BACKGROUND: IL-35 is a novel anti-inflammatory and immunosuppressive cytokine primarily produced by Treg cells, and is involved in inflammatory diseases and autoimmune diseases. However, its roles in tuberculous pleural effusion (TPE) remain unknown. We aimed to investigate the potential involvement of IL-35 in TPE.

MATERIAL AND METHODS: Thirty TPE patients and 20 lung cancer patients with malignant pleural effusion (MPE) were recruited. Samples of pleural effusion (100 mL) were collected after traditional pleurocentesis. Blood was sampled from TPE patients. Mononuclear cells were isolated by Ficoll-Hypaque gradient. Proportions of Th1, Th17, and IL-35-producing cells were analyzed by flow cytometry. IL-35 was assessed by real-time RT-PCR, ELISA, and immunofluorescence. An ELISPOT assay was used to assess the effect of IL-35 on pleural effusion mononuclear cells (PEMCs).

RESULTS: Proportions of IL-35-producing cells were higher in TPE compared with MPE (49.4±6.0 vs. 15.8±5.4%, P<0.001) and blood from TPE patients (49.4±6.0% vs. 16.6±3.1, P<0.001). IL-35, IL-17 and IFN-γ were elevated in TPE compared with MPE (all P<0.01). ELISPOT assay showed that IL-35 reduced the proportion of IFN-γ-producing CD4+ T cells in TPE. IL-35 mRNA expression was higher in TPE compared with MPE (P<0.001). Immunofluorescence showed that IL-35-positive cells were present in pleural tissues from TPE patients.

CONCLUSIONS: Results suggest that there is an imbalance in IL-35 metabolism in TPE. However, further studies are required to assess the exact relationship with the immune system response to tuberculosis. IL-35 might play a role in TPE and might be targeted as a treatment for TPE.

Keywords: Interferon-gamma - analysis, Interleukin-17 - analysis, Interleukins - genetics, Lung Neoplasms - complications, Lymphocyte Count, Neoplasm Proteins - analysis, Pleura - pathology, Pleural Effusion - metabolism, Pleural Effusion, Malignant - metabolism, RNA, Messenger - biosynthesis, Th1 Cells - metabolism, Th17 Cells - metabolism, Tuberculosis, Pleural - metabolism