Distinct susceptibilities of corneal Pseudomonas aeruginosa clinical isolates to neutrophil extracellular trap-mediated immunity.

Ocular bacterial keratitis, often associated with Pseudomonas aeruginosa bacterial infection, commonly occurs in contact lens wearers and may lead to vision impairment. In this study, we analyzed the contribution of neutrophil extracellular traps (NETs) to the mediation of protection during ocular keratitis. Both invasive and cytotoxic P. aeruginosa clinical isolates induced NET release by neutrophils. NETs carried the characteristic histone proteins, elastase, lysozyme, myeloperoxidase, and metabolic enzymes. While the invasive P. aeruginosa strains PAO1 (serogroup O5) and 6294 (serogroup O6) were trapped by NETs, the cytotoxic P. aeruginosa strains 6077, 6206 (serogroup O11), and PA14 (serogroup 010) were less sensitive to NET capture. The mechanism of escape by the cytotoxic strains from adhesion to NETs involved the shedding of outer membrane vesicles (OMVs) that outcompeted the cytotoxic P. aeruginosa strains for NET binding. When ocular infection was caused by an invasive strain in vivo, NETs were released at the ocular surface to capture bacteria, limiting their spread. Treatment with MNase I had a dose-dependent effect, with low doses of MNase speeding up bacterial clearance and high doses of MNase having toxic consequences. Cumulatively, our data suggest that NET-mediated immunity is a two-step process. Initially, pathogens attach to NET fragments; subsequently, upon nuclease activity, active serine proteases, which proteolytically degrade NET-associated proteins and promote DNase activity, are released. Therefore, a balance between NET production and NET degradation is needed to achieve maximal NET immunity.