The global coronavirus disease 2019 (COVID-19) pandemic has a detrimental impact on public health. COVID-19 usually manifests as pneumonia, which can progress into acute respiratory distress syndrome (ARDS) related to uncontrolled TH17 immune reaction. Currently, there is no effective therapeutic agent to manage COVID-19 with complications. The currently available anti-viral drug remdesivir has an effectiveness of 30% in SARS-CoV-2–induced severe complications. Thus, there is a need to identify effective agents to treat COVID-19 and the associated acute lung injury and other complications. The host immunological pathway against this virus typically involves the THαβ immune response. THαβ immunity is triggered by type 1 interferon and interleukin-27 (IL-27), and the main effector cells of the THαβ immune response are IL10-CD4 T cells, CD8 T cells, NK cells, and IgG1-producing B cells. In particular, IL-10 exerts a potent immunomodulatory or anti-inflammatory effect and is an anti-fibrotic agent for pulmonary fibrosis. Concurrently, IL-10 can ameliorate acute lung injury or ARDS, especially those caused by viruses. Owing to its anti-viral activity and anti-pro-inflammatory effects, in this review, IL-10 is suggested as a possible treatment agent for COVID-19.

Patients with pneumonia and parapneumonic effusion (PPE) have elevated mortality and a poor prognosis. The aim of this study was to discover novel biomarkers to help distinguish between uncomplicated PPE (UPPE) and complicated PPE (CPPE). Using an iTRAQ-based quantitative proteomics, we identified 766 proteins in pleural effusions from PPE patients. In total, 45 of these proteins were quantified as upregulated proteins in CPPE. Four novel upregulated candidates (BPI, NGAL, AZU1, and calprotectin) were selected and further verified using enzyme-linked immunosorbent assays (ELISAs) on 220 patients with pleural effusions due to different causes. The pleural fluid levels of BPI, NGAL, AZU1, and calprotectin were significantly elevated in patients with CPPE. Among these four biomarkers, BPI had the best diagnostic value for CPPE, with an AUC value of 0.966, a sensitivity of 97%, and a specificity of 91.4%. A logistic regression analysis demonstrated a strong association between BPI levels > 10 ng/ml and CPPE (odds ratio = 341.3). Furthermore, the combination of pleural fluid BPI levels with LDH levels improved the sensitivity and specificity to 100% and 91.4%, respectively. Thus, our findings provided a comprehensive effusion proteome data set for PPE biomarker discovery and revealed novel biomarkers for the diagnosis of CPPE.

Background We previously demonstrated that the pleural levels of proteins (neutrophil gelatinase-associated lipocalin/NGAL, calprotectin, bactericidal permeability-increasing/BPI, azurocidin 1/AZU-1) were valuable markers for identifying complicated PPE (CPPE). Herein, this study was performed to evaluate whether these proteins are useful as serological markers for identifying CPPE and empyema. Methods A total of 137 participates were enrolled in this study. The levels of NGAL, calprotectin, BPI and AZU-1 were measured in serum and pleural fluid by enzyme-linked immunosorbent assay. We also characterized the diagnostic values of these markers between different groups. Results The serum levels of NGAL, calprotectin, and BPI in PPE patients were significantly higher than those in transudates, noninfectious exudates, and healthy controls. The area under the curve (AUC) values of NGAL, calprotectin, and BPI for distinguishing PPE from transudates or noninfectious exudates were around 0.861 to 0.953. In PPE group, serum NGAL and calprotectin levels were significantly elevated in patients with CPPE and empyema than in those with UPPE, whereas the serum BPI levels were similar between these two groups. In CPPE and empyema patients, the serum NGAL showed a positive correlation with the pleural fluid NGAL ( r = 0.417, p <  0.01). When combined with serum CRP, the sensitivity and specificity of serum calprotectin for identifying CPPE and empyema were the highest at 73.52% and 80.55%, respectively. Conclusions We concluded that serum calprotectin and NGAL were adjuvant serological markers for CPPE and empyema diagnosis. Patients present with pneumonia and pleural effusion signs in the chest x-ray and the combination of serum calprotectin and CRP constitutes a more highly sensitive and specific assay for identifying CPPE and empyema. Electronic supplementary material The online version of this article (10.1186/s12890-019-0877-8) contains supplementary material, which is available to authorized users.