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.
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
Thomas A
TA
Russo
Bruce A
BA
Davidson
Diana M
DM
Topolnycky
Ruth
R
Olson
Stacy A
SA
Morrill
Paul R
PR
Knight
Philip M
PM
Murphy
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