The Effects of CFTR and Mucoid Phenotype on Susceptibility and Innate Immune Responses in a Mouse Model of Pneumococcal Lung Disease

Abstract

Recent studies have reported the isolation of highly mucoid serotype 3 Streptococcus pneumoniae (Sp) from the respiratory tracts of children with cystic fibrosis (CF). Whether these highly mucoid Sp contribute to, or are associated with, respiratory failure among patients with CF remains unknown. Other mucoid bacteria, predominately Pseudomonas aeruginosa, are associated with CF respiratory decline. We used a mouse model of CF to study pneumococcal pneumonia with highly mucoid serotype 3 and non-mucoid serotype 19A Sp isolates. We investigated susceptibility to infection, survival, and bacterial counts from bronchoaviolar lavage samples and lung homogenates, as well as associated inflammatory cytokines at the site of infection, and lung pathology. Congenic CFTR–/– mice and wild-type (WT)-mice were infected intranasally with CHB756, CHB1126, and WU2 (highly mucoid capsular serotype 3, intermediately mucoid serotype 3, and less mucoid serotype 3, respectively), or CHB1058 (non-mucoid serotype 19A). BAL, lung homogenates, and blood were collected from mice 5 days post-infection. Higher CFU recovery and shorter survival were observed following infection of CFTR–/– mice with CHB756 compared to infection with CHB1126, WU2, or CHB1058 (P≤0.001). Additionally, CFTR–/– mice infected with CHB756 and CHB1126 were more susceptible to infection than WT-mice (P≤0.05). Between CFTR–/– mice and WT-mice, no significant differences in TNF-α, CXCL1/KC concentrations, or lung histopathology were observed. Our results indicate that highly mucoid type 3 Sp causes more severe lung disease than non-mucoid Sp, and does so more readily in the lungs of CFTR–/– than WT-mice.

Hyperencapsulated mucoid pneumococcal isolates from patients with cystic fibrosis have increased biofilm density and persistence in vivo

“…Here, our results support the association of a highly mucoid Sp with poor prognosis in CFTR -/mice. Previous work showed no difference in pro-inflammatory cytokine secretion or recruitment of neutrophils to sites of infection between WT and CFTR -/mice infected with mucoid pneumococci (Dennis et al 2015), thus high susceptibility to infection in CF lungs has been attributed in part to bacterial adaptation within the CF airways, specifically to the transition of bacteria to mucoid phenotypes (Martin et al 1993) and biofilm formation (Lee et al 2011). Our observations that mucoid type 3 Sp isolates appear more frequently in the lungs of CF patients than in normal individuals is consistent with previous reports (Hoiby et al 1976), and that CFTR -/mice are more susceptible to highly mucoid Sp than WT-mice, both support the hypothesis that mucoid pneumococci may have an advantage in the environment of the CF lung that may lead to chronic infection.…”

“…Our study demonstrated that mucoid pneumococcal colony phase variants may also have a selective advantage in CF lung disease. Using an aspiration pneumonia disease model, we previously demonstrated more severe pneumococcal lung disease in in CFTR -/mice compared to WT-mice infected with type 3 Sp strains isolated from CF patients (Dennis et al 2015), suggesting that mucoid capsular serotype 3 Sp could exploit the CF defect of the CFTR -/mice. Lack of CFTR in transgenic CF mice has similarly been shown to lead to increased levels of P. aeruginosa in the lung, which are associated with hypersusceptibility of CF mice to mucoid P. aeruginosa infection (Gosselin et al 1998;Williams, Dehnbostel and Blackwell 2010).…”

“…The reaction products were separated by agarose electrophoresis, and visualized under UV light. All of the Sp type 3 strains were observed to be mucoid based on their colony morphology (Dennis et al 2015). Bacteria were cultured at 37 • C in Todd-Hewitt broth containing 0.5% yeast extract (THY) and stored at −80 • C in 10% glycerol.…”

A Review of CXCL1 in Cardiac Fibrosis

“…Besides, CXCL1 is a novel marker for evaluating the severity of chronic obstructive pulmonary disease ( 28 , 53 ). CXCL1 is also involved in airway remodeling, asthma and cystic fibrosis in lung ( 54 – 56 ).…”