Bacteria Strain‐Specific Chlorinated Lipid Production in Neutrophils

Abstract

Neutrophils play vital roles in host defense against infections and acute inflammation. They are the major type of white blood cells first to arrive at the site of infection. Neutrophils are equipped with three major microorganism-killing mechanisms: phagocytosis, release of antibacterial enzymes, and formation of neutrophil extracellular traps (NET). During neutrophil activation, the primary granules release myeloperoxidase (MPO), which is a major antibacterial enzyme. MPO catalyzes hydrogen peroxide and chloride to produce hypochlorous acid (HOCl). HOCl has a significant role as an antimicrobial agent and can also have deleterious effects on host cells. Previous studies have shown that HOCl targets vinyl ether bond at the sn-1 position of plasmalogen phospholipids to liberate 2-chlorofatty aldehyde (2-ClFALD). 2-ClFALD further gets oxidized to 2-chlorofatty acids (2-ClFA). 2-ClFALD and 2-ClFA are linked with inflammatory diseases such as endotoxemia, sepsis and atherosclerosis. The roles of 2-ClFALD and 2-ClFA have been explored in endothelial dysfunction, endoplasmic reticulum stress, apoptosis in monocytes, neutrophil chemotaxis and as a mediator of NET formation. Here we tested the hypothesis that the neutrophils are activated by bacterial stimuli to produce 2-ClFALD and 2-ClFA and the production may vary with the bacterial strain. We co-cultured human neutrophils with CFT073 and JM109, pathogenic and non-pathogenic E.coli strains, respectively. 2-ClFALD production was significantly increased when neutrophils were incubated with either E.coli strains compared to control neutrophils. Interestingly, 2-ClFA was only increased in CFT073 co-culture. We have also observed that neutrophils killed more JM109 cells compared to CFT073 cells. However, CFT073 induced more NET formation suggesting the higher 2-ClFA might be mediating NET formation. Furthermore, JM109 was more susceptible to killing by 2-ClFALD and 2-ClFA indicating their potential role in bactericidal activity. 2-ClFA and 2-ClFALD production was significantly reduced in neutrophil and E.coli co-cultures by the addition of amino triazole (ATZ), an MPO inhibitor, and glutathione (GSH) that makes GSH-FALD adduct as a 2-ClFALD scavenger. ATZ treatment also reduced bacterial killing ability suggesting that MPO is an essential component of neutrophil antibacterial mechanisms. In contrast, GSH supplementation increased bacterial killing capacity. Taken together, these findings suggest that specific bacterial strains play a significant role in neutrophil derived chlorinated lipid production, which may also differentiate their susceptibility to neutrophil killing.