Innate Immunity Mediated by TLR5 as a Novel Antiinflammatory Target for Cystic Fibrosis Lung Disease

Abstract

Novel therapies to target lung inflammation are predicted to improve the lives of people with cystic fibrosis (CF) but specific antiinflammatory targets have not been identified. The goal of this study was to establish whether TLR5 signaling is the key molecular pathway mediating lung inflammation in CF, and to determine whether strategies to inhibit TLR5 can reduce the damaging inflammatory response. The innate immune responses were analyzed in both airway epithelial cells and primary PBMCs from CF patients and matched controls. Additionally, 151 clinical isolates of Pseudomonas aeruginosa from CF patients were assessed for motility and capacity to activate TLR5. Blood and airway cells from CF patients produced significantly more proinflammatory cytokine than did control cells following exposure to the CF pathogens P. aeruginosa and Burkholderia cepacia complex (p < 0.001). Stimulation with pure TLR ligands demonstrated that TLR signaling appears to mediate the excessive cytokine production occurring in CF. Using complementary approaches involving both neutralizing Ab targeting TLR5 and flagellin-deficient bacteria, we established that inhibition of TLR5 abolished the damaging inflammatory response generated by CF airway cells following exposure to P. aeruginosa (p < 0.01). The potential therapeutic value of TLR5 inhibition was further supported by our demonstration that 75% of clinical isolates of P. aeruginosa retained TLR5 activating capacity during chronic CF lung infection. These studies identify the innate immune receptor TLR5 as a novel antiinflammatory target for reducing damaging lung inflammation in CF.

Flagellin Induces Myeloid-Derived Suppressor Cells: Implications for Pseudomonas aeruginosa Infection in Cystic Fibrosis Lung Disease

“…Importantly, flagellin-deficient P. aeruginosa bacteria were significantly impaired in inducing MDSCs, supporting the idea that the effect of P. aeruginosa in vivo and in vitro is mainly mediated through flagellin. The significance of the flagellin-TLR5 axis in P. aeruginosa-host interactions has been previously demonstrated in numerous studies, including experimental infection models using epithelial cells (1,2,5,17,19,20), macrophages (21), neutrophils (18), or in vivo infection strategies (3,22,23). Our study thereby confirms and extends the concept that flagellin acts as a key player in shaping the innate but also the adaptive immune response to P. aeruginosa in CF lung disease and beyond.…”

“…Because our CF patient cohort was characterized by a clear predominance of nonmucoid P. aeruginosa isolates and MDSCs tended to be higher in CF patients featuring nonmucoid than mucoid P. aeruginosa isolates, we speculate that P. aeruginosa-derived flagellin plays an essential role in MDSC induction, at least in pediatric CF cohorts. However, future studies in adult CF patients with a higher proportion of mucoid P. aeruginosa phenotypes, using methods such as the swimming motility assays (5), are required to assess whether motile P. aeruginosa and functional flagella are required to induce MDSCs in CF in vivo. Moreover, representative longitudinal studies should address the question whether MDSCs can be predictive for the course of CF lung disease, such as disease exacerbations.…”

“…3A). To dissect which mechanism(s) induce(s) MDSCs in chronic P. aeruginosa infection, we focused on flagellin because 1) infection with flagellated P. aeruginosa was associated with MDSC induction in our CF patient cohort, whereas nonflagellated microbes did not show any association with MDSCs in vivo; and 2) previous studies showed that among different PAMPs, flagellin recognition through TLR5 in particular plays a key role in leukocyte-P. aeruginosa interactions in CF lung disease (4,5,17,18). Our studies demonstrated that flagellin efficiently and dose-dependently induced MDSCs with a more potent capacity than GM-CSF did (Fig.…”

“…P. aeruginosa potently activates the innate arm of the immune system, an effect mainly mediated through pathogenassociated molecular patterns (PAMPs) and pattern recognition receptors. Among those, the TLR 5 ligand flagellin was found to play a key role in the recognition of P. aeruginosa (1)(2)(3)(4)(5). However, patients with chronic lung diseases, prototypically cystic fibrosis (CF) patients (6), are unable to eradicate the bacterium efficiently.…”

Over-activation of TLR5 signaling by high-dose flagellin induces liver injury in mice

“…20 TLR5 signaling is a key molecular pathway that mediates lung inflammation during cystic fibrosis. 21 The flagellin-TLR5 axis might also trigger cardiac innate immune responses and result in cardiovascular dysfunction. 22 Consistent with previous reports, 23,24 we previously demonstrated that either intranasally or intraperitoneally administered flagellin could induce a significant increase in the serum aminotransferase levels in mice, 25 suggesting that flagellin might be a potent inducer of liver damage.…”