No abstract

Infiltration of neutrophils into colonic mucosa has been associated with the severity of ulcerative colitis (UC). We investigated the effect of disease microenvironment on the release of neutrophil extracellular traps (NETs) as well as the involved mechanisms in NETosis and whether certain NET proteins are correlated with disease phenotype. Peripheral blood neutrophils, sera, and colonic tissue were collected from treatment-naive and mesalazine-treated patients with active UC, treatment-naive patients with active Crohn's disease, patients suffering from infectious colitis, or healthy individuals (controls). Analysis of colonic biopsy specimens and peripheral blood neutrophils for the presence of NET-related markers using immunofluorescence confocal microscopy, ELISA, immunoblotting, flow cytometry, and quantitative PCR were performed. In vitro cell and tissue culture systems were further deployed. The local inflammatory response in colon in UC, but not Crohn's disease, is characterized by the presence of NETs carrying bioactive IL-1β and thrombogenic tissue factor. The inflammatory environment of UC is able to induce neutrophil activation, IL-1β expression, and NET release, as shown both ex vivo and in vitro. REDD1 expression, as a mediator linking inflammation, autophagy, and NET release, was also specifically associated with the inflammatory response of UC. We show that neutrophil expression of REDD1 in colon tissue and the presence of IL-1β in neutrophils/NETs provide candidate biomarkers for the differential diagnosis of inflammatory colitis and possible targets for the treatment of UC, suggesting that UC shares common features with autoinflammatory disorders.

This study provides a link between stress and initiation of inflammatory attacks in patients with FMF. REDD1 emerges as a regulator of neutrophil function upstream to pyrin, is involved in NET release and regulation of IL-1β, and might constitute an important piece in the IL-1β-mediated inflammation puzzle.

eMacrolide antibiotics have been shown to act as immunomodulatory molecules in various immune cells. However, their effect on neutrophils has not been extensively investigated. In this study, we investigated the role of macrolide antibiotics in the generation of neutrophil extracellular traps (NETs). By assessing ex vivo and in vivo NET formation, we demonstrated that clarithromycin is able to induce NET generation both in vitro and in vivo. Clarithromycin utilizes autophagy in order to form NETs, and these NETs are decorated with antimicrobial peptide LL-37. Clarithromycin-induced NETs are able to inhibit Acinetobacter baumannii growth and biofilm formation in an LL-37-dependent manner. Additionally, LL-37 antimicrobial function depends on NET scaffold integrity. Collectively, these data expand the knowledge on the immunomodulatory role of macrolide antibiotics via the generation of LL-37-bearing NETs, which demonstrate LL-37-dependent antimicrobial activity and biofilm inhibition against A. baumannii.