The lipooligosaccharide-modifying enzyme LptA enhances gonococcal defence against human neutrophils

Abstract

Summary Infection with Neisseria gonorrhoeae (Gc) is marked by an influx of neutrophils to the site of infection. Despite a robust immune response, viable Gc can be recovered from neutrophil-rich gonorrheal secretions. Gc enzymatically modifies the lipid A portion of lipooligosaccharide by the addition of phosphoethanolamine (PEA) to the phosphate group at the 4’ position. Loss of LptA, the enzyme catalyzing this reaction, increases bacterial sensitivity to killing by human complement and cationic antimicrobial peptides. Here, we investigated the importance of LptA for interactions between Gc and human neutrophils. We found that lptA mutant Gc was significantly more sensitive to killing by human neutrophils. Three mechanisms underlie the increased sensitivity of lptA mutant Gc to neutrophils. 1) lptA mutant Gc is more likely to reside in mature phagolysosomes than LptA-expressing bacteria. 2) lptA mutant Gc is more sensitive to killing by components found in neutrophil granules, including CAP37/azurocidin, human neutrophil peptide 1, and the serine protease cathepsin G. 3) lptA mutant Gc is more susceptible to killing by antimicrobial components that are exocytosed from neutrophils, including those decorating neutrophil extracellular traps. By increasing the resistance of Gc to the bactericidal activity of neutrophils, LptA-catalyzed modification of lipooligosaccharide enhances survival of Gc from the human inflammatory response during acute gonorrhea.

Neisseria gonorrhoeae Defense against Human Neutrophils and Host-derived Antimicrobials

“…Freed Gc are no longer exposed to the high local concentrations of antimicrobial granule components found in NET structures. Additionally, we have found that LptA is an important factor for protecting Gc during exposure to NETs, which has previously been reported for N. meningitidis (discussed in Chapter 3) (Lappann et al, 2013;Handing and Criss, 2015).…”

“…However, they resist killing from the antimicrobial activity mediated by NETs. Gc and N. meningitidis modify the lipid A portion of their lipooligosaccharide (LOS) with phosphoethanolamine (PEA), which reduces susceptibility to killing by several neutrophil-derived antimicrobial components, and protects them from killing within NETs (Veal et al, 2002;Hobbs et al, 2013;Handing and Criss, 2015). Several of these antimicrobial components are known to decorate NETs, including LL-37 and cathepsin G (Lappann et al, 2013).…”

“…Shafer et al, 1998;Lewis et al, 2015). In particular, LptA modification improves Gc survival during neutrophil exposure, and directly contributes to Gc resistance to several neutrophil components including CAP37/Azurocidin, HNP-1 and cathepsin G (discussed in Chapter 3) (Handing and Criss, 2015). In addition, sialylation of LOS decreases binding of cathepsin G to the Gc surface (W.M.…”

“…We and others have shown that Gc induces NET release in vitro, but is not susceptible to NET-mediated killing (Gunderson and Seifert, 2015;Handing and Criss, 2015;Juneau et al, 2015). Gc expresses a thermonuclease (Nuc) that degrades the NET DNA backbone to facilitate Gc escape (Juneau et al, 2015).…”

“…During NET release, neutrophil DNA and histones mix together with antimicrobial granule contents before being released extracellularly to form the characteristic web-like structure. We have shown that Gc induces NET formation by human neutrophils in vitro and Gc has defenses against NETs, including release of a nuclease and phosphoethanolamine decoration of its lipooligosaccharide (Handing and Criss, 2015;Juneau et al, 2015). We hypothesized MtrCDE would confer protection to Gc that are immobilized in NETs and exposed to antimicrobial proteins in them, such as LL-37.…”