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Vascular permeability is temporarily heightened during inflammation, but excessive inflammation‐associated microvascular leakage can be detrimental, as evidenced in the inflamed lung. Formylated peptides regulate vascular leakage indirectly via formylated peptide receptor‐1 (FPR1)‐mediated recruitment and activation of neutrophils. Here we identify how the GTPase‐activating protein ARAP3 protects against formylated peptide‐induced microvascular permeability via endothelial cells and neutrophils. In vitro, Arap3−/− endothelial monolayers were characterised by enhanced formylated peptide‐induced permeability due to upregulated endothelial FPR1 and enhanced vascular endothelial cadherin internalisation. In vivo, enhanced inflammation‐associated microvascular leakage was observed in Arap3−/− mice. Leakage of plasma protein into the lungs of Arap3−/− mice increased within hours of formylated peptide administration. Adoptive transfer experiments indicated this was dependent upon ARAP3 deficiency in both immune and non‐immune cells. Bronchoalveolar lavages of formylated peptide‐challenged Arap3−/− mice contained neutrophil extracellular traps (NETs). Pharmacological inhibition of NET formation abrogated excessive microvascular leakage, indicating a critical function of NETs in this context. The observation that Arap3−/− mice developed more severe influenza suggests these findings are pertinent to pathological situations characterised by abundant formylated peptides. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland. [ABSTRACT FROM AUTHOR]

Pneumococcal lung infections represent a major cause of death worldwide. Single nucleotide polymorphisms (SNPs) in the NFKBIZ gene, encoding the transcription factor IκBζ, are associated with increased susceptibility to invasive pneumococcal disease. We hence analyzed how IκBζ might regulate inflammatory responses to pneumococcal infection. We first demonstrate that IκBζ is expressed in human blood monocytes but not in bronchial epithelial cells, in response to wild type pneumococcal strain D39. D39 transiently induced IκBζ in a dose dependent manner, with subsequent induction of downstream molecules involved in host defense. Of these molecules, IκBζ knockdown reduced the expression of IL-6 and GMCSF. Furthermore, IκBζ overexpression increased the activity of IL-6 and GMCSF promoters, supporting the knockdown findings. Pneumococci lacking either pneumolysin or capsule still induced IκBζ. While inhibition of TLR1/TLR2 blocked D39 induced IκBζ expression, TLR4 inhibition did not. Blockade of p38 MAP kinase and NFκB suppressed D39 induced IκBζ. Overall, our data demonstrates that IκBζ regulates monocyte inflammatory responses to Streptococcus pneumoniae by promoting the production of IL-6 and GMCSF. [ABSTRACT FROM AUTHOR]

Lung epithelial cell death is critical to the lung injury that occurs in the acute respiratory distress syndrome. It is known that FasL plays a prominent role in this lung cell death pathway and may work in part through activation of the receptor interacting protein-2 (RIP2). RIP2 is serine/threonine kinase with a C-terminal caspase activation and recruitment domain (CARD). This CARD contains a highly conserved, predicted tyrosine phosphorylation site. Thus, involvement of tyrosine phosphorylation in the CARD domain of RIP2 may play a critical role in Fas-mediated apoptosis in the human lung immune system. To test this hypothesis, human lung epithelial cells (BEAS-2B) were induced to undergo cell death in response to the Fas agonist antibody CH11 with and without manipulation of endogenous RIP2 concentrations. We show that CH11 increases lung epithelial cell death in a dose-dependent manner as determined by LDH release and nuclear condensation. Fas-induced LDH release was inhibited by RIP2 knock-down. Reduced levels of RIP2 in BEAS-2B cells after treatment with RIP2 siRNA were confirmed by immunoblot. Overexpression of RIP2 in BEAS-2B cells synergized with Fas ligand-induced LDH release in a dose-dependent manner. Finally, mutation of the tyrosine phosphorylation site in CARD of RIP2 protected BEAS-2B cells from Fas ligand induced cell death. Thus RIP2's CARD tyrosine phosphorylation may represent a new therapeutic target to promote the survival of human lung epithelial cells in disorders that lead to acute lung injury and ARDS. [ABSTRACT FROM AUTHOR]