The Macrophage in Cystic Fibrosis

Background: Cystic fibrosis (CF) is caused by absent/defective CF transmembrane conductance regulator protein (CFTR). CF is characterized by thick airway mucus, chronic infection and neutrophil inflammation leading to respiratory failure. I analysed airway macrophages (MΦs) and their expression of pattern recognition receptors (PRRs) in CF, since these cells are crucial to airway immune defence and they can orchestrate inflammation. I also performed transcript analysis of CF monocyte-derived MΦs (MDMs). Methods: Sputum was induced in CF paediatric and adult cohorts. Phenotype and function of CF MΦ were determined by flow cytometry and compared to controls. Monocytes (>92% purity) were grown in vitro to generate MDMs (n=15). Transcripts encoding the entire human genome were analysed (n=5) and expression of individual genes were confirmed by RT-PCR. Results: In classical CF (n=10) there was an increase in the proportion of monocyte-like small MΦs (of total MΦ) compared to controls (n=10) (73 ± 18% and 16 ± 8%, respectively, p< 0.0001). In non-classical CF (n=4), with milder lung disease, small MΦs increased to 31 ± 20% (p>0.05). PRRs were absent on small MΦs from CF and control. In contrast, clear expression could be detected on large MΦs from control but not CF. In line with this, CF small MΦs showed a strongly reduced uptake of particles compared to controls. Microarray analysis of MDMs revealed α- and β-tryptase as being significantly higher under constitutive and stimulated conditions in CF compared to control. However, using RT-PCR, expression of α- and β-tryptase was similar between groups. Conclusions: The phenotype of small MΦs in CF suggests that these cells are newly recruited monocytes from blood. Low expression of PRRs on these cells in CF and their reduced uptake indicates a reduced capacity to clear inhaled particles, which may contribute to further damage in CF. Further to this I was unable to confirm any transcript differences between CF and control MDMs due to mutant CFTR.