Pleural Fluid Proteomics From Patients With Pleural Infection Shows Signatures of Diverse Neutrophilic Responses: The Oxford Pleural Infection Endotyping Study (TORPIDS 2)

Pleural infection is a common and severe disease with increasing incidence worldwide. The endotypes of pleural infection remain unknown. A better understanding of patient variation in underlying biological response to infection may lead to improved treatments and clinical outcomes. We designed a study with the aim to endotype the disease and assess the association between patient phenotype, microbiology and clinical outcome.

We subjected 80 pleural fluid samples from the PILOT study, a prospective study on pleural infection, to unlabelled mass spectrometry. Proteins were retained if they were detected in at least 50% of the samples resulting in a total of 449 proteins. Unsupervised hierarchical clustering and UMAP analyses were used to cluster samples, Spearman and exact Fischer's methods were used for correlation assessment and protein expression was correlated with clinical outcomes.

UMAP plotting separated the samples in to two different and distinct cohorts. Pathway analysis of the differentially expressed proteins identified neutrophil degranulation, glycolysis, the pentose phosphate pathway, and the liver and retinoid X receptors (LXR-RXR) activation. Higher neutrophil degranulation was associated with increased glycolysis and pentose phosphate activation. Specimens dominated by Streptococcus Pneumoniae exhibited high neutrophil degranulation. Increased activity of the LXR-RXR pathway was associated with better survival.

Pleural infection patients exhibit proteomic signatures indicating diverse responses of neutrophil mediated immunity, glycolysis, and pentose phosphate activation which were associated with microbiology. Therapeutic targeting the LXR-XRX pathway with agonists may improve survival.