Cystic Fibrosis Sputum Impairs the Ability of Neutrophils to Kill Staphylococcus aureus

Abstract

Cystic fibrosis (CF) airway disease is characterized by chronic microbial infections and infiltration of inflammatory polymorphonuclear (PMN) granulocytes. Staphylococcus aureus (S. aureus) is a major lung pathogen in CF that persists despite the presence of PMNs and has been associated with CF lung function decline. While PMNs represent the main mechanism of the immune system to kill S. aureus, it remains largely unknown why PMNs fail to eliminate S. aureus in CF. The goal of this study was to observe how the CF airway environment affects S. aureus killing by PMNs. PMNs were isolated from the blood of healthy volunteers and CF patients. Clinical isolates of S. aureus were obtained from the airways of CF patients. The results show that PMNs from healthy volunteers were able to kill all CF isolates and laboratory strains of S. aureus tested in vitro. The extent of killing varied among strains. When PMNs were pretreated with supernatants of CF sputum, S. aureus killing was significantly inhibited suggesting that the CF airway environment compromises PMN antibacterial functions. CF blood PMNs were capable of killing S. aureus. Although bacterial killing was inhibited with CF sputum, PMN binding and phagocytosis of S. aureus was not diminished. The S. aureus-induced respiratory burst and neutrophil extracellular trap release from PMNs also remained uninhibited by CF sputum. In summary, our data demonstrate that the CF airway environment limits killing of S. aureus by PMNs and provides a new in vitro experimental model to study this phenomenon and its mechanism.

Sputum from People with Cystic Fibrosis Reduces the Killing of Methicillin-Resistant Staphylococcus aureus by Neutrophils and Diminishes Phagosomal Production of Reactive Oxygen Species

“…Our previous results demonstrated that PMNs isolated from PwCF killed MRSA CF clinical isolates to the same extent as PMNs derived from healthy individuals [10] To further confirm this observation, we recruited additional PwCF and age-and sex-matched healthy donors, and obtained the same result (Figure 1A). Additionally, we noticed that PMNmediated killing of only the reference strain, USA300, was impaired in PwCF (Figure 1A).…”

“…Overall, we propose that MRSA is predominantly killed in healthy PMNs via phagocytosis-initiated intracellular mechanisms. We have also shown previously that CF sputum impaired the ability of PMNs lated from healthy donors to kill CF clinical isolates of MRSA [10]. Next, we explo whether CF sputum had similar effects on PMNs isolated from the blood of PwCF, as w PMNs from PwCF were first exposed to the CF sputum cocktail and then infected w MRSA, according to our standard protocol.…”

“…We have also shown previously that CF sputum impaired the ability of PMNs isolated from healthy donors to kill CF clinical isolates of MRSA [10]. Next, we explored whether CF sputum had similar effects on PMNs isolated from the blood of PwCF, as well.…”

Neutrophil-derived extracellular vesicles promote feed-forward inflammasome signaling in cystic fibrosis airways

“…In fact, EVs can be generated from all of the cells present in the CF lung including, but not limited to the neutrophils and epithelial cells, such as macrophages, monocytes, T‐cells, as well as bacteria and fungus 42 . There have been recent studies that EVs from neutrophils can cause activation of other neutrophils, 43 and that EVs from S. aureus can down‐regulate the ability of neutrophils to kill bacterial pathogens 44 . EVs from CFTR‐mutated epithelial cells were able to activate neutrophils 45 and our study now documents communication in the other direction, that is, from neutrophils to epithelial cells.…”

“…42 There have been recent studies that EVs from neutrophils can cause activation of other neutrophils, 43 and that EVs from S. aureus can down-regulate the ability of neutrophils to kill bacterial pathogens. 44 EVs from CFTR-mutated epithelial cells were able to activate neutrophils 45…”