(405) Neutrophil Defect and Pathogen Selection in Cystic Fibrosis

Background: Cystic fibrosis (CF) is a life-threatening genetic disorder caused by mutations in the CF Transmembrane-conductance Regulator (CFTR) chloride channel. Clinically, over 90% of CF patients die of lung complications precipitated by chronic bacterial infections, predominantly by Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA). Despite the well-characterized molecular defect and clearly defined clinical sequelae of CF, the critical link between the chloride channel defect and the host defense failure against these pathogens has not been established. Our previous research has reported that neutrophils from CF patients are defective in phagosomal production of hypochlorous acid (HOCl), a potent microbicidal oxidant. Here we report our studies to investigate if this defect leads to a disproportional killing of CF and non-CF pathogens, thus providing a survival advantage to CF pathogens.

Methods: A polymicrobial mixture of CF pathogens (PA and SA) and non-CF pathogens (Streptococcus pneumoniae (SP), Klebsiella pneumoniae (KP), and Escherichia coli (EC)) was formed. This mixture was exposed to escalating doses of HOCl in vitro; subjected to killing via HL-60-derived wild-type and CF neutrophils; and intubated into the lungs of wild-type, myeloid lineage-specific CF, and full-body CF mice.

Results: Data revealed that the CF pathogens withstood higher doses of HOCl than the non-CF pathogens. Neutrophil-mediated killing of the bacterial mixture revealed differential susceptibilities for different pathogens, and the CF pathogens prevailed in CF neutrophil killing, especially in a chloride-deficient environment. When the polymicrobial mixture was intubated into the lungs of wild-type and CF mice, the CF pathogens outcompeted the non-CF pathogens, and exhibited greater survival in the CF lungs.

Conclusions: CFTR loss of function in neutrophils leads to HOCl production deficiency and creates an environment advantageous to CF pathogen survival, which may serve as a pathogen selection mechanism in the lungs of CF patients.

Acknowledgements: This work was supported by the National Institutes of Health [grant numbers AI140088 and HL150370] and the Cystic Fibrosis Foundation [grant number WANG18I0].

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