Parapneumonic effusions show high concentrations of neutrophil extracellular traps (nets) derived from mitochondrial dna

SESSION TITLE: Pleural Effusions SESSION TYPE: Original Investigations PRESENTED ON: 10/10/2023 10:30 am - 11:30 am PURPOSE: Parapneumonic effusions are known to be highly inflammatory pleural collections. Our previous study showed very high concentrations of NETs in parapneumonic effusions compared to effusions of other etiologies (1). This study aims to extend our knowledge of the inflammatory nature of parapneumonic effusions and empyema. We investigated the source of extracellular DNA as well as various biomarkers within pleural effusions of different causes. METHODS: 112 samples of fluid were collected from patients seeking hospital treatment for undifferentiated pleural effusion and analysed for cytology, microbiology and biochemical findings. Specimens were classified based on these criteria and clinical judgement into four groups (parapneumonic, malignant, transudative and unclassifiable). Concentrations of soluble urokinase plasminogen activator receptor (suPAR), interleukin-6 (IL-6), plasminogen activator inhibitor-1 (PAI-1) and transforming growth factor 1-beta (TGF1-b) were quantified by enzyme-linked immunosorbent assay (ELISA). Mitochondrial DNA (mtDNA) and nuclear DNA (nucDNA) in specimens were measured in pleural effusion cell free supernatant using polymerase chain reaction (PCR) and reported as mean cycle threshold (meanCt, 40 cycle as limit of detection). Differences between groups were analyzed using Kruskal-Wallis one-way analysis of variance. Correlations used Spearman coefficient. Receiver operating characteristic (ROC) curves were calculated. RESULTS: Effusions were classified into four groups: parapneumonic (n=29), malignant (n=36), transudative (n=21) and unclassifiable (n=26). Concentrations of PAI-1 and TGF1-b were not significantly different between groups. IL-6 concentrations were significantly higher in the parapneumonic group than in the malignant and transudative group but not in the unclassifiable group (median IL-6, 177 ng/mL vs 12 ng/mL, 5.6 ng/mL and 28.55 ng/mL [P < 0.03, P < 0.001 and P = 0.16 respectively]). suPAR concentrations were also significantly higher in the parapneumonic group than in the malignant and transudative groups but not in the unclassifiable group (median suPAR, 109.1 mg/mL vs 38.18, 20.25 and 51.45 ng/mL [P < 0.015, P < 0.001 and P =0.59 respectively]). Mean Ct values for mtDNA were significantly lower in the parapneumonic group compared with the other three groups (median mtDNA Ct 22.41 vs 39.85, 40 and 40 [P < 0.001]), indicating much higher concentrations of mtDNA. Mean Ct nucDNA did not show significant differences between groups. Citrullinated histone 3 (citH3) was highly correlated with mtDNA in the parapneumonic group (Spearman r = -0.74, P < 0.002). CONCLUSIONS: Very high IL-6 and suPAR concentrations in parapneumonic effusions likely reflect aggressive immune stimulus. High concentrations of mtDNA in parapneumonic effusions are highly correlated with markers of NETs. This also reflects the highly activated inflammatory environment present in parapneumonic effusions. These findings have not been previously described in pleural effusions. CLINICAL IMPLICATIONS: This study further delineates the nature of highly inflammatory parapneumonic effusions. Further study is required to determine how this inflammatory environment may be modified. DISCLOSURES: No relevant relationships by Katie Baines No relevant relationships by Peter Gibson No disclosure on file for Christopher Grainge No relevant relationships by Michael Schuliga No relevant relationships by Scott Twaddell