The lymphatic system in malignant pleural effusion. Drain or immune switch?

Th17 cells and their related cytokines: vital players in progression of malignant pleural effusion

Malignant pleural effusion (MPE) is an exudative effusion caused by primary or metastatic pleural carcinosis. Th17 cells and their cytokines are critical components in various disease including MPE. In this review, we summarize current published articles regarding the multifunctional roles of Th17 cells and their related cytokines in MPE. Th17 cells are accumulated in MPE compared with paired serum via certain manners. The upregulation of Th17 cells and the interactions between Th17 cells and other immune cells, such as Th1 cells, Th9 cells, regulatory T cells and B cells, are reported to be involved in the formation and development of MPE. In addition, cytokines, which are elaborated by Th17 cells, including IL-17A, IL-17F, IL-21, IL-22, IL-26, GM-CSF, or associated with Th17 cells differentiation, including IL-1β, IL-6, IL-23, TGF-β, are linked to the pathogenesis of MPE through exerting pro- or anti-tumorigenic functions on their own as well as regulating the generation and differentiation of Th17 cells in MPE. Based on these findings, we proposed that Th17 cells and their cytokines might be diagnostic or prognostic tools and potential therapeutic targets for MPE.

HMGB1 Promotes Myeloid Egress and Limits Lymphatic Clearance of Malignant Pleural Effusions

Pleural effusions, when benign, are attributed to cardiac events and suffusion of fluid within the pleural space. When malignant, lymphatic obstruction by tumor and failure to absorb constitutively produced fluid is the predominant formulation. The prevailing view has been challenged recently, namely that the lymphatics are only passive vessels, carrying antigenic fluid to secondary lymphoid sites. Rather, lymphatic vessels can be a selective barrier, efficiently coordinating egress of immune cells and factors within tissues, limiting tumor spread and immune pathology. An alternative explanation, offered here, is that damage associated molecular pattern molecules, released in excess, maintain a local milieu associated with recruitment and retention of immune cells associated with failed lymphatic clearance and functional lymphatic obstruction. We found that levels of high mobility group box 1 (HMGB1) were equally elevated in both benign and malignant pleural effusions (MPEs) and that limited diversity of T cell receptor expressing gamma and delta chain were inversely associated with these levels in MPEs. Acellular fluid from MPEs enhanced γδ T cell proliferation in vitro, while inhibiting cytokine production from γδ T cells and monocytes as well as restricting monocyte chemotaxis. Novel therapeutic strategies, targeting HMGB1 and its neutralization in such effusions as well as direct delivery of immune cells into the pleural space to reconstitute normal physiology should be considered.

Migrated T lymphocytes into malignant pleural effusions: an indicator of good prognosis in lung adenocarcinoma patients

The presence of leukocyte subpopulations in malignant pleural effusions (MPEs) can have a different impact on tumor cell proliferation and vascular leakiness, their analysis can help to understand the metastatic microenvironment. We analyzed the relationship between the leukocyte subpopulation counts per ml of pleural fluid and the tumor cell count, molecular phenotype of lung adenocarcinoma (LAC), time from cancer diagnosis and previous oncologic therapy. We also evaluated the leukocyte composition of MPEs as a biomarker of prognosis. We determined CD4+ T, CD8+ T and CD20+ B cells, monocytes and neutrophils per ml in pleural effusions of 22 LAC and 10 heart failure (HF) patients by flow cytometry. Tumor cells were identified by morphology and CD326 expression. IFNγ, IL-10 and IL-17, and chemokines were determined by ELISAs and migratory response to pleural fluids by transwell assays. MPEs from LAC patients had more CD8+ T lymphocytes and a tendency to more CD4+ T and CD20+ B lymphocytes than HF-related fluids. However, no correlation was found between lymphocytes and tumor cells. In those MPEs which were detected >1 month from LAC diagnosis, there was a negative correlation between pleural tumor cells and CD8+ T lymphocytes. CXCL10 was responsible for the attraction of CD20+ B, CD4+ T and CD8+ T lymphocytes in malignant fluids. Concentrations of IL-17 were higher in MPEs than in HF-related effusions. Survival after MPE diagnosis correlated positively with CD4+ T and CD8+ T lymphocytes, but negatively with neutrophils and IL-17 levels. In conclusion, lymphocyte enrichment in MPEs from LAC patients is mostly due to local migration and increases patient survival.

The role of microRNA-93 regulating angiopoietin2 in the formation of malignant pleural effusion

The biological roles of miRNAs in the development of malignant pleural effusion (MPE) are unclear. In this study, the miRNA microarray analysis was performed in two different prognosis groups of lung adenocarcinoma patients. Expression profiles of miRNAs in MPEs were identified. With the help of quantification PCR, we confirmed the expression differences of miRNAs and further analyzed their biological functions and relative target genes in vitro. The target gene of miR-93 was estimated by online database, and also, the protein was tested. The target gene and the binding sites of specific miRNA were estimated by online database. The combining capacity of binding sites was verified by luciferase reporter gene assay, and the target gene protein was tested by western blot. We detected 107 miRNAs with expression differences (n = 10) and confirmed significant expression differences in miR-93 and miR-146a in two groups of patients (n = 84). By manipulating miR-93 expression of human lymphatic endothelial cells (HLEC) and human umbilical vein endothelial cells (HUVEC), we discovered that high expression of miR-93 inhibited migration, proliferation, and angiogenesis. And also, miR-93 increased not only apoptosis, but also G1 phase cell block. By using luciferase reporter gene assay and western blot, we confirmed that angiopoietin2 (Ang2) was the target of miR-93. The data showed that miR-93 has an inhibiting effect on pleural effusion. By targeting Ang2, miR-93 regulates angiogenesis and lymphangiogenesis and plays a role in pathogenetic mechanism of MPE. MiR-93/Ang2 may shed light on potential new targets in cancer treatment.

Immune Regulation of Interleukin-27 in Malignant Pleural Effusion

BACKGROUND

Interleukin (IL)-27 has been reported to have anti-proliferate and anti-angiogenic activities on cancer cells. However, the involvement of IL-27 in malignant pleural effusion (MPE) remains unknown. Thus, in this research, we compared the immune functions of IL-27, interferon (IFN)-γ, and IL-17 on lung cancer cells and revealed the regulatory mechanism of IL-27 in MPE.

METHODS

The distribution of IL-27 in both MPE and blood was evaluated by enzyme-linked immunosorbent assay and flow cytometry. The expressions of cytokine receptors and the levels of the phosphorylated signal transducer and activator of transcription (STAT) signalings were detected by flow cytometry. As well as the effects of proliferation, apoptosis, migration, and adherent activity of IL-27, IFN-γ, and IL-17 on lung cancer cells were also explored.

RESULTS

The expression of IL-27 was increased in MPE when compared with blood (147.3 ± 25.1 pg/ml vs. 100.3 ± 13.9 pg/ml, P = 0.04). IL-27 was noted to suppress both proliferation (18.33 ± 0.21 vs. 27.77 ± 0.88, P = 0.0005) and migration (1.82 ± 0.44 vs. 3.13 ± 0.07, P = 0.04) of A549 cells, but obviously promoted apoptosis of A549 cells (9.47 ± 1.14 vs. 4.96 ± 0.17, P = 0.02) by activating STAT1 signaling. Interestingly, IL-27 played totally opposite effects on A549 cells by activating STAT3 pathway. Moreover, IL-27 exerted different intercellular adherent activities of A549 cells to pleural mesothelial cell monolayer by activating different STAT signalings.

CONCLUSIONS

IL-27 might exert an important immune regulation on lung cancer cells in human pleural malignant environment.

Pleural involvement in lung cancer

The pleural space, a sterile secluded environment in the thoracic cavity, represents an attractive metastatic site for various cancers of lung, breast and gastrointestinal origins. Whereas lung and breast adenocarcinomas could invade the pleural space because of their anatomic proximity, "distant" cancers like ovarian or gastrointestinal tract adenocarcinomas may employ more active mechanisms to the same end. A pleural metastasis is often accompanied by a malignant pleural effusion (MPE), an unfavorable complication that severely restricts the quality of life and expectancy of the cancer patient. MPE is the net "product" of three different processes, namely inflammation, enhanced angiogenesis and vascular leakage. Current efforts are focusing on the identification of cancer cell autocrine (specific mutation spectra and biochemical pathways) and paracrine (cytokine and chemokine signals) characteristics as well as host features (immunological or other) that underlie the MPE phenotype. Herein we examine the pleural histology, cytology and molecular characteristics that make the pleural cavity an attractive metastasis destination for lung adenocarcinoma. Mesothelial and tumor features that may account for the tumor's ability to invade the pleural space are highlighted. Finally, possible therapeutic interventions specifically targeting MPE are discussed.

Mast cells mediate malignant pleural effusion formation

Mast cells (MCs) have been identified in various tumors; however, the role of these cells in tumorigenesis remains controversial. Here, we quantified MCs in human and murine malignant pleural effusions (MPEs) and evaluated the fate and function of these cells in MPE development. Evaluation of murine MPE-competent lung and colon adenocarcinomas revealed that these tumors actively attract and subsequently degranulate MCs in the pleural space by elaborating CCL2 and osteopontin. MCs were required for effusion development, as MPEs did not form in mice lacking MCs, and pleural infusion of MCs with MPE-incompetent cells promoted MPE formation. Once homed to the pleural space, MCs released tryptase AB1 and IL-1β, which in turn induced pleural vasculature leakiness and triggered NF-κB activation in pleural tumor cells, thereby fostering pleural fluid accumulation and tumor growth. Evaluation of human effusions revealed that MCs are elevated in MPEs compared with benign effusions. Moreover, MC abundance correlated with MPE formation in a human cancer cell-induced effusion model. Treatment of mice with the c-KIT inhibitor imatinib mesylate limited effusion precipitation by mouse and human adenocarcinoma cells. Together, the results of this study indicate that MCs are required for MPE formation and suggest that MC-dependent effusion formation is therapeutically addressable.

Treg/Th17 imbalance in malignant pleural effusion partially predicts poor prognosis

Accumulating evidence shows that an imbalance in regulatory T cells (Tregs)/T helper IL-17-producing cells (Th17) exists in malignant pleural effusion (MPE). However, the cause of this phenomenon in MPE and the underlying mechanism remain uncertain. The percentages of Tregs and Th17 cells in MPE and parapneumonic effusion (PPE) were determined by flow cytometry. Their specific transcription factors, forkhead box P3 (FoxP3) and retinoic acid-related orphan receptor γt (RORγt); related cytokines, interleukin-6 (IL-6), IL-17, IL-10, and transforming growth factor-β1 (TGF‑β1); and chemokines, C-C motif ligand 17 (CCL17) and CCL20, were analyzed by real-time PCR and ELISA, respectively. Compared to patients with PPE, patients with MPE presented a higher percentage of Tregs but a lower frequency of Th17 cells. Foxp3 mRNA expression level in the cells in the pleural effusion was significantly increased in patients with MPE compared to the levels in patients with PPE (MPE vs. PPE: 3.05±0.62 vs. 0.52±0.11, p=0.0012). It was also noted that high levels of IL-10, TGF-β1 and CCL17 were observed in MPE when compared to PPE (MPE vs. PPE: IL-10, 166.3±39.53 vs. 40.38±10.92 pg/ml, p=0.0307; TGF-β1, 10,720±1,274 vs. 1,747±293.2 pg/ml, p<0.0001; CCL17, 341.1±88.22 vs. 119.2±19.80 pg/ml, p=0.0427). Furthermore, a high ratio of Tregs/Th17 cells in MPE was highly correlated to poor survival. An alteration in CCL17 and CCL20 might contribute to the Treg/Th17 imbalance in MPE, which partially predicts a poor prognosis in patients with lung cancer.

Monoclonal antibody targeting of mononuclear cell chemokines driving malignant pleural effusion

Recent evidence suggests that host immune cells contribute to the development of malignant pleural effusion (MPE), a common manifestation of metastatic cancer. We have identified such cells, predominantly mononuclear myeloid cells, recruited by tumor-orchestrated inflammatory chemokines. Moreover, targeting of these inflammation-associated mediators modified the disease course of MPE in mice.