Functional and transcriptional adaptations of blood monocytes recruited to the cystic fibrosis microenvironment in vitro.

Cystic fibrosis (CF) lung disease is dominated by the recruitment of myeloid cells (neutrophils and monocytes) from blood, which fail to clear the lung of colonizing microbes. In prior in vitro studies, we showed that blood neutrophils migrated through well-differentiated lung epithelium into CF airway fluid supernatant (ASN) mimic the dysfunction of CF airway neutrophils in vivo, including decreased bactericidal activity despite an increased metabolism. Here, we hypothesized that, similar to neutrophils, blood monocytes would also undergo significant adaptations upon recruitment to CFASN. To test this hypothesis, primary human blood monocytes were transmigrated in our in vitro model into ASN from healthy control (HC) or CF subjects to mimic in vivo recruitment to normal or CF airways, respectively. Surface phenotype, metabolic and bacterial killing activities, and transcriptomic profile by RNA sequencing (RNASeq), were quantified post-transmigration. Unlike neutrophils, monocytes were not metabolically activated nor showed broad differences in activation and scavenger receptor expression upon recruitment to CFASN compared to HCASN. However, monocytes recruited to CFASN showed decreased bactericidal activity. RNASeq analysis showed large effects of transmigration on monocyte RNA profile with differences between CFASN and HCASN conditions, including in immune and antiviral signaling. While monocytes undergo qualitatively different adaptations from those seen in neutrophils upon recruitment to the CF airway microenvironment, their bactericidal activity is also dysregulated, which could explain why they also fail to protect CF airways from infection.