The role of T-cell immunoglobulin and mucin-domain-containing molecules in inflammation in the cystic fibrosis airways
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The T-cell immunoglobulin and mucin-domain containing molecules (TIMs) have emerged as promising therapeutic targets to correct abnormal immune function in several autoimmune and chronic inflammatory conditions. It has been reported that proinflammatory cytokine dysregulation and neutrophil-dominated inflammation are the main causes of morbidity in cystic fibrosis (CF). However, the role of TIM receptors in CF has note been investigated. The aim of this study was to determine if TIM signalling mechanisms are implicated in the pathogenesis of CF lung disease.
Initially, we characterised TIMs expression in human bronchial epithelial cells. we report for the first time that TIM-1 and TIM-3 are constitutively overexpressed on the CF airway epithelial cell surface. These results were corroborated in patient bronchial brushing samples suggesting a link between CFTR function and TIM expression. Of note, blockade of CFTR function with the CFTR inhibitor-172 caused upregulation of TIM-3 and its ligand galectin-9 in normal cells. Furthermore, TIM-3 was established as a functional receptor in bronchial epithelial cells as galectin-9 induced TIM-3 phosphorylation, resulting in IL-8 and IL-17A production. We have also confirmed that the expression of TIM-3 and its ligand galectin-9 can be modulated by lipopolysaccharide (LPS) which emphasizes the role of TIM-3 under inflammatory conditions.
Additionally, TIM-3 expression was localised on resting and primed neutrophil plasma membrane. Our data suggest a novel role for TIM-3/galection-9 in neutrophil function with potentially important consequences in neutrophil antimicrobial activity. Galectin-9 was found to modulate neutrophil activation triggering mitogen activated protein kinase (MAPK) signalling cascades and calcium mobilisation. We also provided evidence for a role of galection-9 in neutrophil degranulation and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, possibly via TIN-3 interactions. We have demonstrated that TIM-3 expressed on neutrophils plays a direct role in bacterial killing. Opsonisation of PA with a physiologically relevant dose of galectin-9 (50 nM) enhanced eeutrophil-mediated bacterial killing by 25%, and effect abrogated by blockade of neutrophil TIM-3 receptors. This mechanism appeared to be gram-negative bacteria specific and mediate via galectin-9/LPS binding.
Collectively our data revealed a novel role for TIM-3/galectin-9 in the modulation of the inflammatory response in the airways. Under acute inflammatory conditions in the normal lung, galectin-9 and TIM-3 expression would be upregulated in bronchial epithelial cells leading to production of chemokines and neutrophil recruitment to fight bacterial infections. In addition, gram-negative bacteria would be specificaly opsonised by galectin-9 favouring interaction with neutrophils and enhancing neutrophil-mediated bacterial killing. However, in the CF lung, both TIM-3 and its ligand galectin-9 undergo rapid degradation by neutrophil derived proteases, in particular neutrophil elastase and proteinase 3, potentially contributing to the defective bacterial clearance observed within the CF lung despite the high neutrophilic presence.