Toll-like receptor 4 signaling leads to neutrophil migration impairment in polymicrobial sepsis.
OBJECTIVE
We have documented an impaired neutrophil migration toward the infectious focus in severe sepsis. This phenomenon appears to be mediated by nitric oxide, the release of which is stimulated by circulating inflammatory cytokines released by immune cells after stimulation by bacteria and/or their products. Toll-like receptor 4 (TLR4) is the major recognition receptor for lipopolysaccharide, a component of Gram-negative bacterial cell walls. In the present study, we investigated whether TLR4 is involved in the failure of neutrophil migration in mice subjected to polymicrobial or Gram-negative sepsis.


METHODS
Controlled animal study.


METHODS
University research laboratory.


METHODS
Male C3H/HeJ (TLR4-deficient) and C3H/HePas (TLR4-normal) mice.


METHODS
Mice were subjected to sublethal or lethal polymicrobial sepsis, both induced by cecal ligation and puncture or intraperitoneal polymicrobial inoculation, and subjected to sublethal Gram-negative sepsis induced by intraperitoneal Salmonella typhimurium inoculation (GNI). Survival was monitored for 5 days. In separate experiments, mice were killed 6 hrs after sepsis induction, and intraperitoneal neutrophil migration, bacteremia, lung neutrophil sequestration, and levels of cytokines, chemokines, and nitrate were evaluated.


RESULTS
TLR4-deficient (C3H/HeJ) mice presented incapacity to promote neutrophil recruitment to the infectious site after sublethal GNI, resulting in high mortality. However, TLR4 signaling is not essential to display neutrophil migration in sublethal polymicrobial sepsis induced by both cecal ligation and puncture and polymicrobial inoculation models, but surprisingly, it is crucial to establish the impairment of neutrophil migration in lethal polymicrobial sepsis, since TLR4-deficient mice that underwent lethal cecal ligation and puncture or polymicrobial inoculation did not present failure of neutrophil migration to infectious focus. As a consequence, these animals presented low bacteremia and a high survival rate and did not display systemic inflammation, determined by high levels of circulating cytokines and lung neutrophil sequestration and chemokine production.


CONCLUSIONS
These results highlight the harmful role of TLR4 signaling in polymicrobial severe sepsis.
Alves-Filho
José C
JC
Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, São Paulo, Brazil.
de Freitas
Andressa
A
Russo
Momtchilo
M
Cunha
Fernando Q
FQ
D000818:Animals; D002465:Cell Movement; D008297:Male; D051379:Mice; D009504:Neutrophils / Q000378:metabolism / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology*; D010587:Phagocytosis; D018805:Sepsis / Q000503:physiopathology*; D051197:Toll-Like Receptor 4 / Q000172:deficiency / Q000502:physiology*
D051197:Toll-Like Receptor 4; D009569:Nitric Oxide