease and higher bFGF responses go on to have successful pleurodesis, demonstrating that the presence of a mesothelium that is free of tumor enhances the possibility of success. In vitro PMCs stimulated with talc release biologically active bFGF.

Pathogenesis of pleural infection

The pleura responds to the presence of infecting organisms with a vigorous inflammatory response associated with an exudation of white blood cells and proteins. The development and outcome of pleural infections is a function of a balance between the virulence of the invading microorganism and the immune reaction involving professional immune cells as well as the pleural mesothelial cells. Most commonly, pleural infection occurs after invasion through the lung parenchyma and a breach in the viscera pleura resulting in the formation of a parapneumonic process. Upon infection, the microorganisms are recognized by the pleural mesothelial cell, which remains the first line of defence. Pleural responses to infection include those of innate immunity as well as adaptive or acquired immunity. Innate and acquired immune responses are closely linked. In this review, we discuss the different virulence factors that allow microorganisms to infect the pleura and the role of the pleural mesothelial cells in bridging the innate and acquired immune responses.

Pleural mesothelial cell (PMC) defense mechanisms against malignancy

Tumors such as ovarian, lung, and breast have been found to have a predilection for the pleura. Pleural mesothelial cells (PMCs) play an active role in pleural inflammation via release of cytokines. However, mechanisms whereby PMCs defend themselves against invading malignant cells are unknown. In the present study, we hypothesized that PMCs release the antiangiogenic factor endostatin and inhibit malignant cell invasion. We evaluated the endostatin levels in malignant (MAL) and congestive heart failure (CHF) pleural fluids (PF). Endostatin expression by PMC was also demonstrated by Western analysis and confocal microscopy. Our results demonstrate that CHF PF contained significantly higher levels of endostatin when compared with MAL PF. PMCs alone released a significantly greater amount of endostatin when compared with ovarian cancer cells (OCCs). When the PMC were cocultured with OCCs without contact, there was an increase in the endostatin production. However, when the PMCs were cocultured in direct contact with OCCs the endostatin levels significantly decreased. Endostatin production was upregulated in the presence of tumor cells but not when OCCs were adherent to underlying PMC monolayer. Immunofluorescent staining of PMCs for endostatin correlated with endostatin release. These findings suggest that PMCs play a key role in the antiangiogenesis process by producing endostatin in the pleural space, and thus preventing tumor spread and metastasis in the pleura.

Respiratory Syncytial Virus Causes Increased Bronchial Epithelial Permeability

BACKGROUND

Respiratory syncytial virus (RSV)-induced diseases are mediated through active cytokines released during infection. We hypothesized that RSV infection causes bronchial epithelial monolayer permeability in vitro via induction of vascular endothelial growth factor (VEGF).

METHODS

Human bronchial epithelial cells were infected with RSV. In some cultures, VEGF antibody was included to block VEGF response; in other cultures, palivizumab was added to block RSV infection. Permeability was assessed in real-time using electric cell-substrate impedance sensing. VEGF release was assessed using enzyme-linked immunosorbent assay. Gap formation was assessed using live cell imaging.

RESULTS

RSV-infected cells demonstrated a decrease in the resistance of the monolayer indicating an increase in permeability; this increase was blocked with VEGF-specific antibody, and palivizumab. Intercellular gap formation developed in RSV-infected epithelial monolayers.

CONCLUSION

RSV increases permeability of the bronchial airway epithelial monolayer via VEGF induction.

Mycobacteria induces pleural mesothelial permeability by down-regulating beta-catenin expression

Patients with pulmonary tuberculosis develop pleural effusions with a high protein content. Pleural mesothelial adherens junctions promote mesothelial cell-cell adhesion and contribute to pleural integrity. In the present study we have investigated the effect of mycobacterium (BCG) on mesothelial cell adherens junction proteins and pleural permeability. BCG enhanced pleural mesothelial cell (PMC) release of vascular endothelial growth factor (VEGF), and decreased electrical resistance across the PMC monolayer. Neutralizing antibodies to VEGF significantly restored the drop in PMC electrical resistance caused by BCG. BCG infection down regulated beta-catenin (adherens junction protein) expression and caused increased permeability across confluent mesothelial monolayer. Our results suggest that in TB pleurisy, mycobacteria cause VEGF release from mesothelial cells and leads to protein exudation by altering mesothelial adherens junction proteins.

Defensive role of pleural mesothelial cell sialomucins in tumor metastasis

STUDY OBJECTIVES

Sialomucin complex (SMC) is a heterodimeric glycoprotein, and is found on the surfaces of the mesothelia of the pleura, pericardium, and peritoneum. Sialomucins play a significant role in adhesion as well as in defense. In this study, we hypothesized that pleural mesothelial cells (PMCs) express SMC and thus prevent the adherence of ovarian cancer cells (HTB-77) to the pleura.

METHODS

PMCs were plated, and the adherence of HTB-77 cells was observed using a cytofluor. The PMC monolayer was pretreated with sialidase, and HTB-77 adherence was observed using cytofluor. In another set of HTB-77 cells, adherence was observed when the PMC monolayer was pretreated with supernatants of HTB-77 cells. Last, supernatants of HTB-77 cells were assayed for sialidase activity.

RESULTS

The removal of SMC by sialidase greatly increased the adherence of HTB-77 cells to the PMC monolayer, which was statistically significant (p < 0.05). Similar results were obtained when the PMC monolayer was pretreated with the supernatants of HTB-77 cells. Supernatants of HTB-77 cells showed the presence of sialidase.

CONCLUSIONS

The presence of SMC on the PMC acts as a defense layer, and its removal by sialidase increases the susceptibility of the PMC layer to the adherence of malignant cells and to increased metastasis. HTB-77 cells also express sialidase, which by its action on the monolayer aids in the adherence of tumor cells to the pleural surface.

Adherence of ovarian cancer cells induces pleural mesothelial cell (PMC) permeability

Malignant pleural effusion (MPE) carries a grave prognosis with median survival after diagnosis being 5 months. The major causes of MPE are lung, breast, ovary,and gastric cancer. It is still unclear how cancer cells penetrate the pleural mesothelial monolayer and reach the pleural space. In this study we examined the effect of ovarian epithelial cancer cells on a confluent pleural mesothelial cell (PMC) monolayer. We demonstrate that ovarian cancer cells adhere to the mesothelial monolayer in a time-dependent manner and induce PMC barrier dysfunction as evidenced by a drop in electrical resistance on electrical cell substrate impedance-sensing system (ECIS) and increased protein permeability. Barrier dysfunction is attenuated by addition of vascular endothelial growth factor (VEGF) antibody. Significant release of VEOF was noted when ovarian cancer cells were cocultured with PMC. Electron microscopy demonstrated gap formation in PMC monolayer only at the site of cancer cell attachment with surrounding areas remaining confluent.

Low molecular weight hyaluronan induces malignant mesothelioma cell (MMC) proliferation and haptotaxis: role of CD44 receptor in MMC proliferation and haptotaxis

Hyaluronan (HA) is a nonsulfated glycosaminoglycan that is secreted in significant quantities by pleural mesothelial cells (PMC) and malignant mesotheioma cells (MMC). The functional significance of HA deposition in the pleural space has not been fully elucidated. In this study, we hypothesized that low molecular weight but not high molecular weight hyaluronan induces proliferation and migration of MMC, and that the hyaluronan receptor (CD44S) expressed on the mesothelioma cell surface is involved in this process. We evaluated the effect of low molecular weight hyaluronan (LMWHA) and high molecular weight hyaluronan (HMWHA) on four MMC lines (CRL-2081, CRL-5915, CRL-5830, CRL-5820) proliferation and haptotactic migration. We also studied the expression of HA receptor CD44S on MMC by Northern hybridization and flow cytometry. The binding of LMWHA and HMWHA t o MMC surface was determined by FACS analysis using FITC-conjugated hyaluronan. Our results indicate that the MMC line that expressed the highest amount of CD44 receptor showed increased proliferation and haptotactic migration of MMC when stimulated with LMWHA but not HMWHA. Monoclonal antibody against CD44 inhibited proliferation by about 12-40% and migration by 10-35% in the MMC lines that were studied, and thus in part inhibited LMWHA-induced proliferation and migration in MMC. LMWHA binding to MM cell surface was significantly higher than HMWHA. This directly correlated with their CD44 receptor expression. Neutralization of CD44 receptor significantly reduced the LMMHA binding to MMC. These results provide evidence that the interaction between the adhesive protein receptor CD44 and extracellular matrix component (HA) transmits regulatory signals for mediating the locomotion and proliferation of MMC, and thus plays an important role in localized extension of tumor growth.

Immunological mechanisms in pleural disease

The pleural membrane consisting of pleural mesothelial cells and its underlying connective tissue layers play a critical role in immunological responses in both local and systemic diseases. The pleura, because of its intimate proximity to the lung, is positioned to respond to inflammatory changes in the lung parenchyma. Importantly, several systemic diseases have a predilection for expression on the pleural surface. Immunological responses in the pleura include the development of pleural permeability and pleural effusion formation as well as the development of pleural fibrosis and scarring. Under either circumstance, the normal functioning of the pleura is impaired and has multiple consequences leading to increased morbidity and even mortality for the patient. During infections in the pleural space, the pleural mesothelium responds by actively recruiting inflammatory phagocytic cells and allowing the movement of proteins from the vascular compartment into the pleural space. The release of chemokines by the pleural mesothelium allows for directed migration of phagocytic cells from the basilar surface of the pleura towards the apical surface. In malignant disease, the pleura may be the site of primary tumours such as mesothelioma and also the site for malignant metastatic deposits. Certain cancers such as cancers of the breast, ovary, lung, and stomach have a predilection for the pleural mesothelium. The process whereby malignant cells attach to the pleural mesothelium and develop autocrine mechanisms for survival in the pleural space are elucidated in this review. The pleura functions not only as a mechanical barrier, but also as an immunologically and metabolically responsive membrane that is involved in maintaining a dynamic homeostasis in the pleural space.

Pleural mesothelial cells modulate polymorphonuclear leukocyte apoptosis in empyema

In bacterial empyema, the recruited polymorphonuclear leukocytes (PMN) represent important phagocytic cells involved in antibacterial defense. In this study we demonstrate that pleural fluids (PF) obtained from patients with empyema (EMP) contains significantly higher levels of granulocyte colony stimulating factor (GM-CSF), and PMN incubated in empyema (EMP) pleural fluid (PF) showed significantly less apoptosis than congestive heart failure (CHF) PF. Staphylococcus aureus-stimulated PMC released significantly (P < 0.001) higher levels of GM-CSF than resting PMC. Staphylococcus aureus-stimulated PMC (SPMC)-CM significantly (P < 0.001) inhibited PMN apoptosis. In SPMC-CM-incubated PMN the antiapoptotic gene Bcl-xL mRNA and protein expression was up-regulated; Bak mRNA and protein expression was down-regulated compared to control PMN. The active caspases activity significantly decreased. When SPMC-CM and EMP PF were immunodepleted with GM-CSF antibody, PMN apoptosis was significantly higher. The delay in apoptosis of PMN is in part attributable to the release of cytokine GM-CSF by activated PMC. These findings suggest that S. aureus-activated PMC extend PMN life span by modulating Bcl-xL and Bak gene expression and active caspases activity during acute inflammation and empyema.

Induction of MCP-1 expression in airway epithelial cells: role of CCR2 receptor in airway epithelial injury

The repair of an injured bronchial epithelial cell (BEC) monolayer requires proliferation and migration of BECs into the injured area. We hypothesized that BEC monolayer injury results in monocyte chemoattractant protein-1 (MCP-1) production, which initiates the repair process. BECs (BEAS-2B from ATCC) were utilized in this study. MCP-1 interacts with CCR2B receptor (CCR2B), resulting in cell proliferation, haptotaxis, and healing of the monolayer. Reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to verify the presence of CCR2B. CCR2B was not merely present but also inducible by interleukin-2 (IL-2) and lipopolysaccharide (LPS). We demonstrated by immunohistochemistry that BECs express MCP-1 after injury and that receptor expression can be regulated by exposure to IL-2 and LPS. Haptotactic migration of cells was enhanced in the presence of MCP-1 and reduced in the presence of CCR2B antibody. This enhanced or depressed ability of the BECs to perform haptotactic migration was shown to be statistically significant (P < 0.05) when compared to controls. Finally, BECs proliferate in response to MCP-1 as proven by electric cell-substrate impedance sensing (ECIS) technology. MCP-1-specific antibodies were shown to neutralize the MCP-1-mediated BEC proliferation. This cascade of events following injury to the bronchial epithelium may provide insight into the mechanism of the repair process.

Inflammatory cytokines mediate C-C (monocyte chemotactic protein 1) and C-X-C (interleukin 8) chemokine expression in human pleural fibroblasts

Current knowledge implicates pleural mesothelial cells as mainly responsible for inflammatory responses in the pleural space. However, a vast body of recent evidence underscores the important role of fibroblasts in the process of inflammation in several types of tissues. We hypothesize that HPFBs (human pleural fibroblasts) play an important role in pleural responses and also when activated by bacterial endotoxin LPS (lipopolysaccharide), IL-1 beta (interleukin-1 beta), or TNF-alpha (tumor necrosis factor-alpha) release of C-C and C-X-C chemokines-specifically, MCP-1 and IL-8. Our results show that pleural fluid-isolated human fibroblasts release IL-8 and MCP-1 upon stimulation with IL-1 beta, TNF-alpha, and LPS in both a concentration- and time-dependent manner. RT-PCR (reverse-transcriptase-polymerase chain reaction) studies have also confirmed IL-8- and MCP-1-specific mRNA expression in activated pleural fibroblasts. On the time-dependent response curve, IL-8 was found in maximum concentrations at 144 hr, whereas MCP-1 continued to increase even after 196 hr following stimulation. IL-1 beta induced the maximum release of IL-8 (800-fold) and MCP-1 (164-fold), as compared to the controls. TNF-alpha induced a 95-fold increase in IL-8 and an 84-fold increase in MCP-1 levels, as compared to the controls. Collectively, our results show that human pleural fibroblasts contribute to the inflammatory cascade in the pleural space.

Bacterial induction of pleural mesothelial monolayer barrier dysfunction

Pneumonia remains one of the most common infectious causes of mortality. Patients with pneumonia develop parapneumonic effusions with a high neutrophil count as well as high protein concentrations. We hypothesized that pulmonary parenchymal bacterial infection causes a permeability change in the pleural mesothelium by inducing the production of vascular endothelial growth factor (VEGF). Complicated parapneumonic pleural effusions (empyema) have a 19-fold higher VEGF level than pleural fluids secondary to congestive heart failure and a 4-fold higher level than pleural fluids secondary to uncomplicated parapneumonic effusions. We also analyzed the influence of live Staphylococcus aureus on mesothelial barrier function using a model of confluent mesothelial monolayers. There was a significant drop in electrical resistance across S. aureus-infected pleural mesothelial cell (PMC) monolayers. Recombinant VEGF also decreases PMC electrical resistance. Neutralizing antibodies to VEGF significantly inhibited the drop in PMC electrical resistance caused by S. aureus. S. aureus infection also caused a significant increase in protein leak across confluent mesothelial monolayers. Our results suggest that bacterial pathogens induce VEGF release in mesothelial cells and alter mesothelial permeability, leading to protein exudation in empyema.

Polar production of interleukin-8 by mesothelial cells promotes the transmesothelial migration of neutrophils: role of intercellular adhesion molecule-1

Migration of polymorphonuclear neutrophils (PMNL) from the vascular compartment into the pleural space occurs rapidly during the development of parapneumonic effusions. This study investigated the polarized secretion of interleukin (IL)-8 in activated pleural mesothelial cells (PMC) and the migration of PMNL across resting, activated PMC monolayers. Results show that PMC produce IL-8 in a polar manner. When PMC were stimulated with Staphylococcus aureus or IL-1beta at the basal or at the apical surface, significantly (P< .05) more IL-8 was released toward the apical surface. This polarized production of IL-8 was confirmed by in situ hybridization. PMNL migration was higher from the basilar to apical than from the apical to basilar surface of PMC. Neutralizing antibodies against IL-8 and intercellular adhesion molecule (ICAM)-1 significantly (P< .001) blocked PMNL migration across activated monolayers. Thus, during pleural inflammation, PMC regulate the influx of PMNL into the pleural space by polar production of IL-8 and expression of ICAM-1.

Induction of acute pleural inflammation by Staphylococcus aureus. I. CD4+ T cells play a critical role in experimental empyema

Bacterial empyema is a frequent complication of pneumonia in patients with acquired immunodeficiency syndrome (AIDS). A model of Staphylococcus aureus empyema was developed that closely resembles bacterial empyema in patients infected with human immunodeficiency virus (HIV). Results show a compartmentalized chemokine response in bacterial empyema. The chemokine levels were higher in the pleural compartment than in the peripheral circulation. Polymorphonuclear leukocyte counts, murine GRO-alpha (KC), and macrophage inflammatory protein-2 levels were significantly (P<.001) lower in CD4+ knockout (CD4 KO) mice pleural fluid than in CD4+ wild-type (CD4 WT) mice. The CD4 KO mice had poorer bacterial clearance than CD4 WT mice. During S. aureus infection, interleukin-10 levels increased in the CD4 KO mice, whereas interferon-gamma levels were increased in CD4 WT mice. CD4+ T cell depletion results in a decreased pleural chemokine response, decreased neutrophil influx into pleural space, and impaired bacterial clearance in empyema.

MCP-1 in pleural injury: CCR2 mediates haptotaxis of pleural mesothelial cells

Pleural injury results in the death of mesothelial cells and denudation of the mesothelial basement membrane. Repair of the mesothelium without fibrosis requires proliferation and migration of mesothelial cells into the injured area. We hypothesized that monocyte chemoattractant protein-1 (MCP-1) induces proliferative and haptotactic responses in pleural mesothelial cells (PMCs) and that the MCP-1 binding receptor CCR2 mediates the pleural repair process. We demonstrate that PMCs exhibited MCP-1-specific immunostaining on injury. MCP-1 induced proliferative and haptotactic responses in PMCs. PMCs express CCR2 in a time-dependent manner. Fluorescence-activated cell sorting analysis demonstrated that interleukin (IL)-2 upregulated CCR2 protein expression in PMCs, whereas lipopolysaccharide (LPS) downregulated the response at the initial period compared with that in resting PMCs. However, the inhibitory potential of LPS was lost after 12 h and showed a similar response at 24 and 48 h. Haptotactic migration was upregulated in PMCs that were cultured in the presence of IL-2. The increased haptotactic capacity of mesothelial cells in the presence of IL-2 correlated with increased CCR2 mRNA expression. PMCs cultured in the presence of LPS showed decreased haptotactic activity to MCP-1. Blocking the CCR2 with neutralizing antibodies decreased the haptotactic response of PMCs to MCP-1. These results suggest that the haptotactic migration of mesothelial cells in response to MCP-1 are mediated through CCR2, which may play a crucial role in reepithelialization of the denuded basement membrane at the site of pleural injury and may thus contribute to the regeneration of the mesothelium during the process of pleural repair.

Talc induces apoptosis in human malignant mesothelioma cells in vitro

Pleurodesis with talc is an accepted method for the treatment of symptomatic pleural effusions secondary to mesotheliomas. Patients with mesothelioma who have talc-induced pleurodesis have a lower morbidity than do those who do not have pleurodesis. The mechanisms whereby talc mediated these effects were considered to be secondary to a decrease or absence of a pleural effusion. The possibility that talc may directly affect malignant cells was not considered. The present study was designed to evaluate if talc directly effects cell death of malignant mesothelioma cells (MMC) or normal pleural mesothelial cells (PMC). Three confluent MMC and PMC were exposed to talc for 24, 48, and 72 h. In parallel experiments, glass beads similar in size to talc were included as control. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) and DNA electrophoresis. Our results demonstrated that talc at a therapeutically achievable concentration (6 microg/cm(2)) induces significant apoptosis in MMC. Talc-induced maximum apoptosis in MMC (39.50 +/- 2.55%, 31.87 +/- 4.69%, and 15.10 +/- 3.93% in CRL-2081, CRL-5820, and CRL-5915, respectively) at 48 h, which was significantly (p < 0.05) greater than that in control cells. Electrophoresis of DNA isolated from talc-exposed MMC demonstrated the typical ladder pattern of internucleosomal DNA cleavage. Talc did not induce apoptosis in PMC, and glass beads did not cause significant apoptosis in either MMC or PMC. The present study has demonstrated that talc induces apoptosis in MMC without affecting normal mesothelial cells of the pleura.

Inhibition of interleukin-8 reduces human malignant pleural mesothelioma propagation in nude mouse model

Malignant pleural mesothelioma (MPM), despite current therapeutic strategies, is still an aggressive tumor with a very poor prognosis. Interleukin-8 (IL-8), a proinflammatory and angiogenic cytokine, has an important role in tumor-related neovascularization. IL-8 has also been described to function as an autocrine growth factor. The purpose of this study was to evaluate the effect of IL-8 antibody (IL-8 Ab) on progression of MPM in vivo. Athymic nude mice (n = 65) were injected intrapleurally with human MPM cells (CRL-2081), equally divided into three groups (IL-8 Ab, control Ab, untreated), and received IP injection of IL-8 Ab, control Ab, or no treatment, respectively, every 48 h up to 15 days. Pleural fluid and serum IL-8 levels, and tumor and body weight of mice were measured following 5, 10, and 15 days of tumor injection. We found that both pleural fluid and serum IL-8 levels were significantly (P < 0.0001) lower in mice that received IL-8 Ab when compared to the other groups. In this group, lower IL-8 levels were associated with a decreased rate of tumor growth. There was a significant and direct correlation between pleural fluid IL-8 levels and tumor weight of all animals enrolled in this study (P < 0.0001, r = 0.88). We demonstrate that antibody treatment against IL-8 decreased human MPM progression. Our results suggest that treatments targeting the decrease of MPM-associated IL-8 levels or the effects of this protein may inhibit mesothelioma growth.

Mycobacterium-induced transmesothelial migration of monocytes into pleural space: role of intercellular adhesion molecule-1 in tuberculous pleurisy

The pleural mesothelium is a dynamic cellular membrane with multiple key functions. It plays a pivotal role in pleural inflammation through its release of several cytokines and the expression of cell-surface molecules. The expression of intercellular adhesion molecule (ICAM)-1 in the pleural mesothelium of patients with active pleural tuberculosis and the role of ICAM-1 in monocyte transmigration across pleural mesothelium during tuberculous inflammation was investigated. Results indicate pleural mesothelial cells (PMCs) express ICAM-1 in tuberculous pleuritis. When PMCs were stimulated with bacille Calmette-Guérin (BCG) in vitro, they expressed ICAM-1 in a time-dependent manner. Monocyte transmigration was higher across PMC monolayers that had been stimulated with BCG. Blocking ICAM-1 on BCG-activated PMC monolayers inhibited monocyte transmigration against chemotactic gradient generated by macrophage inflammatory protein 1-alpha or monocyte chemotactic protein-1. These results indicate that ICAM-1 expression in PMCs facilitates monocyte transmigration during tuberculous pleural inflammation.

Helper T cell type 1 and 2 cytokines regulate C-C chemokine expression in mouse pleural mesothelial cells

The recruitment of leukocytes to an area of injury or inflammation site is one of the most fundamental host defenses. Pulmonary tuberculosis is characterized by granulomatous inflammation with an extensive infiltration of mononuclear cells. In tuberculous pleurisy pleural mesothelial cells are exposed to mycobacteria in the pleural space. In this study we demonstrate that mouse pleural mesothelial cells (PMCs), when stimulated with BCG or IFN-gamma, produced MIP-1alpha and MCP-1 in vitro. IFN-gamma enhanced the BCG-mediated MIP-1alpha and MCP-1 expression in a concentration-dependent manner. The RT-PCR studies also confirmed that both BCG and IFN-gamma induce chemokine expression. IL-4 inhibited the BCG-mediated MIP-1alpha and MCP-1 expression in a concentration-dependent manner. The lower concentrations of IL-4 were ineffective; however, at higher concentrations, the inhibitory effect of IL-4 persisted for 24 h and decreased thereafter. BCG stimulation resulted in an increase of IFN-gamma and IL-4 receptors on PMCs. Our results demonstrate that Th1 and Th2 cytokines may regulate the C-C chemokine expression in PMCs and thus play a biologically important role in mononuclear cell recruitment to the pleural space.

Pathophysiology of pleural space infections

The pleura responds to the presence of infecting organisms with a vigorous inflammatory response associated with an exudation of white blood cells and proteins. Changes in pleural permeability lead to formation of an exudative pleural effusion. The pleural mesothelial cell is the primary cell lining the pleural space and, when activated by the presence of organisms, initiates the inflammatory response by releasing a battery of chemokines and cytokines. Mesothelial cells are actively phagocytic and also release oxidants and proteases. The acute inflammatory process may resolve with appropriate antibiotic therapy and drainage leaving minimal fibrosis. However, under certain circumstances vigorous pleural fibrosis with scarring and loss of delineation of pleural surfaces can occur. Recognition of the stage of development of the empyema is an important clinical judgement that can affect outcome. The pathogenesis of infections of the pleural space and the role played by the various cell types is delineated in this article.

Interleukin 8: an autocrine growth factor for malignant mesothelioma

Interleukin 8 (IL-8) is a potent chemokine that also has a direct growth-potentiating effect on certain tumors. In the present study, we determined IL-8 levels in human malignant mesothelioma (MM) effusions and congestive heart failure pleural fluids. We also investigated antigenic IL-8 production by different MM cell lines, and we describe the role of IL-8 in the autocrine growth regulation of MMs. Mesothelial (CRL-9444 = MC) and MM (CRL-2081 = MM-1, CRL-5915 = MM-2, and CRL-5820 = MM-3) cell lines were grown using standard culture methods. The bioactive IL-8 levels were measured in supernatants of cultured cells by ELISA, and the expression of cell-associated immunoreactive IL-8 was observed by immunohistochemistry. The proliferative activity was determined by thymidine ([3H]thymidine) incorporation and also by direct cell counts after incubation with varying concentrations of IL-8 in the presence/absence of specific polyclonal IL-8 antibody. We found significantly higher levels of IL-8 in mesothelioma pleural fluids than congestive heart failure and a time-dependent increase in IL-8 levels in MM-1 and MM-2 cell supernatants during 96 h of incubation. IL-8 levels were nearly undetectable in MM-3 and MC cell line supernatants. In MM-1 and MM-2 cells, IL-8 caused a dose-dependent increase of [3H]thymidine incorporation to maximal levels of 46.3 +/- 3.6% and 12.3 +/- 1.6% (P < 0.001), respectively, when compared with serum-free medium as control. Neutralization of IL-8 significantly decreased proliferative activity of MM-1 and MM-2. IL-8 did not induce proliferative activity in MM-3 and MC cells. We conclude that IL-8 had a direct growth-potentiating activity in MMs.