Title: Importance of the adaptive immunity in the pathophysiology of Cystic Fibrosis lung inflammation
Other Titles: Belang van de adaptieve immuniteit in de pathofysiologie van Cystic Fibrosis longinflammatie
Authors: Decraene, Ann
Issue Date: 7-Dec-2011
Abstract: Cystic Fibrosis (CF) is a life-shortening genetic disease affecting 70,000 people worldwide. The major cause of morbidity and mortality in CF is lung damage caused by the vicious cycle of chronic infection and inflammation. A major factor in the respiratory health of CF subjects is chronic infection with pathogens. The most common colonizers in CF are P. aeruginosa and S. aureus and they affect progression of lung disease. It is still not fully understood how the basic genetic defect leads to chronic, neutrophilic inflammation and controversy still exists concerning the influence of the genetic defect on immune cells. Since no therapy is available yet providing a full cure for CF, the focus is on the prevention of lung damage and to slow down the decline of lung function and thus improving quality of life. We hypothesized that the exaggerated neutrophilic inflammation in CF airways is mediated by an abundant presence of Th17 cells and/or Th17 derived cytokines. We aimed to investigate the role of different T cell populations in the early onset of inflammation and whether there is a dysfunctional immune system in CF.Our first aim was to detect the presence of Th17 derived cytokines in CF sputum and to evaluate whether the Th17 response is associated with a more severe lung disease in patients with CF. We showed the presence of IL-17A protein and mRNA and IL-23 mRNA in sputum of a group of stable patients with elevated levels compared to healthy control subjects. These results suggest a potential role for the IL-23/IL-17A axis in CF lung inflammation and confirm that the adaptive immune system is involved in the pathophysiology of CF lung disease. Chronic infection with P. aeruginosa appears to be associated with higher mRNA expression of these cytokines in CF airways while infection with S. aureus did not seem to elevate mRNA levels. IL-17A and IL-23 levels were not correlated with the number of neutrophils present in sputum and also not with the lung function. We also measured the immunosuppressive markers Foxp3 and IL-10 in sputum of these adults with CF. We found significantly elevated levels of both markers compared to healthy controls.Our data suggest a role for the adaptive immunity in two conditions complicating CF, namely CF-related asthma and ABPA. CF-A results in higher levels of sputum eosinophils, IL-5 and IL-17A mRNA, but low IFN-γ. In the ABPA group, if we compared them with non-asthmatic, non-ABPA patients with CF, we found significantly elevated IL-17A levels, but not IL-5 in sputum. We did not find increased eosinophils in ABPA patients, probably due to the fact that some patients were taking oral steroids. In a separate study, we investigated the effects of azithromycin (AZI), an antibiotic agent with anti-inflammatory properties. AZI did not significantly affect IL-17A levels after 3 months of treatment. TNF-α mRNA levels decreased, although not statistically significant.In children with CF, we found a IL-5/IL-17A high but IFN-γ low profile and also elevated sputum neutrophils and eosinophils. We compared children with CF with a group of children with non-CF Bx. They showed the same neutrophilic inflammatory pattern as well as a IL-17A high profile in sputum. Children with non-CF Bx did not have elevated eosinophils. We found fluctuating cytokine levels, but no change in lung function and sputum neutrophils over 1 year. In the children, IL-17A levels were not associated with chronic P. auruginosa infection, but we did find an association with number of exacerbations. One or more exacerbations over 1 year resulted in higher IL-17A levels. To study the role of Th17 cells and cytokines in the early onset of inflammation, we also used a CF mouse model and evaluated spontaneous inflammation in unstimulated mice at different ages. We used the gut-corrected CFTR knock-out mouse model and evaluated them at 10, 20 and 30 weeks and compared results with littermate WT and heterozygous (H) control mice. No signs of inflammation were found, nor in BAL fluid, nor on histology. We did find structural and/or mechanical abnormalities in 20 and 30 week old CF mice when measuring both airway and tissue resistance and tissue elastance with invasive lung function measurements. Lungs of CF mice were stiffer and there was a higher airway resistance as compared to WT and H mice. In 10 week old CF mice, this difference was already present, but not yet significant, suggesting a progressive obstructive lung disease phenotype, which could not be explained by inflammatory changes. Due to the lack of spontaneous inflammation in our CF mouse model, subsequent experiments consisted of exposing mice to a trigger that would activate the immune system. This trigger needed to resemble the first infectious trigger children with CF were likely to undergo, namely chronic infection of upper airways with S. aureus. Staphylococcal enterotoxin B (SEB), an enterotoxin produced by S. aureus was administered intranasally in 10 week old CF, WT and H mice was therefore used. CF mice exposed to SEB showed an increased airway hyperreactivity to MCh and had significantly elevated BAL neutrophils compared to CF mice exposed to saline. In H mice, we saw a similar, yet not significant result while there was no difference in WT mice. Neutrophils present in the BAL fluid, were active since we found elevated levels of MPO. The neutrophilia in BAL of CF SEB mice was not associated with elevated IL-17A protein levels in BAL fluid, which does not agree with the role of the Th17 pathway in causing the early lung inflammation in our CF mice. Additional studies involving different triggers are required to further elucidate the involvement of the Th17 cells/cytokines.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Pneumology
Laboratory of Pediatric Immunology
Pediatric Pulmonology Section (-)

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