Demonstration of extracellular traps in tuberculous pleural effusion from adult patients.

In pleural tuberculosis (TB), pleural effusion is typically characterized by a lymphocytic-rich exudate; however, neutrophils and macrophages predominate during the initial phase of infection. These immune cells are known to combat pathogens via phagocytosis, degranulation, and formation of extracellular traps (ETs)-a recently recognized defence mechanism. Although in-vitro and in-vivo studies have demonstrated ETs formation during Mycobacterium tuberculosis infection, their presence in clinical samples of patients with pleural TB has not been previously demonstrated. In this study, we employed multiple methods to demonstrate the presence of ETs in tuberculous pleural effusion (TPE) from patients with confirmed TB (Xpert MTB/RIF-positive/culture-positive/pleural biopsy Ziehl-Neelsen-stainingacid fast bacilli-positive). Immunofluorescence microscopy revealed DNA co-localized with ET markers like myeloperoxidase, neutrophil elastase, and citrullinated histones-confirming ETs in TPE samples, and this was further supported by immunoblotting. Proteomic analysis of TPE samples revealed the presence of key ET-associated proteins, including histones, myeloperoxidase, matrix metalloproteinase-9, and the S100A8/A9 complex. Protein-protein interaction and gene ontology analyses revealed that these proteins are involved in ET-related biological processes, such as neutrophil degranulation and collagen degradation. To the best of our knowledge, this is the first clinical evidence of ETs in TPE, suggesting a potential role in the immunopathogenesis of pleural TB.