Abstract
Neutrophils, polymorphonuclear leukocytes (PMN), play a critical role in the innate immune response to Staphylococcus aureus, a pathogen that continues to be associated with significant morbidity and mortality. Neutrophil extracellular trap (NET) formation is involved in ensnaring and killing of S. aureus, but this host-pathogen interaction also leads to host tissue damage. Importantly, NET components including neutrophil proteases are under consideration as therapeutic targets in a variety of disease processes. Although S. aureus lipoproteins are recognized to activate cells via TLRs, specific mechanisms of interaction with neutrophils are poorly delineated. We hypothesized that a lipoprotein-containing cell membrane preparation from methicillin-resistant S. aureus (MRSA-CMP) would elicit PMN activation, including NET formation. We investigated MRSA-CMP-elicited NET formation, regulated elastase release, and IL-8 production in human neutrophils. We studied PMN from healthy donors with or without a common single-nucleotide polymorphism in TLR1, previously demonstrated to impact TLR2/1 signaling, and used cell membrane preparation from both wild-type methicillin-resistant S. aureus and a mutant lacking palmitoylated lipoproteins (lgt). MRSA-CMP elicited NET formation, elastase release, and IL-8 production in a lipoprotein-dependent manner. TLR2/1 signaling was involved in NET formation and IL-8 production, but not elastase release, suggesting that MRSA-CMP-elicited elastase release is not mediated by triacylated lipoproteins. MRSA-CMP also primed neutrophils for enhanced NET formation in response to a subsequent stimulus. MRSA-CMP-elicited NET formation did not require Nox2-derived reactive oxygen species and was partially dependent on the activity of peptidyl arginine deiminase (PAD). In conclusion, lipoproteins from S. aureus mediate NET formation via TLR2/1 with clear implications for patients with sepsis.