Pleural Effusions from Patients with Mesothelioma Induce Recruitment of Monocytes and Their Differentiation into M2 Macrophages

Our plain-English summary of Pleural Effusions from Patients with Mesothelioma Induce Recruitment of Monocytes and Their Differentiation into M2 Macrophages, by A.L. Chéné, S. d'Almeida, T. Blondy, et al (Journal of Thoracic Oncology, 2016).

The study

• Authors: A.L. Chéné, S. d'Almeida, T. Blondy, J. Tabiasco, S. Deshayes, J.F. Fonteneau, L. Cellerin, Y. Delneste, M. Grégoire, C. Blanquart
• Journal: Journal of Thoracic Oncology
• Published: 2016;11(10):1765-73
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Mesothelioma is a rare and aggressive cancer related to asbestos exposure. We recently showed that pleural effusions (PEs) from patients with mesothelioma contain high levels of the C-C motif chemokine ligand 2 (CCL2) inflammatory chemokine. In the present work, we studied the effect of CCL2 contained in mesothelioma samples, particularly on monocyte recruitment. Then, we studied the fate of these monocytes in malignant pleural mesothelioma (MPM) PEs and their impact on tumor cells' properties.

Methods: The implication of CCL2 in monocyte recruitment was evaluated using transmigration assays and a CCL2 blocking antibody. The phenotype of macrophages was determined by flow cytometry and enzyme-linked immunosorbent assay. Immunohistochemical analysis was used to support the results. Cocultures of macrophages with mesothelioma cells were performed to study cancer cell proliferation and resistance to treatment.

Results: We showed that CCL2 is a major factor of monocyte recruitment induced by MPM samples. Macrophages obtained in MPM samples were M2 macrophages (high CD14, high CD163, and interleukin-10 secretion after activation). The colony-stimulating factor 1 receptor/macrophage colony-stimulating factor (M-CSF) pathway is implicated in M2 polarization, and high levels of M-CSF were measured in MPM samples compared with benign PE (4.17 ± 2.75 ng/mL and 1.94 ± 1.47 ng/mL, respectively). Immunohistochemical analysis confirmed the presence of M2 macrophages in pleural and peritoneal mesothelioma. Finally, we showed that M2 macrophages increased mesothelioma cell proliferation and resistance to treatment.

Conclusions: These results demonstrate the implication of CCL2 in MPM pathogenesis and designate M-CSF as a new potential biomarker of MPM. This study also identifies CCL2 and colony-stimulating factor 1 receptor/M-CSF as interesting new targets to modulate pro-tumorigenic properties of the tumor microenvironment.

Copyright © 2016 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved.

In plain English

This was a laboratory study, done in Nantes, France, of how fluid from around the lungs of people with malignant pleural mesothelioma affects immune cells called monocytes and macrophages. Asbestos exposure was not studied. The authors used pleural fluid from 22 patients with mesothelioma and 11 with benign (non-cancerous) effusions, fluid from mesothelioma cell lines, and tumor tissue samples. Blocking the signaling protein CCL2 reduced monocyte movement toward mesothelioma pleural fluid by 82.5 percent and toward cell-line fluid by 76.5 percent. Monocytes grown in mesothelioma fluid took on features of the M2 macrophage type. Levels of the protein M-CSF were significantly higher in mesothelioma fluid (4.17 ng/ml) than in benign fluid (1.94 ng/ml). Blood levels did not differ significantly. M2 macrophages were found in all 9 pleural and all 7 peritoneal mesothelioma tissue samples. In lab dishes, M2 macrophages increased mesothelioma cell growth and weakened the effect of cisplatin and pemetrexed. The authors concluded that these pathways are potential treatment targets. They said larger studies are needed to confirm M-CSF as a possible biomarker.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) study using patient pleural effusion samples, mesothelioma cell lines, donor monocytes, and immunohistochemistry on a commercial tumor tissue microarray
• Who was studied: Pleural effusions from 22 patients with malignant pleural mesothelioma (18 epithelioid, 3 sarcomatoid, 1 biphasic; mean age 78.05) and 11 patients with benign pleural effusions (8 fibrosis, 3 pachypleuritis; mean age 75.82), collected at Nantes hospital, France. Collection dates are not given. The authors also used mesothelioma cell lines established from patients' pleural fluids, donor monocytes, and a tissue microarray with 9 pleural and 7 peritoneal mesotheliomas. Individual experiments used subsets, for example 8 or 9 effusions.
• Exposure: Asbestos exposure was not measured or studied. The experiments examined the effects of mesothelioma pleural fluid and mesothelioma cell-culture fluid on monocytes and macrophages.
• Main results:
  • An antibody blocking CCL2 reduced monocyte migration toward mesothelioma pleural effusions by 82.5 plus or minus 5.6% (n=9) and toward mesothelioma cell-culture fluid by 76.5 plus or minus 12.8% (n=8).
  • Monocyte migration did not correlate directly with the CCL2 concentration in the pleural effusions or cell-culture fluids.
  • Monocytes incubated in mesothelioma pleural effusions became macrophages that, after stimulation, produced only IL-10, which the authors took as confirming the M2 type.
  • M-CSF was significantly higher in pleural effusions from mesothelioma patients (4.17 plus or minus 2.75 ng/ml) than in benign pleural effusions (1.94 plus or minus 1.47 ng/ml).
  • No difference in pleural-fluid M-CSF level was seen between mesothelioma subtypes.
  • M-CSF levels in serum (blood) were low and did not differ significantly between benign effusion patients and mesothelioma patients.
  • In monocytes incubated in mesothelioma pleural effusions, the CSF1-R inhibitor GW2580 reduced the M2-related markers CD14 and CD163 by 40% and 50% respectively.
  • CD163-positive (M2) macrophages were present in all 9 pleural and all 7 peritoneal mesothelioma tissue samples on the tissue microarray.
  • In co-culture, adding M2 macrophages significantly increased the growth rate of mesothelioma cells.
  • Mesothelioma cells treated with the cisplatin-pemetrexed combination without macrophages had a viability of 28.46% plus or minus 4.35. Results were from experiments on three mesothelioma cell lines.
  • With M2 macrophages present, viability of the treated mesothelioma cells was higher: 45.67% plus or minus 6.05 with 100 M2 macrophages and 51.34% plus or minus 10.07 with 10 M2 macrophages per well of mesothelioma cells.
• The authors' conclusion: The authors concluded that the CCL2/CCR2 and M-CSF/CSF-1R pathways are potential targets for reducing M2 macrophages in the mesothelioma environment, and in this way for improving chemotherapy and immunotherapy. They also suggested that pleural-fluid M-CSF could help tell benign effusions from mesothelioma.
• Limitations the authors state:
  • The authors stated that M-CSF as a biomarker for mesothelioma is a hypothesis that needs studies on a larger cohort of samples.
  • The authors noted that the complex make-up of the fluids, which may include other attracting factors and inhibitors of migration, may explain the lack of correlation between CCL2 levels and monocyte migration.
  • The inhibitor GW2580 worked less well on pleural effusions than on M-CSF alone. The authors said this raises the question of whether other cytokines are involved.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Effusion, Mesothelioma, Macrophage, Asbestos Exposure, Pleural Mesothelioma, Peritoneal Mesothelioma, Biomarker, Tumor Microenvironment.

Related studies

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• Pleural Effusion of Patients with Malignant Mesothelioma Induces Macrophage-Mediated T Cell Suppression — L.A. Lievense, R. Cornelissen, et al. (2016)
• Asbestos stimulation triggers differential cytokine release from human monocytes and alveolar macrophages — L.J. Geist, L.S. Powers, et al. (2000)
• Lrp5/β-Catenin Signaling Controls Lung Macrophage Differentiation and Inhibits Resolution of Fibrosis — J.A. Sennello, A.V. Misharin, et al. (2017)
• Involvement of the M-CSF/IL-34/CSF-1R pathway in malignant pleural mesothelioma — T. Blondy, S.M. d'Almeida, et al. (2020)

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