Pseudomonas aeruginosa lasR Mutants Resist Phagocytosis and Alter Inflammatory Cytokine Production by Cystic Fibrosis Macrophages

Cystic Fibrosis is characterized by chronic muco-obstructive lung disease and infection. People with CF (pwCF) are often colonized with Pseudomonas aeruginosa for years to decades, allowing for evolutionary adaptation. In chronic P. aeruginosa lung isolates from pwCF, the quorum sensing regulator LasR frequently is nonfunctional, however the factors enabling lasR loss-of-function (LOF) mutant selection are incompletely understood. We hypothesized that LOF mutations in lasR could allow P. aeruginosa to resist the selective pressure of phagocytosis. We found that in multiple strain backgrounds, LasR LOF decreased phagocytosis by both model THP-1 and primary monocyte-derived macrophages. While exogenous administration of the quorum-sensing autoinducer 3-oxo-C12-homoserine-lactone (3OC12HSL) that is made by an enzyme regulated by LasR activity inhibited phagocytosis and mitochondrial respiration, the phagocytosis resistance seen with lasR mutants appears to be bacterial cell intrinsic rather than due to secreted factors. Finally, we found that lasR LOF mutations altered the inflammatory profile upon infection of CF macrophages, with a shift from IL-1 family cytokine expression towards canonical inflammatory markers including IL-6 and TNFα. Collectively these data provide a potential explanation for both the prevalence of lasR mutants in the CF lung as well as their association with worse outcomes.