Human neutrophil chemotaxis is modulated by capsule and O antigen from an extraintestinal pathogenic Escherichia coli strain.
Gram-negative enteric bacilli, such as Escherichia coli, are common causes of nosocomial pneumonia. The interaction between pulmonary neutrophils and the infecting pathogen is a critical step in determining the outcome. Previous studies from our laboratory, for which a rat model of pneumonia was used, established that pulmonary neutrophil recruitment was modulated by the E. coli virulence factors capsule and O-specific antigen. To begin to understand the mechanism by which this recruitment occurs, we conducted in vitro and ex vivo chemotaxis assays, for which we used a clinically relevant E. coli isolate (CP9) and isogenic derivatives that were deficient in only the O antigen (CP921) or capsule (CP9.137) as chemoattractants with or without the high-affinity N-formylmethionyl-leucyl-phenylalanine receptor antagonist N-tert-butoxycarbonyl-methionine-leucine-phenylalanine (N-t-BOC). Given that only live E. coli was used for the initial in vitro chemotaxis assays, it was predicted that only N-t-BOC-sensitive chemotaxis would occur. However, both N-t-BOC-sensitive and -insensitive chemotaxis was observed. N-t-BOC-insensitive chemotaxis was mediated in part by interleukin 8, which was produced by neutrophils that had migrated toward E. coli. N-t-BOC-insensitive chemotaxis was only observed when live E. coli bacteria, not cell-free E. coli culture supernatants, were used as chemoattractants, suggesting that a direct E. coli-neutrophil interaction was necessary. The presence of both capsule and O antigen diminished total, N-t-BOC-sensitive, and N-t-BOC-insensitive neutrophil chemotaxis in vitro. The presence of capsule significantly decreased total, N-t-BOC-sensitive, and N-t-BOC-insensitive neutrophil chemotaxis ex vivo when cell-free bronchoalveolar lavage fluid from infected rats was used as the source of chemotactic factors. These effects of E. coli capsule and O antigen on neutrophil chemotaxis are novel, and they expand our understanding of the mechanisms by which these virulence traits contribute to the pathogenesis of gram-negative pneumonia and other extraintestinal infections.
Russo
Thomas A
TA
Department of Medicine, The Witebsky Center for Microbial Pathogenesis. Veterans Administration Western New York Healthcare System, University at Buffalo, Buffalo, New York 14214, USA. trusso@acsu.buffalo.edu
Davidson
Bruce A
BA
Topolnycky
Diana M
DM
Olson
Ruth
R
Morrill
Stacy A
SA
Knight
Paul R
PR
Murphy
Philip M
PM
D000818:Animals; D016667:Bacterial Capsules / Q000502:physiology*; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D004926:Escherichia coli / Q000472:pathogenicity*; D006801:Humans; D016209:Interleukin-8 / Q000502:physiology; D009504:Neutrophils / Q000276:immunology*; D019081:O Antigens / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans
D016209:Interleukin-8; D019081:O Antigens; D009842:Oligopeptides; C046832:t-butyloxycarbonyl-methionyl-leucyl-phenylalanine