Oxidative mechanisms utilized by human neutrophils to destroy Escherichia coli

Abstract

Serum-opsonized bacteria are efficiently ingested and killed by neutrophils within the phagocytic vacuole, where they are exposed to an array of reactive oxygen metabolites and toxic lysosomal components. Although bacteria may be destroyed by oxygen-independent mechanisms alone, many types of bacteria are not killed effectively unless they are attacked by oxygen metabolites. However, the apparent inability of extracellular scavengers, or inhibitors, of oxygen metabolites to gain access to the phagocytic vacuole makes this system difficult to evaluate. Therefore, we investigated the ability of neutrophils triggered with phorbol myristate acetate to destroy unopsonized E. coli in a serum-free model system. Neutrophils incubated with phorbol myristate acetate at a cell-to-bacteria ratio of 1:4 caused a greater than 95% reduction in colony-forming units (CFU) of E. coli in 60 min at 37 degrees C. Destruction of E. coli by the stimulated neutrophils was dependent on neutrophil number, stimuli concentration, and the incubation period. The neutrophil-mediated bactericidal effect was stimulated by superoxide dismutase, but was inhibited by catalase, azide, or compounds known to scavenge hypochlorous acid. Although stimulated neutrophils can generate long-lived endogenous N- chloroamines , these compounds did not play a direct role in destruction of E. coli in our model system. However, in the presence of exogenous iodide, endogenous N- chloroamines exerted a powerful bactericidal effect. Finally, neutrophils triggered with opsonized zymosan could also mediate E. coli destruction by a qualitatively similar process. Thus, we have demonstrated that neutrophils have the potential to utilize the myeloperoxidase system to generate bactericidal quantities of a species with characteristics similar to, if not identical with, hypochlorous acid.

Programmed cell death of the normal human neutrophil: An in vitro model of senescence

“…The programmed cell death of the neutrophil in vivo occurs by the physiologic process of apoptosis, a form of cell suicide (Ucker, 1991). This form of cell death, in contrast to classical necrosis, ensures that the abundance of hydrolytic enzymes and reactive oxygen metabolites, which represent the neutrophil's defense against invading microbes (Beaman and Beaman, 1984;Klebanoff, 1980;Passo and Weiss, 1984;Roos, 1991), are contained within the cellular confines of the neutrophil itself and the scavenging macrophages. Extracellular release of these degradative compounds, which occurs during cell lysis, can cause extensive damage to nearby normal cells and tissues (Fox et al, 1981;Henson and Johnston, 1987;Varani et al, 1985;Ward and Mulligan, 1991;Weiss, 19891, a phenomenon referred to as "innocent by-stander" injury (Jackson and Cochrane, 1988;Weiss and LoBuglio, 1982).…”

“…Some of the theories of aging emphasize the accumulation of defects in DNA caused by oxidative damage (Adelman et al, 1988;Bernstein and Bernstein, 1991). It is well known that the neutrophil generates reactive oxygen metabolites using the myeloperoxidase-H,O,-halide system in order to kill phagocytized microbes (Beaman and Beaman, 1984;Klebanoff, 1980;Passo and Weiss, 1984;Roos, 1991;Weiss and LoBuglio, 1982). It is possible that the neutrophil, in turn, may cause loss of function (Baehner et al, 1977) and irreversible damage to itself (Clark and Klebanoff, 1977) using this same reactive oxygen-generating system.…”

Glutamine‐Enriched Enteral Diet Enhances Bacterial Clearance in Protracted Bacterial Peritonitis, Regardless of Glutamine Form‡

“…PMNs also phagocytize and kill E. coli. 16 However, Gln apparently has no effect on the phagocytic function of PMNs.4 In contrast, Gln has been shown to augment the in vitro bacterial killing activity of PMNs from burn patients.' Moreover, we have demonstrated that supplemental Gln enhances the in vitro bacterial killing function of PMNs from postoperative patients.17 Thus Gin supplementation may have enhanced the bacterial killing function of PMNs in the present experiment.…”

Isoflavonoids and chronic disease: Mechanisms of action

“…Neutrophils, recruited to the site where a foreign antigen is detected (Fig. 3), produce the enzyme myeloperoxidase to convert the oxidant hydrogen peroxide to hypochlorous acid (HOCl) [42]. Similarly, superoxide anion (O 2 −. )…”