Induction of Necrosis in Human Neutrophils byShigella flexneriRequires Type III Secretion, IpaB and IpaC Invasins, and Actin Polymerization

Abstract

Infection by Shigella flexneri is characterized by infiltration of neutrophils in the intestinal mucosa and by a strong inflammatory reaction. Although neutrophils are constitutively programmed to die by apoptosis, we show that isolated human neutrophils undergo necrosis 2 h after infection with virulent S. flexneri strain M90T but not with the virulence plasmid-cured strain BS176. This was demonstrated by the release of azurophil granule proteins concomitant with the release of lactate dehydrogenase (LDH), disruption of the plasma membrane, and absence of DNA fragmentation. Mutants with the mxiD1 gene, coding for an essential component of the secretion type III machinery, or the genes coding for IpaB or IpaC invasins deleted were not cytotoxic. Neutrophil necrosis occurred independently of the bacterial ability to leave phagosomes, and it involved actin polymerization, as the addition of cytochalasin D after phagocytosis of Shigella inhibited the release of LDH. In conclusion, Shigella kills neutrophils by necrosis, a process characterized by the release of tissue-injurious granular proteins. This probably contributes to disruption of the epithelial barrier, leading to the dysentery observed in shigellosis and allowing Shigella to enter its host cells.

Virulent Shigella flexneri Causes Damage to Mitochondria and Triggers Necrosis in Infected Human Monocyte-Derived Macrophages

“…These findings were recently disputed by Nonaka et al (30). Infection of human neutrophils (9) or human monocyte-derived macrophages (HMDM) (7) with virulent Shigella caused a rapid disruption of the cell membrane in the absence of other apoptotic features. Based on these data, it was concluded that Shigella-infected human macrophages and neutrophils die by a nonapoptotic-necrotic mechanism (7,9).…”

“…Infection of human neutrophils (9) or human monocyte-derived macrophages (HMDM) (7) with virulent Shigella caused a rapid disruption of the cell membrane in the absence of other apoptotic features. Based on these data, it was concluded that Shigella-infected human macrophages and neutrophils die by a nonapoptotic-necrotic mechanism (7,9). A contrary conclusion, that Shigella kills human macrophages by an apoptotic mechanism, has also been reported (11,16).…”

Neutrophil Extracellular Traps Exhibit Antibacterial Activity against Burkholderia pseudomallei and Are Influenced by Bacterial and Host Factors

“…To separate these events, infected PMNs were treated with a concentration of cytochalasin D previously reported to substantially reduce entry of Shigella flexneri into host cells (12). Upon cytochalasin D treatment, the number of bacteria killed fell significantly from approximately 90% (1.0-log 10 -CFU reduction) for untreated cells (Fig.…”

“…It has previously been reported that NETs degrade IpaB of the Shigella T3SS by proteolysis, thereby disarming the secretion apparatus (12). In vitro B. pseudomallei secretes a number of extracellular enzymes that have the potential to counteract activities presented in NETs (1).…”

Interactions among Strategies Associated with Bacterial Infection: Pathogenicity, Epidemicity, and Antibiotic Resistance

“…Several virulent bacteria base their pathogenic characteristics in an intracellular way of life during infection (125). Internalization may be required for the induction of inflammatory cytokines (166) and produce tissue damage through the induction of either necrotic (130) or apoptotic (167,410) responses. A remarkable example is the apoptosis of macrophages induced by pathogens such as Shigella, which both avoid the antibacterial effect of those cells and trigger inflammation (427,428).…”