title: Group A Streptococcus Modulates Host Inflammation by Manipulating Polymorphonuclear Leukocyte Cell Death Responses.
abstract: Polymorphonuclear leukocyte (PMN) cell death strongly influences the resolution of inflammatory episodes, and may exacerbate adverse pathologies in response to infection. We investigated PMN cell death mechanisms following infection by virulent group A Streptococcus (GAS). Human PMNs were infected in vitro with a clinical, virulent GAS isolate and an avirulent derivative strain, and compared for phagocytosis, the production of reactive oxygen species (ROS), mitochondrial membrane depolarization and apoptotic markers. C57BL/6J mice were then infected, in order to observe the effects on murine PMNs in vivo. Human PMNs phagocytosed virulent GAS less efficiently, produced less ROS and underwent reduced mitochondrial membrane depolarization compared with phagocytosis of avirulent GAS. Morphological and biochemical analyses revealed that PMNs infected with avirulent GAS exhibited nuclear fragmentation and caspase-3 activation consistent with an anti-inflammatory apoptotic phenotype. Conversely, virulent GAS induced PMN vacuolization and plasma membrane permeabilization, leading to a necrotic form of cell death. Infection of the mice with virulent GAS engendered significantly higher systemic pro-inflammatory cytokine release and localized infiltration of murine PMNs, with cells associated with virulent GAS infection exhibiting reduced apoptotic potential. Avirulent GAS infection was associated with lower levels of proinflammatory cytokines and tissue PMN apoptosis. We propose that the differences in PMN cell death mechanisms influence the inflammatory responses to infection by GAS.
authors.affiliation: Illawarra Health and Medical Research Institute and School of Biological Sciences, University of Wollongong, Wollongong, N.S.W., Australia.
authors.forename: James A
authors.initials: JA
authors.lastname: Tsatsaronis
authors.forename: Diane
authors.initials: D
authors.lastname: Ly
authors.forename: Aleta
authors.initials: A
authors.lastname: Pupovac
authors.forename: Oliver
authors.initials: O
authors.lastname: Goldmann
authors.forename: Manfred
authors.initials: M
authors.lastname: Rohde
authors.forename: Jude M
authors.initials: JM
authors.lastname: Taylor
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Walker
authors.forename: Eva
authors.initials: E
authors.lastname: Medina
authors.forename: Martina L
authors.initials: ML
authors.lastname: Sanderson-Smith
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D053148:Caspase 3 / Q000276:immunology*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D051336:Mitochondrial Membranes / Q000276:immunology / Q000473:pathology; D009336:Necrosis; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis; D017382:Reactive Oxygen Species / Q000276:immunology; D013290:Streptococcal Infections / Q000276:immunology* / Q000473:pathology; D013297:Streptococcus pyogenes / Q000276:immunology*
chemical_list: D017382:Reactive Oxygen Species; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3